Background: Colorectal carcinoma is the third leading cause of cancer-related mortality in China. MDM2-p53 inhibitor APG-115 is a novel potential anticancer agent. We aim to investigate the anticancer effect and radiosensitivity enhancement of APG-115 in colorectal cancer.

Materials and methods: Human colorectal cancer cell lines (LOVO, HCT116, RKO, HT29, SW480 and SW620) were treated with the APG-115 alone or with radiation (0-8Gy). Transwell, clonogenic survival assays, CCK-8, flow cytometry, RT-qPCR, Western blot were used to assay cell invasion, cell survival, cell cycle progression, quantification of mRNA expression and DNA damage repair. In vivo, xenograft mouse models (RKO Cell line) were established to analyze the anticancer effect and radiosensitivity enhancement of APG-115.

Results: In vitro, APG-115 not only inhibited invasion and proliferation of colorectal cell lines, but also induced cell-cycle arrest in G1/S phase. Meanwhile, APG-115 increased the mRNA and protein expression of p53 downstream targets dependent on MDM2-p53 signal pathway. The combination of APG-115 and radiation caused cells to accumulate in G2/M and resulted in the accumulation of H2AX-related DNA damage, indicating an increasing of radiosensitivity. In xenograft mouse models, single therapy with either radiation or APG-115 was equivalent in delaying tumor growth, although APG-115 slightly outperforming therapy with radiation alone. Combination therapy delayed tumor growth more significantly compared with either single agent therapy. By analyzing proliferation marker Ki67 in xenograft tumor specimens, we found that the number of proliferating cells significantly decreased in tumors receiving combination treatment of APG-115 and radiation compared with tumors receiving single agent treatment. These results strongly confirmed the enhanced antitumor capacity of APG-115 when combined with radiation.

Conclusions: Our data strongly suggest that MDM2-p53 inhibitor APG-115 may serve not only as a stand-alone therapy, but also as an effective adjunct to current radiotherapeutic regimens for treating colorectal cancer dependent on MDM2-p53 axis.

Citation Format: Han-Jie Yi, Xiang-Lei Yan, Qiu-Yun Luo, Luping Yuan, Baoxia Li, Wentao Pan, Lin Zhang, Miao-Zhen Qiu, Guangfeng Wang, Yifan Zhai, Da-Jun Yang. A novel MDM2-p53 antagonist APG-115 induces p53-mediated apoptosis and enhances radiosensitivity in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 314.