Sofosbuvir-velpatasvir in children 3-17 years old with hepatitis C virus infection

BACKGROUND

The safety and efficacy of sofosbuvir-velpatasvir in children aged 3-17 years with chronic hepatitis C virus (HCV) infection of any genotype were evaluated.

METHODS

In this Phase 2, multicenter, open-label study, patients received once daily for 12 weeks either sofosbuvir-velpatasvir 400/100 mg tablet (12-17 years), 200/50 mg low dose tablet or oral granules (3-11 years and ≥17 kg), or 150/37.5 mg oral granules (3-5 years and <17 kg). The efficacy endpoint was sustained virologic response 12 weeks after therapy (SVR12). Dose appropriateness was confirmed by intensive pharmacokinetics in each age group.

FINDINGS

Among 216 patients treated, 76% had HCV genotype 1% and 12% had genotype 3. Rates of SVR12 were 83% (34/41) among 3-5-year-olds, 93% (68/73) among 6-11-year-olds, and 95% (97/102) among 12-17-year-olds. Only two patients experienced virologic failure. The most common adverse events were headache, fatigue, and nausea in 12-17-year-olds; vomiting, cough, and headache in 6-11-year-olds; and vomiting in 3-5-year-olds. Three patients discontinued treatment because of adverse events. Four patients had serious adverse events; all except auditory hallucination (n = 1) were considered unrelated to study drug. Exposures of sofosbuvir, its metabolite GS-331007, and velpatasvir were comparable to those in adults in prior Phase 2/3 studies. Population pharmacokinetic simulations supported weight-based dosing for children in this age range.

INTERPRETATION

The pangenotypic regimen of sofosbuvir-velpatasvir is highly effective and safe in treating children 3-17 years with chronic HCV infection.

Evaluation of Antiviral Activity of Gemcitabine Derivatives against Influenza Virus and Severe Acute Respiratory Syndrome Coronavirus 2

Gemcitabine is a nucleoside analogue of deoxycytidine and has been reported to be a broad-spectrum antiviral agent against both DNA and RNA viruses. Screening of a nucleos(t)ide analogue-focused library identified gemcitabine and its derivatives (compounds 1, 2a, and 3a) blocking influenza virus infection. To improve their antiviral selectivity by reducing cytotoxicity, 14 additional derivatives were synthesized in which the pyridine rings of 2a and 3a were chemically modified. Structure-and-activity and structure-and-toxicity relationship studies demonstrated that compounds 2e and 2h were most potent against influenza A and B viruses but minimally cytotoxic. It is noteworthy that in contrast to cytotoxic gemcitabine, they inhibited viral infection with 90% effective concentrations of 14.5-34.3 and 11.4-15.9 μM, respectively, maintaining viability of mock-infected cells over 90% at 300 μM. Resulting antiviral selectivity was comparable to that of a clinically approved nucleoside analogue, favipiravir. The cell-based viral polymerase assay proved the mode-of-action of 2e and 2h targeting viral RNA replication and/or transcription. In a murine influenza A virus-infection model, intraperitoneal administration of 2h not only reduced viral RNA level in the lungs but also alleviated infection-mediated pulmonary infiltrates. In addition, it inhibited replication of severe acute respiratory syndrome virus 2 infection in human lung cells at subtoxic concentrations. The present study could provide a medicinal chemistry framework for the synthesis of a new class of viral polymerase inhibitors.

A Cyclic Phosphoramidate Prodrug of 2'-Deoxy-2'-Fluoro-2'-C-Methylguanosine for the Treatment of Dengue Virus Infection

