IN-VITRO MUTATIONS IN DIHYDROFOLATE-REDUCTASE THAT CONFER RESISTANCE TO METHOTREXATE - POTENTIAL FOR CLINICAL-APPLICATION

Mammalian cells cultured in the presence of the chemotherapeutic agent , methotrexate, develop resistance to this drug. Sometimes this is due to mutations in the gene for dihydrofolate reductase, the primary tar get of methotrexate, However, it has not been possible to link such po lymorphism to resistance of neoplastic disease to therapy with methotr exate, Nevertheless, interest in this possibility lead to the introduc tion of many mutations into the cDNA for human DHFR by mutagenesis. Mo st of the corresponding enzyme variants have been expressed in Escheri chia coli and characterized. Many mutations in codons for hydrophobic residues at the active site greatly decrease inhibition by methotrexat e, and by the related substrate analogue, trimetrexate, while allowing the retention of considerable catalytic efficiency. Introduction of s ome of these mutants into mammalian cells by retroviral transfer provi des substantial protection from toxic effects of the inhibitors, and h as promise for the myeloprotection of patients receiving therapy with methotrexate or trimetrexate. Another potential use is in therapy for inherited disorders of hematopoiesis, where genetic modification of en ough cells is a perennial problem. After transplantation of bone marro w that has been transduced with a bicistronic vector encoding both the mutant DHFR and a therapeutic gene, subsequent administration of meth otrexate or trimetrexate should permit selection and enrichment of gen etically modified hematopoietic cells. (C) 1998 Wiley-Liss, Inc.