Objective: Resistance to cisplatin-centered chemotherapy is a major cause of treatment failure in human ovarian cancer. Whereas PTEN, a tumor suppressor gene product, is believed to promote apoptosis primarily via inactivation of the PI3K/Akt cell survival pathway, recent evidence suggests that PTEN may function independently of this pathway. Activation of p53 is a key determinant of sensitivity to cisplatin-induced apoptosis. Whether PTEN can facilitate cisplatin sensitivity, and this involves the activation of p53, remains unclear. In this study, we determined whether and how PTEN over-expression sensitizes ovarian cancer cells to CDDP-induced apoptosis.
Methods and results: Using pairs of chemosensitive and chemoresistant ovarian cancer cell lines (OV20028 vs. C13* and A2780-s vs. A2780-cp) as an in vitro model, we have examined the influence of PTEN over-expression in regulation of cisplatin-induced apoptosis. Apoptosis was assessed morphologically by Hoechst staining and confirmed by the detection of cleaved products of caspase-3 and PARP by Western blot. Over-expression of PTEN by PTEN cDNA transfection up-regulates p53 content and increases the sensitivity of chemoresistant cells to cisplatin-induced apoptosis without detectable changes in the levels of phosphorylated Akt and FKHR as well as FasL mRNA abundance as determined by Western blot and RT-PCR, respectively. PTEN-mediated chemosensitization was attenuated by p53 down-regulation by siRNA in C13*, a chemoresistant wild-type p53 cell. Moreover, PTEN over-expression failed to sensitize the chemoresistant p53 mutant ovarian cancer cell line A2780-cp to cisplatin-induced apoptosis, unless wild-type p53 was reconstituted by adenoviral p53 infection.
Conclusion: Taken together, these data suggest that PTEN over-expression may represent a novel therapeutic approach for chemoresistant human ovarian cancer and that this may involve a p53-mediated apoptotic cascade independent of the PI3K/Akt pathway.