title: Gd(DOTAla): a single amino acid Gd-complex as a modular tool for high relaxivity MR contrast agent development.
abstract: MR imaging at high magnetic fields benefits from an increased signal-to-noise ratio; however T(1)-based MR contrast agents show decreasing relaxivity (r(1)) at higher fields. High field, high relaxivity contrast agents can be designed by carefully controlling the rotational dynamics of the molecule. To this end, we investigated applications of the alanine analogue of Gd(DOTA), Gd(DOTAla). Fmoc-protected DOTAla suitable for solid phase peptide synthesis was synthesized and integrated into polypeptide structures. Gd(III) coordination results in very rigid attachment of the metal chelate to the peptide backbone through both the amino acid side chain and coordination of the amide carbonyl. Linear and cyclic monomers (GdL1, GdC1), dimers (Gd(2)L2, Gd(2)C2), and trimers (Gd(3)L3, Gd(3)C3) were prepared and relaxivities were determined at different field strengths ranging from 0.47 to 11.7 T. Amide carbonyl coordination was indirectly confirmed by determination of the hydration number q for the EuL1 integrated into a peptide backbone, q = 0.96 ± 0.09. The water residency time of GdL1 at 37 °C was optimal for relaxivity, τ(M) = 17 ± 2 ns. Increased molecular size leads to increased per Gd relaxivity (from r(1) = 7.5 for GdL1 to 12.9 mM(-1) s(-1) for Gd(3)L3 at 1.4 T, 37 °C). The cyclic, multimeric derivatives exhibited slightly higher relaxivities than the corresponding linearized multimers (Gd(2)C2: r(1) = 10.5 mM(-1) s(-1) versus Gd(2)C2-red r(1) = 9 mM(-1) s(-1) at 1.4 T, 37 °C). Overall, all six synthesized Gd complexes had higher relaxivities at low, intermediate, and high fields than the clinically used small molecule contrast agent [Gd(HP-DO3A)(H(2)O)].
authors.affiliation: The Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, 149 Thirteenth Street, Suite 2301, Charlestown, Massachusetts 02129, United States.
authors.forename: Eszter
authors.initials: E
authors.lastname: Boros
authors.forename: Miloslav
authors.initials: M
authors.lastname: Polasek
authors.forename: Zhaoda
authors.initials: Z
authors.lastname: Zhang
authors.forename: Peter
authors.initials: P
authors.lastname: Caravan
mesh_terms: D002614:Chelating Agents / Q000138:chemical synthesis / Q000737:chemistry; D003287:Contrast Media / Q000138:chemical synthesis / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry; D006571:Heterocyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008279:Magnetic Resonance Imaging; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D012709:Serum Albumin / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D002614:Chelating Agents; D003287:Contrast Media; D056831:Coordination Complexes; D006571:Heterocyclic Compounds; D009942:Organometallic Compounds; D010455:Peptides; D012709:Serum Albumin; D014867:Water; C050823:gadolinium 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetate