Safety, pharmacokinetics and pharmacodynamics of GS-9620, an oral Toll-like receptor 7 agonist

Mapping the interplay between NK cells and HIV: therapeutic implications

Although highly effective at durably suppressing plasma HIV-1 viremia, combination antiretroviral therapy (ART) treatment regimens do not eradicate the virus, which persists in long-lived CD4+ T cells. This latent viral reservoir serves as a source of plasma viral rebound following treatment interruption, thus requiring lifelong adherence to ART. Additionally, challenges remain related not only to access to therapy but also to a higher prevalence of comorbidities with an inflammatory etiology in treated HIV-1+ individuals, underscoring the need to explore therapeutic alternatives that achieve sustained virologic remission in the absence of ART. Natural killer (NK) cells are uniquely positioned to positively impact antiviral immunity, in part due to the pleiotropic nature of their effector functions, including the acquisition of memory-like features, and, therefore, hold great promise for transforming HIV-1 therapeutic modalities. In addition to defining the ability of NK cells to contribute to HIV-1 control, this review provides a basic immunologic understanding of the impact of HIV-1 infection and ART on the phenotypic and functional character of NK cells. We further delineate the qualities of "memory" NK cell populations, as well as the impact of HCMV on their induction and subsequent expansion in HIV-1 infection. We conclude by highlighting promising avenues for optimizing NK cell responses to improve HIV-1 control and effect a functional cure, including blockade of inhibitory NK receptors, TLR agonists to promote latency reversal and NK cell activation, CAR NK cells, BiKEs/TriKEs, and the role of HIV-1-specific bNAbs in NK cell-mediated ADCC activity against HIV-1-infected cells.

Population pharmacokinetic/pharmacodynamic models of JNJ-64794964, a toll-like receptor 7 agonist, in healthy adult participants

BACKGROUND

JNJ-4964 is a TLR7 agonist, which, via a type I interferon (IFN)-dependent mechanism, may enhance host immunity suppressed by persistent exposure to hepatitis B antigens in chronic hepatitis B.

METHODS

PK and PD data were pooled from 2 studies involving 90 participants (n = 74 JNJ-4964, dose range 0.2-1.8 mg; n = 16 placebo) in a fasted state. Food effects on PK were studied in 24 participants (1.2 or 1.25 mg). A population PK model and PK/PD models were developed to characterize the effect of JNJ-4964 plasma levels on the time course of IFN-α, IFN-γ-inducible protein 10 (IP-10 or CXCL10), IFN-stimulated gene 15 (ISG15), neopterin and lymphocytes following single and weekly dosing in healthy adults. Covariate effects, circadian rhythms and negative feedback were incorporated in the models.

RESULTS

A 3-compartment linear PK model with transit absorption adequately described JNJ-4964 PK. Bioavailability was 44.2% in fed state relative to fasted conditions. Indirect response models with maximum effect (Emax) stimulation on production rate constant (kin) described IFN-α, IP-10, ISG15 and neopterin, while a precursor-dependent indirect response model with inhibitory effect described the transient lymphocyte reduction. Emax, EC50 and γ (steepness) estimates varied according to PD markers, with EC50 displaying substantial between-subject variability. Female and Asian race exhibited lower EC50, suggesting higher responsiveness.

CONCLUSIONS

PK/PD models well characterized the time course of immune system markers in healthy adults. Our results supported sex and race as covariates on JNJ-4964 responsiveness, as well as circadian rhythms and negative feedback as homeostatic mechanisms that are relevant in TLR7-induced type I IFN responses.

Recent Drug Development in the Woodchuck Model of Chronic Hepatitis B

Infection with hepatitis B virus (HBV) is responsible for the increasing global hepatitis burden, with an estimated 296 million people being carriers and living with the risk of developing chronic liver disease and cancer. While the current treatment options for chronic hepatitis B (CHB), including oral nucleos(t)ide analogs and systemic interferon-alpha, are deemed suboptimal, the path to finding an ultimate cure for this viral disease is rather challenging. The lack of suitable laboratory animal models that support HBV infection and associated liver disease progression is one of the major hurdles in antiviral drug development. For more than four decades, experimental infection of the Eastern woodchuck with woodchuck hepatitis virus has been applied for studying the immunopathogenesis of HBV and developing new antiviral therapeutics against CHB. There are several advantages to this animal model that are beneficial for performing both basic and translational HBV research. Previous review articles have focused on the value of this animal model in regard to HBV replication, pathogenesis, and immune response. In this article, we review studies of drug development and preclinical evaluation of direct-acting antivirals, immunomodulators, therapeutic vaccines, and inhibitors of viral entry, gene expression, and antigen release in the woodchuck model of CHB since 2014 until today and discuss their significance for clinical trials in patients.

Antiviral effect of vesatolimod (GS-9620) against foot-and-mouth disease virus both in vitro and invivo

Foot-and-mouth disease (FMD) is an acute contagious disease of cloven-hoofed animals such as cows, pigs, sheep, and deer. The current emergency FMD vaccines, to induce early protection, have limited use, as their protective effect in pigs does not begin until 7 days after vaccination. Therefore, the use of antiviral agents would be required for reducing the spread of foot-and-mouth disease virus (FMDV) during outbreaks. Vesatolimod (GS-9620), a toll-like receptor 7 agonist, is an antiviral agent against various human disease-causing viruses. However, its antiviral effect against FMDV has not been reported yet. The aim of this study was to investigate the antiviral effects of GS-9620 against FMDV both in vitro and in vivo. The inhibitory effect of GS-9620 on FMDV in swine cells involved the induction of porcine interferon (IFN)-α and upregulation of interferon-simulated genes. Protective effect in mice injected with GS-9620 against FMDV was maintained for 5 days after injection, and cytokines such as IFN-γ, interleukin (IL)-12, IL-6, and IFN-γ inducible protein-10 could be detected following the treatment with GS-9620. Furthermore, the combination of GS-9620 with an FMD-inactivated vaccine was found to be highly effective for early protection in mice. Overall, we suggest GS-9620 as a novel and effective antiviral agent for controlling FMDV infection.

Therapeutic efficacy of an Ad26/MVA vaccine with SIV gp140 protein and vesatolimod in ART-suppressed rhesus macaques

Developing an intervention that results in virologic control following discontinuation of antiretroviral therapy (ART) is a major objective of HIV-1 cure research. In this study, we investigated the therapeutic efficacy of a vaccine consisting of adenovirus serotype 26 (Ad26) and modified vaccinia Ankara (MVA) with or without an SIV Envelope (Env) gp140 protein with alum adjuvant in combination with the TLR7 agonist vesatolimod (GS-9620) in 36 ART-suppressed, SIVmac251-infected rhesus macaques. Ad26/MVA therapeutic vaccination led to robust humoral and cellular immune responses, and the Env protein boost increased antibody responses. Following discontinuation of ART, virologic control was observed in 5/12 animals in each vaccine group, compared with 0/12 animals in the sham control group. These data demonstrate therapeutic efficacy of Ad26/MVA vaccination with vesatolimod but no clear additional benefit of adding an Env protein boost. SIV-specific cellular immune responses correlated with virologic control. Our findings show partial efficacy of therapeutic vaccination following ART discontinuation in SIV-infected rhesus macaques.

