Jan Paeshuyse

The non-immunosuppressive cyclosporin DEBIO-025 is a potent inhibitor of hepatitis C virus replication in vitro.

Cyclosporin A (CsA) inhibits the in vitro replication of HCV subgenomic replicons. We here report on the potent anti‐HCV activity of the non‐immunosuppressive cyclosporin DEBIO‐025. The 50% effective concentration for inhibition of HCV subgenomic replicon replication in Huh 5‐2 cells (luciferase assay) by DEBIO‐025 was 0.27 ± 0.03 μg/mL and for CsA 2.8 ± 0.4 μg/mL. The concentration that reduced the growth of exponentially proliferating Huh 5‐2 cells by 50% was greater than 27 μg/mL for DEBIO‐025 and 12 ± 6 μg/mL for CsA, resulting in a selectivity index of approximately 900 for DEBIO‐025 and 40 for CsA. The superior activity of DEBIO‐025, as compared with CsA, was corroborated by monitoring HCV RNA levels in Huh 5‐2, two other HCV subgenomic replicon‐containing cell lines, and by monitoring the luciferase signal and viral antigen production in hepatoma cells that had been infected with an infectious full‐length chimeric HCV construct. The combination of interferon alpha 2a with either CsA or DEBIO‐025 resulted in an additive to slightly synergistic antiviral activity. DEBIO‐025, at concentrations of 0.5 and 1 μg/mL, was able to clear cells from their HCV replicon within three to four passages, whereas treatment with CsA at the same concentrations for seven consecutive passages did not result in clearance of the HCV replicon. In conclusion, DEBIO‐025, a compound that is also endowed with potent anti‐HIV activity and is well tolerated in animals and humans, may form an attractive new option for the therapy of HCV infections, particularly in HCV/HIV co‐infected patients. (HEPATOLOGY 2006;43:761–770.)

DEB025 (Alisporivir) Inhibits Hepatitis C Virus Replication by Preventing a Cyclophilin A Induced Cis-Trans Isomerisation in Domain II of NS5A

DEB025/Debio 025 (Alisporivir) is a cyclophilin (Cyp)-binding molecule with potent anti-hepatitis C virus (HCV) activity both in vitro and in vivo. It is currently being evaluated in phase II clinical trials. DEB025 binds to CypA, a peptidyl-prolyl cis-trans isomerase which is a crucial cofactor for HCV replication. Here we report that it was very difficult to select resistant replicons (genotype 1b) to DEB025, requiring an average of 20 weeks (four independent experiments), compared to the typically <2 weeks with protease or polymerase inhibitors. This indicates a high genetic barrier to resistance for DEB025. Mutation D320E in NS5A was the only mutation consistently selected in the replicon genome. This mutation alone conferred a low-level (3.9-fold) resistance. Replacing the NS5A gene (but not the NS5B gene) from the wild type (WT) genome with the corresponding sequence from the DEB025res replicon resulted in transfer of resistance. Cross-resistance with cyclosporine A (CsA) was observed, whereas NS3 protease and NS5B polymerase inhibitors retained WT-activity against DEB025res replicons. Unlike WT, DEB025res replicon replicated efficiently in CypA knock down cells. However, DEB025 disrupted the interaction between CypA and NS5A regardless of whether the NS5A protein was derived from WT or DEB025res replicon. NMR titration experiments with peptides derived from the WT or the DEB025res domain II of NS5A corroborated this observation in a quantitative manner. Interestingly, comparative NMR studies on two 20-mer NS5A peptides that contain D320 or E320 revealed a shift in population between the major and minor conformers. These data suggest that D320E conferred low-level resistance to DEB025 probably by reducing the need for CypA-dependent isomerisation of NS5A. Prolonged DEB025 treatment and multiple genotypic changes may be necessary to generate significant resistance to DEB025, underlying the high barrier to resistance.

Debio 025, a Cyclophilin Binding Molecule, Is Highly Efficient in Clearing Hepatitis C Virus (HCV) Replicon-Containing Cells When Used Alone or in Combination with Specifically Targeted Antiviral Therapy for HCV (STAT-C) Inhibitors

ABSTRACT Debio 025 is a potent inhibitor of hepatitis C virus (HCV) replication (J. Paeshuyse et al., Hepatology 43:761-770, 2006). In phase I clinical studies, monotherapy (a Debio 025 dose of 1,200 mg twice a day) resulted in a mean maximal decrease in the viral load of 3.6 log10 units (R. Flisiak et al., Hepatology 47:817-826, 2008), whereas a reduction of 4.6 log10 units was obtained in phase II studies when Debio 025 was combined with interferon (R. Flisiak et al., J. Hepatol., 48:S62, 2008). We here report on the particular characteristics of the in vitro anti-HCV activities of Debio 025. The combination of Debio 025 with either ribavirin or specifically targeted antiviral therapy for HCV (STAT-C) inhibitors (NS3 protease or NS5B [nucleoside and nonnucleoside] polymerase inhibitors) resulted in additive antiviral activity in short-term antiviral assays. Debio 025 has the unique ability to clear hepatoma cells from their HCV replicon when it is used alone or in combination with interferon and STAT-C inhibitors. Debio 025, when it was used at concentrations that have been observed in human plasma (0.1 or 0.5 μM), was able to delay or prevent the development of resistance to HCV protease inhibitors as well as to nucleoside and nonnucleoside polymerase inhibitors. Debio 025 forms an attractive drug candidate for the treatment of HCV infections in combination with standard interferon-based treatment and treatments that directly target the HCV polymerase and/or protease.

