Discovery of GS-7682, a Novel 4'-Cyano-Modified -Nucleoside Prodrug with Broad Activity against Pneumo- and Picornaviruses and Efficacy in RSV-Infected African Green Monkeys.

Acute respiratory viral infections, such as pneumovirus and respiratory picornavirus infections, exacerbate disease in COPD and asthma patients. A research program targeting respiratory syncytial virus (RSV) led to the discovery of GS-7682 (), a novel phosphoramidate prodrug of a 4'-CN-4-aza-7,9-dideazaadenosine -nucleoside GS-646089 () with broad antiviral activity against RSV (EC = 3-46 nM), human metapneumovirus (EC = 210 nM), human rhinovirus (EC = 54-61 nM), and enterovirus (EC = 83-90 nM). Prodrug optimization for cellular potency and lung cell metabolism identified 5'-methyl [()-hydroxy(phenoxy)phosphoryl]-l-alaninate in combination with 2',3'-diisobutyrate promoieties as being optimal for high levels of intracellular triphosphate formation and .

The oral nucleoside prodrug GS-5245 is efficacious against SARS-CoV-2 and other endemic, epidemic, and enzootic coronaviruses.

Despite the wide availability of several safe and effective vaccines that prevent severe COVID-19, the persistent emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOCs) that can evade vaccine-elicited immunity remains a global health concern. In addition, the emergence of SARS-CoV-2 VOCs that can evade therapeutic monoclonal antibodies underscores the need for additional, variant-resistant treatment strategies. Here, we characterize the antiviral activity of GS-5245, obeldesivir (ODV), an oral prodrug of the parent nucleoside GS-441524, which targets the highly conserved viral RNA-dependent RNA polymerase (RdRp).

Discovery of GS-5245 (Obeldesivir), an Oral Prodrug of Nucleoside GS-441524 That Exhibits Antiviral Efficacy in SARS-CoV-2-Infected African Green Monkeys.

Remdesivir is an phosphoramidate prodrug that releases the monophosphate of nucleoside GS-441524 () into lung cells, thereby forming the bioactive triphosphate . , an analog of ATP, inhibits the SARS-CoV-2 RNA-dependent RNA polymerase replication and transcription of viral RNA. Strong clinical results for have prompted interest in oral approaches to generate .

Efficacy of the oral nucleoside prodrug GS-5245 (Obeldesivir) against SARS-CoV-2 and coronaviruses with pandemic potential.

Despite the wide availability of several safe and effective vaccines that can prevent severe COVID-19 disease, the emergence of SARS-CoV-2 variants of concern (VOC) that can partially evade vaccine immunity remains a global health concern. In addition, the emergence of highly mutated and neutralization-resistant SARS-CoV-2 VOCs such as BA.1 and BA.

Intravenous delivery of GS-441524 is efficacious in the African green monkey model of SARS-CoV-2 infection.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the COVID-19 pandemic, has infected over 260 million people over the past 2 years. Remdesivir (RDV, VEKLURY®) is currently the only antiviral therapy fully approved by the FDA for the treatment of COVID-19. The parent nucleoside of RDV, GS-441524, exhibits antiviral activity against numerous respiratory viruses including SARS-CoV-2, although at reduced in vitro potency compared to RDV in most assays.

Journey of remdesivir from the inhibition of hepatitis C virus to the treatment of COVID-19.

If a planned path reaches a dead-end, one can simply stop. Or one can turn around, walk back to the last intersection and take another path, or one can consider taking few paths in parallel. The last scenario is reflective of the journey of remdesivir, the first antiviral for the treatment of COVID-19, that was approved by FDA less than 10 months after the isolation of SARS-CoV-2, the virus responsible for the COVID-19 pandemic.

Therapeutic treatment with an oral prodrug of the remdesivir parental nucleoside is protective against SARS-CoV-2 pathogenesis in mice.

The coronavirus disease 2019 (COVID-19) pandemic remains uncontrolled despite the rapid rollout of safe and effective severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines, underscoring the need to develop highly effective antivirals. In the setting of waning immunity from infection and vaccination, breakthrough infections are becoming increasingly common and treatment options remain limited. In addition, the emergence of SARS-CoV-2 variants of concern, with their potential to escape neutralization by therapeutic monoclonal antibodies, emphasizes the need to develop second-generation oral antivirals targeting highly conserved viral proteins that can be rapidly deployed to outpatients.

Phosphoramidate Prodrugs Continue to Deliver, The Journey of Remdesivir (GS-5734) from RSV to SARS-CoV-2.

