The Nucleoside Analog BMS-986001 Shows Greater In Vitro Activity against HIV-2 than against HIV-1

Abstract

Treatment options for individuals infected with human immunodeficiency virus type 2 (HIV-2) are restricted by the intrinsic resistance of the virus to nonnucleoside reverse transcriptase inhibitors (NNRTIs) and the reduced susceptibility of HIV-2 to several protease inhibitors (PIs) used in antiretroviral therapy (ART). In an effort to identify new antiretrovirals for HIV-2 treatment, we evaluated the in vitro activity of the investigational nucleoside analog BMS-986001 (2',3'-didehydro-3'-deoxy-4'-ethynylthymidine; also known as censavudine, festinavir, OBP-601, 4'-ethynyl stavudine, or 4'-ethynyl-d4T). In single-cycle assays, BMS-986001 inhibited HIV-2 isolates from treatment-naive individuals, with 50% effective concentrations (EC50s) ranging from 30 to 81 nM. In contrast, EC50s for group M and O isolates of HIV-1 ranged from 450 to 890 nM. Across all isolates tested, the average EC50 for HIV-2 was 9.5-fold lower than that for HIV-1 (64 ± 18 nM versus 610 ± 200 nM, respectively; mean ± standard deviation). BMS-986001 also exhibited full activity against HIV-2 variants whose genomes encoded the single amino acid changes K65R and Q151M in reverse transcriptase, whereas the M184V mutant was 15-fold more resistant to the drug than the parental HIV-2ROD9 strain. Taken together, our findings show that BMS-986001 is an effective inhibitor of HIV-2 replication. To our knowledge, BMS-986001 is the first nucleoside analog that, when tested against a diverse collection of HIV-1 and HIV-2 isolates, exhibits more potent activity against HIV-2 than against HIV-1 in culture.

FIG 1

Chemical structures of deoxythymidine (thymidine), d4T (stavudine; 2′,3′-didehydro-3′-deoxythymidine), and BMS-986001 (2′,3′-didehydro-3′-deoxy-4′-ethynyl-thymidine).

FIG 2

Homology model of the polymerase complex of HIV-2 RT with BMS-986001-5′-triphosphate as the incoming nucleotide substrate. (A) Overall structure of heterodimeric HIV-2 RT (p68 and p58 subunits, shown as light blue and gray ribbons, respectively) with double-stranded DNA template-primer (purple and dark blue ribbons and sticks) and BMS-986001-5′-triphosphate (red sticks). Green spheres represent magnesium ions. This energy-minimized model was based on the structure of HIV-1 RT in complex with deoxythymidine-5′-triphosphate (PDB accession number 1RTD) (44), as described in Materials and Methods. (B) Closeup of the polymerase domain of HIV-2 RT showing BMS-986001-5′-triphosphate (solid Corey-Pauling-Koltun [CPK]-colored spheres) paired with the complementary nucleotide of the template strand (semitransparent CPK spheres). Catalytic aspartate residues D110 and D185 are shown as CPK-colored sticks; the aromatic side chain of F160 is depicted in red. (C) Surface-rendered views of HIV-1 RT and HIV-2 RT showing the 4′ pocket of each enzyme. Surface colors indicate amino acid hydrophobicity according to the Kyte-Doolittle scale (71). (D) Superimposition of BMS-986001-5′-triphosphate and amino acids proximal to the 4′-ethynyl group of the inhibitor in the HIV-1 and HIV-2 RTs. For HIV-1, the carbon atoms of BMS-986001 are shown in dark gray, while the carbons in the amino acid residues are shown as tan sticks. For the HIV-2 model, the carbon atoms for BMS-986001 are depicted in light gray, and those of the amino acids are in light blue. The remaining atoms in both models are shown in CPK coloring. Labels for RT positions 118 and 214 are colored as per the carbon atoms of the corresponding residues (i.e., tan for HIV-1 and light blue for HIV-2). Labels for the remaining residues, which are identical in HIV-1 and HIV-2, are colored as per the HIV-2 model. For clarity, in panels C and D, a single magnesium ion is shown in the polymerase active site. All illustrations were generated in UCSF Chimera (version 1.10).

FIG 3

Predicted structural changes resulting from the K65R, Q151M, and M184V replacements in HIV-2 RT. BMS-986001-5′-triphosphate and amino acid side chains in the wild-type HIV-2 model are colored as described in the legend to Fig. 2D. Carbon atoms in the mutant amino acids are shown in green; the remaining atoms are shown in Corey-Pauling-Koltun coloring. Stippled spheres indicate the van der Waals radii for the 4′-ethynyl moiety of BMS-986001 and the γ-carbon of valine at position 184 of HIV-2 RT. The numbers in red indicate distance (in angstroms).

FIG 4

Antiviral activity of BMS-986001 relative to the activities of other ARVs. All values in this figure were obtained using HIV-2_ROD9 in the single-cycle MAGIC-5A cell assay and are the means from three or more independent determinations. EC₅₀s for d4T and BMS-986001 are from the present study (Tables 1 and 2). Values for the remaining ARVs are from previously published studies by our group (9, 17, 25, 72). Abbreviations for drug classes and names are as follows: INSTI, integrase strand-transfer inhibitor; PI, protease inhibitor; NRTI, nucleoside reverse transcriptase inhibitor; DTG, dolutegravir; RAL, raltegravir; EVG, elvitegravir; SQV, saquinavir; LPV, lopinavir; DRV, darunavir; TDF, tenofovir disoproxil fumarate; AZT, zidovudine; FTC, emtricitabine; d4T, stavudine; 3TC, lamivudine; ABC, abacavir; PMPA, tenofovir [unmodified; (R)-9-(2-phosphonylmethoxypropyl)adenine]; ddI, didanosine.