title: Novel therapeutic approaches for hepatitis B virus covalently closed circular DNA.
abstract: Hepatitis B virus (HBV) infection is a major global health problem. Although current therapies, such as the use of nucleos(t)ide analogs, inhibit HBV replication efficiently, they do not eliminate covalently closed circular DNA (cccDNA), which persists in hepatocyte nuclei. As HBV cccDNA is a viral transcription template, novel therapeutic approaches to directly target HBV cccDNA are necessary to completely eradicate persistent HBV infections. HBV cccDNA levels in HBV-infected human liver cells are extremely low; thus, more reliable and simple measurement methods are needed to correctly monitor their levels during therapeutic treatment. Although reverse transcription-polymerase chain reaction or Southern blot procedures are currently used in research studies, these methods are not completely reliable and are also time-consuming and labor-intensive. Genome editing technologies, such as zinc finger nucleases, transcription activator-like effector nucleases, and the clustered regularly interspaced short palindromic repeats/Cas9 (CRISPR/Cas9) system, which are designed to target specific DNA sequences, represent highly promising potential therapeutic tools. In particular, the CRISPR/Cas9 system is an easily customizable sequence-specific nuclease with high flexibility and may be the most feasible approach to target HBV cccDNA. Further research to develop easier, safer, and more effective protocols should be pursued.
authors.affiliation: Motoko Ohno, Motoyuki Otsuka, Takahiro Kishikawa, Takeshi Yoshikawa, Akemi Takata, Kazuhiko Koike, Department of Gastroenterology, Graduate School of Medicine, the University of Tokyo, Tokyo 113-8655, Japan.
authors.forename: Motoko
authors.initials: M
authors.lastname: Ohno
authors.affiliation: Motoko Ohno, Motoyuki Otsuka, Takahiro Kishikawa, Takeshi Yoshikawa, Akemi Takata, Kazuhiko Koike, Department of Gastroenterology, Graduate School of Medicine, the University of Tokyo, Tokyo 113-8655, Japan.
authors.forename: Motoyuki
authors.initials: M
authors.lastname: Otsuka
authors.affiliation: Motoko Ohno, Motoyuki Otsuka, Takahiro Kishikawa, Takeshi Yoshikawa, Akemi Takata, Kazuhiko Koike, Department of Gastroenterology, Graduate School of Medicine, the University of Tokyo, Tokyo 113-8655, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kishikawa
authors.affiliation: Motoko Ohno, Motoyuki Otsuka, Takahiro Kishikawa, Takeshi Yoshikawa, Akemi Takata, Kazuhiko Koike, Department of Gastroenterology, Graduate School of Medicine, the University of Tokyo, Tokyo 113-8655, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yoshikawa
authors.affiliation: Motoko Ohno, Motoyuki Otsuka, Takahiro Kishikawa, Takeshi Yoshikawa, Akemi Takata, Kazuhiko Koike, Department of Gastroenterology, Graduate School of Medicine, the University of Tokyo, Tokyo 113-8655, Japan.
authors.forename: Akemi
authors.initials: A
authors.lastname: Takata
authors.affiliation: Motoko Ohno, Motoyuki Otsuka, Takahiro Kishikawa, Takeshi Yoshikawa, Akemi Takata, Kazuhiko Koike, Department of Gastroenterology, Graduate School of Medicine, the University of Tokyo, Tokyo 113-8655, Japan.
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Koike
mesh_terms: D000818:Animals; D064130:CRISPR-Associated Proteins / Q000235:genetics / Q000378:metabolism; D064113:CRISPR-Cas Systems; D064112:Clustered Regularly Interspaced Short Palindromic Repeats; D004270:DNA, Circular / Q000235:genetics* / Q000378:metabolism; D004279:DNA, Viral / Q000235:genetics* / Q000378:metabolism; D015316:Genetic Therapy / Q000379:methods*; D006509:Hepatitis B / Q000628:therapy* / Q000821:virology; D006515:Hepatitis B virus / Q000235:genetics* / Q000254:growth & development / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007167:Immunotherapy / Q000379:methods; D014779:Virus Replication
chemical_list: D064130:CRISPR-Associated Proteins; D004270:DNA, Circular; D004279:DNA, Viral
keywords: Covalently closed circular HBV DNA; Genome editing; Hepatitis B virus