In vitro thermal therapy of AT-1 Dunning prostate tumours

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To advance the utility of prostate thermal therapy, this study investigated the thermal thresholds (temperature-time) for prostate tissue destructionin vitro. The AT-1 Dunning prostate tumour model was chosen for the study. Three hundred micron thick sections were subjected to controlled temperature-time heating, which ranged from low (40°C, 15 min) to high thermal exposures (70°C, 2 min) (n = 6). After subsequent tissue culture at 37°C, the sections were evaluated for tissue injury at 3, 24 and 72 h by two independent methods: histology and dye uptake. A graded increase in injury was identified between the low and high thermal exposures. Maximum histologic injury occurred above 70°C, 1 min with >95% of the tissue area undergoing significant cell injury and coagulative necrosis. The control and 40°C, 15 min sections showed histologic evidence of apoptosis following 24 and 72 h in culture. Similar signs of apoptosis were minimal or absent at higher thermal histories. Vital-dye uptake quantitatively confirmed complete cell death after 70°C, 2 min. Using the dye data, Arrhenius analysis showed an apparent breakpoint at 50°C, with activation energies of 135.8 kcal/mole below and 4.7 kcal/mole above the threshold after 3 h in culture. These results can be used as a conservative benchmark for thermal injury in the cancerous prostate. Further characterization of the response to thermal therapy in an animal model and in human tissues will be important in establishing the efficacy of the procedure