Hepatitis B Virus Treatment: 2017 Newcomers

Transcription

1 Clinical Hepatology Update Clinical Hepatology Update Hepatitis B Virus Treatment: 2017 Newcomers Sang Hoon Ahn Department of Internal Medicine, Institute of Gastroenterology, Yonsei Liver Center Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Korea Introduction Chronic hepatitis B virus (HBV) infection is an important public health problem and a leading cause of liver cirrhosis, end-stage liver disease, and hepatocellular carcinoma (HCC) with substantial disease burden. 30% of liver cirrhosis and roughly 53% of HCC is attributed to chronic hepatitis B, especially in Asia and the Western Pacific region.[1] Despite effective HBV vaccine has been recommended from the 1992s, treatments for chronic hepatitis B is still crucial because of low vaccination coverage in many countries and low percentage of individuals with no or low development of antibody. To date, the main goal in HBV therapy has been suppression of HBV replication, because it is associated with reduced rates of liver complications, improving quality of life, and greater long-term survival [2]. During the last three decades, several antiviral drugs have been developed. Two main classes of antiviral drugs for chronic hepatitis B is currently available; two formulation of interferon (IFN)-conventional and pegylated IFN as immunomodulatory agents, and nucleos(t)ide analogues (NAs) including lamivudine, telbivudine, adefovir, entecavir and tenofovir. IFN has multiple mechanisms of action including antiviral, antiproliferative and immunomodulatory effects, and better chances for off-treatment virological response and loss of HBV surface antigen (HBsAg). However, its use is limited by side effects such as flu-like symptoms and exacerbation of underlying immune conditions, and is contraindicated in advanced cirrhosis cases. The effectiveness and safety of NAs are supported by recent systematic review and meta-analyses, suppress viral replication by inhibiting the reverse transcriptase activity of HBV polymerase, and thus prevent viral replication. But NAs do not directly target covalently closed circular DNA (cccdna), which is the template for all viral RNAs, so HBV is often reactivated after discontinuing NAs. Despite many years of antiviral treatment, the low percentage of treated patients achieve HBsAg loss (only 5-8% in 3 years) [3, 4], and lifelong treatment is often needed to prevent viral rebound. Various clinical trials have been conducted on agents that terminate the HBV life cycle in hepatocytes, including inhibitors of HBV-DNA polymerase, virus entry, core assembly, and secretion of hepatitis B surface antigen (HBsAg). [Figure 1][5] Newly antiviral agents are currently in development, including immunomodulatory agents enhancing host immunity and direct virus targeting agents blocking each step of HBV life cycles such as entry inhibitor, inhibitors of nucleocapsid assemblies, new polymerase inhibitors, RNA interference agents, inhibitors of HBsAg release, and agents that target cccdna. These new agents are arranged in [Table 1] and [Table 2]. This review highlights newly investigated therapeutic compounds and approaches in clinical trials and selected preclinical researches

2 The Liver Week 2017 Figure 1. Hepatitis B virus life cycle along with inhibitors targeting the various stages of the hepatitis B virus lifecycle (Adapted from Grimm et al 2011 [5]) Following attachment of virus to the receptors, cell entry and release of nucleocapsid, nuclear import of virus to nucleus, transcription and translation leads to the synthesis of covalently closed circular DNA (cccdna), envelopment of nucleocapsid within endoplasmic reticulum, formation of multivesicular bodies and finally secretion of subviral and virion particles. Moreover red bar lines shows the inhibitors targeting various stages of the virus life cycle such as: entry inhibitors, inhibition of cccdna formation, and inhibition of