Colon-targeted delivery of 9-aminocamptothecin by HPMA copolymer conjugates for the treatment of colon cancer

Due to nonspecific-toxicity, cancer treatment with 9-aminocamptothecin (9-AC) caused severe side effects, and failed to show any meaningful clinical activity. The development of macromolecular drug-delivery systems is a potent strategy to enhance therapeutic efficiency and minimize systemic toxicity by target-selective delivery of toxic anticancer drugs. In this research, water soluble N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-9-AC conjugates were designed, synthesized and evaluated for oral colon-specific delivery of 9-AC for the treatment of colon cancer.;The specific objectives of this project were achieved by four steps. In the first HPMA copolymer-9-AC conjugate for oral colon-specific drug delivery was designed, synthesized, and characterized. The design of the spacer ensured a fast and highly efficient release of unmodified 9-AC from the polymer in the colon by azo bond cleavage followed by an 1,6-elimination reaction. An in vitro degradation study indicated that this conjugate was stable in simulated upper GI tract conditions. In the second step, comparative studies between the polymer conjugate and free drug have been performed to assess their biodistribution and pharmacokinetics in mice. Colon-specific release of 9-AC from the polymer conjugates produced high local-regional drug concentrations. The high and sharp plasma drug concentration profiles from free drug were in contrast to the relatively low and flat pharmacokinetic profiles obtained from drug released from the HPMA copolymers. In the third step, a pharmacokinetic model was developed to quantitate and predict colon-specific drug release from the polymer conjugate and its absorption behavior after oral administration in rats. This model delineated the impact of GI transit, drug absorption rate, and first-pass metabolism on drug disposition. In the fourth step, anticancer efficacy of the colon-specific drug delivery by the polymer conjugates was assessed in nude mice bearing both orthotopic and subcutaneous human colon carcinoma xenografts. It was found that colon-specific release of unmodified 9-AC from HPMA copolymer conjugates enhanced antitumor activity and minimized systemic toxicity compared to free drug treatment in two colon tumor models.;As a consequence of the colon-specific release of unmodified 9-AC from the polymer conjugates, antitumor efficacy can be anticipated in future clinical studies for the treatment of colon cancer.