An experimental model for ovarian tumor invasion of cultured mesothelial cell monolayer.

BACKGROUND: Peritoneal spread of tumor cells is one of the characteristic features of biologic behavior of ovarian cancers. To understand the mechanism by which human tumor cell invasion takes place, we have tried to establish an in vitro experimental model for ovarian tumor cell invasion of the mesothelial cell monolayer. EXPERIMENTAL
DESIGN: Mesothelial cells were isolated from normal rat mesentery by trypsin digestion and the cells (1 x 10(5)/dish) were cultured in Eagle's minimum essential medium supplemented with 10% fetal calf serum. Cultured mesothelial cells (M cells) grew forming a pavement-like monolayer. When M cells grew to a confluent state, tumor cells (1 x 10(5)/dish) were seeded on M cell monolayers and cultured. Four tumor cell lines derived from human ovarian cancers were tested for their invasive behaviors. The penetration of M cell monolayers by the tumor cells was confirmed by a perpendicular section of the cell layers. The number of penetrated single tumor cells and colonies/cm2 was counted under a phase contrast microscope after the tumor cell seeding.
RESULTS: Several hours after the tumor cell seeding, the cells adhered to M cell monolayers and started to penetrate by extending pseudopodia-like cytoplasmic processes through junctional margins of neighboring M cells, resulting in the formation of penetrated single tumor cells that then proliferated to form colonies under the monolayer. The number of penetrated single tumor cells and colonies/cm2 increased up to 24 hours after the tumor cell seeding, and thereafter stayed almost constant. The number increased with the number of tumor cells seeded, when counted at 48 hours, and therefore was taken to be the number of tumor cells invaded. The in vitro invasiveness of tumor cells varied with the tumor cell lines examined.
CONCLUSIONS: Application of this system appears to provide rapid determinations of the invasive potential of ovarian tumor cells and to make it easy to screen substances that modify the invasion of mesothelial cells.