Combined treatment with TRAIL and PPARγ ligands overcomes chemoresistance of ovarian cancer cell lines

Ovarian cancer accounts for the highest mortality among all gynecological cancers, mainly due to the fast developing chemoresistance. The death ligand TRAIL induces apoptosis and is able to sensitize tumor cells to cytostatic drugs without affecting physiological tissue. Combined treatment of TRAIL and the antidiabetic acting PPAR gamma ligands was shown to induce apoptosis synergistically in different ovarian cancer cell lines. To investigate feasible TRAIL-dependent inhibition of proliferation and induction of apoptosis in chemoresistant ovarian cancer cell lines, the drug- and TRAIL-sensitive HEY cell line was utilized to develop subclones with selective resistance against cisplatin, etoposide, docetaxel, paclitaxel, gemcitabine and pemetrexed, as well as against TRAIL as control cell line. Expression of the key factors of the TRAIL signaling pathway, TRAIL receptors 1-4, caspase-8, FLIP and XIAP, was analyzed before and after TRAIL treatment by immunoblotting. Cell proliferation experiments showed TRAIL-dependent inhibition that was further increased by combination treatment with the PPAR gamma ligands. Simultaneous exposure of TRAIL and the PPAR gamma ligands also resulted in enhanced induction of apoptosis even in partial TRAIL-resistant HEY cell lines. In the parental HEY cell line, additional treatment with the PPAR gamma ligands led to an increased protein expression of DR5 and a further decline of XIAP expression. Therefore, the combinational treatment with TRAIL and PPAR gamma ligands might be a promising experimental therapy because the PPAR gamma ligands, especially d15-PGJ(2), sensitize drug-resistant ovarian cancer cells to TRAIL-induced apoptosis.