Inhibition of herpes simplex virus replication by a 2-amino thiazole via interactions with the helicase component of the UL5-UL8-UL52 complex

Novel Thiazolidine-2,4-dione-trimethoxybenzene-thiazole Hybrids as Human Topoisomerases Inhibitors

Cancer is a complex and heterogeneous disease and is still one of the leading causes of morbidity and mortality worldwide, mostly as the population ages. Despite the encouraging advances made over the years in chemotherapy, the development of new compounds for cancer treatments is an urgent priority. In recent years, the design and chemical synthesis of several innovative hybrid molecules, which bring different pharmacophores on the same scaffold, have attracted the interest of many researchers. Following this strategy, we designed and synthetized a series of new hybrid compounds that contain three pharmacophores, namely trimethoxybenzene, thiazolidinedione and thiazole, and tested their anticancer properties on two breast cancer (MCF-7 and MDA-MB-231) cell lines and one melanoma (A2058) cell line. The most active compounds were particularly effective against the MCF-7 cells and did not affect the viability of the normal MCF-10A cells. Docking simulations indicated the human Topoisomerases I and II (hTopos I and II) as possible targets of these compounds, the inhibitory activity of which was demonstrated by the mean of direct enzymatic assays. Particularly, compound 7e was proved to inhibit both the hTopo I and II, whereas compounds 7c,d blocked only the hTopo II. Finally, compound 7e was responsible for MCF-7 cell death by apoptosis. The reported results are promising for the further design and synthesis of other analogues potentially active as anticancer tools.

Synthesis, Structure and Molecular Docking of New 4,5-Dihydrothiazole Derivatives Based on 3,5-Dimethylpyrazole and Cytisine and Salsoline Alkaloids

The interaction results of 1,2-dibromo-3-isothiocyanatopropane with some pyrazoles as well as cytisine and salsoline alkaloids were presented in this paper. It was shown that the reaction resulted in one one-step and rather mild method for the preparation of the corresponding 1,3-thiazoline bromomethyl derivatives. The yield of this reaction was affected by the presence of a base and an order in which reagents were added. Molecular docking of the synthesized 1,3-thiazoline derivatives for putative antibacterial activity was carried out using the penicillin-binding target protein (PBP4) of the bacteria E. coli "Homo sapiens" and S. aureus "Homo sapiens" as an example. Molecular docking demonstrated that the compounds had insignificant binding energies at the level of selected reference drugs (Cephalotin and Chloramphenicol). The presence of natural alkaloids in the structure of thiazoline derivatives somewhat increased the affinity of these substrates for target proteins selected.

Discovery, Chemistry, and Preclinical Development of Pritelivir, a Novel Treatment Option for Acyclovir-Resistant Herpes Simplex Virus Infections

When the nucleoside analogue acyclovir was introduced in the early 1980s, it presented a game-changing treatment modality for herpes simplex virus infections. Since then, work has been ongoing to improve the weaknesses that have now been identified: a narrow time window for therapeutic success, resistance in immunocompromised patients, little influence on frequency of recurrences, relatively fast elimination, and poor bioavailability. The present Drug Annotation focuses on the helicase–primase inhibitor pritelivir currently in development for the treatment of acyclovir-resistant HSV infections and describes how a change of the molecular target (from viral DNA polymerase to the HSV helicase–primase complex) afforded improvement of the shortcomings of nucleoside analogs. Details are presented for the discovery process leading to the final drug candidate, the pivotal preclinical studies on mechanism of action and efficacy, and on how ongoing clinical research has been able to translate preclinical promises into clinical use.

Sulfonated (1 → 6)-β-d-Glucan (Lasiodiplodan): A Promising Candidate against the Acyclovir-Resistant Herpes Simplex Virus Type 1 (HSV-1) Strain

Herpes simplex virus type 1 (HSV-1) is a persistent human pathogen, and the emergence of strains resistant to Acyclovir (ACV, reference drug) shows the urgency to develop new treatments. We report the antiherpetic mechanism of the action of lasiodiplodan (LAS-N, (1 → 6)-β-d-glucan) and its sulfonated derivative (LAS-S3) in vitro and in vivo. LAS-S3 showed anti-HSV-1 action with high selectivity indices for HSV-1 KOS (88.1) and AR (189.2), sensitive and resistant to ACV, respectively. LAS-S3 inhibited >80% of HSV-1 infection in different treatment protocols (virucidal, adsorption inhibition, and post-adsorption effects), even at low doses, and showed a preventive effect and DNA and protein synthesis inhibition. The antiherpetic effect was confirmed in vivo by the cosmetic LAS-S3-CRÈME decreasing cutaneous lesions of HSV-1, including the AR strain. LAS-S3 possessed a broad-spectrum mechanism of action acting in the early and post-adsorption stages of HSV-1 infection, and LAS-S3-CRÈME is a potential antiherpetic candidate for patients infected by HSV-1-resistant strains.

