Obeldesivir (GS-5245, ODV), an orally administered 5'-isobutyryl ester prodrug of GS-441524, has demonstrated anti-SARS-CoV-2 activity in preclinical and clinical settings. ODV is hydrolyzed in plasma to provide high systemic exposures of GS-441524, enabling the efficient intracellular formation of the bioactive 5'-triphosphate GS-443902, an ATP analog inhibiting the SARS-CoV-2 RNA-dependent RNA polymerases. Remdesivir (RDV), the first US FDA-approved antiviral treatment for COVID-19, is also activated to GS-443902. In this paper, we systematically profiled the human enzymes potentially involved in ODV and RDV activation using multiple approaches: (i) biochemical studies on the catalytic efficiency (kcat/Km); (ii) analysis of activation in single-gene knockout cells; and (iii) the antiviral activity assessment in single-gene knockout cells. Our results demonstrated that ODV hydrolysis to GS-441524 is catalyzed by carboxylesterase 1 and 2 with high efficiency. For the enzymes involved in the consecutive formation of 5'-mono-, di-, and tri-phosphates (MP, DP, and TP), adenosine kinase (ADK) likely plays a minor role in forming GS-441524-MP, suggesting the involvement of other phosphotransferases. This was further supported by cell-based single-gene ADK-knockout studies. In contrast, both biochemical and cell-based assay data strongly support adenylate kinase 2 as the key enzyme for the phosphorylation of GS-441524-MP, while nucleoside diphosphate kinase NM23-H2, phosphoglycerate kinase, and pyruvate kinase likely all contribute to the formation of GS-441524-TP. This work leads to a deeper understanding of ODV and RDV metabolism, and suggests further studies are needed to identify the enzyme responsible for the activation of GS-441524 to its 5'-monophosphate.

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 (1), a novel phosphoramidate prodrug of a 4 '-CN-4-aza-7,9-dideazaadenosine C-nucleoside GS-646089 (2) with broad antiviral activity against RSV (EC50 = 3-46 nM), human metapneumovirus (EC50 = 210 nM), human rhinovirus (EC50 = 54-61 nM), and enterovirus (EC50 = 83-90 nM). Prodrug optimization for cellular potency and lung cell metabolism identified 5 '-methyl [(S)-hydroxy(phenoxy)phosphoryl]-l-alaninate in combination with 2 ',3 '-diisobutyrate promoieties as being optimal for high levels of intracellular triphosphate formation in vitro and in vivo. 1 demonstrated significant reductions of viral loads in the lower respiratory tract of RSV-infected African green monkeys when administered once daily via intratracheal nebulized aerosol. Together, these findings support additional evaluation of 1 and its analogues as potential therapeutics for pneumo- and picornaviruses.

The Glucagon-like peptide 1 receptor (GLP-1R) is a class B1 G-protein-coupled receptor (GPCR) that is widely expressed and helps mediate insulin secretion, gastric emptying, and satiety. Currently, GLP-1R peptide agonists are used as standard of care for the treatment of T2DM and more recently for obesity. These GLP-1R peptide agonists require frequent subcutaneous injections or strict dosing guidelines thus increasing the need to develop an oral small-molecule GLP-1R agonist. Here we describe the identification of a novel small molecule GLP-1R agonist (GS-4571) which stimulated a potent cAMP response in pancreatic β-cells (EndoC-BH1) and selective agonism against human and monkey GLP-1R versus other class B GPCRs. In an intraperitoneal glucose tolerance test (IPGTT) it demonstrated improved glucose tolerance in humanized GLP-1R mice. Further studies, in obese cynomolgus monkeys, GS-4571 demonstrated similar improvements in glucose tolerance after a single dose treatment. Once-daily oral administration of GS-4571 in obese diabetic cynomolgus monkeys not only showed improved glycemic control but also showed a reduction in energy intake which led to an increase in weight loss over 36 days. Together these data support the continued development of GS-4571 into the clinic as a novel orally bioavailable GLP-1R small molecule agonist. Disclosure J. Vogel: None. M. Seung: None. B. Marchand: Employee; Gilead Sciences, Inc. Stock/Shareholder; Gilead Sciences, Inc., Pfizer Inc., Arrowhead Pharmaceuticals, Inc., Kronos Bio, Inc., Allogene Therapeutics, Inc., AbCellera Biologics Inc., Arbutus Biopharma Corporation. N. Bhangre: Employee; Gilead Sciences, Inc. Research Support; Gilead Sciences, Inc. Stock/Shareholder; Gilead Sciences, Inc. J. Mukherjee: None. S.E. Ammann: Employee; Gilead Sciences, Inc. M. Armstrong: Employee; Gilead Sciences, Inc. G. Brizgys: Employee; Gilead Sciences, Inc. E. Chin: Employee; Gilead Sciences, Inc. C. Chou: None. J. Cottell: Employee; Gilead Sciences, Inc. S.D. Schroeder: Employee; Gilead Sciences, Inc. R. Thomas-Tran: Employee; Gilead Sciences, Inc. Z. Yang: None. M. Peters: Employee; Gilead Sciences, Inc. G. Budas: Employee; Gilead Sciences, Inc. M.L. Mitchell: Employee; Gilead Sciences, Inc. M. Chojnacka: None. S. Jermain: None. J. Hung: Employee; Gilead Sciences, Inc. S. Kulkarni: None. Q. Yue: None. D.W. Lin: Employee; Gilead Sciences, Inc. D.A. Miranda: None.