Non-nucleoside structured compounds with antiviral activity—past 10 years (2010–2020)

Nucleosides and their derivatives are a well-known and well-described class of compounds with antiviral activity. Currently, in the era of the COVID-19 pandemic, scientists are also looking for compounds not related to nucleosides with antiviral properties. This review aims to provide an overview of selected synthetic antiviral agents not associated to nucleosides developed against human viruses and introduced to preclinical and clinical trials as well as drugs approved for antiviral therapy over the last 10 years. The article describes for the first time the wide classification of such antiviral drugs and drug candidates and briefly summarizes the biological target and clinical applications of the compounds. The described compounds are arranged according to the antiviral mechanism of action. Knowledge of the drug's activity toward specific molecular targets may be the key to researching new antiviral compounds and repositioning drugs already approved for clinical use. The paper also briefly discusses the future directions of antiviral therapy. The described examples of antiviral compounds can be helpful for further drug development.

Safety, tolerability, pharmacokinetics, and pharmacodynamics of oral JNJ-64794964, a TLR-7 agonist, in healthy adults

Background

This Phase I, two-part, first-in-human study assessed safety/tolerability and pharmacokinetics/pharmacodynamics of single-ascending doses (SAD) and multiple doses (MD) of the oral toll-like receptor-7 agonist, JNJ-64794964 (JNJ-4964) in healthy adults.

Methods

In the SAD phase, participants received JNJ-4964 0.2 ( N = 6), 0.6 ( N = 6), 1.25 ( N = 8) or 1.8 mg ( N = 6) or placebo ( N = 2/dose cohort) in a fasted state. Food effect was evaluated for the 1.25 mg cohort following ≥6 weeks washout. In the MD phase, participants received JNJ-4964 1.25 mg ( N = 6) or placebo ( N = 2) weekly (fasted) for 4 weeks. Participants were followed-up for 4 weeks.

Results

No serious adverse events (AEs) occurred. 10/34 (SAD) and 5/8 (MD) participants reported mild-to-moderate (≤Grade 2), transient, reversible AEs possibly related to JNJ-4964. Five (SAD) participants had fever/flu-like AEs, coinciding with interferon-α serum levels ≥100 pg/mL and lymphopenia (<1 × 109/L), between 24–48 h after dosing and resolving approximately 96 h after dosing. One participant (MD) had an asymptomatic Grade 1 AE of retinal exudates (cotton wool spots) during follow-up, resolving 6 weeks after observation. JNJ-4964 exhibited dose-proportional pharmacokinetics, with rapid absorption (tmax 0.5–0.75 h) and distribution, and a long terminal half-life (150–591 h). Overall, no significant differences in JNJ-4964 pharmacokinetic parameters were observed in the fed versus fasted state. JNJ-4964 dose-dependently and transiently induced cytokines with potential anti-HBV activity, including interferon-α, IP-10, IL-1 RA, and/or MCP-1, and interferon-stimulated genes (ISG15, MX1, and OAS1) in serum.

Conclusions

In healthy adults, JNJ-4964 was generally well-tolerated, exhibited dose-proportional pharmacokinetics and induced cytokines/ISGs, with possible anti-HBV activity.

Anti-Viral Pattern Recognition Receptors as Therapeutic Targets

Pattern recognition receptors (PRRs) play a central role in the inflammation that ensues following microbial infection by their recognition of molecular patterns present in invading microorganisms but also following tissue damage by recognising molecules released during disease states. Such receptors are expressed in a variety of cells and in various compartments of these cells. PRR binding of molecular patterns results in an intracellular signalling cascade and the eventual activation of transcription factors and the release of cytokines, chemokines, and vasoactive molecules. PRRs and their accessory molecules are subject to tight regulation in these cells so as to not overreact or react in unnecessary circumstances. They are also key to reacting to infection and in stimulating the immune system when needed. Therefore, targeting PRRs offers a potential therapeutic approach for chronic inflammatory disease, infections and as vaccine adjuvants. In this review, the current knowledge on anti-viral PRRs and their signalling pathways is reviewed. Finally, compounds that target PRRs and that have been tested in clinical trials for chronic infections and as adjuvants in vaccine trials are discussed.

The TLR7 agonist vesatolimod induced a modest delay in viral rebound in HIV controllers after cessation of antiretroviral therapy

Toll-like receptor 7 (TLR7) agonists, in combination with other therapies, can induce sustained control of simian-human immunodeficiency virus (SHIV) or simian immunodeficiency virus (SIV) in nonhuman primates. Here, we report the results of a randomized, double-blind, placebo-controlled phase 1b clinical trial of an oral TLR7 agonist, vesatolimod, in HIV-1-infected controllers on antiretroviral therapy (ART). We randomized participants 2:1 to receive vesatolimod (n = 17) or placebo (n = 8) once every other week for a total of 10 doses while continuing on ART. ART was then interrupted, and the time to viral rebound was analyzed using the Kaplan-Meier method. Vesatolimod was associated with induction of immune cell activation, decreases in intact proviral DNA during ART, and a modest increase in time to rebound after ART was interrupted. The delayed viral rebound was predicted by the lower intact proviral DNA at the end of vesatolimod treatment (13 days after the final dose). Inferred pathway analysis suggested increased dendritic cell and natural killer cell cross-talk and an increase in cytotoxicity potential after vesatolimod dosing. Larger clinical studies will be necessary to assess the efficacy of vesatolimod-based combination therapies aimed at long-term control of HIV infection.

Vesatolimod, a Toll-like Receptor 7 Agonist, Induces Immune Activation in Virally Suppressed Adults Living With Human Immunodeficiency Virus-1

BACKGROUND

Treatment with vesatolimod, an investigational, oral, toll-like receptor 7 (TLR7) agonist, leads to sustained viral remission in some non-human primates when combined with anti-envelope antibodies or therapeutic vaccines. We report results of a Phase Ib study evaluating safety, pharmacokinetics, and pharmacodynamics of vesatolimod in adults living with human immunodeficiency virus (HIV)-1.

METHODS

In this double-blind, multicenter, placebo-controlled trial, participants on antiretroviral therapy with screening plasma HIV-1 RNA levels <50 copies/mL were randomized (6:2) to receive 6-10 doses of vesatolimod (1-12 mg) or matching placebo orally every other week in sequential dose-escalation cohorts. The primary study objectives included establishing the safety and virologic effects of vesatolimod (change from baseline in plasma HIV-1 RNA). Pharmacokinetics and pharmacodynamic/immunologic activity were assessed as secondary objectives.

RESULTS

A total of 48 individuals were randomly assigned to vesatolimod (n = 36) or placebo (n = 12). Vesatolimod was generally well tolerated, with no study drug-related serious adverse events or adverse events leading to study drug discontinuation. There were no statistically significant changes from baseline in plasma HIV-1 RNA in the vesatolimod groups, compared to placebo.Vesatolimod plasma exposures increased dose proportionally; consistent responses in cytokines, interferon-stimulated gene expression, and lymphocyte activation were observed with increasing dose levels above 4 mg. Peak elevations 24 hours after receipt of a 6 mg dose were >3.9-fold higher for interferon gamma-induced protein 10 (IP-10), interleukin-1 receptor antagonist (IL-1RA), interferon-inducible T-cell alpha chemoattractant (ITAC) when compared to baseline values.

CONCLUSIONS

Vesatolimod was well tolerated at doses ranging from 1 to 12 mg. Immune stimulation was observed at doses above 4 mg, providing rationale for future combination trials in people living with HIV.

CLINICAL TRIALS REGISTRATION

NCT02858401.

