TRAIL-induced cytotoxicity in a melphalan-resistant rhabdomyosarcoma cell line via activation of caspase-2.

The prognosis for patients with chemo-refractory rhabdomyosarcoma remains poor. The tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a hopeful candidate for new strategies in chemotherapy. The effects of TRAIL and melphalan (Mel) in the rhabdomyosarcoma cell line TE-671 were investigated by colorimetric caspase assays and flow cytometry. TRAIL induced the activation of caspases-2, -3 and -8, but not the activation of caspase-9, in the Mel-resistant TE-671 cells. Inhibition of caspase-2 with the caspase-2 inhibitor z-VDVAD-fmk significantly down-regulated the TRAIL-induced caspase-3 activation, as well as the TRAIL-induced cytotoxicity. When TE-671 cells were treated with a combination of Mel and TRAIL, a significant synergism of drug-induced cytotoxicity was obtained. The inhibition of caspase-2 could completely abolish caspase-3 activation, suggesting that TRAIL sensitises TE-671 cells for Mel-induced cytotoxicity via a caspase-2- and -3-dependent mechanism. In conclusion, it was shown, for the first time, that TRAIL could sensitise Mel-resistant tumour cells to melphalan.