title: Cyclic RGD peptidomimetics containing bifunctional diketopiperazine scaffolds as new potent integrin ligands.
abstract: The synthesis of eight bifunctional diketopiperazine (DKP) scaffolds is described; these were formally derived from 2,3-diaminopropionic acid and aspartic acid (DKP-1-DKP-7) or glutamic acid (DKP-8) and feature an amine and a carboxylic acid functional group. The scaffolds differ in the configuration at the two stereocenters and the substitution at the diketopiperazinic nitrogen atoms. The bifunctional diketopiperazines were introduced into eight cyclic peptidomimetics containing the Arg-Gly-Asp (RGD) sequence. The resulting RGD peptidomimetics were screened for their ability to inhibit biotinylated vitronectin binding to the purified integrins α(v)β(3) and α(v)β(5), which are involved in tumor angiogenesis. Nanomolar IC(50) values were obtained for the RGD peptidomimetics derived from trans DKP scaffolds (DKP-2-DKP-8). Conformational studies of the cyclic RGD peptidomimetics by (1)H NMR spectroscopy experiments (VT-NMR and NOESY spectroscopy) in aqueous solution and Monte Carlo/Stochastic Dynamics (MC/SD) simulations revealed that the highest affinity ligands display well-defined preferred conformations featuring intramolecular hydrogen-bonded turn motifs and an extended arrangement of the RGD sequence [Cβ(Arg)-Cβ(Asp) average distance ≥8.8 Å]. Docking studies were performed, starting from the representative conformations obtained from the MC/SD simulations and taking as a reference model the crystal structure of the extracellular segment of integrin α(v)β(3) complexed with the cyclic pentapeptide, Cilengitide. The highest affinity ligands produced top-ranked poses conserving all the important interactions of the X-ray complex.
authors.affiliation: Università degli Studi di Milano, Dipartimento di Chimica Organica e Industriale, Via Venezian, 21, I-20133, Milan, Italy.
authors.forename: Mattia
authors.initials: M
authors.lastname: Marchini
authors.forename: Michele
authors.initials: M
authors.lastname: Mingozzi
authors.forename: Raffaele
authors.initials: R
authors.lastname: Colombo
authors.forename: Ileana
authors.initials: I
authors.lastname: Guzzetti
authors.forename: Laura
authors.initials: L
authors.lastname: Belvisi
authors.forename: Francesca
authors.initials: F
authors.lastname: Vasile
authors.forename: Donatella
authors.initials: D
authors.lastname: Potenza
authors.forename: Umberto
authors.initials: U
authors.lastname: Piarulli
authors.forename: Daniela
authors.initials: D
authors.lastname: Arosio
authors.forename: Cesare
authors.initials: C
authors.lastname: Gennari
mesh_terms: D054659:Diketopiperazines / Q000737:chemistry*; D039302:Integrin alphaVbeta3 / Q000737:chemistry / Q000378:metabolism; D016023:Integrins / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D009842:Oligopeptides / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000737:chemistry*; D011485:Protein Binding; D019030:Receptors, Vitronectin / Q000737:chemistry / Q000378:metabolism
chemical_list: D054659:Diketopiperazines; D039302:Integrin alphaVbeta3; D016023:Integrins; D008024:Ligands; D009842:Oligopeptides; D010456:Peptides, Cyclic; D019030:Receptors, Vitronectin; C507169:cyclic arginine-glycine-aspartic acid peptide; C064660:integrin alphaVbeta5