Intracellular Metabolism ofCycloSaligenyl 3′-Azido-2′,3′-dideoxythymidine Monophosphate, a Prodrug of 3′-Azido-2′,3′-dideoxythymidine (Zidovudine)

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Abstract
The administration of CycloSaligenyl 3′-azido-2′,3′-dideoxythymidine monophosphate (CycloSal-AZTMP) to CEM cells resulted in a concentration- and time-dependent conversion to the 5′-monophosphate (AZTMP), 5′-diphosphate (AZTDP), and 5′-triphosphate (AZTTP) derivatives. High ratios of AZTMP/AZTTP were found in the CEM cell cultures treated with CycloSal-AZTMP. The intracellularT1/2 of AZTTP in CEM cell cultures treated with either AZT and CycloSal-AZTMP was approximately 3 h. A variety of human T- and B-lymphocyte cell lines efficiently converted the prodrug to the AZT metabolites, whereas peripheral blood lymphocytes and primary monocyte/macrophages showed at least 10-fold lower metabolic conversion of the prodrug.CycloSal-AZTMP failed to generate marked levels of AZT metabolites in thymidine kinase-deficient CEM/TK− cells, an observation that is in agreement with the substantial loss of antiviral activity of CycloSal-AZTMP in CEM/TK− cells. The inability ofCycloSal-AZTMP to generate AZTMP in CEM/TK−cells is presumably due to a relatively high hydrolysis rate of AZTMP to the parent nucleoside AZT, combined with the inability of CEM/TK− cells to phosphorylate AZT to AZTMP through the cytosolic salvage enzyme thymidine kinase.

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