Production of tissue plasminogen activator (tPA) in two and three dimensionally growing cultures of Bowes melanoma cells

Bowes melanoma cells synthesize more tissue plasminogen activator (tPA) in monolayer cultures than in multicell spheroids. Cellular production of tPA in these cells was measured during a cultivation period of 800 h. Without changing the cell culture assay, we were able to obtain monolayers, multilayers, and multicell spheroids (cell aggregates) by stirring microcarrier beads in 500‐mL spinner flasks operated at 50 rpm. Thus, the medium conditions in the liquid were similar for cells in monolayers and in multicell spheroids. Probes for measurements of intracellular and extracellular parameters were taken from the same culture at distinct times; therefore, their variations during cultivation can directly be compared. Because cells were cultured in an unregulated (with regard to pH, glucose, etc.) spinner flask, their concentration was kept below 106 cells/mL, thus avoiding too fast and too severe depletion of oxygen and other medium factors. Nevertheless, the tPA productivity decreased from 8 ng/h/106 cells (monolayer) to 4 ng/h/106 cells (multicell spheroids with microcarrier nucleus, 800 μm diameter), matching the decrease of total cellular protein. Due to medium depletion, the cell cycle distribution changed from 45% to 68% G1 cells in a characteristic way during growth of multicell spheroids. This is accompanied by changes in amino acids, glucose, lactate, and pH, which may account for the reduction of tPA productivity. © 1996 John Wiley & Sons, Inc.