Development of novel radionuclides for medical applications

The effects of nuclear level density model and alpha optical model potential to the excitation functions of novel therapeutic radionuclides

In this study, the theoretical cross sections of 209Bi(α,2n)211At, 65Cu(α,n)68Ga, 100Ru(α,n)103Pd, and 121Sb(α,n)124I are calculated using TALYS 1.96, incorporating the effects of the alpha optical model potential and nuclear level density models. The validation process involves comparing the calculated cross sections with experimental data and utilizing statistical deviation factors. This comparison allows us to determine the optimal combination of nuclear model parameters for each reaction. The result shows that theoretical calculations which utilized semi microscopic level density models and alpha OMP managed to describe the excitation functions close to the experimental data. The comparison of nuclear model calculations with experimental data plays a crucial role in ensuring the reliability of the data, making it an essential aspect of modern evaluation procedures.

Good practices for the automated production of 18F-SiFA radiopharmaceuticals

BACKGROUND

The positron emitting isotope fluorine-18 (18F) possesses almost ideal physicochemical properties for the development of radiotracers for diagnostic molecular imaging employing positron emission tomography (PET). 18F in its nucleophilic anionic 18F- form is usually prepared by bombarding an enriched 18O water target with protons of various energies between 5 and 20 MeV depending on the technical specifications of the cyclotron. Large thick-target yields between 5 and 14 GBq/µA can be obtained, enough to prepare large batches of radiotracers capable to serve a considerable contingent of patients (50 + per clinical batch). The overall yield of the radiotracer however depends on the efficiency of the 18F labeling chemistry. The Silicon Fluoride Acceptor chemistry (SiFA) has introduced a convenient and highly efficient way to provide clinical peptide-based 18F-radiotracers in a kit-like procedure matching the convenience of 99mTc radiopharmaceuticals.

MAIN BODY

A radiotracer's clinical success primarily hinges on whether its synthesis can be automated. Due to its simplicity, the SiFA chemistry, which is based on isotopic exchange (18F for 19F), does not only work in a manual setup but has been proven to be automatable, yielding large batches of 18F-radiotracers of high molar activity (Am). The production of SiFA radiotracer can be centralized and the radiopharmaceutical be distributed via the "satellite" principle, where one production facility economically serves multiple clinical application sites. Clinically validated tracers such as [18F]SiTATE and [18F]Ga-rhPSMA-7/-7.3 have been synthesized in an automated synthesis unit under good manufacturing practice conditions and used in large patient cohorts. Communication of common guidelines and practices is warranted to further the dissemination of SiFA radiopharmaceuticals and to give easy access to this technology.

CONCLUSION

This current review highlights the most recent achievements in SiFA radiopharmaceutical automation geared towards large batch production for clinical application. Best practice advice and guidance towards a facilitated implementation of the SiFA technology into new and already operating PET tracer production facilities is provided. A brief outlook spotlights the future potential of SiFA radiochemistry within the landscape of non-canonical labeling chemistries.

The Future of Radioactive Medicine

The discovery of X rays in the late 19th century heralded the beginning of a new age in medicine, and the advent of channeling the power of radiation to diagnose and treat human disease. Radiation has been leveraged in medicine in a multitude of ways and is a critical element of cancer care including screening, diagnosis, surveillance, and interventional treatments. Modern radiotherapy techniques include a multitude of methodologies utilizing both externally and internally delivered radiation from a variety of approaches. This review provides a comprehensive overview of contemporary radiotherapy methodologies, the field of radiopharmaceuticals and theranostics, effects of low dose radiation and highlights the phenomena of fear of exposure to radiation and its impact in modern medicine.

