Fulvio Uggeri

Mixed micelles containing lipophilic gadolinium complexes as MRA contrast agents.

Mixed micelles for MRA are multicomponent systems containing a phospholipid, a biocompatible non-ionic surfactant (e.g. Synporonic(k) F-108) and a lipophilic gadolinium complex. A variety of lipophilic gadolinium complexes were designed taking into account features such as: (i) nature of ligand (cyclic versus acyclic); (ii) lipophilic moiety; (iii) global charge of the complex; and (iv) nature of bond connecting the complex to the lipophilic moiety. All the lipophilic gadolinium complexes after formulation as mixed micelles show high relaxivities in water and in blood (rat). Mixed micelles containing gadolinium complexes bearing only one aliphatic chain cannot be used as MRA contrast agents because they have a high haemolytic effect. Furthermore, in rats they are quickly eliminated from the blood stream. These drawbacks are completely circumvented using gadolinium complexes bearing two aliphatic chains. Mixed micelles containing such complexes show high relaxivities. no haemolytic effect and long blood permanence. This makes them promising candidates as MRA contrast agents. However, elimination, which occurs exclusively through the liver, is not complete, even after 7 days. Complexes containing labile (e.g. ester) bonds between the lipophilic moieties and the chelate subunit are eliminated through both the liver and the kidneys. However, elimination is stiil not complete after 7 days.

Equilibrium and Kinetic Properties of the Lanthanoids(III) and Various Divalent Metal Complexes of the Heptadentate Ligand AAZTA

The heptadentate ligand 1,4-bis(hydroxycarbonylmethyl)-6-[bis(hydroxycarbonylmethyl)]amino-6-methylperhydro-1,4-diazepine (AAZTA) and its derivatives were recently reported to give stable complexes with Gd(3+) with superior efficiency as MRI contrast agents. Nevertheless, only preliminary data are available on the coordination behavior of this interesting ligand. In this work, thermodynamic and kinetic stability data are determined for the formation of complexes with AAZTA and the lanthanoid metal ions, and other divalent metal ions of interest for this application. The AAZTA ligand binds the lanthanoid ions with log K(ML) values of 17.53-21.85 with its affinity steadily increasing from La(3+) to Lu(3+), suggesting that the seven-membered skeleton is better suited to accommodate smaller metal ions. Even though the denticity is lower, the stability of the heavier lanthanoid complexes is comparable to those of the classical ligand diethylenetriaminepentaacetic acid (DTPA). The transmetalation reactions of [Gd(AAZTA)](-) with Cu(2+) and Eu(3+) predominantly occur through proton-assisted dissociation of the complex. The role of the direct attack of Cu(2+) or Eu(3+) in the exchange reactions is limited, although the formation of dinuclear complexes decreases the proton-assisted dissociation. Near physiological conditions, [Gd(AAZTA)](-) is significantly more inert than [Gd(DTPA)](2-), allowing its potentially safe use as contrast agent in magnetic resonance imaging.

Magnetic resonance contrast agents : From the bench to the patient

Magnetic Resonance Imaging is gaining a prominent role in the routine clinical investigation. To further improve this technique it is crucial that contrast agents are developed with more optimal organ specificity. This will not only result in a better diagnostic efficiency but also in a reduction of the amount of the agent administered. A combination of techniques has been employed to increase the target selectivity of the contrast agent and thereby the feasibility to visualize different organs. The organ targeting is based on the understanding of the mechanisms involved in the interaction of the agent with plasma proteins (albumin in particular) as well as the different membrane transporters involved in the uptake and in the excretion of the agent from the organ. The physicochemical properties of the contrast agents play a major role in the interaction with these various proteins. In this review we address the relationship between the structure of the contrast agents and their binding to different plasma proteins and membrane transporters in different organs, with special reference to the liver and kidney. The present and potentially future applications of these concepts in the clinical setting are also discussed.

