Jw. Mellors et al., NOVEL MUTATIONS IN REVERSE-TRANSCRIPTASE OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 REDUCE SUSCEPTIBILITY TO FOSCARNET IN LABORATORY AND CLINICAL ISOLATES, Antimicrobial agents and chemotherapy, 39(5), 1995, pp. 1087-1092
Foscarnet (phosphonoformic acid) is a pyrophosphate analog that inhibi
ts the replication of human immunodeficiency virus type 1 (HIV-1) in v
itro and in patients with AIDS. HIV-1 resistance to foscarnet has not
been reported despite long-term foscarnet therapy of AIDS patients wit
h cytomegalovirus disease. We therefore attempted to select foscarnet-
resistant HIV-1 in vitro by serial endpoint passage of virus in 400 mu
M foscarnet. After 13 cycles of passage in MT-2 cells, virus exhibiti
ng greater than or equal to 8.5-fold foscarnet resistance was isolated
. The reverse transcriptase (RT) from resistant virions exhibited a si
milar level of foscarnet resistance in enzyme inhibition assays (simil
ar to 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 th
e coexistence of two mutations in all clones: Gln-161 to Leu (CAA to C
TA) and His-208 to Tyr (CAT to TAT). Sequence analysis of six clinical
HIV-1 isolates showing reduced susceptibility to foscarnet revealed t
he 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 an
d production of mutant recombinant viruses demonstrated that the Leu-1
61, Ser-88, and Tyr-208 mutations reduced HIV-1 susceptibility to fosc
arnet 10.5-, 4.3-, and 2.4-fold, respectively, in MT-2 cells. In the c
rystal 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 dNT
P binding site and its affinity for foscarnet. The location of the Trp
-88 residue in the beta 5a strand of HIV-1 RT suggests that the Ser-88
mutation affects template-primer binding, as do several mutations tha
t affect RT susceptibility to nucleoside analogs.