Chronic hepatitis B virus (HBV) infection remains an important unmet medical need with 240 million patients worldwide. The HBV capsid assembly process has emerged as a key target for more efficient antiviral intervention. Pevifoscorvir sodium (ALG-000184), an oral prodrug of the potent HBV capsid assembly modulator (CAM) ALG-001075 showed significant reductions in HBV DNA, HBV RNA and other viral antigens (HBsAg, HBcrAg and HBeAg) in Phase I clinical participants with chronic HBV infection. We aim to characterize the antiviral properties of ALG-001075. ALG-001075 is a highly potent CAM that inhibited HBV DNA production in cellular settings with EC50 values below 1 nM and an EC99.9 value of only 22 nM. ALG-001075 was shown to induce the formation of empty, but not aberrant viral particles as demonstrated by fluorescence quenching, electron microscopy, size-exclusion chromatography, immunofluorescent staining and NMR analysis, thereby classifying it as a CAM-E. Notably, solid-state NMR spectra of wild-type capsids in the presence of ALG-001075 revealed a characteristic CAM-E fingerprint at atomic resolution. ALG-001075 showed potent antiviral activity against HBV strains from genotypes A-J, nucleoside analogue-resistant virus strains and known CAM-resistance mutations, with the exception of T33N, T33P and V124G, which induced 6-to-28-fold loss in ALG-001075 activity. The in vivo efficacy of ALG-001075 was confirmed in adeno-associated virus-HBV mice, where ALG-001075 demonstrated up to 5 log10 reduction in circulating HBV DNA levels. Because of its robust antiviral potency and favorable preclinical resistance profile, ALG-001075 was selected for further clinical development under the form of its prodrug pevifoscorvir sodium.

The SARS-CoV-2 outbreak of 2019 had a devastating impact on global health and economies worldwide. The viral cysteine protease (3CLpro) is responsible for viral polypeptide bond cleavages and is therefore an essential target to inhibit viral replication. Here, we report the discovery of an orally available, reversible covalent inhibitor of the SARS-CoV-2 main protease that is also highly active across other human coronaviruses and demonstrated oral efficacy in a Syrian hamster infection model at low plasma concentrations. Projection of pharmacokinetics (PK) in humans, based on PK studies in preclinical species and enhanced in vitro/in vivo efficacy of ALG-097558 (7) indicated the potential for BID dosing without the need for ritonavir, the PK boosting component of Paxlovid. After preclinical safety and pharmacological studies, ALG-097558 has progressed to phase 1 clinical trials.

Agonists of thyroid hormone receptor β (THR-β) decreased LDL cholesterol (LDL-C) and triglyceride (TG) levels in human clinical trials for patients with dyslipidemia. The authors present the highly potent and selective compound ALG-055009 (14) as a potential best in class THR-β agonist. The high metabolic stability and good permeability translated well in vivo to afford a long in vivo half-life pharmacokinetic profile with limited liability for DDI, and it overcomes certain drawbacks seen in recent clinical candidates.

Chronic hepatitis B (CHB) represents a significant unmet medical need with few options beyond lifelong treatment with nucleoside analogues, which rarely leads to a functional cure. Novel agents that reduce levels of HBV DNA, RNA and other viral antigens could lead to better treatment outcomes. The capsid assembly modulator (CAM) class of compounds represents an important modality for chronic suppression and to improve functional cure rates, either alone or in combination. GLP-26 is a potent CAM, which in this work was optimized for potency, safety, and other drug-like properties leading to ALG-001075. ALG-001075 was further advanced through clinical development as the highly soluble prodrug ALG-000184. ALG-000184 is currently being explored in multiple clinical trials in HBV-infected subjects where unprecedented reductions in HBV DNA, RNA and other viral antigens have been observed, making ALG-000184 a promising candidate to become a cornerstone for future chronic suppressive and combination treatment regimens for CHB.

