Prospective of ⁶⁸Ga-radiopharmaceutical development

Harnessing Terbium Radioisotopes for Clinical Advancements: A Systematic Review

Background this systematic review was conducted to assess the practical application of terbium radioisotopes, utilizing systematic search methodologies to identify relevant studies. Methods the databases of PubMed, Web of Science, and Scopus were systematically scoured, targeting the research on four terbium isotopes: 149 Tb, 152 Tb, 155 Tb, and 161 Tb. Various combinations of keywords related to terbium and its four radioisotopes were used in the search process. The search encompassed studies conducted up to July 27, 2024. Results following the removal of 335 duplicate research articles, a cohort of 429 papers was curated for potential inclusion in the study. Out of 429 articles reviewed, a mere nine addressed the potential uses of 161 Tb and 152 Tb. Notably, 155 Tb and 149 Tb have yet to be examined in human subjects. Conclusions the research trajectory is now veering towards clinical studies that provide in-human data, with the goal of advancing radiotheranostics and nuclear oncology. The preliminary outcomes are stimulating and have led to the initiation of several clinical trials. The success of these trials and the establishment of production facilities will be critical for the clinical adoption of these agents.

PSMA-Targeted Intracellular Self-Assembled Probe for Enhanced PET Imaging

Positron-emission tomography (PET) offers high sensitivity for cancer diagnosis. However, small-molecule-based probes often exhibit insufficient accumulation in tumor sites, while nanoparticle-based agents typically have limited delivery efficiency. To address this challenge, this study proposes a novel PET imaging probe, 68Ga-CBT-PSMA, designed for prostate cancer. This probe integrates an intracellular self-assembly strategy to enhance PET imaging signals and significantly improve the signal-to-noise ratio. The glutamate-urea-based prostate-specific membrane antigen (PSMA)-targeting motif enables specific recognition of prostate cancer cells and enhances cellular uptake; then the self-assembly process induced by glutathione reduction effectively accumulates the probe within tumor cells, thereby amplifying PET imaging signals. This approach not only enhances signal intensity and resolution but also facilitates precise cancer localization and diagnosis, offering new avenues for advancing cancer diagnostic techniques.

Synthesis and bioevaluation of a new 68Ga-labelled niraparib derivative that targets PARP-1 for tumour imaging

Poly ADP-ribose polymerase (PARP) inhibitors prevent the repair of DNA single-strand breaks in cancer cells with abnormal homologous recombination, producing a synthetic lethal effect. Thus, PARP inhibitors have become clinically effective anticancer drugs. Labelling with radionuclides may extend the use of PARP inhibitors as tracers in nuclear medicine diagnostics, helping to stratify patients. In the present study, niraparib was selected as a skeleton molecule modified with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and labelled with gallium-68 to obtain [68Ga]Ga-DOTANPB with high radiochemical purity (>95 %). To verify the accuracy of the [68Ga]Ga-DOTANPB structure, [natGa]Ga-DOTANPB was also synthesized, and in vitro affinity experiments were performed, which revealed a high affinity for PARP-1 (IC50 = 82.21 nM). [68Ga]Ga-DOTANPB is hydrophilic and has good in vitro stability within 3 h. In in vitro experiments, [68Ga]Ga-DOTANPB has a high uptake in HeLa cells and can enter the cell to target PARP-1. In coronal PET imaging of HeLa tumour-bearing mice, [68Ga]Ga-DOTANPB showed significant radioconcentration at the tumour site at 0.5 h, 1 h, and 2 h. Biodistribution and autoradiography experiments revealed that [68Ga]Ga-DOTANPB has obvious tumour uptake and can be significantly inhibited (3.37 ± 0.33 % ID/g vs. 2.50 ± 0.27 % ID/g, **P < 0.01), suggesting that it has PARP-1 specificity. Thus, these findings suggested that [68Ga]Ga-DOTANPB may be a potential niraparib-based PET tracer for targeting PARP-1.

Trop2-Targeted Molecular Imaging in Solid Tumors: Current Advances and Future Outlook

Trophoblast cell surface antigen 2 (Trop2), a transmembrane glycoprotein, plays a dual role in physiological and pathological processes. In healthy tissues, Trop2 facilitates development and orchestrates intracellular calcium signaling. However, its overexpression in numerous solid tumors shifts its function toward driving cell proliferation and metastasis, thus leading to a poor prognosis. The clinical relevance of Trop2 is underscored by its utility as both a biomarker for diagnostic imaging and a target for therapy. Notably, the U.S. Food and Drug Administration (FDA) has approved sacituzumab govitecan (SG), a novel Trop2-targeted agent, for treating triple-negative breast cancer (TNBC) and refractory urothelial cancer, highlighting the significance of Trop2 in clinical oncology. Molecular imaging, a powerful tool for visualizing and quantifying biological phenomena at the molecular and cellular levels, has emerged as a critical technique for studying Trop2. This approach encompasses various modalities, including optical imaging, positron emission tomography (PET), single photon emission computed tomography (SPECT), and targeted antibodies labeled with radioactive isotopes. Incorporating Trop2-targeted molecular imaging into clinical practice is vital for the early detection, prognostic assessment, and treatment planning of a broad spectrum of solid tumors. Our review captures the latest progress in Trop2-targeted molecular imaging, focusing on both diagnostic and therapeutic applications across diverse tumor types, including lung, breast, gastric, pancreatic, prostate, and cervical cancers, as well as salivary gland carcinomas. We critically evaluate the current state by examining the relevant applications, diagnostic accuracy, therapeutic efficacy, and inherent limitations. Finally, we analyze the challenges impeding widespread clinical application and offer insights into strategies for advancing the field, thereby guiding future research endeavors.

