Synergistic induction of apoptosis by the combination of TRAIL and chemotherapy in chemoresistant ovarian cancer cells

Objectives. The aim of this study was to investigate whether TNF-related ap optosis-inducing ligand (TRAIL) alone or in combination with chemotherapy c ould induce apoptosis in ovarian cancer cells resistant to chemotherapy, Methods. Twelve chemoresistant epithelial cancer cell lines were treated wi th each chemotherapeutic drug alone (cisplatin, doxorubicin, or paclitaxel) , TRAIL alone, or the combination. Toxicity was assessed using the MTS assa y. To assess whether growth inhibition was due to apoptosis, TUNEL assay, c aspase activation (measured by caspase-3 and PARP cleavage), and the sub G0 /G1 fraction of cells were measured. Synergism was confirmed by fractional inhibition and dose- effect analysis. Expression of death and decoy recepto rs was studied by immunoblotting and an RNase protection assay. Statistical comparison of means was performed using Student's t test. Results. The majority of the chemoresistant cells were also resistant to TR AIL alone. In contrast, the combination of TRAIL and chemotherapy resulted in a significant growth inhibition over a wide range of concentrations. Thi s interaction was synergistic by dose-effect analysis. Flow cytometry demon strated a significant increase in the fraction of apoptotic cells by the co mbination compared to each reagent alone. A significant enhancement in casp ase and PARR cleavage was observed upon treatment with the combination. Fin ally, no correlation between induction of apoptosis and level of death rece ptors was found. Conclusions. The data suggest that almost all the ovarian cancer cells, whi ch are resistant to chemotherapy, are also resistant to TRAIL, The combinat ion of TRAIL and chemotherapy overcomes this resistance in a synergistic fa shion by triggering caspase-mediated apoptosis. The combination of TRAIL an d chemotherapy could be useful as a therapy for chemoresistant ovarian canc ers. (C) 2001 Academic Press.