assembly, polymerase inhibition and genetic editing and immunomodulation targeting the cell surface receptors. ISG: Immune serum globulin. Table 1. DIRECT ACTING ANTIVIRALS: Targets the virus and interferes in the HBV replication process Entry Inhibitors: Interferes with HBV getting into liver cells Myrcludex B Entry inhibitor Phase 2 cccdna inhibitors: cccdna degredation, silencing, and elimination ZFNs Block transcription of cccdna, inhibit production, repression of Preclinical TALENs cccdna transcriptional activity, and gene editing to mutate Preclinical CRISPR-Cas9 cccdna Preclinical CCC-0975 directly block the conversion of rcdna to cccdna Preclinical CCC-0346 directly block the conversion of rcdna to cccdna Preclinical LTβR agonist upregulates APOBEC3B Preclinical Capsid Inhibitors: Interferes with the viral DNA protein shield Morphothiadin (GLS4) Capsid inhibitor Phase 2 NVR Capsid inhibitor Phase 2 AIC 649 Capsid inhibitor Phase 1 JNJ Capsid Inhibitor Phase 1 ABI-H0731 Core Protein Allosteric Modifiers (CpAMs) Phase 1 AB-423 Core Protein Allosteric Modifiers (CpAMs) Phase June 22-24, 2017 Grand Hyatt Incheon, Korea

3 Clinical Hepatology Update HBsAg Inhibitors: Interferes with production of HBV surface antigen (sag) Rep 2139 sag inhibitor Phase 2 Rep 2165 sag inhibitor Phase 2 RO (RG7834) sag inhibitor Phase 1 GC1102 Recombinant Hepatitis B Human Immunoglobulin Phase 1 Antisense Molecules: Binds to the viral mrna to prevent it from turning into viral protein IONIS-HBVRx (GSK ) Viral protein inhibitor Phase 1 IONIS-HBVLRx (GSK ) Viral protein inhibitor Phase 1 Silencing RNA s (sirnas): Interferes and destroys viral RNA ARB-1467 RNAi gene silencer (1.0) Phase 2 ARB-1740 RNAi gene silencer (2.0) Phase 2 ALN-HBV RNAi gene silencer Preclinical Hepbarna (BB-HB-331) RNAi gene silencer Preclinical Lunar-HBV RNAi gene silencer Preclinical ARO-HBV RNAi gene silencer Preclinical TDF Pro Drugs: A modified tenofovir drug that can get into liver cells more easily Vemlidy Approved in USA, Prodrug of tenofovir (TAF or tenofovir alafenamide) Nov Besifovir Acyclic nucleotide phosphonate Pending Approval only in Korea TXL (CMX 157) Prodrug of tenofovir Phase 2 AGC-2009 Prodrug of tenofovir Phase 1 MIV-210 Prodrug of tenofovir Phase 1 Table 2. INDIRECT ACTING ANTIVIRALS: Targets the human immune system to attack the HBV virus Innate Immune Defense Pathway: Compounds that activate the innate immune system GS 9620 TLR-7 agonist Phase 2 RO (RG7795, ANA773) TLR-7 agonist Phase 2 SB9200 RIG -1 and NOD2 agonist Phase 2 Therapeutic Vaccines: Vaccine technology used to stimulate the immune system as a treatment INO-1800 Therapeutic vaccine Phase 1 HB-110 Therapeutic vaccine Phase 1 TG1050 Therapeutic vaccine Phase 1 HepTcell Therapeutic vaccine Phase 1 TomegaVax HBV Therapeutic vaccine Preclinical Entry inhibitor The hepatocyte-specific cellular sodium-taurocholate co-transporting polypeptide (NTCP) has been identified as a functional receptor for HBV and hepatitis D virus. Myrcludex B is a synthetic lipopepetide that competes with the viral envelope pre-s1 motif for NTCP binding thereby blocking HBV entry. [6] This prevents the infection of naïve hepatocytes, so could be used to prevent post-exposure infection, such as after liver transplantation in recipients with HBV, and neonates of HBV positive mothers. Entry inhibitor could be less effective in pre-existing infection, but could increase clearance of previously infected hepatocytes by providing proper time window when combinated with NAs, interferon, or other innovative therapies. Myrcludex B showed >1log IU/mL reduction in serum HBV DNA among 75% patients in phase 2a clinical study, but there was no noteworthy change in HBsAg concentrations. Higher dosage was associated with a clinically insignificant hyperbilirubinemia. [7] 293

