Inhibitory effect of trapidil on human meningioma cell proliferation via interruption of autocrine growth stimulation.

In a previous study, the authors demonstrated that meningioma cells secrete platelet-derived growth factor (PDGF)-like molecules that stimulate their own growth in an autocrine manner. Based on that finding, a study was undertaken to examine the effect of trapidil, a drug known to have an antagonistic action against PDGF, on cell proliferation of human meningiomas in culture. Trapidil showed a dose-dependent inhibition of meningioma cell proliferation in the absence of any exogenous mitogenic stimulation. The maximum effect was observed at a concentration of 100 micrograms/ml, with the decrease in cell growth ranging from 16% to 54% compared to control samples. Trapidil similarly inhibited the basal deoxyribonucleic acid (DNA) synthesis assessed by [3H]-thymidine incorporation in three of seven meningiomas. While the conditioned medium generated from meningioma cells remarkably stimulated the proliferation of meningioma cells (166% to 277% of control), this effect was strikingly inhibited by the addition of trapidil. Trapidil also inhibited conditioned medium-stimulated DNA synthesis, even when there was no effect on basal DNA synthesis. Furthermore, trapidil significantly inhibited the epidermal growth factor (EGF)-stimulated proliferation of meningioma cells. This inhibitory effect on EGF-stimulated cell proliferation was also observed in nontumorous fibroblasts, demonstrating that trapidil is not an antagonist specific to PDGF. The addition of trapidil (30 micrograms/ml) in combination with bromocriptine (1 microM) showed an additive inhibitory effect on the meningioma cell growth compared to trapidil or bromocriptine alone. The overall results suggest that trapidil exhibits an inhibitory effect on meningioma cell proliferation through blocking the mitogenic stimulation induced by autocrine or exogenous growth factors, and may be considered as a possible new approach to the medical treatment of meningiomas.