Lacerda J F, Göker E, Kheradpour A, Dennig D, Elisseyeff Y, Jagiello C, O'Reilly R J, Bertino J R
Program of Molecular Pharmacology and Therapeutics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Blood. 1995 May 15;85(10):2675-9.
Impaired transport of methotrexate (MTX) is a common resistance mechanism of tumor cells to this drug. Trimetrexate (TMTX), a second-generation folate antagonist, is still active against MTX-transport-resistant cells because it enters cells by passive diffusion and does not use the reduced folate transport system for cell entry. Therefore, although leucovorin (LV) protects MTX-sensitive cells from TMTX toxicity, MTX-transport defective cells are poorly rescued by LV. Severe combined immunodeficiency mice bearing MTX-transport-resistant CCRF-CEM acute lymphoblastic leukemia tumors were treated with TMTX alone or with the combination of TMTX and LV, with tumor regressions in both groups (P < .001) and without significant toxicity. These results indicate that TMTX with LV protection may be a useful therapeutic regimen for patients with MTX-transport-defective acute lymphoblastic leukemia. Furthermore, resistance to TMTX plus LV may result in reversion to MTX sensitivity.
