Combined modality therapy with bleomycin, hyperthermia, and radiation

In an attempt to develop better combination therapies for use with local radiation, the interaction between bleomycin and hyperthermia +/- radiation was studied in the FSaIIC tumor system. In cells exposed in vitro to bleomycin at 37 degrees C and at pH 7.40, the drug was substantially more toxic toward normally oxygenated than hypoxic cells. At hyperthermic temperatures (42 degrees or 43 degrees C), however, the differential killing between the normally oxygenated and hypoxic cells disappeared and bleomycin became significantly more toxic. Exposure to bleomycin at pH 6.45 did not substantially alter the cytotoxicity of the drug at 42 degrees or 43 degrees C. In tumor growth delay experiments, combining bleomycin, hyperthermia, and radiation induced long delays, and the more successful sequences were bleomycin----radiation----hyperthermia or bleomycin----hyperthermia----radiation. If radiation was given prior to drug and hyperthermia, however, the sequence was significantly less effective. In tumor excision experiments performed 24 h after treatment, increasing doses of bleomycin produced a shallow, log-linear increase in tumor cell kill at 37 degrees C, but bleomycin followed by hyperthermia (43 degrees C, 30 min) led to about 1 log more cell killing. Administration of bleomycin just prior to treatment with a single dose of radiation was cytotoxically additive. In this assay the most effective trimodality treatment sequence was bleomycin----hyperthermia----radiation. In tumor subpopulations defined by Hoechst 33342 dye staining, bleomycin at 37 degrees C was about two-fold more toxic toward the bright (presumably well-oxygenated) cells than toward the dim (presumably hypoxic) cell subpopulation. The addition of hyperthermia following bleomycin produced nearly a log more tumor cell killing in both the bright and dim tumor cells. The combination of bleomycin followed by hyperthermia and then radiation was at least additive in the bright cells and caused a large cell kill, but in comparison, there was marked sparing of the dim cells. These results indicate that treatment with bleomycin and hyperthermia in conjunction with radiation can add substantially to tumor cell killing. This combination is significantly less effective in the hypoxic than oxic tumor regions, however, in spite of in vitro data which demonstrate that the cytotoxicity of bleomycin at hyperthermic temperatures is not oxygen-dependent.