Purpose: Development of autophagy inhibitors has important clinical significance in cancer therapies. We and others demonstrated that over-expression of Caveolin-1 (Cav1), which was the major scaffolding protein of caveolae, was associated with higher tumor stage, metastasis and worse prognosis in various carcinomas, particularly in breast cancer. Furthermore, we identified critical role of Cav1 in breast cancer metastasis via modulation of lysosomal function and autophagy. Based on the above, we screened a series of 2, 645 kinds of small-molecule drugs to find out certain cav1 inhibitors which could suppress autophagy and breast cancer metastasis.

Experimental Design: We conducted the 1st high-throughput screening based on surface plasmon resonance (SPR) analysis of cav-1 interaction with 2, 645 kinds of small-molecule drugs. Secondly, we launched the 2nd high-throughput screening based on CCK8 analysis to validate the anti-cancer potential of the selected compounds. We also carried out the final high-throughput screening to investigate their autophagic effects with high content image cytometry assay. The anti-cancer and anti-metastasis effects of the final drug candidate was investigated using invasive breast cancer cells MDA-MB-231 and BT-549, and its role on autophagy was further investigated by transfection of mRFP-GFP-LC3 adenoviral vector and western blot analysis of autophagic proteins.

Results: 2, 645 kinds of small-molecule drugs were screened based on a series of high-throughput screening. The compound gallic acid was identified as the candidate drug owing to its strong interaction and competitive inhibition with cav1, its potent anti-proliferation potential on both invasive breast cancer cells MDA-MB-231 and BT-549, as well as its potent autophagic inhibition compared with the other 2, 644 drugs. Further experimental validation revealed that gallic acid was a potent late-stage autophagy inhibitor via inhibiting autophagosome-lysosome fusion.

Conclusions: Collectively, these results demonstrated that the cav1 inhibitor gallic acid was a novel late-stage autophagy suppressor with potential clinical application for invasive breast cancer therapy.

Citation Format: Neng Wang, Fengxue Zhang, Zhiyu Wang, Yifeng Zheng, Shengqi Wang, Bowen Yang. Critical role of cav1 in high-throughput identification of gallic acid as a novel late-stage autophagy suppresser against invasive breast 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 1230.