Tumor necrosis factor-related apoptosis-inducing ligand and chemotherapy cooperate to induce apoptosis in mesothelioma cell lines

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can induce apoptosis in certain tumor cells, In addition, TRAIL and chemotherapy can a ct cooperatively, possibly as a result of chemotherapy-induced increases in expression of a TRAIL receptor, DRS. We used cell lines derived from a hig hly chemoresistant tumor, malignant mesothelioma, to learn whether TRAIL wa s effective alone or together with chemotherapy and whether cooperativity d epended on increases in DR5 expression. TRAIL (codons 95-285) was expressed in a bacterial expression vector and purified by nickel affinity chromatog raphy. TRAIL alone (25 to 500 ng/ml) had little effect on mesothelioma call s. TRAIL plus chemotherapy (doxorubicin, cis-platinum, etoposide, or gemcit abine) acted cooperatively to induce apoptosis in mesothelioma cells (M28, REN, VAMT, and MS-1). For example, in M28 cells treated for 18 h, apoptosis from TRAIL (100 ng/ml) plus doxorubicin (0.6 mug/ml; 71 +/- 11%) greatly e xceeded that from TRAIL alone (21 +/- 8%) or from doxorubicin alone (6 +/- 2%) (means +/- standard deviation; P < 0.03). Mesothelioma cells treated wi th chemotherapy showed no change in DRS protein by Western analysis or by i mmunocytochemistry. TRAIL plus chemotherapy was associated with an increase in mitochondrial cytochrome c release and mitochondrial depolarization. We conclude that TRAIL and chemotherapy act cooperatively to kill mesotheliom a cell lines, not by increases in DR5 receptor but in association with mito chondrial amplification of apoptotic signals.