Antiviral breadth and combination potential of peptide triazole HIV-1 entry inhibitors

Synthesis of Novel Aminothiazole Derivatives as Promising Antiviral, Antioxidant and Antibacterial Candidates

It is well-known that thiazole derivatives are usually found in lead structures, which demonstrate a wide range of pharmacological effects. The aim of this research was to explore the antiviral, antioxidant, and antibacterial activities of novel, substituted thiazole compounds and to find potential agents that could have biological activities in one single biomolecule. A series of novel aminothiazoles were synthesized, and their biological activity was characterized. The obtained results were compared with those of the standard antiviral, antioxidant, antibacterial and anticancer agents. The compound bearing 4-cianophenyl substituent in the thiazole ring demonstrated the highest cytotoxic properties by decreasing the A549 viability to 87.2%. The compound bearing 4-trifluoromethylphenyl substituent in the thiazole ring showed significant antiviral activity against the PR8 influenza A strain, which was comparable to the oseltamivir and amantadine. Novel compounds with 4-chlorophenyl, 4-trifluoromethylphenyl, phenyl, 4-fluorophenyl, and 4-cianophenyl substituents in the thiazole ring demonstrated antioxidant activity by DPPH, reducing power, FRAP methods, and antibacterial activity against Escherichia coli and Bacillus subtilis bacteria. These data demonstrate that substituted aminothiazole derivatives are promising scaffolds for further optimization and development of new compounds with potential influenza A-targeted antiviral activity. Study results could demonstrate that structure optimization of novel aminothiazole compounds may be useful in the prevention of reactive oxygen species and developing new specifically targeted antioxidant and antibacterial agents.

Altered Env conformational dynamics as a mechanism of resistance to peptide-triazole HIV-1 inactivators

BACKGROUND

We previously developed drug-like peptide triazoles (PTs) that target HIV-1 Envelope (Env) gp120, potently inhibit viral entry, and irreversibly inactivate virions. Here, we investigated potential mechanisms of viral escape from this promising class of HIV-1 entry inhibitors.

RESULTS

HIV-1 resistance to cyclic (AAR029b) and linear (KR13) PTs was obtained by dose escalation in viral passaging experiments. High-level resistance for both inhibitors developed slowly (relative to escape from gp41-targeted C-peptide inhibitor C37) by acquiring mutations in gp120 both within (Val255) and distant to (Ser143) the putative PT binding site. The similarity in the resistance profiles for AAR029b and KR13 suggests that the shared IXW pharmacophore provided the primary pressure for HIV-1 escape. In single-round infectivity studies employing recombinant virus, V255I/S143N double escape mutants reduced PT antiviral potency by 150- to 3900-fold. Curiously, the combined mutations had a much smaller impact on PT binding affinity for monomeric gp120 (four to ninefold). This binding disruption was entirely due to the V255I mutation, which generated few steric clashes with PT in molecular docking. However, this minor effect on PT affinity belied large, offsetting changes to association enthalpy and entropy. The escape mutations had negligible effect on CD4 binding and utilization during entry, but significantly altered both binding thermodynamics and inhibitory potency of the conformationally-specific, anti-CD4i antibody 17b. Moreover, the escape mutations substantially decreased gp120 shedding induced by either soluble CD4 or AAR029b.

CONCLUSIONS

Together, the data suggest that the escape mutations significantly modified the energetic landscape of Env's prefusogenic state, altering conformational dynamics to hinder PT-induced irreversible inactivation of Env. This work therein reveals a unique mode of virus escape for HIV-1, namely, resistance by altering the intrinsic conformational dynamics of the Env trimer.

Peptide Triazole Thiol Irreversibly Inactivates Metastable HIV-1 Env by Accessing Conformational Triggers Intrinsic to Virus-Cell Entry