Statins potentiate the in vitro anti‐hepatitis C virus activity of selective hepatitis C virus inhibitors and delay or prevent resistance development

Statins are 3‐hydroxyl‐3‐methylglutaryl coenzyme A (HMG CoA) reductase inhibitors used for the treatment of hypercholesterolemia. It was recently reported that statins inhibit in vitro hepatitis C virus (HCV) RNA replication. We here report that, of five statins studied, mevastatin and simvastatin exhibit the strongest in vitro anti‐HCV activity, lovastatin and fluvastatin have moderate inhibitory effects, and pravastatin is devoid of an antiviral effect. A combination of statins with interferon‐alpha (IFN‐α) or HCV nonstructural (NS)5B polymerase or NS3 protease inhibitors results in an additive antiviral activity in short‐term (3 days) antiviral assays. Neither statins, at a concentration of five‐fold their median effective concentration (EC50) value, nor polymerase, protease inhibitors, or IFN‐α, at concentrations 10‐ or 20‐fold their EC50 value, were able to clear cells from their replicon following four or six consecutive passages of antiviral pressure. However, the combination of HCV polymerase or protease inhibitors with mevastatin or simvastatin resulted in an efficient clearance of the cultures from their replicon. In colony formation experiments, mevastatin reduced the frequency or prevented the selection of HCV replicons resistant to the nonnucleoside inhibitor HCV‐796. Conclusion: A combination of specific HCV inhibitors with statins may result in a more profound antiviral effect and may delay or prevent the development of resistance to such inhibitors. (HEPATOLOGY 2009.)

A Novel, Highly Selective Inhibitor of Pestivirus Replication That Targets the Viral RNA-Dependent RNA Polymerase

ABSTRACT We report on the highly potent and selective antipestivirus activity of 5-[(4-bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine (BPIP). The 50% effective concentration (EC50) for inhibition of bovine viral diarrhea virus (BVDV)-induced cytopathic effect formation was 0.04 ± 0.01 μM. Comparable reduction of viral RNA synthesis (EC50 = 0.12± 0.02 μM) and production of infectious virus (EC50 = 0.074 ± 0.003 μM) were observed. The selectivity index (ratio of 50% cytostatic concentration/EC50) of BPIP was ∼2,000. BPIP was inactive against the hepatitis C virus subgenomic replicon and yellow fever virus but demonstrated weak activity against GB virus. Drug-resistant mutants were at least 300-fold less susceptible to BPIP than wild-type virus; showed cross-resistance to N-propyl-N-[2-(2H-1,2,4-triazino[5,6-b]indol-3-ylthio)ethyl]-1-propanamine (VP32947), and carried the F224S mutation in the viral RNA-dependent RNA polymerase (RdRp). When the F224S mutation was introduced into an infectious clone, the drug-resistant phenotype was obtained. BPIP did not inhibit the in vitro activity of recombinant BVDV RdRp, but did inhibit the activity of replication complexes (RCs). Computational docking revealed that F224 is located at the top of the finger domain of the polymerase. Docking of BPIP in the crystal structure of the BVDV RdRp revealed aromatic ring stacking, some hydrophobic contacts, and a hydrogen bond. Since two structurally unrelated compounds, i.e., BPIP and VP32947, target the same region of the BVDV RdRp, this position may be expected to be critical in the functioning of the polymerase or assembly of the RC. The potential of BPIP for the treatment of pestivirus and hepacivirus infections is discussed.

Human pluripotent stem cell-derived hepatocytes support complete replication of hepatitis C virus

BACKGROUND & AIMS Worldwide, about 180 million people are chronically infected with the hepatitis C virus (HCV). Current in vitro culture systems for HCV depend chiefly on human hepatoma cell lines. Although primary human hepatocytes support HCV infection in vitro, and immunodeficient mice repopulated with human hepatocytes support HCV infection in vivo, these models are limited because of shortage of human livers to isolate hepatocytes. Therefore, there is significant interest in the establishment from of a HCV culture system in human stem cell-derived hepatocyte-like cells. METHODS Human embryonic stem cell (hESC)-derived hepatocytes were infected with HCV in the presence or absence of direct acting antivirals. After inoculation, replication of HCV was analyzed extensively. RESULTS We demonstrate that hESC-derived hepatocytes can be infected with the HCV JFH1 genotype 2a, resulting in the production of viral RNA in the stem cell progeny. Viral replication is inhibited by a non-nucleoside HCV polymerase-inhibitor (HCV-796), a cyclophilin binding molecule (Debio 025-Alisporivir) and the protease inhibitor VX-950 (Telaprevir). Stem cell-derived hepatocytes produced, for more than 10 days, the HCV core protein as well as virions that were capable of re-infecting hepatoma cells. CONCLUSIONS Hepatocytes derived from hESC support the complete HCV replication cycle (including the production of infectious virus), and viral replication in these cells is efficiently inhibited by selective inhibitors of HCV replication.