4 The Liver Week 2017 cccdna degredation, silencing, and elimination After binding NTCP receptor, HBV enters hepatocytes through two ways: fusion with the viral envelope at the plasma membrane, or endocytosis, uncoating, and delivery of nucleocapsids to the nucleus where relaxed circular DNA (rcdna) is converted to the highly stable cccdna. This cccdna acts as a template for multiple viral mrna transcripts synthesized via host RNA polymerase II. Nucleos(t)ide analogue-based treatments can block the replication and formation of new cccdna, but they have negligible effect on existing cccdna which is key to viral persistence and reactivation after cessation of therapy. Engineered site-specific nucleases can inhibit HBV replication, and three most commonly used engineered DNA-binding proteins targeting cccdna are below: Zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and the RNA-guided clustered regulatory interspaced short palindromic repeats (CRISPR) and CRISPR associated (Cas) protein endonucleases. These DNA-binding proteins induce site-specific cleavage of DNA by transcriptional block, repression of transcriptional activity, or gene editing to mutate cccdna.[8] In addition, two structurally related disubstituted sulphonamides, called CCC-0975 and CCC-0346, were recently identified through a cell-based screening strategy. These compounds directly block the conversion of rcdna to cccdna, result in inhibition of cccdna formation.[9] These preclinical materials have shown effective inhibition of HBV DNA replication in vitro studies. Other recent studies showed that activation of apolipoprotein B mrna editing enzyme, catalytic polypeptide-like proteins (APOBEC3A and APOBEC3B) in HBV infected cells interacts with the HBV core and translocate to the nucleus, inducing noncytotoxic cccdna degradation. As immune modulators, interferon alpha upregulates APOBEC3A, and lymphotoxin-β receptor (LTβR) agonist upregulates APOBEC3B.[10] In-vivo and in-vitro stimulation of LTβR led to reduction in HBV DNA and cccdna concentration with persistent effects after cessation of therapy and no hepatotoxic effects. But long-term data are needed for LTβR agonists. RNA interference and gene silencing, targeting expression of HBV genes Small interfering RNAs (RNAi) can disturb gene expression by binding and inactivating host or viral mrna. HBV-specific small interfering RNA showed to reduce expression of viral proteins in vitro, and ARC-520, a liver-tropic cholesterol-conjugated small interfering RNA, showed effective knockdown of HBV RNA, proteins, and HBV DNA levels in phase 2a randomized controlled study. [11] Gene silencing can be achieved by introducing a short antisense oligonucleotide complementary to an RNA target, that has shown a dose-dependent reduction of HBsAg concentrations in vivo, and further trials in heterogenous populations with durable endpoints are ongoing. Nucleocapsid assembly inhibitors The HBV core proteins are translated from the pregenomic RNA and self-assemble into nucleocapsids, encapsidating pregenomic RNA and HBV polymerase, and allowing genome replication to proceed. Thus, HBV replication and cccdna replenishment can be prevented by inhibition of nucleocapsid assembly, deestablishing the nucleocapsid and blocking RNA packaging to produce empty capsids without genetic information. Phenylpropenamide derivatives (AT-61 and AT130), and sulfamoylbenzamide derivatives prevent the encapsidation of pregenomic RNA into nucleocapsid, and heteroaryldihydropyrimidines (Bay , GLS4) may induce inappropriate assembly. NVR is another assembly inhibitor that has shown reduction of HBV viral load by alone or combination with pegylated interferons.[12] These occur prior to viral DNA synthesis, so effective against both wild-type and nucleos(t)ide analogues-resistant HBV. Bay and GLS4 are in the phase 1 for clinical trials, and NVR is in the phase 2a. 294 June 22-24, 2017 Grand Hyatt Incheon, Korea

