Discovery of a β-d-2′-Deoxy-2′-α-fluoro-2′-β-C-methyluridine Nucleotide Prodrug (PSI-7977) for the Treatment of Hepatitis C Virus

Biophysical Mode-of-Action and Selectivity Analysis of Allosteric Inhibitors of Hepatitis C Virus (HCV) Polymerase

Allosteric inhibitors of hepatitis C virus (HCV) non-structural protein 5B (NS5B) polymerase are effective for treatment of genotype 1, although their mode of action and potential to inhibit other isolates and genotypes are not well established. We have used biophysical techniques and a novel biosensor-based real-time polymerase assay to investigate the mode-of-action and selectivity of four inhibitors against enzyme from genotypes 1b (BK and Con1) and 3a. Two thumb inhibitors (lomibuvir and filibuvir) interacted with all three NS5B variants, although the affinities for the 3a enzyme were low. Of the two tested palm inhibitors (dasabuvir and nesbuvir), only dasabuvir interacted with the 1b variant, and nesbuvir interacted with NS5B 3a. Lomibuvir, filibuvir and dasabuvir stabilized the structure of the two 1b variants, but not the 3a enzyme. The thumb compounds interfered with the interaction between the enzyme and RNA and blocked the transition from initiation to elongation. The two allosteric inhibitor types have different inhibition mechanisms. Sequence and structure analysis revealed differences in the binding sites for 1b and 3a variants, explaining the poor effect against genotype 3a NS5B. The indirect mode-of-action needs to be considered when designing allosteric compounds. The current approach provides an efficient strategy for identifying and optimizing allosteric inhibitors targeting HCV genotype 3a.

Real-World Efficacy of Daclatasvir and Sofosbuvir, With and Without Ribavirin, in HIV/HCV Coinfected Patients With Advanced Liver Disease in a French Early Access Cohort

Supplemental Digital Content is Available in the Text.

Background:

Efficacious, well-tolerated, direct antiviral agents have drastically changed the prognosis of hepatitis C virus (HCV) disease, but real-world data for oral treatments are limited in key populations such as HIV/HCV coinfection with advanced liver disease. Daclatasvir (DCV) efficacy and safety was assessed in the French “Autorisation Temporaire d'Utilisation” (ATU) program, providing DCV ahead of market authorization to patients with advanced HCV disease without other treatment options.

Methods:

This was a subanalysis of HIV/HCV coinfected ATU patients treated with DCV plus sofosbuvir (SOF). Recommended duration was 24 weeks; addition of ribavirin (RBV) and/or shorter treatment was at the physician's discretion. The primary efficacy analysis was sustained virologic response at posttreatment week 12 (SVR12; modified intention-to-treat). Safety was assessed by spontaneous adverse event reporting.

Results:

The efficacy population (N = 407) was mostly cirrhotic (72%, of whom 18% were decompensated), HCV treatment–experienced (82%), and infected with genotypes 1 (69%), 3 (12%), or 4 (19%). Median CD4 was 555 cells/mm³; 95% had HIV RNA <50 copies/mL. Most (74%) were treated for 24 weeks; 14% received RBV. SVR12 was 92% overall (95% confidence interval: 88.6% to 94.0%); 90% (86.4% to 93.2%) in patients with cirrhosis; 95% (88.9% to 97.5%) in patients without cirrhosis. SVR12 was consistent across HCV genotypes and antiretroviral regimens. Among 617 patients with safety data, 7 discontinued for an adverse event and 10 died.

Conclusions:

DCV+SOF±RBV achieved high SVR12 and was well tolerated in this large real-world cohort of HIV/HCV coinfected patients with advanced liver disease.

Drug-like property-driven optimization of 4-substituted 1,5-diarylanilines as potent HIV-1 non-nucleoside reverse transcriptase inhibitors against rilpivirine-resistant mutant virus

On the basis of our prior structure-activity relationship (SAR) results, our current lead optimization of 1,5-diarylanilines (DAANs) focused on the 4-substituent (R1) on the central phenyl ring as a modifiable position related simultaneously to improved drug resistance profiles and drug-like properties. Newly synthesized p-cyanovinyl-DAANs (8a-8g) with different R1 side chains plus prior active p-cyanoethyl-DAANs (4a-4c) were evaluated not only for anti-HIV potency against both wild-type HIV virus and rilpivirine-resistant (E138K, E138K+M184I) viral replication, but also for multiple drug-like properties, including aqueous solubility, lipophilicity, and metabolic stability in human liver microsomes and human plasma. This study revealed that both ester and amide R1 substituents led to low nanomolar anti-HIV potency against wild-type and rilpivirine-resistant viral strains (E138K-resistance fold changes<3). The N-substituted amide-R1 side chains were superior to ester-R1 likely due to improved aqueous solubility, lipophilicity, and higher metabolic stability in vitro. Thus, three amide-DAANs 8e, 4a, and 4b were identified with high potency against wild-type and rilpivirine-resistant viral strains and multiple desirable drug-like properties.

Synthesis and Anti-HCV Activity of a Novel 2',3'-Dideoxy-2'-α-fluoro-2'-β-C-methyl Guanosine Phosphoramidate Prodrug

A novel 2',3'-dideoxy-2'-α-fluoro-2'-β-C-methyl-6-methoxy guanosine (8) and its phosphoramidate prodrug (1) have been designed and synthesized. Their biological activity was evaluated in both cytotoxicity and cell-based HCV replicon assays. Neither compounds exhibited cytotoxicity up to the highest concentration tested (100 μM) in the Huh-7 cell line. The prodrug (1) displayed nanomolar level antiviral activity (EC₅₀ = 0.39-1.1 μM) against the HCV genotype (GT) 1a, 1b, 2a, and 1b S282T replicons.

