Mechanism of synergistic cytotoxic effect between tumor necrosis factor and hyperthermia.

We previously reported that recombinant human tumor necrosis factor (rhTNF) and hyperthermia had a synergistic effect against tumors, in vitro and in vivo. We have now investigated the mechanism of this synergy by measuring the lysosomal enzyme activity and hydroxyl radical production of L-M cells treated with rhTNF and/or hyperthermia. A synergistic activation of lysosomal enzyme and the induction of hydroxyl radical production in L-M cells treated with both rhTNF and hyperthermia was observed. A synergistic cytotoxic effect was observed when rhTNF and hyperthermia were combined, and was inhibited by the addition of a reactive oxygen scavenger, dimethyl sulfoxide or bipyridine. The results show that the augmenting effect of hyperthermia on lysosomal enzyme activation and induction of hydroxyl radical production by rhTNF plays an important role in the synergistic cytotoxic effect.