Herpes simplex virus helicase-primase inhibitors are active in animal models of human disease

Osteonecrosis of the Jaws Associated with Herpes Zoster Infection: A Systematic Review and a Rare Case Report

The investigation's goal was to obtain further knowledge about the connection between Herpes Zoster infection and dentistry therapy for the osteonecrosis of the jaws, combining the review with a case report relevant to the purpose. It is important to study this association because it is a possible additional factor to be considered in the causes of the osteonecrosis of the jaws. We limited our search to English-language papers published between 1 January 2004 and 7 June 2024 in PubMed, Scopus, and Web of Science that were relevant to our topic. In the search approach, the Boolean keywords "Herpes Zoster AND osteonecros*" were used. Results: This study analyzed 148 papers from Web of Science, PubMed, and Scopus, resulting in 95 articles after removing duplicates. Of these, 49 were removed because they were off topic, and 46 were confirmed. This study includes a qualitative analysis of the final 12 articles, removing 34 articles that were off topic. The literature highlights severe oral complications from Herpes Zoster reactivation, emphasizing the need for early diagnosis, comprehensive management, and multidisciplinary care. Treatment strategies include antiviral therapy, pain management, surgical debridement, and antibiotics. Immunocompromised individuals require vigilant monitoring and balanced immunosuppressive therapy. Further research is needed to enhance therapeutic approaches.

N-Heterocycles as Promising Antiviral Agents: A Comprehensive Overview

Viruses are a real threat to every organism at any stage of life leading to extensive infections and casualties. N-heterocycles can affect the viral life cycle at many points, including viral entrance into host cells, viral genome replication, and the production of novel viral species. Certain N-heterocycles can also stimulate the host's immune system, producing antiviral cytokines and chemokines that can stop the reproduction of viruses. This review focused on recent five- or six-membered synthetic N-heterocyclic molecules showing antiviral activity through SAR analyses. The review will assist in identifying robust scaffolds that might be utilized to create effective antiviral drugs with either no or few side effects.

Accelerating antiviral drug discovery: lessons from COVID-19

During the coronavirus disease 2019 (COVID-19) pandemic, a wave of rapid and collaborative drug discovery efforts took place in academia and industry, culminating in several therapeutics being discovered, approved and deployed in a 2-year time frame. This article summarizes the collective experience of several pharmaceutical companies and academic collaborations that were active in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antiviral discovery. We outline our opinions and experiences on key stages in the small-molecule drug discovery process: target selection, medicinal chemistry, antiviral assays, animal efficacy and attempts to pre-empt resistance. We propose strategies that could accelerate future efforts and argue that a key bottleneck is the lack of quality chemical probes around understudied viral targets, which would serve as a starting point for drug discovery. Considering the small size of the viral proteome, comprehensively building an arsenal of probes for proteins in viruses of pandemic concern is a worthwhile and tractable challenge for the community.

Antiviral activity of amide-appended α-hydroxytropolones against herpes simplex virus-1 and -2

α-Hydroxytropolones (αHTs) have potent antiviral activity against herpes simplex virus-1 and -2 (HSV-1 and HSV-2) in cell culture, including against acyclovir-resistant mutants, and as a result have the potential to be developed as antiviral drugs targeting these viruses. We recently described a convenient final-step amidation strategy to their synthesis, and this was used to generate 57 amide-substituted αHTs that were tested against hepatitis B virus. The following manuscript describes the evaluation of this library against HSV-1, as well as a subset against HSV-2. The structure-function analysis obtained from these studies demonstrates the importance of lipophilicity and rigidity to αHT-based anti-HSV potency, consistent with our prior work on smaller libraries. We used this information to synthesize and test a targeted library of 4 additional amide-appended αHTs. The most potent of this new series had a 50% effective concentration (EC₅₀) for viral inhibition of 72 nM, on par with the most potent αHT antivirals we have found to date. Given the ease of synthesis of amide-appended αHTs, this new class of antiviral compounds and the chemistry to make them should be highly valuable in future anti-HSV drug development.

Quindoline-derivatives display potent G-quadruplex-mediated antiviral activity against herpes simplex virus 1

G-quadruplexes (G4s) are non-canonical nucleic acid structures that regulate key biological processes, from transcription to genome replication both in humans and viruses. The herpes simplex virus-1 (HSV-1) genome is prone to form G4s that, along with proteins, regulate its viral cycle. General G4 ligands have been shown to hamper the viral cycle, pointing to viral G4s as original antiviral targets. Because cellular G4s are also normally present in infected cells, the quest for improved anti-HSV-1 G4 ligands is still open. Here, we evaluated a series of new quindoline-derivatives which showed high binding to and stabilization of the viral G4s. They displayed nanomolar-range anti-HSV-1 activity paralleled by negligible cytotoxicity in human cells, thus proving remarkable selectivity. The best-in-class compound inhibited the viral life cycle at the early times post infection up to the step of viral genome replication. In infected human cells, it reduced expression of ICP4, the main viral transcription factor, by stabilizing the G4s embedded in ICP4 promoter. Quindoline-derivatives thus emerge as a new class of G4 ligands with potent dual anti HSV-1 activity.