An Overview of In Vitro Assays of 64Cu-, 68Ga-, 125I-, and 99mTc-Labelled Radiopharmaceuticals Using Radiometric Counters in the Era of Radiotheranostics

Radionuclides are unstable isotopes that mainly emit alpha (α), beta (β) or gamma (γ) radiation through radiation decay. Therefore, they are used in the biomedical field to label biomolecules or drugs for diagnostic imaging applications, such as positron emission tomography (PET) and/or single-photon emission computed tomography (SPECT). A growing field of research is the development of new radiopharmaceuticals for use in cancer treatments. Preclinical studies are the gold standard for translational research. Specifically, in vitro radiopharmaceutical studies are based on the use of radiopharmaceuticals directly on cells. To date, radiometric β- and γ-counters are the only tools able to assess a preclinical in vitro assay with the aim of estimating uptake, retention, and release parameters, including time- and dose-dependent cytotoxicity and kinetic parameters. This review has been designed for researchers, such as biologists and biotechnologists, who would like to approach the radiobiology field and conduct in vitro assays for cellular radioactivity evaluations using radiometric counters. To demonstrate the importance of in vitro radiopharmaceutical assays using radiometric counters with a view to radiogenomics, many studies based on ⁶⁴Cu-, ⁶⁸Ga-, ¹²⁵I-, and ^99mTc-labeled radiopharmaceuticals have been revised and summarized in this manuscript.

PET Imaging of Lung Cancers in Precision Medicine: Current Landscape and Future Perspective

Despite the recent advances in cancer treatment, lung cancer remains the leading cause of cancer mortality worldwide. Immunotherapies using immune checkpoint inhibitors (ICIs) achieved substantial efficacy in nonsmall cell lung cancer (NSCLC). Currently, most ICIs are still a monoclonal antibody (mAb). Using mAbs or antibody derivatives labeled with radionuclide as the tracers, immunopositron emission tomography (immunoPET) possesses multiple advantages over traditional ¹⁸F-FDG PET in imaging lung cancers. ImmunoPET presents excellent potential in detecting, diagnosing, staging, risk stratification, treatment guidance, and recurrence monitoring of lung cancers. By using radiolabeled mAbs, immunoPET can visualize the biodistribution and uptake of ICIs, providing a noninvasive modality for patient stratification and response evaluation. Some novel targets and associated tracers for immunoPET have been discovered and investigated. This Review introduces the value of immunoPET in imaging lung cancers by summarizing both preclinical and clinical evidence. We also emphasize the value of immunoPET in optimizing immunotherapy in NSCLC. Lastly, immunoPET probes developed for imaging small cell lung cancer (SCLC) will also be discussed. Although the major focus is to summarize the immunoPET tracers for lung cancers, we also highlighted several small-molecule PET tracers to give readers a balanced view of the development status.

Radiolabeling, biological distribution, docking and ADME studies of 99mTc-Ros as a promising natural tumor tracer

Rosmarinic acid (Ros) is one of phenolic metabolites with powerful potency as an anticancer agent, with different mechanisms to diminish the cancer cells. This current study represents radiolabeling of Ros with 99mTc using SnCl2 in pH4 for 15 min at 60 °C, The yield up to 92.2%. Biological evaluation in normal and cancer mice revealed the localization of the tracer in tumor tissue. Furthermore, docking and ADME (Absorption, Distribution, Metabolism, and Excretion) studies were performed, The resulted data clarifies the use of Ros as a promissing natural tracer.

The role of chemistry in accelerator-based production and separation of radionuclides as basis for radiolabelled compounds for medical applications

Radiochemical separations used in large scale routine production of diagnostic and therapeutic radionuclides at a particle accelerator for patient care are briefly outlined. The role of chemistry at various stages of development of a production route of a novel radionuclide, namely nuclear data measurement, high-current targetry, chemical processing and quality control of the product, is discussed in detail. Special attention is paid to production of non-standard positron emitters (e.g. 44gSc, 64Cu, 68Ga, etc.) at a cyclotron and novel therapeutic radionuclides (e.g. 67Cu, 225Ac, etc.) at an accelerator. Some typical examples of radiochemical methods involved are presented.

