New 4-aryl-1,4-dihydropyridines and 4-arylpyridines as P-glycoprotein inhibitors.

Efflux of cytotoxic agents mediated by P-glycoprotein is believed to be an important mechanism of multidrug resistance, which remains a serious limitation to successful chemotherapy in cancers such as metastatic breast cancer. A series of 4-aryl-1,4-dihydropyridines and corresponding aromatized 4-arylpyridines have been synthesized based on structure modifications of niguldipine to enhance multidrug resistance reversal activity, while minimizing calcium channel binding. Thirty new compounds were characterized. [(3)H]Vinblastine accumulation studies indicated that at a concentration level of 3 muM, 15 of 18 4-aryl-1,4-dihydropyridines and all 4-arylpyridines can successfully restore intracellular accumulation of vinblastine in a resistant human breast adenocarcinoma cell line, MCF-7/adr, which overexpresses P-glycoprotein. The most potent compounds led to an approximately 15-fold increase of vinblastine accumulation. All of the test compounds that significantly increased vinblastine accumulation in MCF/adr cells were able to substantially reduce IC(50) values of daunomycin and increase its cytotoxicity in MCF-7/adr-resistant cells, confirming the results of the vinblastine accumulation studies. Calcium channel binding assays for these newly synthesized compounds were conducted using rat cerebral cortex membrane. All but eight compounds demonstrated negligible calcium channel binding over the concentration range from 15 to 2500 nM. The results demonstrate that the newly synthesized series of 1,4-dihydropyridines and pyridines represent P-glycoprotein modulators with negligible calcium channel blocking activity.