Hypoxia generates a more invasive phenotype of tumour cells: an in vivo experimental setup based on the chorioallantoic membrane.

Of all processes involved in carcinogenesis, local invasion and the formation of metastases are the clinically most relevant but the scientifically least well understood at their molecular level. Recent experimental progress has identified that tumour hypoxia not only induces tumour angiogenesis, but also modulates the expression of several genes that have been implicated in tumour invasion and metastasis. Here we developed an in vivo model to understand a number of molecular pathways and cellular mechanisms for tumour invasion in hypoxia. For this purpose fertilized chicken eggs were incubated for 10 days in normoxic conditions. Subsequently colon carcinoma cells (SW-480) were placed on the chorioallantoic membrane. During the following 6 days the eggs were incubated either in normoxic conditions or in stepwise decreasing hypoxic conditions. SW-480 colon carcinoma cells did not invade the epithelial layer in normoxic conditions. In contrast an invasion through the epithelial layer in to the mesoderm was already seen after 3 days when incubated in hypoxic conditions. The chorioallantoic membrane assay described in this paper allows investigating tumour invasion and its cellular mechanisms under defined hypoxic conditions.