Micol Pasquali

Whole-Body Biodistribution and Radiation Dosimetry of the New Cardiac Tracer 99mTc-N-DBODC

Our purpose was to evaluate the safety profile and biodistribution behavior in healthy human volunteers of the new myocardial perfusion tracer bis[(dimethoxypropylphosphanyl)ethyl]ethoxyethylamine N,N′-bis(ethoxyethyl)dithiocarbamato nitrido technetium(V) (99mTc-N-DBODC). Methods: Ten healthy male volunteers were injected with 99mTc-N-DBODC under both stress and rest conditions. Anterior and posterior planar γ-camera images were collected at 5, 30, 60, 240, and 1,440 min after injection, with organ uptake quantified by region-of-interest analysis. Tracer kinetics in body fluids were determined by collecting blood and urine samples at different time points. Results: After injection, 99mTc-N-DBODC showed significant accumulation in the myocardium and prolonged retention. Under rest conditions, uptake in the heart, lungs, and liver at 5 min after injection was 1.67% ± 0.13%, 1.16% ± 0.07%, and 10.85% ± 1.72%, respectively, of administered activity. Under stress conditions, heart uptake was significantly higher (2.07% ± 0.22%). Radioactivity in the liver decreased to 3.64% ± 0.98% and 2.37% ± 0.48% at 60 and 240 min, respectively, after injection. This rapid liver clearance led to favorable heart-to-liver ratios, reaching values of 0.74 ± 0.13 at rest and 1.26 ± 0.28 during exercise 60 min after tracer administration. Radiation dose estimates were comparable to those obtained with other myocardial perfusion cationic compounds. Conclusion: The high uptake in the myocardium and the fast liver washout of 99mTc-N-DBODC will allow SPECT images of the left ventricle to be acquired early and with excellent quality.

Labeling of fatty acid ligands with the strong electrophilic metal fragment [99mTc(N)(PNP)]2+ (PNP=diphosphane ligand).

The electrophilic metal fragment [(99m)Tc(N)(PNP)](2+) (PNP=diphosphane ligand) has been employed for the labeling of fatty acid chains of different lengths. To provide a site-specific group for the attachment of the metallic moiety, the fatty acid derivatives were functionalized by appending a bis-mercapto or, alternatively, a dithiocarbamato pi-donor chelating systems to one terminus of the carbon chain to yield both dianionic and monoanionic bifunctional ligands (L). The resulting complexes, [(99m)Tc(N)(PNP)(L)] (0/+), exhibited the usual asymmetrical structure in which a Tc(triple bond)N group was surrounded by two different bidentate chelating ligands. Dianionic ligands gave rise to neutral complexes, while monoanionic ligands afforded monocationic species. Biodistribution studies were carried out in rats. An isolated perfused rat heart model was employed to assess how structural changes in the radiolabeled fatty acid compound affect the myocardial first pass extraction. Results showed that only monocationic complexes accumulated in myocardium to a significant extent. Conversely, neutral complexes were not efficiently retained into the heart region and rapidly washed out. In isolated perfused rat heart experiments, monocationic complexes exhibited a behavior similar to that of the monocationic flow tracers (99m)Tc-MIBI and (99m)Tc-DBODC with almost identical extraction values, a result that could be attributed to the presence of the monopositive charge. Instead, a slightly lower myocardial extraction was found for neutral complexes. Comparison of the observed kinetic behavior of neutral complexes in the isolated perfused rat heart model with that of the myocardial metabolic tracer [(123)I]IPPA revealed that the introduction of the metallic moiety partially hampers recognition of the labeled fatty acids by cardiac enzymes, and consequently, their behavior did not completely reflect myocardial metabolism.