Dissociation Kinetics of Open‐Chain and Macrocyclic Gadolinium(III)‐Aminopolycarboxylate Complexes Related to Magnetic Resonance Imaging: Catalytic Effect of Endogenous Ligands

The kinetics of the metal exchange reactions between open-chain Gd(DTPA)(2-) and Gd(DTPA-BMA), macrocyclic Gd(DOTA)(-) and Gd(HP-DO3A) complexes, and Cu(2+)  ions were investigated in the presence of endogenous citrate, phosphate, carbonate and histidinate ligands in the pH range 6-8 in NaCl (0.15 M) at 25 °C. The rates of the exchange reactions of Gd(DTPA)(2-) and Gd(DTPA-BMA) are independent of the Cu(2+) concentration in the presence of citrate and the reactions occur via the dissociation of Gd(3+)  complexes catalyzed by the citrate ions. The HCO(3)(-)/CO(3)(2-) and H(2)PO(4)(-) ions also catalyze the dissociation of complexes. The rates of the dissociation of Gd(DTPA-BMA), catalyzed by the endogenous ligands, are about two orders of magnitude higher than those of the Gd(DTPA)(2-). In fact near to physiological conditions the bicarbonate and carbonate ions show the largest catalytic effect, that significantly increase the dissociation rate of Gd(DTPA-BMA) and make the higher pH values (when the carbonate ion concentration is higher) a risk-factor for the dissociation of complexes in body fluids. The exchange reactions of Gd(DOTA)(-) and Gd(HP-DO3A) with Cu(2+) occur through the proton assisted dissociation of complexes in the pH range 3.5-5 and the endogenous ligands do not affect the dissociation rates of complexes. More insights into the interaction scheme between Gd(DTPA-BMA) and Gd(DTPA)(2-) and endogenous ligands have been obtained by acquiring the (13)C NMR spectra of the corresponding diamagnetic Y(III)-complexes, indicating the increase of the rates of the intramolecular rearrangements in the presence of carbonate and citrate ions. The herein reported results may have implications in the understanding of the etiology of nephrogenic systemic fibrosis, a rare disease that has been associated to the administration of Gd-containing agents to patients with impaired renal function.

A newly generated functional antibody identifies Tn antigen as a novel determinant in the cancer cell-lymphatic endothelium interaction

Malignant transformation of epithelial cells is frequently associated with the alteration of glycosylation pathways. Tn is a common tumor-associated carbohydrate antigen present in 90% of human carcinomas and its expression correlates with metastatic potential and poor prognosis. Despite its relevance, the functional role of Tn in tumor biology has not been firmly established probably for the lack of appropriate experimental tools. Our aims were to produce highly reactive monoclonal antibodies against Tn making use of synthetically produced Tn and to test their usefulness for in vivo imaging as well as to define their potential functional activity in tumor cell spread. We immunized mice with Tn clustered on cationized BSA and screened the positive hybridomas with Tn-biotinylated alginate. Enzyme-linked immuno sorbent assay and immunofluorescence assays revealed that the most reactive anti-Tn IgM mAb (2154F12A4) selectively recognized Tn on the MCF7 breast cancer cell line since its binding to the cell membrane was completely abolished by preincubation with purified Tn. Importantly, QDot 800-conjugated mAb injected in MCF7-tumor bearing mice specifically bound to primary tumor lesions as well as to metastases in lymph nodes. In addition, this mAb was able to inhibit cancer cell adhesion to lymphatic endothelium suggesting a novel involvement of Tn in the lymphatic dissemination of cancer cells and hypothesizing future applications in inhibiting lymphatic metastases.

ONE-POT MITSUNOBU-STAUDINGER PREPARATION OF 3-AMINOCHOLAN-24-OIC ACID ESTERS FROM 3-HYDROXYCHOLAN-24-OIC ACID ESTERS

Abstract 3-Hydroxycholan-24-oic acid esters are easily converted into the corresponding 3-amino derivatives via Mitsunobu reaction with diphenylphosphoryl azide (DPPA) and Staudinger reduction with PPh3/H2O of the intermediate azido compound in THF.

