Abstract 3055: Developing the cyclic peptide AD05 as a novel Hsp90 inhibitor for triple-negative breast cancer therapy

Abstract The Heat-shock protein 90 (Hsp90), emerged as an exciting molecular target in the late 90s after being recognized as the driving force behind the Ansamycin antibiotic geldanamycin's antitumoral activity. Since then, extensive research has been conducted to develop Hsp90 inhibitors for clinical applications in cancer therapy. Specifically in triple-negative breast cancer (TNBC), studies have shown that using Hsp90 inhibitors as single agents, or in combination with immunotherapy can offer new leads to better therapeutic efficacy. However, traditional inhibitors targeting the N-terminal domain of Hsp90 often trigger a heat shock response (HSR) or are pan-inhibitors which results in detrimental side effects in clinical trials. Considering this, this study aims to identify and characterize small molecules that can inhibit Hsp90 and degrade its oncogenic client proteins, without inducing the HSR. Using a high-throughput progesterone reconstitution screening assay, a cyclic peptide, AD05, was identified from medicinal plant extracts and their symbiotic microorganisms. This compound is intriguing because it inhibits Hsp90 in a distinct manner from the classical N-terminal Hsp90 inhibitor tested in Phase III clinical trials; 17-N-allylamino-demethoxygeldanamycin (17-AAG) and does not induce the HSR. The binding of AD05 to Hsp90 was further characterized in purified and cell-based systems using IP linked to LC-MS, molecular docking analysis, cellular thermal shift assay (CETSA), and Western blot that showed an efficient degradation of oncogenic client proteins. AD05 exhibited significant cytotoxicity against cancer cells evaluated in MTT assays compared to normal cells, immunohistochemistry (IHC), immunofluorescence, electron microscopy, and Seahorse metabolic analyses. Our findings suggest that bioactive natural products are effective and promising inhibitors against the Hsp90 machine for cancer research and therapy. Citation Format: Ilham Zarguan, Sumin Lu, vamsi Krishna Kommalapati, Alisha Hussain, Dhruvi Paladiya, Wayne Fang, Lamiae Belayachi, Abdelaziz Benjouad, Abdessamad Debbab, Ahmed Chadli. Developing the cyclic peptide AD05 as a novel Hsp90 inhibitor for triple-negative breast cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3055.