Lai-Xi Wang

Design and synthesis of a template-assembled oligomannose cluster as an epitope mimic for human HIV-neutralizing antibody 2G12.

The synthesis and antibody-binding affinity of a novel template-assembled oligomannose cluster as an epitope mimic for human anti-HIV antibody 2G12 are described. Cholic acid was chosen as the scaffold and three high-mannose type oligosaccharide (Man(9)GlcNAc(2)Asn) moieties were selectively attached at the 3alpha, 7alpha, and 12alpha-positions of the scaffold through a series of regioselective transformations. Binding studies revealed that the synthetic oligosaccharide cluster is 46-fold more effective than the subunit Man(9)GlcNAc(2)Asn in inhibiting 2G12-binding to immobilized gp120. The scaffold approach described in this paper provides an avenue to designing more effective epitope mimics for antibody 2G12 in the hope of developing a carbohydrate-based vaccine against HIV-1.

Chemoenzymatic Synthesis of HIV-1 gp41 Glycopeptides: Effects of Glycosylation on the Anti-HIV Activity and α-Helix Bundle-Forming Ability of Peptide C34

C34 is a 34‐mer peptide derived from the C‐terminal ectodomain of HIV‐1 envelope glycoprotein, gp41. The C34 region in native gp41 carries a conserved N‐glycan at Asn637 and the sequence is directly involved in the virus–host membrane fusion, an essential step for HIV‐1 infection. This paper describes the synthesis of glycoforms of C34 which carry a monosaccharide, a disaccharide, and a native oligosaccharide moiety. The synthesis of the glycopeptide which carries a native high‐mannose type N‐glycan was achieved by a chemoenzymatic approach by using an endoglycosidase‐catalyzed oligosaccharide transfer as the key step. The effects of glycosylation on the inhibitory activity and the helix‐bundle forming ability of C34 were investigated. It was found that glycosylation moderately decreases the anti‐HIV activity of C34 and, in comparison with C34, glyco‐C34 forms less compact six‐helix bundles with the corresponding N‐terminal peptide, N36. This study suggests that conserved glycosylation modulates the anti‐HIV activity and conformations of the gp41 C‐peptide, C34.

Modification and structure–activity relationship of a small molecule HIV-1 inhibitor targeting the viral envelope glycoprotein gp120

This paper describes selected modification and structure-activity relationship of the small molecule HIV-1 inhibitor, 4-benzoyl-1-[(4-methoxy-1H-pyrrolo[2,3-b]pyridin-3-yl)oxoacetyl]-2-(R)-methylpiperazine (BMS-378806). The results revealed: i) that both the presence and configuration (R vs. S) of the 3-methyl group on the piperazine moiety are important for the antiviral activity, with the 3-(R)-methyl derivatives showing the highest activity; ii) that the electronegativity of the C-4 substituent on the indole or azaindole ring seems to be important for the activity, with a small, electron-donating group such as a fluoro or a methoxy group showing enhanced activity, while a nitro group diminishes the activity; iii) that the N-1 position of the indole ring is not eligible for modification without losing activity; and iv) that bulky groups around the C-4 position of the indole or azaindole ring diminish the activity, probably due to steric hindrance in the binding. We found that a synthetic bivalent compound with two BMS-378806 moieties being tethered by a spacer demonstrated about 5-fold enhanced activity in an nM range against HIV-1 infection than the corresponding monomeric inhibitor. But the polyacrylamide-based polyvalent compounds did not show inhibitory activity at up to 200 nM.

Design and synthesis of αGal-conjugated peptide T20 as novel antiviral agent for HIV-immunotargeting

An efficient chemo-enzymatic synthesis of alpha Gal-conjugated peptide T20 as novel HIV-immuno-targeting agent is described. The synthesis involves chemo-enzymatic preparation of maleimide-functionalized alpha Gal epitope and its chemoselective ligation with the peptide T20. The title compound contains two functional domains: the trisaccharide alpha Gal epitope that binds to human natural anti-Gal antibodies and the 36-amino acid gp41 peptide (T20) that recognizes the gp41 N-terminal ectodomain of the HIV envelope. Biological assays demonstrated that the synthetic conjugate could readily bind to natural anti-Gal antibodies (both IgG and IgM type) in normal human serum and exhibited potent anti-HIV activity even in the absence of human antibodies and complement system. The experimental data suggest that the synthetic alpha Gal-T20 might be valuable for in vivo HIV-immuno-targeting via antibody-mediated cytotoxicity and/or antibody-dependent, complement-mediated lysis of HIV particles and HIV-infected cells, thus providing an additional dimension of HIV intervention.

Toward a glycopeptide-based HIV-1 vaccine

A major difficulty in HIV-1 vaccine development is to identify conserved neutralizing epitopes. We hypothesize that conserved HIV-1 glycopeptides, a partial structure of the envelope glycoproteins, represent new types of neutralizing epitopes for several reasons: 1) certain HIV-1 glycopeptides are highly conserved and are well accessible; 2) a novel glycan cluster has been identified as the neutralizing epitope for the broadly neutralizing antibody 2G12, indicating N-glycan itself could serve as target of vaccine; and 3) the interactions of the carbohydrate and peptide epitope may generate new conformational epitope that could not be achieved by peptide or carbohydrate alone. To test this hypothesis, we have been exploring HIV-1 V3 domain glycopeptides that combine the conserved N-glycans as an essential epitope in immunogen design. Toward this end, we have developed a novel chemoenzymatic method for constructing large homogeneous HIV-1 V3 glycopeptides that are hitherto unavailable. Preliminary studies have revealed that the glycosylation affects the global conformation of the V3 domain and can protect the V3 domain against protease digestion. The binding of the synthetic HIV-1 glycopeptides with neutralizing antibodies (2G12, 447-52D) and other V3-specific antibodies is in progress and the implications of the results for effective immunogen design will be discussed.

HIV-1 Glycopeptides as Immunogens

One challenge in HIV-1 vaccine design is to identify epitopes able to induce neutralizing antibodies. HIV-1 glycopeptides represent a partial structure of the envelope glycoproteins that contains both peptide and carbohydrate motifs. Several pieces of evidence suggest that HIV-1 glycopeptides may constitute new neutralizing epitopes: 1) certain HIV-1 glycopeptides are highly conserved and are well accessible; 2) selected N-glycans around the V3 domain have been identified as neutralizing epitope for the broadly neutralizing antibody 2G12; and 3) N-glycans can mask unwanted epitopes, redirect the immune focus, and induce conformational epitopes. To explore this new territory for immunogen design, we have focused on exploring the V3 domain glycopeptides that correspond to the so-called principal neutralizing determinant (PND) and the gp41 C-terminal glycopeptides that are involved in viral membrane fusion. We have developed a novel chemoenzymatic method for constructing large homogeneous HIV-1 glycopeptides that are hitherto unavailable. Preliminary studies indicated that glycosylation affects the global conformations and enhances the beta-turn and/or loop structure of the V3 domain in buffer. We also observed that the N-glycans can protect the V3 domain against protease (furin and pronase) digestion. In addition, we found that glycosylation on C34 has a profound effect on its ability to form the six-helix bundles with N36. The interesting glycosylation effects observed urge further immunization studies with the glycopeptide immunogens. from 2005 International Meeting of The Institute of Human Virology Baltimore, USA, 29 August – 2 September 2005