Biodistribution Assessment of a Novel 68Ga-Labeled Radiopharmaceutical in a Cancer Overexpressing CCK2R Mouse Model: Conventional and Radiomics Methods for Analysis.

The aim of the present study consists of the evaluation of the biodistribution of a novel 68Ga-labeled radiopharmaceutical, [68Ga]Ga-NODAGA-Z360, injected into Balb/c nude mice through histopathological analysis on bioptic samples and radiomics analysis of positron emission tomography/computed tomography (PET/CT) images. The 68Ga-labeled radiopharmaceutical was designed to specifically bind to the cholecystokinin receptor (CCK2R). This receptor, naturally present in healthy tissues such as the stomach, is a biomarker for numerous tumors when overexpressed. In this experiment, Balb/c nude mice were xenografted with a human epidermoid carcinoma A431 cell line (A431 WT) and overexpressing CCK2R (A431 CCK2R+), while controls received a wild-type cell line. PET images were processed, segmented after atlas-based co-registration and, consequently, 112 radiomics features were extracted for each investigated organ / tissue. To confirm the histopathology at the tissue level and correlate it with the degree of PET uptake, the studies were supported by digital pathology. As a result of the analyses, the differences in radiomics features in different body districts confirmed the correct targeting of the radiopharmaceutical. In preclinical imaging, the methodology confirms the importance of a decision-support system based on artificial intelligence algorithms for the assessment of radiopharmaceutical biodistribution.

Chromatographic separation of silver-111 from neutron-irradiated palladium target: toward direct labeling of radiotracers.

BACKGROUND: Silver-111 is a promising ß--emitting radioisotope with ideal characteristics for targeted radionuclide therapy and associated single photon emission tomography imaging. Its decay properties closely resemble the clinically established lutetium-177, making it an attractive candidate for therapeutic applications. In addition, the clinical value of silver-111 is further enhanced by the existence of the positron-emitting counterpart silver-103, thus imparting a truly theranostic potential to this element. A so-fitting matching pair could potentially overcome the current limitations associated with the forced use of chemically different isotopes as imaging surrogates of lutetium-177, leading to more accurate and efficient diagnosis and treatment. However, the use of silver-111-based radiopharmaceuticals in vivo has faced obstacles due to the challenges related to its production and radiochemical separation from the target material. To address these issues, this study aims to implement a chromatographic separation methodology for the purification of reactor-produced silver-111. The ultimate goal is to achieve a ready-to-use formulation for the direct radiolabeling of tumour-seeking biomolecules. RESULTS: A two-step sequence chromatographic process was validated for cold Ag-Pd separation and then translated to the radioactive counterpart. Silver-111 was produced via the 110Pd(n,γ)111Pd nuclear reaction on a natural palladium target and the subsequent ß--decay of palladium-111. Silver-111 was chemically separated from the metallic target via the implemented chromatographic process by using commercially available LN and TK200 resins. The effectiveness of the separations was assessed by inductively coupled plasma optical emission spectroscopy and γ-spectrometry, respectively, and the Ag+ retrieval was afforded in pure water. Recovery of silver-111 was > 90% with a radionuclidic purity > 99% and a separation factor of around 4.21·10-4. CONCLUSIONS: The developed separation method was suitable to obtain silver-111 with high molar activity in a ready-to-use water-based formulation that can be directly employed for the labeling of radiotracers. By successfully establishing a robust and efficient production and purification method for silver-111, this research paves the way for its wider application in targeted radionuclide therapy and precision imaging.

Tuning the Framework of Thioether-Functionalized Polyazamacrocycles: Searching for a Chelator for Theranostic Silver Radioisotopes.

