[Augmentation of TNF- and lymphotoxin-mediated cytotoxic effect in the combined use of ACNU and involvement of oxygen free radicals].

Roles of oxygen free radicals in recombinant human TNF- and human lymphotoxin (LT)-mediated cytotoxicity have been examined. Nimustine (ACNU), which inhibits glutathione reductase, and buthionine sulphoximine (BSO), an inhibitor of glutathione (GSH) synthesis, were used to modify the steady-state level of intracellular H2O2. TNF-mediated cytotoxicity was augmented when ACNU was added simultaneously to target L cells or Meth A tumor cells. Similar augmented effect was observed when TNF or LT was added to ACNU-treated target cells. However, the addition of GSH nullified the augmentation of TNF-mediated cytotoxicity to ACNU-treated Meth A tumor cells. Meth A tumor cells were pretreated with BSO for 24 hr, and thereafter TNF or LT was added in the presence or the absence of BSO. The cytotoxic effect of TNF and LT was augmented by the treatment of the cell with BSO or simultaneous addition of BSO. High degree of the augmentation was obtained when the pretreatment with BSO and further addition of BSO were combined. These results suggest that oxygen free radicals are closely involved in TNF- and LT-mediated cytotoxicity and the modulation of intracellular GSH level alters the degree of the cytotoxicity of these cytotoxins.