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Mechanisms of Inhibition of DNA Synthesis by 2-Chlorodeoxyadenosine in Human Lymphoblastic Cells¹

Department of Biochemical and Clinical Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38101 [J. G., R. K., R. L. B.], and Department of Pharmacology, University of Tennessee College of Medicine-Memphis, Memphis, Tennessee 38163 [R. L. B.]

2-Chloro-2'-deoxyadenosine 5'-triphosphate (CldATP) is a strong inhibitor of the reduction of ADP, CDP, UDP and GDP by ribonucleotide reductase in extracts of CCRF-CEM with 50% inhibition at concentrations of 0.1 to 0.3 µM. In cells exposed to 0.3 µM 2-chloro-2'-deoxyadenosine (CldAdo), the intracellular concentration of CldATP reaches 2 µM within 15 min, and DNA synthesis by the cells is inhibited 90% within 30 min. At concentrations of extracellular CldAdo that inhibit DNA synthesis, there is also marked inhibition of intracellular conversion of cytidine to deoxycytidine nucleotides indicating significant intracellular inhibition of ribonucleotide reductase. Exposure of cells to 0.3 µM CldAdo decreases dCTP by 63% in 30 min, dATP and dTTP by 20%, and dGTP by a smaller amount. Similar decreases in these pools occur when other inhibitors of ribonucleotide reductase are present at concentrations causing similar inhibition of DNA synthesis. Deoxycytidine treatment of cells inhibited by CldAdo restores dCTP and other pools, but restoration of DNA synthesis is incomplete, indicating that there is another mechanism for inhibition of DNA synthesis in addition to depletion of deoxyribonucleotide pools. This alternate mechanism is probably related to the incorporation of CldAdo into DNA that occurs despite a 25-times lower intracellular level of CldATP than dATP.

¹ Supported in part by USPHS Grant R01 CA 39242 from the National Cancer Institute and by American Lebanese Syrian Associated Charities.

² To whom requests for reprints should be addressed, at Department of Biochemical and Clinical Pharmacology, St. Jude Children's Research Hospital, 332 North Lauderdale, P. O. Box 318, Memphis, TN 38101.

Received 5/22/89. Revised 9/ 1/89. Accepted 9/21/89.

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