Stromal and vascular invasion in an human in vitro bladder cancer model

In transitional cell carcinoma (TCC) of the urinary bladder, disease spread may occur through local invasion of the bladder wall and/or via hematogenous dissemination. Although the metastatic phenotype is well studied, little is known about the mechanisms that determine and regulate secondary dispersion via stromal and vascular routes. The aim of this study was to develop an in vitro system to study TCC invasion using normal human urinary tract stroma in organ culture. Human de-epithelialized urinary tract stromas were seeded with established human TCC cell lines (RT4, RT112, and EJ) and maintained in organ culture at an air-liquid interface for up to 8 weeks. The composite tissues were analyzed immunohistochemically using antibodies to a proliferation-associated antigen, cell adhesion molecules, extracellular matrix components, and cytokeratin isotypes. The phenotype of TCC cell lines maintained as monolayer cultures were compared with the composite tissues to assess the regulatory effects of the stroma. On a normal urothelial stroma, the TCC cell lines proliferated and underwent a degree of differentiation related to the grade of the original tumor. RT4 cells formed a stratified epithelium with low proliferation, some characteristics of urothelial differentiation, and no evidence of stromal invasion over the 8-week culture period. RT12 cells formed a stratified epithelium with limited differentiation and by 2 weeks showed intravasation of the subepithelial capillary bed. Anaplastic EJ cells did not stratify but diffusely invaded the stromal matrix and the superficial vasculature. In conclusion, the urothelial stroma can support cytodifferentiation in vitro and influence the behavior of malignant TCC cells. The model has application for determining genetic and epigenetic factors that influence whether a tumor progresses by local and/or hematogenous spread. Furthermore, it may offer a useful approach in evaluating prognostic and diagnostic markers and strategies for preventing invasion.