CHARACTERIZATION OF FOSCARNET-RESISTANT STRAINS OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1

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 pa ssage in increasing concentrations of drug. Reduced susceptibility to foscarnet was evident at the levels of both HIV-1 replication and reve rse transcriptase. Biologically cloned, foscarnet-resistant strains wi th distinct genotypes were hypersensitive to zidovudine, azidodeoxyuri dine, nevirapine, and R82913 but had unchanged susceptibility to zalci tibine and didanosine. The reverse transcriptase of foscarnet-resistan t strains had unique substitutions Glu89-Lys, Leu92-lle, or Ser156-Ala , the third being associated with six polymorphic changes. Introductio n of these mutations into wild-type HIV-1 by site-directed mutagenesis confirmed their role in foscarnet resistance. In the three-dimensiona l structure of the reverse transcriptase enzyme these amino acids are located close to the template strand of the template primer and far aw ay from the putative pyrophosphate binding site, suggesting that the m echanism by which HIV-1 becomes resistant to foscarnet is indirect. Fo scarnet resistance is thus likely to be mediated through an altered in teraction of the mutant enzyme with the template strand of the templat e primer which distorts the geometry of the polymerase active site and thereby decreases foscarnet binding. (C) 1995 Academic Press, Inc.