New Perspectives for Cancer Diagnosis and Therapy

*Tumor Progression and Metastasis*

2017;**8**:591-605

2014;**2**:904-908

therapy and current strategies—A review. Journal of Advanced Research. [45] Hossen S, Khalid Hossain M, Basher MK, Mia MNH, Rahman MT, Jalal Uddin M. Smart nanocarrier-based drug delivery systems for cancer therapy and toxicity studies: A review. Journal of Advanced Research. 2019;**15**:1-18

[46] Girish S, Gupta M, Wang B, Lu D, et al. Clinical pharmacology of transtuzumab emtansine (T-DM1): An antibody drug conjugate in development of the treatment for HER2-positive cancer. Cancer Chemotherapy and Pharmacology. 2012;**69**(5):1229-1240

[37] Bazak R, Houri M, Elachy S, Hussein W, Refaat T. Passive targeting of nanoparticles to cancer: A comprehensive review of literature. Molecular and Clinical Oncology.

[38] Narayanan E, Wakaskar R. Utilization of nanoparticulate therapy in cancer targeting. Cogent Medicine. 2018;**5**(1504504):1-9

Reviews. 2016;**99**:28-51

2017;**1**(4):346-357

2001;**19**(4):424-436

[39] Soo Suk J, Xu Q, Kim N, Hanes J, Ensign LM. PEGylation as a strategy for improving nanoparticle-based drug gene delivery. Advanced Drug Delivery

[40] Din F u, Ullah WAI, et al. Effective use of nanocarriers as drug delivery systems for the treatment of selected tumors. International Journal of Nanomedicine. 2017;**12**:7291-7309

[41] Li R, Zheng K, Yuan C, Chen Z, Huang M. Be active or Not: The relative contribution of active and passive tumor targeting of nanomaterials. Nano.

[42] Gabizon A. Pegylated liposomal doxorubicin: Metamorphosis of an old drug into a new form of chemotherapy. Cancer Investigation.

[43] Miele E, Spineli GP, Miele E, Tomao F, Tomao S. Albumin-bound formulation of paclitaxel (Abraxane ABI-007) in the treatment of breast cancer. International Journal of Nanomedicine. 2009;**4**:99-105

[44] Wang K, Kievit FM, Zhang M. Nanoparticles for cancer gene therapy: Recent advances, challenges and strategies. Pharmacological Research. 2016;**114**:56-66

**Chapter 9**

**Abstract**

Multiforme

Stereotactic Radiosurgery for

Glioblastoma multiforme (GBM) is the most aggressive intracranial tumor that primarily affects adults. Since the introduction of temozolomide in 2005, maximal resection surgery with concurrent chemoradiation has become the standard treatment method for patients with newly diagnosed GBM. Although newly discovered chemoagents have been demonstrated to improve the median survival time, GBM still recurs in most patients. Recurrent GBM is still a therapeutic challenge for clinical physicians. Surgical intervention and other conventional chemoagents have been applied to manage recurrent GBM. Stereotactic radiosurgery (SRS) provides a highly precise radiation dose to the tumor lesion and reduces the dose to the adjacent normal brain tissue. After standard treatment for newly diagnosed GBM is completed, conventional re-irradiation therapy is not suitable for patients with recurrent GBMs. Therefore, SRS may become an alternative option in the treatment of recurrent GBMs. In this review, we discuss the relevant literature regarding SRS

for recurrent GBMs and provide treatment advice for clinical physicians.

**Keywords:** stereotactic radiosurgery, recurrent glioblastoma multiforme,

Glioblastoma multiforme (GBM) is the most common primary brain neoplasm in adults [1, 2]. There are 1.6 times more males than females who develop a GBM [1]. According to the latest statistical report of the Central Brain Tumor Registry of the USA, the annual incidence of GBM has been estimated at approximately 3.22 cases per 100,000 people, and the median age is 65 years [3]. The current standard treatment of patients with a newly diagnosed GBM was established in 2005, and it consists of maximal surgical resection of the tumor followed by chemotherapy and conventional radiotherapy [4, 5]. Despite this therapy, the median overall survival

GBM is a refractory malignant and infiltrating tumor that may recur any time after initial multimodal treatments are completed [6]. Managing recurrent GBM has always been challenging, and a balance has to be achieved between significant treatment toxicity and associated morbidities and mortalities [6, 7]. Reoperation with maximal resection at recurrence remains as an independent predictor to improve overall survival [8, 9]. However, repeat gross-total resection may not be

Recurrent Glioblastoma

*Cheng-Ta Hsieh and Da-Tong Ju*

re-irradiation, survival time, prognosis

time is approximately 15–17 months [2].

**1. Introduction**

#### **Chapter 9**

## Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme

*Cheng-Ta Hsieh and Da-Tong Ju*

#### **Abstract**

Glioblastoma multiforme (GBM) is the most aggressive intracranial tumor that primarily affects adults. Since the introduction of temozolomide in 2005, maximal resection surgery with concurrent chemoradiation has become the standard treatment method for patients with newly diagnosed GBM. Although newly discovered chemoagents have been demonstrated to improve the median survival time, GBM still recurs in most patients. Recurrent GBM is still a therapeutic challenge for clinical physicians. Surgical intervention and other conventional chemoagents have been applied to manage recurrent GBM. Stereotactic radiosurgery (SRS) provides a highly precise radiation dose to the tumor lesion and reduces the dose to the adjacent normal brain tissue. After standard treatment for newly diagnosed GBM is completed, conventional re-irradiation therapy is not suitable for patients with recurrent GBMs. Therefore, SRS may become an alternative option in the treatment of recurrent GBMs. In this review, we discuss the relevant literature regarding SRS for recurrent GBMs and provide treatment advice for clinical physicians.

**Keywords:** stereotactic radiosurgery, recurrent glioblastoma multiforme, re-irradiation, survival time, prognosis

#### **1. Introduction**

Glioblastoma multiforme (GBM) is the most common primary brain neoplasm in adults [1, 2]. There are 1.6 times more males than females who develop a GBM [1]. According to the latest statistical report of the Central Brain Tumor Registry of the USA, the annual incidence of GBM has been estimated at approximately 3.22 cases per 100,000 people, and the median age is 65 years [3]. The current standard treatment of patients with a newly diagnosed GBM was established in 2005, and it consists of maximal surgical resection of the tumor followed by chemotherapy and conventional radiotherapy [4, 5]. Despite this therapy, the median overall survival time is approximately 15–17 months [2].

GBM is a refractory malignant and infiltrating tumor that may recur any time after initial multimodal treatments are completed [6]. Managing recurrent GBM has always been challenging, and a balance has to be achieved between significant treatment toxicity and associated morbidities and mortalities [6, 7]. Reoperation with maximal resection at recurrence remains as an independent predictor to improve overall survival [8, 9]. However, repeat gross-total resection may not be

easily achieved when recurrent GBM involves important eloquent brain structures, such as the brainstem or motor area. Extensive bevacizumab and temozolomide are the two main FDA-approved chemoagents used to treat patients with recurrent GBMs, but the prognosis remains poor [10].

Re-irradiation is an alternative option for managing recurrent GBMs [11]. The majority of recurrent tumors occur at the initial or adjacent regional sites [12]. Because a total dose of 60 Gy in 30 fractions has been prescribed for initial radiation therapy, re-irradiation with further dose escalation appears to produce more significant toxicity [10, 11]. Stereotactic radiosurgery (SRS) is a noninvasive treatment that provides a highly precise, targeted additional radiation boost to the tumor lesion, and it maintains an acceptable rate of adverse radiation effects while reducing the dose to adjacent normal brain tissues [13]. In this review, we searched the relevant literature and investigated the role of SRS in the management of recurrent GBMs. Our results may provide treatment information for clinical treatment.

#### **2. Search methodology**

In this study, different combinations of the keywords "recurrent glioblastoma multiple," "high-grade glioma," "stereotactic radiosurgery," and "re-irradiation" were used to search the published literature in the PubMed database until October 31, 2019. The inclusion criteria of the study were (1) patients with recurrent GBMs, (2) treatment with stereotactic radiosurgery (SRS) or a fractionated radiosurgery (less than 5 fractions), and (3) outcomes with overall survival time. Tumor progression was also accepted as a recurrent disease. Potentially relevant studies were identified from the reference lists of the studies obtained from the database search. Articles excluded from the review were those written in languages other than English and those that lacked survival response data. Finally, a total of 49 studies were included in this review.

#### **3. The summary of patients with recurrent GBMs treated with SRS**

A total of 49 studies published from 1994 to 2019 were enrolled in this review, as summarized in **Table 1** [13–61]. There were 6 prospective studies and 43 retrospective studies. About 2066 patients with recurrent glioblastomas treated with SRS, including linear accelerator (LINAC) radiosurgery, Gamma Knife radiosurgery, and Cyberknife radiosurgery, are reported. In all studies, the median age of the patients who received SRS treatment for recurrent GBM ranged from 34 to 62 years. The majority of patients were males. The median prescribed dose of SRS ranged from 6 to 30 Gy. The median targeted volume for treatment ranged from 1.35 to 21.3 cc. The overall survival time from treatment for SRS ranged from 3.9 to 17.9 months, where the progression-free survival time from the treatment of SRS ranged from 2.1 to 14.9 months. In the prognostic analysis of survival time in patients with recurrent GBMs treated with SRS, a small tumor volume, younger age, higher Karnofsky performance scale (KPS) score, lower recursive partitioning analysis (RPA) class, adjuvant bevacizumab, methylated O6-methylguanine-DNAmethyltransferase (MGMT) promoter, and longer interval between the original surgery and SRS were significantly associated with patients'survival outcomes.

#### **3.1 The effect of LINAC radiosurgery in patients with recurrent GBMs**

From 1994 to 2018, a total of 501 patients with recurrent GBMs treated with LINAC SRS were enrolled in 22 studies, including 3 prospective trials and 17

**221**

*Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme*

*DOI: http://dx.doi.org/10.5772/intechopen.91163*

#### *Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme DOI: http://dx.doi.org/10.5772/intechopen.91163*

easily achieved when recurrent GBM involves important eloquent brain structures, such as the brainstem or motor area. Extensive bevacizumab and temozolomide are the two main FDA-approved chemoagents used to treat patients with recurrent

Re-irradiation is an alternative option for managing recurrent GBMs [11]. The majority of recurrent tumors occur at the initial or adjacent regional sites [12]. Because a total dose of 60 Gy in 30 fractions has been prescribed for initial radiation therapy, re-irradiation with further dose escalation appears to produce more significant toxicity [10, 11]. Stereotactic radiosurgery (SRS) is a noninvasive treatment that provides a highly precise, targeted additional radiation boost to the tumor lesion, and it maintains an acceptable rate of adverse radiation effects while reducing the dose to adjacent normal brain tissues [13]. In this review, we searched the relevant literature and investigated the role of SRS in the management of recurrent GBMs. Our results may provide treatment information for clinical treatment.

In this study, different combinations of the keywords "recurrent glioblastoma multiple," "high-grade glioma," "stereotactic radiosurgery," and "re-irradiation" were used to search the published literature in the PubMed database until October 31, 2019. The inclusion criteria of the study were (1) patients with recurrent GBMs, (2) treatment with stereotactic radiosurgery (SRS) or a fractionated radiosurgery (less than 5 fractions), and (3) outcomes with overall survival time. Tumor progression was also accepted as a recurrent disease. Potentially relevant studies were identified from the reference lists of the studies obtained from the database search. Articles excluded from the review were those written in languages other than English and those that lacked survival response data. Finally, a total of 49 studies were included in this review.

**3. The summary of patients with recurrent GBMs treated with SRS**

**3.1 The effect of LINAC radiosurgery in patients with recurrent GBMs**

From 1994 to 2018, a total of 501 patients with recurrent GBMs treated with LINAC SRS were enrolled in 22 studies, including 3 prospective trials and 17

A total of 49 studies published from 1994 to 2019 were enrolled in this review, as summarized in **Table 1** [13–61]. There were 6 prospective studies and 43 retrospective studies. About 2066 patients with recurrent glioblastomas treated with SRS, including linear accelerator (LINAC) radiosurgery, Gamma Knife radiosurgery, and Cyberknife radiosurgery, are reported. In all studies, the median age of the patients who received SRS treatment for recurrent GBM ranged from 34 to 62 years. The majority of patients were males. The median prescribed dose of SRS ranged from 6 to 30 Gy. The median targeted volume for treatment ranged from 1.35 to 21.3 cc. The overall survival time from treatment for SRS ranged from 3.9 to 17.9 months, where the progression-free survival time from the treatment of SRS ranged from 2.1 to 14.9 months. In the prognostic analysis of survival time in patients with recurrent GBMs treated with SRS, a small tumor volume, younger age, higher Karnofsky performance scale (KPS) score, lower recursive partitioning analysis (RPA) class, adjuvant bevacizumab, methylated O6-methylguanine-DNAmethyltransferase (MGMT) promoter, and longer interval between the original surgery and SRS were significantly associated with patients'survival outcomes.

GBMs, but the prognosis remains poor [10].

*Tumor Progression and Metastasis*

**2. Search methodology**

**223**

*Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme*

*DOI: http://dx.doi.org/10.5772/intechopen.91163*

#### *Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme DOI: http://dx.doi.org/10.5772/intechopen.91163*

**222**

#### **Table 1.**

*Summary of the published literature on stereotactic radiosurgery in patients with recurrent glioblastoma multiforme.* retrospective studies [14

11 months.

–16, 19, 21, 23

*Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme*

*DOI: http://dx.doi.org/10.5772/intechopen.91163*

60, 61]. The median age ranged from 34 to 54 years. The median prescribed dose ranged from 13 to 30 Gy. The median targeted tumor volume was 4.5 to 41.3 cc. The

The first study about LINAC radiosurgery for recurrent GBMs was described by Chamerian et al. [14]. The median prescribed dose was 13.4 Gy, and the median treated tumor volume was 17 cc. The median overall survival time was only 8 months, whereas the median progression-free survival time was 4 months. After that, only one retrospective study of more than 100 patients with recurrent highgrade gliomas treated with LINAC SRS has been reported [16]. Shrieve et al. showed that the median survival time of 72 recurrent GBM patients was 10.2 months [16]. Younger age (less than 46 years) and small tumor volume (less than 10.1 cc) were the significant prognostic factors associated with survival time. There were two studies that enrolled patients with only recurrent GBMs [21, 33]. In 2005, Combs et al. reported 32 patients, including 19 males and 13 females with recurrent GBMs treated with LINAC SRS [21]. The median age was 56 years, ranging from 33 to 76 years. The median prescribed radiation dose was 15 Gy, ranging from 10 to 20 Gy. The median targeted tumor volume was 10 cc with a range of 1.2 to 59.2 cc. The median overall survival time and progression-free survival time were 10 and 5 months, respectively. However, no prognostic factor was significant enough to influence the survival time. In a retrospective study of 19 patients with recurrent

median overall survival time from the treatment of SRS ranged from 3.9 to 14.4 months, whereas the median progression-free survival time was 2.1 to

GBMs, Sirin et al. also showed that the median overall survival time and

survival time in patients with recurrent GBMs.

from 3.8 to 14.9 months.

