Specific targeted antiviral therapy for hepatitis C

Searching for anthranilic acid-based thumb pocket 2 HCV NS5B polymerase inhibitors through a combination of molecular docking, 3D-QSAR and virtual screening

A combination of the following computational methods: (i) molecular docking, (ii) 3-D Quantitative Structure Activity Relationship Comparative Molecular Field Analysis (3D-QSAR CoMFA), (iii) similarity search and (iv) virtual screening using PubChem database was applied to identify new anthranilic acid-based inhibitors of hepatitis C virus (HCV) replication. A number of known inhibitors were initially docked into the "Thumb Pocket 2" allosteric site of the crystal structure of the enzyme HCV RNA-dependent RNA polymerase (NS5B GT1b). Then, the CoMFA fields were generated through a receptor-based alignment of docking poses to build a validated and stable 3D-QSAR CoMFA model. The proposed model can be first utilized to get insight into the molecular features that promote bioactivity, and then within a virtual screening procedure, it can be used to estimate the activity of novel potential bioactive compounds prior to their synthesis and biological tests.

Nucleotide prodrugs for the treatment of HCV infection

The HCV RNA-dependent RNA polymerase is an essential enzyme in HCV viral replication and has been a prominent target in the search for therapies to treat individuals infected with HCV. The development of both nucleoside and nucleotide HCV inhibitors has been pursued because of their potential for showing pangenotypic activity and because of their high barrier to resistance. Even though nucleoside inhibitors were shown to be effective in a clinical setting, their potency limited their effectiveness. The exploitation of prodrug strategies to deliver nucleoside 5'-monophosphates has resulted in the development of a number of very potent inhibitors of HCV replication. In addition, several of these nucleotide prodrugs have demonstrated liver-targeting characteristics when administered orally. Human clinical studies have shown that a number of nucleotide prodrugs are potent inhibitors of viral replication leading to significant reductions in viral load when given orally. Combinations of these nucleotide prodrugs with either pegylated interferon-α and ribavirin or another direct acting antiviral alone has lead to cure rates as high as 100% after only 12 weeks of therapy. The combination of a nucleotide prodrug and another direct-acting antiviral agent holds the promise of delivering an interferon-free therapy for HCV patients thus eliminating the undesirable side effects associated with taking interferon.

Comparison of current US risk strategy to screen for hepatitis C virus with a hypothetical targeted birth cohort strategy

OBJECTIVES

We compared the theoretical performance of a 1-time, birth cohort strategy with the currently recommended risk strategy for screening for hepatitis C virus (HCV) infection, which is undetected in an estimated 75% of 4 million affected people in the United States.

METHODS

We applied current American Association for the Study of Liver Disease risk screening guidelines and a targeted birth cohort strategy to National Health and Nutrition Examination Survey data from 2003 to 2006 to estimate their performance in identifying HCV cases.

RESULTS

Risk guidelines would recommend testing 25% of the US population aged 20 years or older and, if fully implemented, identify 82% of the projected HCV-exposed population. A targeted birth cohort (1946-1964) strategy would test 45% of the same population and identify 76% of the projected HCV population.

CONCLUSIONS

In this ideal-world simulation, birth year and risk screening had similar theoretical performances for predicting HCV infection. However, actual implementation of risk screening has not achieved its theoretical performance, and birth cohort screening might increase HCV testing rates.

