title: Improving T₁ and T₂ magnetic resonance imaging contrast agents through the conjugation of an esteramide dendrimer to high-water-coordination Gd(III) hydroxypyridinone complexes.
abstract: Commercial gadolinium magnetic resonance imaging (MRI) contrast agents are limited by low relaxivity (r₁) and coordination to only a single water molecule (q = 1). Consequently, gram quantities of these agents must be injected to obtain sufficient diagnostic contrast. In this study, MRI contrast agents for T(1) and T₂ relaxivity were synthesized using hydroxypyridinone and terephthalamide chelators with mesityl and 1,4,7-triazacyclononane capping moieties. When covalently conjugated to a highly biocompatible esteramide dendrimer, T₂ relaxation rates up to 52 mm(-1)  s(-1) and T₁ relaxation rates up to 31 mm(-1)  s(-1) per gadolinium were observed under clinically relevant conditions. These values are believed to be brought about by using a dendritic macromolecule to decrease the molecular tumbling time of the small molecule complexes. These agents also show high aqueous solubility and low toxicity in vitro. In this study we report six new compounds: three discrete complexes and three dendrimer conjugates.
authors.affiliation: Department of Chemistry, University of California, Berkeley, CA 94720-1460, USA.
authors.forename: Piper J
authors.initials: PJ
authors.lastname: Klemm
authors.forename: William C
authors.initials: WC
authors.lastname: Floyd
authors.forename: Danil E
authors.initials: DE
authors.lastname: Smiles
authors.forename: Jean M J
authors.initials: JM
authors.lastname: Fréchet
authors.forename: Kenneth N
authors.initials: KN
authors.lastname: Raymond
mesh_terms: D003287:Contrast Media / Q000138:chemical synthesis* / Q000737:chemistry / Q000633:toxicity; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry / Q000633:toxicity; D050091:Dendrimers / Q000138:chemical synthesis* / Q000737:chemistry / Q000633:toxicity; D005682:Gadolinium / Q000737:chemistry*; D006367:HeLa Cells / Q000187:drug effects; D006571:Heterocyclic Compounds / Q000737:chemistry*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015394:Molecular Structure; D011522:Protons; D011728:Pyridones / Q000737:chemistry*; D012995:Solubility; D014867:Water
chemical_list: D003287:Contrast Media; D056831:Coordination Complexes; D050091:Dendrimers; D006571:Heterocyclic Compounds; D011522:Protons; D011728:Pyridones; D014867:Water; C075712:1,4,7-triazacyclononane; D005682:Gadolinium