Sofosbuvir and Ribavirin Liver Pharmacokinetics in Patients Infected with Hepatitis C Virus

Major implications of single nucleotide polymorphisms in human carboxylesterase 1 on substrate bioavailability

The number of studies and reviews conducted for the Carboxylesterase gene is limited in comparison with other enzymes. Carboxylesterase (CES) gene or human carboxylesterases (hCES) is a multigene protein belonging to the α/β-hydrolase family. Over the last decade, two major carboxylesterases (CES1 and CES2), located at 16q13-q22.1 on human chromosome 16 have been extensively studied as important mediators in the metabolism of a wide range of substrates. hCES1 is the most widely expressed enzyme in humans, and it is found in the liver. In this review, details regarding CES1 substrates include both inducers (e.g. Rifampicin) and inhibitors (e.g. Enalapril, Diltiazem, Simvastatin) and different types of hCES1 polymorphisms (nsSNPs) such as rs2244613 and rs71647871. along with their effects on various CES1 substrates were documented. Few instances where the presence of nsSNPs exerted a positive influence on certain substrates which are hydrolyzed via hCES1, such as anti-platelets like Clopidogrel when co-administered with other medications such as angiotensin-converting enzyme (ACE) inhibitors were also recorded. Remdesivir, an ester prodrug is widely used for the treatment of COVID-19, being a CES substrate, it is a potent inhibitor of CES2 and is hydrolyzed via CES1. The details provided in this review could give a clear-cut idea or information that could be used for further studies regarding the safety and efficacy of CES1 substrate.

Blood-to-Testis Transport of Ribavirin Involves Carrier-Mediated Processes at the Blood-Testis Barrier

Ribavirin, an antiretroviral agent targeting the hepatitis C virus, causes male reproductive toxicity. This study investigated the mechanism of ribavirin transport at the blood-testis barrier (BTB). In vivo mouse integration plot analysis after intravenous administration revealed that the net influx clearance of [3H]ribavirin in the testis was 3.6-fold greater than that of [14C]D-mannitol, a paracellular transport marker, implying transcellular transport of ribavirin across the BTB. Moreover, [3H]ribavirin uptake by TM4 cells, mouse-derived Sertoli cells, was time- and concentration-dependent, with a Km value of 2.49 mM. S-[(4-nitrophenyl)methyl]-6-thioinosine, an inhibitor of Na+-independent equilibrative nucleoside transporters (ENTs), strongly inhibited the [3H]ribavirin uptake by TM4 cells at 100 µM. Compared to the uptake of [3H]adenosine, a typical endogenous nucleoside, [3H]ribavirin uptake was relatively similar to ENT2 transport. [3H]Ribavirin uptake was also observed in mouse ENT2-expressing Xenopus laevis oocytes, and gene silencing via the transfection of ENT2 small interfering RNA significantly reduced the [3H]ribavirin transport into TM4 cells by 13%. Taken together, these results suggest that ENT2 partially contributes to ribavirin transport at the BTB.

Leveraging opportunities for treatment/user simplicity (LOTUS): Navigating the current treatment landscape for achieving hepatitis C virus elimination among persons who inject drugs

All-oral, direct-acting antivirals can cure hepatitis C virus (HCV) in almost all infected individuals; yet, many individuals with chronic HCV are not treated, and the incidence of acute HCV is increasing in some countries, including the United States. Strains on healthcare resources during the COVID-19 pandemic negatively impacted the progress toward the World Health Organization goal to eliminate HCV by 2030, especially among persons who inject drugs (PWID). Here, we present a holistic conceptual framework termed LOTUS (Leveraging Opportunities for Treatment/User Simplicity), designed to integrate the current HCV practice landscape and invigorate HCV treatment programs in the setting of endemic COVID-19: (A) treatment as prevention (especially among PWID), (B) recognition that HCV cure may be achieved with variable adherence with evidence supporting some forgiveness for missed doses, (C) treatment of all persons with active HCV infection (viremic), regardless of acuity, (D) minimal monitoring (MinMon) during treatment, and (E) rapid test and treat (TnT). The objective of this article is to review the current literature supporting each LOTUS petal; identify remaining gaps in knowledge or data; define the remaining barriers facing healthcare providers; and review evidence-based strategies for overcoming key barriers.

