A starburst-shaped heterometallic compound incorporating six densely packed gd(3+) ions.
ABSTRACT The heterotritopic ligand [bpy(DTTA)2]8- has two diethylenediamine-tetraacetate units for selective lanthanide(III) coordination and one bipyridine function for selective Fe(II) coordination. In aqueous solution and in the presence of these metals, the ligand is capable of self-assembly to form a rigid supramolecular metallostar structure, [Fe[Gd2bpy(DTTA)2(H2O)4]3]4-. We report here the physicochemical characterization of the dinuclear complex [Gd2bpy(DTTA)2(H2O)4]2- and the metallostar [Fe[Gd2bpy(DTTA)2(H2O)4]3]4- with regard to potential MRI contrast agent applications. A combination of pH potentiometry and 1H NMR spectroscopy has been used to determine protonation constants for the ligand [bpy(DTTA)2]8- and for the complexes [Fe[bpy(DTTA)2]3]22- and [Y2bpy(DTTA)2]2-. In addition, stability constants have been measured for the dinuclear chelates [M2bpy(DTTA)2]n- formed with M = Gd3+ and Zn2+ (log K(GdL) = 18.2; log K(ZnL) = 18.0; log K(ZnHL) = 3.4). A multiple field, variable-temperature 17O NMR and proton relaxivity study on [Gd2bpy(DTTA)2(H2O)4]2- and [Fe[Gd2bpy(DTTA)2(H2O)4]3](4-) yielded the parameters for water exchange and the rotational dynamics. The 17O chemical shifts are indicative of bishydration of the lanthanide ion. The exchange rates of the two inner-sphere water molecules are very similar in the dinuclear [Gd2bpy(DTTA)2(H2O)(4)]2- and in the metallostar (k(ex)298 = 8.1 +/- 0.3 x 10(6) and 7.4 +/- 0.2 x 10(6) s(-1), respectively), and are comparable to k(ex)298 for similar Gd(III) poly(amino carboxylates). The rotational dynamics of the metallostar has been described by means of the Lipari-Szabo approach, which involves separating global and local motions. The difference between the local and global rotational correlation times, tau(lO)298 = 190 +/- 15 ps and tau(gO)298 = 930 +/- 50 ps, respectively, shows that the metallostar is not completely rigid. However, the relatively high value of S2 = 0.60 +/- 0.04, describing the restriction of the local motions with regard to the global one, points to a limited flexibility compared with previously reported macromolecules such as dendrimers. As a result of the two inner-sphere water molecules, with their near-optimal exchange rate, and the limited flexibility, the metallostar has a remarkable molar proton relaxivity, particularly at high magnetic fields (r1 = 33.2 and 16.4 mM(-1) s(-1) at 60 and 200 MHz, respectively, at 25 degrees C). It packs six efficiently relaxing Gd(III) ions into a small molecular space, which leads, to the best of our knowledge, to the highest relaxivity per molecular mass ever reported for a Gd(III) complex. The [bpy(DTTA)2]8- ligand is also a prime candidate as a terminal ligand for constructing larger sized, Fe(II) (or Ru(II))-based metallostars or metallodendrimers loaded with Gd(III) on the surface.
Article: In vivo MRI assessment of a novel GdIII-based contrast agent designed for high magnetic field applications.[show abstract] [hide abstract]
ABSTRACT: Gd(3)L is a trinuclear Gd(3+) complex of intermediate size, designed for contrast agent applications in high field magnetic resonance imaging (H(12)L is based on a trimethylbenzene core bearing three methylene-diethylenetriamine- N,N,N'',N''-tetraacetate moieties). Thanks to its appropriate size, the presence of two inner sphere water molecules and a fast water exchange, Gd(3)L has remarkable proton relaxivities at high magnetic field (r(1) = 10.2 vs 3.0 mM(-1) s(-1) for GdDOTA at 9.4 T, 37 degrees C, in H(2)O). Here we report an in vivo MRI feasibility study, complemented with dynamic gamma scintigraphic imaging and biodistribution experiments using the (153)Sm-enriched analog. MRI experiments were performed at 9.4 T in mice with Gd(3)L and the commercial contrast agent gadolinium(III)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (GdDOTA). Gd(3)L was well tolerated by the animals at the dose of 8 micromol Gd kg(-1) body weight. Dynamic contrast enhanced (DCE) images showed considerably higher signal enhancement in the kidney medulla and cortex after Gd(3)L injection than after GdDOTA injection at an identical dose. The relaxation rates, DeltaR(1), were calculated from the IR TrueFISP data. During the excretory phase, the DeltaR(1) for various tissues was similar for Gd(3)L and GdDOTA, when the latter was injected at a three-fold