**225**

factors associated with patients

progression-free survival time were only 9.3 and 5.7 months, respectively [33]. In the bevacizumab era, three studies reported the combination of LINAC SRS, and bevacizumab improved the overall survival time ranging from 11.2 to 14.4 months [35, 39, 40]. In a retrospective study of 48 patients with recurrent GBMs, Cuneo et al. reported that the median progression-free survival time in recurrent patients who received adjuvant bevacizumab and LINAC SRS was 5.2 months vs. 2.1 months for patients who received LINAC SRS alone. The median overall survival times for patients who received a combination of adjuvant bevacizumab/LINAC SRS and LINAC SRS alone were 11.2 and 3.9 months, respectively. The authors concluded that the combination of salvage radiosurgery and bevacizumab to treat recurrent malignant gliomas seemed to be associated with improved outcomes. Younger age and higher KPS were still significant prognostic factors associated with overall

**3.2 The effect of gamma knife radiosurgery in patients with recurrent GBMs**

From 1996 to 2019, a total of 1247 patients with recurrent GBMs in 23 published studies were treated with Gamma Knife SRS [13, 17, 18, 20, 22, 24, 27, 29, 31, 36

38, 41, 45, 47, 50, 52, 53, 55, 57–59, 61]. The median age ranged from 43 to 61 years. The median prescribed marginal dose varied from 6 to 20 Gy. The median targeted tumor volume ranged from 1.35 to 21.4 cc. The median overall survival time ranged from 7 to 30 months, whereas the median progression-free survival time ranged

In a retrospective study of 189 patients with recurrent high-grade gliomas treated with Gamma Knife SRS, Larson et al. first reported that the median overall survival time in 66 patients with recurrent GBMs was 10 months [17]. Younger age, smaller tumor volume, higher KPS, and unifocal tumors were significant prognostic

impact of a combination of Gamma Knife SRS and adjuvant chemoagents on overall

' overall survival times. Several studies reported the

–

–26, 28, 32, 33, 35, 39, 40, 43, 49, 51, 54, 56,

retrospective studies [14–16, 19, 21, 23–26, 28, 32, 33, 35, 39, 40, 43, 49, 51, 54, 56, 60, 61]. The median age ranged from 34 to 54 years. The median prescribed dose ranged from 13 to 30 Gy. The median targeted tumor volume was 4.5 to 41.3 cc. The median overall survival time from the treatment of SRS ranged from 3.9 to 14.4 months, whereas the median progression-free survival time was 2.1 to 11 months.

The first study about LINAC radiosurgery for recurrent GBMs was described by Chamerian et al. [14]. The median prescribed dose was 13.4 Gy, and the median treated tumor volume was 17 cc. The median overall survival time was only 8 months, whereas the median progression-free survival time was 4 months. After that, only one retrospective study of more than 100 patients with recurrent highgrade gliomas treated with LINAC SRS has been reported [16]. Shrieve et al. showed that the median survival time of 72 recurrent GBM patients was 10.2 months [16]. Younger age (less than 46 years) and small tumor volume (less than 10.1 cc) were the significant prognostic factors associated with survival time. There were two studies that enrolled patients with only recurrent GBMs [21, 33]. In 2005, Combs et al. reported 32 patients, including 19 males and 13 females with recurrent GBMs treated with LINAC SRS [21]. The median age was 56 years, ranging from 33 to 76 years. The median prescribed radiation dose was 15 Gy, ranging from 10 to 20 Gy. The median targeted tumor volume was 10 cc with a range of 1.2 to 59.2 cc. The median overall survival time and progression-free survival time were 10 and 5 months, respectively. However, no prognostic factor was significant enough to influence the survival time. In a retrospective study of 19 patients with recurrent GBMs, Sirin et al. also showed that the median overall survival time and progression-free survival time were only 9.3 and 5.7 months, respectively [33]. In the bevacizumab era, three studies reported the combination of LINAC SRS, and bevacizumab improved the overall survival time ranging from 11.2 to 14.4 months [35, 39, 40]. In a retrospective study of 48 patients with recurrent GBMs, Cuneo et al. reported that the median progression-free survival time in recurrent patients who received adjuvant bevacizumab and LINAC SRS was 5.2 months vs. 2.1 months for patients who received LINAC SRS alone. The median overall survival times for patients who received a combination of adjuvant bevacizumab/LINAC SRS and LINAC SRS alone were 11.2 and 3.9 months, respectively. The authors concluded that the combination of salvage radiosurgery and bevacizumab to treat recurrent malignant gliomas seemed to be associated with improved outcomes. Younger age and higher KPS were still significant prognostic factors associated with overall survival time in patients with recurrent GBMs.

#### **3.2 The effect of gamma knife radiosurgery in patients with recurrent GBMs**

From 1996 to 2019, a total of 1247 patients with recurrent GBMs in 23 published studies were treated with Gamma Knife SRS [13, 17, 18, 20, 22, 24, 27, 29, 31, 36– 38, 41, 45, 47, 50, 52, 53, 55, 57–59, 61]. The median age ranged from 43 to 61 years. The median prescribed marginal dose varied from 6 to 20 Gy. The median targeted tumor volume ranged from 1.35 to 21.4 cc. The median overall survival time ranged from 7 to 30 months, whereas the median progression-free survival time ranged from 3.8 to 14.9 months.

In a retrospective study of 189 patients with recurrent high-grade gliomas treated with Gamma Knife SRS, Larson et al. first reported that the median overall survival time in 66 patients with recurrent GBMs was 10 months [17]. Younger age, smaller tumor volume, higher KPS, and unifocal tumors were significant prognostic factors associated with patients' overall survival times. Several studies reported the impact of a combination of Gamma Knife SRS and adjuvant chemoagents on overall

**Table 1.**

**224**

*Tumor Progression and Metastasis*

*Summary of the published literature on stereotactic*

 *radiosurgery*

 *in patients with recurrent glioblastoma*

 *multiforme.* survival times [17, 37, 47, 55, 59]. In 2002, Larson et al. reported a prospective phase II study on patients who received a combination of Gamma Knife SRS, and marimastat had a median overall survival of 8.7 months, whereas the median survival time in patients who received only Gamma Knife SRS alone was 10.1 months. Marimastat did not offer an advantage for patients with recurrent GBMs. However, in a retrospective study of 57 patients with recurrent GBMs, Kim et al. showed that the combination of adjuvant temozolomide and Gamma Knife SRS significantly improved the medium overall survival time from 9.2 to 15.5 months [47]. In the bevacizumab era, two studies reported that the median survival time was approximately 13 months after the combined treatment of Gamma Knife SRS and adjuvant bevacizumab [55, 59].

alternative option for treating recurrent GBMs. In a systematic review and metaanalysis of re-irradiation with external beam radiotherapy for recurrent GBMs, Kazmi et al. showed that the 6- and 12-month overall survival times from the time of re-irradiation were 70 and 34%, respectively, whereas the 6- and 12-month progression-free survival times were 40 and 16%, respectively [11]. The overall

SRS has the ability to combine surgical and radio-oncological treatments to deliver a high dose of focused radiation on the focal tumor lesion and spare the adjacent normal anatomical structures. For recurrent GBMs, the majority of tumors tend to grow within 2 cm of the contrast-enhancing lesion border, and SRS seems to be a reasonable tool to add radiation boost for the focal lesion followed by the standard treatment of initial radiation with 60 Gy in 30 fractions [4, 13]. In our present review, despite the different SRS modalities with the median prescribed dose ranging from 6 to 30 Gy, the overall survival time from the treatment of SRS ranged from 3.9 to 17.9 months, where the progression-free survival time from the treatment of SRS ranged from 2.1 to 14.9 months. Severe prognostic factors, such as small tumor volume, younger age, higher KPS score, and lower RPA class, were mostly suggested to be significantly associated with the overall survival time in patients with recurrent GBMs treated with SRS. These results showed that reirradiation with the SRS modality are an alternative and feasible method to manage

**4.2 The impact of SRS and adjuvant temozolomide for recurrent GBMs**

Since 2005, temozolomide, which is an alkylating agent, is the most important FDA-approved chemoagent for the standard treatment of patients with newly diagnosed GBMs [1, 4]. The median overall survival time significantly improved from 12.1 to 14.6 months after the patients with newly diagnosed GBMs received combined treatments with radiotherapy and adjuvant temozolomide. However, the disease frequently progresses within 6–9 months, and the 2-year survival rate is less than 25% [62]. The failure of temozolomide treatment has been found to be associated with the expression of MGMT protein [63–65]. Among the GBM patients with a methylated MGMT promoter, the median overall survival time was 21.7 months after treatment with radiotherapy and temozolomide, whereas the median survival time was 15.3 months in the unmethylated group treated with radiotherapy alone [64].

Due to the blood-brain barrier, temozolomide rechallenge is considered to be a reasonable option in patients with recurrent GBMs. In this review, the combination of SRS and temozolomide was employed in three studies [34, 42, 47]. Cyberknife SRS was performed in two studies, and the other study used the Gamma Knife SRS. The median overall survival time ranged from 9 to 15.5 months, and the median progression-free survival time was approximately 7 months after the time of SRS treatment. In 2012, Conti et al. analyzed the effect of adjuvant temozolomide in recurrent GBM patients treated with Cyberknife SRS [34]. The median overall survival time significantly improved from 7 to 12 months, whereas the median progression-free survival time improved from 4 to 7 months. Based on 57 recurrent GBM patients, Kim et al. also showed that the improved median overall survival time and progression-free survival time were 15.5 and 6 months, respectively [47]. Otherwise, in a retrospective review of 61 patients who received Gamma Knife SRS as a salvage treatment at the time of the first progression, Kim et al. showed that the median overall survival time was 14 months in the methylated MGMT promoter group and 9 months in the unmethylated group [53]. Methylation of the MGMT promoter was significantly corrected with better overall survival times and progression-free survival times. The results mentioned above indicated that the

toxicity rate was low, ranging from 4 to 10%.

*DOI: http://dx.doi.org/10.5772/intechopen.91163*

*Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme*

patients with recurrent GBMs.

**227**

#### **3.3 The effect of Cyberknife radiosurgery in patients with recurrent GBMs**

From 2009 to 2017, a total of 318 patients with recurrent GBMs in eight published studies were treated with Cyberknife SRS [30, 34, 42, 44, 46, 48, 51, 54]. The median age ranged from 37 to 59.9 years. The median prescribed marginal dose ranged from 15 to 30 Gy. The median targeted tumor volume ranged from 2 to 24 cc. The median overall survival time after Cyberknife SRS ranged from 5.3 to 12 months, whereas the median progression-free survival time ranged from 4 to 7.9 months.

The first report on Cyberknife SRS for patients with recurrent GBMs was published by Villavicencio et al. [30]. The median overall survival time in a total of 26 patients with recurrent GBMs was 7 months. No prognostic factor associated with the overall survival time was identified. In 2015, Pinzi et al. reported a retrospective study of more than 100 patients who had recurrent high-grade glioma treated with Cyberknife SRS [48]. Among 88 patients with recurrent GBMs, the median survival time was 10 months after treatment with Cyberknife SRS. Adjuvant second-line chemotherapy and/or surgery were the significant prognostic factors associated with overall survival times. The effect of adjuvant chemoagents, including bevacizumab, temozolomide, and anti-epidermal factor (125)-mAB 425, on the overall survival times was evaluated in four studies [34, 42, 44, 46]. In 2012, Conti et al. compared the effect of a combination of temozolomide and Cyberknife SRS with that of Cyberknife SRS alone on the overall survival times of patients with recurrent GBMs [34]. The progression-free survival time and median survival time in patients who received the adjuvant temozolomide and Cyberknife SRS were 7 and 12 months, respectively. The patients who received Cyberknife SRS alone had a progression-free survival time and median survival time of only 4 and 7 months, respectively. In the bevacizumab era, Yazici et al. revealed that the median survival time in 37 patients with recurrent GBMs was 10.6 months, whereas the median progression-free survival time was 7.9 months [44]. A tumor volume less than 24 cc was the only significant prognostic factor associated with overall survival times.

#### **4. Discussion**

#### **4.1 The role of SRS for recurrent GBMs**

GBM is an incurable disease with local progression in the majority of patients. The management of recurrent GBMs is a clinically challenging problem, and treatment options are limited [7, 10]. Although reoperation with gross-total removal of the tumor has been shown to improve the overall survival time in patients with recurrent GBMs, surgery may not be preferred for patients with tumors in the eloquent area, older age, or lower performance status [8]. Re-irradiation offers an

#### *Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme DOI: http://dx.doi.org/10.5772/intechopen.91163*

survival times [17, 37, 47, 55, 59]. In 2002, Larson et al. reported a prospective phase

II study on patients who received a combination of Gamma Knife SRS, and marimastat had a median overall survival of 8.7 months, whereas the median survival time in patients who received only Gamma Knife SRS alone was 10.1 months. Marimastat did not offer an advantage for patients with recurrent GBMs. However, in a retrospective study of 57 patients with recurrent GBMs, Kim et al. showed that the combination of adjuvant temozolomide and Gamma Knife SRS significantly improved the medium overall survival time from 9.2 to 15.5 months [47]. In the bevacizumab era, two studies reported that the median survival time was approximately 13 months after the combined treatment of Gamma Knife SRS and adjuvant

**3.3 The effect of Cyberknife radiosurgery in patients with recurrent GBMs**

The first report on Cyberknife SRS for patients with recurrent GBMs was published by Villavicencio et al. [30]. The median overall survival time in a total of 26 patients with recurrent GBMs was 7 months. No prognostic factor associated with the overall survival time was identified. In 2015, Pinzi et al. reported a retrospective study of more than 100 patients who had recurrent high-grade glioma treated with Cyberknife SRS [48]. Among 88 patients with recurrent GBMs, the median survival time was 10 months after treatment with Cyberknife SRS. Adjuvant second-line chemotherapy and/or surgery were the significant prognostic factors associated with overall survival times. The effect of adjuvant chemoagents, including bevacizumab, temozolomide, and anti-epidermal factor (125)-mAB 425, on the overall survival times was evaluated in four studies [34, 42, 44, 46]. In 2012, Conti et al. compared the effect of a combination of temozolomide and Cyberknife SRS with that of Cyberknife SRS alone on the overall survival times of patients with recurrent GBMs [34]. The progression-free survival time and median survival time in patients who received the adjuvant temozolomide and Cyberknife SRS were 7 and 12 months, respectively. The patients who received Cyberknife SRS alone had a progression-free survival time and median survival time of only 4 and 7 months, respectively. In the bevacizumab era, Yazici et al. revealed that the median survival time in 37 patients with recurrent GBMs was 10.6 months, whereas the median progression-free survival time was 7.9 months [44]. A tumor volume less than 24 cc was the only significant prognostic factor associated with overall survival times.

GBM is an incurable disease with local progression in the majority of patients. The management of recurrent GBMs is a clinically challenging problem, and treatment options are limited [7, 10]. Although reoperation with gross-total removal of the tumor has been shown to improve the overall survival time in patients with recurrent GBMs, surgery may not be preferred for patients with tumors in the eloquent area, older age, or lower performance status [8]. Re-irradiation offers an

median progression-free survival time ranged from 4 to 7.9 months.

From 2009 to 2017, a total of 318 patients with recurrent GBMs in eight published studies were treated with Cyberknife SRS [30, 34, 42, 44, 46, 48, 51, 54]. The median age ranged from 37 to 59.9 years. The median prescribed marginal dose ranged from 15 to 30 Gy. The median targeted tumor volume ranged from 2 to 24 cc. The median overall survival time after Cyberknife SRS ranged from 5.3 to 12 months, whereas the

bevacizumab [55, 59].

*Tumor Progression and Metastasis*

**4. Discussion**

**226**

**4.1 The role of SRS for recurrent GBMs**

alternative option for treating recurrent GBMs. In a systematic review and metaanalysis of re-irradiation with external beam radiotherapy for recurrent GBMs, Kazmi et al. showed that the 6- and 12-month overall survival times from the time of re-irradiation were 70 and 34%, respectively, whereas the 6- and 12-month progression-free survival times were 40 and 16%, respectively [11]. The overall toxicity rate was low, ranging from 4 to 10%.

