Discovery and synthesis of 3- and 21-substituted fusidic acid derivatives as reversal agents of P-glycoprotein-mediated multidrug resistance.

In this study, we synthesized 23 fusidic acid (FA) derivatives and screened them for tumor drug resistance reversal activity and cytotoxicity toward the KBV (multidrug-resistant oral epidermoid carcinoma) cell line based on MTT assay. Tumor resistance reversal activity of fusidic acid (FA) derivatives was discovered for the first time. Our results showed that compound 1 enhanced the cytotoxicity of paclitaxel toward the drug-resistant KBV cells at a concentration of 5 μM. And compound 1 sensitized KBV cells toward paclitaxel in arresting cells in the G/M phase and inducing cell apoptosis. Further researches showed that compound 1 inhibited the drug efflux activity of P-glycoprotein (P-gp) by increasing the ATPase activity of P-gp without affecting its expression. The structure-activity relationships (SARs) of the FA derivatives were also preliminarily investigated. Our findings indicate that compound 1 is a promising lead compound for designing FA derivatives with improved tumor drug resistance reversal activity in the future.