13th International HIV Drug Resistance Workshop


8–12 June 2004, Tenerife Sur-Costa Adeje, Canary Islands, Spain




SELECTION FOR AND CHARACTERIZATION OF HIV-1 ISOLATES RESISTANT TO THE MATURATION INHIBITOR PA-457

Antiviral Therapy 2004; 9:S8 (abstract 4)

K Salzwedel1, R Goila-Gaur2, C Adamson2, F Li1, A Castillo1, N Kilgore1, M Reddick1, C Matallana1, D Zoumplis1, D Martin1, G Allaway1, E Freed2 and C Wild1
1Panacos Pharmaceuticals, Gaithersburg, Md.; and 2HIV Drug Resistance Program, National Cancer Institute, Frederick, Md., USA

BACKGROUND: PA-457 is the first in a new class of antiretrovirals that inhibit HIV replication by disrupting virus maturation. PA-457 blocks a late step in Gag processing that results in defective core condensation and the release of non-infectious virus particles. Specifically, PA-457 disrupts the conversion of the capsid precursor, p25 (CA-SP1), to mature CA protein, p24. PA-457’s mechanism of action (MOA) is distinct from that of protease inhibitors in that it appears to directly target the Gag precursor protein rather than the protease enzyme that is responsible for Gag processing.

METHODS: PA-457-resistant virus isolates were selected by continuous culture in the presence of increasing concentrations of compound. Genotyping of resistant virus and preparation of molecular clones with resistance-conferring mutations were carried out using standard methods. PA-457 resistance was characterized using cell-based activity assays and in vitro analysis of Gag processing.

RESULTS: In vitro selection generated PA-457-resistant virus. Genotypic analysis of these isolates revealed two independent patterns of resistance-conferring mutations. Consistent with our MOA studies these mutations mapped to residues flanking the Gag CA-SP1 cleavage site. An A to V change at either the first or third residues at the N-terminus of SP1 (A1V or A3V) resulted in a resistant phenotype. Both the A1V and A3V mutants exhibited reduced replicative fitness compared to WT, however, for the A3V virus a second point change in the C-terminus of capsid restored near-WT levels of replication. While these mutations resulted in a decrease in PA-457 activity, these viruses remained sensitive to all classes of approved HIV drugs.

CONCLUSIONS: These results support and extend previous observations that PA-457 is a specific inhibitor of CA-SP1 cleavage, with no activity against other Gag processing events. Characterizing the determinants of PA-457 activity is the first step in defining the molecular target for this novel HIV maturation inhibitor.

PRESENTING AUTHOR: C Wild

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2004-06-08
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