Development of novel indolin-2-one derivative incorporating thiazole moiety as DHFR and quorum sensing inhibitors: Synthesis, antimicrobial, and antibiofilm activities with molecular modelling study

Nowadays, it's imperative to develop novel antimicrobial agents active against both drug-sensitive and drug-resistant bacterial infections with favorable profiles as high efficacy, low toxicity, and short therapy duration. Accordingly, a series of new thiazolo-indolin-2-one derivatives were synthesized based on acid and base catalyzed condensation or reaction of thiosemicarbazone 8 with different electrophilic reagents. The structure of the new compounds was confirmed based on elemental analysis and spectral data. Based on the MIC results, the most active thiazolo-indoline derivatives 2, 4, 7a, and 12 exhibited promising antibacterial activity against gram-positive and gram-negative bacteria with weak to moderate antifungal activities. Surprisingly, the N-(thiazol-2-yl)benzenesulfonamide derivative 4 was found to be most active on antibiofilm activity against both S. aureus (ATCC 29213) with BIC₅₀ (1.95 ± 0.01 µg/mL), while 5-(2-oxoindolin-3-ylidene)-thiazol-4(5H)-one derivative 7a exhibited the strongest antibiofilm activity against P. aeruginosa pathogens with BIC₅₀ (3.9 ± 0.16 µg/mL). Further, the thiazole derivatives 2, 4 and 12 exhibited a significant inhibition activity against the fsr system in a dose-dependent manner without affecting bacterial growth. The target derivatives behaved synergistic and additively effect against MDR p. aeruginosa, and thiazole derivative 12 exhibited a high synergistic effect with most tested antibiotics except Cefepime with FIC value ranging between 0.249 and 1.0, reducing their MICs. Interestingly, the 3-(2-(4-thiazol-2-yl)hydrazono)indolin-2-one derivative 12 displayed the highest selectivity to DHFR inhibitory with IC₅₀ value 40.71 ± 1.86 nM superior to those of the reference Methotrexate. Finally, in silico molecular modeling simulation, some physicochemical properties and toxicity predictions were performed for the most active derivatives.

High throughput screening identifies inhibitors for parvovirus B19 infection of human erythroid progenitor cells

Parvovirus B19 (B19V) infection can cause hematological disorders and fetal hydrops during pregnancy. Currently, no antivirals or vaccines are available for the treatment or the prevention of B19V infection. To identify novel small-molecule antivirals against B19V replication, we developed a high throughput screening assay, which is based on an in vitro nicking assay using recombinant N-terminal 1-176 amino acids of the viral large nonstructural protein (NS1N) and a fluorescently labeled DNA probe (OriQ) that spans the nicking site of the viral DNA replication origin. We collectively screened 17,040 compounds and identified 2,178 (12.78%) hits that possess >10% inhibition of the NS1 nicking activity, among which 84 hits were confirmed to inhibit nicking in a dose-dependent manner. Using ex vivo expanded primary human erythroid progenitor cells (EPCs) infected by B19V, we validated 24 compounds demonstrated >50% in vivo inhibition of B19V infection at 10 μM, which can be categorized into 7 structure scaffolds. Based on the therapeutic index [half maximal cytotoxic concentration (CC₅₀)/half maximal effective concentration (EC₅₀)] in EPCs, the top 4 compounds were chosen to examine their inhibitions of B19V infection in EPCs at two times of the 90% maximal effective concentration (EC₉₀). A purine derivative (P7), demonstrated an antiviral effect (EC₅₀=1.46 μM) without prominent cytotoxicity (CC₅₀=71.8 μM) in EPCs, exhibited 92% inhibition of B19V infection in EPCs at 3.32 μM, which can be used as the lead compound in future studies for the treatment of B19V infection caused hematological disorders. Importance B19V encodes a large non-structural protein NS1. Its N-terminal domain (NS1N) consisting of 1-176 amino acids binds to viral DNA and serves as an endonuclease to nick the viral DNA replication origins, which is a pivotal step in rolling hairpin-dependent B19V DNA replication. For high throughput screening (HTS) of anti-B19V antivirals, we miniaturized a fluorescence-based in vitro nicking assay, which employs a fluorophore-labeled probe spanning the trs and the NS1N protein, into a 384-well plate format. The HTS assay showed a high reliability and capability in screening 17,040 compounds. Based on the therapeutic index [half maximal cytotoxic concentration (CC₅₀)/half maximal effective concentration (EC₅₀)] in EPCs, a purine derivative demonstrated an antiviral effect of 92% inhibition of B19V infection in EPCs at 3.32 μM (two times EC₉₀). Our study demonstrated a robust HTS assay for screening antivirals against B19V infection.

