Enhanced tumour uptake of radiolabelled antibodies by hyperthermia. Part II: Application of the thermal equivalency equation.
Clinical application of local hyperthermia as a means for modulating drug and macro-molecular tumour uptake have been slow to develop, due in part to the difficulty in designing and comparing heating protocols. The thermal isodose formula developed by Sapareto and Dewey is used in cytotoxicity and radiosensitization hyperthermia protocols to compare different time/temperature combinations; however, its relevance to other end-points has not been evaluated. The current study was undertaken to determine whether heating protocols of different time and temperature, but predicted to be thermally equivalent by this formula, had similar effects on the tumour and normal tissue distribution of radiolabelled tumour-specific (anti-tenascin 81C6) and non-specific (anti-dansyl TPS3.2) monoclonal antibodies (mAbs). Two thermally equivalent heating protocols, 4 h at 41.8 degrees C and 45 min at 43 degrees C, were compared in mice with subcutaneous D54 MG human glioma xenografts. A 4-fold increase in xenograft localization of 81C6 mAb was achieved relative to that in non-heated control groups with both heating protocols. Both hyperthermia protocols also resulted in improved tumour:normal tissue ratios. However, differences in absolute tumour and normal tissue uptake were seen, suggesting that the thermal isodose formula has limited usefulness in the design and comparison of hyperthermia protocols for enhancing the tumour uptake of radiolabelled mAbs.
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