GS-9620

GS-9620 is an orally active TLR7 agonist with EC50 of 291 nM. [1]
Toll-like receptor 7 (TLR7) is a pathogen recognition receptor which plays an important role in the detection of, and the innate immune response to, pathogens. TLR7 signaling is predominantly activated by viral single-stranded RNA and is localized within the endolysosomal compartments of plasmacytoid dendritic cells (pDCs) and B lymphocytes in humans and non-human primates. Activation of pDCs plays an important role in the progress of innate response to viral pathogens and are involved in the majority of type I interferon (IFN) production during the acute phase of an infection by viruses. The induction and secretion of endogenous IFNs, including IFN-α and IFN- β, also induce the development of an efficient adaptive immunological response. Interferons induce the transcription of interferon-stimulated genes (ISGs) which generate an antiviral state within cells, as well as induce the production of other cytokines and chemokines which facilitate intercellular communication and cellular trafficking. GS-9620 could activate TLR7 signaling in immune cells to induce clearance of virus infected cells. [1, 2]
GS-9620 selectively induces IFN-α, cytokines and chemokines. The minimum effective concentrations for IFN-α induction were similar in pDCs and in PBMCs from HCV-positive donors. GS-9620 demonstrates an EC50 of 291 nM for human TLR7, which is 30-fold selectivity over TLR8 with EC50 of 9 μM. [1]
GS-9620 was administered to HBV infected chimpanzees for 8 weeks with an interval of 1 week. Consequently, serum concentrations of HBV surface antigen and HBV antigen, and the number of HBV antigen–positive hepatocytes, were decreased as hepatocyte apoptosis increased. In a phase 1 clinical trial to evaluate the safety and tolerability of GS-9620, treatment of GS-9620 results in dose dependent increases in select cytokines, chemokines, and ISGs beginning at 2mg and is safe in a single dose up to 12mg. Increases in percentages of immunocytes, like T cells, B cells and NK cells, expressing CD69 were also noted in subjects receiving GS-9620 treatment. [2, 3]
References:
[1]. Turnas P, Zheng X, Lu B, et al. 1129 Preclinical characterization of GS-9620, a potent and selective oral TLR7 agonist[J]. Journal of Hepatology, 2011, 54: S446-S447.
[2]. Lanford R E, Guerra B, Chavez D, et al. GS-9620, an oral agonist of Toll-like receptor-7, induces prolonged suppression of hepatitis B virus in chronically infected chimpanzees[J]. Gastroenterology, 2013, 144(7): 1508-1517. e10.
[3]. Lopatin U, Wolfgang G, Kimberlin R, et al. 737 A phase-i, randomized, double-blind, placebo-controlled study to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of single escalating oral doses of GS-9620 in healthy subjects[J]. Journal of Hepatology, 2011, 54: S296.

The oral toll-like receptor-7 agonist GS-9620 in patients with chronic hepatitis B virus infection.[Pubmed:25733157]

J Hepatol. 2015 Aug;63(2):320-8.

BACKGROUND & AIMS: GS-9620 is an oral agonist of toll-like receptor 7, a pattern-recognition receptor whose activation results in innate and adaptive immune stimulation. We evaluated the safety, pharmacokinetics, and pharmacodynamics of GS-9620 in patients with chronic hepatitis B. METHODS: In two double-blind, phase 1b trials of identical design, 49 treatment-naive and 51 virologically suppressed patients were randomized 5:1 to receive GS-9620 (at doses of 0.3mg, 1mg, 2mg, 4mg) or placebo as a single dose or as two doses seven days apart. Pharmacodynamic assessment included evaluation of peripheral mRNA expression of interferon-stimulated gene 15 (ISG15), serum interferon gamma-induced protein 10 and serum interferon (IFN)-alpha. RESULTS: Overall, 74% of patients were male and 75% were HBeAg negative at baseline. No subject discontinued treatment due to adverse events. Fifty-eight percent experienced 1 adverse event, all of which were mild to moderate in severity. The most common adverse event was headache. No clinically significant changes in HBsAg or HBV DNA levels were observed. Overall, a transient dose-dependent induction of peripheral ISG15 gene expression was observed peaking within 48 hours of dosing followed by return to baseline levels within seven days. Higher GS-9620 dose, HBeAg positive status, and low HBsAg level at baseline were independently associated with greater probability of ISG15 response. Most patients (88%) did not show detectable levels of serum IFN-alpha at any time point. CONCLUSIONS: Oral GS-9620 was safe, well tolerated, and associated with induction of peripheral ISG15 production in the absence of significant systemic IFN-alpha levels or related symptoms.

TLR7 Agonist GS-9620 Is a Potent Inhibitor of Acute HIV-1 Infection in Human Peripheral Blood Mononuclear Cells.[Pubmed:27799218]

Antimicrob Agents Chemother. 2016 Dec 27;61(1). pii: AAC.01369-16.