Safety, tolerability, pharmacokinetics, and pharmacodynamics of a TLR7 agonist prodrug RO6870868 in healthy volunteers

RO6870868 is an oral prodrug of the toll‐like receptor 7 (TLR7) specific agonist, RO6871765. TLR7 agonists augment host immune activity and are in development to treat hepatitis B infection. We evaluated the safety, tolerability, pharmacokinetics (PKs), and pharmacodynamics (PDs) of RO6870868 in a first‐in‐human, phase I, randomized, single ascending oral dose study in 60 healthy volunteers at 6 dose levels (200–2000 mg). Single oral doses were generally well‐tolerated with a predictable safety profile associated with dose‐dependent increases in systemic interferon. No serious adverse events (AEs) were reported and no subject withdrew from the study due to an AE. No clinically significant changes were observed in vital signs, electrocardiograms, or laboratory parameters. Following oral RO6870868 doses, plasma RO6871765 concentrations increased rapidly, exhibiting mean terminal half‐life ranging 2–6 h across all cohorts, with area under the plasma concentration versus time curve extrapolated to infinity (AUC_0‐∞) increasing proportionally with dose. A pattern of dose and time‐dependent PD activity was demonstrated consistent with engagement of the TLR7 system. Single RO6870868 doses activated components of the TLR innate immune system in a dose‐dependent manner with adequate safety and tolerability. Single‐dose data in healthy volunteers are useful to evaluate safety, PK, and PD activity of TLR7 agonists and help to guide dose and regimen selection for further trials in patients with chronic hepatitis B.

Safety, pharmacokinetics and pharmacodynamics of TQ-A3334, an oral toll-like receptor 7 agonist in healthy individuals

BACKGROUND & AIMS

TQ-A3334, a selective, oral toll-like receptor (TLR)-7 agonist, is being developed to treat chronic hepatitis B (CHB). This study evaluated the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of TQ-A3334 in healthy participants.

RESEARCH DESIGN AND METHODS

The effects of a single-ascending dose of TQ-A3334 (0.2-1.8 mg) combined with food (1.2 mg) were evaluated in 48 healthy participants.

RESULTS

No serious adverse events or discontinuations occurred in the study. The most common adverse reactions were lymphocyte count decreased and headache, which were generally consistent with IFN-α exposure and the mechanism of action of a TLR7 agonist. TQ-A3334 was rapidly absorbed, with a time to maximum plasma concentration of 0.42-0.5 h. Systemic exposure (C_max and AUC) to TQ-A3334 increased with a slight saturation proportion to dose. Food reduced the exposure of TQ-A3334. The concentrations of MCP-1, ISG-15, MX-1, and OAS-1 were observed to be slightly dose-dependent, ranging from 1.0 to 1.8 mg TQ-A3334.

CONCLUSIONS

Oral doses of 0.2-1.8 mg appeared to be safe and tolerated. PD activity was seen at doses ranging from 1.0 to 1.8 mg, indicating its possible future use to treat CHB.

TRIAL REGISTRATION

The trial is registered at the Chinese Clinical Trial website (http://www.chinadrugtrials.org.cn/index.html # CTR20182248).

Agonist and antagonist ligands of toll-like receptors 7 and 8: Ingenious tools for therapeutic purposes

The discovery of the TLRs family and more precisely its functions opened a variety of gates to modulate immunological host responses. TLRs 7/8 are located in the endosomal compartment and activate a specific signaling pathway in a MyD88-dependant manner. According to their involvement into various autoimmune, inflammatory and malignant diseases, researchers have designed diverse TLRs 7/8 ligands able to boost or block the inherent signal transduction. These modulators are often small synthetic compounds and most act as agonists and to a much lesser extent as antagonists. Some of them have reached preclinical and clinical trials, and only one has been approved by the FDA and EMA, imiquimod. The key to the success of these modulators probably lies in their combination with other therapies as recently demonstrated. We gather in this review more than 360 scientific publications, reviews and patents, relating the extensive work carried out by researchers on the design of TLRs 7/8 modulators, which are classified firstly by their biological activities (agonist or antagonist) and then by their chemical structures, which total syntheses are not discussed here. This review also reports about 90 clinical cases, thereby showing the biological interest of these modulators in multiple pathologies.

Pattern recognition receptors as potential drug targets in inflammatory disorders

Pattern recognition receptors (PRRs) are a key part of the innate immune system, the body's first line of defense against infection and tissue damage. This superfamily of receptors including Toll-like receptors (TLRs), NOD-like receptors (NLRs), C-type lectin-like receptors (CLRs) and RIG-like receptors (RLRs) are responsible for initiation of the inflammatory response by their recognition of molecular patterns present in invading microorganisms (such as bacteria, viruses or fungi) during infection or in molecules released following tissue damage during acute or chronic disease states (such as sepsis or arthritis). These receptors are widely expressed and located on the cell surface, in intracellular compartments or in the cytoplasm can detect a single or subset of molecules including lipoproteins, carbohydrates or nucleic acids. In response, they initiate an intracellular signaling cascade that culminates in the synthesis and release of cytokines, chemokines and vasoactive molecules. These steps are necessary to maintain tissue homeostasis and remove potentially dangerous pathogens. However, during extreme or acute responses or during chronic disease, this can be damaging and even lead to death. Therefore, it is thought that targeting such receptors may offer a therapeutic approach in chronic inflammatory diseases or in cases of acute infection leading to sepsis. Herein, the current knowledge on the molecular biology of PRRs is reviewed along with their association with inflammatory and infectious diseases. Finally, the testing of therapeutic compounds and their future merit as targets is discussed.

Targeting Cellular and Tissue HIV Reservoirs With Toll-Like Receptor Agonists

The elimination of both cellular and tissue latent reservoirs is a challenge toward a successful HIV cure. "Shock and Kill" are among the therapeutic strategies that have been more extensively studied to target these reservoirs. These strategies are aimed toward the reactivation of the latent reservoir using a latency-reversal agent (LRA) with the subsequent killing of the reactivated cell either by the cytotoxic arm of the immune system, including NK and CD8 T cells, or by viral cytopathic mechanisms. Numerous LRAs are currently being investigated in vitro, ex vivo as well as in vivo for their ability to reactivate and reduce latent reservoirs. Among those, several toll-like receptor (TLR) agonists have been shown to reactivate latent HIV. In humans, there are 10 TLRs that recognize different pathogen-associated molecular patterns. TLRs are present in several cell types, including CD4 T cells, the cell compartment that harbors the majority of the latent reservoir. Besides their ability to reactivate latent HIV, TLR agonists also increase immune activation and promote an antiviral response. These combined properties make TLR agonists unique among the different LRAs characterized to date. Additionally, some of these agonists have shown promise toward finding an HIV cure in animal models. When in combination with broadly neutralizing antibodies, TLR-7 agonists have shown to impact the SIV latent reservoir and delay viral rebound. Moreover, there are FDA-approved TLR agonists that are currently being investigated for cancer therapy and other diseases. All these has prompted clinical trials using TLR agonists either alone or in combination toward HIV eradication approaches. In this review, we provide an extensive characterization of the state-of-the-art of the use of TLR agonists toward HIV eradication strategies and the mechanism behind how TLR agonists target both cellular and tissue HIV reservoirs.

