Abstract

Breast cancer resistance protein (BCRP, ABCG2) is a recently identified member of the ATP-binding cassette family of cell surface transport proteins. This study was conducted to investigate the effect of a series of newly synthesized 1,4-dihydropyridines and pyridines, designed as potent P-glycoprotein inhibitors, on BCRP-mediated drug efflux both in vitro and in vivo. The effects of 25 synthesized dihydropyridines and corresponding pyridines along with 4 commercially available dihydropyridines (niguldipine, nicardipine, nifedipine, and nitrendipine) on the intracellular accumulation of the BCRP substrate mitoxantrone were evaluated in BCRP-expressing human breast cancer MCF-7/MX100 and human non-small cell lung cancer H460/MX20 cells. At a 2.5 μM concentration, 24 of 25 newly synthesized dihydropyridines and pyridines produced a significant increase of mitoxantrone accumulation in both cell lines. The most potent compound was able to enhance mitoxantrone accumulation approximately 4.5-fold, greater than that obtained with 10 μM fumitremorgin C, which is a specific BCRP inhibitor. The results from the two cell lines showed good correlation (r² = 0.71, p < 0.01). Niguldipine, nicardipine, and nitrendipine also demonstrated potent BCRP inhibition, whereas nifedipine had no effect. The effects of the dihydropyridine and pyridine compounds on mitoxantrone cytotoxicity paralleled their effects on mitoxantrone accumulation. Coadministration of a selected dihydropyridine compound, I_m [DHP-014; 3-(3-(4,4-diphenylpiperidin-1-yl)propyl) 5-methyl 4-(3,4-dimethoxyphenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate)] with topotecan, a good BCRP substrate and a moderate to poor P-glycoprotein substrate, resulted in significant increases in the systemic exposure and peak concentration of topotecan in Sprague-Dawley rats when oral topotecan (2 mg/kg) was combined with 20 mg/kg DHP-014. The observed increase of topotecan exposure provides proof-of-concept for in vivo inhibition of BCRP by these agents.