Maleimide-oligo(ethylene glycol) derivatives of camptothecin as albumin-binding prodrugs: Synthesis and antitumor efficacy

In situ binding of thiol-reactive prodrugs to the cysteine-34 position of circulating albumin is a new approach in drug delivery. Therefore, five maleimide-bearing derivatives of the anticancer drug camptothecin (CPT) were developed as albumin-binding prodrugs. These compounds were synthesized by reacting heterobifunctional cross-linkers based on oligo(ethylene glycols) [3-6 (O-CH2-CH2) units] bearing a maleimide group on one end and a carboxylic acid group on the other with camptothecin 20-O-glycinate. Incorporating oligo(ethylene glycol) chains into the prodrugs enhanced their water-solubility when compared to the parent compound (up to 27-fold). HPLC studies showed that the prodrugs react almost quantitatively with the cysteine-34 position of endogenous albumin within a few minutes after incubation of the CPT derivatives with human blood plasma. The therapeutic potential of two of the prodrugs was assessed in nude mice bearing a colon xenograft (HT-29). Both albumin-binding derivatives of camptothecin were well-tolerated and showed enhanced antitumor efficacy when compared to CPT.