Objective    To explore the effect RNAi-mediated inhibition of X-linked inhibit apoptosis protein (XIAP) gene on apoptosis and susceptibility to chemical therapy drugs in osteosarcoma cells and its underlying mechanism .    Methods    shRNA plasmid of XIAP gene were constructed. MG63 cells were conventionally cultured and divided into untreated group (group A

non-transfection)

blank plasmid group (group B

psiRNA-Con transfected)

the experimental group (group C

psiRNA-XIAP transfected)

and 2 chemical drug interfered groups

non-transfection+0.3 μmol Dox group (A+Dox group) and psiRNA-XIAP transfection +0.3 μmol Dox group (C+Dox group). The XIAP expression in MG63 cells was detected by Western blotting. The proliferation of above-mentioned MG63 cells was examined by MTT assay. Flow cytometry (FCM) was employed to detect the cell apoptosis

cell cycle and Caspase-9 expression.     Results    Group C had a significantly lower protein level of XIAP and MTT value than group A and B (P0.05)

and had higher apoptotic rate

stronger Caspase-9 expression and larger percentage of G

2

/M arrested cells than group A and B. In C+Dox group

MTT value was more lower and Caspase-9 expression more higher than in A+Dox group (P0.05). There was no cell at G

2

/M stage in C+ Dox group

and its cell cycle was blocked before S stage.     Conclusion     RNAi could specifically suppress XIAP gene expression

effectively inhibit the proliferation and accelerate the apoptosis of MG63 cells

and enhance its susceptibility to chemical therapy drug. The mechanism may be related to the suppression of DNA synthesis and the activation of Caspase signaling pathway.