Respiratory syncytial virus (RSV) can cause pulmonary complications in infants, elderly and immunocompromised patients. While two vaccines and two prophylactic monoclonal antibodies are now available, treatment options are still needed. JNJ-7184 is a non-nucleoside inhibitor of the RSV-Large (L) polymerase, displaying potent inhibition of both RSV-A and -B strains. Resistance selection and hydrogen-deuterium exchange experiments suggested JNJ-7184 binds RSV-L in the connector domain. JNJ-7184 prevented RSV replication and transcription by inhibiting initiation or early elongation. JNJ-7184 was effective in air-liquid interface cultures and therapeutically in neonatal lambs, acting to drastically reverse the appearance of lung pathology.

The 35th International Conference on Antiviral Research (ICAR), sponsored by the International Society for Antiviral Research (ISAR), was held in Seattle, Washington, USA, on March 21-25, 2022 and concurrently through an interactive remote meeting platform. This report gives an overview of the conference on behalf of the society. It provides a general review of the meeting and awardees, summarizing the presentations and their main conclusions from the perspective of researchers active in many different areas of antiviral research and development. Through ICAR, leaders in the field of antiviral research were able to showcase their efforts, as participants learned about key advances in the field. The impact of these efforts was exemplified by many presentations on SARS-CoV-2 demonstrating the remarkable response to the ongoing pandemic, as well as future pandemic preparedness, by members of the antiviral research community. As we address ongoing outbreaks and seek to mitigate those in the future, this meeting continues to support outstanding opportunities for the exchange of knowledge and expertise while fostering cross-disciplinary collaborations in therapeutic and vaccine development. The 36th ICAR will be held in Lyon, France, March 13-17, 2023.

Background and Aims: Effective therapies leading to a functional cure for chronic hepatitis B are still lacking. Class A capsid assembly modulators (CAM-As) are an attractive modality to address this unmet medical need. CAM-As induce aggregation of the HBV core protein (HBc) and lead to sustained HBsAg reductions in a chronic hepatitis B mouse model. Here, we investigate the underlying mechanism of action for CAM-A compound RG7907. Approach and Results: RG7907 induced extensive HBc aggregation in vitro , in hepatoma cells, and in primary hepatocytes. In the adeno-associated virus (AAV)–HBV mouse model, the RG7907 treatment led to a pronounced reduction in serum HBsAg and HBeAg, concomitant with clearance of HBsAg, HBc, and AAV-HBV episome from the liver. Transient increases in alanine transaminase, hepatocyte apoptosis, and proliferation markers were observed. These processes were confirmed by RNA sequencing, which also uncovered a role for interferon alpha and gamma signaling, including the interferon-stimulated gene 15 (ISG15) pathway. Finally, the in vitro observation of CAM-A–induced HBc–dependent cell death through apoptosis established the link of HBc aggregation to in vivo loss of infected hepatocytes. Conclusions: Our study unravels a previously unknown mechanism of action for CAM-As such as RG7907 in which HBc aggregation induces cell death, resulting in hepatocyte proliferation and loss of covalently closed circular DNA or its equivalent, possibly assisted by an induced innate immune response. This represents a promising approach to attain a functional cure for chronic hepatitis B.

ABSTRACT Capsid assembly modulators (CAMs) are a novel class of therapeutic small molecules with the potential to address the continued global challenge posed by chronic hepatitis B (CHB). Class A CAMs (CAM-As) are particularly attractive because they induce loss of hepatitis B virus (HBV)-infected hepatocytes in animal models. All CAM-As described to date are heteroaryldihydropyrimidines (HAPs) which come with several drawbacks. Here, we report on the first non-HAP CAM-As ALG-005398 and ALG-005863 and provide a detailed in vitro intracellular characterization. These non-HAP CAM-As are potent inhibitors of HBV DNA production and also block the establishment of cccDNA. Non-HAP CAM-As can be classified into two distinct profiles: CAM-A i and CAM-A t , which are in turn differentiated from the HAP CAM-A h profile. CAM-A i molecules induce larger and more irregular capsids in electron microscopy and cellular HBV core protein (HBc) staining, whereas CAM-A t -induced capsids and aggregates are smaller but more numerous. CAM-A i and CAM-A t also induce a different subnuclear localization (no co-localization with promyelocytic leukemia bodies) and show a lower propensity to CAM-A-induced HBc-dependent cell death compared to CAM-A h . CAM-A t s ALG-005398 and ALG-006162 showed steady reductions of circulating HBsAg and HBeAg with minimal alanine aminotransferase (ALT) elevation in the adeno-associated virus (AAV)-HBV mouse model, accompanied by loss of the AAV-HBV episome and infected hepatocytes. Moreover, these effects were sustained for at least 13 weeks after end of treatment. The differentiated mechanism of action and sustained in vivo response make non-HAP CAM-As a promising potential component of future functional cure regimens for CHB patients. IMPORTANCE Chronic hepatitis B is the most important cause of liver cancer worldwide and affects more than 290 million people. Current treatments are mostly suppressive and rarely lead to a cure. Therefore, there is a need for novel and curative drugs that target the host or the causative agent, hepatitis B virus itself. Capsid assembly modulators are an interesting class of antiviral molecules that may one day become part of curative treatment regimens for chronic hepatitis B. Here we explore the characteristics of a particularly interesting subclass of capsid assembly modulators. These so-called non-HAP CAM-As have intriguing properties in cell culture but also clear virus-infected cells from the mouse liver in a gradual and sustained way. We believe they represent a considerable improvement over previously reported molecules and may one day be part of curative treatment combinations for chronic hepatitis B.

