scholarly journals Mechanism of molnupiravir-induced SARS-CoV-2 mutagenesis

2021 ◽  
Author(s):  
Florian Kabinger ◽  
Carina Stiller ◽  
Jana Schmitzová ◽  
Christian Dienemann ◽  
Goran Kokic ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Active Form ◽  
Antiviral Drug ◽  
Viral Rna ◽  
Phase Iii ◽  
Drug Candidate ◽  
Base Pairs ◽  
Biochemical Assays ◽  
Phase Iii Trials ◽  
Rna Complexes

AbstractMolnupiravir is an orally available antiviral drug candidate currently in phase III trials for the treatment of patients with COVID-19. Molnupiravir increases the frequency of viral RNA mutations and impairs SARS-CoV-2 replication in animal models and in humans. Here, we establish the molecular mechanisms underlying molnupiravir-induced RNA mutagenesis by the viral RNA-dependent RNA polymerase (RdRp). Biochemical assays show that the RdRp uses the active form of molnupiravir, β-d-N4-hydroxycytidine (NHC) triphosphate, as a substrate instead of cytidine triphosphate or uridine triphosphate. When the RdRp uses the resulting RNA as a template, NHC directs incorporation of either G or A, leading to mutated RNA products. Structural analysis of RdRp–RNA complexes that contain mutagenesis products shows that NHC can form stable base pairs with either G or A in the RdRp active center, explaining how the polymerase escapes proofreading and synthesizes mutated RNA. This two-step mutagenesis mechanism probably applies to various viral polymerases and can explain the broad-spectrum antiviral activity of molnupiravir.

scholarly journals Mechanism of molnupiravir-induced SARS-CoV-2 mutagenesis

2021 ◽  
Author(s):  
Florian Kabinger ◽  
Carina Stiller ◽  
Jana Schmitzová ◽  
Christian Dienemann ◽  
Hauke S. Hillen ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Active Form ◽  
Antiviral Drug ◽  
Phase Iii ◽  
Drug Candidate ◽  
Base Pairs ◽  
Rna Dependent Rna Polymerase ◽  
Biochemical Assays ◽  
Phase Iii Trials ◽  
Rna Complexes

Molnupiravir is an orally available antiviral drug candidate that is in phase III trials for the treatment of COVID-19 patients. Molnupiravir increases the frequency of viral RNA mutations and impairs SARS-CoV-2 replication in animal models and in patients. Here we establish the molecular mechanisms that underlie molnupiravir-induced RNA mutagenesis by the RNA-dependent RNA polymerase (RdRp) of the coronavirus SARS-CoV-2. Biochemical assays show that the RdRp readily uses the active form of molnupiravir, β-D-N4-hydroxycytidine (NHC) triphosphate, as a substrate instead of CTP or UTP. Incorporation of NHC monophosphate into nascent RNA does not impair further RdRp progression. When the RdRp uses the resulting RNA as a template, NHC directs incorporation of either G or A, leading to mutated RNA products. Structural analysis of RdRp-RNA complexes containing mutagenesis products shows that NHC can form stable base pairs with either G or A in the RdRp active center, explaining how the polymerase escapes proofreading and synthesizes mutated RNA. This two-step mutagenesis mechanism likely applies to various viral polymerases and can explain the broad-spectrum antiviral activity of molnupiravir.

scholarly journals Identification of guanylyltransferase activity in the SARS-CoV-2 RNA polymerase

2021 ◽  
Author(s):  
Alexander P Walker ◽  
Haitian Fan ◽  
Jeremy R Keown ◽  
Jonathan M Grimes ◽  
Ervin Fodor
Keyword(s):  
Rna Polymerase ◽  
Rna Synthesis ◽  
Rna Virus ◽  
Active Form ◽  
Antiviral Drug ◽  
Viral Rna ◽  
Protein Domain ◽  
Structural Protein ◽  
Viral Mrnas ◽  
Synthesis Mechanism