5 Clinical Hepatology Update HBsAg release inhibitor HBsAg was seen to suppress cytokine production and induce T-cell tolerance and exhaustion, resulting in suppression of host immune responses. Thus, control of HBsAg secretion can be a strategy to restore HBV-specific T-cell-mediated immune control. REP 2139-ca is an amphipathic DNA polymer, blocks HBsAg secretion from infected hepatocytes in patients with chronic HBV infection, which resulted in the recovery of innate immunity and cytotoxic T cell response in a phase I clinical study.[13] Polymerase inhibitors As described, development of drug resistance is the major limitation of long-term NAs therapy, and new potent polymerase inhibitors are being developed to dodge emergence of drug resistance. Tenofovir alafenamide (TAF, or known as GS-7340) is second-generation prodrug of tenofovir. It is designed to resist rapid metabolism in the plasma, and efficiently delivered to infected hepatocytes and metabolized to active form (tenofovir diphosphate). TAF showed higher intracellular active metabolite form levels as well as lower plasma tenofovir concentrations, and has no renal transporter-dependent cytotoxicity (organic anion transporters, OAT1 and OAT3) which may reduce the risk of renal function impairment, comparing with TDF. Recent randomized phase 3 studies showed that virological response of TAF using group at week 48 was non-inferior to TDF, and TAF treatment had significant improvements in both renal and bone safety than TDF, [14] and approved in November 2016 in USA as Vemlidy. Besifovir is an acyclic nucleotide phosphonate with rapid intracellular phosphorylation to inhibit HBV replication. Its efficacy of viral suppression and HBeAg seroconversion was no different to entecavir therapy in a multicenter randomized trial. [15] Other compounds in phase 2 clinical trials include CMX-157, AGX-1009, and MIV-210 (lagociclovir valactate) which have shown favorable reduction in HBV DNA and cccdna concentrations in phase 1 studies. Immunomodulatory agents Immunomodulators can change the host response to HBV, improving immune control or leading to viral eradication. Novel approaches to host targeting agents include immune-enhancement with the toll-like receptor (TLR) agonists, therapeutic vaccines, cytokines, and immune checkpoint inhibitors such as PD-1 blockers (as known with remarkable tumor responses in various oncologic clinical studies). TLRs are important pathogen recognition receptors that stimulate innate and adaptive immune responses. Several studies reported that HBV downregulates TLR in mice modules resulting in suppression of anti-viral activity, and the expression of TLR in hepatocytes reduces HBV viral products. GS-9620 was developed as a selective oral TLR7 agonist that could induce peripheral interferon-stimulated gene 15 production and suppression of HBV DNA in chimpanzee modules and recent phase 1b study, but unfortunately could not show the superior efficacy in recent phase 2 study. Other agents including RG7795 (ANA773) as a TLR7 agonist and ARB-1598 as a TLR9 agonist are ongoing in phase 1 studies. Therapeutic vaccines theologically can activate the adaptive immune system to neutralize HBV with upregulation of CD4 and CD8 T-cell responses, and provide an effective immune response. GS-4774 and ABX-203 was developed as recombinant therapeutic vaccines with HBV antigenicity that stimulate HBV-specific CD8(+) T-cell, but showed little efficacy in people volunteered or incomplete primary endpoint in each phase 2 and phase 2b/3 studies. NCT , the combination of therapeutic vaccine HB-110 (known novel HBV DNA vaccine that showed increased in vivo immunological potency) and entecavir, complete phase 1 trial and is enrolling patients in phase 2 trials. Other adenovirus-based therapeutic vaccine such as TG1050 is also in phase 1 trials. Induction of immune checkpoint inhibitors such as programmed death-1 (PD-1) and cytotoxic T-lymphocyte angigen 295

