Objective: To investigate the specificity and inhibitory mechanism of RNA interference technology for gastric carcinoma gene therapy by inhibiting COX-2 in nude mice.Methods: Small interference RNAs targeting COX-2 gene were designed.pTZU6+1-siRNA-COX-2 vector was constructed and transfected into hypodermical gastric tumor in nude mice to induce RNAi.The changes of COX-2 gene expression were detected with RT-PCR and immunochemistry

and the expression of PCNA and Ki67 were tested by Western blot.Results: The expression of COX-2 was remarkably inhibited by RNAi in vivo.Tumor size decreased significantly after pTZU6+1-siRNA-COX-2 vector was injected to tumor;the mRNA level of COX-2 decreased from 98.36% to 43.44%

and its protein expression also reduced from 86.24% to 47.59%.PCNA and Ki67 proteins were down-regulated.In contrast

there were almost no changes in control group.Conclusion: RNAi inhibits the COX-2 gene expression and tumor growth with good specificity

which may be the result of up-regulating of p53 protein and down-regulating PCNA and Ki67 proteins.