Comparative in vitro studies of the potentiation of tumor necrosis factor (TNF)-alpha, TNF-beta, and TNF-SAM2 cytotoxicity by hyperthermia.

Hyperthermia can strikingly enhance tumor necrosis factor-alpha (TNF-alpha) cytotoxicity in vitro and in vivo. Other forms of TNF may have tumor therapeutic applications and their interaction with hyperthermia should also be assessed. We have compared the effect of heat on the in vitro cytotoxic response of murine L929 and EMT-6 and human T24 tumor cells to three TNF forms; recombinant human TNF-alpha, TNF-beta (lymphotoxin), and TNF-SAM2. A neutral red assay was used to measure toxicity at 18-20 h after initiating the heat treatment. TNF treatment preceded heating by 0-4 h or followed it by 2 h. Heating was done at 39 or 40.5 degrees C for 24 h, 40.5 or 42 degrees C for 1 h, or 43 degrees C for 1-1.5 h. We found that both TNF-beta and TNF-SAM2 toxicities, like that of TNF-alpha, were markedly enhanced by hyperthermia. Neither EMT-6 nor T24 cells responded consistently to any of these TNFs at heat doses up to 1 h at 43 degrees C, but an increment of only 15 min more at 43 degrees C sensitized EMT-6 cells and 1.5 h at 43 degrees C resulted in extensive EMT-6 cell killing. The T24 cells remained resistant except for variable responses at the highest TNF and heat doses. If TNF treatment was begun immediately before or 2 h after beginning to heat the EMT-6 cells, sensitization was reduced or eliminated, respectively, for all three TNF forms relative to protocols in which TNF was added 1, 2, or 4 h before heating.(ABSTRACT TRUNCATED AT 250 WORDS)