Nucleotide prodrugs for HCV therapy

HCV infection is a significant worldwide health problem and is a major cause of hepatocellular carcinoma. The current standard of care, interferon and ribavirin, is only effective against a proportion of the patient population infected with HCV. To address the shortcomings of existing therapy, the development of direct acting antiviral agents is under investigation. The HCV RNA dependent RNA polymerase is an essential enzyme for viral replication and is therefore a logical target against which to develop novel anti-HCV agents. Nucleosides have been shown to be effective as antiviral agents for other viral diseases and therefore, have been investigated as inhibitors of HCV replication. The development of prodrugs of nucleoside 5'-monophosphates has been pursued to address limitations associated with poor nucleoside phosphorylation. This is required to produce the nucleoside 5'-triphosphate which is the anabolite that is the actual inhibitor of the polymerase enzyme. Prodrugs of nucleoside 5'-monophosphates have been developed that enable their delivery into cells and in vivo into the liver. The implementation of these prodrug strategies has ultimately led to the identification of several prodrugs of nucleoside 5'-monophosphates that are potent inhibitors of HCV replication in vitro. They have progressed into the clinic and the early data demonstrate greatly reduced viral load levels in HCV-infected patients. This review will survey the state of nucleotide prodrugs for the treatment of HCV.

Potential treatment options and future research to increase hepatitis C virus treatment response rate

Hepatitis C virus (HCV) is a liver-tropic blood-borne pathogen that affects more than 170 million people worldwide. Although acute infections are usually asymptomatic, up to 90% of HCV infections persist with the possibility of long-term consequences such as liver fibrosis, cirrhosis, steatosis, insulin resistance, or hepatocellular carcinoma. As such, HCV-associated liver disease is a major public health concern. Although the currently available standard of care therapy of pegylated interferon α plus ribavirin successfully treats infection in a subset of patients, the development of more effective, less toxic HCV antivirals is a health care imperative. This review not only discusses the limitations of the current HCV standard of care but also evaluates upcoming HCV treatment options and how current research elucidating the viral life cycle is facilitating the development of HCV-specific therapeutics that promise to greatly improve treatment response rates both before and after liver transplantation.

Successful HCV eradication and inhibition of HIV replication by intravenous silibinin in an HIV-HCV coinfected patient

INTRODUCTION

The efficacy of antiviral therapy with pegylated interferon (PEGIFN) plus ribavirin (RBV) in patients with HIV and hepatitis C virus (HCV) coinfection is limited. Intravenous silibinin (ivSIL), a milk thistle extract with proven antiviral effects represents a novel therapeutic strategy for virological nonresponders.

METHODS

We report a case of an HIV-HCV coinfected patient, who has not responded to a prior course of PEGIFN-α2a (180 μg/week/s.c.) and RBV (1000 mg/day/p.o.). Testing for IL-28β small nucleotid polymorphism revealed the nonfavourable genotype T/T. Antiretroviral therapy was not prescribed because the patients presented with well-preserved CD4+ cell counts and low HIV-RNA levels. She received retreatment with ivSIL for two weeks followed by PEGIFN/RBV combination therapy starting at week 1.

RESULTS

After 2 weeks of ivSIL therapy both HCV-RNA and HIV-RNA become undetectable. On ivSIL monotherapy we noticed a trend towards an increase of CD4+ cell counts and a decrease of HIV-RNA. After 16 weeks PEGIFN+RBV was discontinued due to patients wish because of adverse events. HCV-RNA was still negative 24 weeks after cessation of therapy, while HIV-RNA returned to baseline levels.

CONCLUSION

ivSIL may represent a potential treatment option for retreatment of HIV-HCV coinfected patients nonresponding to PEGIFN+RBV combination therapy. Further investigations on the possible beneficial effects of ivSIL on CD4+ cell counts and HIV-RNA levels are necessary.

Hepatitis C virus experimental model systems and antiviral drug research

An estimated 130 million people worldwide are chronically infected with hepatitis C virus (HCV) making it a leading cause of liver disease worldwide. Because the currently available therapy of pegylated interferon-alpha and ribavirin is only effective in a subset of patients, the development of new HCV antivirals is a healthcare imperative. This review discusses the experimental models available for HCV antiviral drug research, recent advances in HCV antiviral drug development, as well as active research being pursued to facilitate development of new HCV-specific therapeutics.

