Schedule dependent tumour growth delay, DNA cross-linking and pharmacokinetic parameters in target tissues withcis-diamminedichloroplatinum(II) and etanidazole with or without hyperthermia or radiation

Abstract

It has been reported previously that striking increases in tumour growth delay and cytotoxicity are seen when cis-diamminedichloroplatinum(II) (CDDP) is combined with mild local hyperthermia (43 degrees C, 30 min) and/or etanidazole (ETA). This paper reports a study of CDDP pharmacology and the in vivo tumour DNA cross-linking produced by these combinations. In C3H mice bearing the FSaIIC murine fibrosarcoma, Pt plasma pharmacokinetics were not significantly altered by any of the combination of treatments. Although ETA caused no significant change in CDDP tissue pharmacokinetics, treatment of the tumour-bearing limb with hyperthermia immediately following an i.p. injection of CDDP (10 mg/kg) resulted in an increased peak Pt concentration (3.5 versus 2.8 micrograms Pt/g tumour wet weight) and doubled the t1/2 elimination of Pt (15 to 30 h) from the tumour. Similar heat-induced changes were observed in the Pt pharmacokinetics in skin. There was about a three-fold increase in the Pt area under the curve (AUC) for the tumour, a 1.5-fold increase in the AUC for skin and little change in the AUC for muscle with hyperthermia. When the tumour DNA cross-linking factor (CLF) was determined, it was found that local hyperthermia treatment (43 degrees C, 30 min) increased the CLF of CDDP from 1.7 to 2.7 and hyperthermia (43 degrees C, 1 h) further increased the CLF to 6.1. Misonidazole (MISO) (1 g/kg) increased the CDDP CLF to 2.0, 6.3 and 15.1 in conjunction with 37, 43 (30 min) and 43 degrees C (1 h), respectively. ETA (1 g/kg) was more effective than MISO at increasing the CDDP CLF, producing CLFs of 2.8, 9.1 and 21.5 at 37, 43 (30 min) and 43 degrees C (1 h), respectively. These changes in CLF were reflected in an increased tumour growth delay in the FSaIIC murine fibrosarcoma with CDDP (5 mg/kg) alone from 4.4 to 5.9 days with 43 degrees C (30 min) and then to 11.9 days with ETA (1 g/kg) and 20.9 days with both ETA and local hyperthermia (43 degrees C, 30 min). When CDDP, ETA and hyperthermia were added to a radiation schedule of 300 cGy daily for five days, it was found that giving ETA (1 g/kg), CDDP (5 mg/kg) and hyperthermia (43 degrees C, 30 min) together on day 1 produced the largest tumour growth delay (43 days) and that other schedules which divided the dose of ETA over the other days of the radiation treatment (including one schedule with a second heat treatment on day 4) were significantly inferior.(ABSTRACT TRUNCATED AT 400 WORDS)