A novel small molecular weight compound with a carbazole structure that demonstrates potent human immunodeficiency virus type-1 integrase inhibitory activity

The Advances of Broad-Spectrum and Hot Anti-Coronavirus Drugs

Coronaviruses, mainly including severe acute respiratory syndrome virus, severe acute respiratory syndrome coronavirus 2, Middle East respiratory syndrome virus, human coronavirus OC43, chicken infectious bronchitis virus, porcine infectious gastroenteritis virus, porcine epidemic diarrhea virus, and murine hepatitis virus, can cause severe diseases in humans and livestock. The severe acute respiratory syndrome coronavirus 2 is infecting millions of human beings with high morbidity and mortality worldwide, and the multiplicity of swine epidemic diarrhea coronavirus in swine suggests that coronaviruses seriously jeopardize the safety of public health and that therapeutic intervention is urgently needed. Currently, the most effective methods of prevention and control for coronaviruses are vaccine immunization and pharmacotherapy. However, the emergence of mutated viruses reduces the effectiveness of vaccines. In addition, vaccine developments often lag behind, making it difficult to put them into use early in the outbreak. Therefore, it is meaningful to screen safe, cheap, and broad-spectrum antiviral agents for coronaviruses. This review systematically summarizes the mechanisms and state of anti-human and porcine coronavirus drugs, in order to provide theoretical support for the development of anti-coronavirus drugs and other antivirals.

Antiviral Activities of Carbazole Derivatives against Porcine Epidemic Diarrhea Virus In Vitro

Porcine epidemic diarrhea virus (PEDV), an enteric coronavirus, causes neonatal pig acute gastrointestinal infection with a characterization of severe diarrhea, vomiting, high morbidity, and high mortality, resulting in tremendous damages to the swine industry. Neither specific antiviral drugs nor effective vaccines are available, posing a high priority to screen antiviral drugs. The aim of this study is to investigate anti-PEDV effects of carbazole alkaloid derivatives. Eighteen carbazole derivatives (No.1 to No.18) were synthesized, and No.5, No.7, and No.18 were identified to markedly reduce the replication of enhanced green fluorescent protein (EGFP) inserted-PEDV, and the mRNA level of PEDV N. Flow cytometry assay, coupled with CCK8 assay, confirmed No.7 and No.18 carbazole derivatives displayed high inhibition effects with low cell toxicity. Furthermore, time course analysis indicated No.7 and No.18 carbazole derivatives exerted inhibition at the early stage of the viral life cycle. Collectively, the analysis underlines the benefit of carbazole derivatives as potential inhibitors of PEDV, and provides candidates for the development of novel therapeutic agents.

Carbazole Alkaloids from Clausena anisum-olens: Isolation, Characterization, and Anti-HIV Evaluation

Two new carbazole alkaloids (1,2) and six known carbazole alkaloids (3-8) were isolated from Clausena anisum-olens. Their structures were elucidated based on extensive spectroscopic analysis. All isolated compounds (1-8) were evaluated for their anti-HIV effects on virus replication in MT-4 lymphocytes infected by HIV-1NL4-3 Nanoluc-sec virus, and new carbazole alkaloid 1 exhibited anti-HIV activity with an EC50 value of 2.4 μg/mL and SI of 7.1.

Carbazole Derivatives as Antiviral Agents: An Overview

Keywords: carbazole; tetrahydrocarbazole; antiviral agents.