Stimulator of interferon genes (STING) agonists have shown potent anti-tumor efficacy in various mouse tumor models and have the potential to overcome resistance to immune checkpoint inhibitors (ICI) by linking the innate and acquired immune systems. First-generation STING agonists are administered intratumorally; however, a systemic delivery route would greatly expand the clinical use of STING agonists. Biochemical and cell-based experiments, as well as syngeneic mouse efficacy models, were used to demonstrate the anti-tumoral activity of ALG-031048, a novel STING agonist. In vitro, ALG-031048 is highly stable in plasma and liver microsomes and is resistant to degradation via phosphodiesterases. The high stability in biological matrices translated to good cellular potency in a HEK 293 STING R232 reporter assay, efficient activation and maturation of primary human dendritic cells and monocytes, as well as long-lasting, antigen-specific anti-tumor activity in up to 90% of animals in the CT26 mouse colon carcinoma model. Significant reductions in tumor growth were observed in two syngeneic mouse tumor models following subcutaneous administration. Combinations of ALG-031048 and ICIs further enhanced the in vivo anti-tumor activity. This initial demonstration of anti-tumor activity after systemic administration of ALG-031048 warrants further investigation, while the combination of systemically administered ALG-031048 with ICIs offers an attractive approach to overcome key limitations of ICIs in the clinic.

Paxlovid is the first oral antiviral approved for treatment of SARS-CoV-2 infection. Antiviral treatments are often associated with the development of drug-resistant viruses.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of the COVID-19 pandemic. While the development of vaccines and the emergence of antiviral therapeutics is promising, alternative strategies to combat COVID-19 (and potential future pandemics) remain an unmet need. Coronaviruses feature a unique mechanism that may present opportunities for therapeutic intervention: the RNA polymerase complex of coronaviruses is distinct in its ability to proofread and remove mismatched nucleotides during genome replication and transcription. The proofreading activity has been linked to the exonuclease (ExoN) activity of non-structural protein 14 (NSP14). Here, we review the role of NSP14, and other NSPs, in SARS-CoV-2 replication and describe the assays that have been developed to assess the ExoN function. We also review the nucleoside analogs and non-nucleoside inhibitors known to interfere with the proofreading activity of NSP14. Although not yet validated, the potential use of non-nucleoside proofreading inhibitors in combination with chain-terminating nucleosides may be a promising avenue for the development of anti-CoV agents.

As a result of the multiple gathering and travels restrictions during the SARS-CoV-2 pandemic, the annual meeting of the International Society for Antiviral Research (ISAR), the International Conference on Antiviral Research (ICAR), could not be held in person in 2021. Nonetheless, ISAR successfully organized a remote conference, retaining the most critical aspects of all ICARs, a collegiate gathering of researchers in academia, industry, government and non-governmental institutions working to develop, identify, and evaluate effective antiviral therapy for the benefit of all human beings. This article highlights the 2021 remote meeting, which presented the advances and objectives of antiviral and vaccine discovery, research, and development. The meeting resulted in a dynamic and effective exchange of ideas and information, positively impacting the prompt progress towards new and effective prophylaxis and therapeutics.