Nitric Oxide (NO) and Cyclooxygenase-2 (COX-2) Cross-Talk in Co-Cultures of Tumor Spheroids with Normal Cells

Cyclooxygenases (COX), prostaglandin E(2) (PGE(2)) and nitric oxide (NO) are believed to be some of the most important factors related to colon cancer growth and metastasis. In this study, we aimed to investigate the associations between COX-2, PGE(2) and NO in co-cultures of human colon cancer spheroids obtained from different tumor grades with normal human colonic epithelium and myofibroblast monolayers. L-arginine (2 mM), a substrate for nitric oxide synthases (NOS), decreased COX-2 and PGE(2) levels, while N( G )-nitro-L-arginine methyl ester (L-NAME) (2 mM), a NOS inhibitor, had no influence on COX-2 and PGE(2) levels but limited tumor cell motility. NS398 (75 μM), a selective COX-2 inhibitor, had no significant influence on NO level but decreased motility of tumor cells. COX-2, PGE(2) and NO levels depended on the tumor grade of the cells, being the highest in Duke's stage III colon carcinoma. Summing up, we showed that addition of L-arginine at doses which did not stimulate NO level caused a significant decrease in COX-2 and PGE(2) amounts in co-cultures of colon tumor spheroids with normal epithelial cells and myofibroblasts. Any imbalances in NO level caused by exogenous factors influence COX-2 and PGE(2) amounts depending on the kind of cells, their reciprocal interactions and the local microenvironmental conditions. The knowledge of these effects may be useful in limiting colon carcinoma progression and invasion.