Sofosbuvir in combination with daclatasvir in liver transplant recipients with HCV infection: A systematic review and meta-analysis

BACKGROUND

Studies focusing on the efficacy of SOF+DCV regimen on liver transplantation recipients with HCV infection are still limited. In the current study, we aimed to perform a systematic review and meta-analysis to evaluate the efficacy and tolerability of SOF+DCV regimen, with or without ribavirin, on post-LT setting.

METHODS

A systematic literature search of various databases as well as abstracts of major liver diseases conferences was performed. Studies with SVR data in HCV infected liver transplantation recipients treated with daclatasvir/sofosbuvir regimen were included. All statistical analyses were conducted by R version 3.3.1 (The R Foundation for Statistical Computing, Vienna, Austria).

RESULTS

Seven studies with a total of 379 LT recipients were included in this study. Most of these LT recipients had genotype 1 HCV infection. The overall rate of SVR12 reached 93.3% (95% CI: 83.3% to 99.4%). After excluding the study of Fontana et al., the SVR12 reached 96.8% and heterogeneity was lowered down (P=0.17). In three studies, patients treated with SOF+DCV (n=146) had a higher SVR12 rate than that of patients treated with SOF+DCV+RBV (n=83) (OR 0.33, 95% CI: 0.12 to 0.87; P=0.02). There was no difference in SVR12 between patients infected with HCV genotype 1 and genotype 3 (P=0.57) and no difference was found in SVR12 rate between 12-week therapy and 24-week therapy (P=0.82). The most common adverse effects (AEs) were: anemia 32% (n=64/202), infections 26% (n=38/149), neutropenia 23% (n=35/149), thrombocytopenia 21% (n=32/149) and renal failure 8% (n=12/149).

CONCLUSION

SOF+DCV±RBV regimen is of high efficacy and tolerability in LT recipients with HCV infection.

Treatment of Hepatitis C Virus (HCV) Genotype 1 Disease

The landscape of therapeutic options for HCV infection has dramatically changed with the approval of all-oral direct-acting antiviral (DAA) regimens. DAAs target important steps in the HCV viral life cycle, resulting in higher response rates and fewer adverse events than were afforded with interferon and ribavirin, the prior standard of care. The achievement of sustained virologic response (SVR) rates in excess of 90% with use of DAA regimens has not only translated into HCV eradication for the hundreds of thousands treated but is also anticipated to decrease the incidence of major complications associated with chronic HCV infection. Additionally, the favorable side effect profile of DAAs has made HCV therapy feasible in difficult-to-treat populations, including those with previous exposure to interferon and ribavirin, cirrhosis, decompensated liver disease, HIV and HCV co-infection, and severe renal dysfunction/end stage renal disease. Given this tremendous progress, all patients infected with HCV infection should be treated.

Novel thioglycosyl analogs of glycosyltransferase substrates as antiviral compounds against classical swine fever virus and hepatitis C virus

Hepatitis C virus (HCV) and classical swine fever virus (CSFV) are important pathogens for which new therapeutic approaches are in high demand. Herein, we report the synthesis of newly designed thioglycosyl analogs of glycosyltransferase substrates which were evaluated using cell-based assays for cytotoxicity and antiviral activity against both viruses. The antiviral activity of synthesized compounds against CSFV and HCV was confirmed using pseudo-plaque reduction assays where a significant arrest of viral growth was observed in the presence of selected compounds. We showed that compounds 13 and 14 exerted the most significant inhibitory effect on in vitro CSFV and HCV infections in the series. Glycoconjugates 13 and 14 not only inhibited both viral propagation with IC₅₀ values in low micromolar range, but efficiently suppressed the production of viral proteins in a dose-dependent manner. In addition, studies using in vitro HCV infection and replication models have shown that both compounds are able to significantly reduce viral genomic replication. We demonstrated that compounds 13 and 14 showed a strong inhibition, up to 90% of replication which inscribe them in the promising alternative approach for the development of new anti-CSFV and anti-HCV drugs.

Discovery of β-d-2'-deoxy-2'-dichlorouridine nucleotide prodrugs as potent inhibitors of hepatitis C virus replication

Discovery of sofosbuvir has radically changed hepatitis C treatment and nucleoside/tide NS5B inhibitors are now viewed as one of the key components in combination therapies with other direct-acting antiviral agents. As part of our program to identify new nucleoside inhibitors of HCV replication, we now wish to report on the discovery of β-d-2'-deoxy-2'-dichlorouridine nucleotide prodrugs as potent inhibitors of HCV replication. Although, cytidine analogues have long been recognized to be metabolized to both cytidine and uridine triphosphates through the action of cytidine deaminase, uridine analogues are generally believed to produce exclusively uridine triphosphate. Detailed investigation of the intracellular metabolism of our newly discovered uridine prodrugs, as well as of sofosbuvir, has now revealed the formation of both uridine and cytidine triphosphates. This occurs, not only in vitro in cell lines, but also in vivo upon oral dosing to dogs.

UPLC-MS/MS method for determination of sofosbuvir in human plasma

INTRODUCTION

A sensitive and rapid method for quantitation of Sofosbuvir in human plasma has been established using ultra performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS).

MATERIALS AND METHODS

Sofosbuvir d3 was used as an internal standard. Sofosbuvir and internal standard in plasma sample were extracted using ethyl acetate (liquid liquid extraction). A centrifuged upper layer was then evaporated and reconstituted with the mobile phase of 0.5% formic acid: methanol (30:70, v/v). The reconstituted samples were injected into a Gemini C18 (50×4.6mm, 5μm) column.

