Novel mutations in reverse transcriptase of human immunodeficiency virus type 1 reduce susceptibility to foscarnet in laboratory and clinical isolates

Antimicrob Agents Chemother. 1995 May;39(5):1087-92. doi: 10.1128/AAC.39.5.1087.


Foscarnet (phosphonoformic acid) is a pyrophosphate analog that inhibits the replication of human immunodeficiency virus type 1 (HIV-1) in vitro and in patients with AIDS. HIV-1 resistance to foscarnet has not been reported despite long-term foscarnet therapy of AIDS patients with cytomegalovirus disease. We therefore attempted to select foscarnet-resistant HIV-1 in vitro by serial endpoint passage of virus in 400 microM foscarnet. After 13 cycles of passage in MT-2 cells, virus exhibiting > or = 8.5-fold foscarnet resistance was isolated. The reverse transcriptase (RT) from resistant virions exhibited a similar level of foscarnet resistance in enzyme inhibition assays (approximately 10-fold resistance). Foscarnet-resistant virus showed increased susceptibility to 3'-azido-3'-deoxythymidine (90-fold) and to the HIV-1-specific RT inhibitors TIBO R82150 (30-fold) and nevirapine (20-fold). DNA sequence analysis of RT clones from resistant virus revealed the coexistence of two mutations in all clones: Gln-161 to Leu (CAA to CTA) and His-208 to Tyr (CAT to TAT). Sequence analysis of six clinical HIV-1 isolates showing reduced susceptibility to foscarnet revealed the Tyr-208 mutation in two, the Leu-161 mutation in one, and a Trp-88-to-Ser or -Gly mutation in four isolates. Site-specific mutagenesis and production of mutant recombinant viruses demonstrated that the Leu-161, Ser-88, and Tyr-208 mutations reduced HIV-1 susceptibility to foscarnet 10.5-, 4.3-, and 2.4-fold, respectively, in MT-2 cells. In the crystal structure of HIV-1 RT, the Gln-161 residue lies in the alpha E helix beneath the putative deoxynucleoside triphosphate (dNTP) binding site. The Gln-161-to-Leu mutation may affect the structure of the dNTP binding site and its affinity for foscarnet. The location of the Trp-88 residue in the Beta5a strand of HIV-1 RT suggest that the Ser-88 mutation affects template-primer binding, as do several mutations that affect RT susceptibility to nucleoside analogs.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Base Sequence
  • Cells, Cultured
  • Cloning, Molecular
  • DNA, Viral / analysis
  • Foscarnet / pharmacology*
  • HIV Infections / enzymology
  • HIV Infections / virology*
  • HIV Reverse Transcriptase
  • HIV-1 / drug effects
  • HIV-1 / enzymology*
  • HIV-1 / genetics*
  • Humans
  • Molecular Sequence Data
  • RNA-Directed DNA Polymerase / chemistry
  • RNA-Directed DNA Polymerase / genetics*
  • Recombination, Genetic
  • Reverse Transcriptase Inhibitors


  • DNA, Viral
  • Reverse Transcriptase Inhibitors
  • Foscarnet
  • HIV Reverse Transcriptase
  • RNA-Directed DNA Polymerase