Safety, pharmacokinetics and pharmacodynamics of the oral Toll-like receptor 7 agonist GS-9620 in treatment-naive patients with chronic hepatitis C.

Background: GS-9620 is a potent oral agonist of toll-like receptor 7, a key modulator of the innate immune response. In healthy volunteers, low doses of GS-9620 (2, 4 and 6 mg) induced significant expression of peripheral interferon-stimulated-gene (ISG) mRNA in the absence of detectable serum interferon-alpha and systemic adverse events (AEs). We evaluated the safety, pharmacokinetics and pharmacodynamics of GS-9620 in treatment-naive patients chronically infected with HCV genotype 1. Methods: In this double-blind, placebo-controlled study, 51 patients were randomized 5:1 (active: placebo) to receive either a single dose or two once-weekly doses of GS-9620 at four dose levels (0.3, 1, 2 and 4 mg) or placebo. Pharmacodynamic assessments included peripheral ISG15 mRNA expression, serum interferon-alpha and interferon-gamma-inducible protein (IP)-10 levels and HCV RNA quantification. Results: GS-9620 was well-tolerated at all doses. Most AEs were mild or moderate in severity. GS-9620 exhibited dose-linear pharmacokinetics with a median half-life in plasma of 18 h. Transient, dose-dependent ISG15 induction was observed at 1, 2 and 4 mg, with peak mean fold change within 48 h followed by a decline to baseline levels within 7 days of dosing. Serum interferon-alpha induction post-baseline was detected in 16.7% (8/48) of patients. No clinically significant reductions in HCV RNA were observed. Conclusions: GS-9620 was safe, well-tolerated and biologically active in patients with HCV infection. Induction of ISG15 occurred in the absence of detectable serum interferon-alpha or systemic AEs in most patients, supporting a pre-systemic mechanism of action.