Cyclic RGD and <i>iso</i>DGR Integrin Ligands Containing <i>cis</i>-2-amino-1-cyclopentanecarboxylic (<i>cis</i>-β-ACPC) Scaffolds

• Main Authors: Silvia Panzeri, Daniela Arosio, Silvia Gazzola, Laura Belvisi, Monica Civera, Donatella Potenza, Francesca Vasile, Isabell Kemker, Thomas Ertl, Norbert Sewald, Oliver Reiser, Umberto Piarulli
• Format: Article
• Language: English
• Published: MDPI AG 2020-12-01
• Series: Molecules
• Subjects: peptidomimetics; integrin ligands; beta-amino acids; NMR conformational analysis
• Online Access: https://www.mdpi.com/1420-3049/25/24/5966

Integrin ligands containing the tripeptide sequences Arg-Gly-Asp (RGD) and <i>iso</i>-Asp-Gly- Arg (<i>iso</i>DGR) were actively investigated as inhibitors of tumor angiogenesis and directing unit in tumor-targeting drug conjugates. Reported herein is the synthesis, of two RGD and one <i>iso</i>DGR cyclic peptidomimetics containing (1<i>S</i>,2<i>R</i>) and (1<i>R</i>,2<i>S</i>) <i>cis</i>-2-amino-1-cyclopentanecarboxylic acid (<i>cis</i>-β-ACPC), using a mixed solid phase/solution phase synthetic protocol. The three ligands were examined in vitro in competitive binding assays to the purified α_vβ₃ and α₅β₁ receptors using biotinylated vitronectin (α_vβ₃) and fibronectin (α₅β₁) as natural displaced ligands. The IC50 values of the ligands ranged from nanomolar (the two RGD ligands) to micromolar (the isoDGR ligand) with a pronounced selectivity for α_vβ₃ over α₅β₁. In vitro cell adhesion assays were also performed using the human skin melanoma cell line WM115 (rich in integrin α_vβ₃). The two RGD ligands showed IC₅₀ values in the same micromolar range as the reference compound (<i>cyclo</i>[RGDfV]), while for the <i>iso</i>DGR derivative an IC₅₀ value could not be measured for the cell adhesion assay. A conformational analysis of the free RGD and <i>iso</i>DGR ligands by NMR (VT-NMR and NOESY experiments) and computational studies (MC/EM and MD), followed by docking simulations performed in the α_Vβ₃ integrin active site, provided a rationale for the behavior of these ligands toward the receptor.