Potentiation of angiostatic steroids by a synthetic inhibitor of arylsulfatase.

Sodium 2-hydroxy-5-nitro-alpha-toluenesulfonate (HNT, compound II, Fig. 7) is a synthetic inhibitor of arylsulfatase (E.C. 3.1.6.1.). At 1 to 10 mM, HNT increased the clotting time of heparinized rabbit blood by 7-fold. In the 6-day chick embryo, mixtures of heparin and hydrocortisone applied to the chorioallantoic membrane, are known to inhibit specifically the growth of capillary blood vessels. HNT potentiated this antiangiogenic activity in a dose-dependent manner when the concentration of heparin was suboptimal. Potentiation of the antiangiogenic activity of steroids by HNT correlated inversely with the concentration of exogenous heparin. In the absence of exogenous heparin, hydrocortisone did not inhibit angiogenesis. Hydrocortisone and HNT, however, inhibited angiogenesis to the same extent as hydrocortisone and heparin. An arylsulfatase with a Km of 1.5 mM for nitrocatechol sulfate as substrate and a Ki of 10.0 microM for the inhibition of HNT, was identified in the chick embryo chorioallantoic membrane. Preincubation of heparin with a commercially available arylsulfatase caused a 50% reduction in antiangiogenic activity of heparin-steroid mixtures applied to the chorioallantoic membrane. This loss of activity was prevented completely by addition of HNT to the arylsulfatase-heparin incubation mixture. These results suggest that HNT (a) potentiates the anticoagulant function of heparin, (b) prevents the inactivation of antiangiogenic activity of heparin by an endogenous arylsulfatase in the chorioallantoic membrane and by a commercial arylsulfatase, and (c) in the presence of angiostatic steroids can inhibit angiogenesis in the chick embryo without the addition of exogenous heparin. On the basis of these data, we propose that this inhibitor of arylsulfatase acts to potentiate angiostatic steroids by suppressing the desulfation of tissue heparin.