Monophosphate prodrug analogs of 2'-deoxy-2'-fluoro-2'-C-methylguanosine have been reported as potent inhibitors of hepatitis C virus (HCV) RNA-dependent RNA polymerase. These prodrugs also display potent anti-dengue virus activities in cellular assays although their prodrug moieties were designed to produce high levels of triphosphate in the liver. Since peripheral blood mononuclear cells (PBMCs) are among the major targets of dengue virus, different prodrug moieties were designed to effectively deliver 2'-deoxy-2'-fluoro-2'-C-methylguanosine monophosphate prodrugs and their corresponding triphosphates into PBMCs after oral administration. We identified a cyclic phosphoramidate, prodrug 17, demonstrating well-balanced anti-dengue virus cellular activity and in vitro stability profiles. We further determined the PBMC concentration of active triphosphate needed to inhibit virus replication by 50% (TP₅₀). Compound 17 was assessed in an AG129 mouse model and demonstrated 1.6- and 2.2-log viremia reductions at 100 and 300 mg/kg twice a day (BID), respectively. At 100 mg/kg BID, the terminal triphosphate concentration in PBMCs exceeded the TP₅₀ value, demonstrating TP₅₀ as the target exposure for efficacy. In dogs, oral administration of compound 17 resulted in high PBMC triphosphate levels, exceeding the TP₅₀ at 10 mg/kg. Unfortunately, 2-week dog toxicity studies at 30, 100, and 300 mg/kg/day showed that "no observed adverse effect level" (NOAEL) could not be achieved due to pulmonary inflammation and hemorrhage. The preclinical safety results suspended further development of compound 17. Nevertheless, present work has proven the concept that an efficacious monophosphate nucleoside prodrug could be developed for the potential treatment of dengue virus infection.

[Screening, diagnosis, treatment, and follow up of hepatitis C virus related liver disease. National consensus guideline in Hungary from 22 September 2017]

The treatment of hepatitis C is based on a national consensus guideline updated six-monthly according to local availability and affordability of approved therapies through a transparent allocation system in Hungary. This updated guideline incorporates some special new aspects, including recommendations for screening, diagnostics, use and allocation of novel direct acting antiviral agents. The indication of therapy in patients with no contraindication is based on the demonstration of viral replication with consequent inflammation and/or fibrosis in the liver. Non-invasive methods (elastographies and biochemical methods) are preferred for liver fibrosis staging. The budget allocated for these patients is limited. Interferon-based or interferon-free therapies are available for the treatment. Due to their limited success rate as well as to their (sometimes severe) side-effects, the mandatory use of interferon-based therapies as first line treatment can not be accepted from the professional point of view. However, they can be used as optional therapy in treatment-naïve patients with mild disease. As of interferon-free therapies, priority is given to those with urgent need based on a pre-defined scoring system reflecting mainly the stage of the liver disease, but considering also additional factors, i.e., hepatic decompensation, other complications, activity and progression of liver disease, risk of transmission and other special issues. Approved treatments are restricted to the most cost-effective combinations based on the cost per sustained virological response value in different patient categories with consensus amongst treating physicians, the National Health Insurance Fund of Hungary and patients' organizations. Interferon-free treatments and shorter therapy durations are preferred. Orv Hetil. 2018; 159(Suppl 1): 3-23.

Management of HCV patients in cases of direct-acting antiviral failure

Introduction: Over 70 million people are infected with hepatitis C virus (HCV), increasing the risk of cirrhosis and hepatocellular carcinoma. Areas covered: Since the approval of the first interferon-free direct-acting antiviral (DAA) therapy in 2011, a number of DAAs have been approved, and HCV is now considered curable. Until recently, however, there were no clear guidelines on how to re-treat patients who fail DAA therapy. Current protease inhibitors (PIs) are generally unaffected by earlier resistance-associated variants (RAVs), but many NS5A inhibitors continue to have overlapping resistance profiles, and NS5A RAVs can persist even in the absence of DAAs. Expert opinion: Fortunately, RAVs affecting NS5B polymerase inhibitors are rare, making sofosbuvir a safe choice as the backbone of re-treatment therapies. Recent re-treatment guidelines that take into account genotype, fibrosis, treatment history, and RAV suggest that >90% of patients with prior treatment failures can be successfully re-treated with sofosbuvir/velpatasvir, sofosbuvir/velpatasvir/voxilaprevir or glecaprevir/pibrentasvir.

[Screening, diagnosis, treatment, and follow up of hepatitis C virus related liver disease. National consensus guideline in Hungary from 15 October 2016]

