Contrast media: future aspects.

In spite of the dramatic development in CT, there was no major breakthrough in the iodinated contrast media development. New agents based on hybrid between MRI and CT compounds may be a new innovative alternative. This new approach may also open new indications such as radiotherapy.

Gadofluorine 8: initial experience with a new contrast medium for interstitial MR lymphography.

RATIONALE AND OBJECTIVES: Differential diagnosis of malignant and beign lymph nodes is still a problem in lymphographic imaging modalities. Plain magnetic resonance imaging (MRI) and computed tomography (CT) are inadequate for detecting metastases in normal-sized lymph nodes and for differentiating enlarged nodes. Therefore it is important to have a contrast agent that accumulates in healthy lymphatic tissue but does not accumulate in metastatic deposits. METHODS: The lymphographic contrast agent Gadofluorine 8 (Schering AG, Berlin, Germany) is a lipophilic but water-soluble gadolinium complex. Lymphographic effects were investigated in guinea pigs, dogs, and tumor-bearing rabbits after interstitial (subcutaneous or intracutaneous) injection. MR imaging was performed using T1-weighted gradient-echo sequences until 120 min after administration. RESULTS: After interstitial injection Gadofluorine 8 accumulates in regional lymph nodes, resulting in a pronounced increase in signal intensity in the lymph nodes. Differentiation between normal and metastatic lymph nodes was achieved. CONCLUSIONS: Gadofluorine 8 is an innovative contrast agent that can distinguish between normal and tumorous lymph nodes in interstitial MR lymphography.

Gadolinium neutron capture therapy (GdNCT) of melanoma cells and solid tumors with the magnetic resonance imaging contrast agent Gadobutrol.

RATIONALE AND OBJECTIVES: The therapeutic gain of neutron capture therapy with a neutral macrocyclic gadolinium (Gd) complex (Gadobutrol) was evaluated through in vitro and in vivo studies in a beam of low-energy neutrons. METHODS: Neutron irradiation for both the in vitro and in vivo studies was performed in a beam of low-energy neutrons produced by the research reactor of the Hahn-Meitner-Institut, Berlin. Malignant melanoma cells of human origin were irradiated in the presence or absence of Gadobutrol. In vivo irradiation was performed on tumor-bearing nude mice. The tumor site was irradiated subsequent to intratumoral injection of Gadobutrol and compared with irradiation in the absence of the Gd complex. RESULTS: In vitro studies showed a Gd-dependent delay of cell proliferation as a consequence of neutron irradiation. In animals, intratumoral administration of the Gd complex at a dose of 1.2 mmol Gd/kg before neutron irradiation results in a significant delay in tumor growth with respect to the control groups. CONCLUSIONS: In vitro and in vivo studies showed a therapeutic benefit with the neutral Gd complex and suggest Gd-containing magnetic resonance contrast media are potential candidates for neutron capture therapy. The Gd dose used in the irradiation experiments was four times the presently accepted high dose in clinical magnetic resonance imaging.

Synthesis and Physicochemical Characterization of a New Gadolinium Chelate: The Liver-Specific Magnetic Resonance Imaging Contrast Agent Gd-EOB-DTPA.

A convenient synthesis of disodium S-[4-(4-ethoxybenzyl)-3,6,9-tris[(carboxy-kappaO)methyl]-3,6,9-triazaundecandioato)(5-)-kappa(3)N(3)(),N(6)(),N(9)(),kappa(2)O(1)(),O(11)()]gadolinate(2-) (Gd-EOB-DTPA), 1, is reported. This water-soluble complex is presently undergoing phase III clinical trials as a liver-specific contrast agent for magnetic resonance imaging (MRI). The thermodynamic complex stability constant of 1 and the acid dissociation constants of the ligand have been determined as well as the stability constant of the calcium complex Ca-EOB-DTPA (2), which is used as an additive in the pharmaceutical formulation of the contrast agent. The solid-state structure of the ligand S-4-(4-ethoxybenzyl)-3,6,9-tris(carboxylatomethyl)-3,6,9-triazaundecanedioic acid (H(5)EOB-DTPA), 3, has been elucidated in a single crystal X-ray diffraction study. Additionally, HPLC evidence is given that the enantiomerically pure ligand forms two diastereomeric gadolinium complexes in a 65:35 ratio. The kinetics of isomerization of the isolated diastereomers-as dependent on pH and temperature-has been investigated, and thus, the activation energy for the interconversion of these isomers has been estimated to be 75.3 kJ mol(-1). Finally, the structures of the two components of 1 are discussed in terms of four possible diastereomers.

Synthesis and Structure of a New Macrocyclic Polyhydroxylated Gadolinium Chelate Used as a Contrast Agent for Magnetic Resonance Imaging.

Three approaches to the synthesis of a new ligand 1,4,7-tris(carboxymethyl)-10-(1-(hydroxymethyl)-2,3-dihydroxypropyl)-1,4,7,10-tetraazacyclododecane (6) are described. This ligand forms the both thermodynamically and kinetically very stable gadolinium chelate Gadobutrol (1), which is a neutral and highly hydrophilic compound that is used for magnetic resonance imaging in the clinic. According to the crystal structure the Gd(III) ion in 1 is nine coordinated. The ligand provides eight coordination sites whereas the ninth coordination partner surprisingly is a carboxylate oxygen of a neighboring centrosymmetrically-related complex molecule. Ligand 6 was also utilized to prepare the calcium complex 12 which is used as an additive in the pharmaceutical formulation of 1. For the calcium complex 12, two complex molecules adopting almost identical conformations are present in the crystal.