Liver-Targeted Toll-Like Receptor 7 Agonist Combined With Entecavir Promotes a Functional Cure in the Woodchuck Model of Hepatitis B Virus

Current therapeutics for chronic infection with hepatitis B virus (HBV) rarely induce functional cure due to the immunotolerant status of patients. Small molecule agonists targeting toll-like receptor 7 (TLR7) have been shown to elicit a functional cure in animal models of HBV but sometimes with poor tolerability due to immune-related toxicities. In an effort to increase the therapeutic window of TLR7 agonists to treat chronic hepatitis B (CHB), we developed an oral TLR7 agonist, APR002, designed to act locally in the gastrointestinal tract and liver, thus minimizing systemic exposure and improving tolerability. Here, we describe the pharmacokinetic/pharmacodynamic (PK/PD) profile of APR002 in mice and uninfected woodchucks as well as the safety and antiviral efficacy in combination with entecavir (ETV) in woodchucks with CHB. Treatment of woodchucks chronically infected with woodchuck hepatitis virus (WHV) with weekly oral doses of APR002 was well-tolerated. While APR002 and ETV single agents did not elicit sustained viral control, combination therapy resulted in durable immune-mediated suppression of the chronic infection. These woodchucks also had detectable antibodies to viral antigens, enhanced interferon-stimulated gene expression, and loss of WHV covalently closed circular DNA. Conclusion: APR002 is a novel TLR7 agonist exhibiting a distinct PK/PD profile that in combination with ETV can safely attain a functional cure in woodchucks with chronic WHV infection. Our results support further investigation of liver-targeted TLR7 agonists in human CHB.

TLR7 agonist administration to SIV-infected macaques receiving early initiated cART does not induce plasma viremia

Reduction/elimination of HIV-1 reservoirs that persist despite combination antiretroviral therapy (cART) will likely require induction of viral expression by residual infected cells and enhanced clearance of these cells. TLR7 agonists have potential to mediate these activities. We evaluated immunologic and virologic effects of repeated doses of the TLR7 agonist GS-9620 in SIV-infected rhesus macaques receiving cART, which was initiated at 13 days after infection and was continued for 75 weeks prior to GS-9620 administration. During cART, GS-9620 induced transient upregulation of IFN-stimulated genes in blood and tissues, increases in plasma cytokines, and changes in immune cell population activation and phenotypes but did not result in measurable increases in plasma viremia or viral RNA-to-viral DNA ratio in PBMCs or tissues nor decreases in viral DNA in PBMC or tissues. SIV-specific CD8+ T cell responses, negligible prior to GS-9620 treatment, were not measurably boosted by treatment; a second course of GS-9620 administration overlapping with later cART discontinuation was associated with increased CD8+ T cell responses during viral recrudescence. These results confirm and extend evidence for GS-9620-mediated enhancement of antiviral immune responses in SIV-infected macaques but suggest that GS-9620-mediated viral induction may depend critically on the timing of initiation and duration of cART and resulting characteristics of viral reservoirs.

Safety and efficacy of vesatolimod (GS-9620) in patients with chronic hepatitis B who are not currently on antiviral treatment

Vesatolimod is an oral agonist of toll-like receptor 7 designed to minimize systemic exposure and side effects. We assessed the safety and efficacy of vesatolimod in viremic chronic hepatitis B (CHB) patients not currently on oral antiviral treatment (OAV) in a phase 2, multicentre, double-blind, randomized, placebo-controlled study. A total of 192 patients stratified by HBeAg status and alanine aminotransferase level were randomized 2:2:2:1 to receive oral vesatolimod (1-, 2- or 4-mg) or placebo once weekly for 12 weeks; tenofovir disoproxil fumarate (300-mg daily) was administered daily for 48 weeks. Efficacy was assessed by quantitative serum HBsAg decline at Week 24 from baseline. In addition to safety assessments, changes in whole-blood interferon-stimulated gene (ISG) transcripts and serum cytokines were explored. Most patients were male (64.1%) and HBeAg-negative (60.9%) at baseline. Among vesatolimod-treated patients, most (60.4%-69.1%) experienced ≥1 treatment-emergent adverse event; the majority were mild or moderate in severity. No clinically meaningful differences in HBsAg changes from baseline were observed between treatment groups. No patients experienced HBsAg loss, while 3 patients experienced HBeAg loss and hepatitis B e-antibody seroconversion at week 48. HBV DNA suppression rates were similar across all treatment arms at Week 24. ISG15 induction was dose-dependent and did not correlate with HBsAg changes. A small proportion of patients exhibited dose-dependent interferon-α induction that correlated with grade of influenza-like adverse events. Overall, vesatolimod is safe and well tolerated in CHB patients. Although consistent dose-dependent pharmacodynamic induction of ISGs was demonstrated, it did not result in clinically significant HBsAg decline.

Metabolism of vesatolimod in rat, dog, and human liver microsomes: Metabolic stability assessment, metabolite identification, and interspecies comparison

Vesatolimod (GS-9620) is an agonist of toll-like receptor (TLR7) 7, which has been developed as an anti-hepatitis B virus (HBV) agent. The focus of the present study is on the metabolic stability evaluation and metabolite identification of GS-9620 in rat, dog, and human liver microsomes, as well as interspecies comparison. The average observed in vitro T_1/2 values were 3.06, 13.06, and 15.56 minutes in rat, dog, and human liver microsomes, respectively. The findings suggested that GS-9620 was rapidly metabolized in the presence of reductive nicotinamide adenine dinucleotide phosphate (NADPH) in rat liver microsomes (RLM), and moderately metabolized in dog liver microsomes (DLM) and human liver microsomes (HLM). Subsequently, the metabolites were characterized using an ultra-high performance liquid chromatography coupled with linear ion trap orbitrap tandem mass spectrometer (UHPLC-LTQ-Orbitrap-MS) with dd-MS² on-line data acquisition mode. Under the current conditions, a total of 18 metabolites were detected and their identities were proposed by comparing their accurate masses, fragmental ions, and retention times with those of GS-9620. Three metabolites (M2, M4, and M18) were authentically identified by using reference standards. In RLM, 16 metabolites were identified with M2 being the most abundant metabolite. M4, M5, and M9 were rat-specific. In DLM, 12 minor metabolites were identified with a dog-specific metabolite (M6). In HLM, GS-9620 showed similar metabolic profiles to that in DLM, and 11 minor metabolites were detected with M12 being human-specific. Based on the identified metabolites, the metabolic pathways of GS-9620 were proposed, including hydroxylation, bis-hydroxylation, dehydrogenation, and oxidative deamination.

TLR7 agonists induce transient viremia and reduce the viral reservoir in SIV-infected rhesus macaques on antiretroviral therapy

Antiretroviral therapy (ART) can halt HIV-1 replication but fails to target the long-lived latent viral reservoir. Several pharmacological compounds have been evaluated for their ability to reverse HIV-1 latency, but none has demonstrably reduced the latent HIV-1 reservoir or affected viral rebound after the interruption of ART. We evaluated orally administered selective Toll-like receptor 7 (TLR7) agonists GS-986 and GS-9620 for their ability to induce transient viremia in rhesus macaques infected with simian immunodeficiency virus (SIV) and treated with suppressive ART. In an initial dose-escalation study, and a subsequent dose-optimization study, we found that TLR7 agonists activated multiple innate and adaptive immune cell populations in addition to inducing expression of SIV RNA. We also observed TLR7 agonist-induced reductions in SIV DNA and measured inducible virus from treated animals in ex vivo cell cultures. In a second study, after stopping ART, two of nine treated animals remained aviremic for more than 2 years, even after in vivo CD8+ T cell depletion. Moreover, adoptive transfer of cells from aviremic animals could not induce de novo infection in naïve recipient macaques. These findings suggest that TLR7 agonists may facilitate reduction of the viral reservoir in a subset of SIV-infected rhesus macaques.

