title: Determinants of human immunodeficiency virus type 1 baseline susceptibility to the fusion inhibitors enfuvirtide and T-649 reside outside the peptide interaction site.
abstract: The peptide fusion inhibitor (PFI) enfuvirtide is the first of a new class of entry inhibitors to receive FDA approval. We previously determined the susceptibility of 55 PFI-naïve-patient isolates to enfuvirtide and a second peptide inhibitor, T-649. Seven of the 55 viral isolates were insusceptible to enfuvirtide, T-649, or both inhibitors in the absence of prior exposure. To determine the molecular basis of the insusceptible phenotypes, we PCR amplified and cloned five PFI-insusceptible and one PFI-susceptible, full-length, biologically functional env genes and characterized viruses pseudotyped with the Env proteins in a single-round drug sensitivity assay. Overall, the mean 50% inhibitory concentrations of enfuvirtide and T-649 for the PFI-insusceptible Env pseudotypes were 1.4 to 1.7 log(10) and 1.2 to 1.8 log(10) greater, respectively, than those for a PFI-susceptible lab strain, NLHX; however, all of the PFI-insusceptible Env proteins conserved the sequence of a critical enfuvirtide interaction site (residues 36 to 38 of gp41, GIV) in HR-1. In contrast, multiple amino acid changes were observed C-terminal to HR-1, many of which were located in regions of HR-2 corresponding to the PFI. Nevertheless, peptides based on patient-derived HR-2 sequences were not more potent inhibitors than enfuvirtide or T-649, arguing that the basis of PFI susceptibility is not a higher-affinity, competitive HR-1/HR-2 interaction. These results demonstrate that regions of Env outside the enfuvirtide interaction site can significantly impact the PFI susceptibility of patient-derived Env, even prior to drug exposure. We hypothesize that both gp120 gene- and gp41 gene-encoded determinants that minimize the window of opportunity for PFI to bind provide a growth advantage and possibly a predisposition to resistance to this new class of drugs in vivo.
authors.affiliation: Department of Microbiology, The University of Alabama at Birmingham, Birmingham, AL 35294-2170, USA.
authors.forename: Marintha L
authors.initials: ML
authors.lastname: Heil
authors.forename: Julie M
authors.initials: JM
authors.lastname: Decker
authors.forename: Jeffrey N
authors.initials: JN
authors.lastname: Sfakianos
authors.forename: George M
authors.initials: GM
authors.lastname: Shaw
authors.forename: Eric
authors.initials: E
authors.lastname: Hunter
authors.forename: Cynthia A
authors.initials: CA
authors.lastname: Derdeyn
mesh_terms: D000595:Amino Acid Sequence; D002478:Cells, Cultured; D018920:Coculture Techniques; D024882:Drug Resistance, Viral; D000077560:Enfuvirtide; D015699:HIV Envelope Protein gp120 / Q000737:chemistry / Q000187:drug effects / Q000235:genetics; D015700:HIV Envelope Protein gp41 / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics / Q000494:pharmacology*; D023581:HIV Fusion Inhibitors / Q000494:pharmacology*; D015658:HIV Infections / Q000821:virology; D015497:HIV-1 / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000821:virology; D008826:Microbial Sensitivity Tests / Q000379:methods; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000494:pharmacology*
chemical_list: D015699:HIV Envelope Protein gp120; D015700:HIV Envelope Protein gp41; D023581:HIV Fusion Inhibitors; D010446:Peptide Fragments; C435505:T-649 peptide; D000077560:Enfuvirtide