18th International HIV Drug Resistance Workshop Basic Principles & Clinical Implications June 9–13 2009, Fort Myers, Florida, USA

IDENTIFICATION OF HIV-1 MATRIX DETERMINANTS OF FITNESS COMPENSATION IN A PROTEASE INHIBITOR RESISTANT VIRUS

Antivir Ther 2009; 14 Suppl 1:A37 (abstract no. 35)

CM Parry^1,2, P Cane¹ and D Pillay^1,2
1Virus Reference Department, Health Protection Agency, London, UK; ²UCL/MRC Centre for Medical Molecular Virology, UCL, London, UK

BACKGROUND: Mutations occur in the protease and gag genes of HIV from patients who fail therapy with protease inhibitors (PI). Protease mutations have been extensively explored while studies with gag have mainly been limited to cleavage sites mutations (CSM). We recently showed restoration of replication capacity (RC) for a patient plasma virus-derived (termed mutant) multidrug-resistant protease by full-length mutant Gag, as well as matrix and partial capsid. Mutant gag, as well as matrix and partial capsid also conferred protease inhibitor (PI) resistance with out mutations in protease.

METHODS: Using a single-cycle assay we compared the drug susceptibility of the two different regions of the mutant Gag: matrix and partial capsid, and partial capsid with the remainder of Gag. Site-directed mutagenesis identified changes in matrix and partial capsid that can restore RC to virus with the mutant protease (that alone has 5% RC of wild-type [WT]).

RESULTS: Mutant matrix and partial capsid conferred up to ninefold resistance to PIs (amprenavir 9.1×, atazanavir 5× and indinavir 9.1× the IC₅₀ of WT) without cleavage site mutations. The remainder of mutant Gag (partial capsid to the end of Gag with CSM) conferred lower levels of resistance (amprenavir 3.4×, atazanavir 2.5× and indinavir 5.8× the IC₅₀ of WT). The mutant matrix had 10 amino acid changes compared with HXB2 and an insertion (116TQ). Addition of the insertion to WT Gag had only a minor effect increasing RC of virus with the mutant protease from 5% to 10%. Changing three amino acids within the matrix from WT to those found in the mutant virus (R76K, Y79F and T81A) increased RC of the virus with mutant protease from 5% to 73% of WT.

CONCLUSIONS: We determined that the matrix and part of capsid can confer more PI resistance than regions including the p7-p1 and p1-p6 CSM. We also identified that three amino acid changes in matrix can restore the RC of a multidrug-resistant protease from 5% of WT to over 70%. The mechanism for both findings was unclear but it was independent of CSM, emphasizing that studies using full-length Gag are warranted.

2009-06-09
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