The Discovery of Novel Ferulic Acid Derivatives Incorporating Substituted Isopropanolamine Moieties as Potential Tobacco Mosaic Virus Helicase Inhibitors

Target-based drug design, a high-efficiency strategy used to guide the development of novel pesticide candidates, has attracted widespread attention. Herein, various natural-derived ferulic acid derivatives incorporating substituted isopropanolamine moieties were designed to target the tobacco mosaic virus (TMV) helicase. Bioassays demonstrating the optimized A₁₉, A₂₀, A₂₉, and A₃₁ displayed excellent in vivo antiviral curative abilities, affording corresponding EC₅₀ values of 251.1, 336.2, 347.1, and 385.5 μg/mL, which visibly surpassed those of commercial ribavirin (655.0 μg/mL). Moreover, configurational analysis shows that the R-forms of target compounds were more beneficial to aggrandize antiviral profiles. Mechanism studies indicate that R-A₁₉ had a strong affinity (K_d = 5.4 μM) to the TMV helicase and inhibited its ability to hydrolyze ATP (50.61% at 200 μM). Meanwhile, A₁₉ could down-regulate the expression of the TMV helicase gene in the host to attenuate viral replication. These results illustrate the excellent inhibitory activity of A₁₉ towards the TMV helicase. Additionally, docking simulations uncovered that R-A₁₉ formed more hydrogen bonds with the TMV helicase in the binding pocket. Recent studies have unambiguously manifested that these designed derivatives could be considered as promising potential helicase-based inhibitors for plant disease control.

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.

Clinical Management of Herpes Simplex Virus Keratitis

Herpes simplex virus (HSV) keratitis is one of the leading causes of blindness worldwide. Additionally, up to 90% of the population in some countries is seropositive for HSV. HSV can cause a wide spectrum of ocular disease ranging from blepharitis to retinitis. Although the initial clinical expressions of HSV-1 and HSV-2 are similar, HSV-2 has been reported more frequently in association with recurrent HSV disease. Besides irreversible vision loss from keratitis, HSV also causes encephalitis and genital forms of the disease. Despite these statistics, there remains no vaccine against HSV. Current treatment therapies for related ocular diseases include the use of oral and topical antivirals and topical corticosteroids. While effective in many cases, they fail to address the latency and elimination of the virus, making it ineffective in addressing recurrences, a factor which increases the risk of vision loss. As such, there is a need for continued research of other potential therapeutic targets. This review utilized several published articles regarding the manifestations of HSV keratitis, antiviral immune responses to HSV infection, and clinical management of HSV keratitis. This review will summarize the current knowledge on the host–virus interaction in HSV infections, as well as highlighting the current and potential antiviral therapeutics.

40 Years after the Registration of Acyclovir: Do We Need New Anti-Herpetic Drugs?

Herpes simplex virus types 1 and 2 HSV1 and 2, namely varicella-zoster VZV and cytomegalovirus CMV, are among the most common pathogens worldwide. They remain in the host body for life. The course of infection with these viruses is often asymptomatic or mild and self-limiting, but in immunocompromised patients, such as solid organ or bone marrow transplant recipients, the course can be very severe or even life-threatening. Unfortunately, in the latter group, the highest percentage of infections with strains resistant to routinely used drugs is observed. On the other hand, frequent recurrences of genital herpes can be a problem even in people with normal immunity. Genital herpes also increases the risk of acquiring sexually transmitted diseases, including HIV infection and, if present in pregnant women, poses a risk to the fetus and newborn. Even more frequently than herpes simplex, congenital infections can be caused by cytomegalovirus. We present the most important anti-herpesviral agents, the mechanisms of resistance to these drugs, and the associated mutations in the viral genome. Special emphasis was placed on newly introduced drugs such as maribavir and brincidofovir. We also briefly discuss the most promising substances in preclinical testing as well as immunotherapy options and vaccines currently in use and under investigation.

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.

Characteristics of Helicase-primase Inhibitor Amenamevir-resistant Herpes Simplex Virus

The antiherpetic drug amenamevir (AMNV) inhibits the helicase-primase complex of herpes simplex virus type 1 (HSV-1), HSV-2 and varicella-zoster virus directly as well as inhibiting the replication of these viruses. Although several mutated HSV viruses resistant to helicase-primase inhibitors have been reported, the mutations contributing to the resistance remain unclear as recombinant viruses containing a single mutation have not been analyzed. We obtained AMNV-resistant viruses with amino acid substitutions by several passages under AMNV-treatment. Twenty HSV-1 and 19 HSV-2 mutants with mutation(s) in UL5 helicase and/or UL52 primase, but not in co-factor UL8, were isolated. The mutations in UL5 were located downstream of motif IV, with UL5 K356N in HSV-1 and K355N in HSV-2, in particular, identified as having the highest frequency: 9/20 and 9/19, respectively. We generated recombinant AMNV-resistant HSV-1 with a single amino acid substitution using BAC mutagenesis. As a result, G352C in UL5 helicase and F360C/V and N902T in UL52 primase were identified as novel mutations. The virus with K356N in UL5 showed 10-fold higher AMNV resistance than did other mutants, and showed equivalent viral growth in vitro and virulence in vivo as the parent HSV-1, although other mutants showed attenuated virulence. All recombinant viruses were susceptible to the other antiherpetic drugs, acyclovir and foscarnet. In conclusion, based on BAC mutagenesis, this study identified for the first time mutations in UL5 and UL52 that contributed to AMNV resistance, and found that a mutant with the most frequent K356N mutation in HSV-1 maintained viral growth and virulence equivalent to the parent virus.

