SPONTANEOUS CELL LOSS DURING GROWTH OF POST-CONFLUENT PRIMARY CULTURES FROM MAMMARY ADENOCARCINOMAS

Abstract

Growth properties of cells cultured from primary mammary tumors of C3H mice were analyzed. Cells were seeded at 2 densities (1 .times. 105 and 5 .times. 105/cm2) and were supported with a culture fluid containing 10% fetal calf serum and 5 .mu.g insulin per ml. Mitosis continued after confluence was achieved, but cells did not accumulate in the monolayer. Certain cells were released into the culture fluid. Very few cells detached in this way from subconfluent cultures. Released cells multiplied vigorously if replated. The release of these cells was depressed by adrenal steroids, but other manipulations of culture conditions (hormones, culture substratum) influenced the release process less. Analyses of release kinetics and observations of detachment with the scanning EM suggested that tumor cells that became spheroid (including mitotic cells), and partly detached from the culture dish, were unable to reflatten into the monolayer because neighboring nonmitotic cells spread onto the vacated culture surface. Eventually, such rounded cells apparently lost their attachment to the culture dish. The release process may be related to the critical phase transition and the sarcomatous transformation observed in long-term cultures from mouse epithelial tumors. The event could also reflect the tendency in vivo for cells of mammary tumors to slough into the lymphatics and blood vessels.