A New Functional Role for P-Glycoprotein: Effiux Pump for Benzo(a)pyrene in Human Breast Cancer MCF-7 Cells

We propose that the cellular burden of certain carcinogens may be mitigated by P-glycoprotein (P-gp), the putative drug effiux pump. In a series of multidrug resistant human breast cancer MCF-7 cells with increasing P-gp expression we examined this hypothesis using benzo(a)pyrene, a widely distributed environmental and dietary carcinogen. We found that multidrug resistant cells were cross-resistant to benzo(a)pyrene and the rates of efflux for benzo(a)pyrene were higher in multidrug resistant cells than in wild type cells. Evidence supporting the involvement of P-gp included the inhibition of azidopine binding to P-gp bel,zo(a)pyrene and the inhibition of benzo(a)pyrene efflux by Adriamycin and verapamil. Our findings suggest that P-gp may play a role in the cellular defense to carcinogens. The expression of P-gp and the modulation of its function may affect the susceptibility of normal tissues to transformation by carcinogens.