Evaluation of chelating agents based on pyridine-azacrown compounds H4PATA, PATAM, and H4PATPA for 68Ga and 177Lu

In this article, we present the synthesis and characterization of three macrocyclic chelators, H4PATA, PATAM, and H4PATPA, based on a pyridine-azacrown compound. Their complexation with 68Ga and 177Lu has been thoroughly investigated using MALDI TOF MS, 1H NMR spectroscopy, radiolabeling studies, and experiments in vitro with fetal bovine serum and a 1000-fold molar excess of H4EDTA. Our studies have shown that the chelators H4PATA and H4PATPA form complexes at room temperature with both radionuclides (RCY > 80 % and > 90 % for complexes with H4PATA and H4PATPA after 30 min, respectively). The chelator PATAM requires high temperature (95 °C) for complexation. In vitro stability assays in fetal bovine serum as well as H4EDTA-challenge revealed that transchelation occurs for all complexes with 68Ga. However, complexes of the ligands H4PATA and PATAM with 177Lu were found stable. Thus, taking into account the radiolabeling at room temperature and in vitro stability of the complex [177Lu]Lu·PATA, our investigations revealed the chelator H4PATA is a candidate for radiopharmaceutical use with 177Lu.

Validation of Radiosynthesis and First in-Human Dosimetry of 68Ga-NOTA-UBI-29-41: A Proof of Concept Study

Background: Antimicrobial peptides (AMPs) such as UBI-29-41 offer a distinctive approach for precise detection due to their unique interactions with bacteria and makes them promising candidates for specific and selective imaging. The study was aimed to corroborate the in-house manual synthesis of 68Ga-NOTA-UBI-29-41, evaluate its uptake in patients with suspected infection, and estimate of patient-specific dosimetry to ensure optimal clinical application. Materials and Methods: 68Ga-NOTA-UBI-29-41 was synthesized by using a variable amount of UBI-29-41 (60-90 μg) to 555 MBq of Ga-68 in 0.05 M Hydrochloric acid (HCl) and heating the reaction sample for 12 min at 90°C at pH: 3.5-4 to obtain the radiopeptide with high yield and high radiochemical purity (RCP). 68Ga-NOTA-UBI-29-41 positron emission tomography/Computed tomography (CT) scans at variable timepoints were done to evaluate its biodistribution and maximum uptake time. Furthermore, patient-specific dosimetric estimation was done using the HERMES software. Results: A total of 5 μg/37 MBq (5 μg/mCi) of NOTA-UBI-29-41 for 12 min at 90°C were the optimal parameters to obtain 88%-90% of yield and 98%-99 % of RCP. 68Ga-NOTA-UBI-29-41 showed expeditious blood clearance and high renal excretion. The optimal time for imaging of infection with 68Ga-NOTA-UBI-29-41 was found to be at 60 min postinjection (n = 8). The critical organ was the urinary bladder, receiving an average dose of 138.02 ± 45.92 µSv/MBq, followed by 53.81 ± 13.72 µSv/MBq for kidneys with a mean effective dose of 1.52 ± 0.64 mSv. Conclusion: The protocol for in-house manual labeling of 68Ga-NOTA-UBI-29-41 was reproducible, providing high yield and RCP. 68Ga-NOTA-UBI-29-41 administration was found to be safe and nontoxic. The favorable biodistribution and the first-in-human patient-specific dosimetry ensure optimal clinical application.

Antimicrobial peptide LyeTx I mn∆K labeled with 68Ga is a potential PET radiopharmaceutical for molecular imaging of infections

BACKGROUND

Antimicrobial peptides have been radiolabeled and investigated as molecular diagnostic probes due to their propensity to accumulate in infectious sites rather than aseptic inflammatory lesions. LyeTx I is a cationic peptide from the venom of Lycosa erythrognatha, exhibiting significant antimicrobial activity. LyeTx I mn∆K is a shortened derivative of LyeTx I, with an optimized balance between antimicrobial and hemolytic activities. This study reports the first 68Ga-radiolabeling of the DOTA-modified LyeTx I mn∆K and primarily preclinical evaluations of [68Ga]Ga-DOTA(K)-LyeTx I mn∆K as a PET radiopharmaceutical for infection imaging.

METHODS

DOTA(K)-LyeTx I mn∆K was radiolabeled with freshly eluted 68Ga. Radiochemical yield (RCY), radiochemical purity (RCP), and radiochemical stability (in saline and serum) were evaluated using ascending thin-layer chromatography (TLC) and reversed-phase high-performance liquid chromatography (RP-HPLC). The radiopeptide's lipophilicity was assessed by determining the logarithm of the partition coefficient (Log P). Serum protein binding (SBP) and binding to Staphylococcus aureus (S. aureus) cells were determined in vitro. Ex vivo biodistribution studies and PET/CT imaging were conducted in healthy mice (control) and mice with infection and aseptic inflammation to evaluate the potential of [68Ga]Ga-DOTA(K)-LyeTx I mn∆K as a specific PET radiopharmaceutical for infections.

RESULTS

[68Ga]Ga-DOTA(K)-LyeTx I mn∆K was obtained with a high RCY (>90 %), and after purification through a Sep-Pak C18 cartridge, the RCP exceeded 99 %. Ascending TLC and RP-HPLC showed that the radiopeptide remained stable for up to 3.0 h in saline solution and up to 1.5 h in murine serum. [68Ga]Ga-DOTA(K)-LyeTx I mn∆K exhibited hydrophilic characteristics (Log P = -2.4 ± 0.1) and low SPB (ranging from 23.3 ± 0.4 % at 5 min of incubation to 10.5 ± 1.1 % at 60 min of incubation). The binding of [68Ga]Ga-DOTA(K)-LyeTx I mn∆K to S. aureus cells was proportional to bacterial concentration, with binding percentages of 8.8 ± 0.5 % (0.5 × 109 CFU.mL-1), 16.2 ± 1.4 % (1.0 × 109 CFU.mL-1), and 62.2 ± 0.6 % (5.0 × 109 CFU.mL-1). Ex vivo biodistribution studies and PET/CT images showed higher radiopeptide uptake at the infection site compared to the aseptic inflammation site; the latter was similar to the control group. Target-to-non-target (T/NT) ratios obtained by ex vivo biodistribution data were approximately 1.0, 1.3, and 3.0 at all investigated time intervals for the control, aseptic inflammation, and infection groups, respectively. Furthermore, T/NT ratios obtained from PET/CT images were 1.1 ± 0.1 for the control group and 1.4 ± 0.1 for the aseptic inflammation group. For the infection group, T/NT ratio was 5.0 ± 0.3, approximately 5 times greater compared to the former groups.