RESULTS

Using MS/MS in the multiple reaction monitoring mode, Sofosbuvir and Sofosbuvir d3 were detected without severe interferences from human plasma matrix. Sofosbuvir produced a protonated precursor ion ([M+H]⁺) at m/z 428.35 and a corresponding product ion at m/z 279.26. The internal standard produced a protonated precursor ion ([M+H]⁺) at m/z 431.38 and a corresponding product ion at m/z 282.37. The calibration curves for the analyte was linear (R²≥0.9956, n=4) over the concentration range of 4.063-8000.010ng/mL. Stability studies revealed that Sofosbuvir was stable in plasma during bench top (7h at room temperature), in injector (20h), at the end of five successive freeze and thaw cycles and long term at -70°C±15°C for 15 days.

CONCLUSION

The developed method was validated as per the guidelines of USFDA and the obtained results were found to be within the limits and could be successfully employed for the determination of Sofosbuvir in human plasma for regular and pharmacokinetic studies.

Synthesis of ribavirin 2'-Me-C-nucleoside analogues

An efficient synthetic pathway leading to two carbonated analogues of ribavirin is described. The key-steps in the synthesis of these ribosyltriazoles bearing a quaternary carbon atom in the 2’-position are an indium-mediated alkynylation and a 1,3-dipolar cyclization.

Mechanism-Based Solution to the ProTide Synthesis Problem: Selective Access to Sofosbuvir, Acelarin, and INX-08189

A general and efficient method for the synthesis of pronucleotide (ProTide) 5'-phosphoramidate monoesters is reported. This method consists of a highly stereoselective 5'-phosphorylation mediated by dimethylaluminum chloride to afford the desired target ProTides in excellent yields without employing 3'-protection strategies. The application of this methodology to the synthesis of a number of pharmaceutically relevant compounds currently marketed or under investigation in clinical research is demonstrated.

Effectiveness and safety of sofosbuvir-based regimens plus an NS5A inhibitor for patients with HCV genotype 3 infection and cirrhosis. Results of a multicenter real-life cohort

Patients with HCV genotype 3 (GT3) infection and cirrhosis are currently the most difficult to cure. We report our experience with sofosbuvir+daclatasvir (SOF+DCV) or sofosbuvir/ledipasvir (SOF/LDV), with or without ribavirin (RBV) in clinical practice in this population. This was a multicenter observational study including cirrhotic patients infected by HCV GT3, treated with sofosbuvir plus an NS5A inhibitor (May 2014-October 2015). In total, 208 patients were included: 98 (47%) treatment-experienced, 42 (20%) decompensated and 55 (27%) MELD score >10. In 131 (63%), treatment was SOF+DCV and in 77 (37%), SOF/LDV. Overall, 86% received RBV. RBV addition and extension to 24 weeks was higher in the SOF/LDV group (95% vs 80%, P=.002 and 83% vs 72%, P=.044, respectively). A higher percentage of decompensated patients were treated with DCV than LDV (25% vs 12%, P=.013). Overall, SVR12 was 93.8% (195/208): 94% with SOF+DCV and 93.5% with SOF/LDV. SVR12 was achieved in 90.5% of decompensated patients. Eleven treatment failures: 10 relapses and one breakthrough. RBV addition did not improve SVR (RR: 1.08; P=.919). The single factor associated with failure to achieve SVR was platelet count <75×10E9/mL (RR: 3.50, P=.019). In patients with MELD <10, type of NS5A inhibitor did not impact on SVR12 (94% vs 97%; adjusted RR: 0.49). Thirteen patients (6.3%) had serious adverse events, including three deaths (1.4%) and one therapy discontinuation (0.5%), higher in decompensated patients (16.7% vs 3.6%, P<.006). In patients with GT3 infection and cirrhosis, SVR12 rates were high with both SOF+DCV and SOF/LDV, with few serious adverse events.

The protecting-group free selective 3'-functionalization of nucleosides

The direct and chemoselective 3'-phosphoramidation, phosphorylation and acylation of nucleosides are described. Upon the discovery of a novel 3'-phosphorylamidation of therapeutic nucleoside analogues with DBU, we explored the mechanism of this rare selectivity through a combination of NMR spectroscopy and computational studies. The NMR and computational findings allowed us to develop a predictive computational model that accurately assesses the potential for 3'-functionalization for a broad range of nucleosides and nucleoside mimetics. The synthetic utility of this model was exemplified by demonstration on a broad scope of nucleosides and electrophiles yielding targets that were previously only accessible via a protection/deprotection sequence or an enzymatic approach.

A Novel Inhibitor IDPP Interferes with Entry and Egress of HCV by Targeting Glycoprotein E1 in a Genotype-Specific Manner

Despite recent advances in curing chronic hepatitis C (CHC), the high economic burden to therapy, viral drug resistance, difficult to treat hepatitis C virus (HCV) genotypes and patient groups are still of concern. To address this unmet medical needs, we devised strategies to identify novel viral interventions through target-free high-throughput screening of small molecules utilizing a phenotypic-based HCV infection assay. Thereby, a very potent (EC₅₀ 46 ± 26 pM) iminodipyridinopyrimidine (IDPP) drug candidate was selected, and confirmed in primary human hepatocytes (EC₅₀ 0.5 nM). IDPP mainly targets a post-attachment step of HCV without affecting endosomal acidification, prevents the secretion of infectious particles and viral cell-to-cell spread. The putative molecular target of IDPP is glycoprotein E1, as revealed by selection for viral drug resistance (Gly-257-Arg). IDPP was synergistic in combination with FDA-approved HCV drugs and inhibited pre-existing resistant HCV strains induced by today's therapies. Interestingly, IDPP exclusively inhibited HCV genotype 2. However, we identified the genotype-specificity determining region in E1 and generated HCV genotype 1 susceptible to IDPP by changing one amino acid in E1 (Gln-257-Gly). Together, our results indicate an opportunity to provide an alternative treatment option for CHC and will shed light on the poorly understood function of HCV glycoprotein E1.

