Antiangiogenic effect of somatostatin receptor subtype 2 on pancreatic cancer cell line:Inhibition of vascular endothelial growth factor and matrix metalloproteinase-2 expression in vitro

摘要

AIM:To investigate the anti-angiogenic effect of somatostatin receptor subtype 2 (SSTR2) gene transfer into pancreatic cancer cell line PC-3, and the mechanisms involved in this effect.METHODS: The full length human SSTR2 cDNA was introduced into pancreatic cancer cell line PC-3 by lipofectamine-mediated transfection. Positive clones were screened by G418 and stable expression of SSTR2 was detected by immunohistochemistry SABC methods and RT-PCR. Enzyme-linked immunosorbent assay (ELISA) was used to detect vascular endothelial growth factor (VEGF) levels in the cell culture supernatants of SSTR2-expressing cells, vector control and mock control cells. Furthermore, the expressions of VEGF and matrix metalloproteinase-2 (MMP-2) were detected by immunohistochemistry SABC methods and RT-PCR in these cells.RESULTS: VEGF levels in the cell culture supernatants were significantly reduced in the SSTR2-expressing cells (first week,172.63±21.2ng/L and after two months, 198.85±26.44ng/L)compared with the vector control (first week, 790.39±86.52ng/L and after two months, 795.69±72.35ng/L) and mock control (first week, 786.42±90.62ng/L and after two months,805.32±84.36ng/L) (P<0.05).The immunohistochemical assay showed a significant reduction of the integral optical density of VEGF and MMP-2 in the SSTR2-expressing cells (42.25±8.6 and 70.5±6.25, respectively) compared with the vector control (85.75±12.9 and 110.52±13.5, respectively) and mock control (82.6±9.28 and 113.56±9.62,respectively) (P<0.05).Conversely, the average gray value of VEGF and MMP-2 was significantly increased in the SSTR2-expressing cells (121.56±8.43 and 134.46±19.95, respectively) compared with the vector control (55.72±5.6 and 62.26±12.68,respectively) and mock control cells (58.48±6.2 and 65.49±9.16, respectively) (P<0.05). Moreover, the expressions of VEGF mRNA and MMP-2 mRNA were significantly reduced in the SSTR2-expressing cells (0.1384±0.017 and 0.2343±0.070, respectively) compared with the vector control (1.024±0.117 and 0.806±0.119,respectively) and mock control (1.085±0.105 and 0.714±0.079,respectively) (P<0.05).CONCLUSION: The expression of reintroduced human SSTR2 gene exerts its antiangiogenic effects by downregulating the expressions of the factors involved in tumor angiogenesis and metastasis, suggesting SSTR2 gene transfer as a new strategy of gene therapy for pancreatic cancer.