Abstract 1355: A novel derivative of benzoxazole enhances radiosensitivity of human colon cancer cells through p53-mediated G2/M arrest and mitochondrial apoptotic pathway

Abstract

Abstract The tumor suppressor p53 plays a critical role in cell cycle regulation and apoptotic cell death, and its activation can sensitize cancer cells to radio- or chemotherapy. To identify small molecules that induce apoptotic cell death via increasing p53 transcriptional activity, we designed and synthesized 44 benzoxazole derivative small molecule compounds. Using a cell-based screening with p53-responsive luciferase reporter assay system of benzoxazole derivatives, we found AU14022, which significantly increased p53 transcriptional activity in a concentration dependent manner. Treatment of AU14022 increased p53 protein expression, its phosphorylation on serine 15 and its target p21 gene/protein expression and induced apoptotic cell death measured by FACS analysis using Annexin V/PI double staining in wild-type p53 HCT116 human colon cancer cells but not in p53 knockout HCT116 cells. Furthermore, treatment of HCT116 cells with AU14022 exhibited mitochondrial dysfunction including bcl-2 family modulation and cytochrome c release. Combination treatment of AU14022 and ionizing radiation (IR) synergistically induced apoptotic cell death, compared to IR or AU14022 alone. Further investigation demonstrated that cell cycles are significantly arrested at G2/M phase, and marked inductions of p21 protein expression and phosphorylation of Chk1 protein and a decrease of cyclin B1 protein expression were observed by treatment of AU14022 alone and combination treatment with AU14022 and IR. Our findings indicate that AU14022 induced apoptosis through p53-mediated cell cycle arrest with mitochondrial dysfunction, leading to enhanced radiosensitivity of colon cancer cells. These results provide a basis for the further investigations required for its assessment as a promising anticancer agent. Citation Format: Hwani Ryu, Bitna Seo, Jooyoung Kim, In-Sung Jung, Jie-Young Song, Jiyeon Ahn. A novel derivative of benzoxazole enhances radiosensitivity of human colon cancer cells through p53-mediated G2/M arrest and mitochondrial apoptotic pathway. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1355.