Targeted Complexes of Lanthanide(III) Ions as Therapeutic and Diagnostic Pharmaceuticals

Rational Design of Mono-Substituted Gd-DOTA as Highly Stable and Efficient MRI Contrast Agents for Hepatobiliary and Inflammation Imaging

Hepatobiliary-specific magnetic resonance imaging contrast agents (MRI CAs) play a crucial role in the early diagnosis of hepatocellular carcinoma (HCC). However, only two acyclic CAs, Gd-BOPTA and Gd-EOB-DTPA, exhibit unfavorable kinetic inertness. Our study focused on the development of superior stable innovative macrocyclic CAs. By introducing a lipophilic benzyloxy group (OBn) into the H4DOTA ring (Gd-L1), we achieved significant enhancement in kinetic inertness. In vivo experiments in mice demonstrated that 40% of the dosage was distributed to the liver at 5 min, providing sustained hepatic enhancement for over 35 min. We also developed an MPO-responsive MRI CA (Gd-L3), which can participate in the "peroxidase cycle" as the substrate, generating oligomers with a 3.8-fold increase in relaxivity, and selectively enhance the lesion in an acute gout mouse model. Overall, our work represents a significant advancement in the field of hepatic and inflammatory MRI, offering promising avenues for early diagnosis and improved imaging outcomes.

The crystal structure of aqua-tris (1,3-diphenylpropane-1,3-dionato-κ2 O,O′)-lanthanum(III), C45H35LaO7

C45H35LaO7, trigonal, R3 (no. 146), a = 22.3832(11) Å, c = 6.4522(3) Å, V = 2799.5(3) Å3, Z = 3, R gt (F) = 0.0192, wRref (F 2) = 0.0462, T = 200 K.

Crosslinked shells for nano-assembled capsules: a new encapsulation method for smaller Gd3+-loaded capsules with exceedingly high relaxivities

Nano-assembled capsules can incorporate large payloads of high relaxivity Gd3+, permitting the development of highly detectable molecular imaging agents for MRI. A new encapsulating shell, based upon cross-linked peptides, is found to afford smaller capsules (127 nm average diameter) with exceptionally high per-Gd3+ relaxivities (70.7 s-1 mmolal-1).

Recent Advances on Luminescent Enhancement-Based Porous Silicon Biosensors

Luminescence-based detection paradigms have key advantages over other optical platforms such as absorbance, reflectance or interferometric based detection. However, autofluorescence, low quantum yield and lack of photostability of the fluorophore or emitting molecule are still performance-limiting factors. Recent research has shown the need for enhanced luminescence-based detection to overcome these drawbacks while at the same time improving the sensitivity, selectivity and reducing the detection limits of optical sensors and biosensors. Nanostructures have been reported to significantly improve the spectral properties of the emitting molecules. These structures offer unique electrical, optic and magnetic properties which may be used to tailor the surrounding electrical field of the emitter. Here, the main principles behind luminescence and luminescence enhancement-based detections are reviewed, with an emphasis on europium complexes as the emitting molecule. An overview of the optical porous silicon microcavity (pSiMC) as a biosensing platform and recent proof-of-concept examples on enhanced luminescence-based detection using pSiMCs are provided and discussed.

An electro-amalgamation approach to produce 175Yb suitable for radiopharmaceutical applications

175Yb is a prospective reactor produced radionuclide suitable for preparation of therapeutic radiopharmaceuticals. However, a major restraint in the use of 175Yb produced via the (n, γ) reaction, for therapeutic applications, is the presence of longer-lived 177Lu impurity which is co-produced along with 175Yb on irradiation of natural Yb2O3 target. A radiochemical separation procedure adopting electro-amalgamation approach for the removal of 177Lu impurity from 175Yb has been critically evaluated. The experimental parameters such as applied potential, electrolysis time and the pH of the electrolyte, affecting the electrochemical separation process, were studied and optimized. The developed radiochemical procedure was extensively tested for purification of up to 15 GBq of 175Yb. The purified 175Yb could be obtained in HCl medium with ∼95% yield. The 177Lu impurity could not be detected in the purified product and 175Yb was found suitable for the preparation of potential radiotherapeutic agents.