SRS has the ability to combine surgical and radio-oncological treatments to deliver a high dose of focused radiation on the focal tumor lesion and spare the adjacent normal anatomical structures. For recurrent GBMs, the majority of tumors tend to grow within 2 cm of the contrast-enhancing lesion border, and SRS seems to be a reasonable tool to add radiation boost for the focal lesion followed by the standard treatment of initial radiation with 60 Gy in 30 fractions [4, 13]. In our present review, despite the different SRS modalities with the median prescribed dose ranging from 6 to 30 Gy, the overall survival time from the treatment of SRS ranged from 3.9 to 17.9 months, where the progression-free survival time from the treatment of SRS ranged from 2.1 to 14.9 months. Severe prognostic factors, such as small tumor volume, younger age, higher KPS score, and lower RPA class, were mostly suggested to be significantly associated with the overall survival time in patients with recurrent GBMs treated with SRS. These results showed that reirradiation with the SRS modality are an alternative and feasible method to manage patients with recurrent GBMs.

#### **4.2 The impact of SRS and adjuvant temozolomide for recurrent GBMs**

Since 2005, temozolomide, which is an alkylating agent, is the most important FDA-approved chemoagent for the standard treatment of patients with newly diagnosed GBMs [1, 4]. The median overall survival time significantly improved from 12.1 to 14.6 months after the patients with newly diagnosed GBMs received combined treatments with radiotherapy and adjuvant temozolomide. However, the disease frequently progresses within 6–9 months, and the 2-year survival rate is less than 25% [62]. The failure of temozolomide treatment has been found to be associated with the expression of MGMT protein [63–65]. Among the GBM patients with a methylated MGMT promoter, the median overall survival time was 21.7 months after treatment with radiotherapy and temozolomide, whereas the median survival time was 15.3 months in the unmethylated group treated with radiotherapy alone [64].

Due to the blood-brain barrier, temozolomide rechallenge is considered to be a reasonable option in patients with recurrent GBMs. In this review, the combination of SRS and temozolomide was employed in three studies [34, 42, 47]. Cyberknife SRS was performed in two studies, and the other study used the Gamma Knife SRS. The median overall survival time ranged from 9 to 15.5 months, and the median progression-free survival time was approximately 7 months after the time of SRS treatment. In 2012, Conti et al. analyzed the effect of adjuvant temozolomide in recurrent GBM patients treated with Cyberknife SRS [34]. The median overall survival time significantly improved from 7 to 12 months, whereas the median progression-free survival time improved from 4 to 7 months. Based on 57 recurrent GBM patients, Kim et al. also showed that the improved median overall survival time and progression-free survival time were 15.5 and 6 months, respectively [47]. Otherwise, in a retrospective review of 61 patients who received Gamma Knife SRS as a salvage treatment at the time of the first progression, Kim et al. showed that the median overall survival time was 14 months in the methylated MGMT promoter group and 9 months in the unmethylated group [53]. Methylation of the MGMT promoter was significantly corrected with better overall survival times and progression-free survival times. The results mentioned above indicated that the

combination of salvage SRS and adjuvant temozolomide may offer an important treatment option to improve the overall survival times in patients with recurrent GBMs.

60 Gy typically applied in the first-line treatment [59]. Although younger age is commonly considered as an important independent prognostic factor that is associated with survival, the selected criteria of salvage SRS for better outcomes need to be investigated in further large prospective studies. In the future, individualized precise multi-modality treatment will play an important role in patients with recurrent GBMs, including the combination of cytotoxic chemotherapy, angiogenesis inhibitors, or immunotherapy [76]. Salvage SRS with a combination of other treatment modalities may offer an alternative therapeutic method to manage

*Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme*

*DOI: http://dx.doi.org/10.5772/intechopen.91163*

Our review suggests that salvage SRS is an important treatment protocol for managing patients with recurrent GBMs. The irradiation doses provided by SRS may improve the clinical outcome of patients with recurrent GBMs, which is not hampered by the standard case of 60 Gy prescribed for newly diagnosed GBMs. The dual role of salvage SRS and other cytotoxic chemoagents, such as temozolomide and bevacizumab, also seems to be effective in the management of recurrent GBMs. Further application of salvage SRS combined with other chemoagents or a new

\*

1 Division of Neurosurgery, Department of Surgery, Sijhih Cathay General

2 Department of Medicine, School of Medicine, Fu Jen Catholic University,

3 Department of Neurological Surgery, Tri-Service General Hospital, National

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

patients with recurrent GBMs.

treatment modality needs to be investigated.

The authors declare no conflict of interest.

Cheng-Ta Hsieh1,2,3 and Da-Tong Ju<sup>3</sup>

Hospital, New Taipei City, Taiwan

Defense Medical Center, Taipei City, Taiwan

provided the original work is properly cited.

\*Address all correspondence to<EMAIL_ADDRESS>
New Taipei City, Taiwan

**229**

**5. Conclusion**

**Conflict of interest**

**Author details**

#### **4.3 The impact of SRS and adjuvant bevacizumab for recurrent GBMs**

Bevacizumab is a recombinant human monoclonal antibody that acts against the vascular endothelial growth factor to prevent the growth and maintenance of tumor blood vessels. In 2009, bevacizumab was approved by the USFDA for the treatment of patients with recurrent GBMs [66, 67]. The use of bevacizumab demonstrated a radiological response of up to 40% [68]. However, in a large prospective phase III trial, the use of adjuvant bevacizumab revealed only improvement in the progression-free survival times from 1.5 to 4.2 months but not in the overall survival times [69]. In a systematic review and meta-analysis, Diaz et al. showed that the survival advantage of bevacizumab at recurrence was limited to 4 months [70]. Although bevacizumab may reduce steroid requirements, there was no additional benefit in the health-related quality of life. The role of bevacizumab in combination with other cytotoxic chemoagents remains unclear.

The role of adjuvant bevacizumab in patients with recurrent GBMs treated with SRS has been reported in nine studies, which were included in our review [35, 37, 39, 40, 44, 46, 49, 55, 59]. The median overall survival time ranged from 5.3 to 17.9 months, whereas the median progression-free survival time ranged from 3.9 to 14.9 months. The comparison of SRA with or without adjuvant bevacizumab was investigated in two studies [35, 37]. Among 49 patients with recurrent GBMs, Cuneo et al. showed that the median overall survival time was 11.2 months in patients receiving SRS and adjuvant bevacizumab and 3.9 months in patients receiving SRS therapy alone [35]. The progression-free survival time also improved from 2.1 to 5.2 months. In a case-controlled study of patients with recurrent GBMs treated with SRS and adjuvant bevacizumab plus temozolomide or irinotecan, Park et al. also showed that the median overall survival time and progression-free survival time improved from 12.2 to 17.9 months and 6.7 to 14.9 months, respectively [37]. In a retrospective study and review of the literature, Morris et al. reported that the dual role of bevacizumab and radiosurgery had a benefit in the overall survival times (11.2–17.9 months) and progression-free survival times (3.9–14.9 months). These results showed the potential therapeutic effect of adjuvant bevacizumab in combination with other treatment modalities, such as cytotoxic chemoagents or salvage SRS, in patients with recurrent GBMs.

#### **4.4 The future of SRS for recurrent GBMs**

With the advance of molecular diagnostic techniques, newly diagnosed GBMs should be classified based on the mutant status of isocitrate dehydrogenase 1 defined by the updated guidelines of the World Health Organization in 2016 [71]. These molecular profiles influence the overall survival time and the possible therapeutic effects of chemoagents. Similar to the recurrent GBMs, several main molecules, such as MLH1 [72], CASP8 [73], MSH2 [74], and P53 [74], were found to be different from primary GBMs [75]. The molecular features, intra-tumor heterogeneity, immunogenicity, and microenvironment around the tumor contribute to the clinical prognostic outcomes in patients with recurrent GBMs [7, 10]. Reoperation, re-chemotherapy, and re-irradiation currently remain as the standard treatments for most patients with recurrent GBMs [2, 7, 10, 11]. A growing body of literature, including our current review, demonstrates the tolerability and efficacy of salvage SRS for recurrent GBMs, which did not inhibit re-irradiation, followed by a total of *Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme DOI: http://dx.doi.org/10.5772/intechopen.91163*

60 Gy typically applied in the first-line treatment [59]. Although younger age is commonly considered as an important independent prognostic factor that is associated with survival, the selected criteria of salvage SRS for better outcomes need to be investigated in further large prospective studies. In the future, individualized precise multi-modality treatment will play an important role in patients with recurrent GBMs, including the combination of cytotoxic chemotherapy, angiogenesis inhibitors, or immunotherapy [76]. Salvage SRS with a combination of other treatment modalities may offer an alternative therapeutic method to manage patients with recurrent GBMs.

#### **5. Conclusion**

combination of salvage SRS and adjuvant temozolomide may offer an important treatment option to improve the overall survival times in patients with recurrent

Bevacizumab is a recombinant human monoclonal antibody that acts against the vascular endothelial growth factor to prevent the growth and maintenance of tumor blood vessels. In 2009, bevacizumab was approved by the USFDA for the treatment of patients with recurrent GBMs [66, 67]. The use of bevacizumab demonstrated a radiological response of up to 40% [68]. However, in a large prospective phase III

**4.3 The impact of SRS and adjuvant bevacizumab for recurrent GBMs**

trial, the use of adjuvant bevacizumab revealed only improvement in the

with other cytotoxic chemoagents remains unclear.

salvage SRS, in patients with recurrent GBMs.

**4.4 The future of SRS for recurrent GBMs**

**228**

progression-free survival times from 1.5 to 4.2 months but not in the overall survival times [69]. In a systematic review and meta-analysis, Diaz et al. showed that the survival advantage of bevacizumab at recurrence was limited to 4 months [70]. Although bevacizumab may reduce steroid requirements, there was no additional benefit in the health-related quality of life. The role of bevacizumab in combination

The role of adjuvant bevacizumab in patients with recurrent GBMs treated with SRS has been reported in nine studies, which were included in our review [35, 37, 39, 40, 44, 46, 49, 55, 59]. The median overall survival time ranged from 5.3 to 17.9 months, whereas the median progression-free survival time ranged from 3.9 to 14.9 months. The comparison of SRA with or without adjuvant bevacizumab was investigated in two studies [35, 37]. Among 49 patients with recurrent GBMs, Cuneo et al. showed that the median overall survival time was 11.2 months in patients receiving SRS and adjuvant bevacizumab and 3.9 months in patients receiving SRS therapy alone [35]. The progression-free survival time also improved from 2.1 to 5.2 months. In a case-controlled study of patients with recurrent GBMs treated with SRS and adjuvant bevacizumab plus temozolomide or irinotecan, Park et al. also showed that the median overall survival time and progression-free survival time improved from 12.2 to 17.9 months and 6.7 to 14.9 months, respectively [37]. In a retrospective study and review of the literature, Morris et al. reported that the dual role of bevacizumab and radiosurgery had a benefit in the overall survival times (11.2–17.9 months) and progression-free survival times (3.9–14.9 months). These results showed the potential therapeutic effect of adjuvant bevacizumab in combination with other treatment modalities, such as cytotoxic chemoagents or

With the advance of molecular diagnostic techniques, newly diagnosed GBMs

should be classified based on the mutant status of isocitrate dehydrogenase 1 defined by the updated guidelines of the World Health Organization in 2016 [71]. These molecular profiles influence the overall survival time and the possible therapeutic effects of chemoagents. Similar to the recurrent GBMs, several main molecules, such as MLH1 [72], CASP8 [73], MSH2 [74], and P53 [74], were found to be different from primary GBMs [75]. The molecular features, intra-tumor heterogeneity, immunogenicity, and microenvironment around the tumor contribute to the clinical prognostic outcomes in patients with recurrent GBMs [7, 10]. Reoperation, re-chemotherapy, and re-irradiation currently remain as the standard treatments for most patients with recurrent GBMs [2, 7, 10, 11]. A growing body of literature, including our current review, demonstrates the tolerability and efficacy of salvage SRS for recurrent GBMs, which did not inhibit re-irradiation, followed by a total of

GBMs.

*Tumor Progression and Metastasis*

Our review suggests that salvage SRS is an important treatment protocol for managing patients with recurrent GBMs. The irradiation doses provided by SRS may improve the clinical outcome of patients with recurrent GBMs, which is not hampered by the standard case of 60 Gy prescribed for newly diagnosed GBMs. The dual role of salvage SRS and other cytotoxic chemoagents, such as temozolomide and bevacizumab, also seems to be effective in the management of recurrent GBMs. Further application of salvage SRS combined with other chemoagents or a new treatment modality needs to be investigated.

#### **Conflict of interest**

The authors declare no conflict of interest.

#### **Author details**

Cheng-Ta Hsieh1,2,3 and Da-Tong Ju<sup>3</sup> \*

1 Division of Neurosurgery, Department of Surgery, Sijhih Cathay General Hospital, New Taipei City, Taiwan

2 Department of Medicine, School of Medicine, Fu Jen Catholic University, New Taipei City, Taiwan

3 Department of Neurological Surgery, Tri-Service General Hospital, National Defense Medical Center, Taipei City, Taiwan

\*Address all correspondence to<EMAIL_ADDRESS>
© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

[1] Preusser M, de Ribaupierre S, Wöhrer A, Erridge SC, Hegi M, Weller M, et al. Current concepts and management of glioblastoma. Annals of Neurology. 2011;**70**(1):9-21

[2] Weller M, Cloughesy T, Perry JR, Wick W. Standards of care for treatment of recurrent glioblastoma— Are we there yet? Neuro-Oncology. 2013;**15**(1):4-27

[3] Ostrom QT, Cioffi G, Gittleman H, Patil N, Waite K, Kruchko C, et al. CBTRUS statistical report: Primary brain and other central nervous system tumors diagnosed in the United States in 2012–2016. Neuro-Oncology. 2019;**21** (Suppl. 5):v1-v100

[4] Stupp R, Mason WP, van den Bent MJ, Weller M, Fisher B, Taphoorn MJ, et al. Radiotherapy plus concomitant and adjuvant temozolomide for glioblastoma. The New England Journal of Medicine. 2005;**352**(10):987-996

[5] Sanai N, Polley MY, McDermott MW, Parsa AT, Berger MS. An extent of resection threshold for newly diagnosed glioblastomas. Journal of Neurosurgery. 2011;**115**(1):3-8

[6] Hou LC, Veeravagu A, Hsu AR, Tse VC. Recurrent glioblastoma multiforme: A review of natural history and management options. Neurosurgical Focus. 2006;**20**(4):E5

[7] Mallick S, Benson R, Hakim A, Rath GK. Management of glioblastoma after recurrence: A changing paradigm. Journal of the Egyptian National Cancer Institute. 2016;**28**(4):199-210

[8] Bloch O, Han SJ, Cha S, Sun MZ, Aghi MK, McDermott MW, et al. Impact of extent of resection for recurrent glioblastoma on overall survival: Clinical article. Journal of Neurosurgery. 2012;**117**(6):1032-1038 [9] Lu VM, Goyal A, Graffeo CS, Perry A, Burns TC, Parney IF, et al. Survival benefit of maximal resection for glioblastoma reoperation in the temozolomide era: A meta-analysis. World Neurosurgery. 2019;**127**:31-37

radiosurgery and brachytherapy in the treatment of recurrent glioblastoma multiforme. Neurosurgery. 1995;**36**(2):

*DOI: http://dx.doi.org/10.5772/intechopen.91163*

*Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme*

[23] Mahajan A, McCutcheon IE, Suki D,

Weinberg JS, et al. Case-control study of stereotactic radiosurgery for recurrent glioblastoma multiforme. Journal of Neurosurgery. 2005;**103**(2):210-217

[24] Kong DS, Lee JI, Park K, Kim JH, Lim DH, Nam DH. Efficacy of stereotactic radiosurgery as a salvage treatment for recurrent malignant gliomas. Cancer. 2008;**112**(9):2046-2051

Kavanagh BD, Gaspar LE, Lillehei K, Stuhr K, et al. A phase I dose-escalation study of fractionated stereotactic radiosurgery in combination with gefitinib in patients with recurrent malignant gliomas. International Journal of Radiation Oncology, Biology, Physics.