Discovery of 4-oxoquinolines, a new chemical class of anti-HIV-1 compounds

Antiretroviral therapy (ART) against HIV-1 infection offers the promise of controlling disease progression and prolonging the survival of HIV-1-infected patients. However, even the most potent ART regimens available today cannot cure HIV-1. Because patients will be exposed to ART for many years, physicians and researchers must anticipate the emergence of drug-resistant HIV-1, potential adverse effects of the current drugs, and need for future drug development. In this study, we screened a small-molecule compound library using cell-based anti-HIV-1 assays and discovered a series of novel anti-HIV-1 compounds, 4-oxoquinolines. These compounds exhibited potent anti-HIV-1 activity (EC₅₀ < 0.1 μM) with high selectivity indexes (CC₅₀/EC₅₀ > 2500) and favorable pharmacokinetic profiles in mice. Surprisingly, our novel compounds have a chemical backbone similar to the clinically used integrase (IN) strand transfer inhibitor (INSTI) elvitegravir, although they lack the crucial 3-carboxylate moiety needed for the common INSTI diketo motif. Indeed, the new 4-oxoquinoline derivatives have no detectable INSTI activity. In addition, various drug-resistant HIV-1 strains did not display cross resistance to these compounds. Interestingly, time-of-addition experiments indicated that the 4-oxoquinoline derivative remains its anti-HIV-1 activity even after the viral integration stage. Furthermore, the compounds significantly suppressed p24 antigen production in HIV-1 latently infected cells exposed with tumor necrosis factor alpha. These findings suggest that our 4-oxoquinoline derivatives with no 3-carboxylate moiety may become novel lead compounds in the development of anti-HIV-1 drugs.

Genotoxicity of two new carbazole derivatives with antifungal activity

The class of carbazoles includes compounds with high biological activities and broad spectra of action. PLX01107 and PLX01008 are xenomycins, a new subclass of antimicrobial carbazole derivatives demonstrating strong antifungal activity in vitro. We performed three tests, a bacterial reverse mutation assay (Ames test), in vitro cytokinesis-block micronucleus assay, and chromosome aberration test in mouse bone marrow cells, to investigate the possible genotoxicity of these compounds. Despite their structural similarity, the two compounds had different genotoxicity profiles. PLX01008 showed positive effects in all assays. PLX01107 showed no mutagenicity in the Ames test but demonstrated strong cytogenetic activity in vitro and in vivo. PLX01107 was also tested in the in vivo alkaline comet assay, where a weak but statistically significant increase in DNA damage was seen in liver cells 24h after treatment. Significantly increased levels of formamidopyrimidine DNA glycosylase (FPG)-sensitive sites were found in bone marrow cells of PLX01107-treated mice (FPG-modified comet assay), suggesting induction of oxidative or alkylation damage to DNA.

Antiseptic Effects of New 3'-N-Substituted Carbazole Derivatives In Vitro and In Vivo

Inhibition of high-mobility group box 1 (HMGB1) protein and restoration of endothelial integrity are emerging as attractive therapeutic strategies in the management of sepsis. Here, new five structurally related 3'-N-substituted carbazole derivatives were examined for their effects on lipopolysaccharide (LPS)-mediated or cecal ligation and puncture (CLP)-mediated release of HMGB1 and on modulation of HMGB1-mediated inflammatory responses. We accessed this question by monitoring the effects of posttreatment carbazole derivatives on LPS- and CLP-mediated release of HMGB1 and HMGB1-mediated regulation of proinflammatory responses in human umbilical vein endothelial cells (HUVECs) and septic mice. The new 3'-N-substituted carbazole derivatives 1-5 inhibited the release of HMGB1 and downregulated HMGB1-dependent inflammatory responses in human endothelial cells. New compounds also inhibited HMGB1-mediated hyperpermeability and leukocyte migration in mice. In addition, treatment with each compound reduced CLP-induced release of HMGB1 and sepsis-related mortality and pulmonary injury in mice. These results indicate that the new 3'-N-substituted carbazole derivatives could be candidate therapeutic agents for various severe vascular inflammatory diseases owing to their inhibition of the HMGB1 signaling pathway.