Helicase primase inhibitors (HPIs) are efficacious for therapy of human herpes simplex virus (HSV) disease in an infection mouse model

Although the seroprevalence of Herpes simplex virus type 1 (HSV-1) currently amounts to ∼ 67% worldwide, the annual incidence of a severe disease progression, particularly herpes encephalitis, is approximately 2-4 cases per 1,000,000 infections. Nucleoside analogues, such as acyclovir (ACV), valacyclovir (VACV) or famciclovir, are still the therapeutic treatment of choice for HSV infections. However, nucleoside drugs have limited efficacy against severe HSV disease and for treatment of nucleoside-resistant viral strains, alternative therapies such as helicase-primase inhibitors (HPIs) which are highly potent by inhibiting viral replication are under development. In preclinical studies we analyzed the antiviral efficacy of drug candidates of a novel compound class of HPIs for the treatment of HSV to identify the most active eutomer structure in an intranasal infection mouse lethal challenge model. HSV-1 infected BALB/c mice treated with vehicle control developed fatal disease according to humane endpoints after 5-7 days. In contrast, the animals dosed orally once daily with the HPI compounds at 10 or 4 mg/kg/day showed a significantly increased survival (70% and 100% for 10 mg/kg/day; 90% and 100% for 4 mg/kg/day, respectively) compared to the vehicle treatment (0-10%), when therapy was initiated 6 h post HSV-1 inoculation. We observed a significantly improved outcome in clinical parameters and survival over 21 days in the group receiving novel HPI candidates using even the lowest dose of 4 mg/kg/day. With VACV treatment of 75 mg/kg daily survival was also significantly increased (80%-90% for 75 mg/kg/day) but to lesser extent. Initial IM-250 therapy at 10 mg/kg/day could be delayed up to 72 h resulting in significantly increased survival compared to the vehicle control. Furthermore, we detected significantly fewer viral genome copies in the lungs and brains of HPI treated animals compared to vehicle (440-fold reduction for 4 mg/kg/day IM-250 in the brain) or VACV controls by quantitative PCR. In conclusion the preclinical studies of the novel HPI compounds showed superior efficacy in comparison to the current standard HSV treatment represented by VACV with respect to the survival according humane endpoints, the clinical score and virus load in lungs and brains. Thus, candidates of this new drug class are promising antivirals of HSV infections and further translation into clinical trials is warranted.

Amenamevir, a Helicase-Primase Inhibitor, for the Optimal Treatment of Herpes Zoster

Acyclovir, valacyclovir, and famciclovir are used for the treatment of herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections. Helicase-primase inhibitors (HPIs) inhibit replication fork progression that separates double DNA strands into two single strands during DNA synthesis. The HPIs amenamevir and pritelivir have novel mechanisms of anti-herpetic action, and their once-daily administration has clinical efficacy for genital herpes. Among HPIs, amenamevir has anti-VZV activity. The concentrations of HSV-1 and VZV required for the 50% plaque reduction of amenamevir were 0.036 and 0.047 μM, respectively. We characterized the features of amenamevir regarding its mechanism, resistance, and synergism with acyclovir. Its antiviral activity was not influenced by the viral replication cycle, in contrast to acyclovir. A clinical trial of amenamevir for herpes zoster demonstrated its non-inferiority to valacyclovir. To date, amenamevir has been successfully used in over 1,240,000 patients with herpes zoster in Japan. Post-marketing surveillance of amenamevir in Japan reported side effects with significant potential risk identified by the Japanese Risk Management Plan, including thrombocytopenia, gingival bleeding, and palpitations, although none of these were serious. The clinical efficacy and safety profiles of amenamevir were established in patients with herpes zoster. Therefore, amenamevir as an HPI opens a new era of anti-herpes therapy.

The three-component helicase/primase complex of herpes simplex virus-1

Herpes simplex virus type 1 (HSV-1) is one of the nine herpesviruses that infect humans. HSV-1 encodes seven proteins to replicate its genome in the hijacked human cell. Among these are the herpes virus DNA helicase and primase that are essential components of its replication machinery. In the HSV-1 replisome, the helicase-primase complex is composed of three components including UL5 (helicase), UL52 (primase) and UL8 (non-catalytic subunit). UL5 and UL52 subunits are functionally interdependent, and the UL8 component is required for the coordination of UL5 and UL52 activities proceeding in opposite directions with respect to the viral replication fork. Anti-viral compounds currently under development target the functions of UL5 and UL52. Here, we review the structural and functional properties of the UL5/UL8/UL52 complex and highlight the gaps in knowledge to be filled to facilitate molecular characterization of the structure and function of the helicase-primase complex for development of alternative anti-viral treatments.

