Abstract 483: Hederacolchiside A1 inhibits autophagy via CTSC inhibition and inhibits growth in colon cancer

Abstract

Abstract Background: Autophagy is a normal regulatory process that degrades non-functional or unnecessary cellular components. The degradation of components provides materials for the synthesis of cellular components and, during tumor development, may provide energy. Therefore, autophagy regulation may have potential therapeutic uses in oncology. The triterpenoid saponin hederacolchiside A1 (HA1) has potent antitumor effects; however, its role in autophagy is still unknown. Methods: In the present study, we used human colon cancer cells (SW480 and HT29) and mouse colon cancer cells (CT26) for the main experiments, and several additional cancer cell lines for other experiments. To assess the autophagy dysregulation caused by HA1, we evaluated the protein expressions of two autophagy markers (LC3 and SQSTM1) using Western blotting and the changes in organelles using LC3 puncta assay and transmission electron microscopy. We compared the effects of HA1 and other autophagy inhibitors. Additionally, we compared the HA1-induced decrease in cathepsin C (CTSC) expression in tumors and non-tumors using publicly available data. The effect of HA1 on tumor growth was evaluated in vitro using a three-dimensional spheroid model and patient-derived colon organoids, and in vivo based on tumor growth in a subcutaneous injection mouse model. Results: HA1 treatment resulted in marked vacuolization of colon and other cancer cells. Additionally, autophagy was induced by the accumulation of LC3-II and SQSTM1. These findings were supported by increased LC3 puncta and abnormal organelle morphology. Compared to treatment with other autophagy inhibitors, HA1 treatment resulted in the formation of distinct vacuoles and increased LC3 and SQSTM1, similar to chloroquine treatment. The publicly available data showed that the lysosomal protease CTSC was increased in several cancers, including colon cancer, compared to the normal tissues. Furthermore, HA1 decreased the CTSC expression and enzymatic activity independently of the proteasome degradation, resulting in autophagy dysregulation and, subsequently, autophagy flux inhibition. HA1 inhibited cell growth and induced cell cycle arrest in the two-dimensional culture, three-dimensional spheroids, patient-derived colon cancer organoids, and the in vivo experiments. Conclusion: HA1 inhibits cell growth and induces autophagy dysregulation. Therefore, HA1 may be a potential therapeutic agent in colon cancer. Citation Format: Solbi Kim, Eunji Kim, Minju Han, Youn Seo Oh, Sora Kang, Heung Jin Jeon, Hyo Jin Lee. Hederacolchiside A1 inhibits autophagy via CTSC inhibition and inhibits growth in colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 483.