Dihydrofolic Reductase in Human Blood Cells

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Abstract
(1) Amethopterin administration induces the appearance or a marked increase of dihydrofolic reductase activity in normal marrow cells, in normal leukocytes and erythrocytes, and in cells of chronic myelocytic, chronic lymphocytic and acute leukemia. (2) The increase of enzyme activity follows a different pattern in relation to the different life span of the various types of cells. (3) Repeated administration of the drug resulted in repeated inductions of dihydrofolic reductase activity in leukemic cells. (4) Peak values are reached at different time intervals when chronic leukemia undergoes an acute phase. (5) Concurrent administration of actinomycin C and amethopterin prevents the increase of the enzyme activity usually induced by amethopterin alone. (6) The relationship between the induction of dihydrofolic reductase activity and the resistance to amethopterin, and the schedules of the treatment with methotrexate are discussed.