Emergence of varicella-zoster virus resistance to acyclovir: epidemiology, prevention, and treatment

Introduction: Acyclovir has led to the development of successful systemic therapy for herpes simplex virus and varicella-zoster virus (VZV) infection, and the use of valacyclovir and famciclovir has improved treatment. Additionally, the use of a helicase-primase (HP) inhibitor (HPI), amenamevir, is changing the treatment of herpes zoster (HZ).Area covered: VZV infection is prevented by vaccines and is treated with antiviral agents. Acyclovir and penciclovir are phosphorylated by viral thymidine kinase and work as chain terminators. Improvements in the management of immunocompromised patients have reduced severe and prolonged immunosuppression and chronic VZV infection with acyclovir-resistant mutants has become rarer. The HP is involved in the initial step of DNA synthesis and amenamevir has novel mechanisms of action, efficacy to acyclovir-resistant mutants, and pharmacokinetic characteristics. The literature search for PUBMED was conducted on 10 April 2020 and updated on 4 November 2020.Expert opinion: Amenamevir has been used to treat HZ in Japan. Although the number of patients with VZV infection will decrease owing to the use of vaccines, the addition of HPI will improve treatment and treatment options for resistant viruses. The clinical use of HPIs in addition to current nucleoside analogs opens a new era of antiherpes therapy.

Synthesis of novel thiazole, pyranothiazole, thiazolo[4,5-b]pyridines and thiazolo[5',4':5,6]pyrano[2,3-d]pyrimidine derivatives and incorporating isoindoline-1,3-dione group

Background

Thiazole is a core structural motif presents in a wide range of natural products. Thiazole derivatives also have a wide range of medicinal and biological properties.

Results

The reaction of hydrazonoyl halides with 2-(1-(4-(1,3-dioxoisoindolin-2-yl)phenyl)ethylidene)hydrazinecarbothioamidein ethanol and triethylamine yielded 2-(4-(1-(2-(4-(2-Arylhydrazono)-5-s-4,5-dihydrothiazol-2-yl)hydrazono)-ethyl)phenyl)isoindoline-1,3-dione and 2-(4-(1-(2-(5-(2-Arylhydrazono)-4-oxo-4,5-dihydrothiazol-2-yl)hydrazono)ethyl)-phenyl)isoindoline-1,3-dione.The reaction of 2-(4-(1-(2-(4-oxo-4,5-dihydrothiazol-2-yl)hydrazono)ethyl)phenyl)isoindoline-1,3-dione with arylidenemalononitrile also yielded 5-amino-2-(2-(1-(4-(1,3-dioxoisoindolin-2-yl)phenyl)ethylidene)hydrazinyl)-7-substituted-7H-pyrano[2,3-d]thiazole-6-carbonitrile. The structures of the newly synthesized compound were elucidated whenever possible on the basis of elemental analysis, spectral data, and alternative synthetic routes. Three of them were evaluated against a breast cancer cell line for their antitumor activity.

Conclusions

Compound (1) has been shown to be useful in the synthesis of a new series of 1,3-thiazole, pyrano[2,3-d]thiazole and 4,5-dihydrothiazolo[4,5-b]pyridine derivatives using hydrazonoyl halides as precursors. The anticancer efficacy of compounds (9b), (9e), and (9f) against MCF-7, a breast cancer cell line, was also compared to the standard anticancer drug doxorubicin.

Electronic supplementary material

The online version of this article (10.1186/s13065-019-0559-x) contains supplementary material, which is available to authorized users.

Antiviral Drugs Against Alphaherpesvirus

The discovery of acyclovir and penciclovir has led to the development of a successful systemic therapy for treating herpes simplex virus infection and varicella-zoster virus infection, and the orally available prodrugs, valacyclovir and famciclovir, have improved antiviral treatment compliance. Acyclovir and penciclovir are phosphorylated by viral thymidine kinase and are incorporated into the DNA chain by viral DNA polymerase, resulting in chain termination. Helicase-primase plays an initial step in DNA synthesis to separate the double strand into two single strands (replication fork) and is a new target of antiviral therapy. The helicase-primase inhibitors (HPIs) pritelivir and amenamevir have novel mechanisms of action, drug resistance properties, pharmacokinetic characteristics, and clinical efficacy for treating genital herpes. The clinical study of amenamevir in herpes zoster has been completed, and amenamevir has been submitted for approval for treating herpes zoster in Japan. The clinical use of HPIs will be the beginning of a new era of anti-herpes therapy.