Prolinyl Phosphoramidates of Nucleotides with Increased Reactivity

Nucleoside monophosphates (NMPs) are the subunits of RNA. They are incorporated into growing complementary strands when sequences are copied in enzyme-free reactions using organic leaving groups at the phosphates. Amino acids are rarely considered as leaving groups, but proline can act as a leaving group when N-linked to NMPs, so that prolinyl NMPs hydrolyze in aqueous buffer at 37 °C, with half-life times as short as 2.4 h, and they act as monomers in enzyme-free primer extension. Still, their level of reactivity is insufficient for practical purposes, requiring months for some extensions. Herein we report the synthesis of eight substituted prolinyl AMPs together with seven related compounds and the results of a study of their reactivity. A δ-carboxy prolinyl NMP was found to be converted with a half-life time of just 11 min in magnesium-free buffer, and a δ-isopropyl prolinyl NMP was shown to react sevenfold faster than its prolinyl counterpart in enzyme-free genetic copying of RNA. Our results indicate that both anchimeric and steric effects can be employed to increase the reactivity of aminoacidyl nucleotides, i.e. compounds that combine two fundamental classes of biomolecules in one functional entity.

Differential activity of nucleotide analogs against tick-borne encephalitis and yellow fever viruses in human cell lines

With no approved antiviral therapies, the continuous emergence and re-emergence of tick-borne encephalitis virus (TBEV) and yellow fever virus (YFV) is a rising concern. We performed head-to-head comparisons of the antiviral activity of available nucleos(t)ide analogs (nucs) using relevant human cell lines. Eight existing nucs inhibited TBEV and/or YFV with differential activity between cell lines and viruses. Remdesivir, uprifosbuvir and sofosbuvir were the most potent drugs against TBEV and YFV in liver cells, but they had reduced activity in neural cells, whereas galidesivir retained uniform activity across cell lines and viruses. Ribavirin, valopicitabine, molnupiravir and GS-6620 exhibited only moderate antiviral activity. We found antiviral activity for drugs previously reported as inactive, demonstrating the importance of using human cell lines and comparative experimental assays when screening the activity of nucs. The relatively high antiviral activity of remdesivir, sofosbuvir and uprifosbuvir against TBEV and YFV merits further investigation in clinical studies.

Fitness-Dependent, Mild Mutagenic Activity of Sofosbuvir for Hepatitis C Virus

The concept of a mild mutagen was coined to describe a minor mutagenic activity exhibited by some nucleoside analogues that potentiated their efficacy as antiretroviral agents. In the present study, we report the mild mutagen activity of sofosbuvir (SOF) for hepatitis C virus (HCV). Serial passages of HCV in human hepatoma cells, in the presence of SOF at a concentration well below its cytotoxic concentration 50 (CC50) led to pre-extinction populations whose mutant spectra exhibited a significant increase of C→U transitions, relative to populations passaged in the absence of SOF. This was reflected in an increase in several diversity indices that were used to characterize viral quasispecies. The mild mutagenic activity of SOF was largely absent when it was tested with isogenic HCV populations that displayed high replicative fitness. Thus, SOF can act as a mild mutagen for HCV, depending on HCV fitness. Possible mechanisms by which the SOF mutagenic activity may contribute to its antiviral efficacy are discussed.

Comparative Pharmacology of a Bis-Pivaloyloxymethyl Phosphonate Prodrug Inhibitor of Enolase after Oral and Parenteral Administration

Metabolically labile prodrugs can experience stark differences in catabolism incurred by the chosen route of administration. This is especially true for phosph(on)ate prodrugs, in which successive promoiety removal transforms a lipophilic molecule into increasingly polar compounds. We previously described a phosphonate inhibitor of enolase (HEX) and its bis-pivaloyloxymethyl ester prodrug (POMHEX) capable of eliciting strong tumor regression in a murine model of enolase 1 (ENO1)-deleted glioblastoma following parenteral administration. Here, we characterize the pharmacokinetics and pharmacodynamics of these enolase inhibitors in vitro and in vivo after oral and parenteral administration. In support of the historical function of lipophilic prodrugs, the bis-POM prodrug significantly improves cell permeability of and rapid hydrolysis to the parent phosphonate, resulting in rapid intracellular loading of peripheral blood mononuclear cells in vitro and in vivo. We observe the influence of intracellular trapping in vivo on divergent pharmacokinetic profiles of POMHEX and its metabolites after oral and parenteral administration. This is a clear demonstration of the tissue reservoir effect hypothesized to explain phosph(on)ate prodrug pharmacokinetics but has heretofore not been explicitly demonstrated.

Nucleotide and nucleoside-based drugs: past, present, and future

Nucleotide and nucleoside-based analogue drugs are widely used for the treatment of both acute and chronic viral infections. These drugs inhibit viral replication due to one or more distinct mechanisms. It modifies the virus's genetic structure by reducing viral capacity in every replication cycle. Their clinical success has shown strong effectiveness against several viruses, including ebolavirus, hepatitis C virus, HIV, MERS, SARS-Cov, and the most recent emergent SARS-Cov2. In this review, seven different types of inhibitors have been selected that show broad-spectrum activity against RNA viruses. A detailed overview and mechanism of actionof both analogues are given, and the clinical perspectives are discussed. These inhibitors incorporated the novel SARS-CoV-2 RdRp, further terminating the polymerase activity with variable efficacy. The recent study provides a molecular basis for the inhibitory activity of virus RdRp using nucleotide and nucleoside analogues inhibitors. Furthermore, to identify those drugs that need more research and development to combat novel infections. Consequently, there is a pressing need to focus on present drugs by establishing their cell cultures. If their potencies were evidenced, then they would be explored in the future as potential therapeutics for novel outbreaks.

