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J. Virol., 02 1996, 689-696, Vol 70, No. 2
K de Vreese, V Kofler-Mongold, C Leutgeb, V Weber, K Vermeire, S Schacht, J Anne, E de Clercq, R Datema and G Werner
Bicyclams are a novel class of antiviral compounds which act as potent and
selective inhibitors of the replication of human immunodeficiency virus
type 1 (HIV-1) and HIV-2. They block an early step in the viral life cycle
following adsorption to the CD4 receptor and preceding reverse
transcription. To identify the molecular target of these compounds, we
genetically analyzed variants of the HIV-1 molecular clone NL4-3, which
developed resistance against two structurally related bicyclams, JM2763 and
the more potent SID791. The resistant strains were obtained after long-term
passaging in MT-4 cells in the presence of progressively increasing
compound concentrations. Recombinants between selected genes of the
resistant strains and the parental NL4-3 provirus were generated by
adapting the marker rescue technique to MT-4 cells. The bicyclam-resistant
phenotype was rescued by transferring the envelope gp120 gene of
bicyclam-resistant virus into the NL4-3 parental genetic background. In the
gp120 genes of the resistant strains, we identified several mutations
leading to amino acid substitutions in the V3 loop. Furthermore, two
substitutions of highly conserved amino acids in close proximity to the
disulfide bridges of the V3 and V4 loops were found in both SID791- and
JM2763- resistant strains. Additional mutations in regions encoding V3, C4,
V5, and C5 were present in SID791-resistant viruses. Recombination
experiments with overlapping parts of the envelope gene indicated that
most, if not all, of the mutations were necessary to develop the fully
SID791 resistant phenotype. The mutations in the C-terminal part of gp120
downstream of the V3 loop sequence conferred partial resistance to JM2763
but did not significantly decrease susceptibility to SID791. The genetic
data and the biological properties of the resistant viruses point to
inhibition of entry and fusion as the mode of action of the HIV-inhibitory
bicyclams. A possible mechanism of binding of bicyclams to gp120 leading to
inhibition of unfolding of gp120 and its shedding from the gp41 fusion
domain is discussed.
Copyright © 1996, American Society for Microbiology
The molecular target of bicyclams, potent inhibitors of human immunodeficiency virus replication
Rega Institute for Medical Research, Katholieke Universiteit Leuven, Belgium.
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