Pyrimidine inhibitors synergize with nucleoside analogues to block SARS-CoV-2.

The SARS-CoV-2 virus has infected more than 261 million people and has led to more than 5 million deaths in the past year and a half1 ( https://www.who.org/ ). Individuals with SARS-CoV-2 infection typically develop mild-to-severe flu-like symptoms, whereas infection of a subset of individuals leads to severe-to-fatal clinical outcomes2. Although vaccines have been rapidly developed to combat SARS-CoV-2, there has been a dearth of antiviral therapeutics. There is an urgent need for therapeutics, which has been amplified by the emerging threats of variants that may evade vaccines. Large-scale efforts are underway to identify antiviral drugs. Here we screened approximately 18,000 drugs for antiviral activity using live virus infection in human respiratory cells and validated 122 drugs with antiviral activity and selectivity against SARS-CoV-2. Among these candidates are 16 nucleoside analogues, the largest category of clinically used antivirals. This included the antivirals remdesivir and molnupiravir, which have been approved for use in COVID-19. RNA viruses rely on a high supply of nucleoside triphosphates from the host to efficiently replicate, and we identified a panel of host nucleoside biosynthesis inhibitors as antiviral. Moreover, we found that combining pyrimidine biosynthesis inhibitors with antiviral nucleoside analogues synergistically inhibits SARS-CoV-2 infection in vitro and in vivo against emerging strains of SARS-CoV-2, suggesting a clinical path forward.

An update on the progress of galidesivir (BCX4430), a broad-spectrum antiviral.

Galidesivir (BCX4430) is an adenosine nucleoside analog that is broadly active in cell culture against several RNA viruses of various families. This activity has also been shown in animal models of viral disease associated with Ebola, Marburg, yellow fever, Zika, and Rift Valley fever viruses. In many cases, the compound is more efficacious in animal models than cell culture activity would predict. Based on favorable data from in vivo animal studies, galidesivir has recently undergone evaluation in several phase I clinical trials, including against severe acute respiratory syndrome coronavirus 2, and as a medical countermeasure for the treatment of Marburg virus disease.

Nucleoside analogs assisted with Chinese compound prescription in treating hepatic fibrosis of chronic hepatitis B patients: A protocol of systematic review and meta-analysis.

BACKGROUND: Chronic hepatitis B is often complicated with different degrees of hepatic fibrosis, which affects the quality of life. Nucleoside analogs are recommended by almost all guidelines in the world for the treatment of chronic hepatitis B. At present, there is no specific and effective chemical and biological agents for hepatic fibrosis. In China, Chinese compound prescription combined with nucleoside analogs have been used to treat hepatic fibrosis of chronic hepatitis B patients in more and more cases, and good results have been achieved. Several Chinese compound prescriptions that have been made into proprietary Chinese medicine for the convenience of use. This article aims to systematically evaluate the efficacy and safety of Chinese medicine compounds assisting nucleoside analogs in the treatment of hepatic fibrosis in chronic hepatitis B patients. METHOD: The following databases will be searched from their inception to September 2019: PubMed, EMBASE, EBSCOhost, The Cochrane Library, China National Knowledge Infrastructure (CNKI), Chinese Biomedical literature Database (CBM), VIP Database, Wanfang Database. Languages are limited to Chinese and English. The study includes randomized controlled trials using Chinese compound prescription combined with entecavir and Chinese compound prescription combined with tenofovir disoproxil fumarate to treat hepatic fibrosis of chronic hepatitis B patients. The primary outcomes including effective rate and biochemical parameters (levels of hyaluronic acid, laminin, pre-type-III collagen and type IV collagen will be tested. Additional outcomes include liver function indexes (levels of alanine aminotransferase, aspartate aminotransferase, total bilirubin) and levels of hepatitis B virus DNA. Stata14.0 software will be used for meta-analysis. RESULT: The efficacy and safety of Chinese compound prescriptions assisting nucleoside analogs for hepatic fibrosis of chronic hepatitis B patients will be assessed from the effective rate, biochemical parameters, liver function indexes, and levels of hepatitis B virus DNA. CONCLUSION: The conclusion of this study will be used to evaluate the efficacy and safety of Chinese compound prescriptions assisting nucleoside analogs in the treatment of hepatic fibrosis of chronic hepatitis B patients, as well as the adjuvant effectiveness of Chinese compound prescriptions in combined therapy. PROSPERO REGISTRATION NUMBER: CRD42020156859.

Nucleoside Analogs with Selective Antiviral Activity against Dengue Fever and Japanese Encephalitis Viruses.

Dengue virus (DENV) and Japanese encephalitis virus (JEV) are important arthropod-borne viruses from the Flaviviridae family. DENV is a global public health problem with significant social and economic impacts, especially in tropical and subtropical areas. JEV is a neurotropic arbovirus endemic to east and southeast Asia. There are no U.S. FDA-approved antiviral drugs available to treat or to prevent DENV and JEV infections, leaving nearly one-third of the world's population at risk for infection. Therefore, it is crucial to discover potent antiviral agents against these viruses. Nucleoside analogs, as a class, are widely used for the treatment of viral infections. In this study, we discovered nucleoside analogs that possess potent and selective anti-JEV and anti-DENV activities across all serotypes in cell-based assay systems. Both viruses were susceptible to sugar-substituted 2'-C-methyl analogs with either cytosine or 7-deaza-7-fluoro-adenine nucleobases. Mouse studies confirmed the anti-DENV activity of these nucleoside analogs. Molecular models were assembled for DENV serotype 2 (DENV-2) and JEV RNA-dependent RNA polymerase replication complexes bound to nucleotide inhibitors. These models show similarities between JEV and DENV-2, which recognize the same nucleotide inhibitors. Collectively, our findings provide promising compounds and a structural rationale for the development of direct-acting antiviral agents with dual activity against JEV and DENV infections.

Nucleoside analogue activators of cyclic AMP-independent protein kinase A of Trypanosoma.

Protein kinase A (PKA), the main effector of cAMP in eukaryotes, is a paradigm for the mechanisms of ligand-dependent and allosteric regulation in signalling. Here we report the orthologous but cAMP-independent PKA of the protozoan Trypanosoma and identify 7-deaza-nucleosides as potent activators (EC50 ≥ 6.5 nM) and high affinity ligands (KD ≥ 8 nM). A co-crystal structure of trypanosome PKA with 7-cyano-7-deazainosine and molecular docking show how substitution of key amino acids in both CNB domains of the regulatory subunit and its unique C-terminal αD helix account for this ligand swap between trypanosome PKA and canonical cAMP-dependent PKAs. We propose nucleoside-related endogenous activators of Trypanosoma brucei PKA (TbPKA). The existence of eukaryotic CNB domains not associated with binding of cyclic nucleotides suggests that orphan CNB domains in other eukaryotes may bind undiscovered signalling molecules. Phosphoproteome analysis validates 7-cyano-7-deazainosine as powerful cell-permeable inducer to explore cAMP-independent PKA signalling in medically important neglected pathogens.