OBJECTIVE: To investigate the correlation between cyclin-dependent kinase inhibitor p27kip1 and trastuzumab-resistance in gastric cancer.
 METHODS: We selected HER2-overexpressed human gastric cancer cell line NCI-N87 to establish trastuzumab-resistant NCI-N87/TR cell line by stepwise exposure to different doses of trastuzumab. The 50% inhibitory concentration (IC(50)) of trastuzumab and resistance index (RI) were calculated or analyzed by MTT assay. The expression levels of cdk2 and p27kip1 were detected by Western blot. After the treatment with cdk2 inhibitor (Purvalanol A), the expression levels of relevant proteins in NCI-N87/TR cells were detected by Western blot, and the sensitivity to trastuzumab was analyzed by MTT assay. 
 RESULTS: Compared with NCI-N87 cells, the expression of cdk2 was significantly increased in NCI-N87/TR cells (P<0.001), while the expression of p27kip1 showed a significant decrease (P<0.001). Restoration of the p27kip1 protein expression by cdk2 inhibitor (Purvalanol A) increased the sensitivity of NCI-N87/TR to trastuzumab.
 CONCLUSION Down-regulation of p27kip1 might be a mechanism for triggering trastuzumab resistance to gastric cancer cell line NCI-N87.
Antineoplastic Agents ; pharmacology ; Cell Line, Tumor ; Cyclin-Dependent Kinase 2 ; antagonists & inhibitors ; genetics ; metabolism ; Cyclin-Dependent Kinase Inhibitor p27 ; genetics ; metabolism ; Drug Resistance, Neoplasm ; Humans ; Purines ; pharmacology ; Stomach Neoplasms ; genetics ; metabolism ; pathology ; Trastuzumab ; pharmacology