Cyclophilins are a family of peptidyl-prolyl isomerases that are implicated in a wide range of diseases including hepatitis C. Our aim was to discover through total synthesis an orally bioavailable, non-immunosuppressive cyclophilin (Cyp) inhibitor with potent anti-hepatitis C virus (HCV) activity that could serve as part of an all oral antiviral combination therapy. An initial lead 2 derived from the sanglifehrin A macrocycle was optimized using structure based design to produce a potent and orally bioavailable inhibitor 3. The macrocycle ring size was reduced by one atom, and an internal hydrogen bond drove improved permeability and drug-like properties. 3 demonstrates potent Cyp inhibition ( K = 5 nM), potent anti-HCV 2a activity (EC = 98 nM), and high oral bioavailability in rat (100%) and dog (55%). The synthetic accessibility and properties of 3 support its potential as an anti-HCV agent and for interrogating the role of Cyp inhibition in a variety of diseases.

GS-9688 (selgantolimod) is an oral selective small molecule agonist of toll-like receptor 8 (TLR8) in clinical development for the treatment of chronic hepatitis B (CHB). In this study, we evaluated the antiviral efficacy of GS-9688 in woodchucks chronically infected with woodchuck hepatitis virus (WHV), a hepadnavirus closely related to hepatitis B virus (HBV). WHV-infected woodchucks received eight weekly oral doses of vehicle, 1 mg/kg GS-9688 or 3 mg/kg GS-9688. Vehicle and 1 mg/kg GS-9688 had no antiviral effect, whereas 3 mg/kg GS-9688 induced a >5 log 10 reduction in serum viral load and reduced WHV surface antigen (WHsAg) levels to below the limit of detection in half of the treated woodchucks. In these animals, the antiviral response was maintained until the end of the study (>5 months after the end of treatment). GS-9688 treatment reduced intrahepatic WHV RNA and DNA levels by >95% in animals in which the antiviral response was sustained after treatment cessation, and these woodchucks also developed detectable anti-WHsAg antibodies. The antiviral efficacy of weekly oral dosing with 3 mg/kg GS-9688 was confirmed in a second woodchuck study. The antiviral response to GS-9688 did not correlate with systemic GS-9688 or cytokine levels but was associated with transient elevation of liver injury biomarkers and enhanced proliferative response of peripheral blood mononuclear cells (PBMC) to WHV peptides. Transcriptomic analysis of liver biopsies taken prior to treatment suggested that T follicular helper cells (T FH) and various other immune cell subsets may play a role in the antiviral response to GS-9688. Conclusion: Finite, short-duration treatment with a clinically relevant dose of GS-9688 is well tolerated and can induce a sustained antiviral response in WHV-infected woodchucks. The identification of a baseline intrahepatic transcriptional signature associated with response to GS-9688 treatment provides insights into the immune mechanisms that mediate this antiviral effect. Approximately 260 million individuals are chronically infected with hepatitis B virus (HBV), and over half a million people are estimated to die each year due to liver diseases associated with chronic hepatitis B (CHB), such as cirrhosis and hepatocellular carcinoma (HCC). Immunological control of CHB ("functional cure") is defined as sustained loss of HBV surface antigen (HBsAg) off treatment, with or without seroconversion to anti-HBs antibody. Several nucleos(t)ide analogs, as well as interferon-alpha (IFN-α), are approved for the treatment of CHB. These therapies reduce viremia and

Toll-like receptor 8 (TLR8) recognizes pathogen-derived single-stranded RNA fragments to trigger innate and adaptive immune responses. Chronic hepatitis B (CHB) is associated with a dysfunctional immune response, and therefore a selective TLR8 agonist may be an effective treatment option. Structure-based optimization of a dual TLR7/8 agonist led to the identification of the selective TLR8 clinical candidate (R)-2-((2-amino-7-fluoropyrido­[3,2-d]­pyrimidin-4-yl)­amino)-2-methylhexan-1-ol (GS-9688, (R)-7). Potent TLR8 agonism (IL-12p40 EC50 = 220 nM) and >100-fold TLR7 selectivity (IFN-α EC50 > 50 μM) was observed in human peripheral blood mononuclear cells (PBMCs). The TLR8-ectodomain:(R)-7 complex confirmed TLR8 binding and a direct ligand interaction with TLR8 residue Asp545. Oral (R)-7 had good absorption and high first pass clearance in preclinical species. A reduction in viral markers was observed in HBV-infected primary human hepatocytes treated with media from PBMCs stimulated with (R)-7, supporting the clinical development of (R)-7 for the treatment of CHB.

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