[26] Biswas T, Okunieff P, Schell MC, Smudzin T, Pilcher WH, Bakos RS, et al.

glioblastoma: Retrospective analysis. Radiotherapy and Oncology. 2009;**4**:11

[27] Kida Y, Yoshimoto M, Hasegawa T. Radiosurgery for intracranial gliomas. Progress in Neurological Surgery. 2009;

Mikkelsen T, Rosenblum M, Movsas B, et al. Salvage reirradiation for recurrent

Sherman JH, Jagannathan J, Sheehan JP.

[30] Villavicencio AT, Burneikiene S, Romanelli P, Fariselli L, McNeely L, Lipani JD, et al. Survival following stereotactic radiosurgery for newly

Stereotactic radiosurgery for

[28] Patel M, Siddiqui F, Jin JY,

glioblastoma with radiosurgery: Radiographic response and improved survival. Journal of Neuro-Oncology.

[29] Pouratian N, Crowley RW,

Gamma knife radiosurgery after radiation therapy as an adjunctive treatment for glioblastoma. Journal of Neuro-Oncology. 2009;**94**(3):409-418

2009;**92**(2):185-191

Chang EL, Hassenbusch SJ,

[25] Schwer AL, Damek DM,

2008;**70**(4):993-1001

**22**:122-128

McDermott M, Lamborn K, Sneed PK, Wara WM, et al. Gamma knife for glioma: Selection factors and survival. International Journal of Radiation Oncology, Biology, Physics. 1996;**36**(5):

[18] Kondziolka D, Flickinger JC, Bissonette DJ, Bozik M, Lunsford LD. Survival benefit of stereotactic radiosurgery for patients with malignant glial neoplasms.

Neurosurgery. 1997;**41**(4):776-783

[19] Cho KH, Hall WA, Gerbi BJ, Higgins PD, McGuire WA, Clark HB. Single dose versus fractionated

Physics. 1999;**45**(5):1133-1141

2002;**54**(5):1397-1404

**231**

stereotactic radiotherapy for recurrent high-grade gliomas. International Journal of Radiation Oncology, Biology,

[20] Larson DA, Prados M, Lamborn KR, Smith V, Sneed PK, Chang S, et al. Phase II study of high central dose Gamma knife radiosurgery and marimastat in patients with recurrent malignant glioma. International Journal of Radiation Oncology, Biology, Physics.

[21] Combs SE, Widmer V, Thilmann C, Hof H, Debus J, Schulz-Ertner D. Stereotactic radiosurgery (SRS): Treatment option for recurrent glioblastoma multiforme (GBM). Cancer. 2005;**104**(10):2168-2173

[22] Hsieh PC, Chandler JP, Bhangoo S, Panagiotopoulos K, Kalapurakal JA, Marymont MH, et al. Adjuvant gamma knife stereotactic radiosurgery at the time of tumor progression potentially improves survival for patients with glioblastoma multiforme. Neurosurgery. 2005;**57**(4):684-692 discussion 684

275-282 discussion 82-4

1045-1053

discussion 83-5

[17] Larson DA, Gutin PH,

[10] Chaul-Barbosa C, Marques DF. How we treat recurrent glioblastoma today and current evidence. Current Oncology Reports. 2019;**21**(10):94

[11] Kazmi F, Soon YY, Leong YH, Koh WY, Vellayappan B. Re-irradiation for recurrent glioblastoma (GBM): A systematic review and meta-analysis. Journal of Neuro-Oncology. 2019; **142**(1):79-90

[12] Jayamanne D, Wheeler H, Brazier D, Newey A, Kastelan M, Guo L, et al. Predicting patterns of failure in temporal lobe GBMs: Possible implications on radiotherapy treatment portals. Radiotherapy and Oncology. 2018;**13**(1):133

[13] Niranjan A, Kano H, Iyer A, Kondziolka D, Flickinger JC, Lunsford LD. Role of adjuvant or salvage radiosurgery in the management of unresected residual or progressive glioblastoma multiforme in the pre-bevacizumab era. Journal of Neurosurgery. 2015;**122**(4):757-765

[14] Chamberlain MC, Barba D, Kormanik P, Shea WM. Stereotactic radiosurgery for recurrent gliomas. Cancer. 1994;**74**(4):1342-1347

[15] Hall WA, Djalilian HR, Sperduto PW, Cho KH, Gerbi BJ, Gibbons JP, et al. Stereotactic radiosurgery for recurrent malignant gliomas. Journal of Clinical Oncology. 1995;**13**(7):1642-1648

[16] Shrieve DC, Alexander E 3rd, Wen PY, Fine HA, Kooy HM, Black PM, et al. Comparison of stereotactic

*Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme DOI: http://dx.doi.org/10.5772/intechopen.91163*

radiosurgery and brachytherapy in the treatment of recurrent glioblastoma multiforme. Neurosurgery. 1995;**36**(2): 275-282 discussion 82-4

**References**

2013;**15**(1):4-27

(Suppl. 5):v1-v100

2005;**352**(10):987-996

2011;**115**(1):3-8

Focus. 2006;**20**(4):E5

**230**

[1] Preusser M, de Ribaupierre S, Wöhrer A, Erridge SC, Hegi M, Weller M, et al. Current concepts and management of glioblastoma. Annals of

*Tumor Progression and Metastasis*

[9] Lu VM, Goyal A, Graffeo CS, Perry A, Burns TC, Parney IF, et al. Survival benefit of maximal resection for glioblastoma reoperation in the temozolomide era: A meta-analysis. World Neurosurgery. 2019;**127**:31-37

Reports. 2019;**21**(10):94

**142**(1):79-90

2018;**13**(1):133

[10] Chaul-Barbosa C, Marques DF. How we treat recurrent glioblastoma today and current evidence. Current Oncology

[11] Kazmi F, Soon YY, Leong YH, Koh WY, Vellayappan B. Re-irradiation for recurrent glioblastoma (GBM): A systematic review and meta-analysis. Journal of Neuro-Oncology. 2019;

[12] Jayamanne D, Wheeler H,

[13] Niranjan A, Kano H, Iyer A, Kondziolka D, Flickinger JC, Lunsford LD. Role of adjuvant or salvage radiosurgery in the management of unresected residual or progressive glioblastoma multiforme in the pre-bevacizumab era. Journal of Neurosurgery. 2015;**122**(4):757-765

[14] Chamberlain MC, Barba D, Kormanik P, Shea WM. Stereotactic radiosurgery for recurrent gliomas. Cancer. 1994;**74**(4):1342-1347

[15] Hall WA, Djalilian HR, Sperduto PW, Cho KH, Gerbi BJ, Gibbons JP, et al. Stereotactic

1995;**13**(7):1642-1648

radiosurgery for recurrent malignant gliomas. Journal of Clinical Oncology.

[16] Shrieve DC, Alexander E 3rd, Wen PY, Fine HA, Kooy HM, Black PM,

et al. Comparison of stereotactic

Brazier D, Newey A, Kastelan M, Guo L, et al. Predicting patterns of failure in temporal lobe GBMs: Possible

implications on radiotherapy treatment portals. Radiotherapy and Oncology.

[2] Weller M, Cloughesy T, Perry JR, Wick W. Standards of care for

treatment of recurrent glioblastoma— Are we there yet? Neuro-Oncology.

[3] Ostrom QT, Cioffi G, Gittleman H, Patil N, Waite K, Kruchko C, et al. CBTRUS statistical report: Primary brain and other central nervous system tumors diagnosed in the United States in 2012–2016. Neuro-Oncology. 2019;**21**

[4] Stupp R, Mason WP, van den Bent MJ, Weller M, Fisher B, Taphoorn MJ, et al. Radiotherapy plus concomitant and adjuvant temozolomide for glioblastoma. The New England Journal of Medicine.

[5] Sanai N, Polley MY, McDermott MW, Parsa AT, Berger MS. An extent of resection threshold for newly diagnosed glioblastomas. Journal of Neurosurgery.

[6] Hou LC, Veeravagu A, Hsu AR, Tse VC. Recurrent glioblastoma

[7] Mallick S, Benson R, Hakim A, Rath GK. Management of glioblastoma after recurrence: A changing paradigm. Journal of the Egyptian National Cancer

[8] Bloch O, Han SJ, Cha S, Sun MZ, Aghi MK, McDermott MW, et al. Impact of extent of resection for recurrent glioblastoma on overall survival: Clinical article. Journal of Neurosurgery. 2012;**117**(6):1032-1038

Institute. 2016;**28**(4):199-210

multiforme: A review of natural history and management options. Neurosurgical

Neurology. 2011;**70**(1):9-21

[17] Larson DA, Gutin PH, McDermott M, Lamborn K, Sneed PK, Wara WM, et al. Gamma knife for glioma: Selection factors and survival. International Journal of Radiation Oncology, Biology, Physics. 1996;**36**(5): 1045-1053

[18] Kondziolka D, Flickinger JC, Bissonette DJ, Bozik M, Lunsford LD. Survival benefit of stereotactic radiosurgery for patients with malignant glial neoplasms. Neurosurgery. 1997;**41**(4):776-783 discussion 83-5

[19] Cho KH, Hall WA, Gerbi BJ, Higgins PD, McGuire WA, Clark HB. Single dose versus fractionated stereotactic radiotherapy for recurrent high-grade gliomas. International Journal of Radiation Oncology, Biology, Physics. 1999;**45**(5):1133-1141

[20] Larson DA, Prados M, Lamborn KR, Smith V, Sneed PK, Chang S, et al. Phase II study of high central dose Gamma knife radiosurgery and marimastat in patients with recurrent malignant glioma. International Journal of Radiation Oncology, Biology, Physics. 2002;**54**(5):1397-1404

[21] Combs SE, Widmer V, Thilmann C, Hof H, Debus J, Schulz-Ertner D. Stereotactic radiosurgery (SRS): Treatment option for recurrent glioblastoma multiforme (GBM). Cancer. 2005;**104**(10):2168-2173

[22] Hsieh PC, Chandler JP, Bhangoo S, Panagiotopoulos K, Kalapurakal JA, Marymont MH, et al. Adjuvant gamma knife stereotactic radiosurgery at the time of tumor progression potentially improves survival for patients with glioblastoma multiforme. Neurosurgery. 2005;**57**(4):684-692 discussion 684

[23] Mahajan A, McCutcheon IE, Suki D, Chang EL, Hassenbusch SJ, Weinberg JS, et al. Case-control study of stereotactic radiosurgery for recurrent glioblastoma multiforme. Journal of Neurosurgery. 2005;**103**(2):210-217

[24] Kong DS, Lee JI, Park K, Kim JH, Lim DH, Nam DH. Efficacy of stereotactic radiosurgery as a salvage treatment for recurrent malignant gliomas. Cancer. 2008;**112**(9):2046-2051

[25] Schwer AL, Damek DM, Kavanagh BD, Gaspar LE, Lillehei K, Stuhr K, et al. A phase I dose-escalation study of fractionated stereotactic radiosurgery in combination with gefitinib in patients with recurrent malignant gliomas. International Journal of Radiation Oncology, Biology, Physics. 2008;**70**(4):993-1001

[26] Biswas T, Okunieff P, Schell MC, Smudzin T, Pilcher WH, Bakos RS, et al. Stereotactic radiosurgery for glioblastoma: Retrospective analysis. Radiotherapy and Oncology. 2009;**4**:11

[27] Kida Y, Yoshimoto M, Hasegawa T. Radiosurgery for intracranial gliomas. Progress in Neurological Surgery. 2009; **22**:122-128

[28] Patel M, Siddiqui F, Jin JY, Mikkelsen T, Rosenblum M, Movsas B, et al. Salvage reirradiation for recurrent glioblastoma with radiosurgery: Radiographic response and improved survival. Journal of Neuro-Oncology. 2009;**92**(2):185-191

[29] Pouratian N, Crowley RW, Sherman JH, Jagannathan J, Sheehan JP. Gamma knife radiosurgery after radiation therapy as an adjunctive treatment for glioblastoma. Journal of Neuro-Oncology. 2009;**94**(3):409-418

[30] Villavicencio AT, Burneikiene S, Romanelli P, Fariselli L, McNeely L, Lipani JD, et al. Survival following stereotactic radiosurgery for newly

diagnosed and recurrent glioblastoma multiforme: A multicenter experience. Neurosurgical Review. 2009;**32**(4): 417-424

[31] Elliott RE, Parker EC, Rush SC, Kalhorn SP, Moshel YA, Narayana A, et al. Efficacy of gamma knife radiosurgery for small-volume recurrent malignant gliomas after initial radical resection. World Neurosurgery. 2011;**76** (1–2):128-140 discussion 61-2

[32] Maranzano E, Anselmo P, Casale M, Trippa F, Carletti S, Principi M, et al. Treatment of recurrent glioblastoma with stereotactic radiotherapy: Longterm results of a mono-institutional trial. Tumori. 2011;**97**(1):56-61

[33] Sirin S, Oysul K, Surenkok S, Sager O, Dincoglan F, Dirican B, et al. Linear accelerator-based stereotactic radiosurgery in recurrent glioblastoma: A single center experience. Vojnosanitetski Pregled. 2011;**68**(11): 961-966

[34] Conti A, Pontoriero A, Arpa D, Siragusa C, Tomasello C, Romanelli P, et al. Efficacy and toxicity of Cyberknife re-irradiation and "dose dense" temozolomide for recurrent gliomas. Acta Neurochirurgica. 2012;**154**(2): 203-209

[35] Cuneo KC, Vredenburgh JJ, Sampson JH, Reardon DA, Desjardins A, Peters KB, et al. Safety and efficacy of stereotactic radiosurgery and adjuvant bevacizumab in patients with recurrent malignant gliomas. International Journal of Radiation Oncology, Biology, Physics. 2012;**82**(5):2018-2024

[36] Koga T, Maruyama K, Tanaka M, Ino Y, Saito N, Nakagawa K, et al. Extended field stereotactic radiosurgery for recurrent glioblastoma. Cancer. 2012;**118**(17):4193-4200

[37] Park KJ, Kano H, Iyer A, Liu X, Niranjan A, Flickinger JC, et al. Salvage gamma knife stereotactic radiosurgery followed by bevacizumab for recurrent glioblastoma multiforme: A case-control study. Journal of Neuro-Oncology. 2012; **107**(2):323-333

Ávila R, Guerrero-Tejada R, Saura-Rojas

*DOI: http://dx.doi.org/10.5772/intechopen.91163*

*Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme*

et al. Gamma knife radiosurgery in recurrent glioblastoma. Stereotactic and Functional Neurosurgery. 2016;**94**(4):

[51] Holt DE, Bernard ME, Quan K, Clump DA, Engh JA, Burton SA, et al. Salvage stereotactic radiosurgery for recurrent glioblastoma multiforme with prior radiation therapy. Journal of Cancer Research and Therapeutics.