Psychostimulant Effect of the Synthetic Cannabinoid JWH-018 and AKB48: Behavioral, Neurochemical, and Dopamine Transporter Scan Imaging Studies in Mice

JWH-018 and AKB48 are two synthetic cannabinoids (SCBs) belonging to different structural classes and illegally marketed as incense, herbal preparations, or chemical supply for theirs psychoactive cannabis-like effects. Clinical reports from emergency room reported psychomotor agitation as one of the most frequent effects in people assuming SCBs. This study aimed to investigate the psychostimulant properties of JWH-018 and AKB48 in male CD-1 mice and to compare their behavioral and biochemical effects with those caused by cocaine and amphetamine. In vivo studies showed that JWH-018 and AKB48, as cocaine and amphetamine, facilitated spontaneous locomotion in mice. These effects were prevented by CB1 receptor blockade and dopamine (DA) D1/5 and D2/3 receptors inhibition. SPECT-CT studies on dopamine transporter (DAT) revealed that, as cocaine and amphetamine, JWH-018 and AKB48 decreased the [123I]-FP-CIT binding in the mouse striatum. Conversely, in vitro competition binding studies revealed that, unlike cocaine and amphetamine, JWH-018 and AKB48 did not bind to mouse or human DAT. Moreover, microdialysis studies showed that the systemic administration of JWH-018, AKB48, cocaine, and amphetamine stimulated DA release in the nucleus accumbens (NAc) shell of freely moving mice. Finally, unlike amphetamine and cocaine, JWH-018 and AKB48 did not induce any changes on spontaneous [3H]-DA efflux from murine striatal synaptosomes. The present results suggest that SCBs facilitate striatal DA release possibly with different mechanisms than cocaine and amphetamine. Furthermore, they demonstrate, for the first time, that JWH-018 and AKB48 induce a psychostimulant effect in mice possibly by increasing NAc DA release. These data, according to clinical reports, outline the potential psychostimulant action of SCBs highlighting their possible danger to human health.

Influence of the Generator in-Growth Time on the Final Radiochemical Purity and Stability of Radiopharmaceuticals

At Legnaro laboratories of the Italian National Institute for Nuclear Physics (INFN), a feasibility study has started since 2011 related to accelerated-based direct production of by the 100Mo(p,2n) reaction. Both theoretical investigations and some recent preliminary irradiation tests on 100Mo-enriched samples have pointed out that both the / ratio and the specific activity will be basically different in the final accelerator-produced Tc with respect to generator-produced one, which might affect the radiopharmaceutical procedures. The aim of this work was to evaluate the possible impact of different / isomeric ratios on the preparation of different Tc-labeled pharmaceutical kits. A set of measurements with , eluted from a standard 99Mo/ generator, was performed, and results on both radiochemical purity and stability studies (following the standard quality control procedures) are reported for a set of widely used pharmaceuticals (i.e., -Sestamibi, -ECD, -MAG3, -DTPA, -MDP, -HMDP, -nanocolloids, and -DMSA). These pharmaceuticals have been all reconstituted with either the first [O4]− eluate obtained from a 99Mo/ generator (coming from two different companies) or eluates after 24, 36, 48, and 72 hours from last elution. Results show that the radiochemical purity and stability of these radiopharmaceuticals were not affected up to the value of 11.84 for the / ratio.

PEGylated N-methyl-S-methyl dithiocarbazate as a new reagent for the high-yield preparation of nitrido Tc-99m and Re-188 radiopharmaceuticals.

