Abstract B89: Expression of DNA damage repair enzymes determine the efficacy of a novel dUTPase inhibitor, TAS-114.
Authors: Tsukioka Sayaka , Yano Wakako , Yokogawa Tatsushi , Wakasa Takeshi , Fujioka Akio , Yamamura Keisuke , Itoh Satoko , Fukuoka Masayoshi , Matsuo Kenichi , Noguchi Kazuharu , Utsugi Teruhiro 
Published: August 2014

Abstract
Background: Deoxyuridine 5'-triphosphate nucleotidehydrolase (dUTPase) is a pyrophosphatase, which selectively catalyzes FdUTP and dUTP hydrolysis, and tightly restricts 5-fluorouracil (5-FU) and uracil misincorporation into DNA. TAS-114 is a novel potent inhibitor of dUTPase, and is under clinical development as a fluoropyrimidine enhancer. TAS-114 potentiates the antitumor activity of fluoropyrimidines through increasing misincorporation of 5-FU and uracil into DNA, however, precise mechanisms of cytotoxicity after misincorporation of the aberrant base is unknown. Here, we report relationships between the DNA damage repair function and the efficacy of TAS-114 on the anticancer activity of fluoropyrimidine.
Materials and Methods: The antitumor activities of 5-FU or 5-FU/TAS-114 were evaluated in 9 human tumor xenograft models. Intratumor dUTPase protein was measured by Western blotting, and phosphorylation of histone H2AX was detected by immunohistochemistry. Tissue concentrations of FdUMP and dUMP were measured by HPLC and a thymidylate synthase (TS) binding assay, respectively. Suppression of DNA damage repair proteins were performed by RNA interference technology in HeLa cells, and then, the cells were used to assess an antiproliferative activity of FdUrd/TAS-114.
Results: Oral administration of TAS-114 inhibited dUTPase and synergistically increased antitumor activity of 5-FU in various human tumor xenograft models. The magnitude of dUTPase inhibition was estimated by the change of dUTPase enzymatic products (FdUMP and dUMP) and it appeared to correlate with dUTPase expression and synergistic effect. These data suggest that 5-FU and uracil misincorporation is a primary mechanism of TAS-114 efficacy. In addition, TAS-114 combination with 5-FU increased phosphorylation of histone H2AX, suggesting a TAS-114 activated DNA damage response pathway. Suppression of DNA damage repair proteins involved in base excision repair (BER) and homologous recombination repair (HR) revealed that these DNA repair pathways were important in TAS-114’s synergistic increase of 5-FU cytotoxicity.
Conclusion: Expression levels of DNA damage repair proteins in BER and HR affect TAS-114 sensitivity. DNA repair response appears to be a determinant of TAS-114 efficacy as well as dUTPase expression. These factors will be measured inTAS-114/fluoropyrimidines combination clinical trial.
Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B89.
Citation Format: Sayaka Tsukioka, Wakako Yano, Tatsushi Yokogawa, Takeshi Wakasa, Akio Fujioka, Keisuke Yamamura, Satoko Itoh, Masayoshi Fukuoka, Kenichi Matsuo, Kazuharu Noguchi, Teruhiro Utsugi. Expression of DNA damage repair enzymes determine the efficacy of a novel dUTPase inhibitor, TAS-114. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B89.