New Affinity Probe Targeting VEGF Receptors for Kinase Inhibitor Selectivity Profiling by Chemical Proteomics

Solid
tumors are dependent for growth on nutrients and the supply
of oxygen, which they often acquire via neoangiogenesis. Vascular
endothelial growth factors and the corresponding receptors (VEGFRs)
play central roles in this process, and consequently, the blockade
of this pathway is one therapeutic strategy for cancer treatment.
A number of small molecules inhibiting VEGFR inhibitors have been
developed for clinical use, and a comprehensive view of target selectivity
is important to assess the therapeutic as well as risk potential of
a drug molecule. Recent advances in mass spectrometry-based chemical
proteomics allow analyses of drug–target interactions under
close-to-physiological conditions, and in this study, we report on
the design, synthesis, and application of a small molecule affinity
probe as a tool for the selectivity profiling of VEGFR and other kinase
inhibitors. The probe is capable of binding >132 protein kinases,
including angiokinases such as VEGFRs, PDGFRs, and c-KIT from lysates
of cancer cell lines or human placenta tissue. Combining the new probe
with Kinobeads in competitive binding assays, we were able to identify
nanomolar off-targets of the VEGFR/PDGFR inhibitors pazopanib and
axitinib. Because of its broad binding spectrum, the developed chemical
tool can be generically used for the discovery of kinase inhibitor
targets, which may contribute to a more comprehensive understanding
of the mechanisms of action of such drugs.