title: Multivalent protein polymer MRI contrast agents: controlling relaxivity via modulation of amino acid sequence.
abstract: Magnetic resonance imaging is a noninvasive imaging modality with high spatial and temporal resolution. Contrast agents (CAs) are frequently used to increase the contrast between tissues of interest. To increase the effectiveness of MR agents, small molecule CAs have been attached to macromolecules. We have created a family of biodegradable, macromolecular CAs based on protein polymers, allowing control over the CA properties. The protein polymers are monodisperse, random coil, and contain evenly spaced lysines that serve as reactive sites for Gd(III) chelates. The exact sequence and length of the protein can be specified, enabling controlled variation in lysine spacing and molecular weight. Relaxivity could be modulated by changing protein polymer length and lysine spacing. Relaxivities of up to approximately 14 mM(-1) s(-1) per Gd(III) and approximately 461 mM(-1) s(-1) per conjugate were observed. These CAs are biodegradable by incubation with plasmin, such that they can be easily excreted after use. They do not reduce cell viability, a prerequisite for future in vivo studies. The protein polymer CAs can be customized for different clinical diagnostic applications, including biomaterial tracking, as a balanced agent with high relaxivity and appropriate molar mass.
authors.affiliation: Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA.
authors.forename: Lindsay S
authors.initials: LS
authors.lastname: Karfeld-Sulzer
authors.forename: Emily A
authors.initials: EA
authors.lastname: Waters
authors.forename: Nicolynn E
authors.initials: NE
authors.lastname: Davis
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Meade
authors.forename: Annelise E
authors.initials: AE
authors.lastname: Barron
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D001672:Biocompatible Materials / Q000737:chemistry* / Q000633:toxicity; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002614:Chelating Agents / Q000737:chemistry; D003287:Contrast Media / Q000737:chemistry* / Q000633:toxicity; D004591:Electrophoresis, Polyacrylamide Gel; D005341:Fibrinolysin / Q000737:chemistry; D005682:Gadolinium / Q000737:chemistry; D008279:Magnetic Resonance Imaging; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011994:Recombinant Proteins / Q000737:chemistry* / Q000235:genetics / Q000633:toxicity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D001672:Biocompatible Materials; D002614:Chelating Agents; D003287:Contrast Media; D011994:Recombinant Proteins; D005682:Gadolinium; D005341:Fibrinolysin