Silver-111 is an attractive unconventional candidate for targeted cancer therapy as well as for single photon emission computed tomography and can be complemented by silver-103 for positron emission tomography noninvasive diagnostic procedures. However, the shortage of chelating agents capable of forming stable complexes tethered to tumor-seeking vectors has hindered their in vivo application so far. In this study, a comparative investigation of a series of sulfur-containing structural homologues, namely, 1,4,7-tris[2-(methylsulfanyl)ethyl)]-1,4,7-triazacyclononane (NO3S), 1,5,9-tris[2-(methylsulfanyl)ethyl]-1,5,9-triazacyclododecane (TACD3S), 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclotridecane (TRI4S), and 1,4,8,11-tetrakis[2-(methylsulfanyl)ethyl]-1,4,8,11-tetraazacyclotetradecane (TE4S) was conducted to appraise the influence of different polyazamacrocyclic backbones on Ag+ complexation. The performances of these macrocycles were also compared with those of the previously reported Ag+/[111Ag]Ag+-chelator 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO4S). Nuclear magnetic resonance data supported by density functional theory calculations and X-ray crystallographic results gave insights into the coordination environment of these complexes, suggesting that all of the donor atoms are generally involved in the metal coordination. However, the modifications of the macrocycle topology alter the dynamic binding of the pendant arms or the conformation of the ring around the metal center. Combined pH/pAg-potentiometric and spectroscopic experiments revealed that the 12-member N4 backbone of DO4S forms the most stable Ag+ complex while both the enlargement and the shrinkage of the macrocyclic frame dwindle the stability of the complexes. Radiolabeling experiments, conducted with reactor-produced [111Ag]Ag+, evidenced that the thermodynamic stability trend is reflected in the ligand's ability to incorporate the radioactive ion at high molar activity, even in the presence of a competing cation (Pd2+), as well as in the integrity of the corresponding complexes in human serum. As a consequence, DO4S proved to be the most favorable candidate for future in vivo applications.

Thermal and Structural Characterization of a Titanium Carbide/Carbon Composite for Nuclear Applications.

In the framework of ISOL (isotope separation on-line) facilities, porous carbides are among the most employed target materials for the production of radioactive ion beams for research. As foreseen by the ISOL technique, a production target is impinged by an energetic particle beam, inducing nuclear reactions from such an interaction. The resulting radionuclides are subsequently released, thanks to the high target working temperature (1600-2000 °C); ionized; and extracted into a beam. Since the target microstructure and porosity play a fundamental role in the radionuclide release efficiency, custom-made target materials are often specifically produced, resulting in unknown thermal and structural properties. Considering that such targets might undergo intense thermal stresses during operation, a thermal and structural characterization is necessary to avoid target failure under irradiation. In the presented work, a custom-made porous titanium carbide that was specifically designed for application as an ISOL target was produced and characterized. The thermal characterization was focused on the evaluation of the material emissivity and thermal conductivity in the 600-1400 °C temperature range. For the estimation of a reference material tensile stress limit, the virtual thermoelastic parameter approach was adopted. In particular, for the aforementioned temperature range, an emissivity between 0.7 and 0.8 was measured, whereas a thermal conductivity between 8 and 10 W/mK was estimated.

A New Preclinical Decision Support System Based on PET Radiomics: A Preliminary Study on the Evaluation of an Innovative 64Cu-Labeled Chelator in Mouse Models.

The 64Cu-labeled chelator was analyzed in vivo by positron emission tomography (PET) imaging to evaluate its biodistribution in a murine model at different acquisition times. For this purpose, nine 6-week-old female Balb/C nude strain mice underwent micro-PET imaging at three different time points after 64Cu-labeled chelator injection. Specifically, the mice were divided into group 1 (acquisition 1 h after [64Cu] chelator administration, n = 3 mice), group 2 (acquisition 4 h after [64Cu]chelator administration, n = 3 mice), and group 3 (acquisition 24 h after [64Cu] chelator administration, n = 3 mice). Successively, all PET studies were segmented by means of registration with a standard template space (3D whole-body Digimouse atlas), and 108 radiomics features were extracted from seven organs (namely, heart, bladder, stomach, liver, spleen, kidney, and lung) to investigate possible changes over time in [64Cu]chelator biodistribution. The one-way analysis of variance and post hoc Tukey Honestly Significant Difference test revealed that, while heart, stomach, spleen, kidney, and lung districts showed a very low percentage of radiomics features with significant variations (p-value < 0.05) among the three groups of mice, a large number of features (greater than 60% and 50%, respectively) that varied significantly between groups were observed in bladder and liver, indicating a different in vivo uptake of the 64Cu-labeled chelator over time. The proposed methodology may improve the method of calculating the [64Cu]chelator biodistribution and open the way towards a decision support system in the field of new radiopharmaceuticals used in preclinical imaging trials.