Remdesivir (GS-5734) is a monophenol, 2-ethylbutylalanine phosphoramidate prodrug of a 1'-cyano-4-aza-7,9-dideazaadenosine C-nucleoside (GS-441524) that is FDA approved for the treatment of hospitalized patients with COVID-19. The prodrug, initially invented for respiratory syncytial virus, was later found to have activity toward emerging RNA viruses, including Ebola and coronaviruses. Remdesivir is among the first examples of a phosphoramidate prodrug aimed at delivering a nucleoside monophosphate into lung cells to efficiently generate the nucleoside triphosphate inhibitor of viral RNA polymerases.

Subcutaneous remdesivir administration prevents interstitial pneumonia in rhesus macaques inoculated with SARS-CoV-2.

The utility of remdesivir treatment in COVID-19 patients is currently limited by the necessity to administer this antiviral intravenously, which has generally limited its use to hospitalized patients. Here, we tested a novel, subcutaneous formulation of remdesivir in the rhesus macaque model of SARS-CoV-2 infection that was previously used to establish the efficacy of remdesivir against this virus in vivo. Compared to vehicle-treated animals, macaques treated with subcutaneous remdesivir from 12 h through 6 days post inoculation showed reduced signs of respiratory disease, a reduction of virus replication in the lower respiratory tract, and an absence of interstitial pneumonia.

Inhaled remdesivir reduces viral burden in a nonhuman primate model of SARS-CoV-2 infection.

Remdesivir (RDV) is a nucleotide analog prodrug with demonstrated clinical benefit in patients with coronavirus disease 2019 (COVID-19). In October 2020, the US FDA approved intravenous (IV) RDV as the first treatment for hospitalized COVID-19 patients. Furthermore, RDV has been approved or authorized for emergency use in more than 50 countries.

Oral prodrug of remdesivir parent GS-441524 is efficacious against SARS-CoV-2 in ferrets.

Remdesivir is an antiviral approved for COVID-19 treatment, but its wider use is limited by intravenous delivery. An orally bioavailable remdesivir analog may boost therapeutic benefit by facilitating early administration to non-hospitalized patients. This study characterizes the anti-SARS-CoV-2 efficacy of GS-621763, an oral prodrug of remdesivir parent nucleoside GS-441524.

Therapeutic efficacy of an oral nucleoside analog of remdesivir against SARS-CoV-2 pathogenesis in mice.

The COVID-19 pandemic remains uncontrolled despite the rapid rollout of safe and effective SARS-CoV-2 vaccines, underscoring the need to develop highly effective antivirals. In the setting of waning immunity from infection and vaccination, breakthrough infections are becoming increasingly common and treatment options remain limited. Additionally, the emergence of SARS-CoV-2 variants of concern with their potential to escape therapeutic monoclonal antibodies emphasizes the need to develop second-generation oral antivirals targeting highly conserved viral proteins that can be rapidly deployed to outpatients.

Prodrugs of a 1'-CN-4-Aza-7,9-dideazaadenosine -Nucleoside Leading to the Discovery of Remdesivir (GS-5734) as a Potent Inhibitor of Respiratory Syncytial Virus with Efficacy in the African Green Monkey Model of RSV.

A discovery program targeting respiratory syncytial virus (RSV) identified -nucleoside (RSV A2 EC = 530 nM) as a phenotypic screening lead targeting the RSV RNA-dependent RNA polymerase (RdRp). Prodrug exploration resulted in the discovery of remdesivir (, GS-5734) that is >30-fold more potent than against RSV in HEp-2 and NHBE cells. Metabolism studies in vitro confirmed the rapid formation of the active triphosphate metabolite, -, and in vivo studies in cynomolgus and African Green monkeys demonstrated a >10-fold higher lung tissue concentration of following molar normalized IV dosing of compared to that of .

Safety, pharmacokinetics and pharmacodynamics of selgantolimod, an oral Toll-like receptor 8 agonist: a Phase Ia study in healthy subjects.

Background: Selgantolimod is a novel oral, selective Toll-like receptor 8 (TLR8) agonist in development for the treatment of chronic hepatitis B (CHB). TLR8 is an endosomal innate immune receptor and a target for treatment of viral infections. This first-in-human study investigated the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of selgantolimod in healthy volunteers.

Discovery of GS-9688 (Selgantolimod) as a Potent and Selective Oral Toll-Like Receptor 8 Agonist for the Treatment of Chronic Hepatitis B.

Toll-like receptor 8 (TLR8) recognizes pathogen-derived single-stranded RNA fragments to trigger innate and adaptive immune responses. Chronic hepatitis B (CHB) is associated with a dysfunctional immune response, and therefore a selective TLR8 agonist may be an effective treatment option. Structure-based optimization of a dual TLR7/8 agonist led to the identification of the selective TLR8 clinical candidate ()-2-((2-amino-7-fluoropyrido[3,2-]pyrimidin-4-yl)amino)-2-methylhexan-1-ol (GS-9688, ()-).

Toll-Like Receptor 8 Agonist GS-9688 Induces Sustained Efficacy in the Woodchuck Model of Chronic Hepatitis B.

