16th International HIV Drug Resistance Workshop 12-16 June 2007, Barbados

CHARACTERIZATION OF A NOVEL S68 DELETION IN HIV-1 REVERSE TRANSCRIPTASE

Antivir Ther. 2007; 12:S27 (abstract no. 25)

RF Schinazi, M Ruckstuhl, KL Rapp, J Lennerstrand, M Bennett and M Detorio
Emory University School of Medicine/Veterans Affairs Medical Center, Decatur, GA, USA

BACKGROUND: Nucleoside reverse transcriptase inhibitor (NRTI) treatment of HIV-1 infected individuals often leads to the emergence of mutations in the reverse transcriptase (RT). Less frequently seen are codon insertions or deletions, which either add or subtract three nucleotides and leave other codons in the correct coding frame. Characterization of these mutations is key in determining potential cross-resistance and in treatment management. During the selection of resistant virus to dexelvucitabine (DFC) in primary human lymphocytes, population sequencing revealed a novel deletion of the S68 codon (deletion of AGT) in HIV-1 RT. This S68 deletion was investigated phenotypically against selected antiviral agents for resistance.

METHOD: S68 deletion drug susceptibility assays were conducted with both in vitro selected S68 virus (HIV-1_S68-23) and a site-directed mutant (SDM) virus. The S68 deletion SDM was made in a pNL4-3 background. Cross-resistance was determined by drug susceptibility assays. Virus yields were determined by RT and quantitative real-time PCR assays. In addition, particle derived RT resistance against NRTI-triphosphates was studied with a heteropolymeric- DNA colorimetric RT assay where 3.2 mM ATP was present.

RESULTS: Virus containing the S68 deletion was selected in HIV-1_LAI infected PBM cells after 14 weeks of culture in the presence of DFC, and this mutation became the dominant virus by week 19 based on population sequence and clonal analysis. Drug susceptibility assays indicated that virus with the S68 deletion produced a greater than 30-fold increase resistance to DFC, lamivudine, emtricitabine, tenofovir, abacavir, and amdoxovir. As expected, NNRTI and protease inhibitors demonstrated no resistance. HIV-RT containing the S68 deletion demonstrated a 5.6-, 2.5- and 10-fold increase in resistance to DFC-TP, AZT-TP and emtricitabine-TP, respectively.

CONCLUSION: The S68 deletion demonstrated resistance to several clinically important NRTI. The Stanford database did not reveal matching sequences for the S68 deletions. Codon insertions and deletions have been associated with multidrug resistance (MDR) in clinical samples obtained from antiretroviral-treated individuals (67del, 69del, 69ins, 70del); however, the S68 deletion has never been reported. The novel S68 deletion may prove to be an important variable in NRTI MDR and improve treatment strategies.

2007-06-12
25

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