AbstractSARS-CoV-2 is a positive-sense RNA virus that is responsible for the ongoing Coronavirus Disease 2019 (COVID-19) pandemic, which continues to cause significant morbidity, mortality and economic strain. SARS-CoV-2 can cause severe respiratory disease and death in humans, highlighting the need for effective antiviral therapies. The RNA synthesis machinery of SARS-CoV-2 is an ideal drug target and consists of non-structural protein 12 (nsp12), which is directly responsible for RNA synthesis, and numerous co-factors that are involved in RNA proofreading and 5’ capping of viral mRNAs. The formation of the 5’ cap-1 structure is known to require a guanylyltransferase (GTase) as well as 5’ triphosphatase and methyltransferase activities. However, the mechanism of SARS-CoV-2 mRNA capping remains poorly understood. Here we show that the SARS-CoV-2 RNA polymerase nsp12 functions as a GTase. We characterise this GTase activity and find that the nsp12 NiRAN (nidovirus RdRP-associated nucleotidyltransferase) domain is responsible for carrying out the addition of a GTP nucleotide to the 5’ end of viral RNA via a 5’ to 5’ triphosphate linkage. We also show that remdesivir triphosphate, the active form of the antiviral drug remdesivir, inhibits the SARS-CoV-2 GTase reaction as efficiently as RNA polymerase activity. These data improve understanding of coronavirus mRNA cap synthesis and highlight a new target for novel or repurposed antiviral drugs against SARS-CoV-2.ImportanceSARS-CoV-2 is a respiratory RNA virus responsible for the Coronavirus Disease 2019 (COVID-19) pandemic. Coronaviruses encode an RNA polymerase which, in combination with other viral proteins, is responsible for synthesising capped viral mRNA. mRNA cap synthesis requires a guanylyltransferase enzyme; here we show that the SARS-CoV-2 guanylyltransferase is located in the viral RNA polymerase, and we identify the protein domain responsible for guanylyltransferase activity. Furthermore we demonstrate that remdesivir triphosphate, the active metabolite of remdesivir, inhibits both the guanylyltransferase and RNA polymerase functions of the SARS-CoV-2 RNA polymerase. These findings improve understanding of the coronavirus mRNA cap synthesis mechanism, in addition to highlighting a new target for the development of therapeutics to treat SARS-CoV-2 infection.

scholarly journals Poliovirus Polymerase Leu420 Facilitates RNA Recombination and Ribavirin Resistance

2016 ◽  
Vol 90 (19) ◽  
pp. 8410-8421 ◽  
Author(s):  
Brian J. Kempf ◽  
Olve B. Peersen ◽  
David J. Barton
Keyword(s):  
Molecular Mechanisms ◽  
Antiviral Drug ◽  
Rna Replication ◽  
Viral Rna ◽  
Rna Recombination ◽  
Elongation Complex ◽  
Species Groups ◽  
Nascent Rna ◽  
Substitution Mutations ◽  
And Function

ABSTRACTRNA recombination is important in the formation of picornavirus species groups and the ongoing evolution of viruses within species groups. In this study, we examined the structure and function of poliovirus polymerase, 3Dpol, as it relates to RNA recombination. Recombination occurs when nascent RNA products exchange one viral RNA template for another during RNA replication. Because recombination is a natural aspect of picornavirus replication, we hypothesized that some features of 3Dpolmay exist, in part, to facilitate RNA recombination. Furthermore, we reasoned that alanine substitution mutations that disrupt 3Dpol-RNA interactions within the polymerase elongation complex might increase and/or decrease the magnitudes of recombination. We found that an L420A mutation in 3Dpoldecreased the frequency of RNA recombination, whereas alanine substitutions at other sites in 3Dpolincreased the frequency of recombination. The 3DpolLeu420 side chain interacts with a ribose in the nascent RNA product 3 nucleotides from the active site of the polymerase. Notably, the L420A mutation that reduced recombination also rendered the virus more susceptible to inhibition by ribavirin, coincident with the accumulation of ribavirin-induced G→A and C→U mutations in viral RNA. We conclude that 3DpolLeu420 is critically important for RNA recombination and that RNA recombination contributes to ribavirin resistance.IMPORTANCERecombination contributes to the formation of picornavirus species groups and the emergence of circulating vaccine-derived polioviruses (cVDPVs). The recombinant viruses that arise in nature are occasionally more fit than either parental strain, especially when the two partners in recombination are closely related, i.e., members of characteristic species groups, such as enterovirus species groups A to H or rhinovirus species groups A to C. Our study shows that RNA recombination requires conserved features of the viral polymerase. Furthermore, a polymerase mutation that disables recombination renders the virus more susceptible to the antiviral drug ribavirin, suggesting that recombination contributes to ribavirin resistance. Elucidating the molecular mechanisms of RNA replication and recombination may help mankind achieve and maintain poliovirus eradication.

