Objective  In a previous study, we found that low doses of cyclooxygenase-2 (COX-2) selective inhibitors could induce the proliferation of esophageal squamous cell carcinoma (ESCC) cells, which can be attributed to the activation of a 5-lipoxygenase (5-LOX) shunt by slight COX-2 inhibition. The objective of the present study was to determine whether highly effective COX-2 siRNA inhibition can avoid this shunt.

  Methods  TE-1 and Eca109 (ESCC) cells were divided into blank control, liposome transfection, random sequence siRNA, and COX-2 siRNA groups. Cell proliferation was assessed using Cell Counting Kit-8 assay. Protein and mRNA expressions were determined using Western blot analysis and RT-PCR, respectively. Prostaglandin E2 and leukotriene B4 (LTB4) levels were measured by enzyme-linked immunosorbent assay. A flow cytometer was used for cell cycle measurement.

  Results  Compared with the blank controls, COX-2 siRNA-transfected TE-1 and Eca109 cells showed 79% and 73% inhibition of COX-2 expression, respectively, as well as 45.86% and 48.99% inhibition of cell proliferation, respectively (P < 0.05). The expression of 5-LOX remained unchanged (P>0.05), and prostaglandin E2 and LTB4 levels were highly in accordance with alterations in COX-2 and 5-LOX expressions, respectively. The percentages of cells in G1 stage increased significantly. Bcl-2 expression decreased, whereas the expressions of caspase-9 and Bax increased in the two ESCC cells after COX-2 siRNA transfection (P < 0.05).

  Conclusions  Highly effective inhibition of COX-2 expression may prevent the activation of 5-LOX and the following up-regulation of LTB4, which is a cell proliferation factor. These suggest that only high-dose COX-2 selective inhibitors with significant COX-2 inhibitory effects can achieve anti-cancer effects in ESCCs.