Organ-cultured epithelial tissue as an in vitro model for invasion: quantitation and high-voltage electron microscopy of tumor cell attachment.

An invasion model designed specifically for studying mechanisms of invasion of squamous-cell carcinomas was developed with murine buccal mucosa as the host tissue. The mucosal explants were destratified by growth in low-calcium medium (less than 0.07 mM), which results in a dorsal surface composed of one or two layers of basal epithelial cells. The explant has a three-dimensional histoarchitecture similar to in vivo mucosa. A spontaneously transformed epithelial cell line (Pam 27; Yuspa , S. H., Hawley -Nelson, P., Koehler , B., and Stanley, J. R. Cancer Res., 40: 4694-4703, 1980) was used to seed explants. Attachment and subsequent growth and invasion were monitored. The morphology of attachment was examined by conventional and high-voltage electron microscopy. In addition, attachment was quantitated by using [125I]iododeoxyuridine-labeled tumor cells. Attachment was shown to be an active process which involves an interdigitation of tumor-host cell processes. Junctional complexes were also observed between tumor and host epithelial cells. By 24 hr, tumor cells were spread on the basal cells and were in the process of replacing host cells. Long-term growth of explants showed that tumor cells can repopulate the epithelial surface and invade the stromal region.