Inhibitors of angiogenesis hold potential in the treatment of
cancer and other diseases where the disease is caused or maintained by the inappropriate growth of blood vessels. In the present study, a novel inhibitor of angiogenesis was synthesized by covalently linking a nonanticoagulating derivative of
heparin,
heparin adipic
hydrazide (HAH), by an
acid-labile bond to the antiangiogenic
steroid,
cortisol. The rationale was that the
heparin derivative, which binds to sulfated polyanion receptors on endothelial cells, should concentrate the
steroid on the surface of vascular endothelial cells. Endocytosis of the conjugate and decomposition of the
acid-labile linkage inside lysosomes and other acidic intracellular compartments should then lead to release of the
cortisol and expression of its antiproliferative activity. Analysis of the stability of
HAH-cortisol showed that it was stable at pH 7.4 and broke down rapidly (t1/2 15 min) at pH 4.8 at 37 degrees C. Treatment of murine pulmonary capillary endothelial cells with
HAH-cortisol at 10(-5) M (with respect to
cortisol) suppressed their
DNA synthesis by 50% and inhibited their migration into wounded areas of confluent monolayers.
HAH-cortisol at 10(-4) M (with respect to
cortisol) did not suppress the
DNA synthesis of
Lewis lung carcinoma cells. Daily i.p.
injections of
HAH-cortisol into mice bearing s.c. sponge implants retarded vascularization of the sponge, and
injections directly into the sponge abolished vascularization for as long as the
injections were continued. Daily i.v.
injections of
HAH-cortisol at doses causing no apparent toxicity retarded the growth of solid s.c. Lewis lung
carcinomas in mice by up to 65%. In all of these assays, equivalent treatments with a mixture of the HAH plus
cortisol was significantly less effective. The antiproliferative effect of
HAH-cortisol on endothelial cells appeared independent of the
glucocorticoid activity of the
steroid since HAH conjugated to 5 beta-pregnane-3 alpha,17 alpha,21-triol-20-one, a
steroid lacking
glucocorticoid or
mineralocorticoid activity, was even more effective at inhibiting
DNA synthesis by murine pulmonary capillary endothelial cells than was
HAH-cortisol. In conclusion,
HAH-cortisol represents the prototype of a new class of
angiogenesis inhibitors for the treatment of
cancer and other angiogenic diseases.