Hyperthermic potentiation of bleomycin cytotoxicity in the presence of Bacillus thuringiensis subsp. israelenis delta-endotoxin.

We previously reported that a 25-kDa Bacillus thuringiensis subsp. israelensis (BTI) delta-endotoxin potentiated the antitumor activity of bleomycin (BLM) in both in vitro and in vivo systems. We report here a characteristic hyperthermic synergy toward the cytocidal activity of BLM in the presence of BTI endotoxin in cultured L1210 cells. Cytocidal gain, i.e., the ratio of the IC50 of BLM in the absence versus the presence of BTI delta-endotoxin, reached ca. 20 at 40 degrees C, suggesting that a more effective heat-BLM combination treatment may be achieved in the presence of BTI delta-endotoxin.