A small molecule SMAC mimic LBW242 potentiates TRAIL- and anticancer drug-mediated cell death of ovarian cancer cells.

BACKGROUND: Ovarian cancer remains a leading cause of death in women and development of new therapies is essential. Second mitochondria derived activator of caspase (SMAC) has been described to sensitize for apoptosis. We have explored the pro-apoptotic activity of LBW242, a mimic of SMAC/DIABLO, on ovarian cancer cell lines (A2780 cells and its chemoresistant derivative A2780/ADR, SKOV3 and HEY cells) and in primary ovarian cancer cells. The effects of LBW242 on ovarian cancer cell lines and primary ovarian cancer cells was determined by cell proliferation, apoptosis and biochemical assays. PRINCIPAL FINDINGS: LBW242 added alone elicited only a moderate pro-apoptotic effect; however, it strongly synergizes with tumor necrosis factor-related apoptosis inducing ligand (TRAIL) or anticancer drugs in inducing apoptosis of both ovarian cancer cell lines and primary ovarian cancer cells. Mechanistic studies show that LBW242-induced apoptosis in ovarian cancer cells is associated with activation of caspase-8. In line with this mechanism, c-FLIP overexpression inhibits LBW242-mediated apoptosis. CONCLUSION: LBW242 sensitizes ovarian cancer cells to the antitumor effects of TRAIL and anticancer drugs commonly used in clinic. These observations suggest that the SMAC/DIABLO mimic LBW242 could be of value for the development of experimental strategies for treatment of ovarian cancer.

The cancer stem cell selective inhibitor salinomycin is a p-glycoprotein inhibitor.

Salinomycin, a polyether antibiotic acting as a highly selective potassium ionophore and widely used as an anticoccidial drug, was recently shown to act as a specific inhibitor of cancer stem cells. In the present study we report that salinomycin acts as a potent inhibitor of multidrug resistance gp170, as evidenced through drug efflux assays in MDR cancer cell lines overexpressing P-gp (CEM-VBL 10 and CEM-VBL 100; A2780/ADR). Conformational P-gp assay provided evidence that the inhibitory effect of salinomycin on P-gp function could be mediated by the induction of a conformational change of the ATP transporter. Treatment of the MDR cell lines with salinomycin restored a normal drug sensitivity of these cells. The observation that salinomycin is a MDR-1 inhibitor may have important implications for the understanding of the mechanisms through which this drug impairs the viability of cancer stem cells. Interestingly, nigericin and abamectin, two additional drugs identified as cancer stem cells inhibitors, also act as potent gp170 inhibitors.