higher dose (24 vs 8 micromol Gd kg(-1) body weight). These results point to an approximately three times higher in vivo relaxivity (per Gd) for Gd(3)L relative to GdDOTA, thus the ratio of the relaxivities of the two compounds determined in vitro is retained under in vivo conditions. They also indicate that the two inner sphere water molecules per Gd in Gd(3)L are not substantially replaced by endogenous anions or other donor groups under physiological conditions. Gd(3)L has a pharmacokinetics typical of small, hydrophilic complexes, involving fast renal clearance and no retention in the blood pool. The dynamic gamma scintigraphic studies and the biodistribution experiments performed in Wistar rats with (153)Sm-enriched (*)Sm(3)L are also indicative of a fast elimination via the kidneys.Contrast Media & Molecular Imaging 04/2008; 3(2):78-85. · 3.33 Impact Factor
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ABSTRACT: We have developed a modular architecture for preparing high-relaxivity multiplexed probes utilizing click chemistry. Our system incorporates azide bearing Gd(III) chelates and a trialkyne scaffold with a functional group for subsequent modification. In optimizing the relaxivity of this new complex, we undertook a study of the linker length between a chelate and the scaffold to determine its effect on relaxivity. The results show a strong dependence on flexibility between the individual chelates and the scaffold with decreasing linker length leading to significant increases in relaxivity. Nuclear magnetic resonance dispersion (NMRD) spectra were obtained to confirm a 10-fold increase in the rotational correlation time from 0.049 to 0.60 ns at 310 K. We have additionally obtained a crystal structure demonstrating that modification with an azide does not impact the coordination of the lanthanide. The resulting multinuclear center has a 500% increase in per Gd (or ionic) relaxivity at 1.41 T versus small molecule contrast agents and a 170% increase in relaxivity at 9.4 T.Journal of the American Chemical Society 03/2011; 133(14):5329-37. · 9.91 Impact Factor
Article: Pharmacokinetic and in vivo evaluation of a self-assembled gadolinium(III)-iron(II) contrast agent with high relaxivity.[show abstract] [hide abstract]
ABSTRACT: A high-molecular weight tetrametallic supramolecular complex [(Ln-DTPA-phen)3Fe]- (Ln = Gd, Eu, La) has been obtained upon self-assembly around one iron(II) ion of three 1,10-phenantroline-based molecules substituted in 5'-position with the polyaminocarboxylate diethylenetriamine-N,N,N',N',N'-pentaacetate, DTPA-phen(4-). The ICP-MS measurements indicated that the lanthanide:iron ratio is 3:1. Photoluminescence spectra of [Eu-DTPA-phen](-) and of [(Eu-DTPA-phen)3Fe]- are nearly identical, implying that the first coordination sphere of the lanthanide(III) ion has not been changed upon coordination of phenantroline unit to iron(II) ion. NMRD measurements revealed that at 20 MHz and 310 K the relaxivity of the [(Gd-DTPA-phen)3Fe]- is equal to 9.5 +/- 0.3 s(-1) mM(-1) of Gd (28.5 s(-1) per millimole per liter of complex) which is significantly higher than that for Gd-DTPA (3.9 s(-1) mM(-1)). The pharmacokinetic parameters of [(Gd-DTPA-phen)3Fe]- in rats indicate that the elimination of [(Gd-DTPA-phen)3Fe]- is significantly slower than that of Gd-DTPA and is correlated with a reduced volume of distribution. The low volume of distribution and the longer elimination time (T(e1/2)) suggest that the agent is confined to the blood compartment, so it could have an important potential as a blood pool contrast agent. The biodistribution profile of [(Gd-DTPA-phen)3Fe]- 2 h after injection indicates significantly higher concentrations of [(Gd-DTPA-phen)3Fe]- as compared with Gd-DTPA in kidney, liver, lungs, heart and spleen. The images obtained on rats by MR angiography show the enhancement of the abdominal blood vessels. The signal intensity reaches a maximum of 55% at 7 min post-contrast and remains around 25% after 90 min. MRI-histomorphological correlation studies of [Gd-DTPA-phen]- and [(Gd-DTPA-phen)3Fe]- showed that both agents displayed potent contrast enhancement in organs including the liver. The necrosis avidity tests indicated that, in contrast to the [Gd-DTPA-phen](-) precursor complex, the supramolecular complex [(Gd-DTPA-phen)3Fe]- exhibits necrosis avidity.Contrast Media & Molecular Imaging 12/2006; 1(6):267-78. · 3.33 Impact Factor