Electrochemical deposition of nickel from aqueous electrolytic baths prepared by dissolution of metallic powder

A new method of preparation of aqueous electrolyte baths for electrochemical deposition of nickel targets for medical accelerators is presented. It starts with fast dissolution of metallic Ni powder in a HNO3-free solvent. Such obtained raw solution does not require additional treatment aimed to removal nitrates, such as the acid evaporation and Ni salt precipitation-dissolution. It is used directly for preparation of the nickel plating baths after dilution with water, setting up pH value and after possible addition of H3BO3. The pH of the baths ranges from alkaline to acidic. Deposition of 95% of ca. 50 mg of Ni dissolved in the bath takes ca. 3.5 h for the alkaline electrolyte while for the acidic solution it requires ca. 7 h. The Ni deposits obtained from the acidic bath are physically and chemically more stable and possess smoother and crack-free surfaces as compared to the coatings deposited from the alkaline bath. A method of estimation of concentration of H2O2 in the electrolytic bath is also proposed.

Evaluation of nuclear reaction cross section data of proton and deuteron induced reactions on 75As, with particular emphasis on the production of 73Se

75Se (T1/2 = 120 d), 73gSe (T1/2 = 7.1 h) and 72Se (T1/2 = 8.4 d) are important radioisotopes of selenium, being used in tracer studies, PET investigations and as a generator parent, respectively. Cross section data for the formation of those radionuclides in proton and deuteron induced reactions on 75As were critically analyzed up to about 70 MeV. A well-developed evaluation methodology was applied to generate the statistically fitted cross sections, based on the critically analyzed literature experimental data and the theoretical cross section values of three nuclear model codes ALICE-IPPE, TAYLS 1.9, and EMPIRE 3.2. Using the fitted cross sections the integral yield of each radionuclide was calculated. For the estimation of impurities, the integral yield of each radionuclide was compared with the yields of the other two radionuclides over a given energy region, and therefrom the energy range was suggested for the high purity production of each of the radionuclides 75Se, 73Se and 72Se. For production of the very important non-standard positron emitter 73Se via the 75As(p,3n)73Se reaction, the optimum energy range was deduced to be E p = 40 → 30 MeV, with a thick target yield of 1441 MBq/μAh and the 72,75Se impurity level of <0.1%.

Electrochemical deposition of nickel targets from aqueous electrolytes for medical radioisotope production in accelerators: a review

This paper reviews reported methods of the electrochemical deposition of nickel layers which are used as target materials for accelerator production of medical radioisotopes. The review focuses on the electrodeposition carried out from aqueous electrolytes. It describes the main challenges related to the preparation of suitable Ni target layers, such as work with limited amounts of expensive isotopically enriched nickel; electrodeposition of sufficiently thick, smooth and free of cracks layers; and recovery of unreacted Ni isotopes from the irradiated targets and from used electrolytic baths.

Efficient trace-scale extraction method of reactor produced 199Au adequate for nuclear medicine applications

Production of no carrier-added (NCA) 199Au through natPt(n, γ) reaction and subsequent purification using liquid-liquid extraction from other radioisotopes is studied in the context of theranostic application. Comparative separation of NCA 199Au after dissolution of activated Pt target using three Cyanex compounds (Cyanex-272, Cyanex-302 and Cyanex-923) is evaluated. The extraction process is optimized in terms of the type of extractant, the concentration of extractant, extraction time and aqueous media (HNO3, NH4OH). Among these extractants, the Cynaex-923 is efficient and promising for rapid separation and production of NCA 199Au from HNO3 by high extraction %. Selective extraction of 199Au from other Pt and Ir radioisotopes is observed. High recovery of 199Au was obtained in the case of Cyanex-923 using 0.05 M thiourea dissolved in HCl or 2 M NaOH. Our results find the Cyanex-923 as a promising extractant for efficient separation of 199Au from irradiated Pt target with high yield (99%).

