title: Inhibitory effects of valproic acid in DNA double-strand break repair after irradiation in esophageal squamous carcinoma cells.
abstract: Radiation therapy is one of the most promising therapeutic strategies in unresectable esophageal squamous cell carcinoma (ESCC). The histone deacetylase (HDAC) inhibitor has been shown to enhance radiosensitivity. Valproic acid (VPA) is a well-known drug used to treat seizure disorders and epilepsy, and has been shown to inhibit HDACs. We recently reported that a clinically safe dose of VPA enhances radiation‑induced cytotoxicity in human ESCC cells. However, the mechanism of radiosensitizing effect of VPA has not yet been confirmed. The present study examined the effect of VPA on DNA double-strand break (DSB) repair after radiation in the human ESCC cell lines KES, TE9 and TE11 by examining H2AX phosphorylation (γH2AX) levels as a marker of radiation‑induced DSBs. The present study also examined whether VPA inhibited radiation-induced DNA DSB repair by suppressing non-homologous end joining (NHEJ), focusing particularly on the acetylation of Ku70. VPA was shown to prolong γH2AX levels after irradiation in all three ESCC cell lines. Moreover, prolonged γH2AX foci formation after irradiation was also observed by immunocytochemistry following VPA pretreatment in KES and TE9 cells. VPA was shown to induce Ku70 acetylation after irradiation in all three ESCC cell lines. Our results suggest that VPA prolonged radiation‑induced DSBs by inhibiting NHEJ in DSB repair pathways in ESCC. VPA could therefore be used as an effective radiosensitizer in ESCC radiotherapy.
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Makita
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Itasu
authors.initials: I
authors.lastname: Ninomiya
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Tomoya
authors.initials: T
authors.lastname: Tsukada
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Okamoto
authors.affiliation: Center for Biomedical Research and Education, School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Harada
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Nakanuma
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Seisho
authors.initials: S
authors.lastname: Sakai
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Isamu
authors.initials: I
authors.lastname: Makino
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Kinoshita
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Hironori
authors.initials: H
authors.lastname: Hayashi
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Katsunobu
authors.initials: K
authors.lastname: Oyama
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Hisatoshi
authors.initials: H
authors.lastname: Nakagawara
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Tomoharu
authors.initials: T
authors.lastname: Miyashita
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Tajima
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Takamura
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Sachio
authors.initials: S
authors.lastname: Fushida
authors.affiliation: Department of Gastroenterological Surgery, Division of Cancer Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8641, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Ohta
mesh_terms: D002294:Carcinoma, Squamous Cell; D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects* / Q000528:radiation effects; D004260:DNA Repair / Q000187:drug effects*; D004938:Esophageal Neoplasms; D000077277:Esophageal Squamous Cell Carcinoma; D005455:Fluorescent Antibody Technique; D006657:Histones / Q000096:biosynthesis; D006801:Humans; D011836:Radiation Tolerance / Q000187:drug effects; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D014635:Valproic Acid / Q000494:pharmacology*
chemical_list: C468783:H2AX protein, human; D006657:Histones; D011838:Radiation-Sensitizing Agents; D014635:Valproic Acid