SA selectively inhibits clonogenicity of glioma cells. A, structure of SA, a geranyl stilbene isolated from the Camoeronian plant Macaranga schweinfurthii. B, Clonal growth of SF-295 human glioma cells is inhibited by SA, whereas growth of A549 human lung carcinoma cells is not inhibited after single administration of varying doses of SA, as evaluated by growth of crystal violet stained colonies. Points, mean number of clones from three dishes, error bars are sample standard deviations.