Treatment of hepatitis C is based on a national consensus guideline updated six-monthly according to local availability and affordability of approved therapies through a transparent allocation system in Hungary. This updated guideline incorporates some special new aspects, including recommendations for screening, diagnostics, use and allocation of novel direct acting antiviral agents. Indication of therapy in patients with no contraindication is based on demonstration of viral replication with consequent inflammation and/or fibrosis in the liver. Non-invasive methods (elastographies and biochemical methods) are preferred for liver fibrosis staging. The budget allocated for these patients is limited. Therefore, expensive novel direct acting antiviral combinations as first line treatment are reimbursed only, if the freely available, but less effective and more toxic pegylated interferon plus ribavirin dual therapy deemed to prone high chance of adverse events and/or low chance of cure. Priority is given to those with urgent need based on a pre-defined scoring system reflecting mainly the stage of the liver disease, but considering also additional factors, i.e., hepatic decompensation, other complications, activity and progression of liver disease, risk of transmission and other special issues. Approved treatments are restricted to the most cost-effective combinations based on the cost per sustained virological response value in different patient categories with consensus amongst treating physicians, the National Health Insurance Fund and patient's organizations. Interferon-free treatments and shorter therapy durations are preferred. Orv. Hetil., 2017, 158(Suppl. 1), 3-22.

The Adenosine Analogue NITD008 has Potent Antiviral Activity against Human and Animal Caliciviruses

The widespread nature of calicivirus infections globally has a substantial impact on the health and well-being of humans and animals alike. Currently, the only vaccines approved against caliciviruses are for feline and rabbit-specific members of this group, and thus there is a growing effort towards the development of broad-spectrum antivirals for calicivirus infections. In this study, we evaluated the antiviral activity of the adenosine analogue NITD008 in vitro using three calicivirus model systems namely; feline calicivirus (FCV), murine norovirus (MNV), and the human norovirus replicon. We show that the nucleoside analogue (NA), NITD008, has limited toxicity and inhibits calicivirus replication in all three model systems with EC₅₀ values of 0.94 μM, 0.91 µM, and 0.21 µM for MNV, FCV, and the Norwalk replicon, respectively. NITD008 has a similar level of potency to the most well-studied NA 2′-C-methylcytidine in vitro. Significantly, we also show that continual NITD008 treatment effectively cleared the Norwalk replicon from cells and treatment with 5 µM NITD008 was sufficient to completely prevent rebound. Given the potency displayed by NITD008 against several caliciviruses, we propose that this compound should be interrogated further to assess its effectiveness in vivo. In summary, we have added a potent NA to the current suite of antiviral compounds and provide a NA scaffold that could be further modified for therapeutic use against calicivirus infections.

Discovery of a novel DNA polymerase inhibitor and characterization of its antiproliferative properties

Chromosomal duplication is targeted by various chemotherapeutic agents for the treatment of cancer. However, there is no specific inhibitor of DNA polymerases that is viable for cancer management. Through structure-based in silico screening of the ZINC database, we identified a specific inhibitor of DNA polymerase δ. The discovered inhibitor, Zelpolib, is projected to bind to the active site of Pol δ when it is actively engaged in DNA replication through interactions with DNA template and primer. Zelpolib shows robust inhibition of Pol δ activity in reconstituted DNA replication assays. Under cellular conditions, Zelpolib is taken up readily by cancer cells and inhibits DNA replication in assays to assess global DNA synthesis or single-molecule bases by DNA fiber fluorography. In addition, we show that Zelpolib displays superior antiproliferative properties to methotrexate, 5-flourouracil, and cisplatin in triple-negative breast cancer cell line, pancreatic cancer cell line and platinum-resistant pancreatic cancer cell line. Pol δ is not only involved in DNA replication, it is also a key component in many DNA repair pathways. Pol δ is the key enzyme responsible for D-loop extension during homologous recombination. Indeed, Zelpolib shows robust inhibition of homologous recombination repair of DNA double-strand breaks and induces "BRCAness" in HR-proficient cancer cells and enhances their sensitivity to PARP inhibitors.

Discovery of Beclabuvir: A Potent Allosteric Inhibitor of the Hepatitis C Virus Polymerase

The discovery of beclabuvir occurred through an iterative series of structure-activity relationship studies directed at the optimization of a novel class of indolobenzazepines. Within this research, a strategic decision to abandon a highly potent but physiochemically problematic series in favor of one of lower molecular weight and potency was key in the realization of the program’s objectives. Subsequent cycles of analog design incorporating progressive conformational constraints successfully addressed off-target liabilities and identified compounds with improved physiochemical profiles. Ultimately, a class of alkyl-bridged piperazine carboxamides was found to be of particular interest, and from this series, beclabuvir was identified as having superior antiviral, safety, and pharmacokinetic properties. The clinical evaluation of beclabuvir in combination with both the NS5A replication complex inhibitor daclatasvir and the NS3 protease inhibitor asunaprevir in a single, fixed-dose formulation (Ximency) resulted in the approval by the Japanese Pharmaceutical and Food Safety Bureau for its use in the treatment of patients infected with genotype 1 HCV.

