Preparation and properties evaluation of a novel pH-sensitive liposomes based on imidazole-modified cholesterol derivatives

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As a new kind of drug carries, pH-sensitive liposomes have been widely studied in tumor therapy for their advantages of target ability and sustained-release. Here, we synthesized a pH-sensitive material, N-(3-Aminopropyl)imidazole-cholesterol (IM-Chol) and prepared a novel pH-sensitive liposomes using IM-Chol and phosphatidylcholine. IM-Chol was synthesized through amidation reaction between the amino group of N-(3-Aminopropyl)imidazole and acyl chloride group of cholesteryl chloroformate in a weak base solution. Optimal conditions to prepare liposomes were obtained by the orthogonal experiment with the higher encapsulation efficiency as the evaluation indicator. The properties of liposomes, such as particle size, zeta potential, morphology, encapsulation efficiency, drug release behavior and in vitro cell toxicity were evaluated by transmission electron microscopy (TEM), dynamic light scattering (DLS) and MTT assay respectively. The results showed that the average particle size of IM-Chol liposomes was 141 nm (PDI 0.323). Liposomes can assemble into uniform spheres at pH 7.4, but under the condition of pH 5.0, the spherical structure of IM-Chol liposomes was broken, exhibiting pH-sensitive property. In vitro drug releasing studies demonstrated the controlled-release behavior of the curcumin (CUR) in the IM-Chol liposomes. The cumulative release of CUR reached to 72.5% in the first 24 h at pH 5.0, faster than that at pH 7.4, which confirmed that the drug carrier displayed pH-sensitive release behaviors. In addition, the MTT assay was employed to test the cytotoxicity of IM-Chol liposomes and CUR IM-Chol liposomes. All cell viabilities were greater than 80% after incubating for 24 h, even up to the highest dose of 500 mg/L, indicating that IM-Chol liposomes had good biocompatibility. The tumor inhibitory results towards EC109 cells of free CUR and CUR-loaded IM-Chol liposomes indicated that IM-Chol liposomes indeed enhanced the cell killing effect of CUR. These results showed that the novel IM-Chol liposomes prepared in this paper had pH-sensitive property and were expected to play a huge potential in tumor treatment.

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