AN IN-VITRO MODEL OF INTRAEPITHELIAL EXPANSION OF TRANSFORMED UROTHELIAL CELLS

Replacement of normal urothelium by pre-cancerous epithelium may expla in the high recurrence rate of human bladder cancer. An in vitro model was designed in order to study the mechanisms of expansion of transfo rmed urothelial cells at the expense of normal urothelium. For this pu rpose, mouse bladder explants were allowed to expand on a transparent porous membrane. Subsequently, cell sheets of the non-tumorigenic mous e urothelial cell line NUC-5, the tumorigenic mouse urothelial cell li ne NUC-5 Py and the human bladder-carcinoma cell line T24 were inocula ted adjacent to the primary explant. Daily measurements of the outgrow th of the bladder explant were performed, and all cultures were termin ated on day 24. At this time the post-confluent primary urothelial cel l outgrowths still showed proliferative activity, as demonstrated by b romode-oxyuridine incorporation. In due course the non-tumorigenic NUC -5 cells were replaced by the bladder outgrowth. T24 and NUC-5 Py cell s were able to inhibit the bladder outgrowth, or even infiltrate or re place the explant. This was confirmed by immunohistochemistry with (sp ecies-specific) anti-cytokeratin antibodies and by microscopic evaluat ion of cross-sections of the porous membrane. This co-cultivation mode l appears to be suitable for the in vitro study of the mechanisms of i ntra-epithelial expansion of transformed urothelial cell lines. (C) 19 93 Wiley-Liss, Inc.