Antimicrobial and DNA-cleavage studies of 22-membered N4 tetraaza macrocyclic triazoles: template synthesis and physicochemical characterization

A novel series of 22-membered macrocyclic complexes of the type [MLCl(2)] (M=Co(2+), Ni(2+) and Cu(2+)) have been synthesized with newly derived biologically active ligands (L(1)-L(IV)). These ligands were synthesized by the condensation of ortho-phthalaldehyde and bis-(4-amino-5-mercapto-1, 2, 4-triazole-3-yl)alkanes. The mode of bonding and overall geometry of the complexes have been inferred through IR, EPR, electronic spectral studies, conductivity, magnetic, thermal, and electrochemical studies. All these complexes have been screened for their antibacterial (Escherichia coli, Staphylococus aureus, Salmonella typhi, Pseudomonas aeruginosa) and antifungal activities (Aspergillus niger, Aspergillus flavus, and Cladosporium) by the minimal inhibitory concentration (MIC) method. The DNA cleavage study was done by agarose gel electrophoresis technique.

Conformational behaviour determines the low-relaxivity state of a conditional MRI contrast agent

The conformational behaviour in aqueous solution of the EgadMe complex, a conditional gadolinium-based contrast agent sensitive to beta-galactosidase enzymatic activity, is investigated by means of ab initio calculations and classical molecular dynamics simulations. Furthermore, force field parameterization of gadolinium-ligand interactions is performed, and its reliability is tested on the bench mark [Gd(DOTA)](-) system by MD simulations. Both computational methods highlight the presence in EgadMe of two main conformational isomers. The lowest energy conformation is a "close" form, corresponding to a state of low-relaxivity (MRI "inactive"), in which the ninth coordination site of the gadolinium ion is occupied by one oxygen atom of the galactopyranose residue. The second isomer, which is 2.9 (at ab initio level) and 4.2 (at MD level) kcal mol(-1) above the global minimum, presents an "open" form, corresponding to a state of high-relaxivity (MRI "active") in which one water molecule coordinates the ion. These results are consistent with experimental findings reported for EgadMe, and show that competition at the ninth coordination site of gadolinium ion, between the intra (the galactopyranose residue) and inter (water molecules) molecular interactions, affects the relaxivity of this system.

Template synthesis and physico-chemical characterization of 14-membered tetraimine macrocyclic complexes, [MLX(2)] [M=Co(II), Ni(II), Cu(II) and Zn(II)]. DNA binding study on [CoLCl(2)] complex

The template condensation reaction between glyoxal and 1,8-diaminonaphthalene resulted a few novel mononuclear 14-membered tetraimine macrocyclic complexes of the type, [MLX(2)] [M=Co(II), Ni(II), Cu(II) and Zn(II), for X=Cl or NO(3)]. The stoichiometry and the nature of the complexes have been deduced from the results of elemental analyses and conductance data. The formation of macrocyclic framework has been inferred from the appearance of imine upsilon(CN) and upsilon(MN) band in IR spectra and the resonance signals observed in (1)H and (13)C-NMR spectra. However, the overall geometry of the complexes has been assigned on the positions of bands in electronic spectra and magnetic moment data. The distortion in Cu(II) complexes has been deduced on EPR data. The thermal behavior of these complexes has been studied by TGA analysis. Absorption and circular dichroism studies on the complex proved a significant binding to calf thymus DNA.

Solid-phase oligonucleotide labeling with DOTA

This unit describes a method to construct oligonucleotide conjugates labeled with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) on a solid support. A nucleosidic phosphoramidite that contains a protected DOTA ligand compatible with normal chain assembly is prepared first. As the chain assembly is completed, the oligonucleotide is deprotected and converted to the corresponding gadolinium(III) chelate, resulting in an oligonucleotide conjugate containing the chelate at the 5'-terminus.

