AEGiS-05CROI: Phenotypic mechanism of HIV-1 resistance to 3'-azido-3'-deoxythymidine (AZT).

5th Conference on Retroviruses and Opportunistic Infections

Chicago, IL - February 1-5, 1998

Phenotypic mechanism of HIV-1 resistance to 3'-azido-3'-deoxythymidine (AZT).

Conf Retroviruses Opportunistic Infect 1998 Feb 1-5; 5th:85 (abstract no. 32)

Arion D, Borkow G, Kaushik N, Parniak MA; Lady Davis Institute for Medical Research, Montreal, Quebec, Canada.

While the genotype of HIV-1 resistance to AZT has long been known, the phenotypic mechanism by which multiple mutations (D67N, K70R, T215F, K219Q) in reverse transcriptase (RT) confer high-level AZT resistance has eluded investigators. These mutations arise in two separate subdomains of RT, suggesting that they may contribute differently to overall resistance. We therefore studied the D67N/K70R/T215F/K219Q, the D67N/K70R and the T215F/K219Q mutant enzymes. The D67N/K70R/T215F/K219Q mutant shows increased DNA polymerase processivity, due to decreased RT - template/primer dissociation. This results entirely from the T215F/K219Q substitutions. The AZTTP sensitivity of the D67N/K70R/T215F/K219Q mutant (IC50 approximately 200 nM) is less than wild-type RT (IC50 approximately 60 nM) in the presence of 0.5 mM pyrophosphate. Importantly, the mutant also shows a greatly increased rate of pyrophosphorolysis, the reverse reaction of DNA synthesis. This removes chain-terminating AZT from the 3'-end of viral DNA, allowing RT-catalysed DNA synthesis to resume. The enhanced pyrophosphorolysis is due entirely to the D67N/K70R mutations. We propose AZT resistance results from a net decrease in chain termination due partly to decreased binding of AZTTP but primarily to selective pyrophosphorolytic cleavage of chain-terminated viral DNA at physiological pyrophosphate levels. This, coupled with increased RT processivity, enables facile HIV replication in the presence of AZT. Consistent with this model is our observation that combinations of AZT + UC781, a nonnucleoside that inhibits RT-dependent pyrophosphorolysis, show synergy in inhibiting replication of AZT-resistant HIV, implying that UC781 restores the chainterminating activity of AZT against the resistant virus.

Keywords: AEGIS, Zidovudine, Reverse Transcriptase Inhibitors, Thymine Nucleotides, Anti-HIV Agents, RNA-Directed DNA Polymerase, Templates, Genetic, Virus Replication, DNA, Viral, Diphosphates, DNA Primers, Mutation, Anilides, 3'-azido-3'-deoxythymidine 5'-triphosphate, UC 781, genetics, virology, AIDS

1998-02-01
32

Copyright © 1998 - Foundation for Retrovirology and Human Health (IAS). Reproduction of this abstract (other than one copy for personal reference) must be cleared through the Foundation for Retrovirology and Human Health. Licensed from National Library of Medicine.