We describe the discovery and preclinical characterization of a potent and selective lysophosphatidic acid receptor 1 (LPAR1) antagonist with a direct-acting antifibrotic mechanism. 18a was initially identified as a potent non-carboxylic acid LPAR1 antagonist in an LPA-induced myocardin-related transcription factor A (MRTF-A) nuclear translocation assay. Modifications to the aromatic elements in the structure allowed for improvements in metabolic stability and the mitigation of GSH adduct formation, but in vitro to in vivo clearance disconnects were observed with several potent sulfonamides (e.g., 27b) across preclinical species. Through modification of the sulfonamide, 42 (GS-2278) emerged as a potent LPAR1 antagonist with a suitable in vitro profile and desirable pharmacokinetic properties for oral QD dosing. GS-2278 dose-dependently blocked LPA-induced histamine release and demonstrated efficacy in an interventional model of bleomycin-induced lung fibrosis. However, CNS-related toxicity was observed in dogs, and based on these findings, the clinical development of GS-2278 for IPF was halted.

Protease inhibitors (PIs) remain an important component of antiretroviral therapy for the treatment of HIV-1 infection due to their high genetic barrier to resistance development. Nevertheless, the two most commonly prescribed HIV PIs, atazanavir and darunavir, still require co-administration with a pharmacokinetic boosting agent to maintain sufficient drug plasma levels which can lead to undesirable drug-drug interactions. Herein, we describe GS-9770, a novel investigational non-peptidomimetic HIV PI with unboosted once-daily oral dosing potential due to improvements in its metabolic stability and its pharmacokinetic properties in preclinical animal species. This compound demonstrates potent inhibitory activity and high on-target selectivity for recombinant HIV-1 protease versus other aspartic proteases tested. In cell culture, GS-9770 inhibits Gag polyprotein cleavage and shows nanomolar anti-HIV-1 potency in primary human cells permissive to HIV-1 infection and against a broad range of HIV subtypes. GS-9770 demonstrates an improved resistance profile against a panel of patient-derived HIV-1 isolates with resistance to atazanavir and darunavir. In resistance selection experiments, GS-9770 prevented the emergence of breakthrough HIV-1 variants at all fixed drug concentrations tested and required multiple protease substitutions to enable outgrowth of virus exposed to escalating concentrations of GS-9770. This compound also remained fully active against viruses resistant to drugs from other antiviral classes and showed no in vitro antagonism when combined pairwise with drugs from other antiretroviral classes. Collectively, these preclinical data identify GS-9770 as a potent, non-peptidomimetic once-daily oral HIV PI with potential to overcome the persistent requirement for pharmacological boosting with this class of antiretroviral agents.

