Determining the Significance of a Novel Disease Inducing Rodent Diet on Adenocarcinoma Growth In Vivo

Diet and diet-induced morbidities (such as obesity) are leading risk factors for the development of various forms of cancer worldwide. However, the physiological mechanisms responsible for the interaction of diet and cancer growth are still unclear. Mechanistic studies in animals support the interaction of diet with cancer development and progression, however the animal diets used do not adequately model the true nutritional quality of many Americans. We have developed a novel disease inducing rodent diet referred to as the Americanized diet (AD) that embodies the complex nutritional profile of Americans while also accounting for the differences in human and rodent nutritional requirements. We set out to determine how consumption of the AD would influence the growth of the MC-38 murine adenocarcinoma cells in vivo. All animal experiments were performed following animal protocols approved by the Liberty University IACUC and conform to the FASEB Statement of Principles for the use of animals in research and education. Weanling C57Bl/6 male mice were given ad libitum access to the AD (n=5) or standard rodent chow (n=5) and ddH2O. Food intake and body weights were calculated weekly and circulating total cholesterol (CHOL), HDL-cholesterol (HDL), triglycerides, and glucose were quantified at baseline and again at the end of the study. After 6 weeks, mice were injected with 0.5×106 MC-38 adenocarcinoma cells in the rear flank and injection site was monitored for the presence of a palpable tumor. Tumor volume was calculated using calipers and, after 3 weeks, tumor blood flow was estimated using contrast-enhanced ultrasonography. Animals were then euthanized and tumor tissues collected for assessment of leukocyte content by flow cytometry and quantification of interleukin-10 (IL-10), major histocompatibility complex H2K, and vascular endothelial growth factor (VEGF) gene expression by RT-PCR. Body weights and tumor volumes were analyzed using generalized linear models and the remaining parameters were analyzed using GLM multivariate analyses in SPSS. Mice assigned to ad libitum feeding of the AD consumed more calories and gained more weight (P=0.01) as compared to mice consuming standard chow. After 6 weeks of consuming the diet, mice fed the AD had greater HDL cholesterol (P=0.03); however this difference was lost after MC-38 innoculation (P=0.2). MC-38 growth was significantly reduced (P=0.004 and 0.07 at weeks 1 and 2, respectively) in mice consuming the AD as compared to mice consuming chow. Interestingly, no palpable tumor was observed in 2 of the 5 mice consuming the AD while all 5 mice consuming chow developed tumors. There was a greater relative tissue perfusion (P=0.02) in the tumor-bearing mice fed the AD as compared to the mice fed chow. No difference was observed in the proportion of tumor leukocytes amongst the diets. Similarly, RT-PCR revealed no difference in IL-10, H2K or VEGF gene expression between treatment groups (P= 0.25, 0.98, 0.62 respectively). Based on this study, mice fed the AD had reduced growth of the MC-38 murine adenocarcinoma cell line in vivo despite having greater body weight and caloric intake. While we were unable to detect a significant difference in tumor leukocyte content and/or the expression of IL10, H2K, and VEGF at the end of the study, it is possible these outcomes differed during earlier time points (weeks 1 and 2) and contributed to the reduced tumor growth observed in mice fed the AD