[52] Imber BS, Kanungo I, Braunstein S, Barani IJ, Fogh SE, Nakamura JL, et al. Indications and efficacy of gamma knife stereotactic radiosurgery for recurrent glioblastoma: 2 decades of institutional experience. Neurosurgery. 2017;**80**(1):

[53] Kim BS, Kong DS, Seol HJ, Nam DH, Lee JI. MGMT promoter methylation status as a prognostic factor for the outcome of gamma knife radiosurgery for recurrent glioblastoma. Journal of Neuro-Oncology. 2017;**133**(3):615-622

[54] Sutera PA, Bernard ME, Gill BS, Quan K, Engh JA, Burton SA, et al. Salvage stereotactic radiosurgery for recurrent gliomas with prior radiation therapy. Future Oncology. 2017;**13**(29):

[55] Abbassy M, Missios S, Barnett GH,

[56] Gigliotti MJ, Hasan S, Karlovits SM, Ranjan T, Wegner RE. Re-irradiation with stereotactic radiosurgery/ radiotherapy for recurrent high-grade gliomas: Improved survival in the modern era. Stereotactic and Functional Neurosurgery. 2018;**96**(5):289-295

Simonova G, Novotny J Jr. Gamma knife

Brewer C, Peereboom DM, Ahluwalia M, et al. Phase I trial of radiosurgery dose escalation plus bevacizumab in patients with recurrent/ progressive glioblastoma. Neurosurgery.

[57] Guseynova K, Liscak R,

2018;**83**(3):385-392

2016;**12**(4):1243-1248

265-272

129-139

2681-2690

E, et al. Salvage radiosurgery for selected patients with recurrent malignant gliomas. BioMed Research International. 2014;**2014**:657953

[44] Yazici G, Cengiz M, Ozyigit G, Eren G, Yildiz F, Akyol F, et al. Hypofractionated stereotactic

**120**(1):117-123

2015;**38**(4):705-713

in Oncology. 2015;**5**:106

468-473

**233**

[47] Kim HR, Kim KH, Kong DS, Seol HJ, Nam DH, Lim DH, et al. Outcome of salvage treatment for recurrent glioblastoma. Journal of Clinical Neuroscience. 2015;**22**(3):

[48] Pinzi V, Orsi C, Marchetti M, Milanesi IM, Bianchi LC, DiMeco F, et al. Radiosurgery reirradiation for high-grade glioma recurrence: A retrospective analysis. Neurological Sciences. 2015;**36**(8):1431-1440

[49] Bokstein F, Blumenthal DT, Corn BW, Gez E, Matceyevsky D, Shtraus N, et al. Stereotactic radiosurgery (SRS) in high-grade glioma: Judicious selection of small target volumes improves results. Journal of Neuro-Oncology. 2016;**126**(3):551-557

[50] Frischer JM, Marosi C, Woehrer A, Hainfellner JA, Dieckmann KU, Eiter H,

reirradiation for recurrent glioblastoma. Journal of Neuro-Oncology. 2014;

[45] Bir SC, Connor DE Jr, Ambekar S, Wilden JA, Nanda A. Factors predictive of improved overall survival following stereotactic radiosurgery for recurrent glioblastoma. Neurosurgical Review.

[46] Hasan S, Chen E, Lanciano R, Yang J, Hanlon A, Lamond J, et al. Salvage fractionated stereotactic radiotherapy with or without

chemotherapy and immunotherapy for recurrent glioblastoma multiforme: A single institution experience. Frontiers

[38] Skeie BS, Enger PØ, Brøgger J, Ganz JC, Thorsen F, Heggdal JI, et al. Gamma knife surgery versus reoperation for recurrent glioblastoma multiforme. World Neurosurgery. 2012; **78**(6):658-669

[39] Cabrera AR, Cuneo KC, Desjardins A, Sampson JH, McSherry F, Herndon JE 2nd, et al. Concurrent stereotactic radiosurgery and bevacizumab in recurrent malignant gliomas: A prospective trial. International Journal of Radiation Oncology, Biology, Physics. 2013;**86**(5): 873-879

[40] Clark GM, McDonald AM, Nabors LB, Fathalla-Shaykh H, Han X, Willey CD, et al. Hypofractionated stereotactic radiosurgery with concurrent bevacizumab for recurrent malignant gliomas: The University of Alabama at Birmingham experience. Neurooncology Practice. 2014;**1**(4): 172-177

[41] Dodoo E, Huffmann B, Peredo I, Grinaker H, Sinclair G, Machinis T, et al. Increased survival using delayed gamma knife radiosurgery for recurrent high-grade glioma: A feasibility study. World Neurosurgery. 2014;**82**(5):e623 e632

[42] Greenspoon JN, Sharieff W, Hirte H, Overholt A, Devillers R, Gunnarsson T, et al. Fractionated stereotactic radiosurgery with concurrent temozolomide chemotherapy for locally recurrent glioblastoma multiforme: A prospective cohort study. OncoTargets and Therapy. 2014;**7**:485-490

[43] Martínez-Carrillo M, Tovar-Martín I, Zurita-Herrera M, Del Moral*Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme DOI: http://dx.doi.org/10.5772/intechopen.91163*

Ávila R, Guerrero-Tejada R, Saura-Rojas E, et al. Salvage radiosurgery for selected patients with recurrent malignant gliomas. BioMed Research International. 2014;**2014**:657953

diagnosed and recurrent glioblastoma multiforme: A multicenter experience. Neurosurgical Review. 2009;**32**(4):

*Tumor Progression and Metastasis*

gamma knife stereotactic radiosurgery followed by bevacizumab for recurrent glioblastoma multiforme: A case-control study. Journal of Neuro-Oncology. 2012;

[38] Skeie BS, Enger PØ, Brøgger J, Ganz JC, Thorsen F, Heggdal JI, et al.

reoperation for recurrent glioblastoma multiforme. World Neurosurgery. 2012;

Desjardins A, Sampson JH, McSherry F, Herndon JE 2nd, et al. Concurrent stereotactic radiosurgery and bevacizumab in recurrent malignant

Gamma knife surgery versus

[39] Cabrera AR, Cuneo KC,

gliomas: A prospective trial. International Journal of Radiation Oncology, Biology, Physics. 2013;**86**(5):

[40] Clark GM, McDonald AM,

Nabors LB, Fathalla-Shaykh H, Han X, Willey CD, et al. Hypofractionated stereotactic radiosurgery with

concurrent bevacizumab for recurrent malignant gliomas: The University of Alabama at Birmingham experience. Neurooncology Practice. 2014;**1**(4):

[41] Dodoo E, Huffmann B, Peredo I, Grinaker H, Sinclair G, Machinis T, et al. Increased survival using delayed gamma knife radiosurgery for recurrent high-grade glioma: A feasibility study. World Neurosurgery. 2014;**82**(5):e623-

[42] Greenspoon JN, Sharieff W, Hirte H, Overholt A, Devillers R, Gunnarsson T, et al. Fractionated stereotactic radiosurgery with concurrent temozolomide

chemotherapy for locally recurrent glioblastoma multiforme: A prospective cohort study. OncoTargets and Therapy.

[43] Martínez-Carrillo M, Tovar-Martín I, Zurita-Herrera M, Del Moral-

**107**(2):323-333

**78**(6):658-669

873-879

172-177

e632

2014;**7**:485-490

[31] Elliott RE, Parker EC, Rush SC, Kalhorn SP, Moshel YA, Narayana A, et al. Efficacy of gamma knife

(1–2):128-140 discussion 61-2

[33] Sirin S, Oysul K, Surenkok S, Sager O, Dincoglan F, Dirican B, et al. Linear accelerator-based stereotactic radiosurgery in recurrent glioblastoma:

Vojnosanitetski Pregled. 2011;**68**(11):

[34] Conti A, Pontoriero A, Arpa D, Siragusa C, Tomasello C, Romanelli P, et al. Efficacy and toxicity of Cyberknife

re-irradiation and "dose dense" temozolomide for recurrent gliomas. Acta Neurochirurgica. 2012;**154**(2):

[35] Cuneo KC, Vredenburgh JJ,

2012;**82**(5):2018-2024

2012;**118**(17):4193-4200

**232**

Sampson JH, Reardon DA, Desjardins A, Peters KB, et al. Safety and efficacy of stereotactic radiosurgery and adjuvant bevacizumab in patients with recurrent malignant gliomas. International Journal of Radiation Oncology, Biology, Physics.

[36] Koga T, Maruyama K, Tanaka M, Ino Y, Saito N, Nakagawa K, et al. Extended field stereotactic radiosurgery for recurrent glioblastoma. Cancer.

[37] Park KJ, Kano H, Iyer A, Liu X, Niranjan A, Flickinger JC, et al. Salvage

A single center experience.

961-966

203-209

radiosurgery for small-volume recurrent malignant gliomas after initial radical resection. World Neurosurgery. 2011;**76**

[32] Maranzano E, Anselmo P, Casale M, Trippa F, Carletti S, Principi M, et al. Treatment of recurrent glioblastoma with stereotactic radiotherapy: Longterm results of a mono-institutional trial. Tumori. 2011;**97**(1):56-61

417-424

[44] Yazici G, Cengiz M, Ozyigit G, Eren G, Yildiz F, Akyol F, et al. Hypofractionated stereotactic reirradiation for recurrent glioblastoma. Journal of Neuro-Oncology. 2014; **120**(1):117-123

[45] Bir SC, Connor DE Jr, Ambekar S, Wilden JA, Nanda A. Factors predictive of improved overall survival following stereotactic radiosurgery for recurrent glioblastoma. Neurosurgical Review. 2015;**38**(4):705-713

[46] Hasan S, Chen E, Lanciano R, Yang J, Hanlon A, Lamond J, et al. Salvage fractionated stereotactic radiotherapy with or without chemotherapy and immunotherapy for recurrent glioblastoma multiforme: A single institution experience. Frontiers in Oncology. 2015;**5**:106

[47] Kim HR, Kim KH, Kong DS, Seol HJ, Nam DH, Lim DH, et al. Outcome of salvage treatment for recurrent glioblastoma. Journal of Clinical Neuroscience. 2015;**22**(3): 468-473

[48] Pinzi V, Orsi C, Marchetti M, Milanesi IM, Bianchi LC, DiMeco F, et al. Radiosurgery reirradiation for high-grade glioma recurrence: A retrospective analysis. Neurological Sciences. 2015;**36**(8):1431-1440

[49] Bokstein F, Blumenthal DT, Corn BW, Gez E, Matceyevsky D, Shtraus N, et al. Stereotactic radiosurgery (SRS) in high-grade glioma: Judicious selection of small target volumes improves results. Journal of Neuro-Oncology. 2016;**126**(3):551-557

[50] Frischer JM, Marosi C, Woehrer A, Hainfellner JA, Dieckmann KU, Eiter H, et al. Gamma knife radiosurgery in recurrent glioblastoma. Stereotactic and Functional Neurosurgery. 2016;**94**(4): 265-272

[51] Holt DE, Bernard ME, Quan K, Clump DA, Engh JA, Burton SA, et al. Salvage stereotactic radiosurgery for recurrent glioblastoma multiforme with prior radiation therapy. Journal of Cancer Research and Therapeutics. 2016;**12**(4):1243-1248

[52] Imber BS, Kanungo I, Braunstein S, Barani IJ, Fogh SE, Nakamura JL, et al. Indications and efficacy of gamma knife stereotactic radiosurgery for recurrent glioblastoma: 2 decades of institutional experience. Neurosurgery. 2017;**80**(1): 129-139

[53] Kim BS, Kong DS, Seol HJ, Nam DH, Lee JI. MGMT promoter methylation status as a prognostic factor for the outcome of gamma knife radiosurgery for recurrent glioblastoma. Journal of Neuro-Oncology. 2017;**133**(3):615-622

[54] Sutera PA, Bernard ME, Gill BS, Quan K, Engh JA, Burton SA, et al. Salvage stereotactic radiosurgery for recurrent gliomas with prior radiation therapy. Future Oncology. 2017;**13**(29): 2681-2690

[55] Abbassy M, Missios S, Barnett GH, Brewer C, Peereboom DM, Ahluwalia M, et al. Phase I trial of radiosurgery dose escalation plus bevacizumab in patients with recurrent/ progressive glioblastoma. Neurosurgery. 2018;**83**(3):385-392

[56] Gigliotti MJ, Hasan S, Karlovits SM, Ranjan T, Wegner RE. Re-irradiation with stereotactic radiosurgery/ radiotherapy for recurrent high-grade gliomas: Improved survival in the modern era. Stereotactic and Functional Neurosurgery. 2018;**96**(5):289-295

[57] Guseynova K, Liscak R, Simonova G, Novotny J Jr. Gamma knife radiosurgery for local recurrence of glioblastoma. Neuro Endocrinology Letters. 2018;**39**(4):281-287

[58] Sharma M, Schroeder JL, Elson P, Meola A, Barnett GH, Vogelbaum MA, et al. Outcomes and prognostic stratification of patients with recurrent glioblastoma treated with salvage stereotactic radiosurgery. Journal of Neurosurgery. 2018:1-11

[59] Morris SL, Zhu P, Rao M, Martir M, Zhu JJ, Hsu S, et al. Gamma knife stereotactic radiosurgery in combination with bevacizumab for recurrent glioblastoma. World Neurosurgery. 2019;**127**:e523-e533

[60] Sanghavi S, Skrupky R, Badie B, Robins I, Tome W, Mehta MP. Recurrent malignant gliomas treated with radiosurgery. Journal of Radiosurgery. 1999;**2**(3):119-125

[61] Park JL, Suh JH, Barnett GH, Reddy CA, Peereboom DM, Stevens GHJ, et al. Survival after stereotactic radiosurgery for recurrent glioblastoma multiforme. Journal of Radiosurgery. 2000;**3**(4):169-175

[62] Wen PY, Kesari S. Malignant gliomas in adults. The New England Journal of Medicine. 2008;**359**(5): 492-507

[63] Silber JR, Bobola MS, Blank A, Chamberlain MC. O6-methylguanine-DNA methyltransferase in glioma therapy: Promise and problems. Biochimica et Biophysica Acta. 2012; **1826**(1):71-82

[64] Hegi ME, Diserens AC, Gorlia T, Hamou MF, de Tribolet N, Weller M, et al. MGMT gene silencing and benefit from temozolomide in glioblastoma. The New England Journal of Medicine. 2005;**352**(10):997-1003

[65] Hsieh CT, Su IC, Huang CT, Chang CJ, Wang JS. The prognostic value of O6-methylguanine-DNA methyltransferase gene promoter methylation detected by gel-based methylation-specific polymerase chain reaction in patients with glioblastoma multiforme: A systematic review. International Journal of Clinical and Experimental Medicine. 2016;**9**(6): 10899-10906

[72] Stark AM, Doukas A, Hugo HH, Mehdorn HM. The expression of mismatch repair proteins MLH1, MSH2 and MSH6 correlates with the Ki67 proliferation index and survival in patients with recurrent glioblastoma. Neurological Research. 2010;**32**(8):

*DOI: http://dx.doi.org/10.5772/intechopen.91163*

*Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme*

[73] Martinez R, Setien F, Voelter C, Casado S, Quesada MP, Schackert G,

hypermethylation of the pro-apoptotic gene caspase-8 is a common hallmark of relapsed glioblastoma multiforme. Carcinogenesis. 2007;**28**(6):1264-1268

[74] Stark AM, Witzel P, Strege RJ, Hugo HH, Mehdorn HM. p53, mdm2, EGFR, and msh2 expression in paired initial and recurrent glioblastoma multiforme. Journal of Neurology, Neurosurgery, and Psychiatry. 2003;