KR13, a peptide triazole thiol previously established to inhibit HIV-1 infection and cause virus lysis, was evaluated by flow cytometry against JRFL Env-presenting cells to characterize induced Env and membrane transformations leading to irreversible inactivation. Transiently transfected HEK293T cells were preloaded with calcein dye, treated with KR13 or its thiol-blocked analogue KR13b, fixed, and stained for gp120 (35O22), MPER (10E8), 6-helix-bundle (NC-1), immunodominant loop (50-69), and fusion peptide (VRC34.01). KR13 induced dose-dependent transformations of Env and membrane characterized by transient poration, MPER exposure, and 6-helix-bundle formation (analogous to native fusion events), but also reduced immunodominant loop and fusion peptide exposure. Using a fusion peptide mutant (V504E), we found that KR13 transformation does not require functional fusion peptide for poration. In contrast, simultaneous treatment with fusion inhibitor T20 alongside KR13 prevented membrane poration and MPER exposure, showing that these events require 6-helix-bundle formation. Based on these results, we formulated a model for PTT-induced Env transformation portraying how, in the absence of CD4/co-receptor signaling, PTT may provide alternate means of perturbing the metastable Env-membrane complex, and inducing fusion-like transformation. In turn, the results show that such transformations are intrinsic to Env and can be diverted for irreversible inactivation of the protein complex.

Triazole-Modified Peptidomimetics: An Opportunity for Drug Discovery and Development

Peptidomimetics play a fundamental role in drug design due to their preferential properties regarding natural peptides. In particular, compounds possessing nitrogen-containing heterocycles have been intensively studied in recent years. The triazolyl moiety incorporation decreases the molecule susceptibility to enzymatic degradation, reduction, hydrolysis, and oxidation. In fact, peptides containing triazole rings are a typical example of peptidomimetics. They have all the advantages over classic peptides. Both efficient synthetic methods and biological activity make these systems an interesting and promising object of research. Peptide triazole derivatives display a diversity of biological properties and can be obtained via numerous synthetic strategies. In this review, we have highlighted the importance of the triazole-modified peptidomimetics in the field of drug design. We present an overview on new achievements in triazolyl-containing peptidomimetics synthesis and their biological activity as inhibitors of enzymes or against cancer, viruses, bacteria, or fungi. The relevance of above-mentioned compounds was confirmed by their comparison with unmodified peptides.

1,2,3-Triazole hybrids with anti-HIV-1 activity

The human immunodeficiency virus type 1 (HIV-1) is the major etiological agent responsible for the acquired immunodeficiency syndrome (AIDS), which is a serious infectious disease and remains one of the most prevalent problems at present. Currently, combined antiretroviral therapy is the primary modality for the treatment and management of HIV/AIDS, but the long-term use can result in major drawbacks such as the development of multidrug-resistant viruses and multiple side effects. 1,2,3-Triazole is the common framework in the development of new drugs, and its derivatives have the potential to inhibit various HIV-1 enzymes such as reverse transcriptase, integrase, and protease, consequently possessing a potential anti-HIV-1 activity. This review covers the recent advances regarding the 1,2,3-triazole hybrids with potential anti-HIV-1 activity; it focuses on the chemical structures, structure-activity relationship, and mechanisms of action, covering articles published from 2010 to 2020.

Synthesis, antimicrobial potency with in silico study of Boc-leucine-1,2,3-triazoles

A library of N-Boc protected Leucine-linked 1,4-disubstituted 1,2,3-triazoles was synthesized and fully characterized, in high yield via copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction. In vitro antibacterial activity showed that compound 4h found to be more potent than the reference drug Ciprofloxacin (MIC: 0.0196 µmol/mL) against tested bacterial strains S. entrica, B. subtilis, S. aureus, E. coli and P. auroginosa with MIC: 0.0148, 0.0074, 0.0148, 0.0074, and 0.0074 µmol/mL, respectively and antifungal activity with MIC: 0.0148 µmol/mL as compared to reference drug Fluconazole (MIC: 0.0102 µmol/mL) against A. niger and C. albicans fungal strains. Further, the molecular docking study on 4h and its predecessor alkyne 3 by choosing E. coli topoisomerase II, DNA Gyrase (PDB ID: 1KZN) showed better binding with triazole than alkyne and these results were supported by DFT study using B3LYP/6-311G(d,p) basis set.

Exploring the Chemistry and Therapeutic Potential of Triazoles: A Comprehensive Literature Review

:

Triazole is a valuable platform in medicinal chemistry, possessing assorted pharmacological properties, which could play a major role in the common mechanisms associated with various disorders like cancer, infections, inflammation, convulsions, oxidative stress and neurodegeneration. Structural modification of this scaffold could be helpful in the generation of new therapeutically useful agents. Although research endeavors are moving towards the growth of synthetic analogs of triazole, there is still a lot of scope to achieve drug discovery break-through in this area. Upcoming therapeutic prospective of this moiety has captured the attention of medicinal chemists to synthesize novel triazole derivatives. The authors amalgamated the chemistry, synthetic strategies and detailed pharmacological activities of the triazole nucleus in the present review. Information regarding the marketed triazole derivatives has also been incorporated. The objective of the review is to provide insights to designing and synthesizing novel triazole derivatives with advanced and unexplored pharmacological implications.