Repurposing potential of posaconazole and grazoprevir as inhibitors of SARS-CoV-2 helicase

As the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) pandemic engulfs millions worldwide, the quest for vaccines or drugs against the virus continues. The helicase protein of SARS-CoV-2 represents an attractive target for drug discovery since inhibition of helicase activity can suppress viral replication. Using in silico approaches, we have identified drugs that interact with SARS-CoV-2 helicase based on the presence of amino acid arrangements matching binding sites of drugs in previously annotated protein structures. The drugs exhibiting an RMSD of ≤ 3.0 Å were further analyzed using molecular docking, molecular dynamics (MD) simulation, and post-MD analyses. Using these approaches, we found 12 drugs that showed strong interactions with SARS-CoV-2 helicase amino acids. The analyses were performed using the recently available SARS-CoV-2 helicase structure (PDB ID: 5RL6). Based on the MM-GBSA approach, out of the 12 drugs, two drugs, namely posaconazole and grazoprevir, showed the most favorable binding energy, - 54.8 and - 49.1 kcal/mol, respectively. Furthermore, of the amino acids found conserved among all human coronaviruses, 10/11 and 10/12 were targeted by, respectively, grazoprevir and posaconazole. These residues are part of the crucial DEAD-like helicase C and DEXXQc_Upf1-like/ DEAD-like helicase domains. Strong interactions of posaconazole and grazoprevir with conserved amino acids indicate that the drugs can be potent against SARS-CoV-2. Since the amino acids are conserved among the human coronaviruses, the virus is unlikely to develop resistance mutations against these drugs. Since these drugs are already in use, they may be immediately repurposed for SARS-CoV-2 therapy.

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.

Targeting herpes simplex virus with CRISPR-Cas9 cures herpetic stromal keratitis in mice

Herpes simplex virus type 1 (HSV-1) is a leading cause of infectious blindness. Current treatments for HSV-1 do not eliminate the virus from the site of infection or latent reservoirs in the trigeminal ganglia. Here, we target HSV-1 genomes directly using mRNA-carrying lentiviral particles that simultaneously deliver SpCas9 mRNA and viral-gene-targeting guide RNAs (designated HSV-1-erasing lentiviral particles, termed HELP). We show that HELP efficiently blocks HSV-1 replication and the occurrence of herpetic stromal keratitis (HSK) in three different infection models. HELP was capable of eliminating the viral reservoir via retrograde transport from corneas to trigeminal ganglia. Additionally, HELP inhibited viral replication in human-derived corneas without causing off-target effects, as determined by whole-genome sequencing. These results support the potential clinical utility of HELP for treating refractory HSK.

Antiviral Drugs Against Herpesviruses

The discovery of the nucleoside analogue, acyclovir, represented a milestone in the management of infections caused by herpes simplex virus and varicella-zoster virus. Ganciclovir, another nucleoside analogue, was then used for the management of systemic and organ-specific human cytomegalovirus diseases. The pyrophosphate analogue, foscarnet, and the nucleotide analogue, cidofovir, have been approved subsequently and constitute the second-line antiviral drugs. However, the viral DNA polymerase is the ultimate target of all these antiviral agents with a possible emergence of cross-resistance between these drugs. Recently, letermovir that targets the viral terminase complex was approved for the prophylaxis of human cytomegalovirus infections in hematopoietic stem cell transplant recipients. Other viral targets such as the protein kinase and the helicase-primase complex are also evaluated for the development of novel potent inhibitors against herpesviruses.

Force-dependent stimulation of RNA unwinding by SARS-CoV-2 nsp13 helicase

The superfamily 1 helicase nonstructural protein 13 (nsp13) is required for SARS-CoV-2 replication. The mechanism and regulation of nsp13 has not been explored at the single-molecule level. Specifically, force-dependent unwinding experiments have yet to be performed for any coronavirus helicase. Here, using optical tweezers, we find that nsp13 unwinding frequency, processivity, and velocity increase substantially when a destabilizing force is applied to the RNA substrate. These results, along with bulk assays, depict nsp13 as an intrinsically weak helicase that can be activated >50-fold by piconewton forces. Such force-dependent behavior contrasts the known behavior of other viral monomeric helicases, such as hepatitis C virus NS3, and instead draws stronger parallels to ring-shaped helicases. Our findings suggest that mechanoregulation, which may be provided by a directly bound RNA-dependent RNA polymerase, enables on-demand helicase activity on the relevant polynucleotide substrate during viral replication.

Herpes Simplex Virus 1 (HSV-1) 0ΔNLS Live-Attenuated Vaccine Protects against Ocular HSV-1 Infection in the Absence of Neutralizing Antibody in HSV-1 gB T Cell Receptor-Specific Transgenic Mice

The contribution of T cell and antibody responses following vaccination in resistance to herpes simplex virus 1 (HSV-1) infection continues to be rigorously investigated. In the present article, we explore the contribution of CD8+ T cells specific for the major antigenic epitope for HSV-1 glycoprotein B (gB498-505, gB) in C57BL/6 mice using a transgenic mouse (gBT-I.1) model vaccinated with HSV-1 0ΔNLS. gBT-I.1-vaccinated mice did not generate a robust neutralization antibody titer in comparison to the HSV-1 0ΔNLS-vaccinated wild-type C57BL/6 counterpart. Nevertheless, the vaccinated gBT-I.1 mice were resistant to ocular challenge with HSV-1 compared to vehicle-vaccinated animals based on survival and reduced corneal neovascularization but displayed similar levels of corneal opacity. Whereas there was no difference in the virus titer recovered from the cornea comparing vaccinated mice, HSV-1 0ΔNLS-vaccinated animals possessed significantly less infectious virus during acute infection in the trigeminal ganglia (TG) and brain stem compared to the control-vaccinated group. These results correlated with a significant increase in gB-elicited interferon-γ (IFN-γ), granzyme B, and CD107a and a reduction in lymphocyte activation gene 3 (LAG-3), programmed cell death 1 (PD-1), and T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3) expressed by TG infiltrating gB-specific CD8+ T cells from the HSV-1 0ΔNLS-vaccinated group. Antibody depletion of CD8+ T cells in HSV-1 0ΔNLS-vaccinated mice rendered animals highly susceptible to virus-mediated mortality similar to control-vaccinated mice. Collectively, the HSV-1 0ΔNLS vaccine is effective against ocular HSV-1 challenge, reducing ocular neovascularization and suppressing peripheral nerve virus replication in the near absence of neutralizing antibody in this unique mouse model.IMPORTANCE The role of CD8+ T cells in antiviral efficacy using a live-attenuated virus as the vaccine is complicated by the humoral immune response. In the case of the herpes simplex virus 1 (HSV-1) 0ΔNLS vaccine, the correlate of protection has been defined to be primarily antibody driven. The current study shows that in the near absence of anti-HSV-1 antibody, vaccinated mice are protected from subsequent challenge with wild-type HSV-1 as measured by survival. The efficacy is lost following depletion of CD8+ T cells. Whereas increased survival and reduction in virus replication were observed in vaccinated mice challenged with HSV-1, cornea pathology was mixed with a reduction in neovascularization but no change in opacity. Collectively, the study suggests CD8+ T cells significantly contribute to the host adaptive immune response to HSV-1 challenge following vaccination with an attenuated virus, but multiple factors are involved in cornea pathology in response to ocular virus challenge.

