SUMMARY In response to the burgeoning worldwide obesity pandemic, the rate of obesity-associated colorectal cancer (CRC) remains an enormous public health burden. The metabolic determinants of CRC are complex and remain under debate. Ceramides are pathogenic lipids that signal a state of nutrition excess and accumulate in organs that are not suited for fat storage, driving insulin resistance and dyslipidemia. Our preliminary data also demonstrate that ceramides are critical intermediates linking nutritional inputs like fatty acids to intestinal stem cell proliferation. Our long-term goal is to understand the role of ceramide metabolism in the development of CRC and to identify pharmacologic and dietary strategies to intervene upon ceramide metabolism for cancer prevention. Our central hypothesis is that ceramide metabolism is a key component of metabolic dysregulation underlying CRC. We propose a transdisciplinary collaboration, utilizing epidemiologic and clinical cohorts and animal experiments, to conduct synergistic analyses and interventions to address our hypothesis. In Aim 1a, using a rigorous discovery-replication design, we will characterize a ceramide-based CRC risk score in serum from participants in the European Prospective Investigation into Cancer and Nutrition (EPIC) (n=1260cases/1260 controls), and the Prostate, Lung, Colorectal and Ovarian (PLCO) cancer cohort (n=1234 cases/1234 controls), and identify a dietary pattern strongly linked to ceramides. In Aim 1b, we will determine the effects of medical and surgical weight loss and changes in body composition on the ceramide CRC risk score in our ongoing Utah Bariatric Surgery Cohort. In Aim 1c, we will measure the association of genetically predicted levels of circulating ceramides with risk of CRC using data from 57,873 CRC cases and 67,087 controls in the Genetics and Epidemiology of CRC Consortium (GECCO), and test for gene by dietary pattern interaction. In Aim 2, we will determine whether systemic or tissue-specific reduction of ceramides affects CRC development. We will impede ceramide synthesis by inhibiting dihydroceramide desaturase-1 (DES1) action genetically (Aim 2a) and pharmacologically (Aim 2b), and via a serine or time restricted dietary pattern (Aim 2c), to test for effects on gut, liver and adipose depots and colorectal tumor incidence in an azoxymethane mouse model of CRC. The study leverages a new class of DES1 inhibitors that lower tissue ceramides and ameliorate the pathogenic consequences of obesity. The proposed study fills a major gap in evidence for understanding how ceramides contribute to the metabolic dysregulation underlying CRC. We propose a fully translational approach integrating epidemiologic associations between ceramides and colorectal malignancies and preclinical studies testing the utility of ceramide-lowering interventions on cancer endpoints. Findings will have important implications for understanding the biologic mechanisms underpinning obesity-associated metabolic dysregulation in CRC and for identifying new targets for CRC prevention.

NARRATIVE Ceramides are products of fat and protein metabolism that accumulate in individuals with obesity or dyslipidemia and are strongly linked to insulin resistance. Herein we propose to leverage large-scale epidemiologic and clinical cohorts to identify associations of ceramides with colorectal cancer risk, and animal experiments to study the efficacy of new ceramide-lowering interventions. Our study will clarify the key role of ceramides in the metabolic dysregulation underlying colorectal cancer and identify new targets for colorectal cancer prevention.