Smiles rearrangement as a tool for the preparation of 5-[(2-hydroxyacyl)amino]-2,4,6-triiodo-1,3-benzenedicarboxamides: Main pathway and side reactions

Abstract In the preparation of 5-[(2-hydroxyacyl)amino]-2,4,6-triiodo-1,3-benzenedicarboxamides 1a-h from 2a-h two conditions using stoichiometric amounts of base (method A - aq NaOH at 50°C; method B - MeONa in DMF at r. t.) were used. Yields are good to excellent provided that the right conditions are chosen. Primary amides 2a,b give 1a,b with method B only, whereas with method A extensive hydrolysis of the CONH2 moiety is observed. N-Methyl derivatives 2c,d afford 1c,d with either method. However, with method B long reaction times lead to the formation of large amounts of benzoxazinones, 4c,d. Under the same conditions, the pattern of side products which are formed from N-(hrmhydroxyalkyl)phenoxyacetamides 2e-g is furtherly complicated by: i) intramolecular cyclizations leading to bicyclic (7f,g) and tricyclic structures (5) ii) N-deacylation; iii) double Smiles rearrangement reactions.

Macrocyclic chelants, their chelates and uses thereof in the diagnostic field

This invention relates to novel compounds able to chelate paramagnetic bi- or trivalent metal ions, their chelates with said metal ions and their use as contrast agents in magnetic resonance imaging (MRI).

The Role of Equilibrium and Kinetic Properties in the Dissociation of Gd[DTPA‐bis(methylamide)] (Omniscan) at near to Physiological Conditions

[Gd(DTPA-BMA)] is the principal constituent of Omniscan, a magnetic resonance imaging (MRI) contrast agent. In body fluids, endogenous ions (Zn(2+), Cu(2+), and Ca(2+)) may displace the Gd(3+). To assess the extent of displacement at equilibrium, the stability constants of DTPA-BMA(3-) complexes of Gd(3+), Ca(2+), Zn(2+), and Cu(2+) have been determined at 37 °C in 0.15 M NaCl. The order of these stability constants is as follows: GdL≈CuL>ZnL≫CaL. Applying a simplified blood plasma model, the extent of dissociation of Omniscan (0.35 mM [Gd(DTPA-BMA)]) was found to be 17% by the formation of Gd(PO4), [Zn(DTPA-BMA)](-) (2.4%), [Cu(DTPA-BMA)](-) (0.2%), and [Ca(DTPA-BMA)](-) (17.7%). By capillary electrophoresis, the formation of [Ca(DTPA-BMA)](-) has been detected in human serum spiked with [Gd(DTPA-BMA)] (2.0 mM) at pH 7.4. Transmetallation reactions between [Gd(DTPA-BMA)] and Cu(2+) at 37 °C in the presence of citrate, phosphate, and bicarbonate ions occur by dissociation of the complex assisted by the endogenous ligands. At physiological concentrations of citrate, phosphate, and bicarbonate ions, the half-life of dissociation of [Gd(DTPA-BMA)] was calculated to be 9.3 h at pH 7.4. Considering the rates of distribution and dissociation of [Gd(DTPA-BMA)] in the extracellular space of the body, an open two-compartment model has been developed, which allows prediction of the extent of dissociation of the Gd(III) complex in body fluids depending on the rate of elimination of the contrast agent.

Spectral Discrimination of Chiral Macrocyclic Paramagnetic Metal Complexes by NMR Techniques

Axially symmetric macrocyclic polyaza complexes of lanthanide(III) ions are present in aqueous solution as a racemic mixture of two enantiomers in slow exchange at room temperature. Chiral resolution of an anionic paramagnetic complex has been achieved by exploiting multisite electrostatic and hydrogen-bonding interactions with an optically active organic base, and revealed by NMR techniques as illustrated. The bonding of the optically active substrate to the complex has been elucidated.