Imaging of Tie2 with a Fluorescently Labeled Small Molecule Affinity Ligand

The receptor tyrosine kinase inhibitor, Tie2, has significant roles in endothelial signaling and angiogenesis and is relevant in the pathophysiology of several diseases. However, there are relatively few small molecule probes available to study Tie2, making the evaluation of its activity in vivodifficult. Recently, it was discovered that the small molecule rebastinib (DCC-2036) is a potent Tie2 inhibitor. We hypothesized that fluorescent derivatives of rebastinib could be used as imaging agents for Tie2. On the basis of crystallography structures, we synthesized three fluorescent derivatives, which we then evaluated in both in vitroand in vivoassays. We found that the Rebastinib-BODIPY TMR (Reb-TMR) derivative has superior imaging characteristics in vitro, and we successfully labeled endothelial cells in vivo. We propose that this probe could be further used in in vivoapplications for studying the role of Tie2 in disease.