Characterization and development of a peptide substrate-based phosphate transfer assay for the human vascular endothelial growth factor receptor-2 tyrosine kinase

Real-Time Multiplex Kinase Phosphorylation Sensors in Living Cells

Phosphorylation is an important post-translational modification implicated in cellular signaling and regulation. However, current methods to study protein phosphorylation by various kinases lack spatiotemporal resolution or the ability to simultaneously observe in real time the activity of multiple kinases in live cells. We present a peptide biosensor strategy with time correlated single photon counting-fluorescence lifetime imaging (TCSPC-FLIM) to interrogate the spatial and temporal dynamics of VEGFR-2 and AKT phosphorylation activity in real time in live 2D and 3D cell culture models at single cell resolution. By recording the increase in fluorescence lifetime due to a change in the solvatochromic environment of the sensor upon phosphorylation, we demonstrate that spatiotemporal maps of protein kinase activity can be obtained. Our results suggest that fluorescence lifetime imaging of peptide biosensors can be effectively and specifically used to monitor and quantify phosphorylation of multiple kinases in live cells.

Biochemical characterization of a novel type-II VEGFR2 kinase inhibitor: comparison of binding to non-phosphorylated and phosphorylated VEGFR2

A pyrrolo[3,2-d]pyrimidine-based type-II vascular endothelial growth factor receptor 2 (VEGFR2) kinase inhibitor, compound 20d, displayed time-dependent inhibition of the non-phosphorylated catalytic domain of VEGFR2. In contrast, 20d did not show time-dependent inhibition of the phosphorylated enzyme. Dissociation of 20d from non-phosphorylated VEGFR2 was slow and the half-life of the complex was longer than 4h. In contrast, dissociation of 20d from the phosphorylated enzyme was very fast (half-life <5min). A fluorescent tracer based displacement assay and surface plasmon resonance (SPR) analysis confirmed the slow dissociation of 20d from only non-phosphorylated VEGFR2. Thus, activity based and binding kinetic analyses both supported slow dissociation of 20d from only non-phosphorylated VEGFR2. Additionally SPR analysis revealed that association rates were rapid and nearly identical for these two phosphorylation forms of VEGFR2. From these results, the preferential effect of 20d on non-phosphorylated VEGFR2 is dominated by its slow dissociation from the enzyme and this characteristically long residence time may increase its potency in vivo. The present findings may assist in the design of novel type-II kinase inhibitors.

Biochemical characterization of TAK-593, a novel VEGFR/PDGFR inhibitor with a two-step slow binding mechanism

Inhibition of tumor angiogenesis leads to a lack of oxygen and nutrients in the tumor and therefore has become a standards of care for many solid tumor therapies. Dual inhibition of vascular endothelial growth factor receptor (VEGFR) and platelet-derived growth factor receptor (PDGFR) protein kinase activities is a popular strategy for targeting tumor angiogenesis. We discovered that TAK-593, a novel imidazo[1,2-b]pyridazine derivative, potently inhibits tyrosine kinases from the VEGFR and PDGFR families. TAK-593 was highly selective for these families, with an IC(50) >1 μM when tested against more than 200 protein and lipid kinases. TAK-593 displayed competitive inhibition versus ATP. In addition, TAK-593 inhibited VEGFR2 and PDGFRβ in a time-dependent manner, classifying it as a type II kinase inhibitor. Analysis of enzyme-inhibitor preincubation experiments revealed that the binding of TAK-593 to VEGFR2 and PDGFRβ occurs via a two-step slow binding mechanism. Dissociation of TAK-593 from VEGFR2 was extremely slow (t(1/2) >17 h), and the affinity of TAK-593 at equilibrium (K(i)*) was less than 25 pM. Ligand displacement analysis with a fluorescent tracer confirmed the slow dissociation of TAK-593. The dissociation rate constants were in good agreement between the activity and ligand displacement data, and both analyses supported slow dissociation of TAK-593. The long residence time of TAK-593 may achieve an extended pharmacodynamic effect on VEGFR2 and PDGFRβ kinases in vivo that differs substantially from its observed pharmacokinetic profile.