TLR7 Agonists Display Potent Antiviral Effects against Norovirus Infection via Innate Stimulation

Norovirus infections are a significant health and economic burden globally, accounting for hundreds of millions of cases of acute gastroenteritis every year. In the absence of an approved norovirus vaccine, there is an urgent need to develop antivirals to treat chronic infections and provide prophylactic therapy to limit viral spread during epidemics and pandemics. Toll-like receptor (TLR) agonists have been explored widely for their antiviral potential, and several are progressing through clinical trials for the treatment of human immunodeficiency virus (HIV) and hepatitis B virus (HBV) and as adjuvants for norovirus viruslike particle (VLP) vaccines. However, norovirus therapies in development are largely direct-acting antivirals (DAAs) with fewer compounds that target the host. Our aim was to assess the antiviral potential of TLR7 agonist immunomodulators on norovirus infection using the murine norovirus (MNV) and human Norwalk replicon models. TLR7 agonists R-848, Gardiquimod, GS-9620, R-837, and loxoribine were screened using a plaque reduction assay, and each displayed inhibition of MNV replication (50% effective concentrations [EC₅₀s], 23.5 nM, 134.4 nM, 0.59 μM, 1.5 μM, and 79.4 μM, respectively). RNA sequencing of TLR7-stimulated cells revealed a predominant upregulation of innate immune response genes and interferon (IFN)-stimulated genes (ISGs) that are known to drive an antiviral state. Furthermore, the combination of R-848 and the nucleoside analogue (NA) 2'C-methylcytidine elicited a synergistic antiviral effect against MNV, demonstrating that combinational therapy of host modulators and DAAs might be used to reduce drug cytotoxicity. In summary, we have identified that TLR7 agonists display potent inhibition of norovirus replication and are a therapeutic option to combat norovirus infections.

Safety, efficacy and pharmacodynamics of vesatolimod (GS-9620) in virally suppressed patients with chronic hepatitis B

BACKGROUND & AIMS

Vesatolimod (GS-9620) is an oral agonist of toll-like receptor 7, an activator of innate and adaptive immune responses. Herein the safety and efficacy of vesatolimod is assessed after once-weekly treatment in patients with chronic hepatitis B (CHB) infection suppressed on oral antiviral treatment.

METHODS

In a phase II, double-blind, randomized, placebo (PBO)-controlled study, 162 patients stratified by hepatitis B surface antigen (HBsAg) levels and serum hepatitis B e antigen (HBeAg) status were randomized 1:3:3:3 to once-weekly oral PBO or vesatolimod (1-, 2-, or 4-mg doses) for 4, 8 or 12 weeks per cohort. Efficacy was assessed by change in baseline HBsAg (log₁₀ IU/ml) at the primary endpoint (Week 24). Safety assessments included adverse events (AE) and laboratory abnormality monitoring. Pharmacodynamic assessments included peripheral cytokine level quantification and interferon-stimulated gene (ISG) mRNA expression evaluation.

RESULTS

The majority of patients were male (76%) and HBeAg-negative (79%) at baseline. Most (41-80%) experienced ≥1 AE during the study with the majority of AEs mild or moderate in severity. No significant declines in HBsAg were observed at the primary (Week 24) or secondary endpoints (Weeks 4, 8, 12, and 48). ISG15 induction was dose-dependent and consistent after repeat dosing, returning closer to baseline by one week after treatment at all dose levels; no patient demonstrated significant serum interferon alpha (IFNα) expression at any timepoint evaluated. Multivariate analyses showed that ≥2-fold ISG15 induction is associated with 2- or 4-mg vesatolimod dose and female sex.

CONCLUSIONS

Vesatolimod was safe and well-tolerated in patients with CHB, demonstrating consistent dose-dependent pharmacodynamic induction of ISG15 without significant systemic induction of IFNα expression or related symptoms. However, no significant HBsAg declines were observed.

LAY SUMMARY

In a phase II study, vesatolimod, an oral, once-weekly, experimental immune-activating drug for the treatment of hepatitis B virus (HBV), is safe and well-tolerated in chronic HBV patients who are virally suppressed on oral antiviral treatment. Despite demonstrating on-target biomarker responses in patients, no significant declines in hepatitis B surface antigen were observed. Clinical Trial Number: GS-US-283-1059; NCT 02166047.

New directions in hepatitis B therapy research

Chronic hepatitis B treatment is available for a long period, allowing disease control and infection suppression, but it is rarely responsible for HBsAg clearance. None of the drugs available aim at cccDNA, the obstacle in HBV infection eradication. Complications related to CHB, such as liver insufficiency, cirrhosis, and hepatocellular carcinoma are reduced in conditions of good viremia suppression, but still exist even after HBsAg seroclearance, what makes a need for urgent forthcoming of new therapeutics. Recent years brought promising and interesting results of experimental approaches, which are directed against different phases of HBV life cycle, target ccc DNA, or boost, and restore host immune response. Unfortunately, encouraging results in vitro and on animal models are not always reflected in human. Nevertheless, the multiplicity of novel antivirals allows to expect that at least some of them will enter clinical practice and relieve patients from chronic hepatitis B, fatal and devastating disease.

Toll-Like Receptor 7 Agonist GS-9620 Induces HIV Expression and HIV-Specific Immunity in Cells from HIV-Infected Individuals on Suppressive Antiretroviral Therapy

Antiretroviral therapy can suppress HIV replication to undetectable levels but does not eliminate latent HIV, thus necessitating lifelong therapy. Recent efforts to target this persistent reservoir have focused on inducing the expression of latent HIV so that infected cells may be recognized and eliminated by the immune system. Toll-like receptor (TLR) activation stimulates antiviral immunity and has been shown to induce HIV from latently infected cells. Activation of TLR7 leads to the production of several stimulatory cytokines, including type I interferons (IFNs). In this study, we show that the selective TLR7 agonist GS-9620 induced HIV in peripheral blood mononuclear cells (PBMCs) from HIV-infected individuals on suppressive antiretroviral therapy. GS-9620 increased extracellular HIV RNA 1.5- to 2-fold through a mechanism that required type I IFN signaling. GS-9620 also activated HIV-specific T cells and enhanced antibody-mediated clearance of HIV-infected cells. Activation by GS-9620 in combination with HIV peptide stimulation increased CD8 T cell degranulation, production of intracellular cytokines, and cytolytic activity. T cell activation was again dependent on type I IFNs produced by plasmacytoid dendritic cells. GS-9620 induced phagocytic cell maturation and improved effector-mediated killing of HIV-infected CD4 T cells by the HIV envelope-specific broadly neutralizing antibody PGT121. Collectively, these data show that GS-9620 can activate HIV production and improve the effector functions that target latently infected cells. GS-9620 may effectively complement orthogonal therapies designed to stimulate antiviral immunity, such as therapeutic vaccines or broadly neutralizing antibodies. Clinical studies are under way to determine if GS-9620 can target HIV reservoirs.

