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

Pharmacophore Variants of the Macrocyclic Peptide Triazole Inactivator of HIV-1 Env

Previously we established a family of macrocyclic peptide triazoles (cPTs) that inactivate the Env protein complex of HIV-1, and identified the pharmacophore that engages Env's receptor binding pocket. Here, we examined the hypothesis that the side chains of both components of the triazole Pro - Trp segment of cPT pharmacophore work in tandem to make intimate contacts with two proximal subsites of the overall CD4 binding site of gp120 to stabilize binding and function. Variations of the triazole Pro R group, which previously had been significantly optimized, led to identification of a variant MG-II-20 that contains a pyrazole substitution. MG-II-20 has improved functional properties over previously examined variants, with Kd for gp120 in the nM range. In contrast, new variants of the Trp indole side chain, with either methyl- or bromo- components appended, had disruptive effects on gp120 binding, reflecting the sensitivity of function to changes in this component of the encounter complex. Plausible in silico models of cPT:gp120 complex structures were obtained that are consistent with the overall hypothesisof occupancy by the triazole Pro and Trp side chains, respectively, into the β20/21 and Phe43 sub-cavities. The overall results strengthen the definition of the cPT-Env inactivator binding site and provide a new lead composition (MG-II-20) as well as structure-function findings to guide future HIV-1 Env inactivator design.

Ferrocene-triazole conjugates: do we know why they are biologically active?

The bioorganometallic chemistry of ferrocene has been gaining significance in recent years. This review presents ferrocene-triazole conjugates displaying significant biological properties. The conjugates have been synthesized via azide-alkyne cycloaddition reactions. The data are summarized according to the type of activity (anticancer, antibacterial and/or antifungal, antiprotozoal, and other effects). The results of studies concerning the understanding of the role of the ferrocene core in their biological activity are highlighted. While generally the mode of action of these organometallic species remains unclear, the importance of redox properties of ferrocene has been postulated in several cases.

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.

Microwave-Assisted Regioselective Synthesis and 2D-NMR Studies of New 1,2,3-Triazole Compounds Derived from Acridone

A simple and mild protocol towards the synthesis of new 1,2,3-triazole compounds derived from acridone has been developed via regiospecific 1,3-dipolar cycloaddition reaction between 10-(prop-2-yn-1-yl)acridone derivatives and aromatic azides using CuI as a catalyst. The cycloaddition reaction has been performed using conventional as well as microwave-assisted methods. Microwave-assisted synthesis caused a significant reduction in the reaction times and improvement in the yields of all the synthesized compounds compared with the conventional method. The structure of the 1,4-disubstituted 1,2,3-triazoles has been elucidated by IR, HRMS, 1H-NMR, 13C-NMR, and 2D NMR (1H-13C HMBC, 1H-1H COSY, and 1H-1H NOESY) spectroscopies.

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.

Impact of non-proteinogenic amino acids in the discovery and development of peptide therapeutics

With the development of modern chemistry and biology, non-proteinogenic amino acids (NPAAs) have become a powerful tool for developing peptide-based drug candidates. Drug-like properties of peptidic medicines, due to the smaller size and simpler structure compared to large proteins, can be changed fundamentally by introducing NPAAs in its sequence. While peptides composed of natural amino acids can be used as drug candidates, the majority have shown to be less stable in biological conditions. The impact of NPAA incorporation can be extremely beneficial in improving the stability, potency, permeability, and bioavailability of peptide-based therapies. Conversely, undesired effects such as toxicity or immunogenicity should also be considered. The impact of NPAAs in the development of peptide-based therapeutics is reviewed in this article. Further, numerous examples of peptides containing NPAAs are presented to highlight the ongoing development in peptide-based therapeutics.

Recent applications of click chemistry in drug discovery

Introduction: Click chemistry has been exploited widely in the past to expedite lead discovery and optimization. Indeed, Copper-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry is a bioorthogonal reaction of widespread utility throughout medicinal chemistry and chemical biology. Areas covered: The authors review recent applications of CuAAC click chemistry to drug discovery based on the literature published since 2013. Furthermore, the authors provide the reader with their expert perspectives on the area including their outlook on future developments. Expert opinion: Click chemistry reactions are an important part of the medicinal chemistry toolbox and offer substantial advantages to medicinal chemists in terms of overcoming the limitations of useful chemical synthesis, increasing throughput, and improving the quality of compound libraries. To explore new chemical spaces for drug-like molecules containing a high degree of structural diversity, it may be useful to merge the diversity-oriented synthesis and 'privileged' substructure-based strategy with bioorthogonal reactions using sophisticated automation and flow systems to improve productivity. Large compound libraries obtained in this way should be of great value for the discovery of bioactive compounds and therapeutic agents.