A Novel, Broad-Acting Peptide Inhibitor of Double-Stranded DNA Virus Gene Expression and Replication

Viral infections are a global disease burden with only a limited number of antiviral agents available. Due to newly emerging viral pathogens and increasing occurrence of drug resistance, there is a continuous need for additional therapeutic options, preferably with extended target range. In the present study, we describe a novel antiviral peptide with broad activity against several double-stranded DNA viruses. The 22-mer peptide TAT-I24 potently neutralized viruses such as herpes simplex viruses, adenovirus type 5, cytomegalovirus, vaccinia virus, and simian virus 40 in cell culture models, while being less active against RNA viruses. The peptide TAT-I24 therefore represents a novel and promising drug candidate for use against double-stranded DNA viruses.

Force-dependent stimulation of RNA unwinding by SARS-CoV-2 nsp13 helicase

The superfamily-1 helicase non-structural protein 13 (nsp13) is required for SARS-CoV-2 replication, making it an important antiviral therapeutic target. The mechanism and regulation of nsp13 has not been explored at the single-molecule level. Specifically, force-dependent unwinding experiments have yet to be performed for any coronavirus helicase. Here, using optical tweezers, we find that nsp13 unwinding frequency, processivity, and velocity increase substantially when a destabilizing force is applied to the dsRNA, suggesting a passive unwinding mechanism. These results, along with bulk assays, depict nsp13 as an intrinsically weak helicase that can be potently activated by picoNewton forces. Such force-dependent behavior contrasts the known behavior of other viral monomeric helicases, drawing stronger parallels to ring-shaped helicases. Our findings suggest that mechanoregulation, which may be provided by a directly bound RNA-dependent RNA polymerase, enables on-demand helicase activity on the relevant polynucleotide substrate during viral replication.

Exploiting Existing Molecular Scaffolds for Long-Term COVID Treatment

Discovery and development of COVID-19 prophylactics and treatments remains a global imperative. This perspective provides an overview of important molecular pathways involved in the viral life cycle of SARS-CoV-2, the infectious agent of COVID-19. We highlight past and recent findings in essential coronavirus proteins, including RNA polymerase machinery, proteases, and fusion proteins, that offer opportunities for the design of novel inhibitors of SARS-CoV-2 infection. By discussing the current inventory of viral inhibitors, we identify molecular scaffolds that may be improved by medicinal chemistry efforts for effective therapeutics to treat current and future coronavirus-caused diseases.

Viral ribonucleotide reductase attenuates the anti-herpes activity of acyclovir in contrast to amenamevir

Amenamevir is a helicase-primase inhibitor of herpes simplex virus (HSV) and varicella-zoster virus (VZV) and is used for the treatment of herpes zoster in Japan. The half maximal effective concentrations (EC₅₀s) of acyclovir and sorivudine for VZV increased as the time of treatment was delayed from 6 to 18 h after infection, while those of amenamevir and foscarnet were not affected. Susceptibility of infected cells at 0 and 18 h after infection was examined with four anti-herpes drugs, and the fold increases in EC₅₀ for acyclovir, sorivudine, amenamevir, and foscarnet were 13.1, 6.3, 1.3, and 1.0, respectively. The increase in the EC₅₀s for acyclovir in the late phase of infection in VZV and HSV was abolished by hydroxyurea, a ribonucleotide reductase (RR) inhibitor. The common mechanism affecting antiviral activities of acyclovir to HSV and VZV was examined in HSV-infected cells. The amount of HSV DNA in cells treated with amenamevir at 10 x EC₅₀ was similar at 0 and 12 h but less than that in cells treated with acyclovir at 10 x EC₅₀. dGTP, produced through viral RR, peaked at 4 h and decreased thereafter as it was consumed by viral DNA synthesis. Because acyclovir and amenamevir inhibited viral DNA synthesis, thus making dGTP unnecessary, dGTP was significantly more abundant in the presence of acyclovir and amenamevir than in untreated, infected cells. Abundant dGTP supplied by RR may compete with acyclovir triphosphate and attenuate its antiviral activity. In contrast, abundant dGTP did not influence the inhibitory action of amenamevir on viral helicase-primase activity. ATP was significantly decreased at 12 h after infection and significantly more abundant in untreated infected cells compared to cells treated with acyclovir and amenamevir. The anti-herpetic activity of amenamevir was not affected by the replication cycle of VZV and HSV, indicating the suitability of amenamevir for the treatment of herpes zoster and suppressive therapy for genital herpes.

