Reactor production of 64Cu and 67Cu using enriched zinc target material

Radiocopper in Radiopharmacy and Medical Use: Current Status and Perspective

Of the 32 known copper isotopes, some have interesting properties for nuclear medicine, for example the short-lived 60Cu, 61Cu, 62Cu, the moderate long-lived 64Cu and the long-lived 67Cu. Due to their emission properties, copper isotopes are suitable for both imaging diagnostics (60Cu, 61Cu, 62Cu, 64Cu) and targeted radiotherapy (64Cu and 67Cu). As their chemical properties are virtually identical, a single radiopharmaceutical structure can be labeled with different isotopes, depending on the clinical application. This, combined with the ability to combine radioisotopes with different nuclear properties with the same ligand, makes them extremely versatile. The purpose of this review is to introduce the world of copper radiopharmaceuticals and to summarize recent advances in methods for producing copper radioisotopes and the preclinical research of radiopharmaceuticals labeled with copper radioisotopes.

Improved extraction efficiency of radioactive copper produced via accelerator neutrons method through phosphate buffer-enhanced column pre-treatment

We report a straightforward and robust method for isolating medical copper radioisotopes 64Cu and 67Cu, generated by an accelerator neutrons technique from natZn(n, x). This study reveals the key role of a phosphate buffer pre-treatment of the cation exchange column in the separation process. Incorporating the phosphate buffer into the column pre-treatment markedly enhances the retention of copper isotopes within the column throughout the separation procedure. This approach yields a remarkably high-purity radioactive copper sample with a high extraction efficiency of 94.4 (1.5) % of the initially produced copper, all within a relatively short experimental timeframe of approximately 5 h for 100 g of starting material. This single-step separation scheme is reproducible across a range of starting material target sizes, from small (10 g) to large (100 g). The copper radioisotopes obtained are suitable for use in pre-clinical studies. Thus, this approach offers a more effective means for routine preparation of copper radioisotopes.

Optimized production of 67Cu based on cross section measurements of 67Cu and 64Cu using an 18 MeV medical cyclotron

RadioNuclide Therapy (RNT) in nuclear medicine is a cancer treatment based on the administration of radioactive substances that specifically target cancer cells in the patient. These radiopharmaceuticals consist of tumor-targeting vectors labeled with β^-, α, or Auger electron-emitting radionuclides. In this framework, ⁶⁷Cu is receiving increasing interest as it provides β^--particles accompanied by low-energy γ radiation. The latter allows to perform Single Photon Emission Tomography (SPECT) imaging for detecting the radiotracer distribution for an optimized treatment plan and follow-up. Furthermore, ⁶⁷Cu could be used as therapeutic partner of the β⁺-emitters ⁶¹Cu and ⁶⁴Cu, both currently under study for Positron Emission Tomography (PET) imaging, paving the way to the concept of theranostics. The major barrier to a wider use of ⁶⁷Cu-based radiopharmaceutical is its lack of availability in quantities and qualities suitable for clinical applications. A possible but challenging solution is the proton irradiation of enriched ⁷⁰Zn targets, using medical cyclotrons equipped with a solid target station. This route was investigated at the Bern medical cyclotron, where an 18 MeV cyclotron is in operation together with a solid target station and a 6-m-long beam transfer line. The cross section of the involved nuclear reactions were accurately measured to optimize the production yield and the radionuclidic purity. Several production tests were performed to confirm the obtained results.

67Cu Production Capabilities: A Mini Review

Is the ⁶⁷Cu production worldwide feasible for expanding preclinical and clinical studies? How can we face the ingrowing demands of this emerging and promising theranostic radionuclide for personalized therapies? This review looks at the different production routes, including the accelerator- and reactor-based ones, providing a comprehensive overview of the actual ⁶⁷Cu supply, with brief insight into its use in non-clinical and clinical studies. In addition to the most often explored nuclear reactions, this work focuses on the ⁶⁷Cu separation and purification techniques, as well as the target material recovery procedures that are mandatory for the economic sustainability of the production cycle. The quality aspects, such as radiochemical, chemical, and radionuclidic purity, with particular attention to the coproduction of the counterpart ⁶⁴Cu, are also taken into account, with detailed comparisons among the different production routes. Future possibilities related to new infrastructures are included in this work, as well as new developments on the radiopharmaceuticals aspects.