Building up PtII -Thiosemicarbazone-Lysine-sC18 Conjugates

Three chiral tridentate N^N^S coordinating pyridine-carbaldehyde (S)-N4-(α-methylbenzyl)thiosemicarbazones (HTSCmB) were synthesised along with lysine-modified derivatives. One of them was selected and covalently conjugated to the cell-penetrating peptide sC18 by solid-phase peptide synthesis. The HTSCmB model ligands, the HTSCLp derivatives and the peptide conjugate rapidly and quantitatively form very stable PtII chlorido complexes [Pt(TSC)Cl] when treated with K2 PtCl4 in solution. The Pt(CN) derivatives were obtained from one TSCmB model complex and the peptide conjugate complex through Cl- →CN- exchange. Ligands and complexes were characterised by NMR, IR spectroscopy, HR-ESI-MS and single-crystal XRD. Intriguingly, no decrease in cell viability was observed when testing the biological activity of the lysine-tagged HdpyTSCLp, its sC18 conjugate HdpyTSCL-sC18 or the PtCl and Pt(CN) conjugate complexes in three different cell lines. Thus, given the facile and effective preparation of such Pt-TSC-peptide conjugates, these systems might pave the way for future use in late-stage labelling with Pt radionuclides and application in nuclear medicine.

Recent advances in the synthesis of (99mTechnetium) based radio-pharmaceuticals

Technetium radionuclide (99mTc) has excellent extent of disintegration properties and occupies a special place in the field of nuclear medicinal chemistry and other health disciplines. Current review describes recent approaches of synthesis in detailed ways for radio-pharmaceuticals of technetium which have been developed to treat and diagnose the biotic disorders. These technetium labeled radio-pharmaceuticals have been established to apply in the field of diagnostic nuclear medicine especially for imaging of different body parts such as brain, heart, kidney, bones and so on, through single photon emission computed tomography (SPECT) that is thought to be difficult to image such organs by using common X-ray and MRI (Magnetic Resonance Imaging) techniques. This review highlights and accounts an inclusive study on the various synthetic routes of technetium labeled radio-pharmaceuticals using ligands with various donor atoms such as carbon, nitrogen, sulphur, phosphorus etc. These compounds can be utilized as next generation radio-pharmaceuticals.

Advancements in the use of Auger electrons in science and medicine during the period 2015-2019

Auger electrons can be highly radiotoxic when they are used to irradiate specific molecular sites. This has spurred basic science investigations of their radiobiological effects and clinical investigations of their potential for therapy. Focused symposia on the biophysical aspects of Auger processes have been held quadrennially. This 9th International Symposium on Physical, Molecular, Cellular, and Medical Aspects of Auger Processes at Oxford University brought together scientists from many different fields to review past findings, discuss the latest studies, and plot the future work to be done. This review article examines the research in this field that was published during the years 2015-2019 which corresponds to the period since the last meeting in Japan. In addition, this article points to future work yet to be done. There have been a plethora of advancements in our understanding of Auger processes. These advancements range from basic atomic and molecular physics to new ways to implement Auger electron emitters in radiopharmaceutical therapy. The highly localized doses of radiation that are deposited within a 10 nm of the decay site make them precision tools for discovery across the physical, chemical, biological, and medical sciences.

Expanding PET-applications in life sciences with positron-emitters beyond fluorine-18

Positron-emission-tomography (PET) has become an indispensable diagnostic tool in modern nuclear medicine. Its outstanding molecular imaging features allow repetitive studies on one individual and with high sensitivity, though no interference. Rather few positron-emitters with near favourable physical properties, i.e. carbon-11 and fluorine-18, furnished most studies in the beginning, preferably if covalently bound as isotopic label of small molecules. With the advancement of PET-devices the scope of in vivo research in life sciences and especially that of medical applications expanded, and other than "standard" PET-nuclides received increasing significance, like the radiometals copper-64 and gallium-68. Especially during the last decades, positron-emitters of other chemical elements have gotten into the focus of interest, concomitant with the technical advancements in imaging and radionuclide production. With known nuclear imaging properties and main production methods of emerging positron-emitters their usefulness for medical application is promising and even proven for several ones already. Unfortunate decay properties could be corrected for, and β⁺-emitters, especially with a longer half-life, provided new possibilities for application where slower processes are of importance. Further on, (bio)chemical features of positron-emitters of other elements, among there many metals, not only expanded the field of classical clinical investigations, but also opened up new fields of application. Appropriately labelled peptides, proteins and nanoparticles lend itself as newer probes for PET-imaging, e.g. in theragnostic or PET/MR hybrid imaging. Furthermore, the potential of non-destructive in-vivo imaging with positron-emission-tomography directs the view on further areas of life sciences. Thus, exploiting the excellent methodology for basic research on molecular biochemical functions and processes is increasingly encouraged as well in areas outside of health, such as plant and environmental sciences.