Effects of the 5'-Triphosphate Metabolites of Ribavirin, Sofosbuvir, Vidarabine, and Molnupiravir on CTP Synthase Catalysis and Filament Formation: Implications for Repurposing Antiviral Agents against SARS-CoV-2

Repurposing of antiviral drugs affords a rapid and effective strategy to develop therapies to counter pandemics such as COVID-19. SARS-CoV-2 replication is closely linked to the metabolism of cytosine-containing nucleotides, especially cytidine-5'-triphosphate (CTP), such that the integrity of the viral genome is highly sensitive to intracellular CTP levels. CTP synthase (CTPS) catalyzes the rate-limiting step for the de novo biosynthesis of CTP. Hence, it is of interest to know the effects of the 5'-triphosphate (TP) metabolites of repurposed antiviral agents on CTPS activity. Using E. coli CTPS as a model enzyme, we show that ribavirin-5'-TP is a weak allosteric activator of CTPS, while sofosbuvir-5'-TP and adenine-arabinofuranoside-5'-TP are both substrates. β-d-N⁴ -Hydroxycytidine-5'-TP is a weak competitive inhibitor relative to CTP, but induces filament formation by CTPS. Alternatively, sofosbuvir-5'-TP prevented CTP-induced filament formation. These results reveal the underlying potential for repurposed antivirals to affect the activity of a critical pyrimidine nucleotide biosynthetic enzyme.

Important roles of transporters in the pharmacokinetics of anti-viral nucleoside/nucleotide analogs

INTRODUCTION

Nucleoside analogs are an important class of antiviral agents. Due to the high hydrophilicity and limited membrane permeability of antiviral nucleoside/nucleotide analogs (AVNAs), transporters play critical roles in AVNA pharmacokinetics. Understanding the properties of these transporters is important to accelerate translational research for AVNAs.

AREAS COVERED

The roles of key transporters in the pharmacokinetics of 25 approved AVNAs were reviewed. Clinically relevant information that can be explained by the modulation of transporter functions is also highlighted.

EXPERT OPINION

Although the roles of transporters in the intestinal absorption and renal excretion of AVNAs have been well identified, more research is warranted to understand their roles in the distribution of AVNAs, especially to immune privileged compartments where treatment of viral infection is challenging. P-gp, MRP4, BCRP, and nucleoside transporters have shown extensive impacts in the disposition of AVNAs. It is highly recommended that the role of transporters should be investigated during the development of novel AVNAs. Clinically, co-administered inhibitors and genetic polymorphism of transporters are the two most frequently reported factors altering AVNA pharmacokinetics. Physiopathology conditions also regulate transporter activities, while their effects on pharmacokinetics need further exploration. Pharmacokinetic models could be useful for elucidating these complicated factors in clinical settings.

Factors Influencing the Intracellular Concentrations of the Sofosbuvir Metabolite GS-331007 (in PBMCs) at 30 Days of Therapy

Sofosbuvir (SOF) is an HCV NS5B polymerase inhibitor, and GS-331007 is its major metabolite. The aim of this study was to investigate whether clinical and pharmacological factors could influence GS-331007 intracellular (IC) concentrations in peripheral blood mononuclear cells (PBMCs) associated with a sustained virological response in patients treated with SOF and ribavirin (RBV). Drug levels were analyzed using liquid chromatography at different days of therapy, whereas variants in genes encoding transporters and nuclear factors were investigated using real-time PCR. This study enrolled 245 patients treated with SOF; 245 samples were analyzed for pharmacogenetics and 50 were analyzed for IC pharmacokinetics. The GS-331007 IC concentration at 30 days was associated with its plasma concentration determinate at 30, 60 and 90 days of SOF-therapy and with daclatasvir concentrations at 7 days of therapy. No genetic polymorphism affected IC exposure. In linear multivariate analysis, ledipasvir treatment, baseline albumin and estimated glomerular filtration rate were significant predictors of IC exposure. This study presents data on an IC evaluation in a cohort of patients treated with SOF, also considering pharmacogenetics. These results could be useful for regions where SOF–RBV treatment is considered the standard of care; moreover, they could further deepen the knowledge of IC exposure for similar drugs in the future.

