The thymidine phosphorylase inhibitor 5'-O-tritylinosine (KIN59) is an anti-angiogenic multi-target fibroblast growth factor-2 antagonist.

5'-O-tritylinosine (KIN59) is an allosteric inhibitor of the angiogenic enzyme thymidine phosphorylase (TP). Previous observations showed the capacity of KIN59 to abrogate TP-induced as well as developmental angiogenesis in the chicken chorioallantoic membrane (CAM) assay. Here, we demonstrate that KIN59 also inhibits the angiogenic response triggered by fibroblast growth factor 2 (FGF2) but not by vascular endothelial growth factor (VEGF) in the CAM assay. Immunohistochemical and RT-PCR analyses revealed that the expression of laminin, the major proteoglycan of the basement membrane of blood vessels, is down-regulated by KIN59 administration in control as well as in TP- or FGF2-treated CAMs, but not in CAMs treated with VEGF. Also, KIN59 abrogated FGF2-induced endothelial cell proliferation, FGF receptor activation and Akt signaling in vitro with no effect on VEGF-stimulated biological responses. Accordingly, KIN59 inhibited the binding of FGF2 to FGF receptor-1 (FGFR1), thus preventing the formation of productive heparan sulphate proteoglycan/FGF2/FGFR1 ternary complexes, without affecting heparin interaction. In keeping with these observations, systemic administration of KIN59 inhibited the growth and neovascularization of subcutaneous tumors induced by FGF2-transformed endothelial cells injected in immunodeficient nude mice. Taken together, the data indicate that the TP inhibitor KIN59 is endowed with a significant FGF2-antagonist activity, thus representing a promising lead compound for the design of multi-targeted anti-angiogenic cancer drugs.