Differential growth inhibition and induction of apoptosis by gossypol between HCT116 and HCT116/Bax^-/- colorectal cancer cells

1. Bax is a very important pro-apoptosis molecule. HCT116/Bax^-/- cells do not express the pro-apoptosis Bcl-2 family member, Bax. In the present study, the anticancer effects of gossypol on HCT116 and HCT116/Bax ^-/- cells were compared in terms of inhibition of cell growth, inhibition of colony formation and induction of apoptosis. 2. Following treatment with concentrations more than 20 μmol/L gossypol, only slight differences (not signficant) were seen between HCT116 and HCT116/Bax ^-/- cells in terms of the inhibition of cell growth and induction of apoptosis. No difference was seen in the inhibition of colony formation. Gossypol had no effect at concentrations < 2 μmol/L. The only effective concentration of gossypol to result in differences between HCT116 and HCT116/Bax^-/- cells was 5 μmol/L. However, even at this concentration, Bax deficiency did not result in complete abolition of gossypol-induced growth inhibition or apoptosis. Exposure of cells to 5 μmol/L gossypol for 24 h did not cause any significant difference in the activation of caspase 2 between HCT116 and HCT116/Bax^-/- cells; however, activation of caspase 3, 8 and 9 was significantly elevated in HCT116 cells, with the effect on caspase 3 activation being the greatest, compared with HCT116/Bax^-/- cells. 3. These findings suggest that the contribution of Bax to gossypol-induced growth inhibition and apoptosis is dose dependent and that gossypol-induced apoptosis requires activation of caspase 3, 8, and 9.