Mitochondrial Genotoxicity of Hepatitis C Treatment among People Who Inject Drugs

Antiviral nucleoside analogues (ANA) are newly used therapeutics acting against the hepatitis C virus (HCV). This class of drug is well known to exhibit toxicity on mitochondrial DNA (mtDNA). People who inject drugs (PWID) are particularly affected by HCV infection and cumulated mitotoxic drug exposure from HIV treatments (antiretrovirals, ARV) and other illicit drugs. This study aims to explore the impact of direct-acting antiviral (DAA) treatments on mtDNA among PWID. A total of 470 actively injecting heroin users were included. We used quantitative PCR on whole blood to determine the mitochondrial copy number per cell (MCN) and the proportion of mitochondrial DNA deletion (MDD). These parameters were assessed before and after DAA treatment. MDD was significantly increased after HCV treatment, while MCN did not differ. MDD was even greater when subjects were cotreated with ARV. In multivariate analysis, we identified that poly-exposure to DAA and daily heroin injection or regular consumption of methamphetamines were positively associated with high MCN loss while DAA and ARV treatments or methadone use were identified as risk factors for having mtDNA deletion. These observations deserve attention since they were previously associated with premature cell ageing or cell transformation and therefore call for a long-term follow-up.

Lipophilic Conjugates of Drugs: A Tool to Improve Drug Pharmacokinetic and Therapeutic Profiles

Lipophilic conjugates (LCs) of small molecule drugs have been used widely in clinical and pre-clinical studies to achieve a number of pharmacokinetic and therapeutic benefits. For example, lipophilic derivatives of drugs are employed in several long acting injectable products to provide sustained drug exposure for hormone replacement therapy and to treat conditions such as neuropsychiatric diseases. LCs can also be used to modulate drug metabolism, and to enhance drug permeation across membranes, either by increasing lipophilicity to enhance passive diffusion or by increasing protein-mediated active transport. Furthermore, such conjugation strategies have been employed to promote drug association with endogenous macromolecular carriers (e.g. albumin and lipoproteins), and this in turn results in altered drug distribution and pharmacokinetic profiles, where the changes can be 'general' (e.g. prolonged plasma half-life) or 'specific' (e.g. enhanced delivery to specific tissues in parallel with the macromolecular carriers). Another utility of LCs is to enhance the encapsulation of drugs within engineered nanoscale drug delivery systems, in order to best take advantage of the targeting and pharmacokinetic benefits of nanomedicines. The current review provides a summary of the mechanisms by which lipophilic conjugates, including in combination with delivery vehicles, can be used to control drug delivery, distribution and therapeutic profiles. The article is structured into sections which highlight a specific benefit of LCs and then demonstrate this benefit with case studies. The review attempts to provide a toolbox to assist researchers to design and optimise drug candidates, including consideration of drug-formulation compatibility.

Efficacy and safety of sofosbuvir/velpatasvir versus the standard of care in adults hospitalized with COVID-19: a single-centre, randomized controlled trial

Objectives

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the COVID-19 pandemic. The majority of patients experience asymptomatic to mild self-limited disease, but some cases progress to respiratory and multi-organ failure. However, so far, no approved antiviral therapy has been available for treatment of COVID-19. Sofosbuvir/velpatasvir (SOF/VEL) is an approved anti-HCV drug that is capable of suppressing other families of positive-sense RNA viruses with conserved polymerase and may be effective against SARS-CoV-2. This study was conducted to evaluate the efficacy of the SOF/VEL combination in addition to the national standard of care versus the national standard of care alone (hydroxychloroquine and lopinavir/ritonavir as well as supportive care) in patients with moderate to severe COVID-19 infection.

Methods

This single-centre, randomized, open-labelled, prospective clinical trial was done in patients with moderate to severe COVID-19 admitted to Farabi Hospital in Kermanshah Province, Iran. Eligible patients were randomly assigned in a 1:1 ratio to the SOF/VEL arm (SOF/VEL plus the national standard of care) or the control arm (the national standard of care alone). The main outcome of the study was the mortality on Day 28 after randomization. Secondary outcomes were time from the start of medication to clinical improvement, hospital length of stay, need for mechanical ventilation, duration of mechanical ventilation and conversion of RT–PCR results from positive to negative from the time of randomization to discharge. Adverse events were evaluated in all patients who started their assigned treatment.

Results

Between 11 April and 8 June 2020, 80 patients were recruited and randomly assigned into the SOF/VEL (n = 40) and control (n = 40) arms. The primary outcome was not significantly different between the two arms (P = 1.00). Secondary outcomes, including time to clinical improvement, hospital length of stay, need for mechanical ventilation, duration of mechanical ventilation and RT–PCR conversion, were not significantly different between arms either (P > 0.05). SOF/VEL treatment and the national standard of care were tolerated similarly.