GS-9620 is a potent and selective oral Toll-like receptor 7 (TLR7) agonist that directly activates plasmacytoid dendritic cells (pDCs). GS-9620 suppressed hepatitis B virus (HBV) in animal models of chronic infection and transiently activated HIV expression ex vivo in latently infected peripheral blood mononuclear cells (PBMCs) from virally suppressed patients. Currently, GS-9620 is under clinical evaluation for treating chronic HBV infection and for reducing latent reservoirs in virally suppressed HIV-infected patients. Here, we investigated the in vitro anti-HIV-1 activity of GS-9620. GS-9620 potently inhibited viral replication in PBMCs, particularly when it was added 24 to 48 h prior to HIV infection (50% effective concentration = 27 nM). Depletion of pDCs but not other immune cell subsets from PBMC cultures suppressed GS-9620 antiviral activity. Although GS-9620 was inactive against HIV in purified CD4(+) T cells and macrophages, HIV replication was potently inhibited by conditioned medium derived from GS-9620-treated pDC cultures when added to CD4(+) T cells prior to infection. This suggests that GS-9620-mediated stimulation of PBMCs induced the production of a soluble factor(s) inhibiting HIV replication in trans GS-9620-treated PBMCs primarily showed increased production of interferon alpha (IFN-alpha), and cotreatment with IFN-alpha-blocking antibodies reversed the HIV-1-inhibitory effect of GS-9620. Additional studies demonstrated that GS-9620 inhibited a postentry event in HIV replication at a step coincident with or prior to reverse transcription. The simultaneous activation of HIV-1 expression and inhibition of HIV-1 replication are important considerations for the clinical evaluation of GS-9620 since these antiviral effects may help restrict potential local HIV spread upon in vivo latency reversal.

Toll-Like Receptor 7 Agonist GS-9620 Induces HIV Expression and HIV-Specific Immunity in Cells from HIV-Infected Individuals on Suppressive Antiretroviral Therapy.[Pubmed:28179531]

J Virol. 2017 Mar 29;91(8). pii: JVI.02166-16.

Antiretroviral therapy can suppress HIV replication to undetectable levels but does not eliminate latent HIV, thus necessitating lifelong therapy. Recent efforts to target this persistent reservoir have focused on inducing the expression of latent HIV so that infected cells may be recognized and eliminated by the immune system. Toll-like receptor (TLR) activation stimulates antiviral immunity and has been shown to induce HIV from latently infected cells. Activation of TLR7 leads to the production of several stimulatory cytokines, including type I interferons (IFNs). In this study, we show that the selective TLR7 agonist GS-9620 induced HIV in peripheral blood mononuclear cells (PBMCs) from HIV-infected individuals on suppressive antiretroviral therapy. GS-9620 increased extracellular HIV RNA 1.5- to 2-fold through a mechanism that required type I IFN signaling. GS-9620 also activated HIV-specific T cells and enhanced antibody-mediated clearance of HIV-infected cells. Activation by GS-9620 in combination with HIV peptide stimulation increased CD8 T cell degranulation, production of intracellular cytokines, and cytolytic activity. T cell activation was again dependent on type I IFNs produced by plasmacytoid dendritic cells. GS-9620 induced phagocytic cell maturation and improved effector-mediated killing of HIV-infected CD4 T cells by the HIV envelope-specific broadly neutralizing antibody PGT121. Collectively, these data show that GS-9620 can activate HIV production and improve the effector functions that target latently infected cells. GS-9620 may effectively complement orthogonal therapies designed to stimulate antiviral immunity, such as therapeutic vaccines or broadly neutralizing antibodies. Clinical studies are under way to determine if GS-9620 can target HIV reservoirs.IMPORTANCE Though antiretroviral therapies effectively suppress viral replication, they do not eliminate integrated proviral DNA. This stable intermediate of viral infection is persistently maintained in reservoirs of latently infected cells. Consequently, lifelong therapy is required to maintain viral suppression. Ultimately, new therapies that specifically target and eliminate the latent HIV reservoir are needed. Toll-like receptor agonists are potent enhancers of innate antiviral immunity that can also improve the adaptive immune response. Here, we show that a highly selective TLR7 agonist, GS-9620, activated HIV from peripheral blood mononuclear cells isolated from HIV-infected individuals with suppressed infection. GS-9620 also improved immune effector functions that specifically targeted HIV-infected cells. Previously published studies on the compound in other chronic viral infections show that it can effectively induce immune activation at safe and tolerable clinical doses. Together, the results of these studies suggest that GS-9620 may be useful for treating HIV-infected individuals on suppressive antiretroviral therapy.

Molecular Determinants of GS-9620-Dependent TLR7 Activation.[Pubmed:26784926]

PLoS One. 2016 Jan 19;11(1):e0146835.

GS-9620 is an orally administered agonist of Toll-like receptor (TLR)7 currently being evaluated in clinical studies for the treatment of chronic HBV and HIV patients. GS-9620 has shown antiviral efficacy in preclinical models of chronic hepadnavirus infection in woodchuck as well as chimpanzee. However, the molecular determinants of GS-9620-dependent activation of TLR7 are not well defined. The studies presented here elucidate GS-9620 subcellular distribution and characterize its molecular interactions with human TLR7 using structure-guided mutational analysis. Based on our results we present a molecular model of TLR7 bound to GS-9620. We also determine that several coding SNPs had no effect on GS-9620-dependent TLR7 activation. In addition, our studies provide evidence that TLR7 exists in a ligand-independent oligomeric state and that, TLR7 activation by GS-9620 is likely associated with compound-induced conformational changes. Finally, we demonstrate that activation of NF-kappaB and Akt pathways in primary plasmacytoid dendritic cells occur as immediate downstream cellular responses to GS-9620 stimulation. The data presented here further our understanding of the molecular parameters governing TLR7 activation by GS-9620, and more generally by nucleos/tide-related ligands.