Abstract 6274: Radiosensitizing effect of beta-Apopicropodophyllin is mediated from ER stress against colorectal cancer

Abstract

Abstract β-Apopicropodophyllin (APP) is a synthesized derivative of podophyllotoxin (PPT), which is a natural product that has been used as a traditional drug to decrease immunosuppression, exert antiviral effects for the treatment of influenza, venereal warts, measles and herpes, and even to treat skin cancer. In this study, we tested whether β-apopicropodophyllin (APP) could act as a radiosensitizer in colorectal cancer. To demonstrate radiosensitizing activity of APP, several in vitro tests such as clonogenic assay, immunoblotting, Annexin V-Propidium iodide (PI) assay, detection of mitochondrial ROS/intracellular of H2O2, mitochondrial membrane potential detection were performed. We also tested in vivo radiosensitizing activity of APP as performing colorectal cancer-derived xenograft experiments with mice, and detected tumor volumes and apoptotic cell death. Clonogenic assay showed a combination of APP and γ-ionizing radiation (IR) inhibits cell growth and increases cell death in colorectal cancer cells. Several signal transduction pathways were examined for its potential involvement, and then these results indicated enhanced ER stress is main radiosensitization effect of APP as assessed by immunoblotting analyses. In addition, disrupted mitochondrial membrane potential and increased reactive oxygen species (ROS) were also observed in cells co-treated with APP and IR; these phenomena were followed by the cytosolic release of cytochrome c and consequent activation of caspase-3 and -9. Interestingly, pharmaceutical inhibition of JNK or p38, which prevents caspase activation, blocked the APP/IR-induced activations of ER stress and apoptotic cell death. Therefore, our results implied APP has a radiosensitizing function to induce apoptotic cell death via activation of ER stress, disruption of mitochondrial membrane potential, and induction of the caspase pathway via JNK or p38 induction. Citation Format: A-Ram Kang, Na-Kyung Lee, Hyun-Jin Shin, Hong-Duck Um, Jong Kuk Park. Radiosensitizing effect of beta-Apopicropodophyllin is mediated from ER stress against colorectal cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6274.