Sofosbuvir/velpatasvir in patients with hepatitis C virus genotypes 1-6 and compensated cirrhosis or advanced fibrosis

BACKGROUND & AIMS

Patients with chronic hepatitis C virus infection and advanced fibrosis (Metavir F3) or cirrhosis (Metavir F4) have been identified as a priority group for immediate treatment. We evaluated the safety and efficacy of sofosbuvir-velpatasvir in patients with hepatitis C virus genotype 1-6 infection and compensated cirrhosis or advanced fibrosis.

METHODS

This retrospective analysis included 501 patients with compensated cirrhosis or advanced fibrosis (F3/F4), as defined by >0.59 on Fibrotest, >9.5 kPa on Fibroscan, or F3/F4 (Metavir) or F4 (Ishak) on liver biopsy. Patients received sofosbuvir-velpatasvir for 12 weeks. Sustained virological response 12 weeks after treatment was determined.

RESULTS

Forty-four per cent of patients had cirrhosis. Sustained virological response 12 weeks after treatment was achieved by 98% of patients (490/501; 95% confidence interval, 96-99). Sustained virological response 12 weeks after treatment rates were 100% for hepatitis C virus genotypes 2 (85/85), 4 (60/60), 5 (13/13), and 6 (20/20). Sustained virological response 12 weeks after treatment rates were 98% (167/170) in hepatitis C virus genotype 1 patients and 95% (145/153) in hepatitis C virus genotype 3 patients. Among patients with cirrhosis 96% (212/220) achieved sustained virological response 12 weeks after treatment, vs 99% (278/281) for those with advanced fibrosis. Sustained virological response 12 weeks after treatment was 98% (306/311) for treatment-naïve patients and 97% (184/190) for treatment-experienced patients. No patients discontinued treatment due to adverse events. Eight patients reported nine serious adverse events; none was considered related to study procedures or drugs.

CONCLUSIONS

Sofosbuvir plus velpatasvir is highly effective and safe for treating patients with hepatitis C virus genotypes 1, 2, 3, 4, 5 or 6 and advanced fibrosis or compensated cirrhosis.

Why highly effective drugs are not enough: the need for an affordable solution to eliminating HCV

INTRODUCTION

Because of the rapid pace of development of new direct-acting antiviral (DAA) drugs, chronic hepatitis C virus (HCV) infection is now increasingly considered curable. However, the emphasis on DAA therapies disregards key issues related to cost, availability, and antiviral resistance. Areas covered: This perspective provides an overview of current HCV therapies and the development of DAAs, followed by a discussion of the limitations of DAA therapy. A literature search was used to select relevant studies, and a web search for relevant news articles and press releases was conducted. Expert commentary: Despite cure rates exceeding 90%, now is not the time to declare victory against HCV but to reinforce recent progress by addressing the issues of cost and availability as well as by developing strategies to manage antiviral resistance. Future drug development efforts should place greater emphasis on targeting host factors required for HCV replication, for which the barrier to resistance is higher, and effort should continue to develop a vaccine against HCV. Finally, efforts should be made to facilitate large-scale screening in endemic areas to identify and treat patients as early as possible to reduce long-term risks of advanced liver disease and their attendant costs of management.

Analysis of Ribonucleotide 5'-Triphosphate Analogs as Potential Inhibitors of Zika Virus RNA-Dependent RNA Polymerase by Using Nonradioactive Polymerase Assays

