Purification and structure of neurostatin, an inhibitor of astrocyte division of mammalian brain

Neurostatin was originally described as an inhibitor of astroblast and astr ocytoma division present in rat brain extracts and immunologically related to the sugar moiety of epidermal growth factor receptor and to blood group antigens. It was purified recently from mammalian brain extracts and charac terized as a glycosphingolipid, but its precise structure remained unknown. Neurostatin has now been purified to apparent homogeneity from ganglioside extracts of rat, bovine, and porcine brain. It is cytostatic for astroblas ts, C6 glioma cells, and various human astrocytomas grades III and IV, with IC50 values ranging from 250 to 450 nM, but does not affect the division o f primary or transformed fibroblasts up to concentrations >4 mu M. Matrix-a ssisted laser desorption ionization time-of-flight mass spectrometry of pur ified pig neurostatin showed a molecular ion of 1,905 Da and ions of 1,863 and 1,934 Da, compatible with a disialoganglioside. Mono- and bidimensional NMR spectra, together with biochemical studies, suggest that neurostatin m ay be the 9-O-monoacetyl ester of GD1b.