Thermosensitive poly(organophosphazene)–paclitaxel conjugate gels for antitumor applications

A poly(organophosphazene)–PTX conjugate was synthesized by a covalent ester linkage between PTX and carboxylic acid-terminated poly(organophosphazene), which can be readily modified by various hydrophobic, hydrophilic, and other functional substitutes. The physicochemical properties, hydrolytic degradation and PTX release behaviors of the polymer–PTX conjugate were characterized, in addition to the in vitro and in vivo antitumor activities. The aqueous solutions of these conjugates showed a sol–gel transition behavior that depended on temperature changes. The in vitro antitumor activity of the polymer–PTX conjugate was investigated by an MTT assay against human tumor cell lines. From the in vivo antitumor activity studies with tumor-induced (xenografted) nude mice, the polymer–paclitaxel conjugate hydrogels after local injection at the tumor site were shown to inhibit tumor growth more effectively and longer than paclitaxel and saline alone, indicating that the tumor-active paclitaxel from the polymer–PTX conjugate hydrogel is released slowly over a longer period of time and effectively accumulated locally in the tumor sites. These combined observations suggest that this poly(organophosphazene)–PTX conjugate holds promise for use in clinical studies as single and/or combination therapies.