In vitro Effects of the BH3 Mimetic, (−)-Gossypol, on Head and Neck Squamous Cell Carcinoma Cells

Purpose: Bcl-x L overexpression is common in head and neck squamous cell carcinomas (HNSCC) and correlates with resistance to chemotherapy. Thus, a nonpeptidic, cell-permeable small molecule that mimics the BH3 domain of proapoptotic proteins may inhibit Bcl-x L function and have therapeutic potential for HNSCC by overcoming drug-resistance. (−)-Gossypol, the levorotatory isomer of a natural product isolated from cottonseeds and roots, was recently discovered to bind to the BH3 binding groove of Bcl-x L and Bcl-2. Experimental Design: We investigated the in vitro effects of (−)-gossypol on HNSCC cell lines as well as on fibroblast and keratinocyte cultures by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell survival assays and assessed the results with respect to Bcl-2 family protein expression. Results: We observed dose-dependent growth inhibition of 10 HNSCC cell lines at biologically achievable doses (2.5–10 μmol/L). (−)-Gossypol doses required to inhibit the growth of human fibroblast cell lines by 50% were 2- to 10-fold higher than for HNSCC cell lines. To inhibit human oral keratinocyte growth by 50%, (−)-gossypol concentrations were 2-to 3-fold higher than for HNSCC cell lines. Conclusions: There is a direct correlation between Bcl-x L -to-Bcl-x S ratios and sensitivity to (−)-gossypol. This agent induced apoptosis in a much higher proportion of cells with wild-type p53. Importantly, cell lines resistant to cisplatin were very sensitive to (−)-gossypol. These results demonstrate that (−)-gossypol has potent antitumor activity in HNSCC in vitro . This agent may be developed as a novel therapeutic agent for HNSCC, either alone or in combination with existing chemotherapeutic agents.