A novel nitrido nitrogen atom donor for the preparation of (99m)Tc and (188)Re radiopharmaceuticals containing a metal-nitrogen multiple bond is presented. HO(2)C-PEG(600)-DTCZ was obtained by conjugation of N-methyl-S-methyl dithiocarbazate [H(2)N-N(CH(3))-C(S)SCH(3), HDTCZ] with polyethylene glycol 600 (PEG(600)). Asymmetrical heterocomplexes of the type [M(N)(PNP)(B)](0/+) (M=(99m)Tc, (188)Re; PNP=diphosphine ligands, B=DBODC, DEDC, NSH, H(2)OS, CysNAc, HDTCZ) and symmetrical nitride compounds of the type [M(N)(L)(2)] (L=DEDC, DPDC) have been prepared in high yield by using the newly designed nitride nitrogen atom donor HO(2)C-PEG(600)-DTCZ. A two-step procedure was applied for preparing the above symmetrical and asymmetrical complexes. The first step involved the preliminary formation of a mixture of nitride Tc-99m or Re-188 precursors, which contained the [M≡N](2+) core, through reduction of generator-eluted (99m)Tc-pertechnetate or (188)Re-perrhenate with thin (II) chloride in the presence of HO(2)C-PEG(600)-DTCZ. In the second step, the intermediate mixture was converted either in the final mixed asymmetrical complex by the simultaneous addition of diphosphine ligand and the suitable bidentate ligand B, or in the final symmetrical complex by the only addition of the bidentate ligand L. It was also demonstrated that the novel water-soluble nitride nitrogen atom donor HO(2)C-PEG(600)-DTCZ did not show coordinating properties toward the M≡N ((99m)Tc, (188)Re) core. Biodistribution studies in rats of the hitherto unreported [(99m)Tc(N)(PNP(3))DTCZ](+) and [(99m)Tc(N)(PNP(5))DTCZ](+) complexes showed that they selectively localize in the myocardium of rats with a favourable heart-to-lung and heart-to-liver uptake ratios. In particular, the heart-to-lung and heart-to-liver uptake ratios dramatically increased in the interval between 60 and 120 min postinjection. Hence, the combination of the favourable chemical and biological properties of HO(2)C-PEG(600)-DTCZ might confer to this novel compound an important role for the development of new (99m)Tc and (188)Re-nitrido radiopharmaceuticals.

Automated preparation of Re-188 lipiodol for the treatment of hepatocellular carcinoma

The iodinated oil lipiodol is commonly used as a carrier for in situ delivery of drugs or radioactivity to hepatic tumors. Recently, we reported a new kit formulation for high-activity labeling of lipiodol with the β-emitting radionuclide Re-188. Since the whole preparation involves different steps and complex manipulations of high-activity samples, we describe here an automated synthesis module that allows the easy preparation of sterile and pyrogen-free samples of Re-188 lipiodol ready to be administered to the patient. Important advantages include the possibility to incorporate high Re-188 activity into the lipiodol hydrophobic phase and a sharp reduction of radiation exposure of the operator assisting the labelling procedure. Application of this modular reaction system could be also extended to the preparation of other Re-188 radiopharmaceuticals and to compound labelled with different β-emitting therapeutic radionuclides.

Preparation and first biological evaluation of novel Re-188 Tc-99m peptide conjugates with substance-P

INTRODUCTION New (188)Re and (99m)Tc peptide conjugates with substance- P (SP) were prepared and biologically evaluated. The radiopharmaceuticals have been labelled with the [M≡N](2+) (M=(99m)Tc, (188)Re) core using a combination of π-donor tridentate and π-acceptor monodentate ancillary ligands. METHODS The new radiopharmaceuticals have been prepared through a two-step reaction by simultaneous addition of the tridentate and monodentate ligands to a vial containing a preformed [M≡N](2+) core. The tridentate ligand was formed by linking two cysteine residues to the terminal arginine of the undecapeptide SP, whereas the monodentate ligand was a tertiary phosphine. The preparation of the corresponding Re-188 derivative required developing a more complex chemical procedure to obtain the [Re≡N](2+) core in satisfactory yields. Characterization of the resulting products was obtained by chromatographic methods. Biological evaluation was performed for both Tc-99m and Re-188 derivatives by in-vitro studies on isolated cells expressing NK1-receptors. In-vivo imaging in mice was carried out using a small-animal YAP(S)PET tomograph. CONCLUSION New Tc-99m and Re-188 peptide radiopharmaceuticals with SP have been prepared in high-yield and with high-specific activity. Both Tc-99m and Re-188 peptide radioconjugates exhibit high affinity for NK1 receptors, thus giving further evidence to the empirical rule that structurally related Tc-99m and Re-188 radiopharmaceuticals exhibit identical biological properties.

