A Tyrosine Kinase Inhibitor–Based High-Affinity PET Radiopharmaceutical Targets Vascular Endothelial Growth Factor Receptor

Abstract

Tyrosine kinase receptors including vascular endothelial growth factor receptor (VEGFR) have gained significant attention as pharmacologic targets. However, clinical evaluation of small-molecule drugs or biologics that target these pathways has so far yielded mixed results in a variety of solid tumors. The reasons for response variability remain unknown, including the temporal and spatial patterns of receptor tyrosine kinase expression. Methods to detect and quantify the presence of such cellular receptors would greatly facilitate drug development and therapy response assessment. We aimed to generate specific imaging agents as potential companion diagnostics that could also be used for targeted radionuclide therapy. Here, we report on the synthesis and initial preclinical performance of 64 Cu-labeled probes that were based on the kinase inhibitor already in clinical use, vandetanib (ZD6474), as a VEGFR-selective theranostic radiopharmaceutical. Methods: A monomeric (ZD-G1) and a dimeric (ZD-G2) derivative of ZD6474 were synthesized and conjugated with DOTA for chelation with 64 Cu to produce the probes 64 Cu-DOTA-ZD-G1 and 64 Cu-DOTA-ZD-G2. The binding affinity and specificity to VEGFR were measured using U-87 MG cells known to overexpress VEGFR. Small-animal PET and biodistribution studies were performed with 64 Cu-labeled probes (3-4 MBq) intravenously administered in U-87 MG tumor-bearing mice with or without coinjection of unlabeled ZD-G2 for up to 24 h after injection. Results: Receptor-binding assays yielded a mean equilibrium dissociation constant of 44.7 and 0.45 nM for monomeric and dimeric forms, respectively, indicating a synergistic effect in VEGFR affinity by multivalency. Small-animal PET/CT imaging showed rapid tumor accumulation of 64 Cu-DOTA-ZD-G2, with excellent tumor-to-normal tissue contrast by 24 h. Coinjection of the 64 Cu-DOTA-ZD-G2 with 50 nmol (60 μg) of nonradioactive ZD-G2 effectively blocked tumor uptake. Conclusion: A 64 Cu-labeled probe derived from an approved oncologic drug selective for VEGFR demonstrates excellent tumor targeting, particularly for the dimeric form. The multivalent probe yielded a 100-fold improvement in receptor affinity while maintaining pharmacokinetic and biodistribution properties well suited for PET imaging in our preclinical model. These results indicate that a clinically relevant theranostic platform can be rapidly developed from known small molecules that target key cellular receptors.

Direct myocardial ischemia imaging with exercise 18FDG

“…Using this principle, investigators have been able to image apoptosis, necrosis, angiogenesis, matrix metalloproteinases, and gene expression in experimental animal models as well as in human. [9][10][11][12][13][14][15] The same principles can be applied for myocardial ischemia imaging as well. Myocardial ischemia is associated with very distinctive and profound changes in local and regional pH, pO 2 , substrate utilization, and metabolism.…”

Single‐Molecule Force Measurement Guides the Design of Multivalent Ligands with Picomolar Affinity

“…With the actual distribution information of the receptors in hand, the lengths of the linkers can be rationally selected to design statistical and chelate bivalent binding.S cheme 2 presented aseries of multivalent ligands that were used in this study of hybrid multivalent binding.A ll these compounds were prepared and characterized accordingly (see Supporting Information for details), and their binding affinity to VEGFR was measured by the IC 50 values required to reduce the binding of the parent entity,Z D6474 (ZD-1), in the binding assay of ligand to cell surface receptors as previously described. [6] Thei nhibitory binding curve was presented in Figure 3, and the measured IC 50 values were summarized in Table 1. As designed, al inker with length of approximately 14 that was greatly shorter than the proximal VEGFR distance in HUVECs,was used to tether ZD6474 entities and construct ab ivalent ZD-2, in which the statistical effect was believed to be dominated in the binding.Asecond bivalent ZD-3 with linker of about 47 that corresponded to the estimated distance of neighboring VEGFR was also constructed to assess the chelate effect.…”

Pet Imaging and its Application in Cardiovascular Diseases

“…39 Our group at the Houston Methodist Research Institute developed novel small molecular-based PET probes targeting VEGF receptor (VEGFR) and integrin  V  3 with two patents filed. 40,41 We reported on the successful optimization and initial preclinical performance of a VEGFR-targeting PET probe that was based on the FDA-approved oncologic drug in current clinical use, vandetanib. This designed probe demonstrated approximately two orders of magnitude improvement in VEGFR binding affinity in vitro compared to the vandetanib, and it significantly enhanced tumor angiogenesis imaging with favorable biodistribution and pharmacokinetic properties for clinical translation and potential commercialization.…”

“…This designed probe demonstrated approximately two orders of magnitude improvement in VEGFR binding affinity in vitro compared to the vandetanib, and it significantly enhanced tumor angiogenesis imaging with favorable biodistribution and pharmacokinetic properties for clinical translation and potential commercialization. 40 These studies will enable us to initiate the myocardial angiogenesis imaging project in the near future.…”