Pharmacokinetic stability of macrocyclic peptide triazole HIV-1 inactivators alone and in liposomes

Previously, we reported the discovery of macrocyclic peptide triazoles (cPTs) that bind to HIV-1 Env gp120, inhibit virus cell infection with nanomolar potencies, and cause irreversible virion inactivation. Given the appealing virus-killing activity of cPTs and resistance to protease cleavage observed in vitro, we here investigated in vivo pharmacokinetics of the cPT AAR029b. AAR029b was investigated both alone and encapsulated in a PEGylated liposome formulation that was designed to slowly release inhibitor. Pharmacokinetic analysis in rats showed that the half-life of FITC-AAR029b was substantial both alone and liposome-encapsulated, 2.92 and 8.87 hours, respectively. Importantly, liposome-encapsulated FITC-AAR029b exhibited a 15-fold reduced clearance rate from serum compared with the free FITC-cPT. This work thus demonstrated both the in vivo stability of cPT alone and the extent of pharmacokinetic enhancement via liposome encapsulation. The results obtained open the way to further develop cPTs as long-acting HIV-1 inactivators against HIV-1 infection.

Bifunctional Chimera That Coordinately Targets Human Immunodeficiency Virus 1 Envelope gp120 and the Host-Cell CCR5 Coreceptor at the Virus-Cell Interface

To address the urgent need for new agents to reduce the global occurrence and spread of AIDS, we investigated the underlying hypothesis that antagonists of the HIV-1 envelope (Env) gp120 protein and the host-cell coreceptor (CoR) protein can be covalently joined into bifunctional synergistic combinations with improved antiviral capabilities. A synthetic protocol was established to covalently combine a CCR5 small-molecule antagonist and a gp120 peptide triazole antagonist to form the bifunctional chimera. Importantly, the chimeric inhibitor preserved the specific targeting properties of the two separate chimera components and, at the same time, exhibited low to subnanomolar potencies in inhibiting cell infection by different pseudoviruses, which were substantially greater than those of a noncovalent mixture of the individual components. The results demonstrate that targeting the virus-cell interface with a single molecule can result in improved potencies and also the introduction of new phenotypes to the chimeric inhibitor, such as the irreversible inactivation of HIV-1.

Targeting cell surface HIV-1 Env protein to suppress infectious virus formation

HIV-1 Env protein is essential for host cell entry, and targeting Env remains an important antiretroviral strategy. We previously found that a peptide triazole thiol KR13 and its gold nanoparticle conjugate AuNP-KR13 directly and irreversibly inactivate the virus by targeting the Env protein, leading to virus gp120 shedding, membrane disruption and p24 capsid protein release. Here, we examined the consequences of targeting cell-surface Env with the virus inactivators. We found that both agents led to formation of non-infectious virus from transiently transfected HEK293T cells. The budded non-infectious viruses lacked Env gp120 but contained gp41. Importantly, budded virions also retained the capsid protein p24, in stark contrast to p24 leakage from viruses directly treated by these agents and arguing that the agents led to deformed viruses by transforming the cells at a stage before virus budding. We found that the Env inactivators caused gp120 shedding from the transiently transfected HEK293T cells as well as non-producer CHO-K1-gp160 cells. Additionally, AuNP-KR13 was cytotoxic against the virus-producing HEK293T and CHO-K1-gp160 cells, but not untransfected HEK293T or unmodified CHO-K1 cells. The results obtained reinforce the argument that cell-surface HIV-1 Env is metastable, as on virus particles, and provides a conformationally vulnerable target for virus suppression and infectious cell inactivation.

