Background: Cyclooxygenase-2 (COX-2) is overexpressed in colon cancers. The plasminogen activation (PA) system relates to cancer invasion and metastasis through the degradation of the extracellular matrix. COX-2 also relates to degradation of the extracellular matrix, but the relationship between COX-2 and the plasminogen activator system is unclear.
Study design: In vivo: Colon 38 (G0) primary and (G5) metastatic cell lines were implanted in C57BL/6 mice treated with or without COX-2 inhibitor (NS-398). Animal survival and tumor growth were measured. On day 19, tumors were excised and tumor cell apoptosis measured. For metastasis, G5 cells were injected into the spleen, and, after 23 days, liver metastasis was determined. In vitro: G0 or G5 cells were treated with NS-398. Supernatant prostaglandin E2 and mRNA expressions of COX-2, vascular endothelial growth factor (VEGF), urokinase-type plasminogen activator (u-PA), u-PA receptor, plasminogen activator inhibitor type-1 (PAI-1), and PAI-2 were measured. Tumor cell proliferation was also determined.
Results: In vivo: Mean survival of NS-398-treated animals was higher than controls for both G5 and G0 (G5: p < 0.003, G0: p < 0.02). G5 tumors grew faster than G0 tumors (p < 0.001) and NS-398 significantly inhibited tumor growth (p < 0.001), induced tumor cell apoptosis (p < 0.001), and significantly reduced metastasis (p < 0.003) in G5 animals. In vitro: PGE(2) production was higher in G5 than G0 cells (p < 0.001); NS-398 significantly reduced prostaglandin E(2) levels in G5 cells (p < 0.001). mRNA expression of COX-2, vascular endothelial growth factor, and u-PA receptor was higher in G5 than G0 cells, and NS-398 significantly inhibited u-PA mRNA expression in G5 cells. NS-398 significantly reduced proliferation in G5 cells (p < 0.05).
Conclusions: COX-2 inhibition significantly decreases tumor growth in this model by inducing apoptosis and blocking u-PA production in G5 colon cancer cells, which is associated with significant inhibition of liver metastases.