title: Enhanced safety profiles of the telomerase-specific replication-competent adenovirus by incorporation of normal cell-specific microRNA-targeted sequences.
abstract: OBJECTIVE
  Oncolytic adenoviruses (Ad) have been actively pursued as potential agents for cancer treatment. Among the various types of oncolytic Ads, the telomerase-specific replication-competent Ad (TRAD), which possesses an E1 gene expression cassette driven by the human telomerase reverse transcriptase promoter, has shown promising results in human clinical trials; however, the E1 gene is also slightly expressed in normal cells, leading to replication of TRAD and cellular toxicity in normal cells.
  
  
  METHODS
  To overcome this problem, we utilized a microRNA (miRNA)-regulated gene expression system. Four copies of complementary sequences for miR-143, -145, -199a, or let-7a, which have been reported to be exclusively downregulated in tumor cells, were incorporated into the 3'-untranslated region of the E1 gene expression cassette.
  
  
  RESULTS
  Among the TRAD variants (herein called TRADs) constructed, TRADs containing the sequences complementary to miR-143, -145, or -199a showed efficient oncolytic activity comparable to the parental TRAD in the tumor cells. On the other hand, replication of the TRADs containing the miRNA complementary sequences was at most 1,000-fold suppressed in the normal cells, including primary normal cells. In addition, to suppress the replication of the TRADs in hepatocytes as well as other normal cells, we constructed a TRAD containing 2 distinct complementary sequences for miR-199a and liver-specific miR-122a (TRAD-122a/199aT). TRAD-122a/199aT exhibited more than 10-fold reduction in viral replication in all the normal cells examined, including primary hepatocytes.
  
  
  CONCLUSIONS
  This study showed that oncolytic Ads containing the sequences complementary to normal cell-specific miRNAs showed significantly improved safety profiles without altering tumor cell lysis activity.
authors.affiliation: Departments of Biochemistry and Molecular Biology and Biomedical Innovation, Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan.
authors.forename: Kumiko
authors.initials: K
authors.lastname: Sugio
authors.forename: Fuminori
authors.initials: F
authors.lastname: Sakurai
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Katayama
authors.forename: Katsuhisa
authors.initials: K
authors.lastname: Tashiro
authors.forename: Hayato
authors.initials: H
authors.lastname: Matsui
authors.forename: Kenji
authors.initials: K
authors.lastname: Kawabata
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kawase
authors.forename: Masahiro
authors.initials: M
authors.lastname: Iwaki
authors.forename: Takao
authors.initials: T
authors.lastname: Hayakawa
authors.forename: Toshiyoshi
authors.initials: T
authors.lastname: Fujiwara
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Mizuguchi
mesh_terms: D000256:Adenoviridae / Q000235:genetics* / Q000378:metabolism; D002477:Cells / Q000378:metabolism; D002478:Cells, Cultured; D003001:Cloning, Molecular; D018390:Gene Targeting / Q000379:methods; D005822:Genetic Vectors / Q000009:adverse effects* / Q000235:genetics; D019073:HT29 Cells; D056945:Hep G2 Cells; D006801:Humans; D035683:MicroRNAs / Q000235:genetics / Q000502:physiology*; D009369:Neoplasms / Q000235:genetics / Q000628:therapy; D050130:Oncolytic Virotherapy / Q000009:adverse effects / Q000379:methods; D050504:Oncolytic Viruses / Q000235:genetics / Q000502:physiology; D030781:Organisms, Genetically Modified; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D013379:Substrate Specificity; D019098:Telomerase / Q000378:metabolism* / Q000502:physiology; D014779:Virus Replication / Q000235:genetics*
chemical_list: D035683:MicroRNAs; D019098:Telomerase