Recognition of HIV-inactivating peptide triazoles by the recombinant soluble Env trimer, BG505 SOSIP.664

Peptide triazole (PT) antagonists interact with gp120 subunits of HIV-1 Env trimers to block host cell receptor interactions, trigger gp120 shedding, irreversibly inactivate virus and inhibit infection. Despite these enticing functions, understanding the structural mechanism of PT-Env trimer encounter has been limited. In this work, we combined competition interaction analysis and computational simulation to demonstrate PT binding to the recombinant soluble trimer, BG505 SOSIP.664, a stable variant that resembles native virus spikes in binding to CD4 receptor as well as known conformationally-dependent Env antibodies. Binding specificity and computational modeling fit with encounter through complementary PT pharmacophore Ile-triazolePro-Trp interaction with a 2-subsite cavity in the Env gp120 subunit of SOSIP trimer similar to that in monomeric gp120. These findings argue that PTs are able to recognize and bind a closed prefusion state of Env trimer upon HIV-1 encounter. The results provide a structural model of how PTs exert their function on virion trimeric spike protein and a platform to inform future antagonist design. Proteins 2017; 85:843-851. © 2016 Wiley Periodicals, Inc.

Medicinal attributes of 1,2,3-triazoles: Current developments

1,2,3-Triazoles are important five-membered heterocyclic scaffold due to their extensive biological activities. This framework can be readily obtained in good to excellent yields on the multigram scale through click chemistry via reaction of aryl/alkyl halides, alkynes and NaN₃ under ambient conditions. It has been an emerging area of interest for many researchers throughout the globe owing to its immense pharmacological scope. The present work aims to summarize the current approaches adopted for the synthesis of the 1,2,3-triazole and medicinal significance of these architectures as a lead structure for the discovery of drug molecules such as COX-1/COX-2 inhibitors (celecoxib, pyrazofurin), HIV protease inhibitors, CB1 cannabinoid receptor antagonist and much more which are in the pipeline of clinical trials. The emphasis has been given on the major advancements in the medicinal prospectus of this pharmacophore for the period during 2008-2016.

Short Communication: Inhibition of DC-SIGN-Mediated HIV-1 Infection by Complementary Actions of Dendritic Cell Receptor Antagonists and Env-Targeting Virus Inactivators

The DC-SIGN receptor on human dendritic cells interacts with HIV gp120 to promote both infection of antigen-presenting cells and transinfection of T cells. We hypothesized that in DC-SIGN-expressing cells, both DC-SIGN ligands such as dextrans and gp120 antagonists such as peptide triazoles would inhibit HIV infection with potential complementary antagonist effects. To test this hypothesis, we evaluated the effects of dextran (D66), isomaltooligosaccharides (D06), and several peptide triazoles (HNG156, K13, and UM15) on HIV infection of B-THP-1/DC-SIGN cells. In surface plasmon resonance competition assays, D66 (IC50 = 35.4 μM) and D06 (IC50 = 3.4 mM) prevented binding of soluble DC-SIGN to immobilized mannosylated bovine serum albumin (BSA). An efficacious dose-dependent inhibition of DC-SIGN-mediated HIV infection in both pretreatment and posttreatment settings was observed, as indicated by inhibitory potentials (EC50) [D66 (8 μM), D06 (48 mM), HNG156 (40 μM), UM15 (100 nM), and K13 (25 nM)]. Importantly, both dextrans and peptide triazoles significantly decreased HIV gag RNA levels [D66 (7-fold), D06 (13-fold), HNG156 (7-fold), K-13 (3-fold), and UM15 (6-fold)]. Interestingly, D06 at the highest effective concentration showed a 14-fold decrease of infection, while its combination with 50 μM HNG156 showed a 26-fold decrease. Hence, these compounds can combine to inactivate the viruses and suppress DC-SIGN-mediated virus-cell interaction that as shown earlier leads to dendritic cell HIV infection and transinfection dependent on the DC-SIGN receptor.

Disulfide Sensitivity in the Env Protein Underlies Lytic Inactivation of HIV-1 by Peptide Triazole Thiols

