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The mechanism of action of cidofovir and (S)-9-(3-hydroxy-2-phosphonomethoxypropyl)adenine against viral polymerases Open Access


Other title
DNA Polymerase
Reverse Transcriptase
Nucleotide Analog
Type of item
Degree grantor
University of Alberta
Author or creator
Magee, Wendy C
Supervisor and department
Evans, David H (Medical Microbiology and Immunology)
Examining committee member and department
Tyrrell, D Lorne J (Medical Microbiology and Immunology)
Humar, A (Medicine)
Hobman, T (Cell Biology)
Götte, M (Microbiology and Immunology, McGill University)
Department of Medical Microbiology and Immunology

Date accepted
Graduation date
Doctor of Philosophy
Degree level
The nucleoside phosphonates cidofovir (CDV) and (S)-9-[3-hydroxy-(2-phosphonomethoxy)propyl]adenine [(S)-HPMPA] are analogs of dCMP and dAMP, respectively. Collectively these drugs are effective inhibitors of a wide range of DNA viruses, RNA viruses, and retroviruses. Because they are nucleotide analogs, the drugs are thought to target viral polymerases and inhibit viral genome replication. However, the precise mechanism by which these drugs block viral growth remains unclear. We have studied the mechanism of action of these antivirals against three viral polymerases, vaccinia virus DNA polymerase and the reverse transcriptases from human immunodeficiency virus type 1 (HIV-1) and Moloney murine leukemia virus (MMLV). In vitro experiments using the active intracellular metabolites of CDV and (S)-HPMPA, CDV diphosphate (CDVpp) and (S)-HPMPA diphosphate [(S)-HPMPApp], respectively, showed that the drugs are substrates for each enzyme and can be incorporated into DNA without causing chain termination, although the rate of DNA elongation catalyzed by the vaccinia virus and MMLV polymerases is slowed. We have also found that incorporation of CDV or (S)-HPMPA blocked the 3′-to-5′ proofreading exonuclease activity of the vaccinia virus DNA polymerase. In addition, we determined that when these drugs are incorporated into a template DNA strand, they inhibited replication across the drug lesion. These results indicate that although CDV and (S)-HPMPA can inhibit some enzymes when incorporated into the primer strand, the main effects of drug action occur when they are incorporated into the template strand. Our findings point to a new avenue of targeted drug design, one in which nucleoside or nucleotide analogues are efficient substrates for the viral nucleic acid polymerase, do not inhibit primer strand elongation, but exert their effects in subsequent rounds of nucleic acid synthesis.
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