5'-O-Tritylinosine (KIN59) is an allosteric inhibitor of the angiogenic
enzyme thymidine phosphorylase. Previous observations showed the capacity of KIN59 to abrogate
thymidine phosphorylase-induced as well as developmental angiogenesis in the chicken chorioallantoic membrane (CAM) assay. Here, we show that KIN59 also inhibits the angiogenic response triggered by
fibroblast growth factor-2 (
FGF2) but not by
VEGF in the CAM assay. Immunohistochemical and
reverse transcriptase PCR analyses revealed that the expression of
laminin, the major
proteoglycan of the basement membrane of blood vessels, is downregulated by KIN59 administration in control as well as in
thymidine phosphorylase- 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 biologic 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
thymidine phosphorylase inhibitor KIN59 is endowed with a significant
FGF2 antagonist activity, thus representing a promising lead compound for the design of multitargeted antiangiogenic
cancer drugs.