[Comparison between leucovorin and cisplatin as a modulator of 5-fluorouracil]

Currently, biochemical modulation for 5-fluorouracil (5-FU) by leucovorin (LV) and cisplatin (CDDP) seems one of the most successful chemotherapy for gastro-intestinal tract cancers. The mechanism of the modulation is thought to increase intracellular 5, 10-methylenetetrahydrofolate (CH2-H4 folate) levels. The purpose of this study is to examine the effect of LV and CDDP as a modulator of 5-FU. Either 10, 200, 400 mg/kg of LV or 2, 4, 6 mg/kg of CDDP were administered intravenously to mice bearing Sarcoma-180. Two hrs. later, CH2-FH4 folate levels were measured in tumor, muscle and intestine by thymidylate synthase (TS) binding assay. As the results, after administration of 200, 400 mg/kg of LV or 4, 6 mg/kg of CDDP, CH2-H4 folate level was elevated. This elevation was dose-dependent in LV. In contrast, no more elevation was observed after 6 mg/kg of CDDP injection. There was much smaller increase of CH2-H4 folate level was observed in the muscle and intestine. We conclude that the elevation of CH2-H4 folate levels depends on the organ and this leads to the tumor specificity in these chemotherapy.