Cardiac drug-drug interaction between HCV-NS5B pronucleotide inhibitors and amiodarone is determined by their specific diastereochemistry

Severe bradycardia/bradyarrhythmia following coadministration of the HCV-NS5B prodrug sofosbuvir with amiodarone was recently reported. Our previous preclinical in vivo experiments demonstrated that only certain HCV-NS5B prodrugs elicit bradycardia when combined with amiodarone. In this study, we evaluate the impact of HCV-NS5B prodrug phosphoramidate diastereochemistry (D-/L-alanine, R-/S-phosphoryl) in vitro and in vivo. Co-applied with amiodarone, L-ala,S_P prodrugs increased beating rate and decreased beat amplitude in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), but D-ala,R_P produgs, including MK-3682, did not. Stereochemical selectivity on emerging bradycardia was confirmed in vivo. Diastereomer pairs entered cells equally well, and there was no difference in intracellular accumulation of L-ala,S_P metabolites ± amiodarone, but no D-ala,R_P metabolites were detected. Cathepsin A (CatA) inhibitors attenuated L-ala,S_P prodrug metabolite formation, yet exacerbated L-ala,S_P + amiodarone effects, implicating the prodrugs in these effects. Experiments indicate that pharmacological effects and metabolic conversion to UTP analog are L-ala,S_P prodrug-dependent in cardiomyocytes.

Discovery and Synthesis of a Phosphoramidate Prodrug of a Pyrrolo[2,1-f][triazin-4-amino] Adenine C-Nucleoside (GS-5734) for the Treatment of Ebola and Emerging Viruses

The recent Ebola virus (EBOV) outbreak in West Africa was the largest recorded in history with over 28,000 cases, resulting in >11,000 deaths including >500 healthcare workers. A focused screening and lead optimization effort identified 4b (GS-5734) with anti-EBOV EC50 = 86 nM in macrophages as the clinical candidate. Structure activity relationships established that the 1'-CN group and C-linked nucleobase were critical for optimal anti-EBOV potency and selectivity against host polymerases. A robust diastereoselective synthesis provided sufficient quantities of 4b to enable preclinical efficacy in a non-human-primate EBOV challenge model. Once-daily 10 mg/kg iv treatment on days 3-14 postinfection had a significant effect on viremia and mortality, resulting in 100% survival of infected treated animals [ Nature 2016 , 531 , 381 - 385 ]. A phase 2 study (PREVAIL IV) is currently enrolling and will evaluate the effect of 4b on viral shedding from sanctuary sites in EBOV survivors.

Future of liver disease in the era of direct acting antivirals for the treatment of hepatitis C

Hepatitis C virus (HCV) infection has been a global health problem for decades, due to the high number of infected people and to the lack of effective and well-tolerated therapies. In the last 3 years, the approval of new direct acting antivirals characterized by high rates of virological clearance and excellent tolerability has dramatically improved HCV infection curability, especially for patients with advanced liver disease and for liver transplant recipients. Long-term data about the impact of the new direct acting antivirals on liver fibrosis and liver disease-related outcomes are not yet available, due to their recent introduction. However, previously published data deriving from the use of pegylated-interferon and ribavirin lead to hypothesizing that we are going to observe, in the future, a reduction in mortality and in the incidence of hepatocellular carcinoma, as well as a regression of fibrosis for people previously affected by hepatitis C. In the liver transplant setting, clinical improvement has already been described after treatment with the new direct acting antivirals, which has often led to patients delisting. In the future, this may hopefully reduce the gap between liver organ request and availability, probably expanding liver transplant indications to other clinical conditions. Therefore, these new drugs are going to change the natural history of HCV-related liver disease and the epidemiology of HCV infection worldwide. However, the global consequences will depend on treatment accessibility and on the number of countries that could afford the use of the new direct acting antivirals.

In vitro selection of resistance to sofosbuvir in HCV replicons of genotype-1 to -6

BACKGROUND

Sofosbuvir is a nucleoside analogue inhibitor of the HCV NS5B polymerase approved for treatment of HCV-infected patients in combination with ribavirin or with other antivirals. It has activity against all genotypes of HCV. Resistance to sofosbuvir in genotype-1 and -2 HCV is conferred by the S282T substitution in NS5B.

METHODS

To begin to define the correlates of resistance to sofosbuvir in other genotypes, we performed selection experiments in cell culture using cell lines containing subgenomic replicons derived from genotypes-1b, -2a, -3a and -4a, or chimeric replicons in a genotype-1b background but encoding genotype-2b, -5a and -6a NS5B polymerase.

RESULTS

In every case, S282T was selected following passage in the presence of increasing concentrations of sofosbuvir for 10 to 15 weeks. When introduced as a site-directed mutant, S282T conferred reductions in sofosbuvir susceptibility of between 2.4 and 19.4-fold. Other substitutions observed during the selections had relatively less impact on susceptibility, such as N237S in genotype-6a (2.5-fold). Replication capacity was affected by the introduction of S282T in all genotypes to variable extents (3.2% to 22% of wild type).

CONCLUSIONS

These results confirm that S282T is the primary sofosbuvir resistance-associated substitution and that replication capacity is reduced when it is present in all genotypes of HCV.

Current therapy for chronic hepatitis C: The role of direct-acting antivirals

One of the most exciting developments in antiviral research has been the discovery of the direct-acting antivirals (DAAs) that effectively cure chronic hepatitis C virus (HCV) infections. Based on more than 100 clinical trials and real-world studies, we provide a comprehensive overview of FDA-approved therapies and newly discovered anti-HCV agents with a special focus on drug efficacy, mechanisms of action, and safety. We show that HCV drug development has advanced in multiple aspects: (i) interferon-based regimens were replaced by interferon-free regimens; (ii) genotype-specific drugs evolved to drugs for all HCV genotypes; (iii) therapies based upon multiple pills per day were simplified to a single pill per day; (iv) drug potency increased from moderate (∼60%) to high (>90%) levels of sustained virologic responses; (v) treatment durations were shortened from 48 to 12 or 8 weeks; and (vi) therapies could be administered orally regardless of prior treatment history and cirrhotic status. However, despite these remarkable achievements made in HCV drug discovery, challenges remain in the management of difficult-to-treat patients.

