title: Isolation of thymidine-resistant cells from a thymidine-sensitive acute lymphoblastic leukemia cell line.
abstract: Malignant cells have enhanced sensitivity to inhibition of growth by thymidine. Cell growth of the permanent lymphoid cell line CCRF-CEM, originating from a patient with acute lymphoblastic leukemia, is inhibited by 3 x 10(-5) M thymidine, compared to 1 to 5 x 10(-3) M thymidine required to inhibit growth of normal lymphoid lines. Thymidine-resistant cells were isolated at a frequency of approximately 1/100,000 cells after cloning CCRF-CEM cells in medium containing 5 x 10(-4) M thymidine. The resistant cells lacked the enzyme thymidine kinase, had a 20-fold decrease of thymidine uptake, and were resistant to 1 x 10(-4) M 5-bromo-2-deoxyuridine. The cells were sensitive to 1 x 10(-5) M methotrexate, even in the presence of exogenously added thymidine and hypoxanthine. The data indicate that a small fraction of malignant cells may escape the toxic effect of high thymidine therapy and therefore, require additional chemotherapy for their control.
mesh_terms: D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002469:Cell Separation; D002875:Chromosomes / Q000187:drug effects; D002999:Clone Cells; D004351:Drug Resistance; D006801:Humans; D007945:Leukemia, Lymphoid / Q000378:metabolism / Q000473:pathology; D013936:Thymidine / Q000494:pharmacology*; D013937:Thymidine Kinase / Q000378:metabolism
chemical_list: D013937:Thymidine Kinase; D013936:Thymidine