Zika virus (ZIKV) is an emerging human pathogen that is spreading rapidly through the Americas and has been linked to the development of microcephaly and to a dramatically increased number of Guillain-Barré syndrome cases. Currently, no vaccine or therapeutic options for the prevention or treatment of ZIKV infections exist. In the study described in this report, we expressed, purified, and characterized full-length nonstructural protein 5 (NS5) and the NS5 polymerase domain (NS5pol) of ZIKV RNA-dependent RNA polymerase. Using purified NS5, we developed an in vitro nonradioactive primer extension assay employing a fluorescently labeled primer-template pair. Both purified NS5 and NS5pol can carry out in vitro RNA-dependent RNA synthesis in this assay. Our results show that Mn²⁺ is required for enzymatic activity, while Mg²⁺ is not. We found that ZIKV NS5 can utilize single-stranded DNA but not double-stranded DNA as a template or a primer to synthesize RNA. The assay was used to compare the efficiency of incorporation of analog 5'-triphosphates by the ZIKV polymerase and to calculate their discrimination versus that of natural ribonucleotide triphosphates (rNTPs). The 50% inhibitory concentrations for analog rNTPs were determined in an alternative nonradioactive coupled-enzyme assay. We determined that, in general, 2'-C-methyl- and 2'-C-ethynyl-substituted analog 5'-triphosphates were efficiently incorporated by the ZIKV polymerase and were also efficient chain terminators. Derivatives of these molecules may serve as potential antiviral compounds to be developed to combat ZIKV infection. This report provides the first characterization of ZIKV polymerase and demonstrates the utility of in vitro polymerase assays in the identification of potential ZIKV inhibitors.

The practical management of chronic hepatitis C infection in Japan - dual therapy of daclatasvir + asunaprevir

Without treatment, many of the 200 million people worldwide with chronic hepatitis C virus (HCV) infection will develop cirrhosis or liver cancer. Japan was the first nation to approve an interferon-free therapy for HCV, and sustained viral response (SVR) rates >90% have been achieved with asunaprevir, a protease inhibitor, plus daclatasvir, an inhibitor of the non-structural 5A (NS5A) protein. Areas covered: This review provides an overview of the results from both clinical trials and real world experience with asunaprevir and daclatasvir therapy focused primarily on Japan. A literature search using the keywords 'asunaprevir,' 'daclatasvir,' 'interferon-free therapy,' and 'direct-acting antiviral drugs' was initially used to select relevant literature for inclusion in the review. Expert commentary: While not approved in the United States, dual therapy with asunaprevir plus daclatasvir has already been successfully used in Japan and throughout East Asia to treat many thousands of patients. Pre-existing or treatment-emergent NS5A-Y93 or -L31 resistance-associated variants (RAVs) may lead to viral breakthrough, and alternative therapies should be considered for these patients, but patients who harbor NS5A RAVs only at low frequency are likely to achieve SVR. The therapy has also been shown to be safe and effective with renal dysfunction or liver cirrhosis.

Organization, Function, and Therapeutic Targeting of the Morbillivirus RNA-Dependent RNA Polymerase Complex

The morbillivirus genus comprises major human and animal pathogens, including the highly contagious measles virus. Morbilliviruses feature single stranded negative sense RNA genomes that are wrapped by a plasma membrane-derived lipid envelope. Genomes are encapsidated by the viral nucleocapsid protein forming ribonucleoprotein complexes, and only the encapsidated RNA is transcribed and replicated by the viral RNA-dependent RNA polymerase (RdRp). In this review, we discuss recent breakthroughs towards the structural and functional understanding of the morbillivirus polymerase complex. Considering the clinical burden imposed by members of the morbillivirus genus, the development of novel antiviral therapeutics is urgently needed. The viral polymerase complex presents unique structural and enzymatic properties that can serve as attractive candidates for druggable targets. We evaluate distinct strategies for therapeutic intervention and examine how high-resolution insight into the organization of the polymerase complex may pave the path towards the structure-based design and optimization of next-generation RdRp inhibitors.

Dasabuvir (ABT333) for the treatment of chronic HCV genotype I: a new face of cure, an expert review

Hepatitis C virus (HCV) affects nearly 1.3% of US population and around 2% of people worldwide. It is associated with serious complication of Cirrhosis and Hepatocellular carcinoma leading to significant morbidity and mortality. Until now the only treatment option for this serious disease was interferon based therapy which had poor tolerance and at best SVR (Sustained virological response) in only 50% of cases. With the introduction of other direct - acting antiviral agents the treatment of HCV has been revolutionized with significantly high rates of cure. Among novel Direct acting antivirals are non-nucleoside inhibitor NS5B which is highly effective in treatment of HCV genotype 1 a and 1b including those with compensated cirrhosis achieving high cure rates with SVR more than 97 % in pooled analysis from six different phase 3 trials. This review will discuss the DAA - Dasabuvir, a non - nucleoside NS5B inhibitor, its mechanism of action, efficacy, safety & tolerance, and drug resistance. Dasabuvir is approved by FDA in combination with other DAA agents called as the 3D(Viekira Pak) in various interferon free regimens achieving high cure rates (SVR >95%) with low adverse effects. In Europe, it is approved by European medicines agency for use in combination with Ombitasvir, Paritaprevir, and ritonavir with or without ribavirin. The drug is used in treatment naive as well as previously treated patient with high success rates. It is also approved in patients with compensated cirrhosis, patients with HIV co-infection and liver transplant recipients which were in the past were excluded from treatment with interferon based therapy. Dasabuvir is extensively evaluated in large clinical trials and shown excellent SVR among HCV genotype1 patient population in combination with other oral DAAs, with good safety profile and tolerance. Its drawback is its genotype restriction, need for ribavirin (RBV) for 1a genotype, low resistance barrier and high cost. It is well tolerated with less than 1 % of patients permanently discontinuing treatment and 2% of patient experiencing a serious adverse reaction. It is contraindicated in patients with known hypersensitivity to ritonavir (e.g. Steven - Johnson syndrome) and strong inducers of CYP3A and CYP2CB.