IMPORTANCE Though antiretroviral therapies effectively suppress viral replication, they do not eliminate integrated proviral DNA. This stable intermediate of viral infection is persistently maintained in reservoirs of latently infected cells. Consequently, lifelong therapy is required to maintain viral suppression. Ultimately, new therapies that specifically target and eliminate the latent HIV reservoir are needed. Toll-like receptor agonists are potent enhancers of innate antiviral immunity that can also improve the adaptive immune response. Here, we show that a highly selective TLR7 agonist, GS-9620, activated HIV from peripheral blood mononuclear cells isolated from HIV-infected individuals with suppressed infection. GS-9620 also improved immune effector functions that specifically targeted HIV-infected cells. Previously published studies on the compound in other chronic viral infections show that it can effectively induce immune activation at safe and tolerable clinical doses. Together, the results of these studies suggest that GS-9620 may be useful for treating HIV-infected individuals on suppressive antiretroviral therapy.

Treatment of hepatitis B virus: an update

Chronic hepatitis B virus infection is a global health concern as it affects over 240 million people worldwide and an estimated 686,000 people die annually as a result of complications of the disease. With the development of newer antiviral drugs, viral suppression of HBV is achievable, however elimination of HBV from infected individuals (functional cure) remains an issue. Due to persistence of HBV DNA (cccDNA) in infected cells, chronically infected patients who discontinue therapy prior to HBsAg loss or seroconversion are likely to relapse. Several novel therapeutic strategies are being researched and studied in clinical trials. Here we review these novel strategies to achieve sustained cure or elimination of HBV. These strategies include the targeting of the host or viral factors required for viral persistence as well as therapeutic vaccines.

Activating the innate immune response to counter chronic hepatitis B virus infection

INTRODUCTION

Chronic infection with hepatitis B virus (HBV) is endemic to several populous parts of the world, where resulting complicating cirrhosis and hepatocellular carcinoma occur commonly. Licensed drugs to treat the infection have limited curative efficacy, and development of therapies that eliminate all replication intermediates of HBV is a priority. Areas covered: The recent demonstration that the activation of the innate immune response may eradicate HBV from infected hepatocytes has a promising therapeutic application. Small molecule stimulators of Toll-like receptors (TLRs) inhibit replication of woodchuck hepatitis virus in woodchucks and HBV in chimpanzees and mice. Early stage clinical trials using GS-9620, a TLR7 agonist, indicate that this candidate antiviral is well tolerated in humans. Using an alternative approach, triggering the innate immune response with agonists of lymphotoxin-β receptor caused efficient APOBEC-mediated deamination and degradation of viral covalently closed circular DNA. Expert opinion: Eliminating HBV cccDNA from infected individuals would constitute a cure, and has become the focus of intensive research that employs various therapeutic approaches, including gene therapy. Immunomodulation through innate immune activation shows promise for the treatment of chronic infection of HBV (CHB) and, used in combination with other therapeutics, may contribute to the global control of infections and ultimately to the eradication of HBV.

Oxethazaine inhibits hepatitis B virus capsid assembly by blocking the cytosolic calcium-signalling pathway

Chronic hepatitis B virus (HBV) infection is a serious public health problem and may progress to liver fibrosis, cirrhosis and hepatocellular carcinoma. It is currently treated with PEGylated IFN-α2a and nucleoside/nucleotide analogues (NAs). However, PEGylated IFN treatment has problems of high cost, low efficiency and side effects. Long-term administration of NAs is necessary to avoid virus relapse, which can cause drug resistance and side effects. New efforts are now being directed to develop novel anti-HBV drugs targeting either additional viral targets other than viral DNA polymerase or host targets to improve the treatment of chronic hepatitis B. In this study, we discovered that oxethazaine, approved for clinic use in a few countries such as Japan, India, South Africa and Brazil, can dose-dependently reduce the levels of HBV envelope antigen, extracellular HBV DNA in supernatants and intracellular HBV total DNA. However, the levels of HBV cccDNA and HBV RNAs were not affected by oxethazaine treatment. Further study confirmed that oxethazaine acts on the virus assembly stage of the HBV life cycle. A study of the mechanisms of oxethazaine suggested that this drug inhibits HBV replication and capsid assembly by blocking the cytosolic calcium-signalling pathway. Moreover, oxethazaine could inhibit the replication of lamivudine/entecavir-dual-resistant and adefovir-resistant HBV mutants. In conclusion, our study suggests that oxethazaine may serve as a promising drug, or could be used as a starting point for anti-HBV drug discovery.

Molecular Determinants of GS-9620-Dependent TLR7 Activation

GS-9620 is an orally administered agonist of Toll-like receptor (TLR)7 currently being evaluated in clinical studies for the treatment of chronic HBV and HIV patients. GS-9620 has shown antiviral efficacy in preclinical models of chronic hepadnavirus infection in woodchuck as well as chimpanzee. However, the molecular determinants of GS-9620-dependent activation of TLR7 are not well defined. The studies presented here elucidate GS-9620 subcellular distribution and characterize its molecular interactions with human TLR7 using structure-guided mutational analysis. Based on our results we present a molecular model of TLR7 bound to GS-9620. We also determine that several coding SNPs had no effect on GS-9620-dependent TLR7 activation. In addition, our studies provide evidence that TLR7 exists in a ligand-independent oligomeric state and that, TLR7 activation by GS-9620 is likely associated with compound-induced conformational changes. Finally, we demonstrate that activation of NF-κB and Akt pathways in primary plasmacytoid dendritic cells occur as immediate downstream cellular responses to GS-9620 stimulation. The data presented here further our understanding of the molecular parameters governing TLR7 activation by GS-9620, and more generally by nucleos/tide-related ligands.

New therapeutic agents for chronic hepatitis B

The treatment goal for chronic hepatitis B is true eradication of the hepatitis B virus, but this is rarely achieved with first-line treatment regimens because of an inability to disrupt covalently closed circular DNA and an inadequate host immune response. Therefore, new antiviral agents are needed to target various stages of the hepatitis B virus lifecycle and modulation of the immune system. This Review provides a summary of available regimens with their strengths and limitations, and highlights future therapeutic strategies to target the virus and host immune response. These new agents can hopefully lead to a finite duration of treatment, and provide a functional and durable cure for chronic hepatitis B infection.

Recent developments in antivirals against hepatitis B virus

Chronic hepatitis B virus (HBV) infection (CHB) is a major cause of cirrhosis and hepatocellular carcinoma (HCC). Although the availability of HBV vaccines effectively reduces the incidence of HBV infection, the healthcare burden from CHB remains high. Several antiviral agents, such as (pegylated-) interferon-α and nucleos(t)ide analogs are approved by US FDA for chronic HBV infection management. Entecavir (ETV) and tenofovir disoproxil fumarate (TDF) have been recommended as the first-line anti-HBV drugs for excellent viral suppression with a low risk of antiviral resistance, but the cost and need for essentially life-long treatment are considerable challenges. And none of these current treatments can eradicate the intracellular virus. Given these issues, there is still an unmet medical need for an efficient HBV cure. We summarize here the key developments of antivirals against hepatitis B virus, including HBV replication cycle inhibitors and host immune regulators.

