EFFECTS OF EPIDERMAL GROWTH-FACTOR RECEPTOR BLOCKING IN CULTURED GLIOMA SPHEROIDS

A concentration as high as 1 mu g/ml of non-radioactive epidermal grow th factor, EGF/was necessary to inhibit effectively the binding of I-1 25-EGF in glioma U-343MGaC12:6 cells. This concentration blocked the a vailable EGF receptors within 30 minutes in monolayers, while 24 hour treatments were required in spheroids. The effects on growth, incorpor ation of radioactive thymidine, cell density and on extracellular pH w ere analysed in spheroids after exposure to 1 mu g/ml EGF. The high EG F concentration did not significantly modify the growth curves for mon olayers and small spheroids but increased the volume growth of large s pheroids. The increase was partly due to lower cell density and partly to increased proliferation. The EGF treatment gave an increased incor poration of thymidine in spheroids, for at least up to 5 days after th e administration, while no effect was seen in monolayers. The cell den sity decreased after the EGF treatment as seen from morphometric analy sis in histological sections and by counting the number of cells per v olume unit after trypsinization. The capacity to rake up radiolabelled dextran increased, probably due to the decreased cell density. Other EGF-induced changes were also recognized, such res a reduction in extr acellular pH by 0.1 units in the central regions of spheroids and an i ncrease 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.