Radiotheranostic Agent 64Cu-cyclam-RAFT-c(-RGDfK-)4 for Management of Peritoneal Metastasis in Ovarian Cancer

PURPOSE

Ovarian cancer peritoneal metastases (OCPMs) are a pathophysiologically heterogeneous group of tumors that are rarely curable. αVβ3 integrin (αVβ3) is overexpressed on tumoral neovessels and frequently on ovarian cancer cells. Here, using two clinically relevant αVβ3-positive OCPM mouse models, we studied the theranostic potential of an αVβ3-specific radiopeptide, 64Cu-cyclam-RAFT-c(-RGDfK-)4 (64Cu-RaftRGD), and its intra- and intertumoral distribution in relation to the tumor microenvironment.

EXPERIMENTAL DESIGN

αVβ3-expressing peritoneal and subcutaneous models of ovarian carcinoma (IGR-OV1 and NIH:OVCAR-3) were established in nude mice. 64Cu-RaftRGD was administered either intravenously or intraperitoneally. We performed intratumoral distribution (ITD) studies, PET/CT imaging and quantification, biodistribution assay and radiation dosimetry, and therapeutic efficacy and toxicity studies.

RESULTS

Intraperitoneal administration was an efficient route for targeting 64Cu-RaftRGD to OCPMs with excellent tumor penetration. Using the fluorescence surrogate, Cy5.5-RaftRGD, in our unique high-resolution multifluorescence analysis, we found that the ITD of 64Cu-RaftRGD was spatially distinct from, but complementary to, that of hypoxia. 64Cu-RaftRGD-based PET enabled clear visualization of multiple OCPM deposits and ascites and biodistribution analysis demonstrated an inverse correlation between tumor uptake and tumor size (1.2-17.2 mm). 64Cu-RaftRGD at a radiotherapeutic dose (148 MBq/0.357 nmol) showed antitumor activities by inhibiting tumor cell proliferation and inducing apoptosis, with negligible toxicity.

CONCLUSIONS

Collectively, these results demonstrate the all-in-one potential of 64Cu-RaftRGD for imaging guided radiotherapy of OCPM by targeting both tumoral neovessels and cancerous cells. On the basis of the ITD finding, we propose that pairing αVβ3- and hypoxia-targeted radiotherapies could improve therapeutic efficacy by overcoming the heterogeneity of ITD encountered with single-agent treatments.

IAEA contribution to the development of 64Cu radiopharmaceuticals for theranostic applications

Copper-64 is a very attractive radioisotope with unique nuclear properties that allow using it as both a diagnostic and therapeutic agent, thus providing an almost ideal example of a theranostic radionuclide. A characteristic of Cu-64 stems from the intrinsic biological nature of copper ions that play a fundamental role in a large number of cellular processes. Cu-64 is a radionuclide that reflects the natural biochemical pathways of Cu-64 ions, therefore, can be exploited for the detection and therapy of certain malignancies and metabolic diseases. Beside these applications of Cu-64 ions, this radionuclide can be also used for radiolabelling bifunctional chelators carrying a variety of pharmacophores for targeting different biological substrates. These include peptide-based substrates and immunoconjugates as well as small-molecule bioactive moieties. Fueled by the growing interest of Member States (MS) belonging to the International Atomic Energy Agency (IAEA) community, a dedicated Coordinated Research Project (CRP) was initiated in 2016, which recruited thirteen participating MS from four continents. Research activities and collaborations between the participating countries allowed for collection of an impressive series of results, particularly on the production, preclinical evaluation and, in a few cases, clinical evaluation of various ⁶⁴Cu-radiopharmaceuticals that may have potential impact on future development of the field. Since this CRP was finalized at the beginning of 2020, this short review summarizes outcomes, outputs and results of this project with the purpose to propagate to other MS and to the whole scientific community, some of the most recent achievements on this novel class of theranostic ⁶⁴Cu-pharmaceuticals.