Structural Studies of the HIV-1 Integrase Protein: Compound Screening and Characterization of a DNA-Binding Inhibitor

Understanding the HIV integrase protein and mechanisms of resistance to HIV integrase inhibitors is complicated by the lack of a full length HIV integrase crystal structure. Moreover, a lentiviral integrase structure with co-crystallised DNA has not been described. For these reasons, we have developed a structural method that utilizes free software to create quaternary HIV integrase homology models, based partially on available full-length prototype foamy virus integrase structures as well as several structures of truncated HIV integrase. We have tested the utility of these models in screening of small anti-integrase compounds using randomly selected molecules from the ZINC database as well as a well characterized IN:DNA binding inhibitor, FZ41, and a putative IN:DNA binding inhibitor, HDS1. Docking studies showed that the ZINC compounds that had the best binding energies bound at the IN:IN dimer interface and that the FZ41 and HDS1 compounds docked at approximately the same location in integrase, i.e. behind the DNA binding domain, although there is some overlap with the IN:IN dimer interface to which the ZINC compounds bind. Thus, we have revealed two possible locations in integrase that could potentially be targeted by allosteric integrase inhibitors, that are distinct from the binding sites of other allosteric molecules such as LEDGF inhibitors. Virological and biochemical studies confirmed that HDS1 and FZ41 share a similar activity profile and that both can inhibit each of integrase and reverse transcriptase activities. The inhibitory mechanism of HDS1 for HIV integrase seems to be at the DNA binding step and not at either of the strand transfer or 3' processing steps of the integrase reaction. Furthermore, HDS1 does not directly interact with DNA. The modeling and docking methodology described here will be useful for future screening of integrase inhibitors as well as for the generation of models for the study of integrase drug resistance.

Cell-permeable stapled peptides based on HIV-1 integrase inhibitors derived from HIV-1 gene products

HIV-1 integrase (IN) is an enzyme which is indispensable for the stable infection of host cells because it catalyzes the insertion of viral DNA into the genome and thus is an attractive target for the development of anti-HIV agents. Earlier, we found Vpr-derived peptides with inhibitory activity against HIV-1 IN. These Vpr-derived peptides are originally located in an α-helical region of the parent Vpr protein. Addition of an octa-arginyl group to the inhibitory peptides caused significant inhibition against HIV replication associated with an increase in cell permeability but also relatively high cytotoxicity. In the current study, stapled peptides, a new class of stabilized α-helical peptidomimetics were adopted to enhance the cell permeability of the above lead peptides. A series of stapled peptides, which have a hydrocarbon link formed by a ruthenium-catalyzed ring-closing metathesis reaction between successive turns of α-helix, were designed, synthesized, and evaluated for biological activity. In cell-based assays some of the stapled peptides showed potent anti-HIV activity comparable with that of the original octa-arginine-containing peptide (2) but with lower cytotoxicity. Fluorescent imaging experiments revealed that these stapled peptides are significantly cell permeable, and CD analysis showed they form α-helical structures, whereas the unstapled congeners form β-sheet structures. The application of this stapling strategy to Vpr-derived IN inhibitory peptides led to a remarkable increase in their potency in cells and a significant reduction of their cytotoxicity.

Peptide HIV-1 integrase inhibitors from HIV-1 gene products

Anti-HIV peptides with inhibitory activity against HIV-1 integrase (IN) have been found in overlapping peptide libraries derived from HIV-1 gene products. In a strand transfer assay using IN, inhibitory active peptides with certain sequential motifs related to Vpr- and Env-derived peptides were found. The addition of an octa-arginyl group to the inhibitory peptides caused a remarkable inhibition of the strand transfer and 3'-end-processing reactions catalyzed by IN and significant inhibition against HIV replication.

Peptidic HIV integrase inhibitors derived from HIV gene products: structure-activity relationship studies

Structure-activity relationship studies were conducted on HIV integrase (IN) inhibitory peptides which were found by the screening of an overlapping peptide library derived from HIV-1 gene products. Since these peptides located in the second helix of Vpr are considered to have an alpha-helical conformation, Glu-Lys pairs were introduced into the i and i+4 positions to increase the helicity of the lead compound possessing an octa-arginyl group. Ala-scan was also performed on the lead compound for the identification of the amino acid residues responsible for the inhibitory activity. The results indicated the importance of an alpha-helical structure for the expression of inhibitory activity, and presented a binding model of integrase and the lead compound.

