title: Peptide optimization and conjugation strategies in the development of molecularly targeted magnetic resonance imaging contrast agents.
abstract: Peptides are highly selective, high-affinity ligands for a diverse array of disease targets, but suitably derivatizing them for application as diagnostic or therapeutic agents often presents a significant challenge. Covalent modification with metal chelates frequently results in decreased binding affinity, so a variety of strategies must be explored to find suitable locations for modification and facile peptide conjugation chemistries that maintain or enhance binding affinity. In this chapter, we present a paradigm for systematically optimizing peptide binding and determining the favorable sites and methods for peptide conjugation. This strategy is illustrated by two case studies of peptide-based targeted gadolinium contrast agents: EP-2104R for diagnosis of thrombosis and EP-3533 for diagnosis of cardiac perfusion and fibrosis. Two different architectures for the peptide-metal complex conjugation were designed: EP-2104R contains a total of four gadolinium (Gd) chelates linked at the N- and C-termini, whereas EP-3533 is derivatized with three Gd chelates, two on the N-terminus and one on a lysine side chain. Detailed protocols are provided for two Gd chelate conjugation methods.
authors.affiliation: EPIX Pharmaceuticals, Lexington, MA, USA.
authors.forename: Andrew F
authors.initials: AF
authors.lastname: Kolodziej
authors.forename: Zhaoda
authors.initials: Z
authors.lastname: Zhang
authors.forename: Kirsten
authors.initials: K
authors.lastname: Overoye-Chan
authors.forename: Vincent
authors.initials: V
authors.lastname: Jacques
authors.forename: Peter
authors.initials: P
authors.lastname: Caravan
mesh_terms: D000595:Amino Acid Sequence; D003094:Collagen / Q000737:chemistry / Q000378:metabolism; D003287:Contrast Media / Q000737:chemistry; D005337:Fibrin / Q000378:metabolism; D005682:Gadolinium / Q000737:chemistry; D019786:Gadolinium DTPA / Q000737:chemistry; D006571:Heterocyclic Compounds / Q000737:chemistry; D006801:Humans; D008279:Magnetic Resonance Imaging; D008969:Molecular Sequence Data; D009942:Organometallic Compounds / Q000737:chemistry; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry; D013194:Staining and Labeling; D013329:Structure-Activity Relationship
chemical_list: D003287:Contrast Media; C503783:EP-2104R; D006571:Heterocyclic Compounds; D009942:Organometallic Compounds; D010455:Peptides; D005337:Fibrin; D003094:Collagen; C050823:gadolinium 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetate; D005682:Gadolinium; D019786:Gadolinium DTPA