Conclusions

Although treatment with SOF/VEL was safe, adding SOF/VEL to the standard of care did not improve the clinical status or reduce mortality in patients with moderate to severe COVID-19. However, larger randomized clinical trials including more parameters are needed for accurate estimation of the efficacy of SOF/VEL.

Why Remdesivir Failed: Preclinical Assumptions Overestimate the Clinical Efficacy of Remdesivir for COVID-19 and Ebola

Remdesivir is a nucleoside monophosphoramidate prodrug that has been FDA approved for coronavirus disease 2019 (COVID-19). However, the clinical efficacy of remdesivir for COVID-19 remains contentious, as several trials have not found statistically significant differences in either time to clinical improvement or mortality between remdesivir-treated and control groups. Similarly, the inability of remdesivir to provide a clinically significant benefit above other investigational agents in patients with Ebola contrasts with strong, curative preclinical data generated in rhesus macaque models. For both COVID-19 and Ebola, significant discordance between the robust preclinical data and remdesivir’s lackluster clinical performance have left many puzzled. Here, we critically evaluate the assumptions of the models underlying remdesivir’s promising preclinical data and show that such assumptions overpredict efficacy and minimize toxicity of remdesivir in humans. Had the limitations of in vitro drug efficacy testing and species differences in drug metabolism been considered, the underwhelming clinical performance of remdesivir for both COVID-19 and Ebola would have been fully anticipated.

Pharmacokinetics and tissue distribution of remdesivir and its metabolites nucleotide monophosphate, nucleotide triphosphate, and nucleoside in mice

Remdesivir (RDV) exerts anti-severe acute respiratory coronavirus 2 activity following metabolic activation in the target tissues. However, the pharmacokinetics and tissue distributions of the parent drug and its active metabolites have been poorly characterized to date. Blood and tissue levels were evaluated in the current study. After intravenous administration of 20 mg/kg RDV in mice, the concentrations of the parent drug, nucleotide monophosphate (RMP) and triphosphate (RTP), as well as nucleoside (RN), in the blood, heart, liver, lung, kidney, testis, and small intestine were quantified. In blood, RDV was rapidly and completely metabolized and was barely detected at 0.5 h, similar to RTP, while its metabolites RMP and RN exhibited higher blood levels with increased residence times. The area under the concentration versus time curve up to the last measured point in time (AUC_0-t) values of RMP and RN were 4558 and 136,572 h∙nM, respectively. The maximum plasma concentration (C_max) values of RMP and RN were 2896 nM and 35,819 nM, respectively. Moreover, RDV presented an extensive distribution, and the lung, liver and kidney showed high levels of the parent drug and metabolites. The metabolic stabilities of RDV and RMP were also evaluated using lung, liver, and kidney microsomes. RDV showed higher clearances in the liver and kidney than in the lung, with intrinsic clearance (CL_int) values of 1740, 1253, and 127 mL/(min∙g microsomal protein), respectively.

The nucleotide prodrug CERC-913 improves mtDNA content in primary hepatocytes from DGUOK-deficient rats

Loss-of-function mutations in the deoxyguanosine kinase (DGUOK) gene result in a mitochondrial DNA (mtDNA) depletion syndrome. DGUOK plays an important role in converting deoxyribonucleosides to deoxyribonucleoside monophosphates via the salvage pathway for mtDNA synthesis. DGUOK deficiency manifests predominantly in the liver; the most common cause of death is liver failure within the first year of life and no therapeutic options are currently available. in vitro supplementation with deoxyguanosine or deoxyguanosine monophosphate (dGMP) were reported to rescue mtDNA depletion in DGUOK-deficient, patient-derived fibroblasts and myoblasts. CERC-913, a novel ProTide prodrug of dGMP, was designed to bypass defective DGUOK while improving permeability and stability relative to nucleoside monophosphates. To evaluate CERC-913 for its ability to rescue mtDNA depletion, we developed a primary hepatocyte culture model using liver tissue from DGUOK-deficient rats. DGUOK knockout rat hepatocyte cultures exhibit severely reduced mtDNA copy number (~10%) relative to wild type by qPCR and mtDNA content remains stable for up to 8 days in culture. CERC-913 increased mtDNA content in DGUOK-deficient hepatocytes up to 2.4-fold after 4 days of treatment in a dose-dependent fashion, which was significantly more effective than dGMP at similar concentrations. These early results suggest primary hepatocyte culture is a useful model for the study of mtDNA depletion syndromes and that CERC-913 treatment can improve mtDNA content in this model.

Efficacy and safety of sofosbuvir/ ledipasvir in treatment of patients with COVID-19; A randomized clinical trial

Background:

There is no study regarding the use of SOF/LDP in treatment of COVID-19.