Inhibitors of the Hepatitis C Virus Polymerase; Mode of Action and Resistance

The hepatitis C virus (HCV) is a pandemic human pathogen posing a substantial health and economic burden in both developing and developed countries. Controlling the spread of HCV through behavioural prevention strategies has met with limited success and vaccine development remains slow. The development of antiviral therapeutic agents has also been challenging, primarily due to the lack of efficient cell culture and animal models for all HCV genotypes, as well as the large genetic diversity between HCV strains. On the other hand, the use of interferon-α-based treatments in combination with the guanosine analogue, ribavirin, achieved limited success, and widespread use of these therapies has been hampered by prevalent side effects. For more than a decade, the HCV RNA-dependent RNA polymerase (RdRp) has been targeted for antiviral development. Direct acting antivirals (DAA) have been identified which bind to one of at least six RdRp inhibitor-binding sites, and are now becoming a mainstay of highly effective and well tolerated antiviral treatment for HCV infection. Here we review the different classes of RdRp inhibitors and their mode of action against HCV. Furthermore, the mechanism of antiviral resistance to each class is described, including naturally occurring resistance-associated variants (RAVs) in different viral strains and genotypes. Finally, we review the impact of these RAVs on treatment outcomes with the newly developed regimens.

Dasabuvir : a new direct antiviral agent for the treatment of hepatitis C

INTRODUCTION

Treatment of hepatitis C virus (HCV) infection with direct-acting antivirals (DAAs) has revolutionized the care of infected patients. Among these novel compounds are non-nucleoside analogs, which bind viral RNA-dependent RNA polymerase resulting in a conformational change inhibiting RNA synthesis.

AREAS COVERED

Efficacy and tolerability of treatment regimens containing the non-nucleoside analog polymerase inhibitor dasabuvir (ABT-333).

EXPERT OPINION

Dasabuvir-containing regimens achieve high rates of sustained virologic response in HCV genotype 1a and 1b-infected patients when combined with other DAAs, namely paritaprevir (ABT-450), ritonavir and ombitasvir (ABT-267). In the populations studied, dasabuvir seems to be well tolerated and safe. The major limitations of this novel drug are its genotype-restricted activity, the necessity to include ribavirin for HCV genotype 1a and the emergence of resistance if not combined with other DDAs.

Optimizing triple therapy and IFN/RBV-free regimens for hepatitis C virus infection

Treatment of chronic hepatitis C virus infection has substantially improved following the advent of direct acting antiviral (DAA) agents. Although the first generation protease inhibitors telaprevir and boceprevir improved sustained viral response (SVR) rates, adverse events remain severe and immature termination of the therapy is frequent; however, intensive dose modification has improved completion and SVR rates. Interferon-free DAA combination therapies, such as asunaprevir and daclatasvir dual therapy are under development and promise higher SVR rates with fewer adverse events. Resistance monitoring and modification of DAA therapy based on pre-existing or de novo resistance variants should be considered. Future therapies are expected to have pan-genotypic activity with shorter duration and improved tolerability, even among cirrhotic and liver transplant patients.

Discovery of SCH 900188: A Potent Hepatitis C Virus NS5B Polymerase Inhibitor Prodrug As a Development Candidate

Starting from indole-based hepatitis C virus (HCV) NS5B polymerase inhibitor lead compound 1, structure modifications were performed at multiple indole substituents to improve potency and pharmacokinetic (PK) properties. Bicyclic quinazolinone was found to be the best substituent at indole nitrogen, while 4,5-furanylindole was identified as the best core. Compound 11 demonstrated excellent potency. Its C2 N,N-dimethylaminoethyl ester prodrug 12 (SCH 900188) demonstrated significant improvement in PK and was selected as the development candidate.

