Growth of malignant oral epithelial stem cells after seeding into organotypical cultures of normal mucosa.

Abstract

Oral squamous cell carcinoma (OSCC) is associated both with the local expansion of clones of malignant cells and with their further migration to regional and distant sites. The interactions that occur between normal and malignant cells during these events are not well modelled by standard culture conditions, but organotypical cultures, in which epithelial cells are grown on a matrix containing fibroblasts, provide a suitable environment for such investigations. Cells from five cell lines, each derived from OSCC and marked by retroviral transduction with alkaline phosphatase, were incorporated as small subpopulations (0.1-5%) in uniformly differentiating organotypical cultures constructed from normal oral mucosal cells. The patterns of growth of the malignant cells within the normal epithelium were examined for 3 weeks. There was variation between the different cell lines in their rates and patterns of growth, but all cell lines produced clusters of malignant cells that had expanded within 3 weeks to replace the normal epithelium. The appearance and spacing of these clusters suggested that each was derived from a single progenitor cell. The number of malignant cells initially present within a given area of organotypical epithelium was much greater than the number of expanding cell clusters subsequently formed. Cluster-forming cells thus represented only a subpopulation of the tumour cells. The organotypical model allows examination of interactions occurring between cells derived from OSCC and normal epithelia. The three-dimensional nature of organotypical cultures, together with their more normal patterns of differentiation, provides an environment that more closely mimics the in vivo environment in which tumours develop. The finding that only a subpopulation of tumour cells forms expanding tumour colonies suggests a range of growth potentials within a tumour population and may provide preliminary evidence for some form of stem and amplifying cell pattern.