CONCLUSIONS

The results suggest the potential of [68Ga]Ga-DOTA(K)-LyeTx I mn∆K as a PET radiopharmaceutical for molecular imaging of infections.

Expanding Role for Gallium-68 PET Imaging in Oncology

Gallium-68 has gained substantial momentum since 2003 as a versatile radiometal that is extremely useful for application in the development of novel oncology targeting diagnostic radiopharmaceuticals. It is available through both generator produced radioactivity and via cyclotron production methods and can therefore be implemented in either small- or large-scale production facilities. It can also be implemented within different spectrum of infrastructure settings with relative ease. Whilst many of the radiopharmaceuticals are being development and investigated, which is summarized in this manuscript, [68Ga]Ga-SSTR2 and [68Ga]Ga-PSMA has prominence in current clinical guidelines. The novel tracer [68Ga]Ga-FAPi has also gained significant interest in the clinical context. A comparison of the labelling strategies followed to incorporate gallium-68 and fluorine-18 into the same molecular targeting constructs clearly demonstrate that gallium-68 complexation is the most convenient approach. Recently, cold kit based starting products are available to make the small-scale production of gallium-68 radiopharmaceuticals even more efficient when combined with generator produced gallium-68. The regulatory aspects is currently changing to support the implementation of gallium-68 and other diagnostic radiopharmaceuticals, simplifying the translation towards clinical use. Overall, the development of gallium-68 based radiopharmaceuticals is not only rapidly changing the landscape of diagnosis in oncology, but this growth also promotes innovation and progress in new applications of therapeutic radiometals such as lutetium-177 and actinium-225.

Rapid Concentration of Ga-68 and Proof-of-Concept Microscale Labeling of [68Ga]Ga-PSMA-11 in a Droplet Reactor

The radiometal gallium-68 (Ga-68) has garnered significant interest due to its convenient production via compact and widely available generators and the high performance of 68Ga-labeled compounds for positron-emission tomography (PET) imaging for cancer diagnosis and management of patients undergoing targeted radionuclide therapy. Given the short half life of Ga-68 (68 min), microfluidic-based radiosynthesis is a promising avenue to establish very rapid, efficient, and routine radiolabeling with Ga-68; however, the typical elution volume of Ga-68 from a generator (4-10 mL) is incompatible with the microliter reaction volumes of microfluidic devices. To bridge this gap, we developed a microscale cartridge-based approach to concentrate Ga-68. By optimizing cartridge design, resin type, resin mass, and eluent composition, Ga-68 was reliably concentrated from ~6 mL to ~80 µL with high recovery efficiency (>97%, n = 14). Furthermore, this method is suitable for both single- and dual-generator setups. To demonstrate suitability of the concentrated radiometal for radiolabeling, we performed microdroplet synthesis of [68Ga]Ga-PSMA-11, achieving high radiochemical yield (83 ± 11%, n = 3), excellent radiochemical purity (>99%), and high apparent specific activity (255-320 MBq/μg). The entire process, including Ga-68 concentration, radiosynthesis, purification, and formulation, was completed in 12 min. Starting with activity of 0.81-0.84 GBq, 0.51-0.64 GBq of product was produced, sufficient for multiple patient doses. This work paves the way to clinical-scale production of other 68Ga-labeled compounds using droplet microreactor methods, or high-throughput labeling optimization or compound screening of 68Ga-labeled probes using droplet reaction arrays.

Physicochemical characterization and potential cancer therapy applications of hydrogel beads loaded with doxorubicin and GaOOH nanoparticles

A new type of hybrid polymer particles capable of carrying the cytostatic drug doxorubicin and labeled with a gallium compound was prepared. These microparticles consist of a core and a hydrogel shell, which serves as the structural matrix. The shell can be employed to immobilize gallium oxide hydroxide (GaOOH) nanoparticles and the drug, resulting in hybrid beads with sizes of approximately 3.81 ± 0.09 μm. The microparticles exhibit the ability to incorporate a remarkably large amount of doxorubicin, approximately 0.96 mg per 1 mg of the polymeric carrier. Additionally, GaOOH nanoparticles can be deposited within the hydrogel layer at an amount of 0.64 mg per 1 mg of the carrier. These nanoparticles, resembling rice grains with an average size of 593 nm by 155 nm, are located on the surface of the polymer carrier. In vitro studies on breast and colon cancer cell lines revealed a pronounced cytotoxic effect of the hybrid polymer particles loaded with doxorubicin, indicating their potential for cancer therapies. Furthermore, investigations on doping the hybrid particles with the Ga-68 radioisotope demonstrated their potential application in positron emission tomography (PET) imaging. The proposed structures present a promising theranostic platform, where particles could be employed in anticancer therapies while monitoring their accumulation in the body using PET.

Nanoscale Radiotheranostics for Cancer Treatment: From Bench to Bedside

In recent years, the application of radionuclides-containing nanomaterials in cancer treatment has garnered widespread attention. The diversity of nanomaterials allows researchers to selectively combine them with appropriate radionuclides for biomedical purposes, addressing challenges faced by peptides, small molecules, or antibodies used for radionuclide labeling. However, with advantages come challenges, and nanoradionuclides still encounter significant issues during clinical translation. This review summarized the recent progress of nanosized radionuclides for cancer treatment or diagnosis. The discussion began with representative radionuclides and the methods of incorporating them into nanomaterial structures. Subsequently, new combinations of nanomaterials and radionuclides, along with their applications, were introduced to demonstrate their future trends. The benefits of nanoradionuclides included optimized pharmacokinetic properties, enhanced disease-targeting efficacy, and synergistic application with other treatment techniques. Besides, the basic rule of this section was to summarize how these nanoradionuclides can truly impact the diagnosis and therapy of various cancer types. In the last part, the focus was devoted to the nanoradionuclides currently applicable in clinics and how to address the existing issues and problems based on our knowledge.

