Tumor-induced angiogenesis studied in confrontation cultures of multicellular tumor spheroids and embryoid bodies grown from pluripotent embryonic stem cells

Tumor vascularization is the rate-limiting step for the progression of canc er. Differential steps of tumor-induced angiogenesis were studied by a nove l in vitro confrontation culture of avascular multicellular prostate tumor spheroids and embryoid bodies grown from pluripotent embryonic stem (ES) ce lls. Vascularization in embryoid bodies started on day 5 of cell culture an d was paralleled by down-regulation of hypoxia-inducible factor 1 alpha (HI F-1 alpha) and vascular endothelial growth factor (VEGF). In parallel, a di ssipation of gradients in the pericellular oxygen pressure was observed as measured by O-2-sensitive microelectrodes. After 24-48 h of confrontation c ulture, cells positive for platelet endothelial cell adhesion molecule (PEC AM-1) became visible in the contact region between the embryoid body and th e tumor spheroid and sprouted within the confrontation cultures during subs equent days. Tumor-induced angiogenesis resulted in growth stimulation of t umor spheroids, disappearance of central necrosis and a reduction of the pe ricellular oxygen pressure. Furthermore, tumor vascularization resulted in elevated levels of HIF-1 alpha, VEGF, heat shock protein 27 (HSP27), and P- glycoprotein. Tumor-induced angiogenesis may augment the oxygen consumption in tumors resulting in an increased expression of hypoxia-related, proangi ogenic genes as well as of HSP27 and P-glycoprotein, which are involved in a multidrug resistance phenotype.