Karl Kossen

Antifibrotic activities of pirfenidone in animal models

Pirfenidone is an orally active small molecule that has recently been evaluated in large clinical trials for the treatment of idiopathic pulmonary fibrosis, a fatal disease in which the uncontrolled deposition of extracellular matrix leads to progressive loss of lung function. This review describes the activity of pirfenidone in several well-characterised animal models of fibrosis in the lung, liver, heart and kidney. In these studies, treatment-related reductions in fibrosis are associated with modulation of cytokines and growth factors, with the most commonly reported effect being reduction of transforming growth factor-&bgr;. The consistent antifibrotic activity of pirfenidone in a broad array of animal models provides a strong preclinical rationale for the clinical characterisation of pirfenidone in pulmonary fibrosis and, potentially, other conditions with a significant fibrotic component.

Preclinical Characteristics of the Hepatitis C Virus NS3/4A Protease Inhibitor ITMN-191 (R7227)

ABSTRACT Future treatments for chronic hepatitis C virus (HCV) infection are likely to include agents that target viral components directly. Here, the preclinical characteristics of ITMN-191, a peptidomimetic inhibitor of the NS3/4A protease of HCV, are described. ITMN-191 inhibited a reference genotype 1 NS3/4A protein in a time-dependent fashion, a hallmark of an inhibitor with a two-step binding mechanism and a low dissociation rate. Under preequilibrium conditions, 290 pM ITMN-191 half-maximally inhibited the reference NS3/4A protease, but a 35,000-fold-higher concentration did not appreciably inhibit a panel of 79 proteases, ion channels, transporters, and cell surface receptors. Subnanomolar biochemical potency was maintained against NS3/4A derived from HCV genotypes 4, 5, and 6, while single-digit nanomolar potency was observed against NS3/4A from genotypes 2b and 3a. Dilution of a preformed enzyme inhibitor complex indicated ITMN-191 remained bound to and inhibited NS3/4A for more than 5 h after its initial association. In cell-based potency assays, half-maximal reduction of genotype 1b HCV replicon RNA was afforded by 1.8 nM; 45 nM eliminated the HCV replicon from cells. Peginterferon alfa-2a displayed a significant degree of antiviral synergy with ITMN-191 and reduced the concentration of ITMN-191 required for HCV replicon elimination. A 30-mg/kg of body weight oral dose administered to rats or monkeys yielded liver concentrations 12 h after dosing that exceeded the ITMN-191 concentration required to eliminate replicon RNA from cells. These preclinical characteristics compare favorably to those of other inhibitors of NS3/4A in clinical development and therefore support the clinical investigation of ITMN-191 for the treatment of chronic hepatitis C.

The Carboxy-terminal Domain of the DExDH Protein YxiN is Sufficient to Confer Specificity for 23 S rRNA

DE x DH proteins are believed to modulate the structures of RNAs and ribonucleoprotein complexes by disrupting RNA helices and RNA-protein interactions. All DE x DH proteins contain a two-domain catalytic core that enables their RNA-dependent ATPase and RNA helicase activities. The catalytic core may be flanked by ancillary domains that are proposed to confer substrate specificity and facilitate the unique functions of individual proteins. The Escherichia coli DE x DH protein DbpA and its Bacillus subtilis ortholog YxiN have similar 75aa carboxy-terminal domains, and both proteins are specifically targeted to 23S rRNA. Here we demonstrate that the carboxy-terminal domain of YxiN is sufficient to confer RNA specificity by characterizing a chimera in which this domain is appended to the core domains of E.coli SrmB, a DE x DH protein with no apparent substrate specificity. Both the RNA-dependent ATPase and RNA helicase activities of the chimera are specifically activated by 23S rRNA and abolished by sequence changes within hairpin 92, a critical recognition element for Y x iN. These data support a model in which the carboxy-terminal domain binds hairpin 92 to target the protein to 23S rRNA.