Early clinical evaluation of the intranasal TLR7 agonist GSK2245035: Use of translational biomarkers to guide dosing and confirm target engagement

Modulation of the airways' immune milieu is a key therapeutic goal for remission from respiratory allergies. To explore this hypothesis, GSK2245035, a selective Toll-like receptor 7 (TLR7) agonist with preferential Type-1 interferon (IFN)-stimulating properties, was developed for intranasal application. Doses for clinical assessment were extrapolated from translational biomarker studies in primates. Randomized, double-blind, placebo-controlled trials in healthy volunteers and patients with allergic rhinitis demonstrated that intranasal GSK2245035 doses <100 ng were tolerated and did not cause nasal inflammation. Higher doses were not tested due to considerable cytokine release syndrome-related symptoms observed at 100 ng. Clear target engagement, reflected by local and peripheral increase of IFN-gamma-inducible protein-10, was observed at 20 ng, indicating IFN-stimulated immune changes at tolerated doses. Repeat intranasal administration at weekly intervals did not tolerize or amplify the pharmacological response. Intranasal GSK2245035 has an acceptable safety profile at doses that induce local TLR7-mediated immune responses.

Anti-HBV Drugs: Progress, Unmet Needs, and New Hope

Approximately 240 million people worldwide are chronically infected with hepatitis B virus (HBV), which represents a significant challenge to public health. The current goal in treating chronic HBV infection is to block progression of HBV-related liver injury and inflammation to end-stage liver diseases, including cirrhosis and hepatocellular carcinoma, because we are unable to eliminate chronic HBV infection. Available therapies for chronic HBV infection mainly include nucleos/tide analogues (NAs), non-NAs, and immunomodulatory agents. However, none of them is able to clear chronic HBV infection. Thus, a new generation of anti-HBV drugs is urgently needed. Progress has been made in the development and testing of new therapeutics against chronic HBV infection. This review aims to summarize the state of the art in new HBV drug research and development and to forecast research and development trends and directions in the near future.

The oral toll-like receptor-7 agonist GS-9620 in patients with chronic hepatitis B virus infection

BACKGROUND & AIMS

GS-9620 is an oral agonist of toll-like receptor 7, a pattern-recognition receptor whose activation results in innate and adaptive immune stimulation. We evaluated the safety, pharmacokinetics, and pharmacodynamics of GS-9620 in patients with chronic hepatitis B.

METHODS

In two double-blind, phase 1b trials of identical design, 49 treatment-naïve and 51 virologically suppressed patients were randomized 5:1 to receive GS-9620 (at doses of 0.3mg, 1mg, 2mg, 4mg) or placebo as a single dose or as two doses seven days apart. Pharmacodynamic assessment included evaluation of peripheral mRNA expression of interferon-stimulated gene 15 (ISG15), serum interferon gamma-induced protein 10 and serum interferon (IFN)-alpha.

RESULTS

Overall, 74% of patients were male and 75% were HBeAg negative at baseline. No subject discontinued treatment due to adverse events. Fifty-eight percent experienced ⩾1 adverse event, all of which were mild to moderate in severity. The most common adverse event was headache. No clinically significant changes in HBsAg or HBV DNA levels were observed. Overall, a transient dose-dependent induction of peripheral ISG15 gene expression was observed peaking within 48 hours of dosing followed by return to baseline levels within seven days. Higher GS-9620 dose, HBeAg positive status, and low HBsAg level at baseline were independently associated with greater probability of ISG15 response. Most patients (88%) did not show detectable levels of serum IFN-alpha at any time point.

CONCLUSIONS

Oral GS-9620 was safe, well tolerated, and associated with induction of peripheral ISG15 production in the absence of significant systemic IFN-alpha levels or related symptoms.

Sustained efficacy and seroconversion with the Toll-like receptor 7 agonist GS-9620 in the Woodchuck model of chronic hepatitis B

BACKGROUND & AIMS

New therapies for chronic hepatitis B (CHB) are urgently needed since current treatments rarely lead to cure. We evaluated whether the oral small molecule toll-like receptor (TLR7) agonist GS-9620 could induce durable antiviral efficacy in woodchucks chronically infected with woodchuck hepatitis virus (WHV), a hepadnavirus closely related to human hepatitis B virus (HBV).

METHODS

After evaluating the pharmacokinetics, pharmacodynamics and tolerability of oral GS-9620 in uninfected woodchucks, adult woodchucks chronically infected with WHV (n = 7 per group) were dosed with GS-9620 or placebo for 4 or 8 weeks with different treatment schedules.

RESULTS

GS-9620 treatment induced rapid, marked and sustained reduction in serum viral DNA (mean maximal 6.2log10 reduction), and hepatic WHV DNA replicative intermediates, WHV cccDNA and WHV RNA, as well as loss of detectable serum WHV surface antigen (WHsAg). GS-9620 treatment also induced a sustained antibody response against WHsAg in a subset of animals. Strikingly, treatment reduced the incidence of hepatocellular carcinoma (HCC) from 71% in the placebo group to 8% in GS-9620-treated woodchucks with sustained viral load reduction. GS-9620 treatment was associated with reversible increases in serum liver enzymes and thrombocytopenia, and induced intrahepatic CD8(+) T cell, NK cell, B cell and interferon response transcriptional signatures.

CONCLUSIONS

The data demonstrate that short duration, finite treatment with the oral TLR7 agonist GS-9620 can induce a sustained antiviral response in the woodchuck model of CHB, and support investigation of this compound as a therapeutic approach to attain a functional cure in CHB patients.

Search for a cure for chronic hepatitis B infection: How close are we?

Chronic hepatitis B (CHB) remains a significant unmet medical need, with 240 million chronically infected persons worldwide. It can be controlled effectively with either nucleoside/nucleotide-based or interferon-based therapies. However, most patients receiving these therapies will relapse after treatment withdrawal. During recent years, the advances in molecular biology and immunology have enabled a better understanding of the viral-host interaction and inspired new treatment approaches to achieve either elimination of the virus from the liver or durable immune control of the infection. This review aims to provide a brief overview on the potential new therapies that may overcome the challenge of persistent CHB infection in the near future.

Current and future antiviral drug therapies of hepatitis B chronic infection

Despite significant improvement in the management of chronic hepatitis B virus (HBV) it remains a public health problem, affecting more than 350 million people worldwide. The natural course of the infection is dynamic and involves a complex interplay between the virus and the host’s immune system. Currently the approved therapeutic regimens include pegylated-interferon (IFN)-α and monotherapy with five nucleos(t)ide analogues (NAs). Both antiviral treatments are not capable to eliminate the virus and do not establish long-term control of infection after treatment withdrawal. IFN therapy is of finite duration and associates with low response rates, liver decompensating and numerous side effects. NAs are well-tolerated therapies but have a high risk of drug resistance development that limits their prolonged use. The imperative for the development of new approaches for the treatment of chronic HBV infection is a challenging issue that cannot be over-sided. Research efforts are focusing on the identification and evaluation of various viral replication inhibitors that target viral replication and a number of immunomodulators that aim to restore the HBV specific immune hyporesponsiveness without inducing liver damage. This review brings together our current knowledge on the available treatment and discusses potential therapeutic approaches in the battle against chronic HBV infection.

Novel drugs targeting Toll-like receptors for antiviral therapy

Toll-like receptors (TLRs) are sentinel receptors of the host innate immune system that recognize conserved 'pathogen-associated molecular patterns' of invading microbes, including viruses. The activation of TLRs establishes antiviral innate immune responses and coordinates the development of long-lasting adaptive immunity in order to control viral pathogenesis. However, microbe-induced damage to host tissues may release 'danger-associated molecular patterns' that also activate TLRs, leading to an overexuberant inflammatory response and, ultimately, to tissue damage. Thus, TLRs have proven to be promising targets as therapeutics for the treatment of viral infections that result in inflammatory damage or as adjuvants in order to enhance the efficacy of vaccines. Here, we explore recent advances in TLR biology with a focus on novel drugs that target TLRs (agonists and antagonists) for antiviral therapy.

