Src tyrosine kinase inhibition suppresses lymphangiogenesis in vitro and in vivo

The close association of lymphatic and blood vessels and their coordinated development in vivo suggest that there are parallel mechanisms regulating hemangiogenesis and lymphangiogenesis. Here, we hypothesize that inhibition of the Src tyrosine kinase, apart from anti-hemangiogenic effects, results in a suppression of lymphangiogenesis.

The ability of the Src kinase inhibitor PP2 to block Src in isolated lymphatic endothelial cells (LECs) was analyzed by Western Blot. The effects of PP2 on LEC proliferation, migration, and sprouting were assessed by MTT, Boyden chamber, and spheroid assays, respectively. The level of VEGF-C secreted by L3.6pl pancreatic carcinoma cells was measured by ELISA. For in vivo assessment of lymphangiogenesis, Src kinase inhibitor AZM475271 was used in mouse corneal micropocket and lymphangioma models.

VEGF-C stimulation of isolated LECs led to an increased phosphorylation of Src kinase that was abrogated by PP2. Treatment with PP2 inhibited spheroid sprouting of LECs at even lower concentrations than suggested by the proliferation assay. Src inhibition significantly reduced the level of VEGF-C in L3.6pl supernatant. Treatment with PP2 also resulted in a significant reduction in the migratory activity of LECs. In vivo, Src inhibition reduced de novo formation of lymphangiomas and corneal neovascularization.

Inhibition of Src kinase shows strong anti-lymphangiogenic activity in vitro and in vivo. Together with anti-angiogenic effects mediated by Src inhibition, this strategy may be attractive in the treatment of lymphatic and hematogeneous metastasis of cancer.