Increased Therapeutic Gain of Combined c/5-Diamminedichloroplatinum(II) and Whole Body Hyperthermia Therapy by Optimal Heat/Drug Scheduling1

To maximize therapeutic gain, the timing sequence of whole body hyperthermia (WBH) and cu-diammincdichloroplatinum(II) (DDP) was examined. Normal tissue injury as well as growth of a s.c. transplanted fibrosarcoma »eremeasured in I 344 rats treated with variable schedules of YVBHand DDP. Simultaneous application of DDP (2 mg/kg i.v.) with WBH (120 min at 41.5°C)resulted in severe renal injury, body weight loss, and mortality; while sequential use of the modalities caused minimal to no toxicity. DDP or WBH alone produced only minimal tumor growth delay, whereas supraadditive antitumor effects occurred with all tested schedules of DDP combined with WBH, regardless of sequence or interval between the two modalities. We designated the ratio of antitumor effect to nephrotoxicity as specific therapeutic efficacy (STE). DDP given simultaneously with WBH produced the lowest STE (0.6-1.2), which was less than or equal to either DDP (STE = 1.2) or WBH (STE = 1.5) alone. On the other hand, schedules of DDP prior to and after WBH resulted in a STE of 1.8-3.0, a supraadditive effect. These results indicate that an optimal scheduling of DDP with WBH significantly improves therapeutic gain by reducing normal tissue injury while maintaining enhanced antitumor activity.