Simple separation of 67Cu from bulk zinc by coprecipitation using hydrogen sulfide gas and silver nitrate

Copper-67 (67Cu), a feasible radionuclide for diagnosis and radiotherapy, is commercially generated from a bulk zinc (Zn) target using the 68Zn(p, 2p)67Cu and 68Zn(γ, p)67Cu nuclear reactions. Because it uses a large amount of zinc, the separation is complex – requiring a combination of three ion exchange columns – and is time-consuming (about 1 day). We developed a quick and easy separation method referred to as “double coprecipitation” using H2S gas and silver nitrate as coprecipitation agents in place of ion exchange columns. We compared this method with a conventional separation method using three ion exchange columns (AG50W-X8, AG1-X8, and Chelex-100) for a natural zinc (natZn) target irradiated by a proton beam. The product quality and the recovery rate with the new method were competitive with the conventional method, and the total operation time was reduced from 1 day to <3 h.

A novel approach to medical radioisotope production using inverse kinematics: A successful production test of the theranostic radionuclide 67Cu

A novel method for the production of important medical radioisotopes has been developed. The approach is based on performing the nuclear reaction in inverse kinematics, namely sending a heavy-ion beam of appropriate energy on a light target (e.g. H, d, He) and collecting the isotope of interest. In this work, as a proof-of-concept, we studied the production of the theranostic radionuclide ⁶⁷Cu (T_1/2 = 62 h) via the reaction of a ⁷⁰Zn beam at 15 MeV/nucleon with a hydrogen gas target. The ⁶⁷Cu radionuclide alongside other coproduced isotopes, was collected after the gas target on an aluminum catcher foil and their radioactivity was measured by off-line γ-ray analysis. After 36 h post irradiation, apart from the product of interest ⁶⁷Cu, the main radioimpurity coming from the ⁷⁰Zn + p reaction was ^69mZn (T_1/2 = 13.8 h), which can be reduced by further radio-cooling. Moreover, along with the radionuclide of interest produced in inverse kinematics, the production of additional radioisotopes is possible by making use of the forward-focused neutrons from the reaction and allowing them to interact with a secondary target. A preliminary successful test of this concept was realized in the present study. The main requirement to obtain activities appropriate for preclinical studies is the development of high-intensity heavy-ion primary beams.

Integrated treatment using intraperitoneal radioimmunotherapy and positron emission tomography-guided surgery with 64Cu-labeled cetuximab to treat early- and late-phase peritoneal dissemination in human gastrointestinal cancer xenografts

Peritoneal dissemination is a common cause of death from gastrointestinal cancers and is difficult to treat using current therapeutic options, particularly late-phase disease. Here, we investigated the feasibility of integrated therapy using ⁶⁴Cu-intraperitoneal radioimmunotherapy (ipRIT), alone or in combination with positron emission tomography (PET)-guided surgery using a theranostic agent (⁶⁴Cu-labeled anti-epidermal growth factor receptor antibody cetuximab) to treat early- and late-phase peritoneal dissemination in mouse models. In this study, we utilized the OpenPET system, which has open space for conducting surgery while monitoring objects at high resolution in real time, as a novel approach to make PET-guided surgery feasible. ⁶⁴Cu-ipRIT with cetuximab inhibited tumor growth and prolonged survival with little toxicity in mice with early-phase peritoneal dissemination of small lesions. For late-phase peritoneal dissemination, a combination of ⁶⁴Cu-ipRIT for down-staging and subsequent OpenPET-guided surgery for resecting large tumor masses effectively prolonged survival. OpenPET clearly detected tumors (≥3 mm in size) behind other organs in the peritoneal cavity and was useful for confirming the presence or absence of residual tumors during an operation. These findings suggest that integrated ⁶⁴Cu therapy can serve as a novel treatment strategy for peritoneal dissemination.