Noninvasive temperature measurement in vivo using a temperature-sensitive lanthanide complex and 1H magnetic resonance spectroscopy.

A new lanthanide complex, praseodymium-2-methoxyethyl-DO3A, was tested as a temperature indicator for 1H magnetic resonance spectroscopy under in vivo conditions, using a 2-T imaging system. The chemical shift of the methoxy group of the compound is strongly temperature dependent. In vitro, a shift change of -0.131 ppm/degree C was found. The signal was shifted by about -24 ppm relative to the water signal, allowing easy water suppression and signal identification in vivo. The body temperatures of eight anesthetized rats were measured in the liver after intravenous administration of 1 mmol/kg of the praseodymium complex under different heating conditions of the animal. The temperatures calculated from the spectra were in good agreement (deviation < +/- 1 degree C) with values obtained simultaneously with a thermocouple placed in the rectum of the animals.

Pre-clinical evaluation of gadobutrol: a new, neutral, extracellular contrast agent for magnetic resonance imaging.

The Gd(3+)-complex of 10-(2,3-dihydroxy-1-hydroxymethylpropyl)-1,4,7,10-tetraazacyclo dodecane-1,4,7-triacetic acid(gadobutrol) is a new, neutral Gd-chelate for use as an extracellular contrast agent in magnetic resonance imaging (MRI). The blood level in dogs after intravenous (i.v.) injection decreased with a terminal half-life of about 45 min, the clearance was about 3.75 ml/min per kg and the distribution volume of 0.23 l/kg suggested an extracellular distribution. Biodistribution experiments in rats revealed that only a very small amount (0.16%) of the dose was left in the body 7 days after i.v. injection. Measurable amounts of Gd could be detected only in the liver, kidneys and bones. The osmolality (0.57 osmol/kg at 0.5 mol/l and 1.39 osmol/kg at 1 mol/l) is in the range of other low osmolality contrast media for MRI. Only very little interaction with biologically relevant molecules was suggested by a histamine release test and a lysozyme inhibition test. An i.v.-LD50 of 23 mmol/kg in mice combined with a comparatively high T1-relaxivity (5.6 l/mmol per s at 0.47 T and 6.1 l/mmol per s at 2 T) in plasma promises a high margin of safety. In preliminary imaging experiments, gadobutrol caused high enhancement in different lesions (cerebral infarct, brain tumor) of the rat. Tripling of the typical clinical dose of 0.1 mmol/kg was shown to provide additional diagnostic gain in lesions of this type.

Characterization of a gadolinium-labeled cholesterol derivative as an organ-specific contrast agent for adrenal MR imaging.

The purpose of the study was to determine if derivatization of cholesterol with a paramagnetic label could result in an organ-specific contrast agent for magnetic resonance imaging of the adrenal glands. Gadolinium-DO3A-labeled cholesterol was synthesized and the relaxivities in water and blood plasma determined at 0.47 T and 40 degrees C. Organ distribution was measured at 2 (n = 2) and 24 (n = 2) hours after intravenous injection of a 50 mumol/kg dose of Gd-DO3A-cholesterol in rats weighing 220-240 g. T1-weighted spin-echo images were acquired at 2 T before and after injection of 50 mumol/kg Gd-DO3A-cholesterol (n = 2) and Gd-DTPA (diethylenetriaminepentaacetic acid)-albumin (n = 2). More than 99% of the Gd-DO3A-cholesterol was found to be protein bound in bovine serum. High T1 and T2 relaxivities were found in water and plasma. High tissue concentrations of Gd-DO3A-cholesterol were found only in adrenal glands and liver. At 24 hours, adrenal gadolinium concentrations were about 10 times higher than in blood. At 2 hours after injection of Gd-DO3A-cholesterol, enhancement was 162% in adrenal glands and 146% in liver. With Gd-DTPA-albumin, enhancement values were 57% and 56%, respectively.

Pharmacokinetics, dose proportionality, and tolerability of gadobutrol after single intravenous injection in healthy volunteers.

RATIONALE AND OBJECTIVES: Gadobutrol is a new gadolinium-based hydrophilic and neutral macrocyclic contrast medium for magnetic resonance imaging. In this article, the authors report on the first application of gadobutrol in humans, up to a dose of 0.5 mmol/kg. METHODS: Gadobutrol was investigated after single intravenous administration in two phase-1 studies testing low (0.5 mol/L) and high concentrations (1 mol/L) in healthy, male volunteers using a double-blind, randomized, placebo-controlled study with n = 55 for the low concentration (0.04, 0.1, 0.2, 0.3, and 0.4 mmol/kg body weight), followed by n = 36 for the high concentration (0.3, 0.4, and 0.5 mmol/kg body weight). Vital signs and laboratory parameters were measured for all dose groups investigated, whereas for the calculation of the pharmacokinetic parameters, the dose groups 0.04, 0.1, and 0.4 mmol/kg body weight were selected. RESULTS: Gadobutrol was well tolerated up to doses of 0.5 mmol/kg, and no relevant changes in vital signs and laboratory parameters occurred. The terminal disposition half-life of gadobutrol in plasma was approximately 1.5 hours. Total clearance approximated renal clearance and approximated the value of 120 mL/min, indicating glomerular filtration as the main pathway of elimination. The steady-state volume of distribution indicated predominantly extracellular distribution of gadobutrol. No metabolites were detected. The renal excretion rate was linear over the large dose range tested, indicating dose-proportionate, first-order kinetics of gadobutrol. CONCLUSION: Single intravenous administration of gadobutrol was well tolerated up to the dose level of 0.5 mmol/kg body weight. These factors suggest that gadobutrol will be a safe magnetic resonance imaging contrast agent.