Evaluation of [68Ga]Ga-DOTA-AeK as a Potential Imaging Tool for PET Imaging of Cell Wall Synthesis in Bacterial Infections

The ability of bacteria to recycle exogenous amino acid-based peptides and amino sugars for peptidoglycan biosynthesis was extensively investigated using optical imaging. In particular, fluorescent AeK-NBD was effectively utilized to study the peptidoglycan recycling pathway in Gram-negative bacteria. Based on these promising results, we were inspired to develop the radioactive AeK conjugate [68Ga]Ga-DOTA-AeK for the in vivo localization of bacterial infection using PET/CT. An easy-to-implement radiolabeling procedure for DOTA-AeK with [68Ga]GaCI3 followed by solid-phase purification was successfully established to obtain [68Ga]Ga-DOTA-AeK with a radiochemical purity of ≥95%. [68Ga]Ga-DOTA-AeK showed good stability over time with less protein binding under physiological conditions. The bacterial incorporation of [68Ga]Ga-DOTA-AeK and its fluorescent Aek-NBD analog were investigated in live and heat-killed Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Unfortunately, no conclusive in vitro intracellular uptake of [68Ga]Ga-DOTA-AeK was observed for E. coli or S. aureus live and heat-killed bacterial strains (p > 0.05). In contrast, AeK-NBD showed significantly higher intracellular incorporation in live bacteria compared to the heat-killed control (p < 0.05). Preliminary biodistribution studies of [68Ga]Ga-DOTA-AeK in a dual-model of chronic infection and inflammation revealed limited localization at the infection site with non-specific accumulation in response to inflammatory markers. Finally, our study demonstrates proof that the intracellular incorporation of AeK is necessary for successful bacteria-specific imaging using PET/CT. Therefore, Ga-68 was not a suitable radioisotope for tracing the bacterial uptake of AeK tripeptide, as it required chelation with a bulky metal chelator such as DOTA, which may have limited its active membrane transportation. An alternative for optimization is to explore diverse chemical structures of AeK that would allow for radiolabeling with 18F or 11C.

Beyond transition block metals: exploring the reactivity of phosphine PTA and its oxide [PTA(O)] towards gallium(iii)

The water-soluble cage-like phosphine PTA (1,3,5-triaza-7-phosphaadamantane) and its phosphine oxide derivative [PTA(O)] (1,3,5-triaza-7-phosphaadamantane-7-oxide) were used to explore their reactivity towards two gallium(iii)-halide precursors, namely GaCl3 and GaI3, for the first time. By using various reaction conditions, a series of N-mono-protonated phosphine salts with [GaCl4]- or [I]- as counterions were obtained in all cases, while the formation of coordinated Ga-PTA and Ga-[PTA(O)] complexes was not observed. All compounds were characterized in solution using multinuclear NMR spectroscopy (1H, 13C{1H}, 31P{1H} and 71Ga) and in the solid state using FT-IR spectroscopy and X-ray crystal diffraction. The new Ga-phosphine salts resulted stable and highly soluble in aqueous solution at room temperature. Density functional theory (DFT) calculations were also performed to further rationalize the coordination features of PTA with Ga3+ metal ion, highlighting that the phosphorus-gallium bond is about twice weaker than the phosphorus-metal bond commonly established by PTA with transition metals such as gold. Furthermore, the mono-protonation of PTA (or [PTA(O)]) makes the formation of ionic gallium-PTA coordination complexes thermodynamically unstable, as confirmed experimentally by the formation of Ga-phosphine salts reported herein.

Fluorine-18 labeling PEGylated 6-boronotryptophan for PET scanning of mice for assessing the pharmacokinetics for boron neutron capture therapy of brain tumors

Two tryptophan compound classes 5- and 6-borono PEGylated boronotryptophan derivatives have been prepared for assessing their aqueous solubility as formulation of injections for boron neutron capture therapy (BNCT). The PEGylation has improved their aqueous solubility thereby increasing their test concentration in 1 mM without suffering from toxicity. In-vitro uptake assay of PEGylated 5- and 6-boronotryptophan showed that the B-10 concentration can reach 15-50 ppm in U87 cell whereas the uptake in LN229 cell varies. Shorter PEG compound 6-boronotryptophanPEG200[18F] was obtained in 1.7 % radiochemical yield and the PET-derived radioradioactivity percentage in 18 % was taken up by U87 tumor at the limb of xenograft mouse. As high as tumor to normal uptake ratio in 170 (T/N) was obtained while an inferior radioactivity uptake of 3 % and T/N of 8 was observed in LN229 xenografted mouse.

n Vivo

Noninvasive imaging of amyloid-β (Aβ) species in vivo is important for the early diagnosis of Alzheimer's disease (AD). In this paper, we report a near-infrared (NIR) fluorescence (FL) and positron emission tomography (PET) bimodal probe (NIR-[68Ga]) for in vivo imaging of both soluble and insoluble Aβ species. NIR-[68Ga] holds a high binding affinity, high selectivity and high sensitivity toward Aβ42 monomers, oligomers, and aggregates in vitro. In vivo imaging results show that NIR-[68Ga] can cross the blood-brain-barrier (BBB), and produce significantly higher PET and NIR FL bimodal signals in the brains of APP/PS1 transgenic AD mice relative to that of age-matched wild-type mice, which are also validated by the ex vivo autoradiography and histological staining images. Our results demonstrate that NIR-[68Ga] is an efficient NIR FL and PET bimodal probe for the sensitive imaging of soluble and insoluble Aβ species in AD mice.

Synthesis of new acyclic chelators H4aPyta and H6aPyha and their complexes with Cu2+, Ga3+, Y3+, and Bi3

In this article, we present the synthesis and characterization of new acyclic pyridine-containing polyaminocarboxylate ligands H4aPyta and H6aPyha, which differ in structural rigidity and the number of chelating groups. Their abilities to form complexes with Cu2+, Ga3+, Y3+, and Bi3+ cations, as well as the stability of the complexes, were evaluated by potentiometric titration method, radiolabeling with the corresponding radionuclides, in vitro studies, mass spectrometry, and HPLC. The structures of the resulting complexes were determined using NMR spectroscopy and DFT calculations. The results obtained made it possible to evaluate the influence of the structural features of the complexes on their stability. The developed chelators H4aPyta and H6aPyha were proved to be promising for further research in the field of radiopharmaceuticals.