A solvent-extraction module for cyclotron production of high-purity technetium-99m

The design and fabrication of a fully-automated, remotely controlled module for the extraction and purification of technetium-99m (Tc-99m), produced by proton bombardment of enriched Mo-100 molybdenum metallic targets in a low-energy medical cyclotron, is here described. After dissolution of the irradiated solid target in hydrogen peroxide, Tc-99m was obtained under the chemical form of 99mTcO4-, in high radionuclidic and radiochemical purity, by solvent extraction with methyl ethyl ketone (MEK). The extraction process was accomplished inside a glass column-shaped vial especially designed to allow for an easy automation of the whole procedure. Recovery yields were always >90% of the loaded activity. The final pertechnetate saline solution Na99mTcO4, purified using the automated module here described, is within the Pharmacopoeia quality control parameters and is therefore a valid alternative to generator-produced 99mTc. The resulting automated module is cost-effective and easily replicable for in-house production of high-purity Tc-99m by cyclotrons.

Novel Tc-99m radiotracers for brain imaging

Uma nova classe de complexos de Tc-99m capazes de atravessar a barreira hemato-encefalica foi investigada e descrita neste trabalho. Estes compostos sao formados reagindo os precursores bissubstituidos do nitrido [99mTc(N)(PS)2] (PS = phosphino-tiol ligante) com trietillborano (BEt3) sob restritas condicoes anidras e usando solventes nao aquosos. A estrutura molecular desses tracadores nao foi totalmente estabelecida, mas evidencias experimentais preliminares sugerem que eles resultam da interacao da base de Lewis [99mTc(N)(PS)2] com o acido de Lewis BEt3, levando a formacao do novo aducto -B-No Tc-. Apos purificacao e recuperacao em uma solucao fisiologica, os novos derivados borano-nitrido-Tc-99m foram injetados em ratos para avaliacao de seu comportamento biologico in vivo. Os resultados mostraram uma acumulacao significativa no tecido cerebral, indicando que estes complexos sao capazes de atravessar a barreira hemato-encefalica integra. A captacao pelo sistema nervosa central foi confirmada pela imagem da distribuicao de atividade em animais vivos, usando um scanner para animais pequenos (YAP(S)SPECT).

Recent achievements in Tc-99m radiopharmaceutical direct production by medical cyclotrons

Abstract 99mTc is the most commonly used radionuclide in the field of diagnostic imaging, a noninvasive method intended to diagnose a disease, assess the disease state and monitor the effects of treatments. Annually, the use of 99mTc, covers about 85% of nuclear medicine applications. This isotope releases gamma rays at about the same wavelength as conventional X-ray diagnostic equipment, and owing to its short half-life (t½ = 6 h) is ideal for diagnostic nuclear imaging. A patient can be injected with a small amount of 99mTc and within 24 h almost 94% of the injected radionuclide would have decayed and left the body, limiting the patient’s radiation exposure. 99mTc is usually supplied to hospitals through a 99Mo/99mTc radionuclide generator system where it is produced from the β decay of the parent nuclide 99Mo (t½ = 66 h), which is produced in nuclear reactors via neutron fission. Recently, the interruption of the global supply chain of reactor-produced 99Mo, has forced the scientific community to investigate alternative production routes for 99mTc. One solution was to consider cyclotron-based methods as potential replacement of reactor-based technology and the nuclear reaction 100Mo(p,2n)99mTc emerged as the most worthwhile approach. This review reports some achievements about 99mTc produced by medical cyclotrons. In particular, the available technologies for target design, the most efficient extraction and separation procedure developed for the purification of 99mTc from the irradiated targets, the preparation of high purity 99mTc radiopharmaceuticals and the first clinical studies carried out with cyclotron produced 99mTc are described.