A thermally responsive biopolymer conjugated to an acid-sensitive derivative of paclitaxel stabilizes microtubules, arrests cell cycle, and induces apoptosis.

Poor aqueous solubility limits the therapeutic index of paclitaxel as an anti-cancer drug. Synthesis of soluble prodrugs of paclitaxel, or conjugation of the drug to macromolecular carriers have been reported to increase its water-solubility. Macromolecular drug carriers have an added advantage of targeting the drug to the tumor site due to the abnormal tumor blood and lymphatic vasculature. This study describes a thermally responsive macromolecular carrier, elastin-like polypeptide (ELP) for the delivery of paclitaxel. Paclitaxel was bound to ELP by conjugation with the 6-maleimidocaproyl hydrazone derivative of paclitaxel, an acid-sensitive paclitaxel prodrug, for the potential treatment of breast cancer. Focused hyperthermia above a specific transition temperature at the site of a tumor causes ELP to aggregate and accumulate, thereby increasing the local concentration of the drug cargo. The paclitaxel prodrug described here bears an acid-sensitive linker that is cleavable at the lysosomal/endosomal pH, which allows a controlled intracellular release of the drug. The ELP-delivered paclitaxel in the presence of hyperthermia inhibits MCF-7 cell proliferation by stabilizing the microtubule structures, arresting the cells at the G2/M stage, and inducing apoptosis in a manner similar to conventional paclitaxel. It also inhibits proliferation of a paclitaxel resistant MCF-7 cell line. These data provide an in vitro proof of concept for the use of ELP as a delivery vehicle of paclitaxel.