6,7-Dimethoxy-2-{2-[4-(1H-1,2,3-triazol-1-yl)phenyl]ethyl}-1,2,3,4-tetrahydroisoquinolines as superior reversal agents for P-glycoprotein-mediated multidrug resistance.

P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) is a major obstacle for successful cancer chemotherapy. Based on our previous study, 17 novel compounds with the 6,7-dimethoxy-2-{2-[4-(1H-1,2,3-triazol-1-yl)phenyl]ethyl}-1,2,3,4-tetrahydroisoquinoline scaffold were designed and synthesized. Among them, 2-[(1-{4-[2-(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)ethyl]phenyl}-1H-1,2,3-triazol-4-yl)methoxy]-N-(p-tolyl)benzamide (compound 7 h) was identified as a potent modulator of P-gp-mediated MDR, with high potency (EC50 =127.5 ± 9.1 nM), low cytotoxicity (TI>784.3), and long duration (>24 h) in reversing doxorubicin (DOX) resistance in K562/A02 cells. Compound 7 h also enhanced the effects of other MDR-related cytotoxic agents (paclitaxel, vinblastine, and daunorubicin), increased the accumulation of DOX and blocked P-gp-mediated rhodamine 123 efflux function in K562/A02 MDR cells. Moreover, 7 h did not have any effect on cytochrome (CYP3A4) activity. These results indicate that 7 h is a relatively safe modulator of P-gp-mediated MDR that has good potential for further development.