Uniform intratumoral distribution of radioactivity produced using two different radioagents, 64Cu-cyclam-RAFT-c(-RGDfK-)4 and 64Cu-ATSM, improves therapeutic efficacy in a small animal tumor model

Background

The present study proposed a new concept for targeted radionuclide therapy (TRT) to improve the intratumoral distribution of radioactivity using two different radiopharmaceuticals. We examined the efficacy of a combination of a tetrameric cyclic Arg-Gly-Asp (cRGD) peptide-based radiopharmaceutical, ⁶⁴Cu-cyclam-RAFT-c(-RGDfK-)₄ (⁶⁴Cu-RaftRGD, an α_Vβ₃ integrin [α_Vβ₃] tracer), and ⁶⁴Cu-diacetyl-bis (N⁴-methylthiosemicarbazone) (⁶⁴Cu-ATSM, a supposed tracer for hypoxic metabolism) in a small animal tumor model.

Results

Mice with subcutaneous α_Vβ₃-positive U87MG glioblastoma xenografts were used. The intratumoral distribution of a near-infrared dye, Cy5.5-labeled RAFT-c(-RGDfK-)₄ (Cy5.5-RaftRGD), ⁶⁴Cu-RaftRGD, and ⁶⁴Cu-ATSM was visualized by fluorescence imaging and autoradiography of the co-injected Cy5.5-RaftRGD with ⁶⁴Cu-RaftRGD or ⁶⁴Cu-ATSM at 3 h postinjection. Mice were treated with a single intravenous dose of the vehicle solution (control), 18.5 or 37 MBq of ⁶⁴Cu-RaftRGD or ⁶⁴Cu-ATSM, or a combination (18.5 MBq of each agent). The tumor volume, tumor cell proliferation, body weight, survival, and tumor and organ uptake of radiopharmaceuticals were assessed. It was shown that Cy5.5-RaftRGD colocalized with ⁶⁴Cu-RaftRGD and could be used as a surrogate for the radioactive agent. The intratumoral distribution of Cy5.5-RaftRGD and ⁶⁴Cu-ATSM was discordant and nearly complementary, indicating a more uniform distribution of radioactivity achievable with the combined use of ⁶⁴Cu-RaftRGD and ⁶⁴Cu-ATSM. Neither ⁶⁴Cu-RaftRGD nor ⁶⁴Cu-ATSM showed significant effects on tumor growth at 18.5 MBq. The combination of both (18.5 MBq each) showed sustained inhibitory effects against tumor growth and tumor cell proliferation and prolonged the survival of the mice, compared to that by either single agent at 37 MBq. Interestingly, the uptake of the combination by the tumor was higher than that of ⁶⁴Cu-RaftRGD alone, but lower than that of ⁶⁴Cu-ATSM alone. The kidneys showed the highest uptake of ⁶⁴Cu-RaftRGD, whereas the liver exhibited the highest uptake of ⁶⁴Cu-ATSM. No obvious adverse effects were observed in all treated mice.

Conclusions

The combination of ⁶⁴Cu-RaftRGD and ⁶⁴Cu-ATSM achieved an improved antitumor effect owing to the more uniform intratumoral distribution of radioactivity. Thus, combining different radiopharmaceuticals to improve the intratumoral distribution would be a promising concept for more effective and safer TRT.

Electronic supplementary material

The online version of this article (10.1186/s13550-018-0407-3) contains supplementary material, which is available to authorized users.

64Cu, a powerful positron emitter for immunoimaging and theranostic: Production via natZnO and natZnO-NPs

⁶⁴Cu is one of the most beneficial radionuclide that can be used as a theranostic agent in Positron Emission Tomography (PET) imaging. In this current work, ⁶⁴Cu was produced with zinc oxide nanoparticles (^natZnONPs) and zinc oxide powder (^natZnO) via the ⁶⁴Zn(n,p)⁶⁴Cu reaction in Tehran Research Reactor (TRR) and the activity values were compared with each other. The theoretical activity of ⁶⁴Cu also was calculated with MCNPX-2.6 and the cross sections of this reaction were calculated by using TALYS-1.8, EMPIRE-3.2.2 and ALICE/ASH nuclear codes and were compared with experimental values. Transmission Electronic Microscopy (TEM), Scanning Electronic Microscopy (SEM) and X-Ray Diffraction (XRD) analysis were used for samples characterizations. From these results, it's concluded that ⁶⁴Cu activity value with nanoscale target was achieved more than the bulk state target and had a good adaptation with the MCNPX result.

