Emerging therapies for hepatitis C virus

Combined 3D-QSAR, molecular docking and molecular dynamics study on the benzimidazole inhibitors targeting HCV NS5B polymerase

The hepatitis C virus (HCV)-infected population has continued to grow during recent years, and novel HCV antiviral agents are urgently needed. In this work, a combined theoretical study was performed on the HCV non-structural 5B (NS5B) polymerase and 53 benzimidazole inhibitors. Comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were carried out with ligand-based and receptor-based alignments. Ligand-based QSAR models (cross-validated q² of 0.918 for CoMFA and 0.825 for CoMSIA) were found to be superior to receptor-based approaches (cross-validated q² of 0.765 for CoMFA and 0.740 for CoMSIA). Based on the most predictive CoMFA and CoMSIA models, the structural features that were essential for the inhibitory activity of benzimidazoles were characterized. A molecular dynamics study revealed that the induced fit effect between NS5B and its substrate may be responsible for the inferiority of the receptor-based CoMFA and CoMSIA models. The binding-free energy calculated using the MM/PBSA method correlated well with the experimental results and revealed that the van der Waals and electrostatic interactions most contributed to the binding. In addition, energetically favorable NS5B residues were identified by the per-residue decomposition of binding-free energy. The results presented in this work provide meaningful information for the design of novel benzimidazole inhibitors targeting the NS5B polymerase.Communicated by Ramaswamy H. Sarma.

PEGylation and its impact on the design of new protein-based medicines

PEGylation is the covalent conjugation of PEG to therapeutic molecules. Protein PEGylation is a clinically proven approach for extending the circulation half-life and reducing the immunogenicity of protein therapeutics. Most clinically used PEGylated proteins are heterogeneous mixtures of PEG positional isomers conjugated to different residues on the protein main chain. Current research is focused to reduce product heterogeneity and to preserve bioactivity. Recent advances and possible future directions in PEGylation are described in this review. So far protein PEGylation has yielded more than 10 marketed products and in view of the lack of equally successful alternatives to extend the circulation half-life of proteins, PEGylation will still play a major role in drug delivery for many years to come.

Synthesis of HCV replicase inhibitors: base-catalyzed synthesis of protected α-hydrazino esters and selective aerobic oxidation with catalytic Pt/Bi/C for synthesis of imidazole-4,5-dicarbaldehyde

A robust convergent synthesis of the prodrugs of HCV replicase inhibitors 1-5 is described. The central 5H-imidazo[4,5-d]pyridazine core was formed from acid-catalyzed cyclocondensation of an imidazole-4,5-dicarbaldehyde (20) and a α-hydrazino ester, generated in situ from the bis-BOC-protected precursors 25 and 33. The acidic conditions not only released the otherwise unstable α-hydrazino esters but also were the key to avoid facile decarboxylation to the parent drugs from the carboxylic ester prodrugs 1-5. The bis-BOC α-hydrazino esters 25 and 33 were prepared by addition of ester enolates (from 23 and 32) to di-tert-butyl azodicarboxylate via catalysis with mild inorganic bases, such as Li2CO3. A selective aerobic oxidation with catalytic 5% Pt-Bi/C in aqueous KOH was developed to provide the dicarbaldehyde 20 from the diol 27.

Antifibrotic properties of transarterial oncolytic VSV therapy for hepatocellular carcinoma in rats with thioacetamide-induced liver fibrosis

Recombinant vesicular stomatitis virus (VSV) shows promise for the treatment of hepatocellular carcinoma (HCC), but its safety and efficacy when administered in a setting of hepatic fibrosis, which occurs in the majority of clinical cases, is unknown. We hypothesized that VSV could provide a novel benefit to the underlying fibrosis, due to its ability to replicate and cause cell death specifically in activated hepatic stellate cells. In addition to the ability of VSV to produce a significant oncolytic response in HCC-bearing rats in the background of thioacetamide-induced hepatic fibrosis without signs of hepatotoxicity, we observed a significant downgrading of fibrosis stage, a decrease in collagen content in the liver, and modulation of gene expression in favor of fibrotic regression. Together, this work suggests that VSV is not only safe and effective for the treatment of HCC with underlying fibrosis, but it could potentially be developed for clinical application as a novel antifibrotic agent.

Physiologic functions of cyclophilin D and the mitochondrial permeability transition pore

This review focuses on the role of cyclophilin D (CypD) as a prominent mediator of the mitochondrial permeability transition pore (MPTP) and subsequent effects on cardiovascular physiology and pathology. Although a great number of reviews have been written on the MPTP and its effects on cell death, we focus on the biology surrounding CypD itself and the non-cell death physiologic functions of the MPTP. A greater understanding of the physiologic functions of the MPTP and its regulation by CypD will likely suggest novel therapeutic approaches for cardiovascular disease, both dependent and independent of programmed necrotic cell death mechanisms.  

