PD33-05 TUMOR-SUPPRESSIVE MICRORNA-29S-MEDIATED NOVEL MOLECULAR PATHWAYS IN RENAL CELL CARCINOMA

insulin signaling in the progression of a murine RCC model using metformin to treat hyperinsulinemia induced by a high-carbohydrate diet. METHODS: pT1-T4 tumor specimens from 99 patients with RCC were evaluated for IR expression by immunohistochemistry. Serum insulin and C-peptide levels were measured. The association between biomarker expression and serum concentration, prognostic factors, and clinical outcomes were assessed. C57BL/6 mice were randomized into four groups: low-carbohydrate diet, high-carbohydrate diet, low-carbohydrate diet þ metformin, and high-carbohydrate diet þ metformin groups. RENCA cells were injected subcutaneously. Body weight, glucose tolerance test, serum insulin level, and tumor volume were evaluated. Immunoblotting was performed to assess the insulin signaling pathway in the murine RCC model. RESULTS: The IR expression level was significantly lower in patients with tumor stage pT2-4 and with a preoperative serum Cpeptide level more than 5.14 ng/mL. High IR expression was an independent predictor of favorable progression-free survival after radical nephrectomy. In vivo progression of RENCA in the murine model was not significantly stimulated by hyperinsulinemia induced by a high-carbohydrate diet. However, in vivo progression of RENCA was significantly inhibited by metformin in both the lowand highcarbohydrate diet groups. IR expression was significantly higher in the tumors from the low-carbohydrate diet group and high-carbohydrate diet plus metformin group than that from the high-carbohydrate diet group. CONCLUSIONS: IR expression in RCC was inversely associated with cancer progression and serum insulin levels in both clinical and murine models. The anticancer effect of metformin in the murine RCC model might be derived from the direct effect of the agent on cancer cells rather than the effect of the lower insulin level. The lower expression of IR in the tumor from patients with a poor outcome might be the result of a higher serum insulin level, which is not strong cause of cancer progression.