Breast cancer remains a significant health challenge, with high mortality rates associated with metastatic disease. Triple-negative breast cancer (TNBC) is a particularly aggressive form of breast cancer that lacks effective treatment options. The expression of the protein deacetylase Sirtuin 1 (SIRT1) is significantly downregulated in TNBCs compared to other forms of breast cancer or normal mammary tissue, and this is associated with increased metastasis by TNBC cells. Previous studies have shown that the SIRT1 reduction in breast cancer cells promotes their aggressiveness by altering the secretion and molecular cargo of cancer cell produced exosomes, a major form of extracellular vesicles (EVs) that are derived from the endo-lysosomal degradation pathway. They play a critical role in intercellular communication and cancer progression by transferring cargo between cancer cells and other cancer cells, as well as non-cancer cell types within the local tumor microenvironment (TME) and at distant sites. Hence, I hypothesize that the loss of SIRT1 promotes breast cancer metastasis by transferring exosomes that are enriched with specific cargo to the TME. The proposed research will specifically utilize in vivo mouse models to determine if the loss of SIRT1 in breast cancer promotes the production of exosomes that re-shape the TME, promote the establishment of the pre-metastatic niche, and ultimately drive metastatic spread. Additionally, I will perform untargeted metabolomics to identify metabolite cargo that are enriched in exosomes derived from SIRT1-depleted cancer cells, and then investigate their contribution to promoting aggressive phenotypes. The proposed research has the potential to uncover novel mechanisms underlying SIRT1-regulated exosome production in promoting breast cancer metastasis and identify novel potential therapeutic targets.