Synthesis and antiviral properties of novel tetracyclic nucleoside inhibitors of hepatitis C NS5B polymerase

As part of an ongoing medicinal chemistry effort to identify novel nucleoside inhibitors of HCV NS5B polymerase, we report the discovery of a novel series of 2'-C-Methyl-ribose nucleoside derivatives bearing a 7-aryl and 7-heteroaryl- substituted 7-deaza-adenine nucleobase. A reliable platform for the synthesis and simplified purification of the corresponding nucleoside triphosphates (NTPs) was established, enabling a solid understanding of the SAR relationship within the series. By this approach, we identified the novel analogs 13a and 13b that demonstrated micromolar levels of cellular activity, and the NTPs of which, 16a and 16b, are excellent inhibitors of NS5B with IC(50) = 0.1 μM, a level of intrinsic potency similar to that of previous and current clinical candidates.

Pharmacokinetics, pharmacodynamics, and tolerability of GS-9851, a nucleotide analog polymerase inhibitor, following multiple ascending doses in patients with chronic hepatitis C infection

We conducted this double-blind, parallel-group, placebo-controlled, randomized, multiple-ascending-dose study to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of GS-9851 (formerly PSI-7851) in treatment-naïve patients infected with hepatitis C virus (HCV) genotype 1. Thirty-two patients received active doses up to 400 mg of GS-9851 once daily for 3 days. GS-9851 and the metabolite GS-566500 (formerly PSI-352707) were rapidly cleared from the plasma, with half-life (t(1/2)) values of approximately 1 h for GS-9851 and 3 h for GS-566500. Accumulation (21%) was observed only for GS-331007 (formerly PSI-6206) after multiple dosing. GS-331007 was the primary drug-related moiety in the plasma and urine. Increases in the GS-9851, GS-566500, and GS-331007 maximum concentrations in plasma (C(max)) and area under the concentration-time curve (AUC) were less than dose proportional, particularly at the highest doses. The decline in plasma HCV RNA levels was dose dependent, and a mean maximal change from the baseline of -1.95 log(10) IU/ml was obtained for 400 mg GS-9851, compared with -0.090 log(10) IU/ml for the placebo. Most patients had a decrease in HCV RNA of ≥1.0 log(10) IU/ml after 3 days' dosing with 400 mg GS-9851. No virologic resistance was observed. GS-9851 was generally well tolerated, with no notable differences in adverse event frequency across doses. The pharmacokinetic profile observed in this study was similar to that seen in a single-ascending-dose study in healthy subjects.

Pharmacokinetics, safety, and tolerability of GS-9851, a nucleotide analog polymerase inhibitor for hepatitis C virus, following single ascending doses in healthy subjects

To investigate the pharmacokinetics, safety, and tolerability of GS-9851 (formerly PSI-7851), a new nucleotide analog inhibitor of hepatitis C virus (HCV), we conducted a double-blind, parallel, placebo-controlled, randomized, single-ascending-dose study. Healthy subjects received oral doses of 25 to 800 mg GS-9851. Peak concentrations of GS-9851 in plasma were achieved more rapidly than those of the metabolites GS-566500 (formerly PSI-352707) and GS-331007 (formerly PSI-6206), with time to maximum concentration of drug in plasma (t(max)) values of 1.0 to 1.8 h, 1.5 to 3.0 h, and 3.0 to 6.0 h, respectively. The majority of systemic drug exposure was from the nucleoside GS-331007, with maximum concentration of drug in plasma (C(max)) and area under the concentration-time curve to the last measurable concentration (AUC(0-t)) values at least 7- and 41-fold higher, respectively, than those obtained for GS-9851 after adjusting for differences in molecular weight. The terminal elimination half-life (t(1/2)) of GS-331007 increased with the dose, achieving a t(1/2) of 25.7 h at 800 mg GS-9851. Dose proportionality was not observed for GS-331007. The majority of drug recovered in urine was in the form of GS-331007, with the percentage of this metabolite in urine samples ranging from 57% to 27% with increasing dose. GS-9851 was generally well tolerated, with no maximum tolerated dose identified. In conclusion, GS-9851 and its metabolites demonstrated a favorable pharmacokinetic profile consistent with once-daily dosing, and therefore, further clinical studies evaluating GS-9851 in HCV-infected patients are warranted.

Synthesis and SAR of pyridothiazole substituted pyrimidine derived HCV replication inhibitors

Introduction of a nitrogen atom into the benzene ring of a previously identified HCV replication (replicase) benzothiazole inhibitor 1, resulted in the discovery of the more potent pyridothiazole analogues 3. The potency and PK properties of the compounds were attenuated by the introductions of various functionalities at the R(1), R(2) or R(3) positions of the molecule (compound 3). Inhibitors 38 and 44 displayed excellent potency, selectivity (GAPDH/MTS CC(50)), PK parameters in all species studied, and cross genotype activity.