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HCV genotype-specific drugs evolve to pan-genotypic drugs.

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Drug potency increases from moderate (∼60%) to high (>90%) levels of sustained virologic response.

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Treatment durations are shortened from a 48-week to 12-week or 8-week period.

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HCV therapies based upon multiple pills per day are simplified to a single pill per day.

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HCV therapies are administered orally regardless of prior treatment history and cirrhotic status.

Kinase-independent phosphoramidate S1P1 receptor agonist benzyl ether derivatives

Previously published S1P receptor modulator benzyl ether derivatives have shown potential as being viable therapeutics for the treatment of neurodegenerative diseases, however, two of the most S1P₁-selective compounds are reported as being poorly phosphorylated by kinases in vivo. Phosphoramidates of BED compounds (2a, 2b) were synthesised with the aim of producing kinase-independent S1P receptor modulators. Carboxypeptidase, human serum and cell lysate processing experiments were conducted. ProTide BED analogues were found to have an acceptable level of stability in acidic and basic conditions and in vitro metabolic processing experiments showed that they are processed to the desired pharmacologically active monophosphate. The research describes the development of an entirely novel family of therapeutic agents.

Ester Prodrugs of IHVR-19029 with Enhanced Oral Exposure and Prevention of Gastrointestinal Glucosidase Interaction

IHVR-19029 (6) is a lead endoplasmic reticulum α-glucosidases I and II inhibitor, which efficiently protected mice from lethal Ebola and Marburg virus infections via injection route, but suffered from low bioavailability and off-target interactions with gut glucosidases when administered orally. In an effort to improve efficacious exposure levels and avoid side effects, we designed and synthesized ester prodrugs. Not only were the prodrugs stable in simulated gastric and intestinal fluids and were inactive against glucosidases but they also exhibited antiviral activities against dengue virus infection in a cell based assay. Further in vitro evaluation showed that the bioconversion of the prodrugs is species dependent: in mice, the prodrugs were converted to 6 in the plasma and liver; while in human, the conversion occurred mainly in liver. An in vivo pharmacokinetic study in mice demonstrated that the tetrabutyrate prodrug 8 achieved the most improved overall exposure of 6 upon both oral and intravenous administration.

Amino Acid Mutations in the NS4A Region of Hepatitis C Virus Contribute to Viral Replication and Infectious Virus Production

Hepatitis C virus (HCV) strain JFH-1, which belongs to genotype 2a, replicates autonomously in cultured cells, whereas another genotype 2a strain, J6CF, does not. Previously, we found that replacement of the NS3 helicase and NS5B-to-3'X regions of J6CF with those of JFH-1 confers J6CF replication competence. In this study, we aimed to identify the minimum modifications within these genomic regions needed to establish replication-competent J6CF. We previously identified 4 mutations in the NS5B-to-3'X region that could be used instead of replacement of this region to confer J6CF replication competence. Here, we induced cell culture-adaptive mutations in J6CF by the long-term culture of J6CF/JFH-1 chimeras composed of JFH-1 NS5B-to-3'X or individual parts of this but not the NS3 helicase region. After 2 months of culture, efficient HCV replication and infectious virus production in chimeric RNA-transfected cells were observed, and several amino acid mutations in NS4A were identified in replicating HCV genomes. The introduction of NS4A mutations into the J6CF/JFH-1 chimeras enhanced viral replication and infectious virus production. Immunofluorescence microscopy demonstrated that some of these mutations altered the subcellular localization of the coexpressed NS3 protein and affected the interaction between NS3 and NS4A. Finally, introduction of the most effective NS4A mutation, A1680E, into J6CF contributed to its replication competence in cultured cells when introduced in conjunction with four previously identified adaptive mutations in the NS5B-to-3'X region. In conclusion, we identified an adaptive mutation in NS4A that confers J6CF replication competence when introduced in conjunction with 4 mutations in NS5B-to-3'X and established a replication-competent J6CF strain with minimum essential modifications in cultured cells.

IMPORTANCE

The HCV cell culture system using the JFH-1 strain and HuH-7 cells can be used to assess the complete HCV life cycle in cultured cells. This cell culture system has been used to develop direct-acting antivirals against HCV, and the ability to use various HCV strains within this system is important for future studies. In this study, we aimed to establish a novel HCV cell culture system using another HCV genotype 2a strain, J6CF, which replicates in chimpanzees but not in cultured cells. We identified an effective cell culture-adaptive mutation in NS4A and established a replication-competent J6CF strain in cultured cells with minimum essential modifications. The described strategy can be used in establishing a novel HCV cell culture system, and the replication-competent J6CF clone composed of the minimum essential modifications needed for cell culture adaptation will be valuable as another representative of genotype 2a strains.

N2 -Substituted 2'-Deoxyguanosine Triphosphate Derivatives as Selective Substrates for Human DNA Polymerase κ

N² -Alkyl-2'-deoxyguanosine triphosphate (N² -alkyl-dGTP) derivatives with methyl, butyl, benzyl, or 4-ethynylbenzyl substituents were prepared and tested as substrates for human DNA polymerases. N² -Benzyl-dGTP was equal to dGTP as a substrate for DNA polymerase κ (pol κ), but was a poor substrate for pols β, δ, η, ι, or ν. In vivo reactivity was evaluated through incubation of N² -4-ethynylbenzyl-dG with wild-type and pol κ deficient mouse embryonic fibroblasts. CuAAC reaction with 5(6)-FAM-azide demonstrated that only cells containing pol κ were able to incorporate N² -4-ethynylbenzyl-dG into the nucleus. This is the first instance of a Y-family-polymerase-specific dNTP, and this method could be used to probe the activity of pol κ in vivo.