Synthesis, Anti-Varicella-Zoster Virus and Anti-Cytomegalovirus Activity of 4,5-Disubstituted 1,2,3-(1H)-Triazoles

BACKGROUND

Clinical drugs for herpesvirus exhibit high toxicity and suffer from significant drug resistance. The development of new, effective, and safe anti-herpesvirus agents with different mechanisms of action is greatly required.

OBJECTIVE

Novel inhibitors against herpesvirus with different mechanisms of action from that of clinical drugs.

METHODS

A series of novel 5-(benzylamino)-1H-1,2,3-triazole-4-carboxamides were efficiently synthesized and EC50 values against Human Cytomegalovirus (HCMV), Varicella-Zoster Virus (VZV) and Herpes Simplex Virus (HSV) were evaluated in vitro.

RESULTS

Some compounds present antiviral activity. Compounds 5s and 5t are potent against both HCMV and VZV. Compounds 5m, 5n, 5s, and 5t show similar EC50 values against both TK+ and TK- VZV strains.

CONCLUSION

5-(Benzylamino)-1H-1, 2,3-triazole-4-carboxamides are active against herpesviruses and their activity is remarkably affected by the nature and the position of substituents in the benzene ring. The results indicate that these derivatives are independent of the viral thymidine kinase (TK) for activation, which is indispensable for current drugs. Their mechanisms of action may differ from those of the clinic anti-herpesvirus drugs.

Different solid forms for optimizing route of administration of the herpes drug Pritelivir

Pritelivir (AIC316, BAY 57-1293) was discovered as a highly potent drug against herpes simplex viruses with a novel mode of action, i.e. inhibition of the viral helicase-primase. A side by side comparison of the oral form against Valtrex™ in patients with genital herpes, showed superiority in phase II testing for Pritelivir. A number of different solid forms have been generated for additional, e.g. systemic, or topical applications.

Design, synthesis and molecular docking of pyrazolo [3,4d] thiazole hybrids as potential anti-HIV-1 NNRT inhibitors

A series of pyrazolo[3.4,d]thiazole hybrids 6 were synthesized from 5-arylidene-2-imino-3-(4-arylthiazol-2-yl)-thiazolidin-4-ones 5. The 5-arylidene-2-imino-3-(4-arylthiazol-2-yl)-thiazolidin-4-ones 5 were synthesized from 2-amino-4-arylthiazoles 1 and 2-chloro-acetamido-4-arylthiazoles 2 via the formation of 2-imino-3-(4-substituted-arylthiazol-2-yl)-thiazolidin-4-ones 3 using substituted aldehydes 4. The 5-acrylidene derivative 5 on cyclisation with phenyl hydrazine give the pyrazolo [3, 4, d] thiazole derivatives 6. The obtained pyrazolo [3.4, d]thiazole derivatives were studied as anti-HIV-1 NNRT inhibitors. It was found that these compounds might have potent RT inhibition activity.

A Preclinical Model for Studying Herpes Simplex Virus Infection

Herpes simplex virus (HSV) infections can cause considerable morbidity. Currently, nucleoside analogues such as acyclovir are widely used for treatment. However, HSV infections resistant to these drugs are a clinical problem among immunocompromised patients. To provide more efficient therapy and to counteract resistance, a different class of antiviral compounds has been developed. Pritelivir, a helicase primase inhibitor, represents a promising candidate for improved therapy. Here, we established an HSV-1 infection model on microneedle-pretreated human skin ex vivo. We identified HSV-1–specific histological changes (e.g., cytopathic effects, multinucleated giant cells), down-regulation of nectin-1, nuclear translocation of NF-κB (p65), interferon regulatory factor 3 (IRF3), and signaling of the IFN-inducible protein MxA. Accordingly, this model was used to test the potency of pritelivir compared with the standard drug acyclovir. We discovered that both drugs had a comparable efficacy for inhibiting HSV-1 replication, suggesting that pritelivir could be an alternative therapeutic agent for patients infected with acyclovir-resistant strains. To our knowledge, we present a previously unreported ex vivo HSV-1 infection model with abdominal human skin to test antiviral drugs, thus bridging the gap between in vitro and in vivo drug screening and providing a valuable preclinical platform for HSV research.

Antiviral efficacy of the helicase-primase inhibitor amenamevir in murine models of severe herpesvirus infection

Existing treatments have limited efficacy against severe infection associated with herpes simplex virus (HSV) and herpes zoster virus (VZV), particularly in immunocompromized patients and those with multidermatomal infection. This issue, along with issues regarding drug resistance, support the need for improved therapeutic options. To investigate the antiviral effect of amenamevir, a VZV and HSV helicase-primase inhibitor, in severe infection conditions, mouse models of severe HSV-1 infection were developed by immunosuppression or multidermatomal infection. Mice with cyclosporin-induced immunosuppression and HSV-1 infection via inoculation of a dorsolateral area of skin were orally treated with amenamevir (10-100 mg/kg/day) for different durations (2-5 days). Immunosuppressed mice maintained high skin HSV-1 titers in the absence of treatment. Amenamevir successfully reduced HSV-1 titers at all tested doses in immunosuppressed mice, but required a longer treatment period to avoid a rebound in viral titers due to immunosuppression. To compare the efficacy of amenamevir and valacyclovir, a murine model of multidermatomal HSV-1 infection was generated by scarifying the dorsolateral area of skin in a line and inoculating broadly with HSV-1. The mice were treated with amenamevir or valacyclovir starting on Day 3, 4, or 5 post-infection for 5 days. Although both drugs similarly reduced disease scores when treatment was started on Day 3, amenamevir also reduced disease severity when treatment was initiated on Day 4, whereas valacyclovir did not. Amenamevir was not affected by the host's immune status in terms of effective oral doses and was more efficacious in treating severe cutaneous infection even when treatment initiation was delayed.