Background And Aims: GS-9688 (selgantolimod) is an oral selective small molecule agonist of toll-like receptor 8 in clinical development for the treatment of chronic hepatitis B. In this study, we evaluated the antiviral efficacy of GS-9688 in woodchucks chronically infected with woodchuck hepatitis virus (WHV), a hepadnavirus closely related to hepatitis B virus.

Approach And Results: WHV-infected woodchucks received eight weekly oral doses of vehicle, 1 mg/kg GS-9688, or 3 mg/kg GS-9688.

Structure-guided discovery of a novel, potent, and orally bioavailable 3,5-dimethylisoxazole aryl-benzimidazole BET bromodomain inhibitor.

The bromodomain and extra-terminal (BET) family of proteins, consisting of the bromodomains containing protein 2 (BRD2), BRD3, BRD4, and the testis-specific BRDT, are key epigenetic regulators of gene transcription and has emerged as an attractive target for anticancer therapy. Herein, we describe the discovery of a novel potent BET bromodomain inhibitor, using a systematic structure-based approach focused on improving potency, metabolic stability, and permeability. The optimized dimethylisoxazole aryl-benzimidazole inhibitor exhibited high potency towards BRD4 and related BET proteins in biochemical and cell-based assays and inhibited tumor growth in two proof-of-concept preclinical animal models.

Discovery of a Potent and Orally Bioavailable Cyclophilin Inhibitor Derived from the Sanglifehrin Macrocycle.

Cyclophilins are a family of peptidyl-prolyl isomerases that are implicated in a wide range of diseases including hepatitis C. Our aim was to discover through total synthesis an orally bioavailable, non-immunosuppressive cyclophilin (Cyp) inhibitor with potent anti-hepatitis C virus (HCV) activity that could serve as part of an all oral antiviral combination therapy. An initial lead 2 derived from the sanglifehrin A macrocycle was optimized using structure based design to produce a potent and orally bioavailable inhibitor 3.

Phase 1 First-in-Human, Single- and Multiple-Ascending Dose, and Food Effect Studies to Assess the Safety, Tolerability, and Pharmacokinetics of Presatovir for the Treatment of Respiratory Syncytial Virus Infection.

Respiratory syncytial virus (RSV)-associated respiratory tract infection is a leading cause of hospitalizations in infants for which no effective treatment exists. RSV infection is also an important cause of respiratory disease in adults and immunocompromised patients. Presatovir (GS-5806) is an orally bioavailable antiviral agent that inhibits fusion of RSV with host cell membranes.

Coronavirus Susceptibility to the Antiviral Remdesivir (GS-5734) Is Mediated by the Viral Polymerase and the Proofreading Exoribonuclease.

Emerging coronaviruses (CoVs) cause severe disease in humans, but no approved therapeutics are available. The CoV nsp14 exoribonuclease (ExoN) has complicated development of antiviral nucleosides due to its proofreading activity. We recently reported that the nucleoside analogue GS-5734 (remdesivir) potently inhibits human and zoonotic CoVs and in a severe acute respiratory syndrome coronavirus (SARS-CoV) mouse model.

Control of α/β Anomer Formation by a 2',5' Bridge: Toward Nucleoside Derivatives Locked in the South Conformation.

We describe a novel stereoselective synthesis of nucleoside derivatives with the ribose ring locked in the South conformation by a bridge between C2' and C5'. Despite the intrinsic constraints of the bicyclic structure, we demonstrate that their synthesis can be achieved by ring closing metathesis of readily accessible precursors. The obtained ribose derivatives are, however, very poor substrates for further installation of the nucleobases, and even simple nucleophiles, such as azido or cyano anions, react with unexpected stereo- or regioselectivity under standard glycosylation conditions.

Broad-spectrum antiviral GS-5734 inhibits both epidemic and zoonotic coronaviruses.

Emerging viral infections are difficult to control because heterogeneous members periodically cycle in and out of humans and zoonotic hosts, complicating the development of specific antiviral therapies and vaccines. Coronaviruses (CoVs) have a proclivity to spread rapidly into new host species causing severe disease. Severe acute respiratory syndrome CoV (SARS-CoV) and Middle East respiratory syndrome CoV (MERS-CoV) successively emerged, causing severe epidemic respiratory disease in immunologically naïve human populations throughout the globe.

GS-5734 and its parent nucleoside analog inhibit Filo-, Pneumo-, and Paramyxoviruses.

GS-5734 is a monophosphate prodrug of an adenosine nucleoside analog that showed therapeutic efficacy in a non-human primate model of Ebola virus infection. It has been administered under compassionate use to two Ebola patients, both of whom survived, and is currently in Phase 2 clinical development for treatment of Ebola virus disease. Here we report the antiviral activities of GS-5734 and the parent nucleoside analog across multiple virus families, providing evidence to support new indications for this compound against human viruses of significant public health concern.