Work in progress: the effect of heat on bleomycin cytotoxicity in vitro and on the accumulation of 57Co-bleomycin in heat-treated rat tumors.

The cytotoxic effects of the sequence and timing in combined hyperthermia and bleomycin treatment were tested in vitro using V79 Chinese hamster cells. The order of treatment was important; heat treatment followed by the administration of bleomycin yielded greater cytotoxicity than when the opposite order was used. To determine whether heat-treated tumors have an altered uptake of bleomycin, rat rhabdomyosarcoma (BA 1112) tumors were heated locally with RF current (43 degrees C, 90 min.), injected with 57Co-bleomycin, and imaged on a radioisotope camera. Results of tumor-to-background (T/B) ratio analysis indicate that (a) local hyperthermia (43 degrees C) does not appear to alter tumor uptake patterns of 57Co-bleomycin; and (b) intravenous and intraperitoneal injections produce similar T/B uptake ratios, typically between 2 and 3 at 120 minutes postinjection. In the BA 1112/WAG/Rij tumor system, local hyperthermia treatment does not seem to interfere with the subsequent accumulation of bleomycin in the tumor.