Recent Advances Towards the Development of a Potent Antiviral Against the Hepatitis E Virus

Hepatitis E virus (HEV) is one of the leading causes of acute viral hepatitis. It also causes acute liver failure and acute-on-chronic liver failure in many patients, such as those suffering from other infections/liver injuries or organ transplant/chemotherapy recipients. Despite widespread sporadic and epidemic incidents, there is no specific treatment against HEV, justifying an urgent need for developing a potent antiviral against it. This review summarizes the known antiviral candidates and provides an overview of the potential targets for the development of specific antivirals against HEV.

MODERN ETHIOTROPIC CHEMOTHERAPY OF HERPESVIRUS INFECTIONS: ADVANCES, NEW TRENDS AND PERSPECTIVES. ALPHAHERPESVIRUSES (PART II)

A key role in the treatment of herpesviral infections is played by modified nucleosides and their predecessors - acyclovir, its L-valine ester (valaciclovir) and famciclovir (prodrug of penciclovir). The biological activity of compounds of this class is determined by their similarity to natural nucleosides. After phosphorylation by viral thymidine kinase and then cell enzymes to the triphosphate forms, acyclovir and penciclovir inhibit the activity of viral DNA polymerase and synthesis of viral DNA. The increasing role of herpesvirus infections in human infectious pathology, as well as the development of drug resistance in viruses, mainly in patients with immunodeficiencies of various origins, necessitate the search for new compounds possessing anti-herpesvirus activity, using as a biological target not DNA polymerase, but other viral proteins and enzymes, unique or different from cellular proteins, performing similar functions.

The Human Replicative Helicase, the CMG Complex, as a Target for Anti-cancer Therapy

DNA helicases unwind or rearrange duplex DNA during replication, recombination and repair. Helicases of many pathogenic organisms such as viruses, bacteria, and protozoa have been studied as potential therapeutic targets to treat infectious diseases, and human DNA helicases as potential targets for anti-cancer therapy. DNA replication machineries perform essential tasks duplicating genome in every cell cycle, and one of the important functions of these machineries are played by DNA helicases. Replicative helicases are usually multi-subunit protein complexes, and the minimal complex active as eukaryotic replicative helicase is composed of 11 subunits, requiring a functional assembly of two subcomplexes and one protein. The hetero-hexameric MCM2-7 helicase is activated by forming a complex with Cdc45 and the hetero-tetrameric GINS complex; the Cdc45-Mcm2-7-GINS (CMG) complex. The CMG complex can be a potential target for a treatment of cancer and the feasibility of this replicative helicase as a therapeutic target has been tested recently. Several different strategies have been implemented and are under active investigations to interfere with helicase activity of the CMG complex. This review focuses on the molecular function of the CMG helicase during DNA replication and its relevance to cancers based on data published in the literature. In addition, current efforts made to identify small molecules inhibiting the CMG helicase to develop anti-cancer therapeutic strategies were summarized, with new perspectives to advance the discovery of the CMG-targeting drugs.

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.

Pharmacokinetics and Safety of Amenamevir in Healthy Subjects: Analysis of Four Randomized Phase 1 Studies

Introduction

Amenamevir (ASP2151) is a nonnucleoside antiherpesvirus compound available for the treatment of varicella–zoster virus infections. In this article we summarize the findings of four phase 1 studies in healthy participants.

Methods

Four randomized phase 1 studies investigated the safety and pharmacokinetics of single and multiple doses of amenamevir, including the assessment of age group effect (nonelderly vs elderly), food effect, and the relative bioavailability of two formulations. Amenamevir was administered orally at various doses as a single dose (5–2400 mg) or daily (300 or 600 mg/day) for 7 days.

Results

Following single and multiple oral doses, amenamevir demonstrated a less than dose proportional increase in the pharmacokinetic parameters area under the plasma drug concentration versus time curve from time zero to infinity (AUC_inf) and C_max. After single and multiple oral 300-mg doses of amenamevir, no apparent differences in pharmacokinetics were observed between nonelderly and elderly participants. In contrast, with the amenamevir 600-mg dose both the area under the plasma drug concentration versus time curve from time zero to 24 h and C_max were slightly increased and renal clearance was decreased in elderly participants. The pharmacokinetics of amenamevir was affected by food, with AUC_inf increased by about 90%. In the bioavailability study, AUC_inf and C_max were slightly lower following tablet versus capsule administration (decreased by 14 and 12%, respectively), with relative bioavailability of 86%. The different amenamevir doses and formulations were safe and well tolerated; no deaths or serious adverse events were reported.

Conclusion

Amenamevir had less than dose proportional pharmacokinetic characteristics. Age may have an influence on amenamevir pharmacokinetics; however, the effect was considered minimal. The pharmacokinetics of amenamevir were affected by food, with AUC_inf almost doubling when amenamevir was administered with food. The concentration versus time profile of the tablet was slightly lower than that of the capsule; the relative bioavailability of the tablet versus the capsule was 86%. Amenamevir was safe and well tolerated in the dose range investigated.

Funding

Astellas Pharma.

Trial registration

ClinicalTrials.gov identifiers NCT02852876 (15L-CL-002) and NCT02796118 (15L-CL-003).

Electronic supplementary material

The online version of this article (10.1007/s12325-017-0642-4) contains supplementary material, which is available to authorized users.

The Influence of Hepatic and Renal Impairment on the Pharmacokinetics of a Treatment for Herpes Zoster, Amenamevir (ASP2151): Phase 1, Open-Label, Single-Dose, Parallel-Group Studies

INTRODUCTION

Amenamevir (ASP2151) is a nonnucleoside human herpesvirus helicase-primase inhibitor that was approved in Japan for the treatment of herpes zoster (shingles) in 2017. This article reports the results of two clinical trials that investigated the effects of renal and hepatic impairment on the pharmacokinetics of amenamevir.

