Early activities of invasive malignant cells in vitro

Contact of aggregates of MO4 cells (malignant fibroblastic mouse cells) with precultured fragments of embryonic chick heart in vitro results in attachment within the first 45 minutes. Attachment appears to be an active cellular process, sensitive to cytochalasin B and dependent on ATP energy. Transmissionelectronmicrographs from MO4 cells attached to heart tissue indicate that a number of cellular activities are involved in attachment. The same activities are probably involved as well in invasion as it appears during further incubation of the confronting tissues. These activities, namely adhesion, anchorage and penetration of MO4 cells and destruction of fibroblastic heart cells have been separated experimentally and their sequence during the early steps of invasion has been determined.