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.

Keywords: antiviral agents; hepatitis C virus; protease inhibitors.

FIG 1

Chemical structures of ITMN-8187 and simeprevir. The asterisk denotes the location of the ¹⁴C label in the radiolabeled ITMN-8187 used in the microdose study.

FIG 2

Crystal structure of ITMN-8187 bound to WT NS3/4A protease. Overlay with simeprevir (in white).

FIG 3

Replicon synergy studies support additive behavior of ITMN-8187 in combination with NS5A (daclatasvir) and NS5B (ITMN-8244) inhibitors.

FIG 4

ITMN-8187 viral load reduction in HCV (genotypes 1a and 1b)-infected chimeric mice. HCV genotype 1a demonstrated a 3.3-log₁₀ copies/ml reduction in HCV RNA (initial titer, 1.9 × 10⁸ copies/ml). Those infected with HCV genotype 1b demonstrated a 2.0-log₁₀ copies/ml reduction in HCV RNA and were below the lower limit of detection of the assay by day 2 (initial titer, 3.9 × 10⁶ copies/ml).

FIG 5

Plasma pharmacokinetics of ITMN-8187 after a 3-mg/kg oral dose in rats, dogs, and monkeys compared with simeprevir PK after oral administration in monkeys. The dashed line represents the WT 1b replicon EC₅₀ of 4 nM.

FIG 6

Human microdose pharmacokinetics. (A) Mean oral and i.v. curves for parent drug. (B) Comparison of total [¹⁴C] to parent pharmacokinetics of ITMN-8187.