Patient-derived xenograft approach to explore differential responses to diet dependent on genotypic or phenotypic characteristics of colorectal cancer

Colorectal cancer (CRC), the third most common cause of cancer death worldwide, results from the combination of multiple genetic and epigenetic alterations and environmental risk factors. Several evidence indicate that dietary factors may have a role in the development and prevention of CRC, but more research is needed to clarify the heterogeneity of dietary associations with CRC. We aim at dissecting the role of lipid-rich diet on CRC progression exploiting the patient-derived tumor xenograft (PDX) model, implanting subcutaneously human CRCs at different staging into immunodeficient mice, and feeding with control normal diet (ND) and classical western diet (WD). The response to WD was heterogeneous among all generated PDXs. Only one out of four (CRC at stage IIIc) showed a greater and faster growth in mice fed with WD. Particularly, WD induced transcriptomic perturbations of several genes related to epigenetic regulations; tumor progression, activating RAS/RAF/MAPK signaling, remodeling tumor microenvironment, promoting mucin secretion, mitochondria dysfunction and metabolic reprogramming to aerobic glycolysis to sustain the increased energy demand. This metabolic switch mediated by WD was confirmed by metabolomic analysis in which enhanced glucose and glutamine consumption was observed. Interestingly, the three PDXs responded to the same WD with a distinct metabolomic profile. The same heterogeneous response to WD in tumor growth was observed in xenografts generated with CRC cell lines where WD led to an altered mitochondrial metabolism. Whole exome sequencing revealed somatic cancer mutations affecting some signaling pathways that could play a key role in conditioning response to a specific diet. Interestingly, PDXs did not share the same genetic mutations. To better address the role of different lipid sources in promoting tumor growth, we tested in comparison to classic WD, humanized WD diet, with different lipid source that strictly mimics human diet rich in lipids. Accordingly, CRCs displayed a different tumor growth in response to humanized WD. The analysis of patient derived organoids developed from PDX fed with humanized diets revealed that the altered metabolic reprogramming acquired in vivo is also maintained in vitro in absence of any stimulus, suggesting a metabolic memory of cancer cells. Overall the observed heterogeneous response between patients supports that dietary factors are involved in tumor progression, but also confirms the suspect that the correlation between diet and CRC can be due to intrinsic properties of the tumor. Specific CRC somatic mutations, modifying several signaling pathway and tumor metabolism promote tumor growth and progression, and could be predictive of a response to a specific diet. In this scenario, PDX could be considered as a suitable approach to study the response to the diet and to provide a screening of different diets in order to create a dietary guidance for CRC patients.