Syntheses of new 3-thiazolyl coumarin derivatives, in vitro α-glucosidase inhibitory activity, and molecular modeling studies

3-Thiazolylcoumarin derivatives 1-14 were synthesized via one-pot two step reactions, and screened for in vitro α-glucosidase inhibitory activity. All compounds showed inhibitory activity in the range of IC50 = 0.12 ± 0.01-16.20 ± 0.23 μM as compared to standard acarbose (IC50 = 38.25 ± 0.12 μM), and also found to be nontoxic. Molecular docking study was carried out in order to establish the structure-activity relationship (SAR) which demonstrated that electron rich centers at one and electron withdrawing centers at the other end of the molecules showed strong inhibitory activity. All the synthesized compounds were characterized by spectroscopic techniques such as EI-MS, HREI-MS, (1)H NMR and (13)C NMR. CHN analysis was also performed.

Helicase Primase: Targeting the Achilles Heel of Herpes Simplex Viruses

The majority of the population is infected by several herpesviruses. Once these infections are established the viruses persist for life. Therefore, current therapy may at best reduce symptoms but does not cure the infection. Moreover, the only classes of compounds licensed for systemic treatment of disease are nucleoside, nucleotide and pyrophosphate analogues; all of these ultimately target the herpesvirus DNA polymerase. A vaccine against varicella zoster virus (VZV) is available, but so far no effective vaccines against other human herpesviruses have been launched. At the same time, rising resistance to current medication, especially in the immunocompromised patient population, is a concern. For these reasons, there is an urgent need for new treatment options. Recently, some promising new drugs have been discovered; one of these compounds, developed at Bayer HealthCare under the name BAY 57–1293, is a potent HSV helicase primase inhibitor.

High conservation of herpes simplex virus UL5/UL52 helicase-primase complex in the era of new antiviral therapies

The emergence of herpes simplex virus (HSV) resistance to current antiviral drugs, that all target the viral DNA polymerase, constitutes a major obstacle to antiviral treatment effectiveness of HSV infections, especially in immunocompromised patients. A novel and promising class of inhibitors of the HSV UL5/UL52 helicase-primase (HP) complex has been reported to hinder viral replication with a high potency. In this study, we describe the low natural polymorphism (interstrain identity >99.1% at both nucleotide and amino acid levels) of HSV HP complex subunits pUL5 and pUL52 among 64 HSV (32 HSV-1 and 32 HSV-2) clinical isolates, and we show that the HSV resistance profile to the first-line antiviral drug acyclovir (ACV) does not impact on the natural polymorphism of HSV HP complex. Genotypic tools and polymorphism data concerning HSV HP complex provided herein will be useful to detect drug resistance mutations in a relevant time frame when HP inhibitors (HPIs), i.e., amenamevir and pritelivir, will be available in medical practice.

Production and characterisation of Epstein-Barr virus helicase-primase complex and its accessory protein BBLF2/3

The helicase-primase complex is part of the lytic DNA replication machinery of herpesviruses, but up to now, almost nothing is known about its structure. For Epstein-Barr virus it consists in the helicase BBLF4, the primase BSLF1 and the accessory protein BBLF2/3. The accessory protein shows only weak sequence homology within the herpesvirus family but may be related to an inactive B-family polymerase. BSLF1 belongs to the archaeo-eukaryotic primase family, whereas the helicase BBLF4 has been related either to Dda helicases of caudovirales or to Pif1 helicases. We produced the helicase-primase complex in insect cells using a baculovirus coding for all three proteins simultaneously. The soluble monomeric helicase-primase complex containing the three proteins with 1:1:1 stoichiometry showed ATPase activity, which is strongly stimulated in the presence of ssDNA oligomers. Furthermore, we expressed BBLF2/3 as soluble monomeric protein and performed small-angle X-ray scattering experiments which yielded an envelope whose shape is compatible with B-family polymerases.

Helicase-primase as a target of new therapies for herpes simplex virus infections

The seminal discovery of acyclovir 40 years ago heralded the modern era of truly selective antiviral therapies and this drug remains the therapy of choice for herpes simplex virus infections. Yet by modern standards, its antiviral activity is modest and new drugs against novel molecular targets such as the helicase-primase have the potential to improve clinical outcome, particularly in high-risk patients. A brief synopsis of current therapies for these infections and clinical need is provided to help provide an initial perspective. The function of the helicase-primase complex is then summarized and the development of new inhibitors of the helicase-primase complex, such as pritelivir and amenamevir, is discussed. We review their mechanism of action, propensity for drug resistance, and pharmacokinetic characteristics and discuss their potential to advance current therapeutic options. Strategies that include combinations of these inhibitors with acyclovir are also considered, as they will likely maximize clinical efficacy.

