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Angiogenesis is a process by which new blood vessels are formed from the pre-existing vasculature, and it is a key process that leads to tumour development. Some studies have recognized phenolic compounds as chemopreventive agents; flavonoids, in particular, seem to suppress the growth of tumor cells modifying the cell cycle. Herein, the antiangiogenic activity of Roman chamomile (Chamaemelum nobile L.) extracts (methanolic extract and infusion) and the main phenolic compounds present (apigenin, apigenin-7-O-glucoside, caffeic acid, chlorogenic acid, luteolin, and luteolin-7-O-glucoside) was evaluated through enzymatic assays using the tyrosine kinase intracellular domain of the Vascular Endothelium Growth Factor Receptor-2 (VEGFR-2), which is a transmembrane receptor expressed fundamentally in endothelial cells involved in angiogenesis, and molecular modelling studies. The methanolic extract showed a lower IC50 value (concentration that provided 50% of VEGFR-2 inhibition) than the infusion, 269 and 301 μg mL(-1), respectively. Regarding phenolic compounds, luteolin and apigenin showed the highest capacity to inhibit the phosphorylation of VEGFR-2, leading us to believe that these compounds are involved in the activity revealed by the methanolic extract.

The synthesis and biological evaluation of novel 1-aryl-3-[2-, 3- or 4-(thieno[3,2-b]pyridin-7-ylthio)phenyl]ureas 3, 4 and 5 as VEGFR-2 tyrosine kinase inhibitors, are reported. The 1-aryl-3-[3-(thieno[3,2-b]pyridin-7-ylthio)phenyl]ureas 4a-4h, with the arylurea in the meta position to the thioether, showed the lowest IC₅₀ values in enzymatic assays (10-206 nM), the most potent compounds 4d-4h (IC₅₀ 10-28 nM) bearing hydrophobic groups (Me, F, CF₃ and Cl) in the terminal phenyl ring. A convincing rationalization was achieved for the highest potent compounds 4 as type II VEGFR-2 inhibitors, based on the simultaneous presence of: (1) the thioether linker and (2) the arylurea moiety in the meta position. For compounds 4, significant inhibition of Human Umbilical Vein Endothelial Cells (HUVECs) proliferation (BrdU assay), migration (wound-healing assay) and tube formation were observed at low concentrations. These compounds have also shown to increase apoptosis using the TUNEL assay. Immunostaining for total and phosphorylated (active) VEGFR-2 was performed by Western blotting. The phosphorylation of the receptor was significantly inhibited at 1.0 and 2.5 μM for the most promising compounds. Altogether, these findings point to an antiangiogenic effect in HUVECs., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The vascular endothelial growth factor receptor-2 (VEGFR-2) is a tyrosine kinase receptor involved in the growth and differentiation of endothelial cells that are implicated in tumor-associated angiogenesis. In this study, novel 1-aryl-3-[4-(thieno[3,2-d]pyrimidin-4-yloxy)phenyl]ureas were synthesized and evaluated for the VEGFR-2 tyrosine kinase inhibition. Three of these compounds showed good VEGFR-2 inhibition presenting low IC50 values (150-199 nM) in enzymatic assays, showing also a significant proliferation inhibition of VEGF-stimulated human umbilical vein endothelial cells (HUVECs) at low concentrations (0.5-1 µM), using the Bromodeoxyuridine (BrdU) assay, not affecting cell viability. The determination of the total and phosphorylated (active) VEGFR-2 was performed by western blot, and it was possible to conclude that the compounds significantly inhibit the phosphorylation of the receptor at 1 µM pointing to their antiproliferative mechanism of action in HUVECs. The molecular rationale for inhibiting the tyrosine kinase domain of VEGFR-2 was also performed and discussed using molecular docking studies.

Selective side-chain residue flexibility is an option available on AutoDock Vina docking software. This approach is promising as it attempts to provide a more realistic ligand-protein interaction environment without an unmanageable increase in computer processing time. However, studies validating this approach are still scarce. VEGFR-2 (vascular endothelial growth factor receptor 2), a known protein target for anti-angiogenic agents, was used in this study. Four residues located in the VEGFR-2 kinase site were selected and made flexible: Lys868, Glu885, Cys919, and Asp1046. The docking scores for all possible combinations of flexible residues were compared to the docking scores using a rigid conformation. The best overall docking scores were obtained using the Glu885 flexible conformation, with Pearson and Spearman rank correlation values of 0.568 and 0.543, respectively, and a 51% increase in processing time. Using different VEGFR-2 crystal structures, a similar trend was observed with the Glu885 flexible conformation presenting best scores. This study demonstrates that careful use of selective side-chain residue flexibility can improve AutoDock Vina docking score accuracy, without a significant increase in processing time. This methodology can be a valuable tool in drug design projects using VEGFR-2 but will also probably be useful if applied to other protein targets., (© 2011 John Wiley & Sons A/S.)