Production of the PET radionuclide 61Cu via the 62Ni(p,2n)61Cu nuclear reaction

BACKGROUND

There are only a handful of true theranostic matched pairs, and in particular the theranostic radiocopper trio 61Cu, 64Cu and 67Cu, for diagnosis and therapy respectively, is a very attractive candidate. In fact, the alternative of two imaging radionuclides with different half-lives is a clear advantage over other theranostic pairs, since it offers a better matching for the tracer biological and radionuclide physical half-lives. Due to the high availability of 64Cu, its translation into the clinic is being successfully carried out, giving the example of the FDA approved radiopharmaceutical Detectnet (copper Cu 64 dotatate injection). However, a shorter-lived PET radionuclide such as 61Cu may as well be beneficial.

RESULTS

Proton irradiation of enriched 62Ni electrodeposited targets with a compact cyclotron produced the desired radionuclide via the 62Ni(p,2n)61Cu nuclear reaction, leading to 61Cu activities of up to 20 GBq at end of bombardment and 8 GBq at end of purification. Furthermore, two purification methods are compared leading to comparable results regarding separation yield and product purity. Following the radiochemical separation, quality assessment of this product [61Cu]CuCl2 solution proved radionuclidic purities (RNP) over 99.6% and apparent molar activities (AMA) of 260 GBq/µmol with the 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA) chelator, end of purification corrected.

CONCLUSIONS

In the current article a comprehensive novel production method for the PET radionuclide 61Cu is presented, providing an alternative to the most popular production routes. Characterization of the [61Cu]CuCl2 product showed both high RNP as well as high AMA, proving that the produced activity presented high quality regarding radiolabeling up to 9 h after end of purification. Furthermore, production scalability could be easily achieved by increasing the irradiation time.

Bisphosphonates as Radiopharmaceuticals: Spotlight on the Development and Clinical Use of DOTAZOL in Diagnostics and Palliative Radionuclide Therapy

Bisphosphonates are therapeutic agents that have been used for almost five decades in the treatment of various bone diseases, such as osteoporosis, Paget disease and prevention of osseous complications in cancer patients. In nuclear medicine, simple bisphosphonates such as 99mTc-radiolabelled oxidronate and medronate remain first-line bone scintigraphic imaging agents for both oncology and non-oncology indications. In line with the growing interest in theranostic molecules, bifunctional bisphosphonates bearing a chelating moiety capable of complexing a variety of radiometals were designed. Among them, DOTA-conjugated zoledronate (DOTAZOL) emerged as an ideal derivative for both PET imaging (when radiolabeled with 68Ga) and management of bone metastases from various types of cancer (when radiolabeled with 177Lu). In this context, this report provides an overview of the main medicinal chemistry aspects concerning bisphosphonates, discussing their roles in molecular oncology imaging and targeted radionuclide therapy with a particular focus on bifunctional bisphosphonates. Particular attention is also paid to the development of DOTAZOL, with emphasis on the radiochemistry and quality control aspects of its preparation, before outlining the preclinical and clinical data obtained so far with this radiopharmaceutical candidate.

Impact of GAMP 5, data integrity and QbD on quality assurance in the pharmaceutical industry: How obvious is it?

In the pharmaceutical industry, it is essential to ensure the safety and efficacy of medicinal products. Therefore a robust quality assurance framework is needed. This manuscript examines the impact of GAMP 5 and data integrity (DI) on quality assurance, while also highlighting the role of quality by design (QbD) principles. GAMP 5 is a widely used framework for validating automated systems that establishes quality assurance practices. DI guarantees the reliability of data collected throughout various stages of drug development. The integration of QbD principles promotes a systematic approach to development that emphasizes a deep understanding of critical quality attributes, risk management, and continuous improvement. With their implementation, organizations are able to meet regulatory requirements and provide safe medications to patients worldwide.

Economic Evaluations of Imaging Biomarker-Driven Companion Diagnostics for Cancer: A Systematic Review

INTRODUCTION

There is a boom in imaging biomarker-driven companion and complementary diagnostics (CDx) for cancer, which brings opportunity for personalized medicine. Whether adoption of these technologies is likely to be cost-effective is a relevant question, and studies on this topic are emerging. Despite the growing number of economic evaluations, no review of the methods used, quality of reporting, and potential risk of bias has been done. We report a systematic review to identify, summarize, and critique the cost-effectiveness evidence for the use of biomarker-driven and imaging-based CDx to inform cancer treatments.

METHODS

The Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed. Systematic literature searches until 30 December 2022 were performed in PubMed, Web of Science, Medline, Embase, and Scopus for economic evaluations of imaging biomarker-based CDx for cancer. The inclusion and exclusion of studies were determined by pre-specified eligibility criteria informed by the 'Patient, Intervention, Comparison, Outcome' (PICO) framework. The Consolidated Health Economic Evaluation Reporting Standards (CHEERS) was used to assess the quality of reporting, and the Bias in Economic Evaluation (ECOBIAS) was used to examine the potential risk of bias of included studies.

RESULTS

A total of 12 papers were included, with eight model-based and four trial-based studies. Implementing biomarker-driven, imaging-based CDx was reported to be cost-effective, cost saving, or dominant (cost saving and more effective) in ten papers. Inconsistent methods were found in the studies, and the quality of reporting was lacking against the CHEERS reporting guideline. Several potential sources of 'risk of bias' were identified. These should be acknowledged and carefully considered by researchers planning future health economic evaluations.

CONCLUSION

Despite favorable results towards the implementation of imaging biomarker-based CDx for cancer, there is room for improvement regarding the quantity and quality of economic evaluations, and that is expected as the awareness of current study limitations increases and more clinical data become available in the future.

PET imaging of PARP expression using 68Ga-labelled inhibitors

PURPOSE

Imaging the PARP expression using 18F probes has been approved in clinical trials. Nevertheless, hepatobiliary clearance of both 18F probes hindered their application in monitoring abdominal lesions. Our novel 68Ga-labelled probes aim for fewer abdominal signals while ensuring PARP targeting by optimizing the pharmacokinetic properties of radioactive probes.

METHODS

Three radioactive probes targeted PARP were designed, synthesized, and evaluated based on the PARP inhibitor Olaparib. These 68Ga-labelled radiotracers were assessed in vitro and in vivo.