Substrates and Inhibitors of SAMHD1

SAMHD1 hydrolyzes 2'-deoxynucleoside-5'-triphosphates (dNTPs) into 2'-deoxynucleosides and inorganic triphosphate products. In this paper, we evaluated the impact of 2' sugar moiety substitution for different nucleotides on being substrates for SAMHD1 and mechanisms of actions for the results. We found that dNTPs ((2'R)-2'-H) are only permissive in the catalytic site of SAMHD1 due to L150 exclusion of (2'R)-2'-F and (2'R)-2'-OH nucleotides. However, arabinose ((2'S)-2'-OH) nucleoside-5'-triphosphates analogs are permissive to bind in the catalytic site and be hydrolyzed by SAMHD1. Moreover, when the (2'S)-2' sugar moiety is increased to a (2'S)-2'-methyl as with the SMDU-TP analog, we detect inhibition of SAMHD1’s dNTPase activity. Our computational modeling suggests that (2'S)-2'-methyl sugar moiety clashing with the Y374 of SAMHD1. We speculate that SMDU-TP mechanism of action requires that the analog first docks in the catalytic pocket of SAMHD1 but prevents the A351-V378 helix conformational change from being completed, which is needed before hydrolysis can occur. Collectively we have identified stereoselective 2' substitutions that reveal nucleotide substrate specificity for SAMHD1, and a novel inhibitory mechanism for the dNTPase activity of SAMHD1. Importantly, our data is beneficial for understanding if FDA-approved antiviral and anticancer nucleosides are hydrolyzed by SAMHD1 in vivo.

Safety and efficacy of daclatasvir-sofosbuvir in HCV genotype 1-mono-infected patients

BACKGROUND & AIMS

We report the first real-life results of the sofosbuvir+daclatasvir combination in hepatitis C virus (HCV) genotype 1 infected patients.

METHODS

The France REcherche Nord&Sud Sida-hiv Hépatites (ANRS) CO22 HEPATHER "Therapeutic options for hepatitis B and C: A French cohort" is a multicentre observational cohort which aims to include 15,000 HCV- and 10,000 HBV-infected patients. We selected all participants (n=768) with a HCV genotype 1 who initiated sofosbuvir (400mg/day) and daclatasvir (60mg/day) before October 1st 2014, with or without ribavirin (1-1.2g/day) for a duration of 12weeks or 24weeks. The main endpoint criterion was sustained virological response at 12weeks (SVR12), defined by the absence of detectable HCV-RNA 12weeks after the last treatment intake. Missing SVR12 measurements were imputed using SVR24 measurements (n=45), otherwise considered as virological failure (n=18).

RESULTS

A SVR12 was obtained in 729/768 (95%) patients, ranging from 92% (12-week sofosbuvir+daclatasvir) to 99% (24-week sofosbuvir+daclatasvir+ribavirin). The SVR12 rates did not significantly differ between the 24-week (550/574 (96%)) and the 12-week (179/194 (92%); p=0.0688) durations or between regimens with (165/169 (98%)) or without ribavirin (564/599 (94%); p=0.0850). The SVR12 rate was greater than 97% in non-cirrhotic patients irrespective of the treatment duration or the addition of ribavirin. Among cirrhotic patients, the SVR12 rate was higher with 24 than 12-week regimen (423/444 (95%) vs. 105/119 (88%); p=0.0054).

CONCLUSION

The sofosbuvir+daclatasvir combination is associated with a high rate of SVR12 in patients infected by genotype 1, with an optimal duration of 12weeks in non-cirrhotic and 24weeks in cirrhotic patients. The number of patients receiving ribavirin was too low to adequately assess its impact.

LAY SUMMARY

The sofosbuvir+daclatasvir combination of antiviral drugs is associated with a high rate (95%) of viral eradication in patients infected by HCV genotype 1. The best duration of a ribavirin-free sofosbuvir+daclatasvir combination seems to be 12weeks in non-cirrhotic patients and 24weeks for those with cirrhosis. Clinical trial number: NCT01953458.

Clinical Laboratory Testing in the Era of Directly Acting Antiviral Therapies for Hepatitis C

Directly acting antiviral (DAA) combination therapies for chronic hepatitis C virus (HCV) infection are highly effective, but treatment decisions remain complex. Laboratory testing is important to evaluate a range of viral, host, and pharmacological factors when considering HCV treatment, and patients must be monitored during and after therapy for safety and to assess the viral response. In this review, we discuss the laboratory tests relevant for the treatment of HCV infection in the era of DAA therapy, grouped according to viral and host factors.

Initial results of efficacy and safety of Sofosbuvir among Pakistani Population: A real life trial - Hepatitis Eradication Accuracy Trial of Sofosbuvir (HEATS)

OBJECTIVE

The uridine nucleotide analogue sofosbuvir is a selective inhibitor of hepatitis C virus (HCV) NS5B polymerase approved for the treatment of chronic HCV infection with genotypes 1 - 4. The objective of the study was to evaluate the interim results of efficacy and safety of regimens containing Sofosbuvir (Zoval) among Pakistani population with the rapid virologic response (RVR2/4 weeks) with HCV infections.

METHODS

This is a multicenter open label prospective observational study. Patients suffering from chronic Hepatitis C infection received Sofosbuvir (Zoval) 400 mg plus ribavirin (with or without peg interferon) for 12/24 weeks. The interim results of this study were rapid virological response on week 4. Data was analyzed using SPSS version 21 for descriptive statistics.