Objectives:

In this study, the efficacy and safety of SOF/LDP were assessed in treatment of patients with mild to moderate COVID-19.

Methods:

Among an open-label randomized clinical trial, 82 patients with mild to moderated COVID-19 were assigned to receive either SOF/LDP 400/100 mg daily plus the standard of care (SOF/LDP group, n=42) or the standard of care alone (control group, n=40) for 10 days. Time to clinical response, rate of clinical response, duration of hospital and ICU stay and 14-day mortality were assessed.

Results:

Clinical response occurred in 91.46% of patients. Although rates of clinical response were comparable between the groups but it occurred faster in the SOF/LDP group than the control group (2 vs. 4 days respectively, P= 0.02). Supportive cares were provided in the medical wards for most patients but 17.07% of patients were transferred to ICU during the hospitalization course. However, durations of hospital and ICU stay were comparable between the groups. 14-day mortality rate was 7.14% and 7.5% in the SOF/ LDP and control groups respectively. No adverse effects leading to drug discontinuation occurred. Gastrointestinal events (nausea, vomiting and diarrhea) were the most common side effects (15.85%).

Conclusion:

Added to the standard of care, SOF/LDP accelerated time to the clinical response. However, rate of clinical response, duration of hospital and ICU stay and 14-day mortality were not different. No significant adverse event was detected. More randomized clinical trials with larger sample sizes are needed to confirm the efficacy and safety of SOF/LDP in the treatment of COVID-19. (www.actabiomedica.it)

The Enzyme-Free Release of Nucleotides from Phosphoramidates Depends Strongly on the Amino Acid

Phosphoramidates composed of an amino acid and a nucleotide analogue are critical metabolites of prodrugs, such as remdesivir. Hydrolysis of the phosphoramidate liberates the nucleotide, which can then be phosphorylated to become the pharmacologically active triphosphate. Enzymatic hydrolysis has been demonstrated, but a spontaneous chemical process may also occur. We measured the rate of enzyme-free hydrolysis for 17 phosphoramidates of ribonucleotides with amino acids or related compounds at pH 7.5. Phosphoramidates of proline hydrolyzed fast, with a half-life time as short as 2.4 h for Pro-AMP in ethylimidazole-containing buffer at 37 °C; 45-fold faster than Ala-AMP and 120-fold faster than Phe-AMP. Crystal structures of Gly-AMP, Pro-AMP, βPro-AMP and Phe-AMP bound to RNase A as crystallization chaperone showed how well the carboxylate is poised to attack the phosphoramidate, helping to explain this reactivity. Our results are significant for the design of new antiviral prodrugs.

Sofosbuvir as Repurposed Antiviral Drug Against COVID-19: Why Were We Convinced to Evaluate the Drug in a Registered/Approved Clinical Trial?

COVID-19 is a devastating global pandemic around the world. While the majority of infected cases appear mild, in some cases individuals present respiratory complications with possible serious lung damage. There are no specific treatments for COVID-19 as yet, though a number are under evaluation, including experimental antivirals. Sofosbuvir, the clinically approved anti-hepatitis C virus (HCV) drug, is also capable of suppressing other families of positive-strand RNA viruses; Flaviviridae and Togaviridae. Coronaviruses are a family of positive-strand RNA viruses with conserved polymerase, so SARS-CoV-2 RdRp is very likely to be effectively inhibited by sofosbuvir. More importantly, sofosbuvir is safe and well tolerated at 400 mg daily in a 24 week therapeutic regimen. Sofosbuvir active metabolite, however, shows an extremely high intracellular stability So, it is hypothesized that SARS-CoV-2 infection could also be susceptible to sofosbuvir and we were convinced to design and run a clinical trial to evaluate the effect of sofosbuvir 400 mg (in combination with velpatasvir 100 mg, as add-on treatment, in addition to standard of care) on the COVID-19. However, we believe that this manuscript/correspondence should be made available to the international scientific community as soon as possible, with the help of this esteemed journal.

In Vitro and In Vivo Characterization of the Anti-Zika Virus Activity of ProTides of 2'-C-β-Methylguanosine