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.

Chemical optimization of macrocyclic HIV-1 inactivators for improving potency and increasing the structural diversity at the triazole ring

HIV-1 entry inhibition remains an urgent need for AIDS drug discovery and development. We previously reported the discovery of cyclic peptide triazoles (cPTs) that retain the HIV-1 irreversible inactivation functions of the parent linear peptides (PTs) and have massively increased proteolytic resistance. Here, in an initial structure-activity relationship investigation, we evaluated the effects of variations in key structural and functional components of the cPT scaffold in order to produce a platform for developing next-generation cPTs. Some structural elements, including stereochemistry around the cyclization residues and Ile and Trp side chains in the gp120-binding pharmacophore, exhibited relatively low tolerance for change, reflecting the importance of these components for function. In contrast, in the pharmacophore-central triazole position, the ferrocene moiety could be successfully replaced with smaller aromatic rings, where a p-methyl-phenyl methylene moiety gave cPT 24 with an IC50 value of 180 nM. Based on the observed activity of the biphenyl moiety when installed on the triazole ring (cPT 23, IC50 ∼ 269 nM), we further developed a new on-resin synthetic method to easily access the bi-aryl system during cPT synthesis, in good yields. A thiophene-containing cPT AAR029N2 (36) showed enhanced entropically favored binding to Env gp120 and improved antiviral activity (IC50 ∼ 100 nM) compared to the ferrocene-containing analogue. This study thus provides a crucial expansion of chemical space in the pharmacophore to use as a starting point, along with other allowable structural changes, to guide future optimization and minimization for this important class of HIV-1 killing agents.

Derivation and Characterization of a CD4-Independent, Non-CD4-Tropic Simian Immunodeficiency Virus

CD4 tropism is conserved among all primate lentiviruses and likely contributes to viral pathogenesis by targeting cells that are critical for adaptive antiviral immune responses. Although CD4-independent variants of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) have been described that can utilize the coreceptor CCR5 or CXCR4 in the absence of CD4, these viruses typically retain their CD4 binding sites and still can interact with CD4. We describe the derivation of a novel CD4-independent variant of pathogenic SIVmac239, termed iMac239, that was used to derive an infectious R5-tropic SIV lacking a CD4 binding site. Of the seven mutations that differentiate iMac239 from wild-type SIVmac239, a single change (D178G) in the V1/V2 region was sufficient to confer CD4 independence in cell-cell fusion assays, although other mutations were required for replication competence. Like other CD4-independent viruses, iMac239 was highly neutralization sensitive, although mutations were identified that could confer CD4-independent infection without increasing its neutralization sensitivity. Strikingly, iMac239 retained the ability to replicate in cell lines and primary cells even when its CD4 binding site had been ablated by deletion of a highly conserved aspartic acid at position 385, which, for HIV-1, plays a critical role in CD4 binding. iMac239, with and without the D385 deletion, exhibited an expanded host range in primary rhesus peripheral blood mononuclear cells that included CCR5(+) CD8(+) T cells. As the first non-CD4-tropic SIV, iMac239-ΔD385 will afford the opportunity to directly assess the in vivo role of CD4 targeting on pathogenesis and host immune responses.

IMPORTANCE

CD4 tropism is an invariant feature of primate lentiviruses and likely plays a key role in pathogenesis by focusing viral infection onto cells that mediate adaptive immune responses and in protecting virions attached to cells from neutralizing antibodies. Although CD4-independent viruses are well described for HIV and SIV, these viruses characteristically retain their CD4 binding site and can engage CD4 if available. We derived a novel CD4-independent, CCR5-tropic variant of the pathogenic molecular clone SIVmac239, termed iMac239. The genetic determinants of iMac239's CD4 independence provide new insights into mechanisms that underlie this phenotype. This virus remained replication competent even after its CD4 binding site had been ablated by mutagenesis. As the first truly non-CD4-tropic SIV, lacking the capacity to interact with CD4, iMac239 will provide the unique opportunity to evaluate SIV pathogenesis and host immune responses in the absence of the immunomodulatory effects of CD4(+) T cell targeting and infection.

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.