Induction of thrombospondin-1 partially mediates the anti-angiogenic activity of dexrazoxane

BACKGROUND: Considerable interest lies in the identification of novel anti-angiogenic compounds for cancer therapy. We have investigated whether dexrazoxane has anti-angiogenic properties and if so, the mechanism of the inhibition. METHODS: The phenotypic effects of dexrazoxane on endothelial cell behaviour was investigated both in vitro using human umbilical vein endothelial cells (HUVECs) in cell proliferation, migration, cell cycle and aortic ring assays; and in vivo using the mouse angiogenesis subcutaneous sponge assay. Custom angiogenesis pathway microarrays were used to identify differentially expressed genes in endothelial cells after treatment with dexrazoxane vs a control. The differentially expressed genes were validated using real-time RT–PCR and western blotting; and the functional effect of one induced gene was confirmed using siRNA technology. RESULTS: Treatment of endothelial cells with dexrazoxane resulted in a dose–response inhibition of cell growth lasting for up to 5 days after a single dose of the drug. Dexrazoxane was inhibitory in the aortic ring tube forming assay and strongly anti-angiogenic in vivo in the rodent subcutaneous sponge model. The anti-angiogenic effect in the sponge was seen after systemic injection into the tail vein as well as after direct injection of dexrazoxane into the sponge. Treatment of microvascular endothelial cells in vitro with subtoxic doses of dexrazoxane stimulated thrombospondin-1 (THBS-1) secretion. Knockdown of THBS-1 with siRNA removed the angiogenesis inhibition effect of dexrazoxane, which is consistent with the anti-angiogenic and vascular normalising properties of the drug being principally mediated by THBS-1. CONCLUSION: We show that dexrazoxane administered in small repeated doses is strongly anti-angiogenic and that this activity is mediated by induction of the anti-angiogenic THBS-1 in endothelial cells.