Crystal structure of 4-((1E)-1-{(2Z)-2-[4-(4-bromo-phen-yl)-3-phenyl-2,3-di-hydro-1,3-thia-zol-2-yl-idene]hydrazin-1-yl-idene}eth-yl)phenol hemihydrate

In the title compound, C₂₃H₁₈BrN₃OS·0.5H₂O, the bromo­phenyl, phenyl and phenol rings make dihedral angles of 46.5 (1), 66.78 (8) and 15.4 (2)°, respectively, with the mean squares plane of the thia­zol­idene ring. In the crystal, the lattice water mol­ecule is hydrogen bonded to the phenol group and makes a weaker O—H⋯N connection to an inversion-related mol­ecule, forming a ring while weak pairwise C—H⋯S inter­actions involving inversion-related mol­ecules form a second ring. Both these motifs result in the formation of two-dimensional networks lying parallel to (10-1).

Anti-herpesvirus agents: a patent and literature review (2003 to present)

INTRODUCTION

The standard therapy used to treat herpesvirus infections is based on the application of DNA polymerase inhibitors such as ganciclovir or aciclovir. Unfortunately, all of these compounds exhibit relatively high toxicity and the mutation of herpesviruses results in the appearance of new drug-resistant strains. Consequently, there is a great need for the development of new, effective and safe anti-herpesvirus agents that employ different patterns of therapeutic action at various stages of the virus life cycle.

AREAS COVERED

Patents and patent applications concerning the development of anti-herpesvirus agents displaying different mechanisms of action that have been published since 2003 are reviewed. In addition, major discoveries in this field that have been published in academic papers have also been included.

EXPERT OPINION

Among all the anti-herpesvirus agents described in this article, the inhibitors of viral serine protease seem to present one of the most effective/promising therapeutics. Unfortunately, the practical application of these antiviral agents has not yet been proven in any clinical trials. Nevertheless, the dynamic and extensive work on this subject gives hope that a new class of anti-herpesvirus agents aimed at the enzymatic activity of herpesvirus serine protease may be developed.

Helicase–primase inhibitors for herpes simplex virus: looking to the future of non-nucleoside inhibitors for treating herpes virus infections

Helicase–primase inhibitors (HPIs) are the first new family of potent herpes virus (herpes simplex and varicella-zoster virus) inhibitors to go beyond the preliminary stages of investigation since the emergence of the original nucleoside analog inhibitors. To consider the clinical future of HPIs, this review puts the exciting new findings with two HPIs, amenamevir and pritelivir, into the historical context of antiviral development for the prevention and treatment of herpes simplex virus over the last century and, on this basis, the authors speculate on the potential evolution of these and other non-nucleoside inhibitors in the future.

Design, synthesis and antiviral activity studies of schizonepetin derivatives

A series of schizonepetin derivatives have been designed and synthesized in order to obtain potent antivirus agents. The antiviral activity against HSV-1 and influenza virus H3N2 as well as the cytotoxicity of these derivatives was evaluated by using cytopathic effect (CPE) inhibition assay in vitro. Compounds M2, M4, M5 and M34 showed higher inhibitory activity against HSV-1 virus with the TC₅₀ values being in micromole. Compounds M28, M33, and M35 showed higher inhibitory activity against influenza virus H3N2 with their TC₅₀ values being 96.4, 71.0 and 75.4 μM, respectively. Preliminary biological activity evaluation indicated that the anti-H3N2 and anti-HSV-1 activities improved obviously through the introduction of halogen into the structure of schizonepetin.

The DNA helicase-primase complex as a target for herpes viral infection

INTRODUCTION

The Herpesviridae are responsible for debilitating acute and chronic infections, and some members of this family are associated with human cancers. Conventional anti-herpesviral therapy targets the viral DNA polymerase and has been extremely successful; however, the emergence of drug-resistant virus strains, especially in neonates and immunocompromised patients, underscores the need for continued development of anti-herpes drugs. In this article, we explore an alternative target for antiviral therapy, the HSV helicase/primase complex.

AREAS COVERED

This review addresses the current state of knowledge of HSV DNA replication and the important roles played by the herpesvirus helicase- primase complex. In the last 10 years several helicase/primase inhibitors (HPIs) have been described, and in this article, we discuss and contrast these new agents with established inhibitors.

EXPERT OPINION

The outstanding safety profile of existing nucleoside analogues for α-herpesvirus infection make the development of new therapeutic agents a challenge. Currently used nucleoside analogues exhibit few side effects and have low occurrence of clinically relevant resistance. For HCMV, however, existing drugs have significant toxicity issues and the frequency of drug resistance is high, and no antiviral therapies are available for EBV and KSHV. The development of new anti-herpesvirus drugs is thus well worth pursuing especially for immunocompromised patients and those who develop drug-resistant infections. Although the HPIs are promising, limitations to their development into a successful drug strategy remain.