The ProTide approach has emerged as a powerful tool to improve the intracellular delivery of nucleotide analogs with antiviral and anticancer activity. Here, we characterized the anti-ZIKV (ZIKV, Zika virus) activity of two ProTides of 2'-C-β-methylguanosine. ProTide UMN-1001 is a 2'-C-β-methylguanosine tryptamine phosphoramidate monoester, and ProTide UMN-1002 is a 2-(methylthio)-ethyl-2'-C-β-methylguanosine tryptamine phosphoramidate diester. UMN-1002 undergoes stepwise intracellular activation to the corresponding nucleotide monophosphate followed by P-N bond cleavage by intracellular histidine triad nucleotide binding protein 1 (Hint1). UMN-1001 is activated by Hint1 but is less cell-permeable than UMN-1002. UMN-1001 and UMN-1002 were found to be more potent than 2'-C-β-methylguanosine against ZIKV in human-derived microvascular endothelial and neuroblastoma cells and in reducing ZIKV RNA replication. Studies with a newborn mouse model of ZIKV infection demonstrated that, while treatment with 2'-C-β-methylguanosine and UMN-1001 was lethal, treatment with UMN-1002 was nontoxic and significantly reduced ZIKV infection. Our data suggests that anchimeric activated ProTides of 2'-C-β-methyl nucleosides should be further investigated for their potential as anti-ZIKV therapeutics.

Development of a long-acting direct-acting antiviral system for hepatitis C virus treatment in swine

Chronic hepatitis C virus (HCV) infection is a leading cause of cirrhosis worldwide and kills more Americans than 59 other infections, including HIV and tuberculosis, combined. While direct-acting antiviral (DAA) treatments are effective, limited uptake of therapy, particularly in high-risk groups, remains a substantial barrier to eliminating HCV. We developed a long-acting DAA system (LA-DAAS) capable of prolonged dosing and explored its cost-effectiveness. We designed a retrievable coil-shaped LA-DAAS compatible with nasogastric tube administration and the capacity to encapsulate and release gram levels of drugs while resident in the stomach. We formulated DAAs in drug-polymer pills and studied the release kinetics for 1 mo in vitro and in vivo in a swine model. The LA-DAAS was equipped with ethanol and temperature sensors linked via Bluetooth to a phone application to provide patient engagement. We then performed a cost-effectiveness analysis comparing LA-DAAS to DAA alone in various patient groups, including people who inject drugs. Tunable release kinetics of DAAs was enabled for 1 mo with drug-polymer pills in vitro, and the LA-DAAS safely and successfully provided at least month-long release of sofosbuvir in vivo. Temperature and alcohol sensors could interface with external sources for at least 1 mo. The LA-DAAS was cost-effective compared to DAA therapy alone in all groups considered (base case incremental cost-effectiveness ratio $39,800). We believe that the LA-DAA system can provide a cost-effective and patient-centric method for HCV treatment, including in high-risk populations who are currently undertreated.

Species differences in liver accumulation and metabolism of nucleotide prodrug sofosbuvir

Sofosbuvir (SOF) is a nucleotide prodrug which has been used as a backbone for the clinical treatment of hepatitis C viral infection. Because sofosbuvir undergoes complex first pass metabolism, including metabolic activation to form its pharmacologically active triphosphate (GS-331007-TP) to inhibit the viral RNA polymerase in the liver, it is difficult to project the human dose for clinical evaluation based on preclinical data. Selecting an appropriate animal model for drug exposure in the target tissue is challenging due to differences in absorption, stability, hepatic uptake, and intracellular activation across species. Efficient liver delivery has been established in human liver following administration in a clinical trial of patients receiving sofosbuvir prior to liver transplantation. Using the clinical liver exposure as a benchmark, we assessed and compared the pharmacokinetic profile in mouse, rat, hamster, dog and monkey. Liver accumulation was also assessed in the PXB mouse model in which the liver is mostly populated with human hepatocytes. At human equivalent dose, the hepatic concentrations of GS-331007-TP in dog and PXB mouse were comparable to those observed in the human livers. In these species, high and sustained levels of GS-331007-TP were observed in both primary hepatocytes in vitro and the liver in vivo.

In silico study of chikungunya polymerase, a potential target for inhibitors

Non-structural protein 4 (nsP4) polymerase of chikungunya virus (CHIKV) has a crucial role in genome replication and hence could act as a promising target for novel therapeutics. Though, nsP4 is important in viral life cycle, but it is less explored as therapeutic target. The catalytic core of nsP4 Polymerase includes conserved GDD motif which is present not only across different CHIKV strains but also across other Alphaviruses. This emphasizes the uniqueness and importance of this motif in the functioning of nsP4 polymerase and hence, we focused on GDD motif for docking of drug molecules. Herein, a model of nsP4 polymerase was developed using Swiss Model, validated by Ramachandran plot and molecular dynamic simulation. Molecular docking was performed using LeadIT FlexX flexible docking module with FDA approved drug molecule library. On the basis of flexX score, top 5 leads with flexX scores - 33.7588, - 30.2555, - 29.6043, - 28.916 and - 28.5042 were selected. The bonding pattern of these leads were analysed in discovery studio and were further screened on the basis of molecular dynamic simulation studies. Simulation analysis revealed that only the top lead, Mitoxantrone Hydrochloride which is an anticancer drug and is currently indicated in leukemias and lymphomas interacted favourably and stably with nsP4. Our findings suggest that Mitoxantrone Hydrochloride can be a potential novel inhibitor of CHIKV polymerase and should be further validated by in vitro assays.