Gadolinium(III) complexes as MRI contrast agents: ligand design and properties of the complexes

Magnetic resonance imaging is a commonly used diagnostic method in medicinal practice as well as in biological and preclinical research. Contrast agents (CAs), which are often applied are mostly based on Gd(III) complexes. In this paper, the ligand types and structures of their complexes on one side and a set of the physico-chemical parameters governing properties of the CAs on the other side are discussed. The solid-state structures of lanthanide(III) complexes of open-chain and macrocyclic ligands and their structural features are compared. Examples of tuning of ligand structures to alter the relaxometric properties of gadolinium(III) complexes as a number of coordinated water molecules, their residence time (exchange rate) or reorientation time of the complexes are given. Influence of the structural changes of the ligands on thermodynamic stability and kinetic inertness/lability of their lanthanide(III) complexes is discussed.

Lanthanides to quantum dots resonance energy transfer in time-resolved fluoro-immunoassays and luminescence microscopy

A time-resolved fluoro-immunoassay (TR-FIA) format is presented based on resonance energy transfer from visible emitting lanthanide complexes of europium and terbium, as energy donors, to semiconductor CdSe/ZnS core/shell nanocrystals (quantum dots, QD), as energy acceptors. The spatial proximity of the donor-acceptor pairs is obtained through the biological recognition process of biotin, coated at the surface of the dots (Biot-QD), and streptavidin labeled with the lanthanide markers (Ln-strep). The energy transfer phenomenon is evident from simultaneous lanthanide emission quenching and QD emission sensitization with a 1000-fold increase of the QD luminescence decay time reaching the hundred mus regime. Delayed emission detection allows for quantification of the recognition process and demonstrated a nearly quantitative association of the biotins to streptavidin with sensitivity limits reaching 1.2 pM of QD. Spectral characterization permits calculation of the energy transfer parameters. Extremely large Förster radii (R(0)) values were obtained for Tb (104 A) and Eu (96 A) as a result of the relevant spectral overlap of donor emission and acceptor absorption. Special attention was paid to interactions with the varying constituents of the buffer for sensitivity and transfer efficiency optimization. The energy transfer phenomenon was also monitored by time-resolved luminescence microscopy experiments. At elevated concentration (>10(-)(5) M), Tb-strep precipitated in the form of pellets with long-lived green luminescence, whereas addition of Biot-QD led to red emitting pellets, with long excited-state decay times. The Ln-QD donor-acceptor hybrids appear as highly sensitive analytical tools both for TR-FIA and time-resolved luminescence microscopy experiments.

Use of Lanthanide-Grafted Inorganic Nanoparticles as Effective Contrast Agents for Cellular Uptake Imaging

The improvement of commonly used Gd3+ -based MRI agents requires the design of new systems with optimized in vivo efficacy, pharmacokinetic properties, and specificity. To design these contrast agents, two parameters are usually considered: increasing the number of coordinated water molecules or increasing the rotational correlation time by increasing molecular weight and size. This has been achieved by noncovalent or covalent binding of low-molecular weight Gd3+ chelates to macromolecules or polymers. The grafting of these high-spin paramagnetic gadolinium chelates on metal oxide nanoparticles (SiO2, Al2O3) is proposed. This new synthetic strategy presents at least two main advantages: (1) a high T1-relaxivity for MRI with a 275% increase of the MRI signal and (2) the ability of nanoparticles to be internalized in cells. Results indicate that these new contrast agents lead to a huge reconcentration of Gd3+ paramagnetic species inside microglial cells. This reconcentration phenomenon gives rise to high signal-to-noise ratios on MR images of cells after particle internalization, from 1.4 to 3.75, using Al2O3 or SiO2 particles, respectively. The properties of these new particles will be further used to get new insight into gene therapy against glioma, using microglial cells as vehicles to simultaneously transport a suicide gene and contrast agents. Since microglia are chemoattracted to brain tumors, the presence of these new contrast agents inside the cells will lead to a better MRI determination of the in vivo location, shape, and borders of the tumors. These Gd3+-loaded microglia can therefore provide effective localization of tumors by MRI before applying any therapeutic treatment. The rate of carcinoma remission following a suicide gene strategy is also possible.

Simple synthesis of a building block for solid-phase labeling of oligonucleotides with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)

Synthesis of a nucleosidic phosphoramidite building block which allows solid-phase introduction of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) to synthetic oligonucleotides using a standard oligonucleotide synthesizer is described.