Synthesis of new N-substituted 5-arylidene-2,4-thiazolidinediones as anti-inflammatory and antimicrobial agents

A novel series of 5-arylidene-2,4-thiazolidinediones (TZDs) 2a-p was synthesized from the condensation of 3-((2-phenylthiazol-4-yl)methyl)thiazolidine-2,4-dione with different benzaldehyde derivatives. All the structures were confirmed by their spectral (IR, ¹H NMR, ¹³C NMR and mass) and elemental analytical data. The new molecules were evaluated in vivo as anti-inflammatory agents in an acute experimental inflammation, evaluating the acute phase bone marrow response and phagocyte activity. All compounds, excepting one, reduced the absolute leukocytes count due to the lower neutrophil percentage. Phagocytary index was decreased by the same molecules, while only half of them reduced the phagocytary activity. The effect was superior to meloxicam, the reference anti-inflammatory drug, for the majority of the TZD derivatives. The new molecules were also investigated for their antimicrobial properties on Gram-positive and Gram-negative bacteria and one fungal strain. Two compounds (2e and 2n) manifested growth inhibition capacity on all the tested strains.

A cutting-edge view on the current state of antiviral drug development

Prominent in the current stage of antiviral drug development are: (i) for human immunodeficiency virus (HIV), the use of fixed-dose combinations (FDCs), the most recent example being Stribild(TM); (ii) for hepatitis C virus (HCV), the pleiade of direct-acting antivirals (DAAs) that should be formulated in the most appropriate combinations so as to obtain a cure of the infection; (iii)-(v) new strategies (i.e., AIC316, AIC246, and FV-100) for the treatment of herpesvirus infections: herpes simplex virus (HSV), cytomegalovirus (CMV), and varicella-zoster virus (VZV), respectively; (vi) the role of a new tenofovir prodrug, tenofovir alafenamide (TAF) (GS-7340) for the treatment of HIV infections; (vii) the potential use of poxvirus inhibitors (CMX001 and ST-246); (viii) the usefulness of new influenza virus inhibitors (peramivir and laninamivir octanoate); (ix) the position of the hepatitis B virus (HBV) inhibitors [lamivudine, adefovir dipivoxil, entecavir, telbivudine, and tenofovir disoproxil fumarate (TDF)]; and (x) the potential of new compounds such as FGI-103, FGI-104, FGI-106, dUY11, and LJ-001 for the treatment of filoviruses (i.e., Ebola). Whereas for HIV and HCV therapy is aimed at multiple-drug combinations, for all other viruses, HSV, CMV, VZV, pox, influenza, HBV, and filoviruses, current strategies are based on the use of single compounds.

The helicase-primase complex as a target for effective herpesvirus antivirals

Herpes simplex virus and varicella-zoster virus have been treated for more that half a century using nucleoside analogues. However, there is still an unmet clinical need for improved herpes antivirals. The successful compounds, acyclovir; penciclovir and their orally bioavailable prodrugs valaciclovir and famciclovir, ultimately block virus replication by inhibiting virus-specific DNA-polymerase. The helicase-primase (HP) complex offers a distinctly different target for specific inhibition of virus DNA synthesis. This review describes the synthetic programmes that have already led to two HP-inhibitors (HPI) that have commenced clinical trials in man. One of these (known as AIC 316) continues in clinical development to date. The specificity of HPI is reflected by the ability to select drug-resistant mutants. The role of HP-antiviral resistance will be considered and how the study of cross--resistance among mutants already shows subtle differences between compounds in this respect. The impact of resistance on the drug development in the clinic will also be considered. Finally, herpesvirus latency remains as the most important barrier to a therapeutic cure. Whether or not helicase primase inhibitors alone or in combination with nucleoside analogues can impact on this elusive goal remains to be seen.

Advances in the treatment of varicella-zoster virus infections

Varicella-zoster virus (VZV) causes two distinct diseases, varicella (chickenpox) and shingles (herpes zoster). Chickenpox occurs subsequent to primary infection, while herpes zoster (usually associated with aging and immunosuppression) appears as a consequence of reactivation of latent virus. The major complication of shingles is postherpetic neuralgia. Vaccination strategies to prevent varicella or shingles and the current status of antivirals against VZV will be discussed in this chapter. Varivax®, a live-attenuated vaccine, is available for pediatric varicella. Zostavax® is used to boost VZV-specific cell-mediated immunity in adults older than 50 years, which results in a decrease in the burden of herpes zoster and pain related to postherpetic neuralgia. Regardless of the availability of a vaccine, new antiviral agents are necessary for treatment of VZV infections. Current drugs approved for therapy of VZV infections include nucleoside analogues that target the viral DNA polymerase and depend on the viral thymidine kinase for their activation. Novel anti-VZV drugs have recently been evaluated in clinical trials, including the bicyclic nucleoside analogue FV-100, the helicase-primase inhibitor ASP2151, and valomaciclovir (prodrug of the acyclic guanosine derivative H2G). Different candidate VZV drugs have been described in recent years. New anti-VZV drugs should be as safe as and more effective than current gold standards for the treatment of VZV, that is, acyclovir and its prodrug valacyclovir.