METHODS

These studies were phase 1, open-label, single-dose (oral 400 mg), parallel-group studies evaluating the pharmacokinetics, safety, and tolerability of amenamevir in healthy participants and participants with moderate hepatic impairment and mild, moderate, and severe renal impairment.

RESULTS

In the hepatic impairment study, the pharmacokinetic profile of amenamevir in participants with moderate hepatic impairment was generally similar to that of participants with normal hepatic function. In the renal impairment study, the area under the amenamevir concentration versus time curve from the time of dosing up to the time of the last sample with extrapolation to infinity of the terminal phase was increased by 78.1% in participants with severe renal impairment. There was a positive relationship between creatinine clearance and oral and renal clearance for amenamevir in the renal impairment study. In both studies, amenamevir was safe and well tolerated.

CONCLUSION

The findings of the hepatic impairment study indicate that no dosing adjustment is required in patients with moderate hepatic impairment. In the renal impairment study, systemic amenamevir exposure was increased by renal impairment. However, it is unlikely that renal impairment will have a significant effect on the safety of amenamevir given that in previous pharmacokinetic and safety studies in healthy individuals amenamevir was safe and well tolerated after a single dose (5-2400 mg, fasted condition) and repeated doses for 7 days (300 or 600 mg, fed condition), and the amount of amenamevir exposure in the renal impairment study was covered by those studies. These findings suggest that amenamevir does not require dosage reduction in accordance with the creatinine clearance FUNDING: Astellas Pharma.

Identification of a Ligand-Binding Site on the Staphylococcus aureus DnaG Primase C-Terminal Domain

The interface between the DnaG primase C-terminal domain (CTD) and the N-terminal domain of DnaB helicase is essential for bacterial DNA replication because it allows coordinated priming of DNA synthesis at the replication fork while the DNA is being unwound. Because these two proteins are conserved in all bacteria and distinct from those in eukaryotes, their interface is an attractive antibiotic target. To learn more about this interface, we determined the solution structure and dynamics of the DnaG primase CTD from Staphylococcus aureus, a medically important bacterial species. Comparison with the known primase CTD structures shows there are two biologically relevant conformations, an open conformation that likely binds to DnaB helicase and a closed conformation that does not. The S. aureus primase CTD is in the closed conformation, but nuclear magnetic resonance (NMR) dynamic studies indicate there is considerable movement in the linker between the two subdomains and that N564 is the most dynamic residue within the linker. A high-throughput NMR ligand affinity screen identified potential binding compounds, among which were acycloguanosine and myricetin. Although the affinity for these compounds and adenosine was in the millimolar range, all three bind to a common pocket that is present only on the closed conformation of the CTD. This binding pocket is at the opposite end of helices 6 and 7 from N564, the key hinge residue. The identification of this binding pocket should allow the development of stronger-binding ligands that can prevent formation of the CTD open conformation that binds to DnaB helicase.

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.

Luteolin inhibits Epstein-Barr virus lytic reactivation by repressing the promoter activities of immediate-early genes

The lytic reactivation of Epstein-Barr virus (EBV) has been reported to be strongly associated with several human diseases, including nasopharyngeal carcinoma (NPC). Inhibition of the EBV lytic cycle has been shown to be of great benefit in the treatment of EBV-associated diseases. The administration of dietary compounds is safer and more convenient than other approaches to preventing EBV reactivation. We screened several dietary compounds for their ability to inhibit EBV reactivation in NPC cells. Among them, the flavonoid luteolin showed significant inhibition of EBV reactivation. Luteolin inhibited protein expression from EBV lytic genes in EBV-positive epithelial and B cell lines. It also reduced the numbers of EBV-reactivating cells detected by immunofluorescence analysis and reduced the production of virion. Furthermore, luteolin reduced the activities of the promoters of the immediate-early genes Zta (Zp) and Rta (Rp) and also inhibited Sp1-luc activity, suggesting that disruption of Sp1 binding is involved in the inhibitory mechanism. CHIP analysis revealed that luteolin suppressed the activities of Zp and Rp by deregulating Sp1 binding. Taken together, luteolin inhibits EBV reactivation by repressing the promoter activities of Zp and Rp, suggesting luteolin is a potential dietary compound for prevention of virus infection.

The Spring α-Helix Coordinates Multiple Modes of HCV (Hepatitis C Virus) NS3 Helicase Action

Genomic DNA replication requires helicases to processively unwind duplexes. Although helicases encoded by positive-strand RNA viruses are necessary for RNA genome replication, their functions are not well understood. We determined structures of the hepatitis C virus helicase (NS3h) in complex with the transition state ATP mimic ADP·AlF4 (-) and compared them with the previous nucleic acid-associated ternary complexes. The results suggested that nucleic acid binding promotes a structural change of the spring helix at the transition state, optimizing the interaction network centered on the nucleophilic water. Analysis of ATP hydrolysis with and without conformational restraints on the spring helix further supported the importance of its action for both nucleic acid-stimulated and basal catalysis. We further found that an F238P substitution, predicted to destabilize the helix, diminished viral RNA replication without significantly affecting ATP-dependent duplex unwinding. The stability of the secondary structure, thus, seems critical for additional functions of NS3h. Taken together, the results suggest that the spring helix may be central to the coordination of multiple modes of NS3h action. Further characterization centered on this element may help understand the molecular details of how the viral helicase facilitates RNA replication. This new structural information may also aid efforts to develop specific inhibitors targeting this essential viral enzyme.

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.

