Defibrotide, an Endothelium Protecting and Stabilizing Drug, Has Anti-Angiogenic Potential In Vitro and In Vivo.

DF is a polydisperse mixture of single-stranded polydeoxyribunucleotides which is successfully used in the treatment of hepatic veno-occlusive disease and other endothelial disorders. Recent pre-clinical evidence suggests that DF might also have anti-neoplastic properties. We addressed the question whether this might be due to the prevention of tumor blood vessel formation (angiogenesis). The anti-angiogeneic potential of DF was tested in vitro (Matrigel^™ tube formation and aortic ring assay) and in vivo (dorsal skin-fold chamber model). Our results show that DF quantitatively (100%) blocks tube formation of trans-differentiated human endothelial-like cells (ELC) at concentrations corresponding to pharmacologic DF blood levels (100 μg/mL). Similarly, the sprouting of rat aorta endothelial cells in Matrigel^™ was prevented by nearly 100%, when DF was applied on a daily basis. In vivo tumor angiogenesis in a human gastric cancer (TMK-1) grown in skin-fold chambers (nude mice) was also attenuated on day 5 by DF, as measured by microvascular density. Although the exact mechanism of DF action remains to be elucidated, initial Western blotting results show that DF reduces phosphorylation-activation of p70S6 kinase, which is a key target in the PI3K/Akt/mTOR signaling pathway linked to endothelial cell and pericyte proliferation and activation. Taken together, our data suggest that while DF is known for its endothelium-protecting function, it also inhibits tumor blood vessel formation, and thus should be considered for further testing as an anticancer agent.