Activation of the nitric oxide synthase pathway represents a key componentof tumor necrosis factor-related apoptosis-inducing ligand-mediated cytotoxicity on hematologic malignancies

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induc ed both cytotoxic (apoptosis) and cytostatic (cell cycle perturbation) effe cts on the human myeloid K562 cell line. TRAIL stimulated caspase 3 and nit ric oxide synthase (NOS) activities, and both pathways cooperate In mediati ng Inhibition of K562 survival/growth. This was demonstrated by the ability of z-VAD-fmk, a broad inhibitor of effector caspases, and N-nitro-L-argini ne methyl ester (L-NAME), an NOS pharmacologic Inhibitor, to completely (z- VAD-fmk) or partially (L-NAME) suppress the TRAIL-mediated Inhibitory activ ity. Moreover, z-VAD-fmk was able to block TRAIL-mediated apoptosis and cel l cycle abnormalities and increase of NOS activity. The addition of the NO donor sodium nitroprusside (SNP) to K562 cells reproduced the cytostatic ef fect of TRAIL without Inducing apoptosis. When TRAIL was associated to SNP, a synergistic increase of apoptosis and Inhibition of clonogenic activity was observed in K562 cells as well as In other myeloblastic (HEL, HL-60), l ymphoblastic (Jurkat, SupT1), and multiple myeloma (RPMI 8226) cell lines. Although SNP greatly augmented TRAIL-mediated antileukemic activity also on primary leukemic blasts, normal erythroid and granulocytic cells were less sensitive to the cytotoxicity mediated by TRAIL with or without SNP. These data Indicate that TRAIL promotes cytotoxicity in leukemic cells by activa ting effector caspases, which directly lead to apoptosis and stimulate NO p roduction, which mediates cell cycle abnormalities. Both mechanisms seem to be essential for TRAIL-mediated cytotoxicity. (C) 2001 by The American Soc iety of Hematology.