title: Characterisation of foscarnet-resistant strains of human immunodeficiency virus type 1.
abstract: Foscarnet is a broad-spectrum viral DNA polymerase inhibitor active in vitro and in vivo against human immunodeficiency virus type 1 (HIV-1). Strains of HIV-1 resistant to foscarnet were selected by in vitro passage in increasing concentrations of drug. Reduced susceptibility to foscarnet was evident at the levels of both HIV-1 replication and reverse transcriptase. Biologically cloned, foscarnet-resistant strains with distinct genotypes were hypersensitive to zidovudine, azidodeoxyuridine, nevirapine, and R82913 but had unchanged susceptibility to zalcitibine and didanosine. The reverse transcriptase of foscarnet-resistant strains had unique substitutions Glu89-Lys, Leu92-Ile, or Ser156-Ala, the third being associated with six polymorphic changes. Introduction of these mutations into wild-type HIV-1 by site-directed mutagenesis confirmed their role in foscarnet resistance. In the three-dimensional structure of the reverse transcriptase enzyme these amino acids are located close to the template strand of the template primer and far away from the putative pyrophosphate binding site, suggesting that the mechanism by which HIV-1 becomes resistant to foscarnet is indirect. Foscarnet resistance is thus likely to be mediated through an altered interaction of the mutant enzyme with the template strand of the template primer which distorts the geometry of the polymerase active site and thereby decreases foscarnet binding.
authors.affiliation: National Centre in HIV Virology Research, Macfarlane Burnet Centre for Medical Research, Fairfield, Australia.
authors.forename: G
authors.initials: G
authors.lastname: Tachedjian
authors.forename: D J
authors.initials: DJ
authors.lastname: Hooker
authors.forename: A D
authors.initials: AD
authors.lastname: Gurusinghe
authors.forename: H
authors.initials: H
authors.lastname: Bazmi
authors.forename: N J
authors.initials: NJ
authors.lastname: Deacon
authors.forename: J
authors.initials: J
authors.lastname: Mellors
authors.forename: C
authors.initials: C
authors.lastname: Birch
authors.forename: J
authors.initials: J
authors.lastname: Mills
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D017931:DNA Primers / Q000737:chemistry; D004352:Drug Resistance, Microbial; D017245:Foscarnet / Q000494:pharmacology*; D015751:Genes, pol; D054303:HIV Reverse Transcriptase; D015497:HIV-1 / Q000187:drug effects*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012194:RNA-Directed DNA Polymerase / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship
chemical_list: D017931:DNA Primers; D017245:Foscarnet; D054303:HIV Reverse Transcriptase; D012194:RNA-Directed DNA Polymerase