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  • Title: The reversal of methotrexate cytotoxicity to mouse bone marrow cells by leucovorin and nucleosides.
    Author: Pinedo HM, Zaharko DS, Bull JM, Chabner BA.
    Journal: Cancer Res; 1976 Dec; 36(12):4418-24. PubMed ID: 1087180.
    Abstract:
    The cytotoxic effect of methotrexate (MTX) for mouse bone marrow cells has been studied by in vitro of the granulocyte precursor cell (CFU-C) in a medium containing dialyzed fetal calf serum and dialyzed L-cell supernatant. The formation of 50-cell colonies was inhibited to 50% of control by 10(-8) M MTX. Further increases in MTX concentration rapidly abolished colony formation by CFU-C. The potential of leucovorin and nucleosides to rescue the CFU-C from MTX toxicity was studied. Toxicity of 10(-7) M MTX was completely reversed by equimolar concentrations of leucovorin, but with higher MTX concentrations, relatively more leucovorin was required. While 10(-5) M MTX was rescued by 10(-3) M leucovorin, rescue of the toxic effect of 10(-4) M MTX by 10(-3) M leucovorin was not observed. In contrast to the rescue by Leucovorin, toxicity of all MTX concentrations up to 10(-4) M was completely prevented by 10(-5) M thymidine with 10(-5) M adenosine, inosine, or hypoxanthine. Single nucleosides or thymidine with guanosine were ineffective, as were lower concentrations (less than or equal to 10(-6)M) of the effective combinations. Thus, while leucovorin reversed the MTX toxicity to CFU-C competitively, rescue by nucleosides was noncompetitive. The significance and possible usefulness of these findings for chemotherapeutic protocols are discussed.
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