Abstract 6584: Slamming the breaks on extracellular vesicles that cause breast cancer

Abstract Breast cancer (BC) recurrence and metastasis are significant causes of death, mainly due to the emergence of therapy-resistant cells. Secreted factors known as extracellular vesicles (EVs), especially small EVs (SEVs) or exosomes less than 100 nanometers in size, have been implicated in the plasticity associated with drug resistance, BC recurrence, and metastasis. EVs derived from BC cells can transform local or distal non-tumor cells, induce the epithelial-to-mesenchymal transition, and trigger uncontrolled proliferation, angiogenesis, and immune suppression of tumor cells. EVs also mediate resistance to hormone therapy and chemotherapy. Given these oncogenic activities, the production of EVs by BC cells presents an attractive target for inhibition. However, the complexity of EV biogenesis and uptake hampers the effectiveness of most pharmacological inhibitors that target single or specific EV synthetic pathways. Because protein synthesis and sorting are the initial steps in the biogenesis of EVs, we inferred that protein folding is a necessary part of EV synthesis. Previous studies revealed that the protein-folding complex, Chaperonin-Containing TCP-1 (CCT), is upregulated in cancer cells to mitigate the damage from misfolded proteins that accumulate due to increased somatic gene alterations and driver mutations. Using RNA sequencing and optimized methods of EV characterization by flow cytometry and nanoparticle tracking analysis (NTA), we determined that CCT has a role in the production of EVs by BC cells. Inhibition of CCT2, the second subunit of the CCT complex, in BC cells deregulated the gene expression of critical components involved in the early stages of EV biogenesis and decreased the release of CCT2-containing EVs. The exogenous expression of CCT2 in BC cells produced small EVs (SEVs) with increased and selective loading of CCT2 RNA and protein cargo. BC cell culture media, enriched for CCT2-containing SEVs using a 0.1 micromolar filter, increased CCT production and activity in recipient cells. Exogenously expressed CCT2 in BC cells also enriched gene expression associated with extracellular exosomes (GO:0070062). Hence, CCT may be essential for the biogenesis of SEVs with transformative properties and a promising therapeutic target for inhibiting cancer-causing EVs. These studies show that CCT directly regulates components of EV biogenesis in BC cells and advances CCT as an essential driver of BC progression through the production of oncogenic EVs. Citation Format: Annette R. Khaled, Carolyn Dang, Lam Truong, Sydney Laxton, James Velazquez, Shoba Kankipati, Priya Gopalan, SA Litherland. Slamming the breaks on extracellular vesicles that cause breast cancer [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 6584.