Synthesis, in silico, in vitro, and in vivo investigation of 5-[11C]methoxy-substituted sunitinib, a tyrosine kinase inhibitor of VEGFR-2

Sunitinib® (SU11248) is a highly potent tyrosine kinase inhibitor targeting vascular endothelial growth factor receptor (VEGFR). Radiolabeled inhibitors of receptor tyrosine kinases (RTKs) might be useful tools for monitoring RTKs levels in tumor tissue giving valuable information for anti-angiogenic therapy. Herein we report the synthesis of 5-methoxy-sunitinib 5 and its 11C-radiolabeled analog [11C]-5. The non-radioactive reference compound 5 was prepared by Knoevenagel condensation of 5-methoxy-2-oxindole with the corresponding substituted 5-formyl-1H-pyrrole. A binding constant (Kd) of 20 nM for 5 was determined by competition binding assay against VEGFR-2. In addition, the binding mode of sunitinib® and its 5-methoxy substituted derivative was studied by flexible docking simulations. These studies revealed that the substitution of the fluorine at position 5 of the oxindole scaffold by a methoxy group did not affect the inhibitor orientation, but affected the electrostatic and van der Waals interactions of the ligand with residues near the DFG motif of VEGFR-2. 5-[11C]methoxy-sunitinib ([11C]-5) was synthesized by reaction of the desmethyl precursor with [11C]CH3I in the presence of DMF and NaOH in 17 ± 3% decay-corrected radiochemical yield at a specific activity of 162–205 GBq/μmol (EOS). In vivo stability studies of [11C]-5 in rat blood showed that more than 70% of the injected compound was in blood stream, 60 min after administration.

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► 5-Methoxy-sunitinib is an inhibitor of VEGFR-2 tyrosine kinase (Kd = 20 nM).
► Docking simulations show that methoxy-group does not affect inhibitor orientation.
► The electrostatic and van der Waals interactions with VEGFR-2 are affected.
► The 11C-labeled analog was synthesized as potential radiotracer.
► Radiotracer is metabolic stable in vivo (70% intact after 60 min).