Establishment of hypoxia induction in an in vivo animal replacement model for experimental evaluation of pancreatic cancer.

Transplantation of tumor xenografts to fertilized chicken eggs is a promising animal replacement method, which has successfully been used for xenotransplantation of pancreatic ductal adenocarcinoma (PDA) cells. PDA is characterized by a pronounced tumor hypoxia, which mediates aggressive growth, therapy resistance and cancer stem cell (CSC) features. For in vivo experimental evaluation of hypoxia-targeting therapeutic strategies, the xenografting of tumors to chicken eggs combined with the induction of hypoxia is necessary. However, the chicken embryos do not survive the conventional method of hypoxia induction by a gas mixture of 1% O2, 5% CO2, 94% N2, not even when hypoxia is applied for only 30 min. Therefore, we employed chemical induction of hypoxia by the hypoxia mimetic agent cobalt chloride (CoCl2). Whereas CoCl2 did not further increase tumor growth, it mediated the induction of carbonic anhydrase IX (CAIX) in the tumor xenografts and led to enhanced expression of the human CSC markers CD133, Sox2 and CD44. Side-effects in chicken embryos were not observed as evaluated by H&E staining of embryo-derived liver sections and the determination of the embryo weight. These results suggest the successful induction of hypoxia in chicken eggs and xenografted tumors by CoCl2. For therapeutic intervention and as a control, we treated the eggs with the plant-derived anti-inflammatory agent triptolide, which recently showed promising effects toward hypoxia-induced tumor progression in experimental PDA. Triptolide abolished tumor growth and the CoCl2-induced hypoxic effects, without inducing obvious side-effects. Collectively, our data present a new in vivo animal replacement method for the successful induction of tumor hypoxia in PDA.