[75] Campos B, Olsen LR, Urup T, Poulsen HS. A comprehensive profile of recurrent glioblastoma. Oncogene. 2016;

[76] Seystahl K, Gramatzki D, Roth P, Weller M. Pharmacotherapies for the treatment of glioblastoma—Current evidence and perspectives. Expert Opinion on Pharmacotherapy. 2016;

et al. CpG island promoter

816-820

**74**(6):779-783

**35**(45):5819-5825

**17**(9):1259-1270

**235**

[66] Kreisl TN, Kim L, Moore K, Duic P, Royce C, Stroud I, et al. Phase II trial of single-agent bevacizumab followed by bevacizumab plus irinotecan at tumor progression in recurrent glioblastoma. Journal of Clinical Oncology. 2009; **27**(5):740-745

[67] Friedman HS, Prados MD, Wen PY, Mikkelsen T, Schiff D, Abrey LE, et al. Bevacizumab alone and in combination with irinotecan in recurrent glioblastoma. Journal of Clinical Oncology. 2009;**27**(28):4733-4740

[68] Chinot OL, Wick W, Mason W, Henriksson R, Saran F, Nishikawa R, et al. Bevacizumab plus radiotherapytemozolomide for newly diagnosed glioblastoma. The New England Journal of Medicine. 2014;**370**(8):709-722

[69] Wick W, Gorlia T, Bendszus M, Taphoorn M, Sahm F, Harting I, et al. Lomustine and bevacizumab in progressive glioblastoma. The New England Journal of Medicine. 2017; **377**(20):1954-1963

[70] Diaz RJ, Ali S, Qadir MG, De La Fuente MI, Ivan ME, Komotar RJ. The role of bevacizumab in the treatment of glioblastoma. Journal of Neuro-Oncology. 2017;**133**(3):455-467

[71] Louis DN, Perry A, Reifenberger G, von Deimling A, Figarella-Branger D, Cavenee WK, et al. The 2016 World Health Organization classification of tumors of the central nervous system: A summary. Acta Neuropathologica. 2016; **131**(6):803-820

*Stereotactic Radiosurgery for Recurrent Glioblastoma Multiforme DOI: http://dx.doi.org/10.5772/intechopen.91163*

[72] Stark AM, Doukas A, Hugo HH, Mehdorn HM. The expression of mismatch repair proteins MLH1, MSH2 and MSH6 correlates with the Ki67 proliferation index and survival in patients with recurrent glioblastoma. Neurological Research. 2010;**32**(8): 816-820

radiosurgery for local recurrence of glioblastoma. Neuro Endocrinology value of O6-methylguanine-DNA methyltransferase gene promoter methylation detected by gel-based methylation-specific polymerase chain reaction in patients with glioblastoma multiforme: A systematic review. International Journal of Clinical and Experimental Medicine. 2016;**9**(6):

[66] Kreisl TN, Kim L, Moore K, Duic P, Royce C, Stroud I, et al. Phase II trial of single-agent bevacizumab followed by bevacizumab plus irinotecan at tumor progression in recurrent glioblastoma. Journal of Clinical Oncology. 2009;

[67] Friedman HS, Prados MD, Wen PY, Mikkelsen T, Schiff D, Abrey LE, et al. Bevacizumab alone and in combination

[68] Chinot OL, Wick W, Mason W, Henriksson R, Saran F, Nishikawa R, et al. Bevacizumab plus radiotherapytemozolomide for newly diagnosed glioblastoma. The New England Journal of Medicine. 2014;**370**(8):709-722

[69] Wick W, Gorlia T, Bendszus M, Taphoorn M, Sahm F, Harting I, et al. Lomustine and bevacizumab in progressive glioblastoma. The New England Journal of Medicine. 2017;

[70] Diaz RJ, Ali S, Qadir MG, De La Fuente MI, Ivan ME, Komotar RJ. The role of bevacizumab in the treatment of

[71] Louis DN, Perry A, Reifenberger G, von Deimling A, Figarella-Branger D, Cavenee WK, et al. The 2016 World Health Organization classification of tumors of the central nervous system: A summary. Acta Neuropathologica. 2016;

glioblastoma. Journal of Neuro-Oncology. 2017;**133**(3):455-467

**377**(20):1954-1963

**131**(6):803-820

with irinotecan in recurrent glioblastoma. Journal of Clinical Oncology. 2009;**27**(28):4733-4740

10899-10906

**27**(5):740-745

[58] Sharma M, Schroeder JL, Elson P, Meola A, Barnett GH, Vogelbaum MA,

stratification of patients with recurrent glioblastoma treated with salvage stereotactic radiosurgery. Journal of

[59] Morris SL, Zhu P, Rao M, Martir M, Zhu JJ, Hsu S, et al. Gamma knife stereotactic radiosurgery in combination

Letters. 2018;**39**(4):281-287

*Tumor Progression and Metastasis*

et al. Outcomes and prognostic

with bevacizumab for recurrent glioblastoma. World Neurosurgery.

with radiosurgery. Journal of Radiosurgery. 1999;**2**(3):119-125

[61] Park JL, Suh JH, Barnett GH, Reddy CA, Peereboom DM, Stevens GHJ, et al. Survival after stereotactic radiosurgery for recurrent glioblastoma multiforme. Journal of Radiosurgery. 2000;**3**(4):169-175

[62] Wen PY, Kesari S. Malignant gliomas in adults. The New England Journal of Medicine. 2008;**359**(5):

[63] Silber JR, Bobola MS, Blank A, Chamberlain MC. O6-methylguanine-DNA methyltransferase in glioma therapy: Promise and problems. Biochimica et Biophysica Acta. 2012;

[64] Hegi ME, Diserens AC, Gorlia T, Hamou MF, de Tribolet N, Weller M, et al. MGMT gene silencing and benefit from temozolomide in glioblastoma. The New England Journal of Medicine.

492-507

**1826**(1):71-82

**234**

2005;**352**(10):997-1003

[65] Hsieh CT, Su IC, Huang CT, Chang CJ, Wang JS. The prognostic

[60] Sanghavi S, Skrupky R, Badie B, Robins I, Tome W, Mehta MP. Recurrent malignant gliomas treated

Neurosurgery. 2018:1-11

2019;**127**:e523-e533

[73] Martinez R, Setien F, Voelter C, Casado S, Quesada MP, Schackert G, et al. CpG island promoter hypermethylation of the pro-apoptotic gene caspase-8 is a common hallmark of relapsed glioblastoma multiforme. Carcinogenesis. 2007;**28**(6):1264-1268

[74] Stark AM, Witzel P, Strege RJ, Hugo HH, Mehdorn HM. p53, mdm2, EGFR, and msh2 expression in paired initial and recurrent glioblastoma multiforme. Journal of Neurology, Neurosurgery, and Psychiatry. 2003; **74**(6):779-783

[75] Campos B, Olsen LR, Urup T, Poulsen HS. A comprehensive profile of recurrent glioblastoma. Oncogene. 2016; **35**(45):5819-5825

[76] Seystahl K, Gramatzki D, Roth P, Weller M. Pharmacotherapies for the treatment of glioblastoma—Current evidence and perspectives. Expert Opinion on Pharmacotherapy. 2016; **17**(9):1259-1270

**237**

**Chapter 10**

Anticancer Photodynamic

Photosensitizers

contemporary anticancer therapies.

**1. Introduction**

*and Mark Roufaiel*

**Abstract**

Therapy Using Ruthenium(II)

and Os(II)-Based Complexes as

*Pavel Kaspler, Arkady Mandel, Roger Dumoulin-White*

Photodynamic therapy (PDT) is an approved procedure using a photosensitizer (PS) activated by light to selectively destroy malignant/premalignant cells. Transition metal complexes, such as Ru(II)- and Os(II)-based PSs (Theralase Technologies Inc., Ontario. Canada), are activated in a wide range of wavelengths, are resistant to photobleaching and have a high singlet oxygen quantum yield and ability to produce cytotoxic reactive oxygen species (ROS). Their design allows fine-tuning of the photophysical and photochemical properties. They demonstrate Type I and II photoreactions, and some are activated in hypoxia. High PDT potency and activation under NIR light and even X-ray may provide an advantage over the approved PSs. Their ability to associate with transferrin (Tf) as an endogenous delivery system increases photobleaching resistance, ROS production, selective cellular uptake, and PDT efficacy in combination with a decreased systemic toxicity. This makes these PSs attractive for systemic therapy of recurrent/progressive cancers. Their PDT efficacy has been demonstrated in various in vitro and in vivo clinically relevant models. The unique properties of the mentioned PSs allow bypassing such limitations of PDT as low specific uptake ratio, insufficiently broad absorption band, and low efficacy in hypoxia. One of these PSs (TLD-1433) was successful against non-muscle invasive urinary bladder cancer unresponsive to

**Keywords:** photodynamic therapy, photosensitizer, transition metal, Ru(II), Os(II),

Photodynamic therapy (PDT) is an actively developing anticancer modality that

offers advantages compared to conventional treatments (ionizing radiation and chemotherapy). PDT utilizes two components, light and a photosensitizing compound (PS) activated by light upon photon absorption and producing in its activated state highly cytotoxic reactive oxygen species (ROS) [1]. The attractiveness of PDT is in the use of safe nonthermal doses of light and nontoxic concentrations of the PS and evoking cytotoxic and immunologic effects upon activation of the PS by

complex, transferrin, selectivity, tumor, cancer, urinary bladder

#### **Chapter 10**

## Anticancer Photodynamic Therapy Using Ruthenium(II) and Os(II)-Based Complexes as Photosensitizers

*Pavel Kaspler, Arkady Mandel, Roger Dumoulin-White and Mark Roufaiel*

#### **Abstract**

Photodynamic therapy (PDT) is an approved procedure using a photosensitizer (PS) activated by light to selectively destroy malignant/premalignant cells. Transition metal complexes, such as Ru(II)- and Os(II)-based PSs (Theralase Technologies Inc., Ontario. Canada), are activated in a wide range of wavelengths, are resistant to photobleaching and have a high singlet oxygen quantum yield and ability to produce cytotoxic reactive oxygen species (ROS). Their design allows fine-tuning of the photophysical and photochemical properties. They demonstrate Type I and II photoreactions, and some are activated in hypoxia. High PDT potency and activation under NIR light and even X-ray may provide an advantage over the approved PSs. Their ability to associate with transferrin (Tf) as an endogenous delivery system increases photobleaching resistance, ROS production, selective cellular uptake, and PDT efficacy in combination with a decreased systemic toxicity. This makes these PSs attractive for systemic therapy of recurrent/progressive cancers. Their PDT efficacy has been demonstrated in various in vitro and in vivo clinically relevant models. The unique properties of the mentioned PSs allow bypassing such limitations of PDT as low specific uptake ratio, insufficiently broad absorption band, and low efficacy in hypoxia. One of these PSs (TLD-1433) was successful against non-muscle invasive urinary bladder cancer unresponsive to contemporary anticancer therapies.

**Keywords:** photodynamic therapy, photosensitizer, transition metal, Ru(II), Os(II), complex, transferrin, selectivity, tumor, cancer, urinary bladder

#### **1. Introduction**

Photodynamic therapy (PDT) is an actively developing anticancer modality that offers advantages compared to conventional treatments (ionizing radiation and chemotherapy). PDT utilizes two components, light and a photosensitizing compound (PS) activated by light upon photon absorption and producing in its activated state highly cytotoxic reactive oxygen species (ROS) [1]. The attractiveness of PDT is in the use of safe nonthermal doses of light and nontoxic concentrations of the PS and evoking cytotoxic and immunologic effects upon activation of the PS by

light. PDT is supposed to selectively destroy unwanted and/or malignant cells while largely sparing the surrounding healthy tissue. Another desirable property is the ability to induce antigen-specific therapeutic and/or protective immune responses.

Preferential PS uptake by the tumors would make them exclusive targets for cytotoxicity while sparing normal tissues. Light delivery (both source location and emitted energy) can also be controlled more carefully (within the confines of the effective light attenuation in the tissue), which could make PDT a very efficient and safe modality. PDT effects reply upon a variety of photoreactions. The most commonly considered are the two types dependent on oxygen and associated with ROS production: electron transfer from the excited PS generating hydroxyl radical OH among other species (Type I) and energy transfer to a ground-state molecular oxygen 3O2 generating singlet oxygen 1O2 and superoxide radical anions (Type II) [2]. It is proposed that two more types are possible and are oxygen-independent: Type III as the interaction of the activated PS with native free radicals and Type IV as light-induced structural changes in PS allowing it to bind to subcellular targets [3].

PDT has been approved almost 20 years ago as an anticancer treatment. Nevertheless, despite the potential advantages, it is still underutilized clinically. Only a small number of porphyrin- and chlorine-like photosensitizers, as well as one bacteriochlorophyll-based PS, are approved. The number of indications for each photosensitizer is also very limited and includes primarily superficial cancerous/precancerous lesions and other conditions such as actinic keratosis, basal cell carcinoma, high-grade dysplasia in Barrett's esophagus, and age-related macular degeneration. As a palliative measure, PDT is approved for obstructive esophageal or lung cancer and centrally located lung cancer [4, 5]. There are several reasons for this.

One of them is a small depth of penetration of visible light into the tissues restricting PDT to superficial lesions with a thickness not exceeding few millimeters. For deeper organs/tissues, an invasive direct delivery of light is required. Light absorbance of longer wavelengths by the PSs is therefore very advantageous. Light in the range of 650–1350 nm (known as "near-infrared window") [6] has the greatest penetrating ability into biological tissues. This includes parts of red (625– 740 nm) and near-infrared (>750 nm) range that can be used for the PS activation.

Another problem is an unsatisfactory selectivity for malignant tissues resulting in PDT-associated damage of normal tissues. For example, Photofrin® is known for this [4]. Prolonged retention of many porphyrin-based PSs in healthy tissues leads to a problem of sensitivity to sunlight and potentially serious damage to the patients' skin and eye [7, 8]. This could be mitigated by delivery systems selectively targeting malignant cells. These systems employ two modes of action [9]. Passive targeting relies upon the morphological and physiological peculiarities of tumor tissue in combination with physicochemical properties of the PS carrier. Active targeting, in contrast, is based on a molecular recognition of the PS carrier by cancer cells such as binding of specific ligands or antibodies to overexpressed cancer cell receptors. Passive PS delivery systems include nanoparticles, fullerenes, and liposomes and have the advantage of protecting the PS from degradation upon injection. Active systems, on the other hand, have the advantage of improved uptake of the PS. The carriers belonging by themselves to passive targeting systems can be nevertheless supplemented with molecular recognition capacity belonging to the features of active systems, such as decoration with Tf to target Tf receptors overexpressed in malignant cells [10–12]. Nevertheless, smaller active targeting systems (such as PS-Tf conjugates discussed further in this chapter) could have an advantage of greater mobility upon intracellular uptake and potentially the advantage of the blood-brain barrier crossing.

Lastly, PDT-induced ROS production strongly relies upon oxygen availability, which is well known for the porphyrin-based PSs [13, 14]. Deep bulky tumors have

**239**

Photofrin (0.89).

PSs in PDT [27].