Treatment of hepatitis C virus genotype 3-infection

The treatment of hepatitis C virus (HCV) infection with pegylated interferon (PEG-IFN) alfa and ribavirin (800 mg daily) (RBV) is the standard of care (SOC) for hepatitis C virus genotype 3-infection leading to a sustained virological response (SVR) in around 65% of patients. A better understanding of the HCV life-cycle has recently resulted in the development of several potential direct-acting antiviral drugs (DAAs) targeting viral proteins (NS3/4A protease, NS5B nucleos(t)idic and non-nucleos(t)idic polymerase, NS5A viral replication complex). First generation protease inhibitors in combination with PEG-IFN/RBV are not efficient in genotype 3-infected patients. The combination of PEG-IFN/RBV with Daclatasvir, a NS5A inhibitor for 12-24 weeks results in a SVR in around 75% while the triple combination of PEG-IFN/RBV with the oral nucleotidic polymerase inhibitor Sofosbuvir (GS-7977) for 12 weeks in naïve patients results in a SVR in more than 95%. The results of the first oral combination of Sofosbuvir and RBV for 12 weeks in genotype 3-infected patients have been rather disappointing with a slightly lower SVR than after 24 weeks of PEG-IFN: around 60%, and only 30% in patients with cirrhosis. Extending treatment from 12 to 16 weeks in treatment experienced patients doubled the SVR rate and an 80% SVR rate is expected by extending treatment to 24 weeks. The best oral combination of new DAAs is probably the combination of Sofosbuvir and a NS5A inhibitor (Daclatasvir, Ledipasvir…) for 24 weeks, which resulted in a 100% SVR rate in a limited series. The use of cyclophilin inhibitors, a host-targeted antiviral, in association with DAAs and/or RBV may also be of interest. The oral combination of new DAAs (dual or triple combination of different antivirals) or of DAAs and host targets such as cyclophilin will probably become the SOC for genotype 3-infected treatment-naïve or -experienced patients.

Characteristics of human infection with avian influenza viruses and development of new antiviral agents

Since 1997, several epizootic avian influenza viruses (AIVs) have been transmitted to humans, causing diseases and even deaths. The recent emergence of severe human infections with AIV (H7N9) in China has raised concerns about efficient interpersonal viral transmission, polygenic traits in viral pathogenicity and the management of newly emerging strains. The symptoms associated with viral infection are different in various AI strains: H5N1 and newly emerged H7N9 induce severe pneumonia and related complications in patients, while some H7 and H9 subtypes cause only conjunctivitis or mild respiratory symptoms. The virulence and tissue tropism of viruses as well as the host responses contribute to the pathogenesis of human AIV infection. Several preventive and therapeutic approaches have been proposed to combat AIV infection, including antiviral drugs such as M2 inhibitors, neuraminidase inhibitors, RNA polymerase inhibitors, attachment inhibitors and signal-transduction inhibitors etc. In this article, we summarize the recent progress in researches on the epidemiology, clinical features, pathogenicity determinants, and available or potential antivirals of AIV.

Emerging treatment options for recurrent ovarian cancer: the potential role of olaparib

Olaparib has shown promising anticancer activity as a single agent in the treatment and maintenance of recurrent ovarian cancer in early clinical trials, but it is far from standard therapy. This article outlines the problem of relapsed ovarian cancer and the mechanisms of poly(ADP-ribose) polymerase inhibitors and reviews the recent literature pertaining to olaparib in ovarian cancer.

