Synergism between alkylating agent and cis-platin with moderate local hyperthermia: the effect of multidrug chemotherapy in an animal system.

The combined effect of multidrug chemotherapy given in combination with hyperthermia was investigated using early-generation isotransplants of a spontaneous fibrosarcoma, FSa-II in C3Hf/Sed mice. Combinations of various types of chemotherapeutic agents, including alkylating agents, cyclophosphamide (CY) and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU); antibiotics, bleomycin (BLM) and mitomycin C (MMC); an antimetabolite, 5-fluorouracil (5FU); and a platinum complex, cis-diamminedichloroplatinum(II) (cDDP), were examined using the tumour growth (TG) time assay. Simultaneously, the effect of glucose on the response to thermochemotherapy was investigated. Graded doses of the multidrugs were given i.p. immediately before hyperthermia with or without a glucose dose of 5 g/kg given i.p. 60 min before hyperthermia. Hyperthermia was given by immersing the tumour-bearing murine feet into a water bath set at 41.5 +/- 0.05 degrees C for 60 min. Dose-response curves were obtained between the TG time and drug dose. The thermal enhancement ratio (TER) was expressed as a ratio of the slope of the dose-response curve obtained at 41.5 degrees C to that obtained at room temperature. To evaluate normal tissue damage, the number of white blood cells (WBC) was counted from a day before treatment to the 21st day after treatment. A substantial thermal enhancement of the anti-tumour effect was observed in all five multidrug regimens tested. Glucose administered prior to thermochemotherapy further enhanced the antitumour effect. The TER was largest for the combination of CY+cDDP (TER was 5 without glucose). The second largest TER was obtained for a combination of CY+cDDP+MMC (TER was 4.1 without glucose and 6.5 with glucose). The antitumour effects of these two combinations were synergistic at a test elevated temperature only. No synergistic effect was found at room temperature for any of the drug combinations tested. The smaller TERs were observed in the treatment regimens that included 5FU. In general, a decrease in the number of WBC following multidrug chemotherapy was slightly less than that following the individual drugs.