Inhibition and Binding Kinetics of the Hepatitis C Virus NS3 Protease Inhibitor ITMN-191 Reveals Tight Binding and Slow Dissociative Behavior

The protease activity of hepatitis C virus nonstructural protein 3 (NS3) is essential for viral replication. ITMN-191, a macrocyclic inhibitor of the NS3 protease active site, promotes rapid, multilog viral load reductions in chronic HCV patients. Here, ITMN-191 is shown to be a potent inhibitor of NS3 with a two-step binding mechanism. Progress curves are consistent with the formation of an initial collision complex (EI) that isomerizes to a highly stable complex (EI*) from which ITMN-191 dissociates very slowly. K(i), the dissociation constant of EI, is 100 nM, and the rate constant for conversion of EI to EI* is 6.2 x 10(-2) s(-1). Binding experiments using protein fluorescence confirm this isomerization rate. From progress curve analysis, the rate constant for dissociation of ITMN-191 from the EI* complex is 3.8 x 10(-5) s(-1) with a calculated complex half-life of approximately 5 h and a true biochemical potency (K(i)*) of approximately 62 pM. Surface plasmon resonance studies and assessment of enzyme reactivation following dilution of the EI* complex confirm slow dissociation and suggest that the half-life may be considerably longer. Abrogation of the tight binding and slow dissociative properties of ITMN-191 is observed with proteases that carry the R155K or D168A substitution, each of which is likely in drug resistant mutants. Slow dissociation is not observed with closely related macrocyclic inhibitors of NS3, suggesting that members of this class may display distinct binding kinetics.

Virologic Escape during Danoprevir (ITMN-191/RG7227) Monotherapy Is Hepatitis C Virus Subtype Dependent and Associated with R155K Substitution

ABSTRACT Danoprevir is a hepatitis C virus (HCV) NS3/4A protease inhibitor that promotes multi-log10 reductions in HCV RNA when administered as a 14-day monotherapy to patients with genotype 1 chronic HCV. Of these patients, 14/37 experienced a continuous decline in HCV RNA, 13/37 a plateau, and 10/37 a rebound. The rebound and continuous-decline groups experienced similar median declines in HCV RNA through day 7, but their results diverged notably at day 14. Plateau group patients experienced a lesser, but sustained, median HCV RNA decline. Baseline danoprevir susceptibility was similar across response groups but was reduced significantly at day 14 in the rebound group. Viral rebound in genotype 1b was uncommon (found in 2/23 patients). Population-based sequence analysis of NS3 and NS4A identified treatment-emergent substitutions at four amino acid positions in the protease domain of NS3 (positions 71, 155, 168, and 170), but only two (155 and 168) were in close proximity to the danoprevir binding site and carried substitutions that impacted danoprevir potency. R155K was the predominant route to reduced danoprevir susceptibility and was observed in virus isolated from all 10 rebound, 2/13 plateau, and 1/14 continuous-decline patients. Virus in one rebound patient additionally carried partial R155Q and D168E substitutions. Treatment-emergent substitutions in plateau patients were less frequently observed and more variable. Single-rebound patients carried virus with R155Q, D168V, or D168T. Clonal sequence analysis and drug susceptibility testing indicated that only a single patient displayed multiple resistance pathways. These data indicate the ascendant importance of R155K for viral escape during danoprevir treatment and may have implications for the clinical use of this agent.

HCV NS5B polymerase inhibitors 1: Synthesis and in vitro activity of 2-(1,1-dioxo-2H-[1,2,4]benzothiadiazin-3-yl)-1-hydroxynaphthalene derivatives

2-(1,1-Dioxo-2H-[1,2,4]benzothiadiazin-3-yl)-1-hydroxynaphthalene derivatives as potential anti-HCV drugs targeting NS5B polymerase have been investigated. Their synthesis, HCV NS5B polymerase inhibition and replicon activity are discussed.

HCV NS5B polymerase inhibitors 3: Synthesis and in vitro activity of 3-(1,1-dioxo-2H-[1,2,4]benzothiadiazin-3-yl)-4-hydroxy-2H-quinolizin-2-one derivatives

3-(1,1-Dioxo-2H-[1,2,4]benzothiadiazin-3-yl)-4-hydroxy-2H-quinolizin-2-one derivatives as potential anti-HCV drugs targeting NS5B polymerase have been investigated. Their synthesis, HCV NS5B polymerase inhibition, and replicon activity are discussed.

