Abstract 2874: Kevetrin targets both MDM2-p53 and Rb-E2F pathways in tumor suppression
Abstract Our studies showed that Kevetrin™, a small molecule currently under development, has potent antitumor activity in several wild type and mutant p53 human tumor xenografts e.g. A549, PC-3, MDA-MB-231, HT-29, NCI-H1975, HCT-15, K-562, LNCaP. To investigate the mechanism of action of its antitumor activity in different xenograft models, we assessed Kevetrin's effects on apoptosis and cell cycle progression. Rb-E2F and MDM2-p53 pathways are crucial regulators of cell cycle progression. Remarkably, both Rb-E2F and MDM2-p53 pathways are defective in most, if not all, human tumors. There is extensive crosstalk between the Rb-E2F and MDM2-p53 pathways, especially between the transcription factors E2F1 and p53, which influence vital cellular decisions. In wild type p53 human lung carcinoma (A549), Kevetrin showed a concentration dependent increase in activation of p53 by Western blot analysis. Activated p53 triggered apoptosis by inducing the expression of PUMA. Kevetrin also increased the expression of the target gene p21, an inhibitor of cell cycle progression. Kevetrin induced apoptosis in a transcriptional independent way by altering the E3 ligase processivity of MDM2. Kevetrin strongly induced apoptosis in multiple tumor cell lines characterized by activation of caspase3 and PARP. E2F1 is a pivotal transcription factor that integrates signals from a variety of G1/S phase regulators and modulates diverse functions, such as DNA synthesis, mitosis, apoptosis and senescence. E2F1 overexpression, observed in most tumors, is associated with tumor growth. Cells which overexpress E2F1 proved to be immune to induction of senescence. A recent study showed that depletion of E2F1 hinders cell cycle progression and induces senescence. Kevetrin down regulated E2F1 expression in various p53 wild type and mutant cell lines. Kevetrin also down regulated the E2F1 target gene thymidylate synthase (TS) in various tumor cell lines. Several reports have shown E2F1 overexpression correlates with TS expression. Effective inhibition of TS by Kevetrin could play a crucial role in tackling the problem of resistance. Kevetrin acting through both major pathways of tumor suppression, Rb-E2F and MDM2-p53, has far reaching consequences. Due to the complexity of proapoptotic and antiapoptotic pathways with multiple players involved and redundant signaling networks, blocking only one antiapoptotic factor may not result in robust antitumor activity. However, Kevetrin acts via multiple targets to produce potent efficacy in various xenograft tumor models. We have also demonstrated that Kevetrin is non-genotoxic. DNA damaging drugs result in rapid phosphorylation of H2A.X at Ser 139 by PI3K-like kinases; however, Kevetrin did not induce phosphorylation of H2A.X. Since Kevetrin was well-tolerated in GLP safety pharmacology and toxicity studies, we have submitted an IND application for a Phase I clinical trial at Dana Farber / Harvard Cancer Center for 2012. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2874. doi:1538-7445.AM2012-2874