Somatostatin enhances growth inhibition by cisplatin in gallbladder cancer cells through inducing PTEN expression

Abstract

Objective To investigate the combined effects of somatostatin (SST) and cisplatin (DDP) on proliferation and apoptosis in gallbladder cancer cells, and to investigate the mechanism of the combined effects. Methods We performed immunohistochemistry to detect the PTEN expression in gallbladder cancer. We then investigated the combined effects of SST and DDP on cell proliferation in vitro with CCK-8 assay and analyzed the interaction between these two drugs using isobologram analysis. We also investigated the combined effects on cell proliferation in vivo using a xenograft nude mouse model. FITC-Annexin V/PI assay and TUNEL staining assay were performed to detect the proportion of apoptosis after combined treatment in vitro and in vivo. Reactive oxygen species and mitochondrial membrane potential were detected with DCFH-DA assay and JC-1 staining assay after the combined treatment. We finally detected the PTEN and p-AKT associated proteins using western blotting after the combined treatment. Results PTEN was abnormally decreased in gallbladder cancer tissues. PTEN expression was negatively correlated with cancer differentiation and was positively correlated with patients' survival time. DDP treatment decreased while combined treatment with SST induced PTEN expression and inhibited AKT activation by reversing resistance to DDP. Isolated SST or DDP treatment inhibited gallbladder cancer GBC-SD and SGC996 cell proliferation which was dose-dependence. These two drugs synergistically inhibited gallbladder cancer cell growth in vivo and in vitro. Isolated SST or DDP treatment induced cell apoptosis and combined treatment induced cell apoptosis the most. SST inhibited AKT activation but did not induce ROS. DDP induced ROS resulting in increased cell apoptosis. Either SST or DDP alone increased the levels of cytoplasmic cytochrome C protein and activated caspase-3. Conclusions SST enhanced growth inhibition by cisplatin in gallbladder cancer cells through inducing PTEN expression. This study provides the theoretical basis for further combined clinical chemotherapeutic applications. Key words: Somatostatin; Cisplatin; PTEN protein; Gallbladder cancer