Acute respiratory viral infections (ARVI), 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 ( 1 ) a novel phosphoramidate prodrug of a 4′-CN-4-aza-7,9-dideazaadenosine C -nucleoside GS-646089 ( 2 ) with broad antiviral activity against RSV EC50 = 3-46 nM, human metapneumovirus (hMPV) EC50 = 210 ± 50 nM, human rhinovirus (RV) EC50 = 54-61 nM, and enterovirus (EV) EC50 = 83-90 nM. Prodrug optimization for cellular potency and lung cell metabolism identified the 5’-methyl(( S )-hydroxy(phenoxy)phosphoryl)-L-alaninate in combination with 2’,3’-diisobutyrate promoieties as optimal for high intracellular triphosphate formation in vitro and in vivo. 1 demonstrated significant reductions of viral loads in the lower respiratory tract of RSV-infected African green monkeys when administered once daily via intratracheal nebulized aerosol. Together these finding support additional evaluation of 1 and its analogs as a potential therapeutic for pneumo- and picornaviruses. ### Competing Interest Statement Some authors are current or former employees of Gilead Sciences and may own company stock.

Dysregulated hepatocyte lipid metabolism is a hallmark of hepatic lipotoxicity and contributes to the pathogenesis of nonalcoholic steatohepatitis (NASH). Acetyl CoA carboxylase (ACC) inhibitors decrease hepatocyte lipotoxicity by inhibiting de novo lipogenesis and concomitantly increasing fatty acid oxidation (FAO), and firsocostat, a liver-targeted inhibitor of ACC1/2, is under evaluation clinically in patients with NASH. ACC inhibition is associated with improvements in indices of NASH and reduced liver triglyceride (TG) content, but also increased circulating TG in subjects with NASH and preclinical rodent models. Here we evaluated whether enhancing hepatocyte FAO by combining ACC inhibitors with peroxisomal proliferator-activated receptor (PPAR) or thyroid hormone receptor beta (THRβ) agonists could drive greater liver TG reduction and NASH/antifibrotic efficacy, while ameliorating ACC inhibitor-induced hypertriglyceridemia. In high-fat diet-fed dyslipidemic rats, the addition of PPAR agonists fenofibrate (Feno), elafibranor (Ela), lanifibranor (Lani), seladelpar (Sela) or saroglitazar (Saro), or the THRb agonist resmetirom (Res), to an analogue of firsocostat (ACCi) prevented ACCi-induced hypertriglyceridemia. However, only PPARα agonists (Feno and Ela) and Res provided additional liver TG reduction. In the choline-deficient high-fat diet rat model of advanced liver fibrosis, neither PPARα (Feno) nor THRβ (Res) agonism augmented the antifibrotic efficacy of ACCi. Conclusion: These data suggest that combination therapies targeting hepatocyte lipid metabolism may have beneficial effects on liver TG reduction; however, they may not be sufficient to drive fibrosis regression.

Background & Aims: Non-alcoholic steatohepatitis (NASH) is a chronic liver disease characterized by hepatic lipid accumulation, inflammation, and progressive fibrosis. Acetyl-CoA carboxylase (ACC) catalyzes the rate-limiting step of de novo lipogenesis and regulates fatty acid beta-oxidation in hepatocytes. ACC inhibition reduces hepatic fat content and markers of liver injury in patients with NASH; however, the effect of ACC inhibition on liver fibrosis has not been reported. Methods: A direct role for ACC in fibrosis was evaluated by measuring de novo lipogenesis, procollagen production, gene expression, glycolysis, and mitochondrial respiration in hepatic stellate cells (HSCs) in the absence or presence of small molecule inhibitors of ACC. ACC inhibitors were evaluated in rodent models of liver fibrosis induced by diet or the hepatotoxin, diethylnitrosamine. Fibrosis and hepatic steatosis were evaluated by histological and biochemical assessments. Results: Inhibition of ACC reduced the activation of TGF-beta-stimulated HSCs, as measured by both alpha-SMA expression and collagen production. ACC inhibition prevented a metabolic switch necessary for induction of glycolysis and oxidative phosphorylation during HSC activation. While the molecular mechanism by which inhibition of de novo lipogenesis blocks glycolysis and oxidative phosphorylation is unknown, we definitively show that HSCs require de novo lipogenesis for activation. Consistent with this direct antifibrotic mechanism in HSCs, ACC inhibition reduced liver fibrosis in a rat cholinedeficient, high-fat diet model and in response to chronic diethylnitrosamine-induced liver injury (in the absence of hepatic lipid accumulation). Conclusions: In addition to reducing lipid accumulation in hepatocytes, ACC inhibition also directly impairs the profibrogenic activity of HSCs. Thus, small molecule inhibitors of ACC may lessen fibrosis by reducing lipotoxicity in hepatocytes and by preventing HSC activation, providing a mechanistic rationale for the treatment of patients with advanced liver fibrosis due to NASH. Lay summary: Hepatic fibrosis is the most important predictor of liver-related outcomes in patients with non-alcoholic steato-hepatitis (NASH). Small molecule inhibitors of acetyl-CoA carboxylase (ACC) reduce hepatic fat content and markers of liver injury in patients with NASH. Herein, we report that inhibition of ACC and de novo lipogenesis also directly suppress the activation of hepatic stellate cells - the primary cell responsible for generating fibrotic scar in the liver - and thus fibrosis. These data provide further evidence for the use of ACC inhibitors to treat patients with NASH and advanced fibrosis. (C) 2020 European Association for the Study of the Liver. Published by Elsevier B.V.

