Targeting Lipid Metabolism in Colorectal Cancer

Metastasis is the main cause of death from solid tumors including colorectal cancer (CRC). Our long-term goal is to develop more selective therapeutic options to prevent or reduce the incidence of CRC metastasis by understanding how changes in fatty acid metabolism contribute to metastatic disease. Fatty acid synthase (FASN), a key enzyme of de novo lipid synthesis, is significantly upregulated and activated in CRC, and its activity is associated with poor prognosis, higher risk of disease recurrence, and death. We identified FASN as a potential target for advanced CRC and showed that upregulation of this enzyme is a key mechanism supporting metastasis in CRC. However, the underlying mechanisms of FASN regulation of metastasis and potential mechanism of resistance to FASN inhibition are not understood. The current application proposes a comprehensive research plan to study novel mechanisms of regulation of CRC metastasis by lipid metabolism. Our preliminary data suggest that the primary product of de novo fatty acid synthesis, palmitate, is selectively used for sphingolipid synthesis. Overexpression of FASN selectively regulates activity of SphK1 and SphK2 and increases the level of sphingosine-1-phosphate (S1P), a bioactive sphingolipid implicated in metastasis. Therefore, in Aim 1, we will test the hypothesis that FASN enhances metastasis by upregulating the SphK/S1P axis and we will determine the contributions of SphK1 and SphK2 to CRC metastasis. Furthermore, our preliminary studies show a correlation between expression of FASN and CD36, a fatty acid translocase responsible for exogenous FA uptake. Our data show that inhibition of FASN leads to upregulation of CD36 and it can be a potential mechanism of resistance to novel FASN inhibitors that are currently being tested in Phase II clinical trials. Therefore, in Aim 2, we will elucidate how FASN regulates CD36 and determine molecular mechanisms by which upregulation of CD36 contributes to CRC metastasis including the effect of CD36 upregulation on sphingolipid metabolism and S1P synthesis. In Aim 3, we will test whether inhibition of FA uptake via CD36 will increase efficacy of a novel FASN inhibitor TVB-3664 in CRC. We will utilize biological samples from patients, human primary CRC cells, tumor organoids established from genetically modified mice and CRC metastasis models, which are the most advanced models for pre-clinical target and drug evaluations. These models will be used in conjunction with state-of-the-art approaches, including targeted and stable isotope-resolved metabolomics (SIRM), to evaluate the effect of alteration in lipid synthesis and FA uptake on cancer cell metabolism. These studies have a high translational impact since CD36 and FASN inhibitors are currently tested in multiple pre-clinical studies and Phase I-II clinical trials and there is urgent need for more research and knowledge on their effects in CRC. Beside validation of FASN, SphKs and CD36 as therapeutic targets in CRC, the comprehensive analysis of metabolic and signaling pathways proposed in the current application also have the potential to identify new druggable targets and therapeutic strategies for CRC.