Mechanistic Characterization of GS-9190 (Tegobuvir), a Novel Nonnucleoside Inhibitor of Hepatitis C Virus NS5B Polymerase

ABSTRACT GS-9190 (Tegobuvir) is a novel imidazopyridine inhibitor of hepatitis C virus (HCV) RNA replication in vitro and has demonstrated potent antiviral activity in patients chronically infected with genotype 1 (GT1) HCV. GS-9190 exhibits reduced activity against GT2a (JFH1) subgenomic replicons and GT2a (J6/JFH1) infectious virus, suggesting that the compounds mechanism of action involves a genotype-specific viral component. To further investigate the GS-9190 mechanism of action, we utilized the susceptibility differences between GT1b and GT2a by constructing a series of replicon chimeras where combinations of 1b and 2a nonstructural proteins were encoded within the same replicon. The antiviral activities of GS-9190 against the chimeric replicons were reduced to levels comparable to that of the wild-type GT2a replicon in chimeras expressing GT2a NS5B. GT1b replicons in which the β-hairpin region (amino acids 435 to 455) was replaced by the corresponding sequence of GT2a were markedly less susceptible to GS-9190, indicating the importance of the thumb subdomain of the polymerase in this effect. Resistance selection in GT1b replicon cells identified several mutations in NS5B (C316Y, Y448H, Y452H, and C445F) that contributed to the drug resistance phenotype. Reintroduction of these mutations into wild-type replicons conferred resistance to GS-9190, with the number of NS5B mutations correlating with the degree of resistance. Analysis of GS-9190 cross-resistance against previously reported NS5B drug-selected mutations showed that the resistance pattern of GS-9190 is different from other nonnucleoside inhibitors. Collectively, these data demonstrate that GS-9190 represents a novel class of nonnucleoside polymerase inhibitors that interact with NS5B likely through involvement of the β-hairpin in the thumb subdomain.

Ribavirin for the treatment of chronic hepatitis C virus infection: a review of the proposed mechanisms of action

Roughly 20 years after the discovery of the hepatitis C virus (HCV), and 10 years after the launch of the current standard of care (SOC) therapy, i.e. the combination of pegylated interferon-alpha and ribavirin, antiviral treatment of chronic hepatitis C is at the dawn of a new era. The current SOC will be combined with a direct acting antiviral (DAA), i.e. either the HCV NS3 protease inhibitor Telaprevir or Boceprevir. Combinations of DAAs may have the potential to completely cure chronic HCV infection. Clinical data suggest that ribavirin may remain at least for some time, an important component even in combinations of different DAAs. Ironically, and much in contrast to the DAAs, the precise mechanism(s) by which ribavirin exerts its anti-HCV activity in infected patients still waits to be unravelled. Here we review the current views on the mechanism of action of ribavirin against chronic infections with HCV. Concerted efforts of modern pharmacogenetics, novel insights into innate immunity and contributions from molecular virology will hopefully allow deciphering the precise mechanism(s) that are at the basis of the antiviral effect of this nucleoside analogue. Such insights may help design improved strategies to fight chronic infections with HCV.

Interferons, Interferon Inducers, and Interferon-Ribavirin in Treatment of Flavivirus-Induced Encephalitis in Mice

ABSTRACT We evaluated the prophylactic and therapeutic efficacy of interferon α-2b, pegylated interferon α-2b, poly(I · C), and Ampligen against Modoc virus encephalitis in an animal model for flavivirus infections. All compounds significantly delayed virus-induced morbidity (paralysis) and mortality (due to progressive encephalitis). Viral load (as measured on day 7 postinfection) was significantly reduced by 80 to 100% in the serum, brain, and spleen in mice that had been treated with either interferon α-2b, pegylated interferon α-2b, poly(I · C), or Ampligen. We also studied whether a combination of interferon α-2b and ribavirin (presently the standard therapy for the treatment of infections with hepatitis C virus) would be more effective than treatment with interferon alone. However, ribavirin did not enhance the inhibitory effect of interferon therapy in this animal model for flavivirus infections.

Ribavirin Antagonizes the In Vitro Anti-Hepatitis C Virus Activity of 2′-C-Methylcytidine, the Active Component of Valopicitabine

ABSTRACT Ribavirin antagonizes the in vitro anti-hepatitis C virus (HCV) activity of the pyrimidine nucleoside analogue 2′-C-methylcytidine, the active component of the experimental anti-HCV drug valopicitabine. In contrast, the combination of ribavirin with either the purine nucleoside analogue 2′-C-methyladenosine or the HCV protease inhibitor VX-950 resulted in an additive antiviral activity. These findings may have implications when planning clinical studies with valopicitabine.