RESULTS

Precursors that did not lose binding affinity for PARP were designed, synthesized, and then labelled with 68Ga in high radiochemical purity (> 97%). The 68Ga-labelled radiotracers were stable. Due to the increased expression of PARP-1 in SK-OV-3 cells, the uptake of the three radiotracers by SK-OV-3 cells was significantly greater than that by A549 cells. PET/CT imaging of the SK-OV-3 models indicated that the tumor uptake of 68Ga-DOTA-Olaparib (0.5 h: 2.83 ± 0.55%ID/g; 1 h: 2.37 ± 0.64%ID/g) was significantly higher than that of the other 68Ga-labelled radiotracers. There was a significant difference in the T/M (tumor-to-muscle) ratios between the unblocked and blocked groups as calculated from the PET/CT images (4.07 ± 1.01 vs. 1.79 ± 0.45, P = 0.0238 < 0.05). Tumor autoradiography revealed high accumulation in tumor tissues, further confirming the above data. PARP-1 expression in the tumor was confirmed by immunochemistry.

CONCLUSION

As the first 68Ga-labelled PARP inhibitor, 68Ga-DOTA-Olaparib displayed high stability and quick PARP imaging in a tumor model. This compound is thus a promising imaging agent that can be used in a personalized PARP inhibitor treatment regimen.

Preparation and quality control of a new porphyrin complex labeled with 45Ti for PET imaging

This study aims to produce and quality control of a new porphyrin complex labeled with ⁴⁵Ti for PET imaging, so at the first step, the cross-section of ⁴⁵Sc(p,n)⁴⁵Ti was investigated by TALYS-1.6 and the optimal target thickness and theoretical yield were calculated by SRIM code. The purified ⁴⁵Ti was labeled with the anticancer agent of tetrakis (pentafluorophenyl) porphyrin (TFPP). The radiochemical purity and the percentage of labeling were evaluated by radiation layer chromatography then the division coefficient of [⁴⁵Ti]-TFPP was calculated. The dual coincidence imaging system was used for imaging 1 and 2 h after injection [⁴⁵Ti]-TFPP to rats. Immediately after imaging, the mean percent injected dose per gram and specific activity of different tissues including blood, heart, lungs, stomach, liver, bone, kidney, spleen, intestine, muscle, feces, and skin were measured. The yield of ⁴⁵Ti production was measured 468 MBq/μAh and the labeling rate was observed more than 98%. The highest activity was observed in the liver (%ID/g = 2.27%, 1 h) and spleen (2.2%, 1 h), respectively, because of the high lipophilic of ⁴⁵Ti-TFPP. SPECT images showed a significant uptake of radiopharmaceuticals in the abdomen. The labeling rate of ⁴⁵Ti-TFPP was high and this compound has the potential for clinical application in different ways than PSMA, it can be joined with photodynamic therapy (Severin et al., 2015).

68Ga-Labeled Trastuzumab Fragments for ImmunoPET Imaging of Human Epidermal Growth Factor Receptor 2 Expression in Solid Cancers

Background: Trastuzumab, the first humanized antibody approved for therapeutic use has shown promising results for the treatment of patients with human epidermal growth factor receptor 2 (HER2) positive cancers. The aim of this study was to formulate immunoPET agents based on trastuzumab fragments and demonstrate their potential for early diagnosis of HER2-positive tumors. Materials and Methods: F(ab')₂ and F(ab') fragments of trastuzumab were prepared by enzymatic digestion and conjugated with chelator NOTA for labeling with ⁶⁸Ga. For comparison, intact trastuzumab was also radiolabeled. In vitro stability, immunoreactivity, and binding affinity of radio formulations toward HER2 receptors were evaluated by performing in vitro studies in cancer cell lines. Biodistribution and PET imaging studies were performed in animal model bearing tumors. Results: ⁶⁸Ga-NOTA-F(ab')-trastuzumab, ⁶⁸Ga-NOTA-F(ab')₂-trastuzumab, and ⁶⁸Ga-NOTA-trastuzumab could be prepared with >98% radiochemical purity (% RCP) and were found to be stable when studied up to 4 h. In vitro binding studies revealed high affinity and specificity of formulations toward HER2 receptors. Specific tumor uptake of ⁶⁸Ga-NOTA-F(ab')-trastuzumab and ⁶⁸Ga-NOTA-F(ab')₂-trastuzumab in HER2-positive tumors was observed in biodistribution and PET imaging studies. Conclusions: This study describes optimization of protocol for the formulation of ⁶⁸Ga-NOTA-F(ab')-trastuzumab and ⁶⁸Ga-NOTA-F(ab')₂-trastuzumab for targeting HER2-overexpressing tumors. Further studies with these radioformulations are warranted to confirm their potential as immunoPET agents for management of HER2-positive breast and other solid tumors.

Imaging of the Glucose-Dependent Insulinotropic Polypeptide Receptor Using a Novel Radiolabeled Peptide Rationally Designed Based on Endogenous GIP and Synthetic Exendin-4 Sequences

Imaging and radiotherapy targeting the glucose-dependent insulinotropic polypeptide receptor (GIPR) could potentially benefit the management of neuroendocrine neoplasms (NENs), complementing clinically established radiopharmaceuticals. The aim of this study was to evaluate a GIPR-targeting positron emission tomography (PET) radioligand with receptor-specific binding, fast blood clearance, and low liver background uptake. The peptide DOTA-bioconjugate, C803-GIP, was developed based on the sequence of the endogenous GIP(1-30) and synthetic exendin-4 peptides with selective amino acid mutations to combine their specificity for the GIPR and in vivo stability, respectively. The ⁶⁸Ga-labeled bioconjugate was evaluated in vitro in terms of binding affinity, specificity, and internalization in HEK293 cells transfected with the human GIPR, GLP1, or GCG receptors and in sections of human insulinoma and NENs. In vivo binding specificity, biodistribution, and tissue background were investigated in mice bearing huGIPR-HEK293 xenografts and in a pig. Ex vivo organ distribution, pharmacokinetics, and dosimetry were studied in normal rats. [⁶⁸Ga]Ga-C803-GIP was stable and demonstrated a high affinity to the huGIPR-HEK293 cells. Binding specificity was demonstrated in vitro in frozen sections of NENs and huGIPR-HEK293 cells. No specific uptake was observed in the negative controls of huGLP1R and huGCGR cells. A novel rationally designed PET radioligand, [⁶⁸Ga]Ga-C803-GIP, demonstrated promising binding characteristics and specificity towards the GIPR.

