title: A gene transfer strategy for making bone marrow cells resistant to trimetrexate.
abstract: Trimetrexate (TMTX) is an anticancer drug with potential advantages over the more commonly used antifolate, methotrexate (MTX); however, its use has been limited by severe myelosuppression. Retroviral vectors containing mutant dihydrofolate reductase (DHFR) genes have been used to protect bone marrow cells from MTX, suggesting a similar approach could be used for TMTX. We first screened six variants of human DHFR to determine which allowed maximal TMTX resistance in fibroblasts. A variant enzyme containing a Leu-to-Tyr mutation in the 22nd codon (L22Y) was best, allowing a 100-fold increase in resistance over controls. Murine hematopoietic progenitor cells transduced with an L22Y-containing retroviral vector also showed high-level TMTX resistance in vitro. Mice reconstituted with L22Y-transduced bone marrow cells were challenged with a 5-day course of TMTX to determine whether hematopoiesis could be protected in vivo. Transfer of the L22Y vector resulted in consistent protection from TMTX-induced neutropenia and reticulocytopenia at levels that correlated with the proviral copy number in circulating leukocytes. We conclude that the L22Y vector is highly effective in protecting hematopoiesis from TMTX toxicity and may provide a means for increasing the therapeutic utility of TMTX in certain cancers.
authors.affiliation: Department of Biochemistry, St Jude Children's Research Hospital, Memphis, TN 38101 USA.
authors.forename: H T
authors.initials: HT
authors.lastname: Spencer
authors.forename: S E
authors.initials: SE
authors.lastname: Sleep
authors.forename: J E
authors.initials: JE
authors.lastname: Rehg
authors.forename: R L
authors.initials: RL
authors.lastname: Blakley
authors.forename: B P
authors.initials: BP
authors.lastname: Sorrentino
mesh_terms: D000818:Animals; D001483:Base Sequence; D001853:Bone Marrow / Q000187:drug effects*; D001854:Bone Marrow Cells; D016026:Bone Marrow Transplantation; D018076:DNA, Complementary / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology; D015316:Genetic Therapy; D005822:Genetic Vectors; D006412:Hematopoietic Stem Cells / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics*; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D014162:Transfection; D016597:Trimetrexate / Q000494:pharmacology*
chemical_list: D018076:DNA, Complementary; D011993:Recombinant Fusion Proteins; D013762:Tetrahydrofolate Dehydrogenase; D016597:Trimetrexate