title: NGR Tumor-Homing Peptides: Structural Requirements for Effective APN (CD13) Targeting.
abstract: Cyclic CNGRC (cCNGRC) peptides are very important targeting ligands for Aminopeptidase N (APN or CD13), which is overexpressed on the surface of many cancer cells. In this work we have (1) developed an efficient solid-phase synthesis and (2) tested on purified porcine APN and APN-expressing human cells two different classes of cCNGRC peptides: the first carrying a biotin affinity tag or a fluorescent tag attached to the carboxyl Arg-Cys-COOH terminus and the second with the tags attached to the amino H2N-Cys-Asn terminus. Carboxyl-terminus functionalized cCNGRC peptides 3, 6, and 8 showed good affinity for porcine APN and very good capacity to target and be internalized into APN-expressing cells. In contrast, amino-terminus functionalized cCNGRC peptides 4, 5, and 7 displayed significantly decreased affinity and targeting capacity. These results, which are in agreement with the recently reported X-ray structure of a cCNGRC peptide bound to APN showing important stabilizing interactions between the unprotected cCNGRC amino terminus and the APN active site, indicate that the carboxyl and not the amino-terminus of cCNGRC peptides should be used as a "handle" for the attachment of toxic payloads for therapy or isotopically labeled functions for imaging and nuclear medicine.
authors.affiliation: Kosterlitz Centre for Therapeutics and Aberdeen Biomedical Imaging Centre, University of Aberdeen , Aberdeen, AB25 2ZD, Scotland, United Kingdom.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Graziadio
authors.affiliation: Kosterlitz Centre for Therapeutics and Aberdeen Biomedical Imaging Centre, University of Aberdeen , Aberdeen, AB25 2ZD, Scotland, United Kingdom.|C.N.R. - I.C.R.M. , via Mancinelli 7, 20131 Milan, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Zanda
authors.affiliation: Kosterlitz Centre for Therapeutics and Aberdeen Biomedical Imaging Centre, University of Aberdeen , Aberdeen, AB25 2ZD, Scotland, United Kingdom.
authors.forename: Simona
authors.initials: S
authors.lastname: Frau
authors.affiliation: Kosterlitz Centre for Therapeutics and Aberdeen Biomedical Imaging Centre, University of Aberdeen , Aberdeen, AB25 2ZD, Scotland, United Kingdom.
authors.forename: Ian N
authors.initials: IN
authors.lastname: Fleming
authors.affiliation: Kosterlitz Centre for Therapeutics and Aberdeen Biomedical Imaging Centre, University of Aberdeen , Aberdeen, AB25 2ZD, Scotland, United Kingdom.
authors.forename: Manuele
authors.initials: M
authors.lastname: Musolino
authors.affiliation: Kosterlitz Centre for Therapeutics and Aberdeen Biomedical Imaging Centre, University of Aberdeen , Aberdeen, AB25 2ZD, Scotland, United Kingdom.
authors.forename: Sergio
authors.initials: S
authors.lastname: Dall'Angelo
authors.affiliation: Kosterlitz Centre for Therapeutics and Aberdeen Biomedical Imaging Centre, University of Aberdeen , Aberdeen, AB25 2ZD, Scotland, United Kingdom.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Baldassarre
authors.affiliation: Kosterlitz Centre for Therapeutics and Aberdeen Biomedical Imaging Centre, University of Aberdeen , Aberdeen, AB25 2ZD, Scotland, United Kingdom.
authors.forename: Monica
authors.initials: M
authors.lastname: Piras
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018826:CD13 Antigens / Q000378:metabolism*; D045744:Cell Line, Tumor; D006801:Humans; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D013552:Swine
chemical_list: C526428:NGR peptide; D009842:Oligopeptides; D018826:CD13 Antigens