Antiviral agents against equid alphaherpesviruses: Current status and perspectives

Equid herpesvirus infections cause respiratory, neurological and reproductive syndromes. Despite preventive and control measures and the availability of vaccines and immunostimulants, herpesvirus infections still constitute a major threat to equine health and for the equine industry worldwide. Antiviral drugs, particularly nucleoside analogues and foscarnet, are successfully used for the treatment of human alphaherpesvirus infections. In equine medicine, the use of antiviral medications in alphaherpesvirus infections would decrease the excretion of virus and diminish the risk of contagion and the convalescent time in affected horses, and would also improve the clinical outcome of equine herpesvirus myeloencephalopathy. The combined use of antiviral compounds, along with vaccines, immune modulators, and effective preventive and control measures, might be beneficial in diminishing the negative impact of alphaherpesvirus infections in horses. The purpose of this review is to analyse the available information regarding the use of antiviral agents against alphaherpesviruses, with particular emphasis on equine alphaherpesvirus infections.

Thiophene and benzodioxole appended thiazolyl-pyrazoline compounds: Microwave assisted synthesis, antimicrobial and molecular docking studies

A novel series of thiophene and benzodioxole appended thiazolyl-pyrazoline derivatives have been designed, synthesized and evaluated against different bacteria and fungi. The antimicrobial activity of the synthesized compounds were screened using MIC method and were proved synthesized compounds 7o, 7r and 7t to show good antimicrobial activity against bacteria and fungi. In silico molecular docking studies revealed that all the synthesized molecules showed good binding energy toward the target receptor DNA topoisomerase IV, ranging from -10.42 to -11.66 kcal/mol.

Label-free luminescence switch-on detection of hepatitis C virus NS3 helicase activity using a G-quadruplex-selective probe

A series of luminescent Ir(iii) complexes were synthesised and evaluated for their ability to act as luminescent G-quadruplex-selective probes. The Ir(iii) complex 9, [Ir(phq)2(phen)]PF6 (where phq = 2-phenylquinoline; phen = 1,10-phenanthroline), exhibited high luminescence in the presence of G-quadruplex DNA compared to dsDNA and ssDNA, and was employed to construct a label-free G-quadruplex-based assay for hepatitis C virus NS3 helicase activity in aqueous solution. Moreover, the application of the assay for screening potential helicase inhibitors was demonstrated. To our knowledge, this is the first G-quadruplex-based assay for helicase activity.

Benzothiazole and Pyrrolone Flavivirus Inhibitors Targeting the Viral Helicase

The flavivirus nonstructural protein 3 (NS3) is a protease and helicase, and on the basis of its similarity to its homologue encoded by the hepatitis C virus (HCV), the flavivirus NS3 might be a promising drug target. Few flavivirus helicase inhibitors have been reported, in part, because few specific inhibitors have been identified when nucleic acid unwinding assays have been used to screen for helicase inhibitors. To explore the possibility that compounds inhibiting NS3-catalyzed ATP hydrolysis might function as antivirals even if they do not inhibit RNA unwinding in vitro, we designed a robust dengue virus (DENV) NS3 ATPase assay suitable for high-throughput screening. Members of two classes of inhibitory compounds were further tested in DENV helicase-catalyzed RNA unwinding assays, assays monitoring HCV helicase action, subgenomic DENV replicon assays, and cell viability assays and for their ability to inhibit West Nile virus (Kunjin subtype) replication in cells. The first class contained analogues of NIH molecular probe ML283, a benzothiazole oligomer derived from the dye primuline, and they also inhibited HCV helicase and DENV NS3-catalyzed RNA unwinding. The most intriguing ML283 analogue inhibited DENV NS3 with an IC₅₀ value of 500 nM and was active against the DENV replicon. The second class contained specific DENV ATPase inhibitors that did not inhibit DENV RNA unwinding or reactions catalyzed by HCV helicase. Members of this class contained a 4-hydroxy-3-(5-methylfuran-2-carbonyl)-2H-pyrrol-5-one scaffold, and about 20 μM of the most potent pyrrolone inhibited both DENV replicons and West Nile virus replication in cells by 50%.

pH-dependent conformational changes in the HCV NS3 protein modulate its ATPase and helicase activities

The hepatitis C virus (HCV) infects 170 to 200 million people worldwide and is, therefore, a major health problem. The lack of efficient treatments that specifically target the viral proteins or RNA and its high chronicity rate make hepatitis C the cause of many deaths and hepatic transplants annually. The NS3 protein is considered an important target for the development of anti-HCV drugs because it is composed of two domains (a serine protease in the N-terminal portion and an RNA helicase/NTPase in the C-terminal portion), which are essential for viral replication and proliferation. We expressed and purified both the NS3 helicase domain (NS3hel) and the full-length NS3 protein (NS3FL) and characterized pH-dependent structural changes associated with the increase in their ATPase and helicase activities at acidic pH. Using intrinsic fluorescence experiments, we have observed that NS3hel was less stable at pH 6.4 than at pH 7.2. Moreover, binding curves using an extrinsic fluorescent probe (bis-ANS) and ATPase assays performed under different pH conditions demonstrated that the hydrophobic clefts of NS3 are significantly more exposed to the aqueous medium at acidic pH. Using fluorescence spectroscopy and anisotropy assays, we have also observed more protein interaction with DNA upon pH acidification, which suggests that the hydrophobic clefts exposure on NS3 might be related to a loss of stability that could lead it to adopt a more open conformation. This conformational change at acidic pH would stimulate both its ATPase and helicase activities, as well as its ability to bind DNA. Taken together, our results indicate that the NS3 protein adopts a more open conformation due to acidification from pH 7.2 to 6.4, resulting in a more active form at a pH that is found near Golgi-derived membranes. This increased activity could better allow NS3 to carry out its functions during HCV replication.

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.