INHIBITION OF IN-VITRO MENINGIOMA PROLIFERATION AFTER GROWTH-FACTOR STIMULATION BY CALCIUM-CHANNEL ANTAGONISTS .2. ADDITIONAL GROWTH-FACTORS, GROWTH-FACTOR RECEPTOR IMMUNOHISTOCHEMISTRY, AND INTRACELLULAR CALCIUM MEASUREMENTS

WE HAVE PREVIOUSLY reported that calcium channel antagonists can block both the growth of meningiomas in culture and the potent growth stimu lation of meningioma cells by epidermal growth factor (EGF) and platel et-derived growth factor (PDGF). This study further defines the nature of this growth inhibition. Primary meningioma cultures were establish ed, and cells were characterized, Fibroblast growth factor or insulin- like growth factor-1 growth stimulation in the presence of calcium cha nnel antagonists was examined. in addition, the effects of ethylene gl ycol-bis-(aminoethylether) N,N,N',N ''-tetraacetic acid and Bay K 8644 , a calcium channel agonist, on the growth factors were analyzed. Grow th factor receptor immunohistochemistry was performed on the original tumors and the in vitro meningioma cells. Twelve of 17 (71%) meningiom as in this study were positive for the EGF receptor, and 14 of 17 (82% ) were positive for the PDGF receptor. Five of six (83%) of the cultur e cells were positive for the EGF receptor, and four of five (80%) wer e positive for the PDCF receptor. Intracellular calcium changes were q uantified using the intracellular calcium-chelating, fluorescent dye, Fura-2. The growth stimulation of fibroblast growth factor and insulin -like growth factor-1 on meningioma cells in culture was decreased in a dose-dependent manner by calcium channel antagonists. The growth sti mulation of fibroblast growth factor and insulin-like growth factor-1 was not affected by a reduction of extracellular calcium, whereas the growth stimulation of EGF and PDGF was. interestingly, intracellular c alcium was not increased after exposure to growth factors but was incr eased after serum stimulation. This increase could be blocked by prein cubation with verapamil. Calcium channel antagonists can inhibit proli feration of meningioma cells in culture after stimulation with a numbe r of growth factors. These drugs might disrupt intracellular calcium h omeostasis or interfere with key elements of the growth factor signal transduction pathways. These mechanisms as well as the potential clini cal relevance of these findings are discussed.