Effects of High-Fat and Low-Carbohydrate Diet Combined with Radiation Therapy on Tumor Microenvironment in LLC Tumor-Bearing Mice

e20543 Background: Metabolic reprogramming of tumor immune cells can regulate immune function. To add a sentence linking tumor metabolism with radioimmunity. In this study, the high heterogeneity and reprogramming of tumor cell metabolism were utilized to explore the effects of high fat and low carbohydrate diet combined with radiotherapy on tumor immune microenvironment of tumor mice bearing LLC from the perspective of tumor microenvironment. Methods: Lewis lung cancer (LLC) model was established in female C57BL/6J mice aged 6 to 8 weeks and around 18g, and they were given a high fat and low carbohydrate diet (45F, fat 45.00% of energy) combined with radiotherapy. The body weight, tumor growth, blood glucose and blood ketone (βHB) values, survival time, median survival time and treatment safety of tumor-bearing mice were observed. Immunohistochemistry, multiple immunofluorescence and flow cytometry were used to detect the expression of tumor-associated microangiogenesis molecules (CD34), lymphatic microvessels (LYVE-1), collagen fibers and immune cell phenotypes (CD3, CD4, CD8, Treg and PD1). Results: High fat and low carbohydrate diet combined with radiotherapy (45F+RT) group had the best tumor control, and the tumor volume was significantly smaller than the control group (p < 0.001), and tumor weight in the combined treatment group (45F+RT) was significantly lower than that in the normal diet (PT, fat 12.11% of energy) and 45F group (p < 0.001); The blood glucose in 45F group was lower than that in PT group, but there was no statistical difference (p < 0.05); It was found that the βHB value in the high-fat and low-carbohydrate diet group was higher than that in the normal diet group. There were statistically significant differences in the second and third weeks (1.00±0.20mmol/L vs 0.63±0.06mmol/L, 0.90±0.17mmol/L vs 0.70±0.10mmol/L, p < 0.05). The median survival time of mice in each group was 38 days in the PT group, 55 days in the PT+RT group and 41 days in the 45F group, but not in the 45F+RT group. Immunohistochemistry and Multiple immunofluorescence showed that CD8 expression was up-regulated and PD1, CD34, LYVE-1 and collagen fiber expression were down-regulated in 45F+RT group. Flow cytometry showed that the proportion of CD8+T cells in 45F+RT group was higher than that in PT group and PT+RT group (p < 0.05) and higher than 45F group, but the difference was not statistically significant (p < 0.05); The proportion of CD4+T cells in PT+RT and 45F+RT groups was higher than that in PT and 45F groups (p < 0.05); The proportion of Treg in T cells in 45F+RT group was lower than that in PT+RT group, but the difference was not statistically significant (p < 0.05). Conclusions: High fat and low carbohydrate diet combined with radiotherapy can enhance the recruitment and function of immune effector cells in tumor microenvironment and inhibit tumor microangiogenesis, thereby inhibiting tumor growth.