On-cell saturation transfer difference NMR study of Bombesin binding to GRP receptor.

• On-cell STD NMR allowed to study BN binding to GRP-R without receptor purification. • BN interaction with GRP-R was analysed in a physiologically relevant environment. • Trp8, His12, Leu13 and Met14 side chains constitute BN binding epitope. • This methodology will permit the rapid screening of new potential GRP-R ligands. We report the NMR characterization of the molecular interaction between Gastrin Releasing Peptide Receptor (GRP-R) and its natural ligand bombesin (BN). GRP-R is a transmembrane G-protein coupled receptor promoting the stimulation of cancer cell proliferation; in addition, being overexpressed on the surface of different human cancer cell lines, it is ideal for the development of new strategies for the selective targeted delivery of anticancer drugs and diagnostic devices to tumor cells. However, the design of new GRP-R binders requires structural information on receptor interaction with its natural ligands. The experimental protocol presented herein, based on on-cell STD NMR techniques, is a powerful tool for the screening and the epitope mapping of GRP-R ligands aimed at the development of new anticancer and diagnostic tools. Notably, the study can be carried out in a physiological environment, at the surface of tumoral cells overespressing GRP-R. Moreover, to the best of our knowledge, this is the first example of an NMR experiment able to detect and investigate the structural determinants of BN/GRP-R interaction. [ABSTRACT FROM AUTHOR]