Inhibition of P-glycoprotein (ABCB1)- and multidrug resistance-associated protein 1 (ABCC1)-mediated transport by the orally administered inhibitor, CBT-1((R)).
Purpose and methods: To develop a clinically useful approach to circumvent P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) in MDR human small-cell lung cancer (SCLC), we examined the ability of a novel quinoline compound, MS-209, to reverse MDR by inhibition of P-gp function in combination with other MDR-reversing drugs using a cytotoxicity assay. Results: We established MDR human SCLC cells by culture in medium with gradually increasing concentrations of adriamycin (ADM). Compared with the parental human SCLC cells, SBC-3, the MDR variant SBC-3 cells obtained (SBC-3/ADM) were highly resistant to various chemotherapeutic agents due to P-gp expression. MS-209 reversed the resistance to ADM and vincristine (VCR) of SBC-3/ADM and H69/VP cells in a dose-dependent manner. Moreover, MS-209 in combination with cyclosporin A (CsA) or verapamil (VER) synergistically enhanced the antitumor effects of ADM and VCR on SBC-3/ADM cells. MS-209 restored ADM incorporation and this effect was enhanced by CsA and VER, suggesting that these synergistic effects were due to competitive inhibition of P-gp function. Conclusion: MS-209 in combination with CsA or VER might increase the efficacy of these chemotherapeutic agents against MDR human SCLC cells.