Rodrigues GO, M. Lopes CE, Queiroz-Junior CM, Lima CX, Costa VV, Teixeira MM, Bozza FA, Bozza PT, Boechat N, Tanuri A, Souza TML. Yellow fever virus is susceptible to sofosbuvir both in vitro and in vivo

Yellow fever virus (YFV) is a member of the Flaviviridae family. In Brazil, yellow fever (YF) cases have increased dramatically in sylvatic areas neighboring urban zones in the last few years. Because of the high lethality rates associated with infection and absence of any antiviral treatments, it is essential to identify therapeutic options to respond to YFV outbreaks. Repurposing of clinically approved drugs represents the fastest alternative to discover antivirals for public health emergencies. Other Flaviviruses, such as Zika (ZIKV) and dengue (DENV) viruses, are susceptible to sofosbuvir, a clinically approved drug against hepatitis C virus (HCV). Our data showed that sofosbuvir docks onto YFV RNA polymerase using conserved amino acid residues for nucleotide binding. This drug inhibited the replication of both vaccine and wild-type strains of YFV on human hepatoma cells, with EC₅₀ values around 5 μM. Sofosbuvir protected YFV-infected neonatal Swiss mice and adult type I interferon receptor knockout mice (A129^-/-) from mortality and weight loss. Because of its safety profile in humans and significant antiviral effects in vitro and in mice, Sofosbuvir may represent a novel therapeutic option for the treatment of YF. Key-words: Yellow fever virus; Yellow fever, antiviral; sofosbuvir

Yellow fever virus is transmitted by mosquitoes and its infection may be asymptomatic or lead to a wide clinical spectrum ranging from a mild febrile illness to a potentially lethal viral hemorrhagic fever characterized by liver damage. Although a yellow fever vaccine is available, low coverage allows 80,000–200,000 cases and 30,000–60,000 deaths annually worldwide. There are no specific therapy and treatment relies on supportive care, reinforcing an urgent need for antiviral repourposing. Here, we showed that sofosbuvir, clinically approved against hepatitis C, inhibits yellow fever virus replication in liver cell lines and animal models. In vitro, sofosbuvir inhibits viral RNA replication, decreases the number of infected cells and the production of infectious virus particles. These data is particularly relevante since the liver is the main target of yellow fever infection. Sofosbuvir also protected infected animals from mortality, weight loss and liver injury, especially prophylatically. Our pre-clinical results supports a second use of sofosbuvir against yellow fever.

Follicular helper T cell and memory B cell immunity in CHC patients

Chronic hepatitis C (CHC) is associated with biological activity of T follicular helper (Tfh) cells and memory B cells (MBCs). However, the nature of Tfh cell subsets that are responsible for MBCs in CHC patients has not been evaluated. This study aimed to investigate Tfh and MBC immunity before and after direct-acting antiviral (DAA) therapy in patients with CHC. A total of 31 CHC patients and 15 healthy controls (HCs) were recruited. Individual patients were treated with sofosbuvir/ribavirin (SOF/RBV) or in combination with pegylated interferon alpha-2a (PEG-IFN-α-2a) for 12 weeks. Immunofluorescence revealed the frequency of ICOS⁺CD4⁺CXCR5⁺ active Tfh cells in liver tissue of CHC patients was higher than that of healthy control. Tfh and B cell co-culture experiments showed that Tfh2 cells from CHC patients have potential ability to induce B cell differentiation and IgG production. Flow cytometry showed that the frequencies of CD21^-CD27⁺IgD^- activated MBCs, ICOS⁺CD4⁺CXCR5⁺ activated Tfh cells, Tfh1 (IFN-γ⁺CD4⁺CXCR5⁺) cells, and Tfh2 (IL-4⁺CD4⁺CXCR5⁺) cells, but not of Tfh17 (IL-17⁺CD4⁺CXCR5⁺) cells, increased in CHC patients before and after DAA therapy. Collectively, ICOS⁺ Tfh, Tfh1, Tfh2 cells, and MBCs participated in the antiviral treatment process of SOF/RBV with or without PEG-IFN-α-2a in CHC patients, and their activity was further enhanced during the treatment. KEY MESSAGES: This study aimed to investigate Tfh cells and MBC immunity in CHC patients. CD21^-CD27⁺IgD^- activated MBCs increased in CHC patients before and after treatment. Tfh1 and Tfh2 cells increased in CHC patients before and after antiviral treatment. Intrahepatic activated Tfh cells increased in CHC patients before treatment. Tfh2 cells from CHC patients have a stronger ability to induce B cell differentiation.