RESULTS

A total of 573 patients with HCV infection were included in the study. The mean age of patients was 46.07 ± 11.41 years. Out of 573 patients 535 (93.3%) were treatment naive, 26 (4.5%) were relapser, 7 (1.2%) were non-responders and 5 (1.0%) were partial responders. A rapid virologic response was reported in 563(98.2%) of patients with HCV infection after four weeks of treatment. The treatment was generally well tolerated.

CONCLUSION

Sofosbuvir (Zoval) is effective and well tolerated in combination with ribavirin in HCV infected patients.

Efficacy and Safety of Ledipasvir/Sofosbuvir with and without Ribavirin in Patients with Chronic Hepatitis C Virus Genotype 1 Infection: a meta-analysis

BACKGROUND

The addition of ribavirin (RBV) to the combination treatment of Ledipasvir (LDV) and Sofosbuvir (SOF) remains controversial in the treatment of hepatitis C virus (HCV) infection. We performed a meta-analysis to assess the efficacy and safety of the LDV-SOF with and without RBV in treating HCV genotype 1 patients.

METHOD

The electronical databases of PubMed Medline, EMBASE database, Cochrane Central Register of Controlled Trials (CENTRAL) and ClinicalTrials.gov website with registered trials were searched. Eligible studies were randomized controlled trials (RCTs) and prospective cohort studies that assessed the efficacy and safety of LDV-SOF with or without RBV in patients with HCV genotype 1 (GT 1). Two reviewers independently screened studies, extracted data and assessed methodology quality. Review Manager 5.3 software was used to analyze the data.

RESULTS

Seven studies involving 2,626 patients with HCV GT 1 - some of whom had cirrhosis - were included in this meta-analysis. The addition of RBV to LDV- SOF regimen neither significantly improved sustained viral response at 12 weeks (SVR12) after the last dose of treatment (RR=1.00, 95%CI 0.99-1.01, p=0.99) nor decreased virologic breakthrough (RR=1.01, 95%CI 0.14-7.19, p=0.99) and relapse (RR=1.36, 95% CI 0.81-2.29, p=0.24). There was no significant difference in the incidence of discontinuation (RR=0.61, 95%CI 0.25-1.53, p=0.30) between LDV- SOF therapy and LDV- SOF plus RBV. LDV- SOF plus RBV therapy had significantly higher rate of the overall adverse events (RR=0.88, 95%CI=0.84- 0.92, p<0.00001). LDV - SOF therapy had higher incidence of serious adverse events (RR=1.60, 95%CI=1.00-2.56, p=0.05) than LDV-SOF plus RBV.

CONCLUSION

This meta-analysis suggests that LDV-SOF based therapy is a safe and effective treatment for patients with GT 1 HCV. The addition of RBV to LDV-SOF may increase toxicity without achieving improved efficacy. However, due to the relatively small sample sizes and moderate risk of bias of included studies, large-scale and high-quality clinical research is still needed to confirm the results.

Discovery of 2'-α-C-Methyl-2'-β-C-fluorouridine Phosphoramidate Prodrugs as Inhibitors of Hepatitis C Virus

2'-α-C-Methyl-2'-β-C-fluorouridine and its phosphoramidate prodrugs were synthesized and evaluated for their inhibitory activity against HCV. The structure-activity relationship analysis of the phosphoramidate moiety found that 17m, 17q, and 17r exhibit potent activities against HCV, with EC₅₀ values of 1.82 ± 0.19, 0.88 ± 0.12, and 2.24 ± 0.22 μM, respectively. The docking study revealed that the recognition of the 2'-β-F by Arg158, 3'-OH by N291, and the Watson-Crick pairing with the template allowed 23 to form the in-line conformation necessary for its incorporation into the viral RNA chain.

ProTides of BVdU as potential anticancer agents upon efficient intracellular delivery of their activated metabolites

Nucleosides represent a major chemotherapeutic class for treating cancer, however their limitations in terms of cellular uptake, nucleoside kinase-mediated activation and catabolism are well-documented. The monophosphate pro-nucleotides known as ProTides represents a powerful strategy for bypassing the dependence on active transport and nucleoside kinase-mediated activation. Herein, we report the structural tuning of BVdU ProTides. Forty six phosphoramidates were prepared and biologically evaluated against three different cancer cell lines; murine leukemia (L1210), human CD4+ T-lymphocyte (CEM) and human cervical carcinoma (HeLa). Twenty-fold potency enhancement compared to BVdU was achieved against L1210 cells. Interestingly, a number of ProTides showed low micromolar activity against CEM and HeLa cells compared to the inactive parent BVdU. The ProTides showed poor, if any measurable toxicity to non-tumourigenic human lung fibroblast cell cultures. Separation of four pairs of the diastereoisomeric mixtures and comparison of their spectral properties, biological activities and enzymatic activation rate is reported.

Adenosine triphosphate analogs can efficiently inhibit the Zika virus RNA-dependent RNA polymerase

We describe the expression and purification of an active recombinant Zika virus RNA-dependent RNA polymerase (RdRp). Next, we present the development and optimization of an in vitro assay to measure its activity. We then applied the assay to selected triphosphate analogs and discovered that 2'-C-methylated nucleosides exhibit strong inhibitory activity. Surprisingly, also carbocyclic derivatives with the carbohydrate locked in a North-like conformation as well as a ribonucleotide with a South conformation exhibited strong activity. Our results suggest that the traditional 2'-C-methylated nucleosides pursued in the race for anti-HCV treatment can be superseded by brand new scaffolds in the case of the Zika virus.

