A novel conformationally constrained RGD-based cyclic peptide targeting integrin αvβ6 protein for antitumor therapeutic applications.

The arginine-glycine-aspartic acid (RGD) tripeptide sequence is widely distributed in extracellular matrix proteins enabling efficient targeting of integrin receptors that are overexpressed on the surface of tumor cells, thereby facilitating the selective delivery of therapeutic molecules to tumor tissues. Cyclic RGD peptides are widely recognized for their higher target affinity relative to linear counterparts, and numerous RGD-based peptides have been evaluated in clinical trials. In this study, we report the synthesis and bioactivity of a novel cyclic RGD peptide incorporating a conformationally constrained isoindolinone scaffold. The target cyclopeptide was prepared via an intramolecular photoinduced single-electron transfer cyclization reaction, and the absolute configuration was unambiguously determined through combined experimental and theoretical electronic circular dichroism (ECD) analyses. We also systematically screened potential targets of the prepared peptide using pharmacophore mapping (TargetNet) combined with reverse molecular docking (GalaxySagittarius-AF), which predicted high binding affinity of the synthesized cyclic peptide for the integrin αvβ6 receptor. This finding was further validated through experimental bio-layer interferometry assays, and molecular docking and molecular dynamics simulations. Comprehensive in vitro and in vivo biological evaluations revealed that cyclic peptide effectively suppresses tumor cell proliferation and induces both apoptosis and autophagy.