Production, separation and supply prospects of 67Cu with the development of fast neutron sources and photonuclear technology

Experimental investigations have been carried out on the production of a promising therapeutic radionuclide 67Cu via the 67Zn(n,p)67Cu, 68Zn(n,x)67Cu, and 68Zn(γ,p)67Cu reaction routes. Natural zinc metal foils were irradiated with 14.1 MeV neutrons and bremsstrahlung of end-point energy 15 MeV. Radioactivity levels of 67Cu and other radioisotopes co-produced were determined by the quantification of photo-peaks by off-line γ-ray spectrometry. No carrier added 67Cu was separated from the irradiated zinc by solvent extraction. Yields >90% and high levels of radionuclidic purity were achieved. These studies indicate that the growth and development of intense fast neutron sources and photonuclear technology, will possibly aid in the sustained supply of 67Cu.

Study on a new design of Tehran Research Reactor for radionuclide production based on fast neutrons using MCNPX code

The aim of this work is to increase the magnitude of the fast neutron flux inside the flux trap where radionuclides are produced. For this purpose, three new designs of the flux trap are proposed and the obtained fast and thermal neutron fluxes compared with each other. The first and second proposed designs were a sealed cube contained air and D₂O, respectively. The results of calculated production yield all indicated the superiority of the latter by a factor of 55% in comparison to the first proposed design. The third proposed design was based on changing the surrounding of the sealed cube by locating two fuel plates near that. In this case, the production yield increased up to 70%.

Theoretical estimation of 64Cu production with neutrons emitted during 18F production with a 30MeV medical cyclotron

PURPOSE

This work presents the theoretical estimation of a combined production of ¹⁸F and ⁶⁴Cu isotopes for PET applications. ⁶⁴Cu production is induced in a secondary target by neutrons emitted during a routine ¹⁸F production with a 30MeV cyclotron: protons are used to produce ¹⁸F by means of the ¹⁸O(p,n)¹⁸F reaction on a [¹⁸O]-H₂O target (primary target) and the emitted neutrons are used to produce ⁶⁴Cu by means of the ⁶⁴Zn(n,p)⁶⁴Cu reaction on enriched zinc target (secondary target).

METHODS

Monte Carlo simulations were carried out using Monte Carlo N Particle eXtended (MCNPX) code to evaluate flux and energy spectra of neutrons produced in the primary (Be+[¹⁸O]-H₂O) target by protons and the attenuation of neutron flux in the secondary target. ⁶⁴Cu yield was estimated using an analytical approach based on both TENDL-2015 data library and experimental data selected from EXFOR database.

RESULTS

Theoretical evaluations indicate that about 3.8 MBq/μA of ⁶⁴Cu can be obtained as a secondary, 'side' production with a 30MeV cyclotron, for 2h of irradiation of a proper designed zinc target. Irradiating for 2h with a proton current of 120 μA, a yield of about 457 MBq is expected. Moreover, the most relevant contaminants result to be ^63,65Zn, which can be chemically separated from ⁶⁴Cu contrarily to what happens with proton irradiation of an enriched ⁶⁴Ni target, which provides ⁶⁴Cu mixed to other copper isotopes as contaminants.

CONCLUSIONS

The theoretical study discussed in this paper evaluates the potential of the combined production of ¹⁸F and ⁶⁴Cu for medical purposes, irradiating a properly designed target with 30MeV protons. Interesting yields of ⁶⁴Cu are obtainable and the estimation of contaminants in the irradiated zinc target is discussed.