The Differential Sensitivity of Human and Rhesus Macaque CCR5 to Small-Molecule Inhibitors of Human Immunodeficiency Virus Type 1 Entry Is Explained by a Single Amino Acid Difference and Suggests a Mechanism of Action for These Inhibitors

Abstract

AD101 and SCH-C are two chemically related small molecules that inhibit the entry of human immunodeficiency virus type 1 (HIV-1) via human CCR5. AD101 also inhibits HIV-1 entry via rhesus macaque CCR5, but SCH-C does not. Among the eight residues that differ between the human and macaque versions of the coreceptor, only one, methionine-198, accounts for the insensitivity of macaque CCR5 to inhibition by SCH-C. Thus, the macaque coreceptor engineered to contain the natural human CCR5 residue (isoleucine) at position 198 is sensitive to HIV-1 entry inhibition by SCH-C, whereas a human CCR5 mutant containing the corresponding macaque residue (methionine) is resistant. Position 198 is in CCR5 transmembrane (TM) helix 5 and is not located within the previously defined binding site for AD101 and SCH-C, which involves residues in TM helices 1, 2, 3, and 7. SCH-C binds to human CCR5 whether residue 198 is isoleucine or methionine, and it also binds to macaque CCR5. However, the binding of a conformation-dependent monoclonal antibody to human CCR5 is inhibited by SCH-C only when residue 198 is isoleucine. These observations, taken together, suggest that the antiviral effects of SCH-C and AD101 involve stabilization, or induction, of a CCR5 conformation that is not compatible with HIV-1 infection. However, SCH-C is unable to exert this effect on CCR5 conformation when residue 198 is methionine. The region of CCR5 near residue 198 has, therefore, an important influence on the conformational state of this receptor.

Use of G-Protein-Coupled and -Uncoupled CCR5 Receptors by CCR5 Inhibitor-Resistant and -Sensitive Human Immunodeficiency Virus Type 1 Variants

“…Instead, our modeling shows that introducing a positively charged lysine at this position within TM2 causes a substantial structural rearrangement within the body of CCR5. Note that an Ile-Met change at position 189 in TM5 indirectly compromises the antiviral activity of a different CCR5 inhibitor, SCH-C, again without this residue being part of the inhibitor-binding site (48). Another probable long-range effect on the CCR5 structure involves the T82A substitution, which partially impairs the inhibitory activity of TAK779 but not that of other small molecules, including AD101 and SCH-C (7,27).…”

CCR5 Antagonist TD-0680 Uses a Novel Mechanism for Enhanced Potency against HIV-1 Entry, Cell-mediated Infection, and a Resistant Variant

“…At 48 h post-infection, cells were lysed and assayed for luciferase activity. Mutants that support viral entry above 14% were considered to have significantly reduced sensitivity (21,22). (ii) 293T cells were transfected with wild-type huCCR5, rhCCR5, or huCCR5 mutants and infected with SIV mac1A11 Env-pseudotyped luciferase reporter viruses with or without a fixed concentration of 150 nM CCR5 antagonist.…”

One Percent Tenofovir Applied Topically to Humanized BLT Mice and Used According to the CAPRISA 004 Experimental Design Demonstrates Partial Protection from Vaginal HIV Infection, Validating the BLT Model for Evaluation of New Microbicide Candidates

“…Yet because many new-generation microbicides being considered contain antiretrovirals that often exhibit exquisite specificity for HIV, multiple SIV/SHIV macaque models need to be developed for efficacy testing in vivo (20,27,28,38,46,50,52). Furthermore, within different NHP models there are differences in viral (i.e., HIV versus SHIV envelope variable region 3) and host (i.e., human versus macaque CCR5) sequences, resulting in distinctions that preclude the use of certain HIV-specific inhibitors and can confound the interpretation of the data obtained (4,33,42,49). These factors together with the expense of NHP testing and the limited availability of female animals have severely limited their broad utilization in the evaluation of novel HIV prevention interventions.…”