The host structural maintenance of chromosomes 5/6 complex (Smc5/6) suppresses hepatitis B virus (HBV) transcription. HBV counters this restriction by expressing the X protein (HBx), which redirects the cellular DNA damage-binding protein 1 (DDB1)-containing E3 ubiquitin ligase to target Smc5/6 for degradation. However, the details of how HBx modulates the interaction between DDB1 and Smc5/6 remain to be determined. In this study, we performed biophysical analyses of recombinant HBx and functional analysis of HBx mutants in HBV-infected primary human hepatocytes (PHH) to identify key regions and residues that are required for HBx function. We determined that recombinant HBx is soluble and exhibits stoichiometric zinc binding when expressed in the presence of DDB1. Mass spectrometry-based hydrogen-deuterium exchange and cysteine-specific chemical footprinting of the HBx:DDB1 complex identified several HBx cysteine residues (located between amino acids 61 and 137) that are likely involved in zinc binding. These cysteine residues did not form disulfide bonds in HBx expressed in human cells. In line with the biophysical data, functional analysis demonstrated that HBx amino acids 45 to 140 are required for Smc6 degradation and HBV transcription in PHH. Furthermore, site-directed mutagenesis determined that C61, C69, C137, and H139 are necessary for HBx function, although they are likely not essential for DDB1 binding. This CCCH motif is highly conserved in HBV as well as in the X proteins from various mammalian hepadnaviruses. Collectively, our data indicate that the essential HBx cysteine and histidine residues form a zinc-binding motif that is required for HBx function.IMPORTANCE The structural maintenance of chromosomes 5/6 complex (Smc5/6) is a host restriction factor that suppresses HBV transcription. HBV counters this restriction by expressing HBV X protein (HBx), which redirects a host ubiquitin ligase to target Smc5/6 for degradation. Despite this recent advance in understanding HBx function, the key regions and residues of HBx required for Smc5/6 degradation have not been determined. In the present study, we performed biochemical, biophysical, and cell-based analyses of HBx. By doing so, we mapped the minimal functional region of HBx and identified a highly conserved CCCH motif in HBx that is likely responsible for coordinating zinc and is essential for HBx function. We also developed a method to produce soluble recombinant HBx protein that likely adopts a physiologically relevant conformation. Collectively, this study provides new insights into the HBx structure-function relationship and suggests a new approach for structural studies of this enigmatic viral regulatory protein.

We hereby disclose the discovery of inhibitors of CaMKII (7h and 7i) that are highly potent in rat ventricular myocytes, selective against hERG and other off-target kinases, while possessing good CaMKII tissue isoform selectivity (cardiac γ/δ vs. neuronal α/β). In vitro and in vivo ADME/PK studies demonstrated the suitability of these CaMKII inhibitors for PO (7h rat F = 73%) and IV pharmacological studies.