Thermal and Mechanical Characterization of Carbides for High Temperature Nuclear Applications.

In the facilities for the production of Radioactive Ion Beams (RIBs) according to the Isotope Separation On-Line (ISOL) technique, a production target is typically impinged by a high-power primary beam, generating radioactive isotopes for basic research and technological applications. With the aim to guarantee an efficient extraction of the aforementioned isotopes, the production target must work in a high vacuum environment, at temperatures that are usually between 1600 °C and 2200 °C. Its main components are often characterized by intense temperature gradients and consequently by severe thermal stresses. Carbides are widely used for target manufacturing, and in this work a specific method for their thermal and mechanical characterization is presented and discussed. It is based on the comparison between experimental measurements and numerical simulations, with the introduction of the novel Virtual Thermoelastic Parameters approach for the structural verification procedure. High-performance silicon carbides (SiC) are taken as a reference to describe the method. Measured emissivity and thermal conductivity data are presented and discussed, together with the experimental estimation of material limitations for both temperature and stress fields. The aforementioned results can be promptly used for the design process of high-power ISOL targets.

Preliminary evaluation of the production of non-carrier added 111Ag as core of a therapeutic radiopharmaceutical in the framework of ISOLPHARM_Ag experiment.

Research in the field of radiopharmaceuticals is increasingly promoted by the widespread and growing interest in applying nuclear medicine procedures in both disease diagnosis and treatment. The production of radionuclides of medical interest is however a challenging issue. Along with the conventional techniques other innovative approaches are being investigated and, among those, the ISOLPHARM project is being developed at INFN-LNL (Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Legnaro). Such technique foresees the employment of the SPES ISOL facility to produce isobarically pure Radioactive Ion Beams (RIBs), obtained thanks to electromagnetic mass separation and collected on appropriate substrates. The latter are successively recovered and dissolved, allowing thus the chemical separation and harvesting of the nuclides of interest, free from any isotopic contaminant. Although ISOLPHARM can be potentially employed for most of the routinely used medical radioisotopes, its innovation potential is better expressed considering its capability to provide carrier free unconventional nuclides, difficult to produce with state-of-art techniques, such as 111Ag, a ß- emitter potentially interesting for therapeutic applications. Thus, in the framework of ISOLPHARM, INFN supported a two-years experiment, called ISOLPHARM_Ag, aimed at evaluating the feasibility of the production of a111Ag labelled radiopharmaceutical. The ISOL production yields are estimated by computing intensive Monte Carlo codes, that require an appropriate custom Information Technology infrastructure. The presented work is focused on the first part of the production chain including the capability to extract, ionize, and collect stable Ag beams with SPES technologies. MC calculations were used to estimate the expected 111Ag in-target yields, whereas experiments with stable Ag were performed to test the ionization, transport and collection of Ag beams.

Highly Stable Silver(I) Complexes with Cyclen-Based Ligands Bearing Sulfide Arms: A Step Toward Silver-111 Labeled Radiopharmaceuticals.

