Heparan sulphate/heparin glycosaminoglycans with strong affinity for the growth-promoter spermine have high antiproliferative activity

Depletion of intracellular polyamine pools inhibits cell proliferation. Polyamine pools are maintained by intracellular synthesis and by uptake from the extracellular environment. It may be expected that cationic polyamines are sequestered by the polyanionic glycosaminoglycan substituents of extracellular proteoglycans. Moreover, highly sulphated heparin-related glycans inhibit growth of human embryonic lung fibroblasts. We have therefore investigated interactions between polyamines and heparin-related glycosaminoglycans. Affinity chromatography of various polyamines on heparin-agarose indicated that spermine was the only polyamine that bound efficiently to this type of glycan. By using equilibrium dialysis we found that spermine binds to a highly sulphated heparan sulphate/heparin preparation with a dissociation constant of 3.7 x 10(-5)M. Enzymatic degradation of heparan sulphate using three different heparan sulphate/heparin lyases, separately or in combination and in the absence or presence of spermine, was used to generate spermine-binding and degradation-protected oligosaccharides. As indicated by chromatographic and electrophoretic analysis a size- and chargeheterogeneous collection was obtained. However, protected oligosaccharides derived from antiproliferative heparan sulphates were inactive. Highly sulphated, antiproliferative heparan sulphates were subfractionated on spermine-agarose yielding high-affinity material with increased antiproliferative activity. A very potent material was obtained from pig skin. Although there was generally a clear correlation between high spermine-affinity and strong growth-inhibition, no correlation with sulphate content or oligosaccharide mapping patterns could be detected. Beef lung heparan sulphate comprised naturally occurring fragments of eicosasaccharide size with substantially increased specific activity. As these fragments were longer than oligosaccharides generated by enzymatic degradation in the presence of spermine (hexa- to tetradecasaccharide), multiple spermine-binding sites in tandem may be necessary to induce antiproliferative activity.