ImmunoPET: Concept, Design, and Applications

Immuno-positron emission tomography (immunoPET) is a paradigm-shifting molecular imaging modality combining the superior targeting specificity of monoclonal antibody (mAb) and the inherent sensitivity of PET technique. A variety of radionuclides and mAbs have been exploited to develop immunoPET probes, which has been driven by the development and optimization of radiochemistry and conjugation strategies. In addition, tumor-targeting vectors with a short circulation time (e.g., Nanobody) or with an enhanced binding affinity (e.g., bispecific antibody) are being used to design novel immunoPET probes. Accordingly, several immunoPET probes, such as ⁸⁹Zr-Df-pertuzumab and ⁸⁹Zr-atezolizumab, have been successfully translated for clinical use. By noninvasively and dynamically revealing the expression of heterogeneous tumor antigens, immunoPET imaging is gradually changing the theranostic landscape of several types of malignancies. ImmunoPET is the method of choice for imaging specific tumor markers, immune cells, immune checkpoints, and inflammatory processes. Furthermore, the integration of immunoPET imaging in antibody drug development is of substantial significance because it provides pivotal information regarding antibody targeting abilities and distribution profiles. Herein, we present the latest immunoPET imaging strategies and their preclinical and clinical applications. We also emphasize current conjugation strategies that can be leveraged to develop next-generation immunoPET probes. Lastly, we discuss practical considerations to tune the development and translation of immunoPET imaging strategies.

Production of 67Cu by enriched 70Zn targets: first measurements of formation cross sections of 67Cu, 64Cu, 67Ga, 66Ga, 69mZn and 65Zn in interactions of 70Zn with protons above 45 MeV

Despite its insufficient availability, Copper-67 is currently attracting much attention for its enormous potential for cancer therapy as theranostic radionuclide. This work aims to accurately measure the unexplored cross section 70Zn(p,x)67Cu in the energy range 45–70 MeV and to evaluate its potential advantages in the case of high-intensity proton beams provided by compact cyclotrons. Thin target foils of enriched 70Zn were manufactured by lamination at the INFN-LNL and irradiated at the ARRONAX facility using the stacked-foils method. A radiochemical procedure for the separation of Cu, Ga and Zn contaminants and the isolation of 67Cu from the irradiated material was developed. The efficiency of the chemical processing was determined for each foil by monitoring the activity of selected tracer radionuclides (61Cu, 66Ga and 69mZn) through γ-spectrometry. Experimental data of the 70Zn(p,x)67Cu, 64Cu, 67Ga, 66Ga, 69mZn, 65Zn cross sections were measured for the first time in the energy range 45–70 MeV and compared with the theoretical results obtained by using the TALYS code. The 67Cu production yield by using enriched 70Zn thick targets was compared with the results obtained by using 68Zn targets in the same irradiation conditions.

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.

Positron-emitting radionuclides for applications, with special emphasis on their production methodologies for medical use

A survey of the positron-emitting radionuclides over the whole mass range of the Periodic Table of Elements was carried out. As already known, positrons are preferably emitted from light mass neutron deficient radionuclides. Their emission from heavier mass nuclides is rather rare. The applications of positron annihilation in three areas, namely materials research, plant physiology and medical diagnosis, are reported. The methods of production of positron emitters are discussed, with emphasis on radionuclides presently attracting more attention in theranostics and multimodal imaging. Some future perspectives of radionuclide development technologies are considered.

