SYSTEMIC HYPERTHERMIA AND MISONIDAZOLE CHEMOPOTENTIATION

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The radiation sensitizer Misonidzaole (MISO) can selectively potentiate the effectiveness of certain conventional chemotherapeutic agents in vitro and in vivo. In preliminary experiments we have demonstrated that this chemopotentiating effect of MISO can be significantly augmented by mild hyperthermia (41 degrees C, 1 hr) under oxygen-deficient, but not aerobic conditions, suggesting that the addition of hyperthermia to drug-sensitizer combinations might result in a significant therapeutic advantage. The overall objectives of the proposed research are 1) to evaluate this hypothesis in vivo comparing enhancement of tumor response (KHT sarcoma) and normal tissues damage when MISO-drug combinations are administered in conjunction with whole-body hyperthermia, 2) define parameters influencing the interactions among the three variables in vitro in controlled experimental environments and 3) determine the mechanism(s) of the interactions and the influence of oxygen concentration on their expression. Experiments indicate that hyperthermia, independent of its effect on the chemotherapeutic agent, increases the chemopotentiating efficiency of a dose of MISO, possibly by increasing nitroreductase (NR) activity, an oxygen sensitive reaction. This enhanced chemopotentiating efficiency might prove clinically significant as the success of chemopotentiation in patients may be limited by an inability to deliver adequate MISO doses. The proposed research will make extensive use of statistically- motivated experimental designs to determine the significance of temperature, oxygen-concentration, sensitizer dose, and sequencing on expression of chemopotentiation using cell survival, tumor-growth delay and nitroreductase activity as endpoints. Other experiments will utilize the multi-cell tumor spheroid model and selective trypsinization techniques to determine the effect of treatment on aerobic and hypoxic populations exposed simultaneously and to determine whether thermal enhancements are possible at MISO concentrations and pharmaco-kinetics achievable in the clinic. These later experiments will make use of a spheroid treatment device designed to permit pharmacokinetic modeling in vitro. Finally, the effect of heat on the chemopotentiation of nitrosourea-resistant, chemopotentiation- resistant Mer+ tumor cells (about 80% of human tumors express the Mer+ phenotype) will also be evaluated as preliminary experiments indicate that the addition of heat can overcome the resistance of this phenotype.