Review Article Inhibitor-Based Therapeutics for Treatment of Viral Hepatitis Debajit Dey and Manidipa Banerjee* Kusuma School of Biological Sciences, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India Abstract When such inflammation, as manifested in symptoms such as jaundice, nausea, abdominal pain, malaise etc, is caused Viral hepatitis remains a significant worldwide threat, in spite by viral infections, the condition is referred to as viral hepatitis.1 of the availability of several successful therapeutic and vacci- Five hepatotropic viruses – named hepatitis A, B, C, D and nation strategies. Complications associated with acute and E viruses – target liver cells in humans and cause acute and chronic infections, such as liver failure, cirrhosis and hepato- chronic hepatitis. In addition, other viruses such as the cellular carcinoma, are the cause of considerable morbidity adenovirus, cytomegalovirus (CMV) and Epstein-Barr virus and mortality. Given the significant burden on the healthcare (EBV), occasionally cause symptoms of hepatitis.2 system caused by viral hepatitis, it is essential that novel, While an acute infection in healthy, immunocompetent more effective therapeutics be developed. The present review individuals is cleared spontaneously, complications like cir- attempts to summarize the current treatments against viral rhosis, hepatocellular carcinoma (HCC) and fulminant hepatic hepatitis, and provides an outline for upcoming, promising failure (FHF) may arise in immunocompromised individuals, new therapeutics. Development of novel therapeutics requires due to associated secondary reasons such as existing infec- an understanding of the viral life cycles and viral effectors in tions, alcohol abuse, or genetic predisposition.1,3 HCC, the molecular detail. As such, this review also discusses virally- third leading cause of cancer-related deaths worldwide,4 is encoded effectors, found to be essential for virus survival closely associated with hepatitis B virus (HBV) infections. and replication in the host milieu, which may be utilized as Even though the therapeutic strategies devised till date are potential candidates for development of alternative therapies targeted towards chronic infections, treatment options in the future. become severely limited for advanced stage patients.1 In addi- © 2016 The Second Affiliated Hospital of Chongqing Medical tion, current medications have significant side-effects, which University. Published by XIA & HE Publishing Inc. All rights poses an issue with disease management. Hence, there is an reserved. urgent requirement for safer and more potent drugs. This review will focus on the therapeutics currently avail- able for treating viral hepatitis of all forms. In addition, the potential of new therapeutics and targeted inhibitor-based Introduction therapies against viral membrane-penetrating peptides and viroporins, a group of virally encoded proteins involved in Hepatitis is a medical condition wherein the liver undergoes facilitating replication and other specific steps in the viral life inflammation due to a plethora of reasons, including drug cycle, are also discussed. abuse, excessive alcohol abuse, disease conditions etc.1 Life cycle of hepatotropic viruses Keywords: Viral hepatitis; Viroporin; Inhibitor. Abbreviations: CMV, Cytomegalovirus; EBV, Epstein-Barr virus; HCC, Hepatocel- Life cycles of the known hepatotropic viruses – particularly A, lular carcinoma; FHF, Fulminant hepatic failure; HBV, Hepatitis B virus; HAV, B, C and E – have been studied in significant detail. Although Hepatitis A virus; HCV, Hepatitis C virus; HEV, Hepatitis E virus; HDV, Hepatitis D virus; HAVcr-1/TIM-1, Hepatitis A virus cellular receptor 1/T-cell immunoglobulin the lack of appropriate cell culture systems, and the slow- and mucin domain 1; IRES, Internal ribosome entry site; 5’-UTR, 5’-Untranslated growing nature of the virus, has hampered studies, consid- region; L-SIGN, Liver/lymph node-specific intercellular adhesion molecule-3- erable information is available on the entry, replication and grabbing integrin; DC-SIGN, Dendritic cell-specific intercellular adhesion mole- exit mechanisms of these viruses, and on specific host- cule-3; GAG, glycosaminoglycan; HSC70, Heat shock cognate 70 protein; HSPG, Heparan sulfate proteoglycans; Grp78, Glucose-regulated protein 78; HSP90, Heat interacting partners for each virus. Hepatitis A virus (HAV) is shock protein 90; ORF1, Open reading frame 1; NTCP, sodium taurocholate cotrans- thought to associate with a cell-surface protein receptor, porting polypeptide; cccDNA, covalently closed circular DNA; PK, Protein kinase; HAVcr-1/TIM-1 (Hepatitis A virus cellular receptor 1/T-cell