Integration of human immunodeficiency virus as a target for antiretroviral therapy

PURPOSE OF REVIEW

Most of the studies investigating inhibition of human immunodeficiency virus integration have focused on blocking the enzymatic functions of HIV integrase, with the predominant judgment that integration inhibitors need to block at least one of the integrase-catalyzed reactions. Recent studies, however, have highlighted the importance of other proteins and their contacts with integrase in the preintegration complex, and their involvement in chromosomal integration of the viral DNA.

RECENT FINDINGS

Promising results of clinical trials for two new integrase inhibitors were announced recently, providing the proof of the concept for using HIV-1 integrase inhibitors as antiretroviral therapy. Two strategies are currently employed for the development of novel inhibitors of HIV integrase: synthesis of hybrid molecules comprising core structures of two or more known inhibitors, and three-dimensional pharmacophore searches based on previously discovered compounds. By highlighting the role of the cellular cofactor LEDGF/p75 in HIV integration, novel approaches are indicated that aim to develop compounds altering contact between HIV integrase and integration cofactors.

SUMMARY

By the discovery of novel inhibitors and targets for HIV integration, coupled with recent studies in characterizing preintegration complex formation, new insight is provided for the rational design of anti-HIV integration inhibitors.

HIV-1 integrase inhibitors: 2005-2006 update

HIV-1 integrase (IN) catalyzes the integration of proviral DNA into the host genome, an essential step for viral replication. Inhibition of IN catalytic activity provides an attractive strategy for antiretroviral drug design. Currently two IN inhibitors, MK-0518 and GS-9137, are in advanced stages of human clinical trials. The IN inhibitors in clinical evaluation demonstrate excellent antiretroviral efficacy alone or in combination regimens as compared to previously used clinical antiretroviral agents in naive and treatment-experienced HIV-1 infected patients. However, the emergence of viral strains resistant to clinically studied IN inhibitors and the dynamic nature of the HIV-1 genome demand a continued effort toward the discovery of novel inhibitors to keep a therapeutic advantage over the virus. Continued efforts in the field have resulted in the discovery of compounds from diverse chemical classes. In this review, we provide a comprehensive report of all IN inhibitors discovered in the years 2005 and 2006.

Dihydroxythiophenes are novel potent inhibitors of human immunodeficiency virus integrase with a diketo acid-like pharmacophore

We have identified dihydroxythiophenes (DHT) as a novel series of human immunodeficiency virus type 1 (HIV-1) integrase inhibitors with broad antiviral activities against different HIV isolates in vitro. DHT were discovered in a biochemical integrase high-throughput screen searching for inhibitors of the strand transfer reaction of HIV-1 integrase. DHT are selective inhibitors of integrase that do not interfere with virus entry, as shown by the inhibition of a vesicular stomatitis virus G-pseudotyped retroviral system. Moreover, in quantitative real-time PCR experiments, no effect on the synthesis of viral cDNA could be detected but rather an increase in the accumulation of 2-long-terminal-repeat cycles was detected. This suggests that the integration of viral cDNA is blocked. Molecular modeling and the structure activity relationship of DHT demonstrate that our compound fits into a two-metal-binding motif that has been suggested as the essential pharmacophore for diketo acid (DKA)-like strand transfer inhibitors (Grobler et al., Proc. Natl. Acad. Sci. USA 99:6661-6666, 2002.). This notion is supported by the profiling of DHT on retroviral vectors carrying published resistance mutations for DKA-like inhibitors where DHT showed partial cross-resistance. This suggests that DHT bind to a common site in the catalytic center of integrase, albeit with an altered binding mode. Taken together, our findings indicate that DHT are novel selective strand transfer inhibitors of integrase with a pharmacophore homologous to DKA-like inhibitors.