We investigated the mode of action underlying lytic inactivation of HIV-1 virions by peptide triazole thiol (PTT), in particular the relationship between gp120 disulfides and the C-terminal cysteine-SH required for virolysis. Obligate PTT dimer obtained by PTT SH cross-linking and PTTs with serially truncated linkers between pharmacophore isoleucine-ferrocenyltriazole-proline-tryptophan and cysteine-SH were synthesized. PTT variants showed loss of lytic activity but not binding and infection inhibition upon SH blockade. A disproportionate loss of lysis activity vs binding and infection inhibition was observed upon linker truncation. Molecular docking of PTT onto gp120 argued that, with sufficient linker length, the peptide SH could approach and disrupt several alternative gp120 disulfides. Inhibition of lysis by gp120 mAb 2G12, which binds at the base of the V3 loop, as well as disulfide mutational effects, argued that PTT-induced disruption of the gp120 disulfide cluster at the base of the V3 loop is an important step in lytic inactivation of HIV-1. Further, PTT-induced lysis was enhanced after treating virus with reducing agents dithiothreitol and tris (2-carboxyethyl)phosphine. Overall, the results are consistent with the view that the binding of PTT positions the peptide SH group to interfere with conserved disulfides clustered proximal to the CD4 binding site in gp120, leading to disulfide exchange in gp120 and possibly gp41, rearrangement of the Env spike, and ultimately disruption of the viral membrane. The dependence of lysis activity on thiol-disulfide interaction may be related to intrinsic disulfide exchange susceptibility in gp120 that has been reported previously to play a role in HIV-1 cell infection.

Macrocyclic Envelope Glycoprotein Antagonists that Irreversibly Inactivate HIV-1 before Host Cell Encounter

We derived macrocyclic HIV-1 antagonists as a new class of peptidomimetic drug leads. Cyclic peptide triazoles (cPTs) retained the gp120 inhibitory and virus-inactivating signature of parent PTs, arguing that cyclization locked an active conformation. The six-residue cPT 9 (AAR029b) exhibited submicromolar antiviral potencies in inhibiting cell infection and triggering gp120 shedding that causes irreversible virion inactivation. Importantly, cPTs were stable to trypsin and chymotrypsin compared to substantial susceptibility of corresponding linear PTs.

Peptide Triazole Inactivators of HIV-1 Utilize a Conserved Two-Cavity Binding Site at the Junction of the Inner and Outer Domains of Env gp120

We used coordinated mutagenesis, synthetic design, and flexible docking to investigate the structural mechanism of Env gp120 encounter by peptide triazole (PT) inactivators of HIV-1. Prior results demonstrated that the PT class of inhibitors suppresses binding at both CD4 and coreceptor sites on Env and triggers gp120 shedding, leading to cell-independent irreversible virus inactivation. Despite these enticing anti-HIV-1 phenotypes, structural understanding of the PT-gp120 binding mechanism has been incomplete. Here we found that PT engages two inhibitor ring moieties at the junction between the inner and outer domains of the gp120 protein. The results demonstrate how combined occupancy of two gp120 cavities can coordinately suppress both receptor and coreceptor binding and conformationally entrap the protein in a destabilized state. The two-cavity model has common features with small molecule gp120 inhibitor binding sites and provides a guide for further design of peptidomimetic HIV-1 inactivators based on the PT pharmacophore.

Mechanism of multivalent nanoparticle encounter with HIV-1 for potency enhancement of peptide triazole virus inactivation

Entry of HIV-1 into host cells remains a compelling yet elusive target for developing agents to prevent infection. A peptide triazole (PT) class of entry inhibitor has previously been shown to bind to HIV-1 gp120, suppress interactions of the Env protein at host cell receptor binding sites, inhibit cell infection, and cause envelope spike protein breakdown, including gp120 shedding and, for some variants, virus membrane lysis. We found that gold nanoparticle-conjugated forms of peptide triazoles (AuNP-PT) exhibit substantially more potent antiviral effects against HIV-1 than corresponding peptide triazoles alone. Here, we sought to reveal the mechanism of potency enhancement underlying nanoparticle conjugate function. We found that altering the physical properties of the nanoparticle conjugate, by increasing the AuNP diameter and/or the density of PT conjugated on the AuNP surface, enhanced potency of infection inhibition to impressive picomolar levels. Further, compared with unconjugated PT, AuNP-PT was less susceptible to reduction of antiviral potency when the density of PT-competent Env spikes on the virus was reduced by incorporating a peptide-resistant mutant gp120. We conclude that potency enhancement of virolytic activity and corresponding irreversible HIV-1 inactivation of PTs upon AuNP conjugation derives from multivalent contact between the nanoconjugates and metastable Env spikes on the HIV-1 virus. The findings reveal that multispike engagement can exploit the metastability built into virus the envelope to irreversibly inactivate HIV-1 and provide a conceptual platform to design nanoparticle-based antiviral agents for HIV-1 specifically and putatively for metastable enveloped viruses generally.

