Verotoxins inhibit the growth of and induce apoptosis in human astrocytomacells

Verotoxin 1 (VT1) is an E. coli toxin comprising an A subunit with N-glycan ase activity, and five smaller B subunits capable of binding to the functio nal receptor globotriaosylceramide (Gal alpha 1-4-Gal beta 1-4-Glcceramide- Gb(3)). VT is implicated in hemorrhagic colitis and the more serious hemoly tic uremic syndrome. Vn is active against various tumor cell lines in vitro and in vivo. To extend the anti-cancer spectrum of activity of VT to human brain tumors, in the present analysis we studied the effects of VT on the growth of 6 permanent human astrocytoma cell lines. All astrocytoma cell li nes analyzed express Gb(3) and were sensitive to VT-1 at a dose of 50 ng/ml , but sensitivity was not proportional to the relative Gb(3) concentration. VT induced apoptosis in these cells was shown by electron microscopy. Morp hological evidence (nuclear shrinkage and chromatin condensation) of apopto sis could be clearly distinguished 1.5 hrs after toxin addition. Ultrastruc tural preservation of organelles was observed in conjunction with blebbing of the plasma membrane, condensation of chromatin within the nucleus and nu clear shrinkage. Apoptosis was also induced by the recombinant toxin B subu nit alone, suggesting that the ligation of Gb(3) is the primary induction m echanism. These studies indicate that verotoxin/Gb(3) targetting may provid e a novel basis for the inhibition of astrocytoma tumour cell growth.