Preparation, characterization, and in vitro efficacy of O-carboxymethyl chitosan conjugate of melphalan

•We synthesized a series of melphalan-O-carboxymethyl chitosan (Mel-OCM-chitosan) conjugates.•We studied in vitro drug release of these Mel-OCM-chitosan conjugates.•These Mel-OCM-chitosan conjugates have enzyme-responsive characteristic.•The novel Mel-OCM-chitosan conjugates may be used as a new polymeric prodrug. A series of melphalan-O-carboxymethyl chitosan (Mel-OCM-chitosan) conjugates with different spacers were prepared and structurally characterized. All conjugates showed satisfactory water-solubility (160-217 times of Mel solubility). In vitro drug release behaviors by both chemical and enzymatic hydrolysis were investigated. The prodrugs released Mel rapidly within papain and lysosomal enzymes of about 40–75%, while released only about 4–5% in buffer and plasma, which suggested that the conjugates have good plasma stability and the hydrolysis in both papain and lysosomes occurs mostly via enzymolysis. It was found that the spacers have important effect on the drug content, water solubility, drug release properties and cytotoxicity of Mel-OCM-chitosan conjugates. Cytotoxicity studies by MTT assay demonstrated that these conjugates had 52–70% of cytotoxicity against RPMI8226 cells in vitro as compared with free Mel, indicating the conjugates did not lose anti-cancer activity of Mel. Overall these studies indicated Mel-OCM-chitosan conjugates as potential prodrugs for cancer treatment.