Amino acid based gallium-68 chelators capable of radiolabeling at neutral pH

Gallium-68 ( 68 Ga) has been the subject of increasing interest for its potential in the production of radiotracers for diagnosis of diseases. In this work we report the complexation of 68 Ga by the amino acid based tripodal chelate H 3 Dpaa, and two bifunctional derivatives, H 3 Dpaa.dab and H 4 Dpaa.ga, under a range of conditions with particular emphasis on the rapid complexation of 68 Ga at pH 7.4. 100 μM H 3 Dpaa achieved a radiochemical yield of 95% at pH 7.4 in 5 minutes at 37 °C. The bifunctional derivatives H 4 Dpaa.ga and H 3 Dpaa.dab achieved 94% and 84% radiochemical yields, respectively, under the same conditions. The resulting Ga(iii) complexes show thermodynamic stabilities of logK GaDpaa = 18.53, logK GaDpaa.dab = 22.08, logK GaDpaa.ga = 18.36. Unfortunately, the resulting radiolabelled species do not present sufficient serum stability for in vivo application. Herein we show a flexible synthesis for bifunctional chelators based on amino acids that rapidly complex 68 Ga under physiological conditions

Ga(III) complexes with DOTA-like ligand - thermodynamic and kinetic stability

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Gallium(iii) complexes of nota-bis (phosphonate) conjugates as pet radiotracers for bone imaging

Ligands with geminal bis(phosphonic acid) appended to 1,4,7-triazacyclonone-1,4-diacetic acid fragment through acetamide (NOTAM(BP)) or methylenephosphinate (NO2AP(BP)) spacers designed for Ga-68 were prepared. Ga-III complexation is much faster for ligand with methylenephosphinate spacer than that with acetamide one, in both chemical (high reactant concentrations) and radiolabeling studies with no-carrier-added Ga-68. For both ligands, formation of Ga-III complex was slower than that with NOTA owing to the strong out-of-cage binding of bis(phosphonate) group. Radiolabeling was efficient and fast only above 60 degrees C and in a narrow acidity region (pH similar to 3). At higher temperature, hydrolysis of amide bond of the carboxamide-bis(phosphonate) conjugate was observed during complexation reaction leading to Ga-NOTA complex. In vitro sorption studies confirmed effective binding of the Ga-68 complexes to hydroxyapatite being comparable with that found for common bis(phosphonate) drugs such as pamindronate. Selective bone uptake was confirmed in healthy rats by biodistribution studies ex vivo and by positron emission tomography imaging in vivo. Bone uptake was very high, with SUV (standardized uptake value) of 6.19 +/- 1.27 for [Ga-68]NO2AP(BP)) at 60min p.i., which is superior to uptake of Ga-68-DOTA-based bis(phosphonates) and [F-18]NaF reported earlier (SUV of 4.63 +/- 0.38 and SUV of 4.87 +/- 0.32 for [Ga-68]DO3AP(BP) and [F-18]NaF, respectively, at 60min p.i.). Coincidently, accumulation in soft tissue is generally low (e.g. for kidneys SUV of 0.26 +/- 0.09 for [Ga-68]NO2AP(BP) at 60min p.i.), revealing the new Ga-68 complexes as ideal tracers for noninvasive, fast and quantitative imaging of calcified tissue and for metastatic lesions using PET or PET/CT

Gallium(III) Complexes of DOTA and DOTA-Monoamide: Kinetic and Thermodynamic Studies

International audienceGiven the practical advantages of the Ga-68 isotope in positron emission tomography applications, gallium complexes are gaining increasing importance in biomedical imaging. However, the strong tendency of Ga3+ to hydrolyze and the slow formation and very high stability of macrocyclic complexes altogether render Ga3+ coordination chemistry difficult and explain why stability and kinetic data on Ga3+ complexes are rather scarce. Here we report solution and solid-state studies of Ga3+ complexes formed with the macrocyclic ligand 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, (DOTA)(4-), and its mono(n-butylamide) derivative, (DO3AM(Bu))(3-). Thermodynamic stability constants, log K(GaDOTA) = 26.05 and log K(GaDO3AM(Bu)) = 24.64, were determined by out-of-cell pH-potentiometric titrations. Due to the very slow formation and dissociation of the complexes, equilibration times of up to similar to 4 weeks were necessary. The kinetics of complex dissociation were followed by Ga-71 NMR under both acidic and alkaline conditions. The GaDOTA complex is significantly more inert (tau(1/2) similar to 12.2 d at pH = 0 and tau(1/2) similar to 6.2 h at pH = 10) than the GaDO3AM(Bu) analogue (tau(1/2) similar to 2.7 d at pH = 0 and tau(1/2) similar to 0.7 h at pH = 10). Nevertheless, the kinetic inertness of both chelates is extremely high and approves the application of Ga3+ complexes of such DOTA-like ligands in molecular imaging. The solid-state structure of the GaDOTA complex, crystallized from a strongly acidic solution (pH < 1), evidenced a diprotonated form with protons localized on the free carboxylate pendants