**2.1 Molecular structure**

*Anticancer Photodynamic Therapy Using Ruthenium(II) and Os(II)-Based Complexes…*

extensive hypoxic regions, which are also associated with the tumor aggressiveness [15, 16]. Although hypoxic regions still can be treated (at a slower rate) by application of fractionated exposure or inducing reperfusion [17, 18], hypoxia severely decreases PDT efficacy [19]. Together with the limited light penetration, this is another reason why PDT in its current state is usually limited to relatively superficial lesions. This problem could be bypassed by PSs employing photoreactions that

Considering the said above, an advanced PS should have the ability for targeted delivery; penetration through the blood-brain barrier (BBB) and blood-tumor cell barrier (BTCB); activation by a wide range of wavelengths, including NIR light; and employing of different types of photoreactions enabling induction of immune responses to tumor antigens. Solubility in water and/or saline is a great asset for a successful PS as it makes its delivery both easier and safer, without the use of excipi-

Metal-based coordination complexes are among the obvious candidates to satisfy these requirements. Specifically, transition metal complexes possess a wide range of metal oxidation states and the complex geometries [5, 20]. These complexes (e.g., Ru(II) polypyridyl complexes) are of increasing interest as PSs in photodynamic therapy (PDT) and, more recently, for photochemotherapy (PCT) [21]. Importantly, they can have their properties fine-tuned by choosing the central metal and organic ligands (such as bipyridine and 2,2′-biquinoline). These PSs can employ a great variety of excited states associated with the central metal, ligands, or metal-ligand interactions. This is manifested in photoreactions that are ROS-dependent (Type I/II) or ROS-independent (electron transfer to substrates other than molecular oxygen), excitation at different wavelengths, solubility, systemic toxicity, and finally PDT efficacy. Historically, Pt(IV)-, Ru(II)-, and Rh(III)-based complexes were most actively studied as PSs followed by Ir(III) and Os(II) complexes; see the review by Monro et al. [5]. The examples of the most recent studies [22–26] include a summary on the use of ruthenium complexes as

This chapter reviews the results obtained by our group and collaborators. The properties and PDT efficacy of Theralase Technologies Inc. PSs [28] and Ru(II)- and Os(II)-based complexes are discussed in the perspective of their clinical application.

**2. Physical and chemical properties of the transitional metal-based PSs**

The molecular structure of Ru(II)- and Os(II)-based PSs (later referred to as Ru- and Os-based) is shown in **Tables 1**–**3**. These are relatively small (approximately 1 kDa) complexes with the ligands involving bipyridine (bip), 2,2′-biquinoline (biq), imidazo[4,5-f ][1,10]phenanthroline, and a variable number of thiophene units. A variety of the ligands defines some of the PS properties. For example, the biq ligand is responsible for relatively good absorbance in near-infrared (NIR) light, while the number of thiophene units may be associated with the PS solubility in water [5]. Water solubility, as it was mentioned, represents a serious advantage for this group of PSs as many of the established PSs have poor water solubility [29, 30]. Ru-based PSs are characterized by <sup>1</sup>

quantum yield that is much higher (up to 99%) than for the established (FDAapproved) porphyrin-based PSs: PPIX, an active metabolite of ALA (0.56) and

O2

*DOI: http://dx.doi.org/10.5772/intechopen.88519*

have little or no dependency on oxygen.

ents with potential toxicity/side effects on their own.

#### *Anticancer Photodynamic Therapy Using Ruthenium(II) and Os(II)-Based Complexes… DOI: http://dx.doi.org/10.5772/intechopen.88519*

extensive hypoxic regions, which are also associated with the tumor aggressiveness [15, 16]. Although hypoxic regions still can be treated (at a slower rate) by application of fractionated exposure or inducing reperfusion [17, 18], hypoxia severely decreases PDT efficacy [19]. Together with the limited light penetration, this is another reason why PDT in its current state is usually limited to relatively superficial lesions. This problem could be bypassed by PSs employing photoreactions that have little or no dependency on oxygen.

Considering the said above, an advanced PS should have the ability for targeted delivery; penetration through the blood-brain barrier (BBB) and blood-tumor cell barrier (BTCB); activation by a wide range of wavelengths, including NIR light; and employing of different types of photoreactions enabling induction of immune responses to tumor antigens. Solubility in water and/or saline is a great asset for a successful PS as it makes its delivery both easier and safer, without the use of excipients with potential toxicity/side effects on their own.

Metal-based coordination complexes are among the obvious candidates to satisfy these requirements. Specifically, transition metal complexes possess a wide range of metal oxidation states and the complex geometries [5, 20]. These complexes (e.g., Ru(II) polypyridyl complexes) are of increasing interest as PSs in photodynamic therapy (PDT) and, more recently, for photochemotherapy (PCT) [21]. Importantly, they can have their properties fine-tuned by choosing the central metal and organic ligands (such as bipyridine and 2,2′-biquinoline). These PSs can employ a great variety of excited states associated with the central metal, ligands, or metal-ligand interactions. This is manifested in photoreactions that are ROS-dependent (Type I/II) or ROS-independent (electron transfer to substrates other than molecular oxygen), excitation at different wavelengths, solubility, systemic toxicity, and finally PDT efficacy. Historically, Pt(IV)-, Ru(II)-, and Rh(III)-based complexes were most actively studied as PSs followed by Ir(III) and Os(II) complexes; see the review by Monro et al. [5]. The examples of the most recent studies [22–26] include a summary on the use of ruthenium complexes as PSs in PDT [27].

This chapter reviews the results obtained by our group and collaborators. The properties and PDT efficacy of Theralase Technologies Inc. PSs [28] and Ru(II)- and Os(II)-based complexes are discussed in the perspective of their clinical application.

#### **2. Physical and chemical properties of the transitional metal-based PSs**

#### **2.1 Molecular structure**

The molecular structure of Ru(II)- and Os(II)-based PSs (later referred to as Ru- and Os-based) is shown in **Tables 1**–**3**. These are relatively small (approximately 1 kDa) complexes with the ligands involving bipyridine (bip), 2,2′-biquinoline (biq), imidazo[4,5-f ][1,10]phenanthroline, and a variable number of thiophene units. A variety of the ligands defines some of the PS properties. For example, the biq ligand is responsible for relatively good absorbance in near-infrared (NIR) light, while the number of thiophene units may be associated with the PS solubility in water [5]. Water solubility, as it was mentioned, represents a serious advantage for this group of PSs as many of the established PSs have poor water solubility [29, 30]. Ru-based PSs are characterized by <sup>1</sup> O2 quantum yield that is much higher (up to 99%) than for the established (FDAapproved) porphyrin-based PSs: PPIX, an active metabolite of ALA (0.56) and Photofrin (0.89).

*Tumor Progression and Metastasis*

light. PDT is supposed to selectively destroy unwanted and/or malignant cells while largely sparing the surrounding healthy tissue. Another desirable property is the ability to induce antigen-specific therapeutic and/or protective immune responses. Preferential PS uptake by the tumors would make them exclusive targets for cytotoxicity while sparing normal tissues. Light delivery (both source location and emitted energy) can also be controlled more carefully (within the confines of the effective light attenuation in the tissue), which could make PDT a very efficient and safe modality. PDT effects reply upon a variety of photoreactions. The most commonly considered are the two types dependent on oxygen and associated with ROS production: electron transfer from the excited PS generating hydroxyl radical OH among other species (Type I) and energy transfer to a ground-state molecular oxygen 3O2 generating singlet oxygen 1O2 and superoxide radical anions (Type II) [2]. It is proposed that two more types are possible and are oxygen-independent: Type III as the interaction of the activated PS with native free radicals and Type IV as light-induced structural changes in PS allowing it to bind to subcellular targets [3]. PDT has been approved almost 20 years ago as an anticancer treatment. Nevertheless, despite the potential advantages, it is still underutilized clinically. Only a small number of porphyrin- and chlorine-like photosensitizers, as well as one bacteriochlorophyll-based PS, are approved. The number of indications for each photosensitizer is also very limited and includes primarily superficial cancerous/precancerous lesions and other conditions such as actinic keratosis, basal cell carcinoma, high-grade dysplasia in Barrett's esophagus, and age-related macular degeneration. As a palliative measure, PDT is approved for obstructive esophageal or lung cancer

and centrally located lung cancer [4, 5]. There are several reasons for this.

One of them is a small depth of penetration of visible light into the tissues restricting PDT to superficial lesions with a thickness not exceeding few millimeters. For deeper organs/tissues, an invasive direct delivery of light is required. Light absorbance of longer wavelengths by the PSs is therefore very advantageous. Light in the range of 650–1350 nm (known as "near-infrared window") [6] has the greatest penetrating ability into biological tissues. This includes parts of red (625– 740 nm) and near-infrared (>750 nm) range that can be used for the PS activation. Another problem is an unsatisfactory selectivity for malignant tissues resulting in PDT-associated damage of normal tissues. For example, Photofrin® is known for this [4]. Prolonged retention of many porphyrin-based PSs in healthy tissues leads to a problem of sensitivity to sunlight and potentially serious damage to the patients' skin and eye [7, 8]. This could be mitigated by delivery systems selectively targeting malignant cells. These systems employ two modes of action [9]. Passive targeting relies upon the morphological and physiological peculiarities of tumor tissue in combination with physicochemical properties of the PS carrier. Active targeting, in contrast, is based on a molecular recognition of the PS carrier by cancer cells such as binding of specific ligands or antibodies to overexpressed cancer cell receptors. Passive PS delivery systems include nanoparticles, fullerenes, and liposomes and have the advantage of protecting the PS from degradation upon injection. Active systems, on the other hand, have the advantage of improved uptake of the PS. The carriers belonging by themselves to passive targeting systems can be nevertheless supplemented with molecular recognition capacity belonging to the features of active systems, such as decoration with Tf to target Tf receptors overexpressed in malignant cells [10–12]. Nevertheless, smaller active targeting systems (such as PS-Tf conjugates discussed further in this chapter) could have an advantage of greater mobility upon intracellular uptake and potentially the advantage of the blood-brain barrier crossing. Lastly, PDT-induced ROS production strongly relies upon oxygen availability, which is well known for the porphyrin-based PSs [13, 14]. Deep bulky tumors have

**241**

TLD-OsH2B

TLD-OsH2IP

TLD-Os10H

TLD-Os14H

MW = 954.0

MW = 994.0

MW = 1158.2

MW = 1240.3

1

O2 quantum yield = 0.03

Fluorescent quantum yield =0.0009

1

O2 quantum yield = 0.035

Fluorescent quantum yield =0.0013

1

O2 quantum yield = 0.044

Fluorescent quantum yield =0.0008

1

O2 quantum yield = 0.035

Fluorescent quantum yield

= 0.0011

TLD-OsH2dppn

MW = 1106.1

1

O2 quantum yield n/d

Fluorescent quantum yield

n/d

**Table 2.**

*Molecular structures of Os(II)-based complexes. Quantum yields are measured in solution rather than in cells.*

*Anticancer Photodynamic Therapy Using Ruthenium(II) and Os(II)-Based Complexes…*

*DOI: http://dx.doi.org/10.5772/intechopen.88519*

*Anticancer Photodynamic Therapy Using Ruthenium(II) and Os(II)-Based Complexes… DOI: http://dx.doi.org/10.5772/intechopen.88519*

###

*Molecular structures of Os(II)-based complexes. Quantum yields are measured in solution rather than in cells.*

*Tumor Progression and Metastasis*

**240**

TLD-1011

TLD-1411

TLD-1611

MW = 868.8

MW = 950.9

MW = 1033.1

1

n/d

Fluorescent quantum yield

n/d

TLD-1633

O2 quantum yield

1

O2 quantum yield

≈ 0.99

Fluorescent quantum yield

< 0.01

TLD-1433

MW = 1007.1

MW = 1089.2

1

n/d

Fluorescent quantum yield

n/d

O2 quantum yield

1

O2 quantum yield

≈ 0.99

Fluorescent quantum yield

< 0.01

**Table 1.**

*Ru(II)-based complexes. Quantum yields are measured in solution rather than in cells.*

1

O2 quantum yield

= 0.74

Fluorescent quantum yield

= 0.001

#### **Table 3.** *Ligands involved in the PSs' molecular structure.*

#### **2.2 Absorbance spectra**

The absorbance spectra of the Ru- and Os-based PSs are shown in **Figure 1**. Among the Ru-based PSs, methylation of bidentate ligands (bip) decreases absorbance. An increase in the number of thiophene rings redshifts the main absorbance peak and eventually results in a considerable increase in absorbance at longer wavelengths (see TLD-1633).

Os-based PSs having biq ligands, in contrast to the Ru-based PSs, have similar spectra. They demonstrate rather uniformly located strong main peak at approximately 340 nm attributed to ligand-centered transitions and a characteristic secondary peak at ≈550 nm attributed to metal-to-ligand charge transfer (MLCT) centered on the non-biq ligands. Importantly, these PSs demonstrate consistent

**243**

1

hυ−<sup>1</sup>

*Anticancer Photodynamic Therapy Using Ruthenium(II) and Os(II)-Based Complexes…*

absorbance at longer wavelengths (red to NIR range). The NIR absorbance is attributed to MLCT that involves biq ligands. Altogether, the spectra similarity suggests similar accessible electronic transitions and ground and excited states. Broad absorption band of the Os-based PSs allows for a wider range of photon attenuation coefficients. Considerable absorbance in a clinically important PDT window of 700–900 nm suggests a capacity for one-photon absorption [31]. This asset is emphasized by a good solubility of these PSs in water. Poor solubility in water may hamper PDT potential of PSs even with a good absorbance in this range of the spectrum, as in the case of porphyrin- and phthalocyanine-based PSs [32]. The inclusion of thiophenes and the increase in their number in the ligands (from TLD-OsH2B to TLD-Os14H) not only decreases the main absorbance peak but also markedly redshifts its shape, with a minimal effect on the secondary peak and

If the PS is resistant to photobleaching, this allows less PS being destroyed by the light exposure. In turn, this makes ROS production and subsequent cytotoxic action more efficient, because the process of conversion of photons to cytotoxicity becomes catalytic without stoichiometric consumption of the PS. This allows making the efficacy of PDT treatment independent on the availability of the PS during the treatment. The bleaching resistance is hence a very valuable property, especially if the delivered light energy must be increased to achieve the desired PDT efficacy. This could be a drawback though in the case of bleaching-based dosimetry during the

Ru-based PSs show notable bleaching under exposure to green light (525 nm). TLD-1433 is slightly more bleaching resistant than TLD-1411 although they have almost identical absorbance at 525 nm. Nevertheless, more than 50% of each PS

the 416–417 nm UV peak, TLD-1433 absorbance in clinically useful range rapidly increases (1.7-fold at 525 nm, 2.0-fold at 625 nm, 1.8-fold at 800 nm) and remains

for TLD-OsH2IP, and 1.5\*10<sup>−</sup><sup>2</sup>

[31]. For comparison, the photobleaching rate for the approved PSs can be much

Production of ROS represents a final event of the PS activation by light leading to PDT cytotoxicity. Ru-based TLD-1433 is able to generate hydroxyl

O2 production is not detected. Importantly, ROS is generated despite very low

Os-based PSs having biq ligands show variable bleaching resistance under green light (525 nm); TLD-OsH2B is the most resistant and TLD-OsH2dppn the most vulnerable. Compared to the Ru-based PS, the bleaching resistance of the Os-based PSs with biq ligands is greater in general, with at least 75% of their initial absorbance retained. The best performers, TLD-OsH2B and TLD-OsH2IP, showed no more than 10% loss of absorbance in the UV peak, with no absorbance loss in green-NIR range. This provides the photobleaching rates in aqueous solution (calculated based

of radiant exposure corresponding to 6.6x1019-

. Moreover, while bleaching results in the deterioration of

).

cm<sup>−</sup><sup>2</sup>

cm<sup>−</sup><sup>2</sup>

6 M hυ−<sup>1</sup>

for TLD-OsH2dppn,

for PPIX, and 4.8\*10<sup>−</sup>16 M

), although singlet oxygen

for TLD-OsH2B

for benzoporphyrin

cm<sup>−</sup><sup>2</sup>

cm<sup>−</sup><sup>2</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.88519*

absorbance in the longer wavelengths (**Figure 1B**).