Pyridofuran substituted pyrimidine derivatives as HCV replication (replicase) inhibitors

Introduction of nitrogen atom into the benzene ring of a previously identified HCV replication (replicase) benzofuran inhibitor 2, resulted in the discovery of the more potent pyridofuran analogue 5. Subsequent introduction of small alkyl and alkoxy ligands into the pyridine ring resulted in further improvements in replicon potency. Replacement of the 4-chloro moiety on the pyrimidine core with a methyl group, and concomitant monoalkylation of the C-2 amino moiety resulted in the identification of several inhibitors with desirable characteristics. Inhibitor 41, from the monosubstituted pyridofuran and inhibitor 50 from the disubstituted series displayed excellent potency, selectivity (GAPDH/MTS CC(50)) and PK parameters in all species studied, while the selectivity in the thymidine incorporation assay (DNA·CC(50)) was low.

Synthesis and antiviral properties of novel 7-heterocyclic substituted 7-deaza-adenine nucleoside inhibitors of Hepatitis C NS5B polymerase

Previous investigations in our laboratories resulted in the discovery of a novel series of potent nucleoside inhibitors of Hepatitis C virus (HCV) NS5B polymerase bearing tetracyclic 7-substituted 7-deaza-adenine nucleobases. The planarity of such modified systems was suggested to play a role in the high inhibitory potency observed. This paper describes how we envisaged to maintain the desired planarity of the modified nucleobase by means of an intra-molecular H-bond, engaging a H-bond donor atom on an appropriately substituted 7-heterocyclic residue with the adjacent amino group of the nucleobase. The success of this strategy is reflected by the identification of several novel potent nucleoside inhibitors of HCV NS5B bearing a 7-heterocyclic substituted 7-deaza-adenine nucleobase. Amongst these, the 1,2,4-oxadiazole analog 11 showed high antiviral potency against HCV replication in replicon cells and efficient conversion to the corresponding NTP in vivo, with high and sustained levels of NTP measured in rat liver following intravenous and oral administration.

5-Benzothiazole substituted pyrimidine derivatives as HCV replication (replicase) inhibitors

Based on a previously identified HCV replication (replicase) inhibitor 1, SAR efforts were conducted around the pyrimidine core to improve the potency and pharmacokinetic profile of the inhibitors. A benzothiazole moiety was found to be the optimal substituent at the pyrimidine 5-position. Due to potential reactivity concern, the 4-chloro residue was replaced by a methyl group with some loss in potency and enhanced rat in vivo profile. Extensive investigations at the C-2 position resulted in identification of compound 16 that demonstrated very good replicon potency, selectivity and rodent plasma/target organ concentration. Inhibitor 16 also demonstrated good plasma levels and oral bioavailability in dogs, while monkey exposure was rather low. Chemistry optimization towards a practical route to install the benzothiazole moiety resulted in an efficient direct C-H arylation protocol.

Insurance status and treatment candidacy of hepatitis C patients: analysis of population-based data from the United States

Successful treatment with antiviral therapy could potentially reduce morbidity and mortality in patients with hepatitis C virus (HCV) infection. However, at the population level, these benefits may be offset by a limited number of patients who have access to antiviral treatment. Using data from the National Health and Nutrition Examination Survey conducted in 2005-2008, we analyzed the health insurance status and treatment candidacy of HCV-positive (HCV+) individuals. A total of 10,582 subjects were examined; of those, 1.16% had detectable HCV RNA and were defined as HCV+. The HCV+ patients were less likely to be insured than HCV-negative individuals (61.2% versus 81.2%; P = 0.004). Among those with health insurance, HCV+ patients were less likely to have private insurance, whereas the coverage by Medicare/Medicaid and other government-sponsored plans was similar to the rest of the population. In multivariate analysis, HCV infection was an independent predictor of being uninsured even after adjustment for demographic disparity of the HCV+ cohort (odds ratio, 0.43; 95% confidence interval, 0.24-0.78). Of all HCV+ patients, 66.7% were eligible for anti-HCV treatment. However, only 54.3% of HCV+ treatment candidates had any type of insurance coverage. Finally, only 36.3% of HCV+ patients were potentially eligible for treatment and had health insurance.

CONCLUSION

A high proportion of HCV+ patients are currently uninsured, and many have publicly funded health insurance. Among those who could be candidates for treatment, the rate of insurance coverage is even lower. These findings can have important implications for health insurance coverage of these patients under the new health care reform legislation in the United States.