Danoprevir Monotherapy Decreases Inflammatory Markers in Patients with Chronic Hepatitis C Virus Infection

ABSTRACT Danoprevir is a potent and selective direct-acting antiviral agent that targets the protease activity of hepatitis C virus (HCV) NS3/4A. This agent results in a significant rapid decline in HCV RNA levels when it is used in monotherapy. The present study evaluated whether plasma concentrations of the inflammatory markers gamma interferon-inducible protein 10 (IP-10) and neopterin or the interferon-stimulated gene product 2′-5′-oligoadenylate synthetase (OAS-1) were correlated with the plasma HCV RNA concentration before or during 14-day danoprevir monotherapy. In contrast to pegylated interferon and ribavirin treatment, a higher baseline IP-10 concentration was positively correlated with a greater first-phase HCV RNA decline upon danoprevir administration. Changes in the IP-10 plasma concentration during danoprevir administration were also associated with categorical changes in HCV RNA concentration at days 7 and 14. The neopterin concentration appeared to be moderately decreased during danoprevir administration, although these changes were not statistically significant. However, changes in neopterin concentration showed a statistically significant correlation with changes in IP-10 concentration. Considerable variation in the OAS-1 concentration was observed before and during treatment, including in patients treated with placebo and/or patients with minimal virologic response. Overall, these results suggest that effective treatment with a direct-acting antiviral agent may reduce hepatic inflammation and that first-phase HCV RNA decline during treatment with an NS3/4A protease inhibitor is more robust in patients with high baseline IP-10 concentrations.

Optimization of the multiple enzymatic activities of the hepatitis C virus NS3 protein

The hepatitis C virus (HCV) nonstructural protein 3 (NS3) is known to possess multiple enzymatic activities. In addition to its well-characterized protease activity, HCV NS3 also has ATP hydrolase (ATPase) and nucleic acid unwinding (helicase) activities. We systematically studied the effect of common reagents on all three enzymatic activities with a view to improving assay sensitivity for compound screening and profiling. Inclusion of the detergent lauryl dimethylamine oxide (LDAO) improves protease and helicase activities significantly, allowing robust assays at much lower NS3 concentrations. These conditions enable a particularly sensitive protease assay that uses picomolar concentrations of NS3.

Preclinical Characterization and Human Microdose Pharmacokinetics of ITMN-8187, a Nonmacrocyclic Inhibitor of the Hepatitis C Virus NS3 Protease.

Abstract The current paradigm for the treatment of chronic hepatitis C virus (HCV) infection involves combinations of agents that act directly on steps of the HCV life cycle. Here we report the preclinical characteristics of ITMN-8187, a nonmacrocyclic inhibitor of the NS3/4A HCV protease. X-ray crystallographic studies of ITMN-8187 and simeprevir binding to NS3/4A protease demonstrated good agreement between structures. Low nanomolar biochemical potency was maintained against NS3/4A derived from HCV genotypes 1, 2b, 4, 5, and 6. In cell-based potency assays, half-maximal reduction of genotype 1a and 1b HCV replicon RNA was afforded by 11 and 4 nM doses of ITMN-8187, respectively. Combinations of ITMN-8187 with other directly acting antiviral agents in vitro displayed additive antiviral efficacy. A 30-mg/kg of body weight dose of ITMN-8187 administered for 4 days yielded significant viral load reductions through day 5 in a chimeric mouse model of HCV. A 3-mg/kg oral dose administered to rats, dogs, or monkeys yielded concentrations in plasma 16 h after dosing that exceeded the half-maximal effective concentration of ITMN-8187. Human microdose pharmacokinetics showed low intersubject variability and prolonged oral absorption with first-order elimination kinetics compatible with once-daily dosing. These preclinical characteristics compare favorably with those of other NS3/4A inhibitors approved for the treatment of chronic HCV infection.