Identification of a small molecule PriA helicase inhibitor

PriA helicase catalyzes the initial steps of replisome reloading onto repaired DNA replication forks in bacterial DNA replication restart pathways. We have used a high-throughput screen to identify a small molecule inhibitor of PriA-catalyzed duplex DNA unwinding. The compound, CGS 15943, targets Neisseria gonorrhoeae PriA helicase with an IC(50) of 114 ± 24 μM. The PriA helicase of Escherichia coli is also inhibited, although to a lesser extent than N. gonorrhoeae PriA. CGS 15943 decreases rates of PriA-catalyzed ATP hydrolysis and reduces the affinity with which PriA binds DNA. Steady-state kinetic data indicate that CGS 15943 inhibits PriA through a mixed mode of inhibition with respect to ATP and with respect to DNA, indicating that it binds to a site on PriA that participates in both substrate binding and catalysis. Inhibitor binding constants derived from steady-state kinetic experiments reveal that CGS 15943 has the highest binding affinity for the PriA·PriB·ATP complex, intermediate binding affinity for the PriA·PriB·DNA complex, and the lowest binding affinity for the PriA·PriB·DNA·ATP complex, suggesting that PriA assumes different conformations in each of these complexes. We propose that CGS 15943 binds to PriA at a site distinct from the DNA and primary ATP binding sites, perhaps at PriA's weak nucleotide binding site, and induces a conformational change in PriA that renders it less catalytically proficient or prevents conformational changes in PriA that are necessary for ATP hydrolysis and duplex DNA unwinding.

Characterization of 8-hydroxyquinoline derivatives containing aminobenzothiazole as inhibitors of dengue virus type 2 protease in vitro

Four serotypes of dengue virus (DENV1-4), mosquito-borne members of Flaviviridae family cause frequent epidemics causing considerable morbidity and mortality in humans throughout tropical regions of the world. There is no vaccine or antiviral therapeutics available for human use. In a previous study, we reported that compounds containing the 8-hydroxyquinoline (8-HQ) scaffold as inhibitors of West Nile virus serine protease. In this study, we analyzed potencies of some compounds with (8-HQ)-aminobenzothiazole derivatives for inhibition of DENV2 protease in vitro. We identified analogs 1-4 with 2-aminothiazole or 2-aminobenzothiazole scaffold with sub-micromolar potencies (IC(50)) in the in vitro protease assays. The kinetic constant (K(i)) for the most potent 8-HQ-aminobenzothiazole inhibitor (compound 1) with an IC(50) value of 0.91±0.05μM was determined to be 2.36±0.13μM. This compound inhibits the DENV2 NS2B/NS3pro by a competitive mode of inhibition.

1-(5-Bromo-4-phenyl-1,3-thia-zol-2-yl)pyrrolidin-2-one

The asymmetric unit of the title compound, C₁₃H₁₁BrN₂OS, consists of two crystallographically independent mol­ecules (A and B). In each mol­ecule, the pyrrolidine ring adopts an envelope conformation with a methyl­ene C atom as the flap atom. In mol­ecule A, the central thia­zole ring makes a dihedral angle of 36.69 (11)° with the adjacent phenyl ring, whereas the corresponding angle is 36.85 (12)° in mol­ecule B. The pyrrolidine ring is slightly twisted from the thia­zole ring, with C—N—C—N torsion angles of 4.8 (3) and 3.0 (4)° in mol­ecules A and B, respectively. In the crystal, C—H⋯π and π–π [centroid-to-centroid distance = 3.7539 (14) Å] inter­actions are observed. The crystal studied was a pseudo-merohedral twin with twin law (-100 0-10 101) and a refined component ratio of 0.7188 (5):0.2812 (5).

Helicase–primase inhibitors as the potential next generation of highly active drugs against herpes simplex viruses

Since the introduction of the nucleoside analogs decades ago, treatment of herpes simplex virus (HSV) infections has not seen much innovation, except for the development of their respective prodrugs. The inhibitors of the helicase–primase complex of HSV represent a very innovative approach to the treatment of herpesvirus disease, and this article considers the development of some representatives of this class of therapeutics. The molecular and biochemical features of the helicase–primase complex are considered and the development of three inhibitors of helicase–primase, BILS 179 BS, AIC316 and ASP2151, is described. The clinical development of AIC316 is at an advanced stage and displays general safety as well as favorable, long-lasting exposures in healthy volunteers. The first efficacy data from a Phase II trial with more than 150 HSV-2-positive subjects demonstrated dose-dependent antiviral activity.