Synthesis and ex vivo biodistribution of two 68Ga-labeled tetrazine tracers: Comparison of pharmacokinetics

Pretargeted PET imaging allows the use of radiotracers labeled with short-living PET radionuclides for tracing drugs with slow pharmacokinetics. Recently, especially methods based on bioorthogonal chemistry have been under intensive investigation for pretargeted PET imaging. The pharmacokinetics of the radiotracer is one of the factors that determine the success of the pretargeted strategy. Here, we report synthesis and biological evaluation of two ⁶⁸Ga-labeled tetrazine (Tz)-based radiotracers, [⁶⁸Ga]Ga-HBED-CC-PEG₄-Tz ([⁶⁸Ga]4) and [⁶⁸Ga]Ga-DOTA-PEG₄-Tz ([⁶⁸Ga]6), aiming for development of new tracer candidates for pretargeted PET imaging based on the inverse electron demand Diels-Alder (IEDDA) ligation between a tetrazine and a strained alkene, such as trans-cyclooctene (TCO). Excellent radiochemical yield (RCY) was obtained for [⁶⁸Ga]4 (RCY > 96%) and slightly lower for [⁶⁸Ga]6 (RCY > 88%). Radiolabeling of HBED-CC-Tz proved to be faster and more efficient under milder conditions compared to the DOTA analogue. The two tracers exhibited excellent radiolabel stability both in vitro and in vivo. Moreover, [⁶⁸Ga]4 was successfully used for radiolabeling two different TCO-functionalized nanoparticles in vitro: Hepatitis E virus nanoparticles (HEVNPs) and porous silicon nanoparticles (PSiNPs).

Optimized 68Ga-Labeled Urea-Based PSMA-Targeted PET Tracers for Prostate Cancer

Prostate-specific membrane antigen (PSMA)-targeting radiopharmaceuticals have become some of the most promising tools for the diagnosis and therapy prostate cancer (PCa). The structure of existing PSMA-targeted PET tracers still needs to be optimized to improve their pharmacokinetic properties and tumor-to-background ratio. In this study, we modified the structure of a well-studied PSMA tracer, and six novel tracers with variable hydrophilicity and pharmacokinetics were developed and evaluated both in vitro and in vivo. All of the novel tracers showed high hydrophilicity (log p = −2.99 ± 0.33 to −3.49 ± 0.01), rapid clearance rates (elimination half-times = 15.55 to 35.97 min), and high affinity for PSMA (Ki = 8.11 ± 0.49 to 42.40 ± 2.11 nM) in vitro. Specific cell binding and micro-PET experiments showed that [⁶⁸Ga]Ga-PSMA-Q displayed the highest specific PSMA+ cell uptake (3.75 ± 0.35 IA%/10⁶ at 60 min), tumor uptake (SUVmax = 0.97 ± 0.24 at 60 min p.i.), and tumor-to-muscle ratio (59.33 ± 5.72 at 60 min p.i.), while the tumor-to-muscle ratio was much higher than that of [⁶⁸Ga]Ga-PSMA-617. The results of this study validate the clinical potential of [⁶⁸Ga]Ga-PSMA-Q for PET imaging and further targeted therapy of prostate cancer.

New Imaging Modality of COVID-19 Pneumonia Developed on the Basis of Alzheimer’s Disease Research

Viral pneumonia caused by highly infectious SARS-CoV-2 poses a higher risk to older people and those who have underlying health conditions, including Alzheimer’s disease. In this work we present newly designed tacrine-based radioconjugates with physicochemical and biological properties that are crucial for the potential application as diagnostic radiopharmaceuticals. A set of ten tacrine derivatives was synthesized, labelled with gallium-68 and fully characterized in the context of their physicochemical properties. Based on these results, the final two most promising radioconjugates, [⁶⁸Ga]Ga-NODAGA-Bn-NH(CH₂)₉Tac and [⁶⁸Ga]Ga-THP-NH(CH₂)₉Tac, were selected for biodistribution studies. The latter compound was proven to be a good inhibitor of cholinesterases with significant affinity toward the lungs, according to the biodistribution studies. On the basis of molecular modelling combined with in vitro studies, we unraveled which structural properties of the developed tacrine derivatives are crucial for high affinity toward acetylcholinesterase, whose increased levels in lung tissues in the course of coronavirus disease indicate the onset of pneumonia. The radiopharmaceutical [⁶⁸Ga]Ga-THP-NH(CH₂)₉Tac was ultimately selected due to its increased accuracy and improved sensitivity in PET imaging of lung tissue with high levels of acetylcholinesterase, and it may become a novel potential diagnostic modality for the determination of lung perfusion, including in inflammation after COVID-19.

The Chemical Scaffold of Theranostic Radiopharmaceuticals: Radionuclide, Bifunctional Chelator, and Pharmacokinetics Modifying Linker

Therapeutic radiopharmaceuticals have been researched extensively in the last decade as a result of the growing research interest in personalized medicine to improve diagnostic accuracy and intensify intensive therapy while limiting side effects. Radiometal-based drugs are of substantial interest because of their greater versatility for clinical translation compared to non-metal radionuclides. This paper comprehensively discusses various components commonly used as chemical scaffolds to build radiopharmaceutical agents, i.e., radionuclides, pharmacokinetic-modifying linkers, and chelators, whose characteristics are explained and can be used as a guide for the researcher.

Radiopharmaceutical Labelling for Lung Ventilation/Perfusion PET/CT Imaging: A Review of Production and Optimization Processes for Clinical Use

Lung ventilation/perfusion (V/Q) positron emission tomography-computed tomography (PET/CT) is a promising imaging modality for regional lung function assessment. The same carrier molecules as a conventional V/Q scan (i.e., carbon nanoparticles for ventilation and macro aggregated albumin particles for perfusion) are used, but they are labeled with gallium-68 (⁶⁸Ga) instead of technetium-99m (^99mTc). For both radiopharmaceuticals, various production processes have been proposed. This article discusses the challenges associated with the transition from ^99mTc- to ⁶⁸Ga-labelled radiopharmaceuticals. The various production and optimization processes for both radiopharmaceuticals are reviewed and discussed for optimal clinical use.

