Roberto Pasqualini

Influence of a 99mTcN core on the biological and physicochemical behavior of 99mTc complexes of L,L-EC and L,L-ECD

99mTc-nitrido complexes of L,L-ethylene dicysteine (99mTcN-L,L-EC) and 99mTcN-L,L-ethylene dicysteine diethylester (99mTcN-L,L-ECD) were prepared and their characteristics compared to those of the respective 99mTc-oxo complexes. 99mTcN-L,L-EC and 99mTcO-L,L-EC migrate to similar extents during electrophoresis at pH 12, but, at pH6, 99mTcN-L,L-EC migrates further than 99mTcO-L,L-EC. Renal excretion of 99mTcN-L,L-EC is inferior to that of 99mTcO-L,L-EC, indicating that the TcN-glycine sequence has lower affinity for the renal tubular system. Both 99mTcO-L,L-ECD and 99mTcN-L,L-ECD are neutral, but 99mTcN-L,L-ECD is hydrophilic and shows minimal brain uptake in both mice and the baboon.

Cellular Uptake Mechanisms of 99mTcN-NOET in Cardiomyocytes From Newborn Rats Calcium Channel Interaction

BACKGROUND Bis[N-ethoxy,N-ethyl(dithiocarbamato)]nitrido Tc (V) (TcN-NOET) is a new technetium complex proposed as a tracer of myocardial perfusion. However, its cellular uptake mechanisms are unknown, although membrane localization on rat heart preparations and preferential binding to polymorphonuclear neutrophils (PMNs) have been reported. Because of the central role of calcium in PMN actions, a relationship was hypothesized between this ion flux and TcN-NOET cellular uptake. METHODS AND RESULTS The mechanisms of cellular uptake of TcN-NOET were investigated in newborn rat cardiomyocytes by study of the effect of calcium channel modulators on tracer binding. Nifedipine had no effect on tracer uptake at 1 minute. However, verapamil 0.1 micromol/L and diltiazem 0.5 micromol/L induced a 40% decrease in uptake. Conversely, Bay K 8644 0.25 micromol/L increased TcN-NOET uptake by 73%. Alterations in other membrane ion transports failed to modify tracer uptake, indicating the specificity of the relationship between TcN-NOET uptake and calcium channels. Kinetic studies indicated that cellular net accumulation of the tracer was slow (t1/2=28.5 minutes) and retention was prolonged (84% of initial activity retained after 120 minutes of washout). The energy dependence of TcN-NOET uptake was investigated after 60 minutes of metabolic inhibition by iodoacetic acid plus rotenone. The ATP decrease was not associated with reduction in tracer uptake at 1 minute (114.9+/-21.9% of control, P=NS). CONCLUSIONS The decrease in uptake observed with verapamil and diltiazem, the increase with Bay K 8644, and the lack of effect with nifedipine suggest that TcN-NOET binds to L-type calcium channels in the open configuration, without entering cardiomyocytes. The kinetics of TcN-NOET accumulation and retention are slow, and the mechanism for cellular uptake is not energy-dependent. From a clinical point of view, the effect of concurrent treatment by calcium inhibitors on myocardial binding of TcN-NOET should be taken into account.

New bis(dithiocarboxylato)nitridotechnetium-99m radiopharmaceuticals for leucocyte labelling: In vitro and In vivo studies

Dithiocarboxylate ligands were synthesized and characterised. New nitrido 99m-technetium complexes were obtained with these ligands and identified by thin layer chromatography. The nitrido complexes were tested in vitro in whole blood for leucocyte labelling and the design of the ligand was optimized. Best results were obtained with aliphatic linear ligands, containing 9 to 11 atoms of carbon. The in vivo experiment failed because an inflammated area could not be visualized by gamma imaging, the cell labelling mechanism being probably different.

Synthesis and biodistribution of nitrido technetium-99m radiopharmaceuticals with dithiophosphinate ligands: a class of brain imaging agents

The symmetrical complexes [99mTc][TcN(R2PS2)2] [R = CH3, CH2CH3, CH2CH2CH3, CH2(CH3)2], and the unsymmetrical complex [99mTc][TcN(Me2PS2)(Et2PS2)] have been prepared, at tracer level, through a two-step procedure involving the preliminary formation of a prereduced technetium nitrido intermediate followed by substitution reaction onto this species by the appropriate dithiophosphinate ligand [R2PS2]Na. The chemical identity of the resulting complexes have been established by comparison with the corresponding 99Tc-analogs prepared, at macroscopic level, by reacting the complex [99TcNCl4] [n-Bu4N] (n-Bu = n-butyl) with an excess of ligand in methanol, and characterized by elemental analyses and spectroscopic techniques. The complexes are neutral and lipophilic, and possess a square pyramidal geometry, with an apical Tc identical to N group and two dithiophosphinate ligands spanning the four positions on the basal plane through the four sulfur atoms of the > PS2 group. In vitro studies showed that these radiopharmaceuticals are stable in solution and that their chemical identity was not altered after incubation with rat blood. Biodistribution studies have been carried out in rats and primates. The results demonstrate that these compounds are significantly retained into the brain of these animals for a prolonged time. Planar gamma camera images have been obtained in monkeys showing a good visualization of the cerebral region. However, the existence of persistent blood activity yields a brain/blood ratio lower than that observed with other 99mTc-based brain perfusion imaging agents.

Comparison of reversed phase and reversed phase ion pair high performance liquid chromatography for analysis of TcO and TcN complexes of l,l-ethylene dicysteine di-ethylester and its acid analogues☆

99mTc(V)-oxo complexes of L,L-ethylene dicysteine (L,L-EC) and its di-ester derivative L,L-ethyl cysteinate dimer (L,L-ECD) are useful tracer agents for evaluation of renal function and cerebral blood flow respectively. Labelling of these molecules with a 99mTc(V)-nitrido core instead of the 99mTc(V)-oxo core alters their biological and physiochemical behavior. In the reversed phase high performance liquid chromatography (HPLC) method presently used to analyse 99mTc(V)-oxo preparations of L,L-EC and L,L-ECD, the 99mTc(V)-nitrido-L,L-EC complex and the possible impurities of a 99mTc(V)-nitrido-L,L-ECD preparation were found to elute with the void volume. In this study, a reversed phase ion pair HPLC method has been developed that is useful for the analysis of both 99mTc(V)-oxo and 99mTc(V)-nitrido preparations of L,L-EC and L,L-ECD. Tetrabutylammonium hydroxide is used as a cationic ion pairing agent.