Biological Function and Prognostic Significance of Peroxisome Proliferator-Activated Receptor δ in Rectal Cancer

Purpose: To investigate the expression significance of PPAR beta/delta in relation to radiotherapy (RT), clinicopathologic, and prognostic variables of rectal cancer patients. Experimental Design: We included 141 primary rectal cancer patients who participated in a Swedish clinical trial of preoperative RT. Tissue microarray samples from the excised rectal cancers and the adjacent or distant normal mucosa and lymph node metastases were stained with PPAR delta antibody. Survival probability was computed by the Kaplan-Meier method and Cox regression model. The proliferation of colon cancer cell lines KM12C, KM12SM, and KM12L4a was assayed after PPAR delta knockdown. Results: PPAR delta was increased from adjacent or distant normal mucosa to primary cancers, whereas it decreased from primary cancers to lymph node metastases. After RT, PPAR delta was increased in normal mucosa, whereas it decreased in primary cancers and lymph node metastases. In primary cancers, the high expression of PPAR delta was related to higher frequency of stage I cases, lower lymph node metastasis rate, and low expression of Ki-67 in the unirradiated cases, and related to favorable survival in the cases either with or without RT. The proliferation of the KM12C, KM12SM, or KM12L4a cells was significantly accelerated after PPAR delta knockdown. Conclusions: RT decreases the PPAR delta expression in primary rectal cancers and lymph node metastases. PPAR delta is related to the early development of rectal cancer and inhibits the proliferation of colorectal cancer cells. Increase of PPAR delta predicts favorable survival in the rectal cancer patients either with or without preoperative RT. Clin Cancer Res; 17(11); 3760-70. (C)2011 AACR.