The cyclophilin inhibitor SCY-635 suppresses viral replication and induces endogenous interferons in patients with chronic HCV genotype 1 infection.

BACKGROUND & AIMS: SCY-635 is a non-immunosuppressive analog of cyclosporin A that inhibits cyclophilins A and B and hepatitis C virus (HCV) replication in vitro. In a phase 1b multi-dose escalation study, we evaluated the safety, plasma pharmacokinetics, and antiviral activity of 15 days of monotherapy with SCY-635 in adults with chronic genotype 1 HCV infection. METHODS: Twenty adults with chronic HCV genotype 1 were randomized to SCY-635 oral doses of 100, 200, or 300 mg three times daily for 15 days. RESULTS: No dose-limiting clinical or laboratory toxicities were identified. On day 15, the mean decline in plasma viremia was 2.24±1.74 log(10) IU/ml with SCY-635 900 mg/d. Individual antiviral responses correlated with host IL28B genotype. Post hoc analyses indicated treatment with SCY-635 increased plasma protein concentrations of interferon α (IFNα), IFNs λ(1) and λ(3), and 2'5' oligoadenylate synthetase 1 (2'5'OAS-1), with the greatest increases in IL28B CC and CT subjects. Changes in plasma concentrations for all markers were coincident with changes in the plasma concentration of SCY-635. Peaks of IFNs α, λ(1), and λ(3) and 2'5'OAS-1 were observed within 2 h after drug administration. In replicon cells, SCY-635 enhanced secretion of type I and type III IFNs and increased the expression of IFN-stimulated genes (ISG). CONCLUSIONS: These studies establish clinical proof of concept for SCY-635 as a novel antiviral agent and suggest that restoration of the host innate immune response to chronic hepatitis C infection may represent a major mechanism through which cyclophilin inhibitors exert clinical antiviral activity.

SCY-635, a novel nonimmunosuppressive analog of cyclosporine that exhibits potent inhibition of hepatitis C virus RNA replication in vitro.

SCY-635 is a novel nonimmunosuppressive cyclosporine-based analog that exhibits potent suppression of hepatitis C virus (HCV) replication in vitro. SCY-635 inhibited the peptidyl prolyl isomerase activity of cyclophilin A at nanomolar concentrations but showed no detectable inhibition of calcineurin phosphatase activity at concentrations up to 2 microM. Metabolic studies indicated that SCY-635 did not induce the major cytochrome P450 enzymes 1A2, 2B6, and 3A4. SCY-635 was a weak inhibitor and a poor substrate for P-glycoprotein. Functional assays with stimulated Jurkat cells and stimulated human peripheral blood mononuclear cells indicated that SCY-635 is a weaker inhibitor of interleukin-2 secretion than cyclosporine. A series of two-drug combination studies was performed in vitro. SCY-635 exhibited synergistic antiviral activity with alpha interferon 2b and additive antiviral activity with ribavirin. SCY-635 was shown to be orally bioavailable in multiple animal species and produced blood and liver concentrations of parent drug that exceeded the 50% effective dose determined in the bicistronic con1b-derived replicon assay. These results suggest that SCY-635 warrants further investigation as a novel therapeutic agent for the treatment of individuals who are chronically infected with HCV.