| For many cancers, metastasis and burden of the secondary tumors account for nearly 90% of cancer-related mortality. The process of metastasis is a highly organized mechanism involving interplay between cell adhesion, migration, and invasion via proteolytic systems. Metastasis is heavily dependent upon changes in cell morphology caused by internal cytoskeletal rearrangements. Previous work in our laboratory has focused on the various effects of the antiprogestin, mifepristone (MF). Most recently we have investigated the growth inhibitory properties of MF on cancer cells of the ovary, prostate, breast, brain, and bone. Not only was cell growth inhibited by MF treatment, but cells also displayed drastic changes in morphology. Due to observed MF-induced changes in cell morphology, and the significance of cell structure in the metastatic process, we questioned whether MF could be inhibiting the metastatic capability of cancer cells. Human cancer cell lines of the ovary (SKOV-3), breast (MDA-MB-231), prostate (LNCaP), and brain (U87MG) were chosen from the panel of cell lines previously studied. The morphological changes induced by MF were confirmed and further characterized with the use of phase contrast microscopy, immunofluorescence, and confocal microscopy. In addition, cytoskeletal and adhesion proteins, as well as epithelial-to-mesenchymal transition (EMT) markers, were examined by Western blot analysis. Interestingly, MF induced a similar morphology change in all cell lines, which included shrinkage of the cell body, long, thin cellular extensions, and a loss of cell-to-cell connections. Morphology changes were associated with disruption in the organization of actin and tubulin filaments, whereas EMT markers remained relatively unchanged. The metastatic capability of cells was then studied by examining the cells' ability to adhere, migrate, and invade using in vitro and in vivo approaches. For all cell lines, MF caused a decrease in cell adhesion to various extracellular matrix substrates and accelerated trypsin-induced cellular detachment. Also, MF significantly inhibited the ability of cells to migrate in wound healing and Boyden chamber assays, and to invade extracellular matrix (ECM) proteins. When tested in vivo, pretreatment with MF was capable of inhibiting tumor development in the chick chorioallantoic membrane (CAM) and impairing establishment of micro-tumor foci when injected into the mesoderm. Our results suggest that MF could be used therapeutically, not only to slow primary tumor growth, but also to halt metastatic spread of tumor cells. |
