Sustained efficacy and seroconversion with the Toll-like receptor 7 agonist GS-9620 in the Woodchuck model of chronic hepatitis B.

BACKGROUND & AIMS: New therapies for chronic hepatitis B (CHB) are urgently needed since current treatments rarely lead to cure. We evaluated whether the oral small molecule toll-like receptor (TLR7) agonist GS-9620 could induce durable antiviral efficacy in woodchucks chronically infected with woodchuck hepatitis virus (WHV), a hepadnavirus closely related to human hepatitis B virus (HBV). METHODS: After evaluating the pharmacokinetics, pharmacodynamics and tolerability of oral GS-9620 in uninfected woodchucks, adult woodchucks chronically infected with WHV (n = 7 per group) were dosed with GS-9620 or placebo for 4 or 8 weeks with different treatment schedules. RESULTS: GS-9620 treatment induced rapid, marked and sustained reduction in serum viral DNA (mean maximal 6.2log10 reduction), and hepatic WHV DNA replicative intermediates, WHV cccDNA and WHV RNA, as well as loss of detectable serum WHV surface antigen (WHsAg). GS-9620 treatment also induced a sustained antibody response against WHsAg in a subset of animals. Strikingly, treatment reduced the incidence of hepatocellular carcinoma (HCC) from 71% in the placebo group to 8% in GS-9620-treated woodchucks with sustained viral load reduction. GS-9620 treatment was associated with reversible increases in serum liver enzymes and thrombocytopenia, and induced intrahepatic CD8(+) T cell, NK cell, B cell and interferon response transcriptional signatures. CONCLUSIONS: The data demonstrate that short duration, finite treatment with the oral TLR7 agonist GS-9620 can induce a sustained antiviral response in the woodchuck model of CHB, and support investigation of this compound as a therapeutic approach to attain a functional cure in CHB patients.

Pharmacokinetic and pharmacodynamic properties of GS-9620, a novel Toll-like receptor 7 agonist, demonstrate interferon-stimulated gene induction without detectable serum interferon at low oral doses.

GS-9620 [8-(3-(pyrrolidin-1-ylmethyl)benzyl)-4-amino-2-butoxy-7,8-dihydropteridin-6(5H)-one] is a potent, orally bioavailable small-molecule agonist of Toll-like receptor 7 (TLR7) developed for finite treatment of chronic hepatitis B viral (HBV) infection, with the goal of inducing a liver-targeted antiviral effect without inducing the adverse effects associated with current systemic interferon-α (IFN-α) therapies. We characterized the pharmacodynamic response of GS-9620 in CD-1 mice and cynomolgus monkeys following intravenous or oral administration and showed that GS-9620 induces the production of select chemokines and cytokines, including IFN-α and interferon-stimulated genes (ISGs). It is noteworthy that we also demonstrated that, in animals and healthy human volunteers, oral administration of GS-9620 can induce a type I interferon-dependent antiviral innate immune response, as measured by whole-blood mRNA of the ISGs 2'5'-oligoadenylate synthetase 1 (OAS1) and myxovirus resistance 1 (MX1), without the induction of detectable systemic IFN-α, i.e., a presystemic response. Additionally, presystemic induction of hepatic OAS1 and MX1 mRNA was observed in CD-1 mice in the absence of detectable systemic IFN-α. We propose that the mechanism of this presystemic response is likely its high intestinal absorption, which facilitates localized activation of TLR7, probably in plasmacytoid dendritic cells at the level of gut-associated lymphoid tissue and/or the liver. This localized response is further supported by data that indicate only minimal contributions of systemic immune stimulation to the overall pharmacodynamic response to orally administered GS-9620. These data demonstrate that GS-9620 can induce an antiviral innate immune response without inducing a systemic IFN-α response and thus suggest the therapeutic potential of this approach in the treatment of chronic HBV infection.

GS-9620, an oral agonist of Toll-like receptor-7, induces prolonged suppression of hepatitis B virus in chronically infected chimpanzees.

BACKGROUND & AIMS: Direct-acting antiviral agents suppress hepatitis B virus (HBV) load, but they require life-long use. Stimulation of the innate immune system could increase its ability to control the virus and have long-lasting effects after a finite regimen. We investigated the effects of immune activation with GS-9620--a potent and selective orally active small molecule agonist of Toll-like receptor 7--in chimpanzees with chronic HBV infection. METHODS: GS-9620 was administered to chimpanzees every other day (3 times each week) for 4 weeks at 1 mg/kg and, after a 1-week rest, for 4 weeks at 2 mg/kg. We measured viral load in plasma and liver samples, the pharmacokinetics of GS-9620, and the following pharmacodynamics parameters: interferon-stimulated gene expression, cytokine and chemokine levels, lymphocyte and natural killer cell activation, and viral antigen expression. Clinical pathology parameters were monitored to determine the safety and tolerability of GS-9620. RESULTS: Short-term oral administration of GS-9620 provided long-term suppression of serum and liver HBV DNA. The mean maximum reduction of viral DNA was 2.2 logs, which occurred within 1 week of the end of GS-9620 administration; reductions of >1 log persisted for months. Serum levels of HBV surface antigen and HBV e antigen, and numbers of HBV antigen-positive hepatocytes, were reduced as hepatocyte apoptosis increased. GS-9620 administration induced production of interferon-α and other cytokines and chemokines, and activated interferon-stimulated genes, natural killer cells, and lymphocyte subsets. CONCLUSIONS: The small molecule GS-9620 activates Toll-like receptor 7 signaling in immune cells of chimpanzees to induce clearance of HBV-infected cells. This reagent might be developed for treatment of patients with chronic HBV infection.

Assessment of two external telemetry systems (PhysioJacket and JET) in beagle dogs with telemetry implants.

INTRODUCTION: Regulatory guidelines recommend the use of conscious, unrestrained animals for comprehensive cardiovascular safety assessment of a new therapeutic agent. Cardiovascular safety pharmacology studies normally use internal telemetry (surgical implants) in free-moving animals to monitor key ECG endpoints, like the QTc interval, but this technical approach is highly resource intensive. In toxicology studies, ECG recording is also typically performed under chemical or physical restraint, which has a number of disadvantages, e.g., anesthesia confounds, handling stress and limited data collection. External telemetry for ECG recording has the potential to overcome many of these restraint limitations, with the benefit of being a surgically non-invasive method. To evaluate this method, we used two jacket systems: Data Sciences International (DSI) JET and Integrated Telemetry Systems (ITS) PhysioJacket in implanted beagle dogs. METHODS: Heart rate and cardiac intervals were monitored continuously for 22-24 h following oral administration of vehicle (water) or 1 mg/kg E-4031. Data obtained from each jacket system was compared with implant-derived data in the same animal. RESULTS: Significant increases in QT/QTcV (25-30 ms) were noted following treatment with 1 mg/kg E-4031 in both external jacket systems and with implanted telemetry. Throughout the recording periods, the normal variations in heart rate and ECG intervals observed in conscious dogs as detected with the jacket systems, mirrored the changes observed via implant telemetry. DISCUSSION: The overall findings from this study support the use of external telemetry technology as a viable alternative to implants. The data demonstrated that jackets were sufficiently sensitive to detect QT/QTcV changes following E-4031 administration, that were comparable to those derived from implants. As such, this method is an invaluable tool for obtaining high quality ECG data from repeat-dose toxicology studies.