Radiobromine and radioiodine for medical applications

The halogens bromine and iodine have similar chemical properties and undergo similar reactions due to their closeness in Group 17 of the periodic chart. There are a number of bromine and iodine radionuclides that have properties useful for diagnosis and therapy of human diseases. The emission properties of radiobromine and radioiodine nuclides with half-lives longer than 1 h are summarized along with properties that make radionuclides useful in PET/SPECT imaging and β/Auger therapy, such that the reader can assess which of the radionuclides might be useful for medical applications. An overview of chemical approaches that have been used to radiolabel molecules with radiobromine and radioiodine nuclides is provided with examples. Further, references to a large variety of different organ/cancer-targeting agents utilizing the radiolabeling approaches described are provided.

A Picture of Modern Tc-99m Radiopharmaceuticals: Production, Chemistry, and Applications in Molecular Imaging

Even today, techentium-99m represents the radionuclide of choice for diagnostic radio-imaging applications. Its peculiar physical and chemical properties make it particularly suitable for medical imaging. By the use of molecular probes and perfusion radiotracers, it provides rapid and non-invasive evaluation of the function, physiology, and/or pathology of organs. The versatile chemistry of technetium-99m, due to its multi-oxidation states, and, consequently, the ability to produce a variety of complexes with particular desired characteristics, are the major advantages of this medical radionuclide. The advances in technetium coordination chemistry over the last 20 years, in combination with recent advances in detector technologies and reconstruction algorithms, make SPECT’s spatial resolution comparable to that of PET, allowing 99mTc radiopharmaceuticals to have an important role in nuclear medicine and to be particularly suitable for molecular imaging. In this review the most efficient chemical methods, based on the modern concept of the 99mTc-metal fragment approach, applied to the development of technetium-99m radiopharmaceuticals for molecular imaging, are described. A specific paragraph is dedicated to the development of new 99mTc-based radiopharmaceuticals for prostate cancer.

Radionuclide-Labeled Peptides for Imaging and Treatment of CXCR4- Overexpressing Malignant Tumors

Malignant tumors are a major cause of death. The lack of methods that provide an early diagnosis and adequate treatment of cancers is the main obstacle to precision medicine. The C-X-C chemokine receptor 4 (CXCR4) is overexpressed in various tumors and plays a key role in tumor pathogenesis. Therefore, CXCR4-targeted molecular imaging can quickly and accurately detect and quantify CXCR4 abnormalities in real time. The expression level and activation status of CXCR4 are very important for screening susceptible populations and providing an accurate diagnosis and optimal treatment. In view of the fact that radionuclide-labeled peptides have become widely used for the diagnosis and treatment of tumors, this manuscript reviews the potential of different radionuclide-labeled peptide inhibitors for the targeted imaging of CXCR4- positive tumors and targeted treatment. The article also discusses the specificity and in vivo distribution of radionuclide-labeled peptide inhibitors, and translation of these inhibitors to the clinic.

Therapeutic Radiometals: Worldwide Scientific Literature Trend Analysis (2008⁻2018)

Academic journals have published a large number of papers in the therapeutic nuclear medicine (NM) research field in the last 10 years. Despite this, a literature analysis has never before been made to point out the research interest in therapeutic radionuclides (RNs). For this reason, the present study aims specifically to analyze the research output on therapeutic radiometals from 2008 to 2018, with intent to quantify and identify global trends in scientific literature and emphasize the interdisciplinary nature of this research field. The data search targeted conventional (¹³¹I, ⁹⁰Y, ¹⁷⁷Lu, ¹⁸⁸Re, ¹⁸⁶Re, ¹⁵³Sm, ⁸⁹Sr, ¹⁸⁶Er) and emergent (⁶⁷Cu, ⁴⁷Sc, ²²³Ra, ¹⁶⁶Ho, ¹⁶¹Tb, ¹⁴⁹Tb, ²¹²Pb/²¹²Bi, ²²⁵Ac, ²¹³Bi, ²¹¹At, ^117mSn) RNs. Starting from this time frame, authors have analyzed and interpreted this scientific trend quantitatively first, and qualitatively after.