Synthesis and properties of a neutral derivative of diethylenetriaminepentaacetic acid (DTPA)

A neutral bifunctional derivative of diethylenetriaminepentaacetic acid europium(III) (11) was synthesized and its suitability to dissociation-enhanced lanthanide fluorescence immunoassay was investigated.

Synthesis of building blocks for solid-phase introduction of diethylenetriaminepentaacetic acid (DTPA) to oligonucleotides and oligopeptides

Synthesis of building blocks that allow site-specific incorporation of diethylenetriaminepentaacetic acid (DTPA) to oligonucleotides and oligopeptides using phosphoramidite and Fmoc chemistries, respectively, is described.

Synthesis and relaxivity studies of a tetranuclear gadolinium(III) complex of DO3A as a contrast-enhancing agent for MRI

A tetranuclear gadolinium(III) complex, [Gd4(H2O)8], of DO3A appended onto the pentaerythrityl framework was synthesized to improve the water proton relaxivity for MRI application. The longitudinal relaxivity of [Gd4(H2O)8] is 28.13 mM-1 s-1 (24 MHz, 35+/-0.1 degrees C, pH 5.6) which is 5.86 times higher than that of [Gd(DO3A)(H2O)2]. The relaxivity is based on "molecular" relaxivity of the tetramer and the r1p value is "7 per Gd". The high relaxivity of the tetramer is the result of the decrease in the rotational correlation (tauR) and the presence of eight inner-sphere water molecules (q=8). The complex exhibits pH-dependent longitudinal relaxivity, and the high relaxivity both at low and high pH (r1p=28.13 mM-1 s-1 at pH 5.6 and 16.52 mM-1 s-1 at pH 9.5) indicates that it could be used as a pH-responsive MRI contrast agent. The transverse relaxivity of the tetramer is 129.97 mM-1 s-1 (24 MHz, 35+/-0.1 degrees C, pH 5.6), and the r2p/r1p ratio of 4.6 shows that it could be used as a T2-weighted contrast agent.

PAMAM Dendrimeric Conjugates with a Gd−DOTA Phosphinate Derivative and Their Adducts with Polyaminoacids: The Interplay of Global Motion, Internal Rotation, and Fast Water Exchange

A series of dendrimeric conjugates based on a PAMAM (polyamidoamine) backbone with macrocyclic Gd-DO3A-P(ABn) complexes (monophosphinated analogue of DOTA) was prepared. The chelates were covalently attached to the G1-, G2-, and G4-PAMAM dendrimers through a thiourea linker in high loads (>90%). The prepared conjugates G1-(Gd-DO3A-P(BnN{CS}))(8), G2-(Gd-DO3A-P(BnN{CS}))(16), and G4-(Gd-DO3A-P(BnN{CS}))(59) showed relaxivities of 10.1, 14.1, and 18.6 s(-)(1) mM(-)(1) at 20 MHz and 37 degrees C and pH = 7.5, respectively. A variable-pH study (range 2-12) revealed up to 30% increase in the relaxivity at low pH for the G2-(Gd-DO3A-P(BnN{CS}))(16) conjugate. As confirmed by (1)H NMR titration of the unmodified G2 dendrimer, this is due to protonation of core tertiary amines leading to a more open and rigid structure. The variable-temperature (17)O NMR and (1)H NMRD relaxometric studies confirmed that the relaxivity is not controlled by water exchange but by rotational dynamics. A multiparametrical data evaluation using the Lipari-Szabo approach revealed that the water residence lifetime, (298)tau(M), for the conjugates studied was ca. 45-70 ns, which is longer than the value found for the monomeric model compound Gd-DO3A-P(ABn) (16 ns) but short enough so as not to limit the relaxivity. The global rotational correlation time, (298)tau(Rg), varied from 1.5 to 3.1 ns and seemed to indicate a sufficiently slow molecular tumbling to achieve the high relaxivities measured; however, the rigidity factor S(2) (approximately 0.26), describing the internal flexibility, was far from optimum. The overall relaxivity was significantly increased (e.g. by a factor of 1.8 for the G1-(Gd-DO3A-P(BnN{CS}))(8) conjugate) when a positively charged polyaminoacid like poly(Arg) or poly(Lys) was added to the conjugate solutions. The electrostatic interactions partially "freeze" the internal mobility of the conjugate and also slow down global motion. This assumption was confirmed by an evaluation of (1)H relaxometric data obtained for the G2-(Gd-DO3A-P(BnN{CS}))(16)-poly(Lys)(59) adduct. Importantly, it was proved that the adduct formation did not hamper the water exchange process.