Covalent conjugation of a peptide triazole to HIV-1 gp120 enables intramolecular binding site occupancy

The HIV-1 gp120 glycoprotein is the main viral surface protein responsible for initiation of the entry process and, as such, can be targeted for the development of entry inhibitors. We previously identified a class of broadly active peptide triazole (PT) dual antagonists that inhibit gp120 interactions at both its target receptor and coreceptor binding sites, induce shedding of gp120 from virus particles prior to host–cell encounter, and consequently can prevent viral entry and infection. However, our understanding of the conformational alterations in gp120 by which PT elicits its dual receptor antagonism and virus inactivation functions is limited. Here, we used a recently developed computational model of the PT–gp120 complex as a blueprint to design a covalently conjugated PT–gp120 recombinant protein. Initially, a single-cysteine gp120 mutant, E275C_YU-2, was expressed and characterized. This variant retains excellent binding affinity for peptide triazoles, for sCD4 and other CD4 binding site (CD4bs) ligands, and for a CD4-induced (CD4i) ligand that binds the coreceptor recognition site. In parallel, we synthesized a PEGylated and biotinylated peptide triazole variant that retained gp120 binding activity. An N-terminally maleimido variant of this PEGylated PT, denoted AE21, was conjugated to E275C gp120 to produce the AE21–E275C covalent conjugate. Surface plasmon resonance interaction analysis revealed that the PT–gp120 conjugate exhibited suppressed binding of sCD4 and 17b to gp120, signatures of a PT-bound state of envelope protein. Similar to the noncovalent PT–gp120 complex, the covalent conjugate was able to bind the conformationally dependent mAb 2G12. The results argue that the PT–gp120 conjugate is structurally organized, with an intramolecular interaction between the PT and gp120 domains, and that this structured state embodies a conformationally entrapped gp120 with an altered bridging sheet but intact 2G12 epitope. The similarities of the PT–gp120 conjugate to the noncovalent PT–gp120 complex support the orientation of binding of PT to gp120 predicted in the molecular dynamics simulation model of the PT–gp120 noncovalent complex. The conformationally stabilized covalent conjugate can be used to expand the structural definition of the PT-induced “off” state of gp120, for example, by high-resolution structural analysis. Such structures could provide a guide for improving the subsequent structure-based design of inhibitors with the peptide triazole mode of action.

Interactions of peptide triazole thiols with Env gp120 induce irreversible breakdown and inactivation of HIV-1 virions

Background

We examined the underlying mechanism of action of the peptide triazole thiol, KR13 that has been shown previously to specifically bind gp120, block cell receptor site interactions and potently inhibit HIV-1 infectivity.

Results

KR13, the sulfhydryl blocked KR13b and its parent non-sulfhydryl peptide triazole, HNG156, induced gp120 shedding but only KR13 induced p24 capsid protein release. The resulting virion post virolysis had an altered morphology, contained no gp120, but retained gp41 that bound to neutralizing gp41 antibodies. Remarkably, HIV-1 p24 release by KR13 was inhibited by enfuvirtide, which blocks formation of the gp41 6-helix bundle during membrane fusion, while no inhibition of p24 release occurred for enfuvirtide-resistant virus. KR13 thus appears to induce structural changes in gp41 normally associated with membrane fusion and cell entry. The HIV-1 p24 release induced by KR13 was observed in several clades of HIV-1 as well as in fully infectious HIV-1 virions.

Conclusions

The antiviral activity of KR13 and its ability to inactivate virions prior to target cell engagement suggest that peptide triazole thiols could be highly effective in inhibiting HIV transmission across mucosal barriers and provide a novel probe to understand biochemical signals within envelope that are involved in membrane fusion.

