Targeting the multifunctional HBV core protein as a potential cure for chronic hepatitis B

Abstract

The core (capsid) protein of hepatitis B virus (HBV) is the building block of nucleocapsids where viral DNA reverse transcriptional replication takes place and mediates virus-host cell interaction important for the persistence of HBV infection. The pleiotropic role of core protein (Cp) in HBV replication makes it an attractive target for antiviral therapies of chronic hepatitis B, a disease that affects more than 257 million people worldwide without a cure. Recent clinical studies indicate that core protein allosteric modulators (CpAMs) have a great promise as a key component of hepatitis B curative therapies. Particularly, it has been demonstrated that modulation of Cp dimerdimer interactions by several chemical series of CpAMs not only inhibit nucleocapsid assembly and viral DNA replication, but also induce the disassembly of double-stranded DNA-containing nucleocapsids to prevent the synthesis of cccDNA. Moreover, the different chemotypes of CpAMs modulate Cp assembly by interaction with distinct amino acid residues at the HAP pocket between Cp dimer-dimer interfaces, which results in the assembly of Cp dimers into either non-capsid Cp polymers (type I CpAMs) or empty capsids with distinct physical property (type II CpAMs). The different CpAMs also differentially modulate Cp metabolism and subcellular distribution, which may impact cccDNA metabolism and host antiviral immune responses, the critical factors for the cure of chronic HBV infection. This review article highlights the recent research progress on the structure and function of core protein in HBV replication cycle, the mode of action of CpAMs, as well as the current status and perspectives on the discovery and development of core proteintargeting antivirals. This article forms part of a symposium in Antiviral Research on "Wideranging immune and direct-acting antiviral approaches to curing HBV and HDV infections."

A pocket-factor–triggered conformational switch in the hepatitis B virus capsid

“…NMR chemical shift changes clearly localize the conformational differences to Cp’s hydrophobic pocket and its delimiting residues, and we elucidated the cause to be a high-affinity molecular binder, identified as Triton X-100. Form B corresponds to the unbound state, while the addition of Triton X-100 fills the hydrophobic pocket and induces form A. Interestingly, this binding is distinct from that of the small molecule capsid assembly modulators (e.g., the heteroaryldihydropyrimidine [HAP] compounds and others), which all target the so-called hydrophobic cavity at the interdimer interface ( 49 ). As Cp mutations preventing access to the pocket lock the capsid in form B and impede formation of enveloped virions, we propose that form A relates to a previously undetected envelopment-ready conformation of the HBV capsid.…”

Discovery of New Small Molecule Hits as Hepatitis B Virus Capsid Assembly Modulators: Structure and Pharmacophore-Based Approaches

“…In addition, Cp is also implicated in transporting the HBV genome to the nucleus and epigenetic regulation of HBV gene expression [ 12 , 13 ]. Therefore, Cp represents an attractive target in anti-HBV drug discovery [ 14 , 15 ]. Small molecules can destabilize the HBV core protein, increase the capsid assembly rate, and form either aberrant or empty, nonfunctional capsid particles [ 15 ].…”

Synthesis of 4-oxotetrahydropyrimidine-1(2H)-carboxamides derivatives as capsid assembly modulators of hepatitis B virus

“…Therefore, development of novel antivirals targeting other steps of HBV replication as well as drugs that can activate host antiviral immune response is required to achieve the functional cure of chronic hepatitis B [4,5]. Particularly, selective packaging of viral pregenomic (pg) RNA-DNA polymerase complex by 120 core protein (Cp) dimers into a nucelocapsid for viral DNA synthesis to take place is a key step of HBV replication and thus an ideal target for novel antiviral development [6]. In the last two decades, multiple small molecule inhibitors of HBV pgRNA encapsidation have been discovered and several leads from three chemotypesheteroaryldihydropyrimidine (HAPs, 1), dibenzothiazepine derivatives (DBTs, 2), and sulfamoylbenzamides (SBAs, 3)-have been extensively developed and are currently in clinical trials for the treatment of chronic hepatitis B (Figs 1 and 2) [6,7].…”

“…Particularly, selective packaging of viral pregenomic (pg) RNA-DNA polymerase complex by 120 core protein (Cp) dimers into a nucelocapsid for viral DNA synthesis to take place is a key step of HBV replication and thus an ideal target for novel antiviral development [6]. In the last two decades, multiple small molecule inhibitors of HBV pgRNA encapsidation have been discovered and several leads from three chemotypesheteroaryldihydropyrimidine (HAPs, 1), dibenzothiazepine derivatives (DBTs, 2), and sulfamoylbenzamides (SBAs, 3)-have been extensively developed and are currently in clinical trials for the treatment of chronic hepatitis B (Figs 1 and 2) [6,7]. Mechanistically, all the structurally diversified capsid assembly modulators or core protein allosteric modulators (CpAMs) bind to a hydrophobic pocket (HAP pocket) between Cp dimer-dimer interfaces to misdirect the assembly of Cp dimers into non-capsid polymers (type I CpAM) or morphologically "normal" capsids devoid of pgRNA and viral DNA polymerase (type II CpAM) [6,8].…”

“…In the last two decades, multiple small molecule inhibitors of HBV pgRNA encapsidation have been discovered and several leads from three chemotypesheteroaryldihydropyrimidine (HAPs, 1), dibenzothiazepine derivatives (DBTs, 2), and sulfamoylbenzamides (SBAs, 3)-have been extensively developed and are currently in clinical trials for the treatment of chronic hepatitis B (Figs 1 and 2) [6,7]. Mechanistically, all the structurally diversified capsid assembly modulators or core protein allosteric modulators (CpAMs) bind to a hydrophobic pocket (HAP pocket) between Cp dimer-dimer interfaces to misdirect the assembly of Cp dimers into non-capsid polymers (type I CpAM) or morphologically "normal" capsids devoid of pgRNA and viral DNA polymerase (type II CpAM) [6,8]. Of over a dozen families of CpAMs discovered thus far, These authors contributed equally: Nicky Hwang, Haiqun Ban SBAs have received much attention due to their structural simplicity, availability of the cocrystal structures with capsids or Y132A mutant Cp heximers, and potential for structural modifications [9,10].…”