With a half-life of 7.45 days, silver-111 (ßmax 1.04 MeV, Eγ 245.4 keV [Iγ 1.24%], Eγ 342.1 keV [Iγ 6.7%]) is a promising candidate for targeted cancer therapy with ß- emitters as well as for associated SPECT imaging. For its clinical use, the development of suitable ligands that form sufficiently stable Ag+-complexes in vivo is required. In this work, the following sulfur-containing derivatives of tetraazacyclododecane (cyclen) have been considered as potential chelators for silver-111: 1,4,7,10-tetrakis(2-(methylsulfanyl)ethyl)-1,4,7,10-tetraazacyclododecane (DO4S), (2S,5S,8S,11S)-2,5,8,11-tetramethyl-1,4,7,10-tetrakis(2-(methylsulfanyl)ethyl)-1,4,7,10-tetraazacyclododecane (DO4S4Me), 1,4,7-tris(2-(methylsulfanyl)ethyl)-1,4,7,10-tetraazacyclododecane (DO3S), 1,4,7-tris(2-(methylsulfanyl)ethyl)-10-acetamido-1,4,7,10-tetraazacyclododecane (DO3SAm), and 1,7-bis(2-(methylsulfanyl)ethyl)-4,10,diacetic acid-1,4,7,10-tetraazacyclododecane (DO2A2S). Natural Ag+ was used in pH/Ag-potentiometric and UV-vis spectrophotometric studies to determine the metal speciation existing in aqueous NaNO3 0.15 M at 25 °C and the equilibrium constants of the complexes, whereas NMR and DFT calculations gave structural insights. Overall results indicated that sulfide pendant arms coordinate Ag+ allowing the formation of very stable complexes, both at acidic and physiological pH. Furthermore, radiolabeling, stability in saline phosphate buffer, and metal-competition experiments using the two ligands forming the strongest complexes, DO4S and DO4S4Me, were carried out with [111Ag]Ag+ and promising results were obtained.

Chemical purification of 111Ag from isobaric impurity 111Cd by solid phase extraction chromatography: a proof of concept study.

Silver-111 (111Ag, t1/2 = 7.47 d) is a ß- emitter suitable for targeted cancer therapy due to favourable decay properties. The production of no-carrier added 111Ag via Isotope Separation On-Line (ISOL) technique is being investigated at the Legnaro National Laboratories of the Italian Institute of Nuclear Physics (ISOLPHARM project). Stable Cadmium-111 (111Cd) is co-produced as isobaric contaminant, hence a chemical separation process must be developed to selectively harvest 111Ag. In this study, a chromatographic procedure employing the commercially available CL resin was investigated by using stable Ag+ and Cd2+. Results indicate that CL resin allows to efficiently separate Ag+ from Cd2+ and recover the former with high yields.

Experimental study of consistency degradation of different greases in mixed neutron and gamma radiation.

Many of the moving components in accelerator and target environments require lubrication. Lubricants in such environments are exposed to high fluxes of secondary radiation, which originates from beam interactions with the target and from beam losses. The secondary radiation is a mix of components, which can include significant fractions of neutrons. Lubricants are radiation-sensitive polymeric materials. The radiation-induced modifications of their structure reduce their service lifetime and impose additional facility maintenance, which is complicated by the environmental radioactivity. The study of the lubricants radiation resistance is therefore necessary for the construction of new generation accelerators and target systems. Nevertheless, data collected in mixed radiation fields are scarce. Nine commercial greases were irradiated at a TRIGA Mark II Research Reactor to serve for the construction of new accelerator projects like the European Spallation Source (ESS) at Lund (Sweden) and Selective Production of Exotic Species (SPES) at Legnaro, (Italy). Mixed neutron and gamma doses ranging from 0.1 MGy to 9.0 MGy were delivered to the greases. For an experimental quantification of their degradation, consistency was measured. Two of the greases remained stable, while the others became fluid. Post-irradiation examinations evidence the cleavage of the polymeric structure as the dominant radiation effect. Dose and fluence limits for the use of each product are presented. Apart from the scientific significance, the results represent an original and useful reference in selecting radiation resistant greases for accelerator and target applications.