A model of peptide triazole entry inhibitor binding to HIV-1 gp120 and the mechanism of bridging sheet disruption

Peptide triazole (PT) entry inhibitors prevent HIV-1 infection by blocking the binding of viral gp120 to both the HIV-1 receptor and the coreceptor on target cells. Here, we used all-atom explicit solvent molecular dynamics (MD) to propose a model for the encounter complex of the peptide triazoles with gp120. Saturation transfer difference nuclear magnetic resonance (STD NMR) and single-site mutagenesis experiments were performed to test the simulation results. We found that docking of the peptide to a conserved patch of residues lining the "F43 pocket" of gp120 in a bridging sheet naïve gp120 conformation of the glycoprotein led to a stable complex. This pose prevents formation of the bridging sheet minidomain, which is required for receptor-coreceptor binding, providing a mechanistic basis for dual-site antagonism of this class of inhibitors. Burial of the peptide triazole at the gp120 inner domain-outer domain interface significantly contributed to complex stability and rationalizes the significant contribution of hydrophobic triazole groups to peptide potency. Both the simulation model and STD NMR experiments suggest that the I-X-W [where X is (2S,4S)-4-(4-phenyl-1H-1,2,3-triazol-1-yl)pyrrolidine] tripartite hydrophobic motif in the peptide is the major contributor of contacts at the gp120-PT interface. Because the model predicts that the peptide Trp side chain hydrogen bonding with gp120 S375 contributes to the stability of the PT-gp120 complex, we tested this prediction through analysis of peptide binding to gp120 mutant S375A. The results showed that a peptide triazole KR21 inhibits S375A with 20-fold less potency than WT, consistent with predictions of the model. Overall, the PT-gp120 model provides a starting point for both the rational design of higher-affinity peptide triazoles and the development of structure-minimized entry inhibitors that can trap gp120 into an inactive conformation and prevent infection.

Non-natural peptide triazole antagonists of HIV-1 envelope gp120

We investigated the derivation of non-natural peptide triazole dual receptor site antagonists of HIV-1 Env gp120 to establish a pathway for developing peptidomimetic antiviral agents. Previously we found that the peptide triazole HNG-156 [R-I-N-N-I-X-W-S-E-A-M-M-CONH(2), in which X=ferrocenyltriazole-Pro (FtP)] has nanomolar binding affinity to gp120, inhibits gp120 binding to CD4 and the co-receptor surrogate mAb 17b, and has potent antiviral activity in cell infection assays. Furthermore, truncated variants of HNG-156, typified by UM-24 (Cit-N-N-I-X-W-S-CONH(2)) and containing the critical central stereospecific (L)X-(L)W cluster, retain the functional characteristics of the parent peptide triazole. In the current work, we examined the possibility of replacing natural with unnatural residue components in UM-24 to the greatest extent possible. The analogue with the critical "hot spot" residue Trp 6 replaced with L-3-benzothienylalanine (Bta) (KR-41), as well as a completely non-natural analogue containing D-amino acid substitutions outside the central cluster (KR-42, (D)Cit-(D)N-(D)N-(D)I-X-Bta-(D)S-CONH(2)), retained the dual receptor site antagonism/antiviral activity signature. The results define differential functional roles of subdomains within the peptide triazole and provide a structural basis for the design of metabolically stable peptidomimetic inhibitors of HIV-1 Env gp120.

HIV-1 Env gp120 structural determinants for peptide triazole dual receptor site antagonism

Despite advances in HIV therapy, viral resistance and side-effects with current drug regimens require targeting new components of the virus. Dual antagonist peptide triazoles (PT) are a novel class of HIV-1 inhibitors that specifically target the gp120 component of the viral spike and inhibit its interaction with both of its cell surface protein ligands, namely the initial receptor CD4 and the co-receptor (CCR5/CXCR4), thus preventing viral entry. Following an initial survey of 19 gp120 alanine mutants by ELISA, we screened 11 mutants for their importance in binding to, and inhibition by the PT KR21 using surface plasmon resonance. Key mutants were purified and tested for their effects on the peptide's affinity and its ability to inhibit binding of CD4 and the co-receptor surrogate mAb 17b. Effects of the mutations on KR21 viral neutralization were measured by single-round cell infection assays. Two mutations, D474A and T257A, caused large-scale loss of KR21 binding, as well as losses in both CD4/17b and viral inhibition by KR21. A set of other Ala mutants revealed more moderate losses in direct binding affinity and inhibition sensitivity to KR21. The cluster of sensitive residues defines a PT functional epitope. This site is in a conserved region of gp120 that overlaps the CD4 binding site and is distant from the co-receptor/17b binding site, suggesting an allosteric mode of inhibition for the latter. The arrangement and sequence conservation of the residues in the functional epitope explain the breadth of antiviral activity, and improve the potential for rational inhibitor development.