Pharmacokinetics and antitumor efficacy of micelles assembled from multiarmed amphiphilic copolymers with drug conjugates in comparison with drug-encapsulated micelles.
The premature drug release and structural dissociation before reaching pathological sites have posed major challenges for self-assembled micelles. To address these challenges, star-shaped amphiphilic copolymers derived from 4-armed poly(ethylene glycol) (PEG) were proposed for chemical conjugation of chemotherapeutic drugs and assembly into drug-conjugated micelles (DCM) with reductive sensitivity. The current study aimed to elucidate the in vitro and in vivo performance of DCM and a comparison with conventional drug-encapsulated micelles (DEM) was initially launched. DEM carriers were constructed with a similar structure to DCM from 4-armed PEG, and disulfide linkages were located between the hydrophilic and hydrophobic segments. Both DCM and DEM had an average size of around 130 nm, camptothecin (CPT) loadings of around 7.7% and critical micelle concentrations of around 0.95 μg/ml. Compared with DEM, DCM showed a lower initial drug release, a lower sensitivity of drug release to glutathione, and a higher structural stability after incubation with human serum albumin (HSA). The CPT derivatives (CPT-SH) released from DCM indicated cytotoxicities similar to CPT and remained a higher lactone stability than CPT in the presence of HSA. DCM showed slightly higher cytotoxicities to 4T1 cells and significantly lower cytotoxicities to normal cells than DEM. Pharmacokinetic analyses after intravenous administration of DCM indicated around 2.65 folds higher AUC0-∞, 2.66 folds lower clearance, and 1.87 folds higher tumor accumulation than those of DEM. In addition to a less disturbance to hematological and biochemical parameters and a lower acute toxicity to small intestines, DCM showed more significant tumor suppression efficacy and less tumor metastasis to lungs than DEM. It is suggested that DCM could overcome the limitation of conventional micelles by alleviating the premature drug release during blood circulation, relieving the systemic toxicity and promoting the therapeutic efficacy.