PROJECT SUMMARY/ ABSTRACT Colorectal cancer (CRC) is the third most diagnosed cancer in the United States. Though CRC cases in adults (55 and older) have decreased, the incidence of CRC in young adults, ages 15-40, is on an alarming rise. It is estimated that by the year 2030, a staggering 11-12% increase in early-onset (EO) cancers will be observed. Adult cases of CRC typically harbor driver mutations in Apc, a tumor suppressor that regulates Wnt signaling, in addition to second hits in Kras, Braf, p53 and Smad4. Apc mutations are also found in early-onset CRC (EO- CRC), but a decrease in the typical second hit driver pathways has been reported. Therefore, there is an urgent need to better define the root cause of EO-CRC. Moreover, clinical evidence suggests that diet is likely a root underlying cause of the increased incidence in sporadic cases of EO-CRC. Interestingly, dietary challenge and timing of food intake directly impinge on the circadian clock, which is our internal pacemaker that governs sleep/wake cycles, feeding, hormonal and other cyclic rhythms. This suggests that disruption of the circadian clock could be a major risk factor for EO cancers. In further support of this idea, clinical data indicates that clock genes are broadly downregulated in human colorectal tumors, suggesting that suppression of the clock could be important for transformation in the intestinal epithelium. To directly address the potential links between the clock and CRC, we have developed a novel genetic mouse model to define how disruption of the circadian clock drives CRC pathogenesis. Our preliminary data demonstrates that disruption of the clock in the intestinal epithelium drives a statistically significant increase in polyp formation. Using our mouse model system, organoid cultures reveal that clock disruption accelerates transformation in the intestinal epithelium. Based on these findings, we hypothesize that clock disruption impinges on intestinal transformation and rewires cellular metabolism to sustain the heightened demand of hyperproliferative cells. Aim 1 will define how the clock machinery regulates genome instability and transformation in the intestine. Aim 2 will determine the role of the circadian clock in governing metabolism of intestinal epithelial cells in both mouse and human organoid systems, established from EO-CRC patient samples. Aim 3 will delineate how dietary paradigms that disrupt the circadian clock accelerate intestinal transformation. The broader impact of our findings will outline new prevention strategies for eradicating EO-CRC and other cancers that potentially relate to disruption of the circadian clock. Additionally, our long-term goal is to achieve targeted pharmacological approaches to regulate the circadian clock and therefore minimize behavioral and lifestyle factors that potentially impinge on tumorigenesis.