ISOLPHARM, a new production method of high specific activity beta-emitting radionuclides as radiopharmaceutical precursors / ISOLPHARM, un nuevo método de producción de radionúclidos emisores beta de actividad específica alta como precursores radiofarmacéuticos

Abstract At INFN-LNL (Istituto Nazionale di Fisica Nucleare- Laboratori Nazionali di Legnaro) SPES (Selective Production of Exotic Species), a new facility for the production of radioactive ion beams is being constructed at INFN-LNL (Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Legnaro). Radioactive ion beams of neutron-rich nuclei with high purity, in the range of mass between 80 and 160 amu, will be produced by nuclear reactions induced by 40 MeV protons from a cyclotron. The goal of the ISOLPHARM project is to provide a feasibility study for an innovative technology for the production of extremely very high specific activity beta emitting radionuclides as radiopharmaceutical precursors. The ISOL method, adopted in the ISOLPHARM project (a branch of the SPES project), gives the possibility of obtaining pure isobaric beams. In this way, no isotopic contaminations will be present in the beam and afterwards in a proper trapping substrate. The ground-breaking idea of the ISOLPHARM method was granted an International patent (INFN).

Resumen En INFN-LNL (Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Legnaro) SPES (Producción selectiva de especies exóticas), se está construyendo una nueva instalación para la producción de haces de iones radiactivos en INFN-LNL (Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Legnaro). Se producirán haces de iones radiactivos de núcleos ricos en neutrones con alta pureza, en el rango de masa entre 80 y 160 amu, por reacciones nucleares inducidas por protones de 40 MeV de un ciclotrón. El objetivo del proyecto ISOLPHARM es proporcionar un estudio de viabilidad para una tecnología innovadora para la producción de radionúclidos emisores de beta de actividad específica extremadamente alta como precursores radiofarmacéuticos. El método ISOL, adoptado en el proyecto ISOLPHARM (una rama del proyecto SPES), ofrece la posibilidad de obtener haces isobáricos puros. De esta manera, no habrá contaminaciones isotópicas en el haz y luego en un sustrato de atrapamiento adecuado. La idea pionera del método ISOLPHARM recibió una patente internacional (INFN).

Early Evaluation of Copper Radioisotope Production at ISOLPHARM.

The ISOLPHARM (ISOL technique for radioPHARMaceuticals) project is dedicated to the development of high purity radiopharmaceuticals exploiting the radionuclides producible with the future Selective Production of Exotic Species (SPES) Isotope Separation On-Line (ISOL) facility at the Legnaro National Laboratories of the Italian National Institute for Nuclear Physics (INFN-LNL). At SPES, a proton beam (up to 70 MeV) extracted from a cyclotron will directly impinge a primary target, where the produced isotopes are released thanks to the high working temperatures (2000 °C), ionized, extracted and accelerated, and finally, after mass separation, only the desired nuclei are collected on a secondary target, free from isotopic contaminants that decrease their specific activity. A case study for such project is the evaluation of the feasibility of the ISOL production of 64Cu and 67Cu using a zirconium germanide target, currently under development. The producible activities of 64Cu and 67Cu were calculated by means of the Monte Carlo code FLUKA, whereas dedicated off-line tests with stable beams were performed at LNL to evaluate the capability to ionize and recover isotopically pure copper.

First results on Ge resonant laser photoionization in hollow cathode lamp.

In the framework of the research and development activities of the SPES project regarding the optimization of the radioactive beam production, a dedicated experimental study has been recently started in order to investigate the possibility of in-source ionization of germanium using a set of tunable dye lasers. Germanium is one of the beams to be accelerated by the SPES ISOL facility, which is under construction at Legnaro INFN Laboratories. The three-step, two color ionization schemes have been tested using a Ge hollow cathode lamp. The slow and the fast optogalvanic signals were detected and averaged by an oscilloscope as a proof of the laser ionization inside the lamp. As a result, several wavelength scans across the resonances of ionization schemes were collected with the fast optogalvanic signal. Some comparisons of ionization efficiency for different ionization schemes were made. Furthermore, saturation curves of the first excitation transitions have been obtained. This investigation method and the setup built in the laser laboratory of the SPES project can be applied for the photo-ionization scheme studies also for the other possible radioactive elements.