Therapy of spontaneously metastatic HSV-2 induced hamster tumours with cortisone acetate administered with or without heparin

Differential effects of angiostatic steroids and dexamethasone on angiogenesis and cytokine levels in rat sponge implants

1. Subcutaneous implantation of sterile polyether sponges elicited a reproducible neovascular response in rats, as determined by blood flow measurement with a 133Xe clearance technique and confirmed histologically. This model was used to monitor the levels of two cytokines during angiogenesis and to compare the activities of angiostatic steroids and anti-inflammatory steroids. 2. Initial experiments followed the neovascular development over a 20-day period. Daily local injection of hydrocortisone caused a dose-dependent (0.5, 5 and 50 micrograms per sponge) inhibition of the basal sponge-induced angiogenesis. However, daily systemic treatment of hydrocortisone (2, 10 and 50 mg kg-1, s.c.) was less effective at inhibiting angiogenesis, and this inhibition was not sustained by day 20 after sponge implantation. 3. To investigate the involvement of cytokines during the course of angiogenesis, we measured the endogenous levels of tumour necrosis factor-alpha (TNF-alpha) and interleukin 6 (IL-6) in sponge implants. Levels of IL-6 and TNF-alpha peaked at day 7 and day 11 after implantation, respectively. These cytokine levels subsided through the completion of angiogenesis by day 20. 4. Subsequent experiments were carried out over a 14-day period. Among the three angiostatic steroids tested, U-24067 (6 alpha-fluoro-17,21 - dihydroxy-16 alpha-methylpregna -4,9(11)-diene-3,20-dione-21-acetate) showed a dose-dependent inhibition (0.5, 5 and 50 micrograms per sponge per day) of sponge-induced angiogenesis. Tetrahydro-S was also effective at 5 micrograms doses, but medroxyprogesterone failed to affect the angiogenic response. None of these steroids caused atrophies of the spleen and thymus. 5. Daily local injection of dexamethasone (0.5 microgram per sponge) inhibited the basal sponge-induced angiogenesis almost completely. Although higher doses of dexamethasone (5 and 50 micrograms per sponge) did not produce further inhibition of angiogenesis, they caused severe spleen and thymus weight losses, indicative of immunosuppression. 6. At the daily dose of 5 micrograms per sponge, dexamethasone inhibited angiogenesis and produced a marked reduction in the levels of TNF-alpha and IL-6 at day 14. In contrast, hydrocortisone, U-24067 and tetrahydro-S did not influence the levels of TNF-alpha and IL-6. 7. We concluded that the anti-angiogenic activity of angiostatic steroids and anti-inflammatory steroids in the rat sponge model is independent of their ability to reduce the production of TNF-alpha and IL-6. The differential effects of angiostatic and anti-inflammatory steroids suggest that U-24067 and its derivatives may have therapeutic potential in the management of angiogenic diseases such as rheumatoid arthritis.

Control of angiogenesis with synthetic heparin substitutes

Many diseases are dominated by persistent growth of capillary blood vessels. Tumor growth is also angiogenesis-dependent. Safe and effective angiogenesis inhibitors are needed to determine whether control of angiogenesis would be therapeutic. Heparin and certain steroids, administered together, can inhibit angiogenesis in a synergistic manner. This "pair" effect suggested that specific hydrophilic cycloamyloses may be suitable heparin substitutes. beta-Cyclodextrin tetradecasulfate administered with a steroid inhibits angiogenesis at 100 to 1000 times the effectiveness of heparin in the chick embryo bioassay. This cyclic oligosaccharide also augments the anti-angiogenic effect of angiostatic steroids against corneal neovascularization in rabbits when beta-cyclodextrin tetradecasulfate and a steroid are inserted into the cornea or applied topically as eyedrops.