Abstract: ObjectiveTo investigate the relationship between miR21 expression and sensitivity of gastric cancer cells to apatinib and its possible mechanism. 
MethodsAGS cells and drugresistant AGSAR cells were cultured in vitro and transfected with miR21 inhibitor or miR21 mimics respectively. QPCR was used to detect the expression level of miR21 in AGS and AGSAR cells. QPCR was used to detect the effects of apatinib on the expression of pVEGFR2 and pAkt mRNA in AGS and AGSAR cells with different concentrations （0， 2， 5， 10 μmol／L）， as well as the effects of different miR21 expressions on the pVEGFR2， pAkt and pAkt expression levels of AGS and AGSAR cells. The effects of apatinib on proliferation and migration of AGS and AGSAR cells were detected by MTT and scratch test. 
ResultsThe expression of miR21， pVEGFR2 and pAkt in AGS cells were 082±009， 073±009 and 068±008 respectively， which were higher than 035±010， 033±007 and 025±004 of AGSAR， and the difference was statistically significant （P＜005）. After the treatment of apatinib， the proliferation and migration activity of AGSAR cells was significantly higher than that of AGS cells （P＜005）. After 10 μmol／L apatinib treatment for 24 h， the survival rate and migration distance of AGS cells in negative control group were （3948±745）％ and （7044±1157） μm respectively， significantly lower than that of miR21 inhibitor transfected AGS cells [（8063±827）％ and （10846±1039） μm]， and the difference was statistically significant （P＜005）. The survival rate and migration distance of AGSAR cells in negative control group （7882±814）％ and （9315±986） μm were significantly higher than （2995±674）％ and （6143±985） μm of AGSAR cells transfected by miR21 mimics， and the difference was statistically significant （P＜005）. After transfection of miR21 inhibitor， the relative expression levels of pVEGFR2 and pAkt mRNA in AGS cells were 112±013 and 082±010 respectively， which were significantly higher than 073±011 and 064±011 in the negative control group， while the expression level of PTEN mRNA was down （018±004 vs. 051±008）， and the differences were statistically significant （P＜005）. After transfection of miR21 mimics， the relative expression levels of pVEGFR2 and pAkt mRNA in AGSAR cells were 017±004 and 012±003 respectively， which were significantly lower than 030±004 and 025±002 in the negative control group， while the expression level of PTEN mRNA was up （053±006 vs. 044±003）， and the difference was statistically significant （P＜005）. 
ConclusionUp regulation of miR21 expression can increase the phosphorylation level of VEGFR2 and Akt， thereby enhancing the sensitivity of gastric cancer cells to apatinib.

Key words: Gastric cancer, microRNAs, Apatinib, Sensitivity, Angiogenesis