1a/1b subtype profiling of nonnucleoside polymerase inhibitors of hepatitis C virus

The RNA-dependent RNA polymerase (NS5B) of hepatitis C virus (HCV) is an unusually attractive target for drug discovery since it contains five distinct drugable sites. The success of novel antiviral therapies will require nonnucleoside inhibitors to be active in at least patients infected with HCV of subtypes 1a and 1b. Therefore, the genotypic assessment of these agents against clinical isolates derived from genotype 1-infected patients is an important prerequisite for the selection of suitable candidates for clinical development. Here we report the 1a/1b subtype profiling of polymerase inhibitors that bind at each of the four known nonnucleoside binding sites. We show that inhibition of all of the clinical isolates tested is maintained, except for inhibitors that bind at the palm-1 binding site. Subtype coverage varies across chemotypes within this class of inhibitors, and inhibition of genotype 1a improves when hydrophobic contact with the polymerase is increased. We investigated if the polymorphism of the palm-1 binding site is the sole cause of the reduced susceptibility of subtype 1a to inhibition by 1,5-benzodiazepines by using reverse genetics, X-ray crystallography, and surface plasmon resonance studies. We showed Y415F to be a key determinant in conferring resistance on subtype 1a, with this effect being mediated through an inhibitor- and enzyme-bound water molecule. Binding studies revealed that the mechanism of subtype 1a resistance is faster dissociation of the inhibitor from the enzyme.

HCV NS5B polymerase inhibitors

Chronic hepatitis C virus (HCV) infection affects approximately 4 million persons and is the major indication for liver transplantation in the United States. The current standard for treatment of HCV is pegylated interferon in combination with ribavirin. Despite significant advances in treatment, only approximately 50% of patients of treated patients clear HCV infection. Polymerase inhibitors, given their potent antiviral effects, represent a major contribution to the future of HCV treatment. Whether these new drugs will have a role in the treatment of the difficult patient (non-responders, those co-infected with HIV, decompensated liver disease and liver transplant recipients) remains to be determined.

Hepatitis C protease and polymerase inhibitors in development

Hepatitis C infection (HCV) remains a global problem and the current anti-HCV therapies available in the clinic have sustained virologic response rates (SVR) of only about 50%, especially in HCV genotype 1-infected subjects. The SVR is even lower in HIV-HCV co-infected patients, estimated at only about 30-40%. However, exciting new research is under way to find new anti-HCV therapies. Presently, efforts to develop new anti-HCV agents for HCV-infected persons who fail pegylated interferon and ribavirin-based therapies have focused on inhibitors of key HCV enzymes such as the HCV NS3 protease and the NS5B polymerase. There are two protease inhibitors, telaprevir (VX-950, Vertex) and boceprevir (SCH 503034, Schering-Plough); and three polymerase inhibitors, valopicitabine (NM283, Idenix), R1626 (Roche), and HCV-796 (Viropharma) that have advanced to late-stage clinical trials. Of these aforementioned agents, telaprevir is the most advanced in clinical development. Early trial results on efficacy, safety, and HCV drug-resistance profiles of these novel agents will be discussed in this review paper.

Small molecule and novel treatments for chronic hepatitis C virus infection

The development of molecular-based therapies for the treatment of chronic hepatitis C virus (HCV) infection is an area of intense clinical research, driven by the inability of the current standard of care, combination therapy with pegylated interferon alfa (PEG-IFNalpha) and ribavirin (RBV), to achieve a sustained virologic response (SVR) in a large proportion of patients and by the lack of approved alternative therapies for PEG-IFNalpha/RBV nonresponders and relapsers. Agents being developed against specific HCV viral proteins have recently been termed Specifically Targeted Antiviral Therapy for HCV (STAT-C). Preliminary data for several agents show they have high antiviral activity, especially when used in combination with PEG-IFNalpha, and are tolerable, but resistance mutations have been identified. Further study is needed to clarify the safety, tolerability, and efficacy of these compounds. Once established, the potential for shorter treatment strategies could then be evaluated. Other novel therapies in development that may improve both outcomes and tolerability include a prodrug of RBV and an albumin-modified IFNalpha. In conclusion, small molecule and novel therapies for HCV infection are showing promise in clinical trials, and research to develop new agents and optimize treatment regimens is ongoing.