A novel tetraazamacrocycle bearing a thiol pendant arm for labeling biomolecules with radiolanthanides

International audienceThe novel tetraazamacrocycle 10-(2-sulfanylethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (H(4)DO3ASH) was synthesized and characterized by multinuclear NMR spectroscopy, 2D NMR techniques and mass spectrometry. The protonation constants of H(4)DO3ASH were determined by potentiometry at 25 degrees C in 0.1 M KCl ionic strength, and the protonation sequence was assigned based on H-1- and C-13-NMR titrations. The stability constants of the DO3ASH complexes with Ce3+, Sm3+ and Ho3+ have been determined by potentiometry and UV-Vis spectroscopy. They are very similar, comprising a narrow range (logK(ML) = 21.0-22.0). UV-Vis spectrophotometric data on Ce3+-DO3ASH and relaxivity measurements on the Gd3+-DO3ASH complex suggest that the thiol group does not coordinate to the metal, even in its deprotonated form. For labeling with radioactive lanthanides(III), various conditions were tested and both complexes, Sm-153/Ho-166-DO3ASH, were obtained in quantitative yield (> 98%) at pH = 6. At room temperature, formation kinetics were faster for the Sm-153 than for the Ho-166 complex (5 vs. 60 min, respectively, needed for complete labeling). The stability of these hydrophilic complexes (Sm-153, logD = -2.1; Ho-166, logD = -1.6) has been studied in different buffers, in human serum and in the presence of excess of cysteine and glutathione. Sm-153-DO3ASH has shown a high stability under these conditions and a relatively low protein binding (2.1%), while Ho-166-DO3ASH was less stable, including in the presence of cysteine and glutathione, and had a slightly higher protein binding (6.7%). In vivo studies have been performed only for the more stable Sm-153-DO3ASH complex and its biological pro. le and in vivo stability has been compared to that of Sm-153-DO3A in the same animal model. The biodistribution pro. le presents a similar trend with rapid total excretion from the whole animal body, mainly via the urinary pathway. The most striking difference found is related to a slightly slower clearance of Sm-153-DO3ASH from organs like blood, bone and muscle as compared to Sm-153-DO3A. Additionally, the fraction of Sm-153-DO3ASH taken by the hepatobiliar tract is also modestly higher than that of Sm-153-DO3A

Synthesis, Characterization and Biological Evaluation of In(III) Complexes Anchored by DOTA-like Chelators Bearing a Quinazoline Moiety

International audienceFollowing previous studies with a DOTA-like bifunctional chelator (H(3)L1) containing an ethylenic linker between the macrocycle backbone and a quinazoline pharmacophore, we synthesized and fully characterized a congener rnacrocyclic ligand (H(3)L2) having a longer, five-carbon spacer for the linkage of the quinazoline moiety. Both H(3)L1 and H(3)L2 were used to prepare indium(III) complexes aiming at their evaluation as radioactive probes for in vivo targeting of EGFR-TK. The protonation constants (log K-Hi) of H(3)L2 were determined by potentiometry and UV-Vis spectrophotometry and the values found are 12.18, 9.74, 4.99, 3.91 and 2.53. The stability and protonation constants of InL (L = L1, L2) were also obtained from a combined potentiometry and UV-VIS spectrophotometry study. The reaction of InCl3 with H(3)L1 and H(3)L2 led to the formation of the well-defined complexes InL1 and InL2, containing In(III) ions coordinated by a seven (N-4,O-3) donor atom set. These new complexes were fully characterized by spectroscopic methods (IR, NMR, ESI-MS), HPLC and by X-ray diffraction analysis in the case of InL1. The radioactive congener (III)InL2 was prepared from the reaction of In-III-chloride with H(3)L2, in high yield and high radiochemical purity. (III)InL2 is a neutral complex that presents a hydrophilic character and exhibits a high in vitro and in vivo stability. H(3)L2 and InL2 do not inhibit the cell growth of A431 cervical carcinoma cells. In this EGFR-expressing cell line, (III)InL2 has shown very low cell internalization. These findings indicate that these DOTA-like chelators are not the best suited bifunctional ligands to obtain In(III) complexes with adequate biological properties for targeting the EGFR-TK

Lanthanide complexes as imaging agents anchored on nano-sized particles of boehmite

International audienceThe synthesis of boehmite nanoparticles modified with lanthanides (Eu, Tb and Gd) is described. Their synthesis, characterization and in vitro assays with HeLa cells were performed. The nuclear magnetic relaxation dispersion (NMRD) profiles of the two chelating moieties were studied. Imaging data from laser scanning confocal fluorescence microscopy and flow cytometry revealed that the nanoscaffolds were taken up by the cells, distributed throughout the cytoplasm and showed no toxicity. This platform could represent an alternative to silica-based inert matrices as imaging vehicles