Inhibition of ribonucleotide reductase by 2'-substituted deoxycytidine analogs: possible application in AIDS treatment.

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Abstract
After phosphorylation to the corresponding diphosphates, 29-azido-29-deoxycytidine and 29-difluorocytidine act as powerful inhibitors of ribonucleotide reductase. Phosphorylation requires deoxycytidine kinase, an enzyme with particularly high activity in lymphoid cells. Therefore, the deoxycytidine analogs can be expected to inhibit the reductase with some specificity for the lymphoid system. Pretreatment of human CEM lymphoblasts with the analogs considerably increased the phosphorylation of 39-deoxy-39-azidothymidine (AzT). The increased phosphorylation of AzT is caused by a prolongation of the S phase of the cell cycle. Our results suggest the possibility of a combination of 29-substituted deoxycytidine analogs with AzT in the treatment of AIDS. Gao et al. [Gao, W.-Y., Cara, A., Gallo, R. C. & Lori, F. (1993) Proc. Natl. Acad. Sci. USA 90, 8925-8928] have suggested the use of the ribonucleotide reductase inhibitor hydroxyurea for this purpose, since the resulting decrease in the size of deoxyribonucleotide pools decreases the processivity of the HIV reverse transcriptase. From our results it would appear that the 29-substituted deoxycytidine analogs might be preferable to hydroxyurea.