Safety, pharmacokinetics and pharmacodynamics of the oral toll-like receptor 7 agonist GS-9620 in treatment-naive patients with chronic hepatitis C

BACKGROUND

GS-9620 is a potent oral agonist of toll-like receptor 7, a key modulator of the innate immune response. In healthy volunteers, low doses of GS-9620 (2, 4 and 6 mg) induced significant expression of peripheral interferon-stimulated-gene (ISG) mRNA in the absence of detectable serum interferon-α and systemic adverse events (AEs). We evaluated the safety, pharmacokinetics and pharmacodynamics of GS-9620 in treatment-naive patients chronically infected with HCV genotype 1.

METHODS

In this double-blind, placebo-controlled study, 51 patients were randomized 5:1 (active:placebo) to receive either a single dose or two once-weekly doses of GS-9620 at four dose levels (0.3, 1, 2 and 4 mg) or placebo. Pharmacodynamic assessments included peripheral ISG15 mRNA expression, serum interferon-α and interferon-γ-inducible protein (IP)-10 levels and HCV RNA quantification.

RESULTS

GS-9620 was well-tolerated at all doses. Most AEs were mild or moderate in severity. GS-9620 exhibited dose-linear pharmacokinetics with a median half-life in plasma of 18 h. Transient, dose-dependent ISG15 induction was observed at 1, 2 and 4 mg, with peak mean fold change within 48 h followed by a decline to baseline levels within 7 days of dosing. Serum interferon-α induction post-baseline was detected in 16.7% (8/48) of patients. No clinically significant reductions in HCV RNA were observed.

CONCLUSIONS

GS-9620 was safe, well-tolerated and biologically active in patients with HCV infection. Induction of ISG15 occurred in the absence of detectable serum interferon-α or systemic AEs in most patients, supporting a pre-systemic mechanism of action. ClinicalTrials.gov identifier: NCT01591668.

Analysis of the transcriptome and immune function of monocytes during IFNα-based therapy in chronic HCV revealed induction of TLR7 responsiveness

Although in vitro studies have been performed to dissect the mechanism of action of IFNα, detailed in vivo studies on the long-term effects of IFNα on monocytes have not been performed. Here we examined peripheral blood from 14 chronic HCV patients at baseline and 12 weeks after start of IFNα-based therapy. Monocytes were phenotyped by flow-cytometry and their function evaluated upon TLR stimulation and assessed by multiplex cytokine assays. During therapy of HCV patients, monocytes displayed a hyperactive state as evidenced by increased TLR-induced pro-inflammatory cytokine levels, as well as enhanced CD69 and CD83 mRNA and protein expression. Moreover, monocytes from 8 patients at baseline and 12 weeks after start of IFNα-based therapy were transcriptomically profiled by high throughput RNA-sequencing. Detailed RNA-seq analysis of monocytes showed significant ISG mRNA induction during therapy. Importantly, IFNα-based therapy activated TLR7 signaling pathways, as demonstrated by up-regulated expression of TLR7, MyD88, and IRF7 mRNA, whereas other TLR family members as well as CD1c, CLEC4C, and CLEC9A were not induced. The induction of TLR7 responsiveness of monocytes by IFNα in vivo in HCV patients is relevant for the development of TLR7 agonists that are currently under development as a promising immunotherapeutic compounds to treat chronic viral hepatitis.

Emerging antivirals for the treatment of hepatitis B

Chronic infection with hepatitis B virus (HBV) constitutes a major global public health threat, causing substantial disease burdens such as liver cirrhosis and hepatocellular carcinoma, thus representing high unmet medical needs. Currently available therapies are safe, well tolerated, and highly effective in decreasing viremia and improving measured clinical outcomes with low rates of antiviral resistance. However, long-term management remains a clinical challenge, mainly due to the slow kinetics of HBV surface antigen clearance. In this article, we review emerging antivirals directed at novel targets derived from mechanisms of viral cellular entry, viral replication, viral assembly, and the host immune response, leading to preclinical and clinical trials for possible future therapeutic intervention. The recent therapeutic advances in the development of all categories of HBV inhibitors may pave the way for regimens of finite duration that result in long-lasting control of chronic hepatitis B infection.

Tickling the TLR7 to cure viral hepatitis

Chronic hepatitis B and C are the leading causes of liver disease and liver transplantation worldwide. Ability to mount an effective immune response against both HBV and HCV is associated with spontaneous clearance of both infections, while an inability to do so leads to chronicity of both infections. To mount an effective immune response, both innate and adaptive immune responses must work in tandem. Hence, developing protective immunity to hepatitis viruses is an important goal in order to reduce the global burden of these two infections and prevent development of long-term complications. In this regard, the initial interactions between the pathogen and immune system are pivotal in determining the effectiveness of immune response and subsequent elimination of pathogens. Toll-like receptors (TLRs) are important regulators of innate and adaptive immune responses to various pathogens and are often involved in initiating and augmenting effective antiviral immunity. Immune-based therapeutic strategies that specifically induce type I interferon responses are associated with functional cure for both chronic HBV and HCV infections. Precisely, TLR7 stimulation mediates an endogenous type I interferon response, which is critical in development of a broad, effective and protective immunity against hepatitis viruses. This review focuses on anti-viral strategies that involve targeting TLR7 that may lead to development of protective immunity and eradication of hepatitis B.

Strategies to eliminate HBV infection

Chronic HBV infection is a major public health concern affecting over 240 million people worldwide. Although suppression of HBV replication is achieved in the majority of patients with currently available newer antivirals, discontinuation of therapy prior to hepatitis B surface antigen loss or seroconversion is associated with relapse of HBV in the majority of cases. Thus, new therapeutic modalities are needed to achieve eradication of the virus from chronically infected patients in the absence of therapy. The basis of HBV persistence includes viral and host factors. Here, we review novel strategies to achieve sustained cure or elimination of HBV. The novel approaches include targeting the viral and or host factors required for viral persistence, and novel immune-based therapies, including therapeutic vaccines.

Targeting toll-like receptors: promising therapeutic strategies for the management of sepsis-associated pathology and infectious diseases

Toll-like receptors (TLRs) are pattern recognition receptors playing a fundamental role in sensing microbial invasion and initiating innate and adaptive immune responses. TLRs are also triggered by danger signals released by injured or stressed cells during sepsis. Here we focus on studies developing TLR agonists and antagonists for the treatment of infectious diseases and sepsis. Positioned at the cell surface, TLR4 is essential for sensing lipopolysaccharide of Gram-negative bacteria, TLR2 is involved in the recognition of a large panel of microbial ligands, while TLR5 recognizes flagellin. Endosomal TLR3, TLR7, TLR8, TLR9 are specialized in the sensing of nucleic acids produced notably during viral infections. TLR4 and TLR2 are favorite targets for developing anti-sepsis drugs, and antagonistic compounds have shown efficient protection from septic shock in pre-clinical models. Results from clinical trials evaluating anti-TLR4 and anti-TLR2 approaches are presented, discussing the challenges of study design in sepsis and future exploitation of these agents in infectious diseases. We also report results from studies suggesting that the TLR5 agonist flagellin may protect from infections of the gastrointestinal tract and that agonists of endosomal TLRs are very promising for treating chronic viral infections. Altogether, TLR-targeted therapies have a strong potential for prevention and intervention in infectious diseases, notably sepsis.