levoleucovorin and Leukemia-L5178

ZD9331 is a drug that was developed from a potent class of water-soluble, C7-methyl-substituted, quinazoline-based inhibitors of thymidylate synthase (TS) that are transported into cells via a saturable, carrier-mediated system (reduced folate carrier, or RFC) but are not substrates for folylpolyglutamate synthetase. ZD9331 is the gamma-tetrazole analogue of 2-desamino-2, 7-dimethyl-N10-propargyl-2'fluoro-5,8-dideaza folate (ZM214888), with a TS Ki of approximately 0.4 nM. ZD9331 exhibits potent growth inhibitory and cytotoxic activity; e.g., IC50 for the inhibition of human W1L2 lymphoblastoid cell line was 7 nM. The addition of thymidine to the culture medium increased the IC50 in W1L2 cells >10, 000-fold, demonstrating the high specificity of the drug for TS. ZD9331 is transported into cells predominantly via the RFC. Accordingly, it competes with methotrexate (MTX) and folinic acid for cellular uptake and has reduced activity against two cell lines with low expression of the RFC (L1210:1565 and CEM/MTX). In addition, a cell line with acquired resistance to ZD9331 displays reduced uptake of both ZD9331 and MTX. A mouse cell line (L1210:RD1694), with acquired resistance to ZD1694 due to reduced folylpolyglutamate synthetase activity, was not significantly cross-resistant to ZD9331. The flux through TS, as measured by 3H release from 5-[3H]deoxyuridine, was rapidly inhibited when cells were incubated with ZD9331. However, because ZD9331 cannot form polyglutamates, TS activity recovered rapidly once cells were placed in drug-free medium. The minimum curative dose of ZD9331 in the i.m. L5178Y TK-/- tumor model was approximately 3 mg/kg when given by 24-h continuous infusion, and it was 25-50 mg/kg when given by a single i.p. or i.v. injection. ZD9331 had antitumor activity against the L5178Y TK+/- tumor when administered by 7-day continuous infusion; growth delays of more than 5 days (and some cures) were seen at doses of 25-50 mg/kg/day. At higher doses, significant weight loss (gastrointestinal toxicity) and myelosuppression (neutropenia and thrombocytopenia) were observed, suggesting that these may be dose-limiting toxicities in the Phase I clinical studies.

Topics: Animals; Antineoplastic Agents; Biological Transport; Cell Division; Female; Humans; Kinetics; Leucovorin; Leukemia L1210; Leukemia L5178; Methotrexate; Mice; Mice, Inbred DBA; Quinazolines; Thymidylate Synthase; Tumor Cells, Cultured; Tumor Stem Cell Assay

Topics: Animals; Biological Transport; Cells, Cultured; Drug Resistance; Leucovorin; Leukemia L5178; Methotrexate; Mice; Tetrahydrofolate Dehydrogenase; Time Factors

The ability of CF to protect cells from methotrexate toxicity was measured in a series of murine lymphoma cells of varying degrees of sensitivity to methotrexate. The cells that were the most resistant to methotrexate showed the least degree of protection from methotrexate cytotoxicity. The extent of protection afforded by CF was found to correlate with the capacity of the cells to take up C14-5-methyltetrahydrofolate. That is, the cells with the lowest extent of uptake of reduced folate were afforded the least degree of protection from methotrexate by CF.

Topics: Animals; Biological Transport; Cell Line; Cell Survival; Kinetics; Leucovorin; Leukemia L1210; Leukemia L5178; Leukemia, Experimental; Methotrexate; Mice; Tetrahydrofolates