title: Genotypic changes in human immunodeficiency virus type 1 envelope glycoproteins on treatment with the fusion inhibitor enfuvirtide and their influence on changes in drug susceptibility in vitro.
abstract: BACKGROUND
  Previous studies have established the importance of substitutions at amino acids 36-45 of HIV-1 gp41 in the development of viral resistance to the peptide fusion inhibitor enfuvirtide. However, the influence of other loci in the HIV-1 envelope is not well established.
  
  
  OBJECTIVE
  To identify positions showing genotypic changes that are associated with particularly high levels of changes in enfuvirtide susceptibility.
  
  
  METHODS
  We examined full-length baseline and on treatment sequences of gp120 and gp41 for isolates from 369 patients in Phase III studies of enfuvirtide, including 281 patients receiving ENF+OB and 88 patients receiving OB alone. Individual changes in gp41 and gp120 were evaluated for correlations with on treatment phenotype changes by analysis of variance (ANOVA). This modeling was done with (two-way) and without (one-way) ANOVA adjusting for the effects of any changes in gp41 amino acids 36-45 modeled as a single variable (ANY(36-45)). Positions displaying significance levels of p<0.05 by either one- or two-way ANOVA were then studied by multi-way ANOVA (stepwise regression).
  
  
  RESULTS
  In addition to changes at gp41 amino acids 36-45, changes at three positions in the HR2 domain (126, 129 and 133) occurred significantly more often in patients undergoing virologic failure on enfuvirtide. However, ANY(36-45) alone accounted for slightly more than 90% of the variation in phenotype explained by the ANOVA models. Relative to ANY(36-45) alone, significant increases in the geometric mean of the fold-change in inhibitory concentration (19.6-236.3-fold higher) were observed for amino acid changes at positions gp41: 18, 42,126, 247, 256 and 312; gp120: 330, 389 and 424 and significant reductions (18.8-29.7-fold lower) for gp41: 3, 46, 165, 232 and 324.
  
  
  CONCLUSIONS
  This study represents a statistical approach to highlight positions in HIV envelope that undergo mutations in the presence of enfuvirtide. Several of the identified positions have been implicated in the viral fusion process by other studies. The specific impact of positions 330. Three hundred and eighty-nine and 424 on viral fusion kinetics remains to be studied further by site-directed mutagenesis experiments.
authors.affiliation: Roche Pharmaceuticals, Palo Alto, CA 94304, USA.
authors.forename: C
authors.initials: C
authors.lastname: Su
authors.forename: T
authors.initials: T
authors.lastname: Melby
authors.forename: R
authors.initials: R
authors.lastname: DeMasi
authors.forename: P
authors.initials: P
authors.lastname: Ravindran
authors.forename: G
authors.initials: G
authors.lastname: Heilek-Snyder
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D024882:Drug Resistance, Viral / Q000235:genetics*; D000077560:Enfuvirtide; D005838:Genotype; D015699:HIV Envelope Protein gp120 / Q000737:chemistry / Q000235:genetics*; D015700:HIV Envelope Protein gp41 / Q000737:chemistry / Q000235:genetics* / Q000627:therapeutic use; D023581:HIV Fusion Inhibitors / Q000627:therapeutic use*; D015497:HIV-1 / Q000235:genetics* / Q000302:isolation & purification; D006801:Humans; D066298:In Vitro Techniques; D010446:Peptide Fragments / Q000627:therapeutic use*; D017434:Protein Structure, Tertiary
chemical_list: D015699:HIV Envelope Protein gp120; D015700:HIV Envelope Protein gp41; D023581:HIV Fusion Inhibitors; D010446:Peptide Fragments; D000077560:Enfuvirtide