Gossypol inhibits basal and estrogen-stimulated DNA synthesis in human breast carcinoma cells.

Estrogen stimulates the growth of hormone-dependent human breast cancer. Failure of chemotherapy frequently results from the development of multidrug resistance. Gossypol (GP), a naturally occurring toxin, inhibits the growth of various carcinoma cells. Thus, the effects of GP on 17 beta-estradiol (E2)-stimulated DNA synthesis were studied in two hormone-dependent human breast carcinoma cell lines: the wild-type MCF-7 and the multidrug-resistant MCF-7 Adr cells. Cells (5 x 104/well) were cultured for 24 hrs in a chemically-defined, serum-free medium consisting of 1:1 mixture of Dulbecco's Modified Eagle's medium and Ham's nutrient mixture F12 (DMEM/F12) supplemented with insulin (5.0 micrograms/ml), transferrin (5.0 micrograms/ml), epidermal growth factor (EGF; 10.0 ng/ml) and antibiotics E2 (0 or 10.0 nM), GP (0, 2.5, 5.0, 10.0 or 20.0 microM) and bovine serum albumin (BSA; 0 or 0.1 mg/ml) were used as treatments in a factorial experimental design. Cells were treated for 24 hrs and finally pulsed with 3H-thymidine (5.0 microCi/ml) for 3 hrs. E2 significantly stimulated 3H-thymidine incorporation in both MCF-7 and MCF-7 Adr cells. GP at 10.0 and 20.0 microM inhibited both basal and E2-stimulated DNA synthesis in human breast cancer cells. The inhibitory effects of GP at 10.0 microM, but not at 20.0 microM, were blocked by BSA treatment. Results from the present study indicate that GP treatment was antiproliferative in both drug-sensitive and multidrug-resistant cancer cells and that the antiproliferative effects of GP on human breast cancer cells were mediated through mechanisms independent of estrogenic responses. Thus, GP could be potentially very useful for treatment of human breast cancer patients, especially those who have developed multidrug resistance.