Tetrachloro(d,l-trans)1,2-diaminocyclohexane platinum (IV) (tetraplatin), a new platinum analogue, showed greater therapeutic efficacy after i.p. administration than either cis-dichlorodiammineplatinum (II) (cisplatin) or cis-diammine-1,1-cyclobutanedicarboxylate platinum (II) (carboplatin) in mice bearing i.p. implanted L1210 leukemia. At an optimal dose of 5.7 mg/kg/injection given as a single dose on days 1, 5, and 9, tetraplatin increased the median life span over controls by more than 566% with 5 of 8 long-term (50-day) survivors. In contrast, cisplatin at the same optimal dose increased survival by 186% with 2 of 8 long-term survivors, and carboplatin at an optimal dose of 75.6 mg/kg/injection increased survival by only 120% with no long-term survivors. Tetraplatin also was more effective than cisplatin when treatment was delayed until days 3, 7, and 11 after i.p. implant.

A combination of tetraplatin and Adriamycin in mice bearing i.p. implanted L1210 leukemia produced more long-term survivors over a wider range of doses than could be achieved with either drug alone. Tetraplatin at 5.7 mg/kg/injection and Adriamycin at 3 mg/kg/injection on days 1, 5, and 9 increased survival by more than 566% with 8 of 8 50-day survivors. Using the same treatment schedule, combinations of tetraplatin with either cisplatin, carboplatin, daunomycin, or 5-fluorouracil did not produce therapeutic efficacy greater than that seen with tetraplatin alone.

The in vitro cellular uptake of platinum by L1210 cells at 37°C was about 4-fold higher after exposure to tetraplatin compared to cisplatin following a 2-h incubation at the two concentrations examined (2.5 and 5 µg/ml). Comparative pharmacological studies were performed in rats at a single dose of 3 mg/kg i.v. The t½β for total platinum in plasma was 29.10 h (7.47 h for unbound platinum) after the administration of tetraplatin and 23.70 h (13.09 h for unbound platinum) after cisplatin. By 48 h the urinary excretion of platinum after tetraplatin and cisplatin was 30.1% and 41.4%, respectively. Tissue distribution of platinum was similar after either complex. Thus, tetraplatin has similar pharmacological properties to cisplatin and like cisplatin is a candidate for combination chemotherapy. However, tetraplatin may be superior to cisplatin in some therapeutic situations based on its greater efficacy against selected tumors.

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