**2.3 Photobleaching resistance**

remains intact even after 200 Jcm<sup>−</sup><sup>2</sup>

at this level up to the end of light exposure (200 Jcm<sup>−</sup><sup>2</sup>

on the incident irradiance) equal to 8.7\*10<sup>−</sup>28 M hυ−<sup>1</sup>

derivative mono acid A (BPD), 7.3\*10<sup>−</sup>23 M hυ−<sup>1</sup>

radical \*OH under red light (625 nm, 119 mWcm<sup>−</sup><sup>2</sup>

for curcumin [35–37].

higher (by several orders of magnitude): 5.6\*10<sup>−</sup>24 M hυ−<sup>1</sup>

cm<sup>−</sup><sup>2</sup>

absorbed photons per cm3

treatment [33, 34].

4.1\*10<sup>−</sup>27 M hυ−<sup>1</sup>

cm<sup>−</sup><sup>2</sup>

**2.4 ROS production**

**Figure 1.** *Absorbance spectra of the Ru(II)- and the Os(II)-based PSs (panels A and B, respectively) in water.* *Anticancer Photodynamic Therapy Using Ruthenium(II) and Os(II)-Based Complexes… DOI: http://dx.doi.org/10.5772/intechopen.88519*

absorbance at longer wavelengths (red to NIR range). The NIR absorbance is attributed to MLCT that involves biq ligands. Altogether, the spectra similarity suggests similar accessible electronic transitions and ground and excited states. Broad absorption band of the Os-based PSs allows for a wider range of photon attenuation coefficients. Considerable absorbance in a clinically important PDT window of 700–900 nm suggests a capacity for one-photon absorption [31]. This asset is emphasized by a good solubility of these PSs in water. Poor solubility in water may hamper PDT potential of PSs even with a good absorbance in this range of the spectrum, as in the case of porphyrin- and phthalocyanine-based PSs [32]. The inclusion of thiophenes and the increase in their number in the ligands (from TLD-OsH2B to TLD-Os14H) not only decreases the main absorbance peak but also markedly redshifts its shape, with a minimal effect on the secondary peak and absorbance in the longer wavelengths (**Figure 1B**).

#### **2.3 Photobleaching resistance**

*Tumor Progression and Metastasis*

Bipyridine

Thiophene

2,2′-biquinoline

Methylated bipyridine

Imidazo[4,5-f][1,10]phenanthroline

benzo[*i*]dipyrido[3,2-*a*:2′,3′-c]phenazine

*Ligands involved in the PSs' molecular structure.*

**2.2 Absorbance spectra**

TLD-1633).

**Table 3.**

The absorbance spectra of the Ru- and Os-based PSs are shown in **Figure 1**. Among the Ru-based PSs, methylation of bidentate ligands (bip) decreases absorbance. An increase in the number of thiophene rings redshifts the main absorbance peak and eventually results in a considerable increase in absorbance at longer wavelengths (see

Os-based PSs having biq ligands, in contrast to the Ru-based PSs, have similar spectra. They demonstrate rather uniformly located strong main peak at approximately 340 nm attributed to ligand-centered transitions and a characteristic secondary peak at ≈550 nm attributed to metal-to-ligand charge transfer (MLCT) centered on the non-biq ligands. Importantly, these PSs demonstrate consistent

*Absorbance spectra of the Ru(II)- and the Os(II)-based PSs (panels A and B, respectively) in water.*

**242**

**Figure 1.**

If the PS is resistant to photobleaching, this allows less PS being destroyed by the light exposure. In turn, this makes ROS production and subsequent cytotoxic action more efficient, because the process of conversion of photons to cytotoxicity becomes catalytic without stoichiometric consumption of the PS. This allows making the efficacy of PDT treatment independent on the availability of the PS during the treatment.

The bleaching resistance is hence a very valuable property, especially if the delivered light energy must be increased to achieve the desired PDT efficacy. This could be a drawback though in the case of bleaching-based dosimetry during the treatment [33, 34].

Ru-based PSs show notable bleaching under exposure to green light (525 nm). TLD-1433 is slightly more bleaching resistant than TLD-1411 although they have almost identical absorbance at 525 nm. Nevertheless, more than 50% of each PS remains intact even after 200 Jcm<sup>−</sup><sup>2</sup> of radiant exposure corresponding to 6.6x1019 absorbed photons per cm3 . Moreover, while bleaching results in the deterioration of the 416–417 nm UV peak, TLD-1433 absorbance in clinically useful range rapidly increases (1.7-fold at 525 nm, 2.0-fold at 625 nm, 1.8-fold at 800 nm) and remains at this level up to the end of light exposure (200 Jcm<sup>−</sup><sup>2</sup> ).

Os-based PSs having biq ligands show variable bleaching resistance under green light (525 nm); TLD-OsH2B is the most resistant and TLD-OsH2dppn the most vulnerable. Compared to the Ru-based PS, the bleaching resistance of the Os-based PSs with biq ligands is greater in general, with at least 75% of their initial absorbance retained. The best performers, TLD-OsH2B and TLD-OsH2IP, showed no more than 10% loss of absorbance in the UV peak, with no absorbance loss in green-NIR range. This provides the photobleaching rates in aqueous solution (calculated based on the incident irradiance) equal to 8.7\*10<sup>−</sup>28 M hυ−<sup>1</sup> cm<sup>−</sup><sup>2</sup> for TLD-OsH2dppn, 4.1\*10<sup>−</sup>27 M hυ−<sup>1</sup> cm<sup>−</sup><sup>2</sup> for TLD-OsH2IP, and 1.5\*10<sup>−</sup><sup>2</sup> 6 M hυ−<sup>1</sup> cm<sup>−</sup><sup>2</sup> for TLD-OsH2B [31]. For comparison, the photobleaching rate for the approved PSs can be much higher (by several orders of magnitude): 5.6\*10<sup>−</sup>24 M hυ−<sup>1</sup> cm<sup>−</sup><sup>2</sup> for benzoporphyrin derivative mono acid A (BPD), 7.3\*10<sup>−</sup>23 M hυ−<sup>1</sup> cm<sup>−</sup><sup>2</sup> for PPIX, and 4.8\*10<sup>−</sup>16 M hυ−<sup>1</sup> cm<sup>−</sup><sup>2</sup> for curcumin [35–37].

#### **2.4 ROS production**

Production of ROS represents a final event of the PS activation by light leading to PDT cytotoxicity. Ru-based TLD-1433 is able to generate hydroxyl radical \*OH under red light (625 nm, 119 mWcm<sup>−</sup><sup>2</sup> ), although singlet oxygen 1 O2 production is not detected. Importantly, ROS is generated despite very low absorbance of TLD-1433 in red light. This, however, requires certain molecular and ionic environment because ROS is generated only in incomplete DMEM cell culture medium (not complemented with FBS and antibiotics) but not in DI water despite almost identically low absorbance.

Exposure to NIR light (808 nm, 720 mWcm<sup>−</sup><sup>2</sup> ) produces some amount of ROS (\*OH), but it at least an order of magnitude less than under red light. This occurs despite a similar number of absorbed photons and absorbance at 808 nm only 18% less than at 625 nm and greater delivered energy. This may suggest that not only the total delivered energy and number of the absorbed photons but also the photon energy is important for the efficacy in ROS production.

#### **3. Association of the PSs with transferrin**

#### **3.1 Delivery platforms**

To address the challenge of selective uptake of the PSs by tumors, it would be attractive to utilize serum proteins and natural transmembrane transporters as delivery vehicles. Despite numerous approaches for targeted delivery of the PSs including receptors-assisted uptake (as mentioned in the chapter introduction), neither is related to the use of Tf as a vehicle for transition metal-based complexes. The notable exceptions are the works on the interaction between Tf and Cr(III) complexes [38, 39]. It is also known that Ru(II) complexes can associate with albumin and iron transporter transferrin (Tf) [40, 41]. In addition, overexpression of Tf receptors is a common feature of malignant cells that tend to have an increased Fe3+ uptake [42]. The effect of the association of Ru(II)-based PSs with Tf on their photophysical and photobiological properties needs however more elucidation.

#### **3.2 Association signatures and effect of Tf on absorbance spectra**

Upon subtraction of the spectra of the complex and Tf from the spectrum of their premix, a characteristic signature of association between the Ru-based complex and Tf can be detected, with two peaks in UV and visible range. The UV peak indicates conformational changes in aromatic rings (the complex itself or transferrin molecule), and the visible range peak is interpreted as an indicator of LMCT (ligand to metal charge transfer) that represents the interaction between the metal of the complex and transferrin [43].

Premixing of Ru-based complexes with apo-Tf (the Tf not saturated with Fe3+) at 4:1 molar ratio demonstrates the signature with UV and visible range peaks (**Figure 2A**). The absorbance increase in UV range could be due to conformation changes either in the Tf molecule or the complex (as both have UV maxima at similar wavelengths). The peak in visible range indicates a new spectral component distinct (redshifted) from the comparable absorbance peak for the PS alone. This indicates the complex-Tf association and is related to the interaction between the metal in the complex and the Tf molecule.

There is also an increase in absorbance between the signature peaks and, importantly, in the long wavelength tail of the spectrum in the visible range and further into the NIR, which is clinically relevant for PDT. Notably, the absorbance of TLD-1433 alone is very low in red to NIR. The increase in absorbance upon the association with Tf is 16.2-fold (MEC = 3125 vs. 193 M<sup>−</sup><sup>1</sup> cm<sup>−</sup><sup>1</sup> ) in red (635 nm) and 5.7-fold (MEC = 1676 vs. 294 M<sup>−</sup><sup>1</sup> cm<sup>−</sup><sup>1</sup> ) in NIR (800 nm), compared to 5.0-fold (MEC = 8027 vs. 1600 M<sup>−</sup><sup>1</sup> cm<sup>−</sup><sup>1</sup> ) increase in the green (535 nm). Notably, the ability of the PS to associate with Tf depends on the number of thiophene rings in the complex. One

**245**

lesser than for apo-Tf [43].

tude is much lesser.

**Figure 2.**

*media (panel C).*

different pH values.

*Anticancer Photodynamic Therapy Using Ruthenium(II) and Os(II)-Based Complexes…*

thiophene ring is not enough for this as evident for TLD-1011. Hence, not only metal

*Spectral signatures of association of the Ru(II)-based (panel A) and Os(II)-based (panels B and C) PSs with apo-Tf. The incubation of Ru-based PSs was performed in 10 mM phosphate buffer +100 mM NaCl (pH = 7.4) and of Os(II)-based PSs in the phosphate buffer (panel B) or incomplete RPMI1640 cell culture*

The association signatures seem to be insensitive to the source of apo-Tf and are very similar for bovine and human Tf. The signatures resemble the signature of Fe3+−Tf binding but are not identical to it. Notably, TLD-1433 can also be associated with Fe3+ saturated holo-Tf although the magnitude of the association signature is

Os-based PSs with biq ligands are also able to associate with apo-Tf, but their signatures (**Figure 2C**) are distinct from those of Ru-based PSs. The visible range peak (observed for TLD-OsH2B and TLD-OsH2dppn but not for TLD-OsH2IP) is however more redshifted (in the range of 500–600 nm), and the signature magni-

Physiologically, when Tf bound with Fe3+ is taken up into a cell, it releases iron in endosomes when pH is decreased to ≈5.5 [44]. TLD-1433-Tf conjugate, in contrast, remains stable during the gradual acidification emulating this process [43]. This is evident by the stability of absorbance at the two peaks of the signature across

Notably, an association of TLD-1433 with holo-Tf also survives the acid environment. The magnitude of the signature peaks is 31–33% lower than for TLD-1433 & apo-Tf at pH = 7.4, but by pH = 5 it increases so the UV peak magnitude catches up with that of TLD-1433 & apo-Tf, and the visible peak magnitude even becomes about 20% greater. Hence, TLD-1433 may remain associated with Tf in the acidic endosome environment. Acidification resistance does not hold however for the

but also organic ligands play a role in the association of the complex with Tf.

**3.3 Stability of the TLD-1433 + Tf association at low pH**

*DOI: http://dx.doi.org/10.5772/intechopen.88519*

*Anticancer Photodynamic Therapy Using Ruthenium(II) and Os(II)-Based Complexes… DOI: http://dx.doi.org/10.5772/intechopen.88519*

**Figure 2.**

*Tumor Progression and Metastasis*

**3.1 Delivery platforms**

water despite almost identically low absorbance. Exposure to NIR light (808 nm, 720 mWcm<sup>−</sup><sup>2</sup>

energy is important for the efficacy in ROS production.

**3. Association of the PSs with transferrin**

metal of the complex and transferrin [43].

metal in the complex and the Tf molecule.

with Tf is 16.2-fold (MEC = 3125 vs. 193 M<sup>−</sup><sup>1</sup>

cm<sup>−</sup><sup>1</sup>

(MEC = 1676 vs. 294 M<sup>−</sup><sup>1</sup>

cm<sup>−</sup><sup>1</sup>

absorbance of TLD-1433 in red light. This, however, requires certain molecular and ionic environment because ROS is generated only in incomplete DMEM cell culture medium (not complemented with FBS and antibiotics) but not in DI

(\*OH), but it at least an order of magnitude less than under red light. This occurs despite a similar number of absorbed photons and absorbance at 808 nm only 18% less than at 625 nm and greater delivered energy. This may suggest that not only the total delivered energy and number of the absorbed photons but also the photon

To address the challenge of selective uptake of the PSs by tumors, it would be attractive to utilize serum proteins and natural transmembrane transporters as delivery vehicles. Despite numerous approaches for targeted delivery of the PSs including receptors-assisted uptake (as mentioned in the chapter introduction), neither is related to the use of Tf as a vehicle for transition metal-based complexes. The notable exceptions are the works on the interaction between Tf and Cr(III) complexes [38, 39]. It is also known that Ru(II) complexes can associate with albumin and iron transporter transferrin (Tf) [40, 41]. In addition, overexpression of Tf receptors is a common feature of malignant cells that tend to have an increased Fe3+ uptake [42]. The effect of the association of Ru(II)-based PSs with Tf on their photophysical and photobiological properties needs however more elucidation.

**3.2 Association signatures and effect of Tf on absorbance spectra**

Upon subtraction of the spectra of the complex and Tf from the spectrum of their premix, a characteristic signature of association between the Ru-based complex and Tf can be detected, with two peaks in UV and visible range. The UV peak indicates conformational changes in aromatic rings (the complex itself or transferrin molecule), and the visible range peak is interpreted as an indicator of LMCT (ligand to metal charge transfer) that represents the interaction between the

Premixing of Ru-based complexes with apo-Tf (the Tf not saturated with Fe3+)

There is also an increase in absorbance between the signature peaks and, importantly, in the long wavelength tail of the spectrum in the visible range and further into the NIR, which is clinically relevant for PDT. Notably, the absorbance of TLD-1433 alone is very low in red to NIR. The increase in absorbance upon the association

associate with Tf depends on the number of thiophene rings in the complex. One

cm<sup>−</sup><sup>1</sup>

) increase in the green (535 nm). Notably, the ability of the PS to

) in red (635 nm) and 5.7-fold

) in NIR (800 nm), compared to 5.0-fold (MEC = 8027