Synthesis of Aminooxy-Functionalized Lanthanide(III) Chelates for Carbonyl-Group Conjugation

The syntheses of three new aminooxy-tethered lanthanide(III) chelates, compounds 1-3, incorporating DOTA (= 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), DTPA (= diethylenetriaminepentaacetic acid), or a substituted terpyridine (2,2',2'',2'''-[2,2': 6',2''-terpyridine-6,6''-diylbis(methylenenitrilo)]tetraacetic acid), respectively, are described. Reagents 1-3 can be used for carbonyl 'labeling', as shown by the formation of the corresponding oxime-ether bioconjugates of naltrexone (16) and 2-deoxy-beta-D-glucose (17) (Scheme 4).

Relaxometric and solution NMR structural studies on ditopic lanthanide(iii) complexes of a phosphinate analogue of DOTA with a fast rate of water exchange

A novel "ditopic" ligand containing two monophosphinate triacetate DOTA-like units linked by a thiourea bridge has been synthesized and its complexes with Ln3+ ions (Ln = Y, Eu, Gd, Dy) investigated by NMR spectroscopy and relaxometry. The presence of one water molecule in the first coordination sphere has been determined by the measurement of the dysprosium(III)-induced 17O NMR shifts. The 1H and 31P NMR spectra of the Eu(III) derivative indicate a higher abundance of the fast-exchanging twisted square antiprismatic (m) isomer than the isomeric square antiprismatic (M; m/M = 3:2) complex. The analysis of the 89Y and 13C T1 NMR relaxation times in the Gd(III)/Y(III) mixed complex have provided useful structural information. Values of ca. 6.3 and 8.2 A for the Gd...Y and Gd...C distances, respectively, have been estimated which indicate a rather compact solution structure. This result finds support in the value of the relaxivity whose increase (at 20 MHz and 298 K) on passing from the monomeric (5.7 s(-1) mM(-1)) to the ditopic complex (8.2 s(-1) mM(-1)) can be attributed to the doubling of the inner-sphere term following the doubling of the molecular size. The structural and dynamic relaxivity-controlling parameters were assessed by a simultaneous fitting of the variable temperature 17O NMR and 1H NMRD relaxometric data. The mean water residence lifetime (298tauM) has been found to be 53 ns, one of the shortest values reported for ditopic complexes. The reorientational correlation time is two times longer (298tauR = 183 ps) than the corresponding value of the parent monomeric Gd(III) complex, thus supporting the view of a limited degree of internal rotation. The possible influence of magnetic Gd-Gd coupling has been excluded by a comparison of the 1H NMRD profiles of the homodinuclear Gd(III)/Gd(III) and the heterodinuclear Gd(III)/Y(III) complexes.

Towards the rational design of MRI contrast agents: a practical approach to the synthesis of gadolinium complexes that exhibit optimal water exchange

The gadolinium(iii) complex of S-SSSS-NO(2)BnDOTMA exhibits water exchange kinetics that are optimal for use in high relaxivity or targeted contrast agents. However, the synthesis of this ligand is hampered by the steric encumbrance imparted upon the cyclen ring by the nitrobenzyl substituent. A relatively simple modification has been used to enable the synthesis of larger quantities of a bifunctional ligand that retains similar fast water exchange properties. The gadolinium complex of S-SSS-NO(2)BnDO3MA-1A is shown to retain the rapid water exchange kinetics characteristic of a twisted square antiprismatic (TSAP) coordination geometry (tau(M)= 6 +/- 0.4 ns).