In vivo intracellular signaling as a marker of antiangiogenic activity

Alterations in endothelial cell (EC) signaling could serve as a marker of e ffective antiangiogenic therapy. We determined the effect of an antiangioge nic tyrosine kinase inhibitor, SU6668, on tumor EC signaling in liver metas tases in mice. In vitro immunofluorescence verified that pretreatment of EC s with SU6668 before exposure to VEGF decreased in vitro phosphorylation of Erk and Akt. Using double-fluorescence immunohistochemistry, phosphorylate d Erk and Akt were constitutively expressed in ECs in liver metastases in u ntreated mice, but SU6668 blocked activation of these signaling intermediat es. Determining the activation status of the Erk and Akt signaling pathways in tumor ECs may serve as a surrogate marker for the effectiveness of anti angiogenic regimens.