Effects of epidermal growth factor receptor blocking in cultured glioma spheroids.

A concentration as high as 1 microgram/ml of non-radioactive epidermal growth factor, EGF/was necessary to inhibit effectively the binding of 125I-EGF in glioma U-343MGaC12:6 cells. This concentration blocked the available EGF receptors within 30 minutes in monolayers, while 24 hour treatments were required in spheroids. The effects on growth, incorporation of radioactive thymidine, cell density and on extracellular pH were analysed in spheroids after exposure to 1 microgram/ml EGF. The high EGF concentration did not significantly modify the growth curves for monolayers and small spheroids but increased the volume growth of large spheroids. The increase was partly due to lower cell density and partly to increased proliferation. The EGF treatment gave an increased incorporation of thymidine in spheroids, for at least up to 5 days after the administration, while no effect was seen in monolayers. The cell density decreased after the EGF treatment as seen from morphometric analysis in histological sections and by counting the number of cells per volume unit after trypsinization. The capacity to take up radiolabelled dextran increased, probably due to the decreased cell density. Other EGF-induced changes were also recognized, such as a reduction in extracellular pH by 0.1 units in the central regions of spheroids and an increase in intracellular pH by 0.47 units in analysed monolayer cells. The results showed that it is not possible to block the EGF-receptors without imposing changes in growth and metabolism.