Clinical implications and outcomes of the ORION Phase III trials

2020 ◽  
Author(s):  
Julia Brandts ◽  
Kausik K Ray
Keyword(s):  
Familial Hypercholesterolemia ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Phase Iii ◽  
Atherosclerotic Cardiovascular Disease ◽  
Low Density Lipoprotein Cholesterol ◽  
Clinical Safety ◽  
Phase Iii Trials ◽  
Phase Ii And Iii ◽  
Ongoing Phase

Inclisiran is a siRNA inhibiting hepatic PCSK9 synthesis. As a first-in-class therapy, inclisiran has been assessed within the ORION trial program for its low-density lipoprotein cholesterol (LDL-C) lowering efficacy and clinical safety. Phase II and III trials have shown that inclisiran lowers LDL-C by about 50% with an infrequent dosing schedule in patients with established atherosclerotic cardiovascular disease and those at high risk, including patients with heterozygous familial hypercholesterolemia. Ongoing Phase III trials will provide evidence on longer-term safety and effectiveness, and inclisiran’s efficacy in patients with homozygous familial hypercholesterolemia. Furthermore, the ORION-4 trial will assess inclisiran’s impact on cardiovascular outcomes.

scholarly journals Potential Dual Role of West Nile Virus NS2B in Orchestrating NS3 Enzymatic Activity in Viral Replication

Viruses ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 216
Author(s):  
Alanna C. Tseng ◽  
Vivek R. Nerurkar ◽  
Kabi R. Neupane ◽  
Helmut Kae ◽  
Pakieli H. Kaufusi
Keyword(s):  
West Nile Virus ◽  
Enzymatic Activity ◽  
Nonstructural Protein ◽  
Antiviral Drug ◽  
West Nile ◽  
Biochemical Assays ◽  
In Trans ◽  
Viral Polyprotein ◽  
Ns3 Protease

West Nile virus (WNV) nonstructural protein 3 (NS3) harbors the viral triphosphatase and helicase for viral RNA synthesis and, together with NS2B, constitutes the protease responsible for polyprotein processing. NS3 is a soluble protein, but it is localized to specialized compartments at the rough endoplasmic reticulum (RER), where its enzymatic functions are essential for virus replication. However, the mechanistic details behind the recruitment of NS3 from the cytoplasm to the RER have not yet been fully elucidated. In this study, we employed immunofluorescence and biochemical assays to demonstrate that NS3, when expressed individually and when cleaved from the viral polyprotein, is localized exclusively to the cytoplasm. Furthermore, NS3 appeared to be peripherally recruited to the RER and proteolytically active when NS2B was provided in trans. Thus, we provide evidence for a potential additional role for NS2B in not only serving as the cofactor for the NS3 protease, but also in recruiting NS3 from the cytoplasm to the RER for proper enzymatic activity. Results from our study suggest that targeting the interaction between NS2B and NS3 in disrupting the NS3 ER localization may be an attractive avenue for antiviral drug discovery.

scholarly journals Immunotherapy Predictive Molecular Markers in Advanced Gastroesophageal Cancer: MSI and Beyond

Cancers ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1715
Author(s):  
Robin Park ◽  
Laercio Lopes ◽  
Anwaar Saeed
Keyword(s):  
Treatment Options ◽  
Unmet Need ◽  
Predictive Biomarkers ◽  
Phase Iii ◽  
Gastroesophageal Cancer ◽  
Programmed Death ◽  
Phase Iii Trials ◽  
Tumor Mutational Burden ◽  
Large Phase ◽  
Programmed Death 1

Advanced gastroesophageal cancer (GEC) has a poor prognosis and limited treatment options. Immunotherapy including the anti-programmed death-1 (PD-1) antibodies pembrolizumab and nivolumab have been approved for use in various treatment settings in GEC. Additionally, frontline chemoimmunotherapy regimens have recently demonstrated promising efficacy in large phase III trials and have the potential to be added to the therapeutic armamentarium in the near future. There are currently several immunotherapy biomarkers that are validated for use in the clinical setting for GEC including programmed death ligand-1 (PD-L1) expression as well as the tumor agnostic biomarkers such as mismatch repair or microsatellite instability (MMR/MSI) and tumor mutational burden (TMB). However, apart from MMR/MSI, these biomarkers are imperfect because none are highly sensitive nor specific. Therefore, there is an unmet need for immunotherapy biomarker development. To this end, several biomarkers are currently being evaluated in ongoing trials with some showing promising predictive potential. Here, we summarize the landscape of immunotherapy predictive biomarkers that are currently being evaluated in GEC.

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