Defective autophagy in multidrug resistant cells may lead to growth inhibition by BH3-mimetic gossypol.

The clinical efficacy of many chemotherapeutic agents has been reduced due to the development of drug resistance. In this article, we aimed to validate gossypol, a natural BH3 mimetic found in cottonseeds, as a potential therapeutic to overcome multidrug resistance (MDR). Gossypol was found to retain its efficacy in v-Ha-ras-transformed NIH 3T3 cells that overexpressed P-glycoprotein (Ras-NIH 3T3/Mdr), which was similar to the efficacy observed in their parental counterparts (Ras-NIH 3T3). A rhodamine assay revealed that the alteration of MDR activity did not contribute to the cytotoxic effect of gossypol. Gossypol caused a G2 /M arrest by the induction of p21(Cip1) and the down-regulation of p27(Kip1) expression in Ras-NIH 3T3 cells, whereas no significant G2 /M arrest was exhibited in Ras-NIH 3T3/Mdr cells. Surprisingly, a 48-h treatment with gossypol induced apoptotic cell death in Ras-NIH 3T3 cells; however, gossypol induced both apoptosis and necrosis in Ras-NIH 3T3/Mdr cells, as determined with flow cytometry analysis. More notably, gossypol preferentially induced autophagy in Ras-NIH 3T3 cells but not in Ras-NIH 3T3/Mdr cells. Coimmunoprecipitation and flow cytometric analysis revealed that gossypol-induced autophagy is independent of the dissociation of Beclin 1 from Bcl-2 in Ras-NIH 3T3 cells. Taken together, these results suggest that the antiproliferative activity of gossypol appears to be due to cell-cycle arrest at the G2 /M phase, with the induction of apoptosis in Ras-NIH 3T3 cells. In addition, defective autophagy might contribute to apoptotic and necrotic cell death in response to gossypol in Ras-NIH 3T3/Mdr cells.