17th International HIV Drug Resistance Workshop 10-14 June 2008, Sitges, Spain

HIV-1 SUSCEPTIBILITY TO THE MATURATION INHIBITOR BEVIRIMAT IS MODULATED BY NATURAL POLYMORPHISMS AT POSITIONS 369–371 IN GAG SPACER PEPTIDE 1

Antivir Ther. 2008; 13(Suppl. 3):A30 (abstract no. 28)

K Van Baelen¹, K Salzwedel², H De Wolf¹, Y Verlinden¹ and LJ Stuyver^1
1Virco BVBA, Mechelen, Belgium; ²Panacos Pharmaceuticals, Gaithersburg, MD, USA

BACKGROUND: The HIV-1 maturation inhibitor bevirimat inhibits cleavage of spacer peptide 1 (SP1) from the C terminus of capsid resulting in defective core condensation. Recent clinical studies found that a subset of patients respond poorly to bevirimat. Genotypic analysis of patient samples suggested that poor response is associated with baseline polymorphisms at positions 369, 370 and 371 in SP1. In this study, we evaluated baseline susceptibility to bevirimat by phenotypic testing of 20 patient-derived HIV-1 isolates.

METHODS: Viral RNA was extracted from virus samples and used to generate Gag-protease (PR) amplicons by one-step reverse transcriptase (RT)-PCR followed by nested PCR. Gag-PR amplicons were sequenced and recombined with an HXB2-based backbone by nucleofection into MT4 cells. Replication-competent recombinant viruses were titrated and subjected to antiviral testing using FDA-approved PR and RT inhibitors and bevirimat. Fold change (FC) values were calculated using IIIB as reference strain. Results were compared with the routine PR-RT genotyping (VircoType) and phenotyping results (Antivirogram) using the same compounds.

RESULTS: Gag-PR and PR-RT were successfully amplified, genotyped and phenotyped from 20 patient isolates. Reference strain IIIB wild-type virus showed an IC₅₀ value for bevirimat of 55 ±16 nM. PR-RT genotyping and phenotyping demonstrated no correlation of bevirimat susceptibility with resistance to PR and RT inhibitors. Gag-PR phenotyping showed three different levels of susceptibility to bevirimat: six highly susceptible viruses had FC values between 1.0 and 4.8, five viruses had intermediate susceptibility (FC values 31.8–71.3) and nine viruses had FC values >140.3. Gag-PR genotyping found wild-type QVT amino acid sequence at positions 369–371 in all six of the highly susceptible viruses, whereas all nine of the least susceptible viruses contained polymorphisms in this region. The five viruses with intermediate susceptibility were either wild-type (three) or polymorphic (two).

CONCLUSIONS: Using a Gag-PR phenotypic and genotypic assay, three levels of susceptibility to bevirimat were observed for a set of 20 patient-derived virus isolates. Reduced susceptibility correlated with polymorphisms at Gag residues 369–371 in SP1. The 11 viruses containing polymorphisms all had the highest FC values. Testing of additional virus isolates should help to further clarify the role of individual polymorphisms in bevirimat susceptibility.

2008-06-10
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