Fatty Acid Synthase Driven Exosome Secretion in Colorectal Cancer Metastasis - Abstract Metastasis is the major cause of death in patients with colorectal cancer (CRC). More than 50% of CRC patients develop metastases over the course of their disease, with the liver being the most common site of distant metastasis. Surgery and chemotherapy are standard treatments for metastatic CRC; however, even with systemic regimens, the majority of patients experience recurrence, primarily in the liver. Therefore, there is an urgent need to develop novel, more effective therapeutic strategies for these patients. Establishment of a pre- metastatic niche (PMN) is an essential step in the development of distant metastasis. Primary tumors facilitate this process by secreting tumor-derived factors and tumor-derived exosomes to establish a PMN-permissive microenvironment for metastatic colonization. Exosomes are composed of a lipid bilayer membrane and carry a wide range of bioactive molecules, including lipids, proteins, and nucleic acids. Exosomes promote fibroblast activation, with hepatic stellate cells (HSCs) considered the primary source of cancer-associated fibroblasts (CAFs), which contribute to PMN formation. Fatty acid synthase (FASN), a key enzyme of de novo lipid synthesis, is overexpressed and strongly associated with metastasis and poor prognosis in CRC. FASN catalyzes the biosynthesis of palmitate, an essential component of structural lipids which are crucial for rapid tumor growth, membrane formation, and energy production. Interestingly, we found that FASN overexpression in CRC cells promotes exosome secretion by increasing the number of secreted exosomes. Consistently, pharmacological inhibition of FASN in cancer cells using novel FASN inhibitor TVB-2640 significantly reduces secretion of exosomes. Furthermore, we show that high expression of FASN in CRC cells is associated with an increase in the protein level of FASN in exosomes. Importantly, exosomes secreted by CRC cells with higher expression of FASN have a higher ability to activate HSCs, suggesting the role of FASN in PMN formation. Therefore, we hypothesize that overexpression of FASN promotes liver metastasis via an increase in exosome secretion with distinct cargo that promotes formation of PMN. In aim 1, we will determine if overexpression of FASN in CRC cells promotes CAF phenotype in liver cells via CRC cell-derived exosomes. Expression of FASN will be altered in established and primary CRC cells using genetic and pharmacological approaches, and exosome secretion, cargo, and effect on CAF phenotype will be examined. Clinical specimens will be used to validate our in vitro findings. In aim 2, we will determine if FASN overexpression promotes liver metastasis via CRC cell-derived exosomes in vivo using liver metastasis orthotopic and syngeneic mouse models. Metastasis is the main cause of death in CRC patients due mainly to the lack of effective treatment for managing liver metastasis. Potent and selective FASN inhibitor TVB-2640 is being tested in several clinical trials, thus understanding of the mechanisms by which FASN promotes metastasis will contribute to the development of more efficacious therapeutic strategies using FASN as a therapeutic target.
