Purpose: To investigate the reversal mechanisms of a novel semisynthetic taxane derivative, Syl611. Syl611 is a structurally modified compound from Sinenxan A, and the chemical structure is entirely new. It was found to significantly increase paclitaxel-induced cytotoxicity in drug-resistant cells, while presenting a low level of cytotoxicity.
Methods: The in vitro cytotoxic and MDR-reversing activities of the Syl611 were determined by MTT assays. The cytotoxicity enhancement of paclitaxel was performed using the acridine orange/ethidium bromide double staining. Rhodamine 123 accumulation and retention assay in KB/V cells, Caco-2 monolayer model were used to find mechanism of action.
Results: The cytotoxicity of Syl611 was wondrously lower in all tested cell lines than that of paclitaxel. Cytotoxicity enhancement from Syl611 was dramatically higher than that of verapamil of the same concentration (10 muM): the reversal fold index for A549/Paclitaxel, KB/V, and Bel7402/5-FU were 45.95, 73.56, and 107.13 (Syl611) and 11.36, 23.92, and 70.42 (verapamil). AO/EB double staining assay equally showed that Syl611 could enhance the cytotoxicity induced by paclitaxel. Furthermore, Syl611 could also increase the intracellular accumulation of Rhodamine 123 in KB/V cells without affecting P-gp's expression, and this accumulation was reversible. In bidirectional permeability assay, Syl611 increased the permeability of paclitaxel but decreased the net secretory of paclitaxel.
Conclusions: Syl611 is an effective and potential agent in reversing multidrug resistance (MDR) by multiple actions, which attributed to p-glycoprotein inhibition and drug permeability enhancement.