Abstract 5129: Molecular markers in brain metastases: Role of PI3K/mTOR pathway in epithelial-to-mesenchymal transition

Abstract Brain metastasis (BM) is a devastating disease that causes significant morbidity and reduced overall survival; however, the underlying mechanisms of metastatic dissemination to the brain remain to be elucidated. The metastatic cascade involves orderly cellular reprogramming processes, termed epithelial-to-mesenchymal transition (EMT) and mesenchymal-to-epithelial transition (MET), facilitating tumor cells to acquire a stem cell-like phenotype and migrate, colonize, and grow at secondary sites. The mechanistic target of rapamycin (mTOR) pathway controls cellular functions and stem cell regulation. Thus, we hypothesize that the mTOR pathway plays an important role in BM, perhaps via EMT/MET. Immunohistochemical analysis of markers for EMT and MET (Snail, TWIST, STAT3, Vimentin, NF-kB) and stem cells (CD44) were performed. In addition, the expression of Akt/mTOR and its components (Rictor and Raptor) were also examined immunohistochemically. Functional analyses of proliferation, migration, and S-phase entry were performed in BM breast cancer cells (MDA-MB-231). Epithelial (E-cadherin) and mesenchymal (Vimentin) expression were analyzed following inhibition of the mTOR pathway using mTOR complex 1 (mTORC1) inhibitor (rapamycin), combined mTORC1/2 inhibitor (PP242), or with SiRNAs targeting mTOR, Raptor and Rictor. Results demonstrated: 1) Higher levels of phosphorylated AktSer473(93%) with significant overlap with STAT3 (87%); 2) Enhanced expression of mTOR/Raptor/Rictor (50%). EMT and CD44 were expressed in 80% of tumors; 3) Gene expression analysis showed high presence of transcriptional factors associated with differentiation and reprogramming; 4) Migration and proliferation were enhanced in astrocytic media and inhibited by rapamycin or PP242; 5) EdU-pulsing showed enhanced S-phase entry in astrocytic media, which was inhibited by rapamycin; 6) Inhibition of mTOR forced translocation of E-cadherin to the nucleus and enhanced Vimentin expression. These results provide evidence that the mTOR pathway is involved in metastatic brain tumors, suggesting its critical role in achieving a metastatic potential to the brain. Furthermore, these findings point to its role in diagnosis, prognosis, and clinical management in patients with metastatic brain tumors. Citation Format: Monica C. Mureb, Sabrina L. Zeller, Eris Spirollari, Simon Hanft, Chirag D. Gandhi, Meena Jhanwar-Uniyal. Molecular markers in brain metastases: Role of PI3K/mTOR pathway in epithelial-to-mesenchymal transition [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 5129.