Inhibition of mammalian dna polymerase-associated 3′ to 5′ exonuclease activity by 5′-monophosphates of 3′-azido-3′-deoxythymidine and 3′-amino-3′-deoxythymidine

Abstract

3′-Azido-3′-deoxythymidine 5′-monophosphate (AZT-MP) has been hypothesized by us to possibly affect 3′-azido-3′-deoxythymidine (AZT) excision from host cell DNA. In the present study, AZT-MP inhibited 3′ to 5′ exonuclease activity of calf thymus DNA polymerase δ at pharmacological relevant intracellular concentrations. Other 2′,3′-dideoxynucleoside-5′-monophosphate (ddN-MP) analogs, including 3′-amino-3′-deoxythymidine-5′-monophosphate (AMT-MP), were also assayed as potential inhibitors of 3′ to 5′ exonuclease activity. The monophosphate derivative of 3′-amino-3′-deoxythymidine (AMT), an in vivo toxic catabolite of AZT, was the most potent of the ddN-MP analogs tested, inhibiting this activity by more than 50% at 100 μM. These results suggest that inhibition of 3′ to 5′ exonuclease activities by AZT-MP and AMT-MP may increase steady-state levels of AZT in host DNA, accounting in part for the cell toxicity associated with this drug. The present study also raises the question of whether AZT-MP inhibition of this activity may lead to potential mutagenic effects due to inhibition of 3′ to 5′ exonuclease-mediated proofreading functions involved in DNA replication.