NA, Nucleos(t)ide analog; IFN, Interferon; L-HBsAg, Large hepatitis B surface immunoglobulin and mucin domain 1), a member of the antigen; HDAg, Hepatitis D antigen; PegIFN-a, Pegylated IFN-a,SVR,Sustained virological response; HBeAg, Hepatitis B e antigen; HBIg, Hepatitis B immunoglo- immunoglobulin superfamily, by which it gains entry into 5 bulin; CHB, Chronic hepatitis B; DAAs, Direct-acting antivirals; ZFNs, Zinc finger host cells. Post-entry, translation of the positive-sense RNA nucleases; TALEN’s, Transcription activator-like effector nucleases; CRISPR, Clus- genome by the host ribosomal machinery, mediated via the tered regulatory interspaced short palindromic repeats; RNAi, RNA interference; presence of an internal ribosome entry site (IRES) encoded HMA, Hexamethylene amilorides; NN-DNJ, N-nonyl deoxynojirimycin. ’ Received: 08 June 2016; Revised: 14 September 2016; Accepted: 14 September in the 5 -untranslated region (UTR) of viral RNA, results in 2016 the production of a large viral polyprotein. The polyprotein is q DOI: 10.14218/JCTH.2016.00025. cleaved into structural (VP1-2A, VP2, VP3, VP4) and non- *Correspondence to: Dr. Manidipa Banerjee, Kusuma School of Biological Scien- structural proteins (2B, 2C, 3A, 3B, 3C, 3D) as well as inter- ces, Indian Institute of Technology Delhi, Block 1A, Hauz Khas, New Delhi pro 110016, India. Tel: +91-11-26597538, Fax: +91-11-26597530, E-mail: mbanerjee@ mediates (3CD, 2BC etc) by a virally-encoded protease 3C . bioschool.iitd.ac.in Following the cleavage event, the viral RNA replicase 248 Journal of Clinical and Translational Hepatology 2016 vol. 4 | 248–257 This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial 4.0 Unported License, permitting all non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Dey D. et al: Inhibitors for viral hepatitis synthesizes a minus-sense strand corresponding to the viral transcriptase and the nucleocapsid (pregenomic). In addition, RNA genome, which serves as a template for the production transcripts encoding the surface antigens (subgenomic) are of multiple plus-sense strands. Meanwhile, structural proteins also produced. Both pre- and subgenomic transcrpits are assemble to form virions, which package a majority of the transferred to the cytosol. Surface protein synthesis, to gen- plus-sense RNA generated during replication. Two specific erate core and subviral particles, occurs in the ER. Translation cleavage events result in generation of mature infectious products (viral polymerase and core protein) of the prege- virions - the VP1-2A precursor cleavage and the VP4/VP2 nomic RNA associate with protein kinases (PKs),26,27 junctional cleavage.6–11 Virions are subsequently released HSPs27,28 and pregenomic RNA to yield mature core particles, from the apical membrane of infected hepatocytes.11 which are either released from infected cells, or are recircu- Entry of hepatitis C virus (HCV) into target host cells is a lated to the nucleus to maintain the cccDNA level.25,28 Inter- multistep event, requiring several host components. The estingly, while subviral particles are released via the secretory cellular receptors and surface molecules, which are thought pathway involving the Golgi and ER, mature core particles are to be involved in this process, include the C-type lectins liver/ released through multivesicular particles.25 lymph node-specific ICAM-3-grabbing integrin (L-SIGN) and Although not much is known regarding the cellular entry dendritic cell (DC)-specific intercellular adhesion molecule-3 process of hepatitis D virus (HDV), studies have suggested (ICAM-3)-grabbing nonintegrin (DC-SIGN), glycosaminogly- similarities with the HBV entry pathway involving interaction cans (GAGs), claudins 6 and 9 and CD-81.12–14 Binding to of HSPGs and NTCPs with the viral large hepatitis B surface cellular receptor(s) is primarily mediated by the viral envelope antigen (L-HBsAg; pre-S1 domain).24,29 Post-entry, transfer proteins E1 and E2. Post-entry, the virus nucleocapsid disas- of the RNA genome to the nucleus is facilitated by the virally- sembles releasing the plus-sense RNA genome in the cell encoded hepatitis D antigen (HDAg).30 Within the nucleus, cytosol, which acts as a template for 5’-IRES mediated trans- host RNA polymerases initiate genome replication, which lation. The single HCV polyprotein generated during transla- proceeds via a rolling circle mechanism.30 Subsequent tran- tion, like the corresponding HAV polypeptide, also undergoes scriptional and translational events lead to the production of protease mediated co- and post-processing to yield the entire the large delta antigen which undergoes prenylation prior to repertoire of viral structural and non-structural