[Phase I study of 5-fluorouracil and l-leucovorin]

Leucovorin, given usually by i.v. injection or orally changes to 5, 10-methylene tetrahydrofolate in tumor as well as normal cells. And in normal FdUMP, an active metabolite of 5-FU, binds tightly to thymidylate synthase in the presence of cofactor, 5, 10-methylene tetrahydrofolate. This interaction leads to potentiate the cytotoxic effect of 5-FU by prolonged inhibition of thymidylate synthase. Phase I study using l-leucovorin (l-LV), an active form of leucovorin, combined with 5-FU, was conducted. In the weekly schedule, 5-FU was fixed to 600mg/m2, and l-LV dose was escalated from 125 mg/m2 to 250mg/m2, if toxicity was acceptable. On the other hand, in the five consecutive-day schedule, 5-FU was fixed to 370mg/m2 and l-LV was escalated from 25mg/m2 to 50mg/m2, 100mg/m2 and 200 mg/m2. l-LV 10mg/m2 was tested as reference. On weekly schedule of l-LV 250mg/m2, grade III diarrhea was seen in 2 cases and grade IV leucopenia was seen in one. In five consecutive-day schedule, at each dose of l-LV, stomatitis, nausea plus vomiting, anorexia, anemia and leucopenia were seen. However, the increase of toxicities were not seen by dose escalation of l-LV. Then, we have been conducted a randomized early phase II study using 250 mg/m2 of l-LV weekly (arm A) and 100mg/m2 (arm B) or 10mg/m2 (arm C) of l-LV for 5 consecutive days in gastric and colorectal cancer by multicenter cooperative study. Plasma concentrations of l-LV were maintained > 10(-5) mol/L for over 5 hrs. after 2 hrs. infusion of 250 mg/m2 of l-LV and for over one hr. after a rapid injection of 100mg/m2 of l-LV.