The FDA-approved drug sofosbuvir inhibits Zika virus infection

The rapidly expanding Zika virus (ZIKV) epidemic has affected thousands of individuals with severe cases causing Guillain-Barré syndrome, congenital malformations, and microcephaly. Currently, there is no available vaccine or therapy to prevent or treat ZIKV infection. We evaluated whether sofosbuvir, an FDA-approved nucleotide polymerase inhibitor for the distantly related hepatitis C virus, could have antiviral activity against ZIKV infection. Cell culture studies established that sofosbuvir efficiently inhibits replication and infection of several ZIKV strains in multiple human tumor cell lines and isolated human fetal-derived neuronal stem cells. Moreover, oral treatment with sofosbuvir protected against ZIKV-induced death in mice. These results suggest that sofosbuvir may be a candidate for further evaluation as a therapy against ZIKV infection in humans.

Daclatasvir plus sofosbuvir, with or without ribavirin, in real-world patients with HIV-HCV coinfection and advanced liver disease

BACKGROUND

HIV-HCV-coinfected patients respond just as well to modern direct-acting antiviral HCV therapy as HCV-monoinfected patients. However, clinical data for all-oral HCV treatments are sparse in HIV-HCV-coinfected patients with an advanced stage of liver cirrhosis.

METHODS

A subanalysis of efficacy and safety for a daclatasvir (DCV) and sofosbuvir (SOF) regimen, with or without ribavirin (RBV), was undertaken in HIV-HCV-coinfected patients with advanced liver disease and no other treatment options enrolled into a European DCV compassionate use programme.

RESULTS

Fifty five HIV-HCV (mostly genotypes 1, 3, 4) coinfected patients were treated with DCV+SOF with (n=16) or without RBV (n=39), mostly for 24 weeks. Patients were predominantly (95%) cirrhotic (50% were Child-Pugh class B or C) and were receiving a wide range of antiretrovirals; 40% were injection drug users and 25% were receiving oral opioid substitution. Sustained virological response at post-treatment week 12 (SVR12) by modified intention-to-treat analysis (n=52) was 92% overall (95% CI 81.5, 97.9), and was similar with (94% [95% CI 69.8, 99.8]) or without RBV (92% [95% CI 77.5, 98.2]). Only one patient relapsed (Child-Pugh class B). The overall SVR12 rate after excluding non-virological failures (n=49) was 98% (95% CI 89.1, 99.9). Four patients discontinued treatment for adverse events and one died during treatment (not treatment-related). No patient lost opioid maintenance or required a change of antiretrovirals due to drug-drug interactions.

CONCLUSIONS

DCV+SOF, with or without RBV, showed high SVR12 rates and was well tolerated in this real-world cohort of HIV-HCV-coinfected patients with very advanced liver disease. ClinicalTrials.gov ID NCT02097966 (Study AI444-237).

Process Chemistry in Antiviral Research

This article reviews antiviral therapies that have been approved for human use during the last decade, with a focus on the process chemistry that enabled access to these important drugs. In particular, process chemistry highlights from the practical syntheses of the HCV drugs sofosbuvir (Gilead), grazoprevir (Merck), and elbasvir (Merck), the HIV therapy darunavir (Tibotec) and the influenza treatment peramivir (BioCryst) are presented.

Daclatasvir plus sofosbuvir, with or without ribavirin, achieved high sustained virological response rates in patients with HCV infection and advanced liver disease in a real-world cohort

OBJECTIVE

We assessed the effectiveness and safety of daclatasvir (DCV) plus sofosbuvir (SOF), with or without ribavirin (RBV), in a large real-world cohort, including patients with advanced liver disease.

DESIGN

Adults with chronic HCV infection at high risk of decompensation or death within 12 months and with no available treatment options were treated in a European compassionate use programme. The recommended regimen was DCV 60 mg plus SOF 400 mg for 24 weeks; RBV addition or shorter duration was allowed at physicians' discretion. The primary endpoint was sustained virological response at post-treatment week 12 (SVR12).

RESULTS

Of the 485 evaluable patients, 359 received DCV+SOF and 126 DCV+SOF+RBV. Most patients were men (66%), white (93%) and treatment-experienced (70%). The most frequent HCV genotypes were 1b (36%), 1a (33%) and 3 (21%), and 80% of patients had cirrhosis (42% Child-Pugh B/C; 46% Model for End-Stage Liver Disease score >10). SVR12 (modified intention-to-treat) was achieved by 91% of patients (419/460); 1 patient had virological breakthrough and 13 patients relapsed. Virological failure was not associated with treatment group (adjusted risk difference DCV+SOF minus DCV+SOF+RBV: 1.06%; 95% CI -2.22% to 4.35%). High SVR12 was observed regardless of HCV genotype or cirrhosis, liver transplant or HIV/HCV coinfection status. Twenty eight patients discontinued treatment due to adverse events (n=18) or death (n=10) and 18 died during follow-up. Deaths and most safety events were associated with advanced liver disease and not considered treatment related.

CONCLUSIONS

DCV+SOF with or without RBV achieved high SVR12 and was well tolerated in a diverse cohort of patients with severe liver disease.

TRIAL REGISTRATION NUMBER

NCT02097966.

Synthesis and antiviral evaluation of fluorinated acyclo-nucleosides and their phosphoramidates

A novel series of tetrafluoro and hexafluoro acyclic nucleosides and their phosphoramidates were successfully prepared from commercially available 2,2,3,3-tetrafluoro-1,4-butanediol and 2,2,3,3,4,4-hexafluoro-1,5-pentanediol in four to six steps. Their ability to block HIV, HCV, HSV-1, and HBV replication along with their cytotoxicity toward HepG2, human lymphocyte, CEM, and Vero cells was assessed.

Pioneering a Global Cure for Chronic Hepatitis C Virus Infection

This year's Lasker∼Debakey Clinical Medical Research Award honors Ralf Bartenschlager, Charles Rice, and Michael Sofia, pioneers in the development of curative and safe therapies for the 170 million people with hepatitis C virus infection.