Analysis of structural features of dihydropyridine analogs needed to reverse multidrug resistance and to inhibit photoaffinity labeling of P-glycoprotein.

Synthetic dihydropyridine analogs were screened to determine whether they would reverse multidrug resistance of a multidrug-resistant human KB carcinoma cell line, KB-C1. Among twenty-four dihydropyridine analogs examined, thirteen almost completely overcame drug resistance (group A), nine partially overcame resistance (group B) and two did not reverse resistance (group C). The twenty-two compounds that reversed drug-resistance (groups A and B) were hydrophobic dihydropyridine derivatives. Three compounds that reversed resistance, NK-113, NK-138 and NK-194, increased the accumulation of [3H]vincristine in the resistant KB-C1 cells, but not in the parental KB cells, nor in a revertant cell line, KB-C1-R2. NK-101 (group C), which did not reverse resistance, had no effect on drug accumulation. Enhanced efflux of vincristine from the resistant cells was inhibited completely by NK-194, but NK-194 did not affect vincristine influx. Nine of the twenty-four compounds were screened to determine whether they inhibited photoaffinity labeling of the cell surface protein gp170 (P-glycoprotein) in KB-C1 cells by N-(p-azido-[3-125I]-salicyl)-N'-beta-aminoethylvindesine [( 125I]NASV). All five compounds of group A, NK-138, NK-194, NK-200, NK-203 and NK-220, inhibited the photoaffinity labeling of gp170 at less than 10-100 microM, whereas NK-113 and NK-196 of group B inhibited the labeling at 100-200 microM. By contrast, NK-101 and NK-102 of group C did not inhibit labeling even at 2000 microM. These studies confirm the relationship among reversal of multidrug resistance, decreased efflux of vincristine, and inhibition of [125I]NASV labeling of P-glycoprotein.