6 The Liver Week (CTLA-4) can be increased in chronic HBeAg-positive patients with high viral load. [16] PD-1 blockade can increase CD8(+) T cell proliferation and enhanced HBcAg-specific interferon-gamma production in intrahepatic lymphocytes in vitro and in vivo, leading to increased HBV-specific T-cell cytotoxicity and antiviral immunity. If possible, development of more selective and protective PD-1 blockades and therapeutic plans such as combining with nucleos(t)ide analogues therapy can lead to archive protective immunity against HBV with a subsequent cure of HBV. Conclusion Pegylated interferon and NAs such as tenofovir and entecavir are present and mainstream treatment for chronic hepatitis B. However, currently available antiviral agents do not provide complete cure, and the development of cirrhosis, HCC, liver-related complication and mortality are still remaining a major threat. Potential treatment strategies and new agents are emerging to cure HBV, and combinations of current and new anti-hbv agents may increase the rate of HBsAg seroclearance. Although most agents are under early phase development, more safe agents such as TAF, and other novel agents targeting various steps in the HBV lifecycle and host immune responses showed a possibility of functional cure in many preclinical research and clinical trials. With these efforts, a cure for chronic HBV and global HBV control can be hopefully expected. References 1. Global Burden of Disease Study Collaborators. Global, regional, and national incidence, prevalence, and years lived with disability for 301 acute and chronic diseases and injuries in 188 countries, : a systematic analysis for the Global Burden of Disease Study Lancet. 2015;386: Chen CJ, Yang HI, Su J, et al. Risk of hepatocellular carcinoma across a biological gradient of serum hepatitis B virus DNA level. JAMA 2006; 295: Heathcote EJ, Marcellin P, Buti M, et al. Three-year efficacy and safety of tenofovir disoproxil fumarate treatment for chronic hepatitis B. Gastroenterology 2011; 140: Marcellin P, Heathcote EJ, Buti M, et al. Tenofovir disoproxil fumarate versus adefovir dipivoxil for chronic hepatitis B. N Engl J Med 2008; 359: Grimm D, Thimme R, Blum HE. HBV life cycle and novel drug targets. Hepatol Int 2011; 5: Volz T, Allweiss L, MBarek MB, et al. The entry inhibitor Myrcludex-B effi ciently blocks intrahepatic virus spreading in humanized mice previously infected with hepatitis B virus. J Hepatol 2013; 58: Bogomolov P, Voronkova N, Allweiss L, et al. A proofof-concept Phase 2a clinical trial with HBV/HDV entry inhibitor Myrcludex B. Hepatology 2014; 60: 1279A-80A. 8. Maepa MB, Roelofse I, Ely A, Arbuthnot P. Progress and prospects of ant-hbv gene therapy development. Int J Mol Sci 2015; 16: Cai D, Mills C, Yu W, et al. Identification of disubstituted sulfonamide compounds as specific inhibitors of hepatitis B virus covalently closed circular DNA formation. Antimicrob Agents Chemother 2012; 56: Lucifora J, Xia Y, Reisinger F, et al. Specific and nonhepatotoxic degradation of nuclear hepatitis B virus cccdna. Science 2014; 343: Wooddell CI, Rozema DB, Hossbach M, et al. Hepatocyte targeted RNAi therapeutics for the treatment of chronic hepatitis B virus infection. Mol Ther 2013; 21: Yuen M-F, et al. Abstract LB06. Presented at: International Liver Congress; April 13-17, 2016; Barcelona. 13. Mahtab MA, Bazinet M, Vaillant A. REP 9 AC: a potent HBsAg release inhibitor that elicits durable immunological control of chronic HBV infection. Hepatology 2011; 54(Suppl 1): 478A. 14. Chan HLY, Fung S, Seto WK, et al. A phase 3 study of tenofovir alafenamide compared with tenofovir disoproxil fumarate in patients with HBeAg positive chronic HBV: week 48 efficacy and safety results. J Hepatol 2016; 64:S Yuen MF, Ahn SH, Lee KS, et al. Two-year treatment outcome of chronic hepatitis B infection treated with besifovir vs. entecavir: results from a multicentre study. J Hepatol 2015; 62: Peng G, Luo B, Li J, et al. Hepatitis B e-antigen persistency is associated with the properties of HBV-specific CD8 T cells in CHB patients. J Clin Immunol 2011; 31: June 22-24, 2017 Grand Hyatt Incheon, Korea