HIF-1α is a crucial factor in the development of peritoneal dissemination via natural metastatic routes in scirrhous gastric cancer

The molecular mechanisms underlying the peritoneal dissemination of gastric cancer remain unclear. Using in vivo metastatic models, this study attempted to clarify the role of hypoxia inducible factor (HIF)-1 alpha in the development of peritoneal dissemination of gastric cancer. HIF-1 alpha knockdown (KD) cells were established in the scirrhous gastric cancer cell line 58As9. Using KD and control (SC) cells, the presence of peritoneal dissemination was assessed in orthotopic implantation (o.i.) and intraperitoneal injection (i.p.) models. A series of in vitro analyses were also conducted. Finally, tumor angiogenesis was immunohistochemically analyzed. In the o.i. model, peritoneal dissemination was more frequently observed in the SC mice (93%) compared to the KD mice (13%) (P<0.001). In the i.p. model, peritoneal dissemination occurred at a high rate in both types of mice; however, a greater number of nodules was observed in the KD mice (P=0.017). The in vitro assays showed that HIF-1 alpha exerts unfavorable effects on anoikis resistance and adhesion to extracellular matrix. Angiogenesis and vascular invasion were more aggressive in the SC gastric tumors. Vascular invasion was present in the intratumoral regions of the disseminated nodules in the SC o.i., but not the i.p., mice. HIF-1 alpha was found to be crucial for the development of peritoneal dissemination in o.i. model, which mimics natural metastasis. In contrast, HIF-1 alpha played an inhibitory role in suppressing peritoneal dissemination in the i.p. model. These results indicate that peritoneal dissemination in o.i. mice may not act through a seeding mechanism. An immunohistochemical analysis demonstrated HIF-1 alpha-activated angiogenesis and vascular invasion in stomach tumors. Furthermore, the results showed that the disseminated nodules observed in SC o.i. mice were formed via extravasation of cancer cells. We provide a possible mechanism in which peritoneal dissemination of gastric cancer develops via a vascular network whereby HIF-1 alpha activates tumor angiogenesis.