Oral antiviral therapies for chronic hepatitis C infection

The treatment of hepatitis C virus (HCV) infection with pegylated interferon alpha and ribavirin leads to a sustained virologic response in around 50% of patients with HCV genotype 1, 65% with HCV genotype 4, 75% with HCV genotype 3 and around 80% with HCV genotype 2. A better understanding of the HCV lifecycle has resulted in the development of several potential direct-acting antiviral drugs (DAAs) targeting viral proteins [NS3/4A protease inhibitors, NS5B nucleos(t)idic and non-nucleos(t)idic polymerase inhibitors, NS5A replication complex inhibitors]. This review summarizes the main clinical data for the combinations of oral DAAs. DAAs, either in combination with pegylated interferon alpha or in interferon-free regimens, have demonstrated a high level of antiviral efficacy and a generally well-tolerated safety profile in treatment-naïve patients and in prior nonresponders to pegylated interferon alpha/ribavirin. Oral combination of new DAAs is likely to become the standard of care for chronic HCV in treatment-naïve or treatment-experienced patients. However, most studies so far have included small numbers of 'easy-to-treat' patients with short post-treatment periods for defining the sustained virologic response. Extension of the number of treated patients (including 'difficult-to-treat' patients, i.e. patients infected with genotype 3, who failed to respond to first-generation protease inhibitors or with cirrhosis as well as immunocompromised patients) and of the post-treatment follow up in a real-life setting could significantly worsen the rate of recovery. In these 'difficult-to-treat' patients, the rate of virologic cure with new DAAs could be lower than expected and consequently interferons may be still necessary in combination with the new drugs.

Inhibition of hepatitis C viral RNA-dependent RNA polymerase by α-P-boranophosphate nucleotides: exploring a potential strategy for mechanism-based HCV drug design

Improved treatments for chronic HCV infections remain a challenge, and new chemical strategies are needed to expand the current paradigm. The HCV RNA polymerase (RdR(P)) has been a target for antiviral development. For the first time we show that the boranophosphate (BP) modification increases the substrate efficiency of ATP analogs into HCV NS5BΔ55 RdRP-catalyzed RNA. Boranophosphate nucleotides contain a borane (BH₃) group substituted for a non-bridging phosphoryl oxygen of a normal phosphate group, resulting in a class of modified isoelectronic DNA and RNA mimics capable of modulating the reading and writing of genetic information. We determine that HCV NS5BΔ55, being a stereospecific enzyme, incorporates the Rp isomer of both ATPαB and the two boranophosphate analogs: 2'-O-methyladenosine 5'-(α-P-borano) triphosphate (2'-OMe ATPαB, 5a) and 3'-deoxyadenosine 5'-(α-P-borano) triphosphate (3'-dATPαB, 5b). The R(p) diastereomer of ATPαB (6), having no ribose modifications, was found to be a slightly better substrate than natural ATP, showing a 42% decrease in the apparent Michaelis-Menten constant (K(m)). The IC₅₀ of both 2'-O-Me and 3'-deoxy ATP was decreased with the boranophosphate modification up to 16-fold. This "borano effect" was further confirmed by determining the steady-state inhibitory constant (K(i)), showing a comparable potency shift (21-fold). These experiments also indicate that the boranophosphate analogs 5a and 5b inhibit HCV NS5B through a competitive mode of inhibition. This evidence, together with previous crystal structure data, further supports the idea that HCV NS5B (in a similar manner to HIV-1 RT) discriminates against the 3'-deoxy modification via lost interactions between the 3'-OH on the ribose and the active site residues, or lost intramolecular hydrogen bonding interactions between the 3'-OH and the pyrophosphate leaving group during phosphoryl transfer. To our knowledge, these data represent the first time a phosphate modified NTP has been studied as a substrate for HCV NS5B RdRP.

New hepatitis C therapies in clinical development

With the current standard of care for the treatment of chronic hepatitis C, a combination of pegylated interferon alfa and ribavirin, sustained virologic response rates can be achieved in approximately 50% of patients only. - Improved understanding of the viral life cycle has led to the identification of numerous potential targets for novel, direct-acting antiviral compounds. Inhibitors of the NS3/4A protease are currently the most advanced in clinical development. Recently completed phase 3 studies of the two protease inhibitors telaprevir and boceprevir, each given in combination with standard of care, yielded sustained virologic response rates in the range of 66-75% in treatment-naive patients and 59-66% in treatment-experienced patients with HCV genotype 1 infection. Studies of second-generation protease inhibitors, with the potential advantage of improved potency, drug metabolism and pharmacokinetics profile, are already underway. - Inhibitors of the HCV NS5A protein and NS5B polymerase are potentially active across different HCV genotypes and have shown promising antiviral efficacy in early clinical studies. Other emerging mechanisms include silymarin components and inhibitors of cell proteins required for HCV replication. - While improved formulations of current HCV therapies are also being developed, future hopes lie on the combination of direct-acting antivirals with the eventual possibility of interferon-free treatment regimens.