68Ga-WRWWWW Is a Potential Positron Emission Tomography Probe for Imaging Inflammatory Diseases by Targeting Formyl Peptide Receptor 2

Inflammation plays a significant role in many physiological and pathological processes. Molecular imaging could provide functional as well as anatomical information for visualizing various inflammatory diseases. Advancements in imaging tracers for inflammation would improve the accuracy of diagnosis and monitoring, thus facilitating patient care. The positron emission tomography (PET) imaging tracer, ⁶⁸Ga-labeled antagonist peptide Trp-Arg-Trp-Trp-Trp-Trp (WRWWWW, WRW⁴), targets formyl peptide receptor 2 (FPR2), which is in turn widely distributed in a variety of tissues and is associated with many inflammatory diseases. In the current study, we aimed to investigate the potential of ⁶⁸Ga-WRW⁴ for detecting and monitoring inflammatory lesions in mice. We established an inflammation mouse model by the intramuscular injection of turpentine oil into the left thigh. WRW⁴ was labeled with ⁶⁸Ga with an overall radiochemical yield >90% and radiochemical purity >99%. ⁶⁸Ga-WRW⁴ uptake in inflamed muscle peaked on day 2 (1.14 ± 0.01 percentage of the injected dose per gram of tissue (%ID/g)) and the uptake ratio of inflammatory/normal muscle also reached a maximum (12.36 ± 2.35). Strong PET signals were detected in the left thigh at 60 min after the injection of ⁶⁸Ga-WRW⁴ in experimental mice, but weak or no signals were detected in mice in the blocking and control groups. ⁶⁸Ga-WRW⁴ uptake was in agreement with the dynamics of immune cell infiltration during the inflammatory reaction. These results suggest that ⁶⁸Ga-WRW⁴ is a promising PET tracer suitable for the noninvasive detection of FPR2 expression and for monitoring inflammatory activity in inflammation-bearing mice.

Optimization of Precursor Preparation in PSMA-11 Radiolabeling to Obtain a Highly Reproducible Radiochemical Yield

[⁶⁸Ga]Ga-PSMA-11 PET/CT plays a pivotal role in the diagnosis and staging of prostate cancer because of its higher sensitivity and detection rate compared with traditional choline PET/CT. A highly reproducible radiochemical yield of the radiopharmaceutical to be used in the clinical routine is an important parameter for planning and optimization of clinical activity. During radiometallation of PSMA-11, the presence of metal ion contaminants in the peptide precursor may cause a decrease in the [⁶⁸Ga]Ga-PSMA-11 radiochemical yield because of metal ion contaminants competition with gallium-68. To optimize the radiochemical yield of [⁶⁸Ga]Ga-PSMA-11 radiosynthesis, data obtained by preparing the solution of the PSMA-11 precursor with three different methods (A, B, and C) were compared. Methods A and B consisted of the reconstitution of different quantities of precursor (1000 µg and 30 µg, respectively) to obtain a 1 µg/mL solution. In Method A, the precursor solution was aliquoted and stored frozen, while the precursor solution obtained with Method B was entirely used. Method C consisted of the reconstitution of 1000 µg of precursor taking into account net peptide content as described in European Pharmacopoeia. Radiosynthesis data demonstrated that reconstitution methods B and C gave a consistently higher and reproducible radiochemical yield, highlighting the role of metals and precursor storage conditions on the synthesis performance.

Cold Kit Labeling: The Future of 68Ga Radiopharmaceuticals?

Over the last couple of decades, gallium-68 (68Ga) has gained a formidable interest for PET molecular imaging of various conditions, from cancer to infection, through cardiac pathologies or neuropathies. It has gained routine use, with successful radiopharmaceuticals such as somatostatin analogs ([68Ga]Ga-DOTATOC and [68Ga]GaDOTATATE) for neuroendocrine tumors, and PSMA ligands for prostate cancer. It represents a major clinical impact, particularly in the context of theranostics, coupled with their 177Lu-labeled counterparts. Beside those, a bunch of new 68Ga-labeled molecules are in the preclinical and clinical pipelines, with some of them showing great promise for patient care. Increasing clinical demand and regulatory issues have led to the development of automated procedures for the production of 68Ga radiopharmaceuticals. However, the widespread use of these radiopharmaceuticals may rely on simple and efficient radiolabeling methods, undemanding in terms of equipment and infrastructure. To make them technically and economically accessible to the medical community and its patients, it appears mandatory to develop a procedure similar to the well-established kit-based 99mTc chemistry. Already available commercial kits for the production of 68Ga radiopharmaceuticals have demonstrated the feasibility of using such an approach, thus paving the way for more kit-based 68Ga radiopharmaceuticals to be developed. This article discusses the development of 68Ga cold kit radiopharmacy, including technical issues, and regulatory aspects.

Nanomaterial Probes for Nuclear Imaging

Nuclear imaging is a powerful non-invasive imaging technique that is rapidly developing in medical theranostics. Nuclear imaging requires radiolabeling isotopes for non-invasive imaging through the radioactive decay emission of the radionuclide. Nuclear imaging probes, commonly known as radiotracers, are radioisotope-labeled small molecules. Nanomaterials have shown potential as nuclear imaging probes for theranostic applications. By modifying the surface of nanomaterials, multifunctional radio-labeled nanomaterials can be obtained for in vivo biodistribution and targeting in initial animal imaging studies. Various surface modification strategies have been developed, and targeting moieties have been attached to the nanomaterials to render biocompatibility and enable specific targeting. Through integration of complementary imaging probes to a single nanoparticulate, multimodal molecular imaging can be performed as images with high sensitivity, resolution, and specificity. In this review, nanomaterial nuclear imaging probes including inorganic nanomaterials such as quantum dots (QDs), organic nanomaterials such as liposomes, and exosomes are summarized. These new developments in nanomaterials are expected to introduce a paradigm shift in nuclear imaging, thereby creating new opportunities for theranostic medical imaging tools.

Development and Validation of an Analytical HPLC Method to Assess Chemical and Radiochemical Purity of [68Ga]Ga-NODAGA-Exendin-4 Produced by a Fully Automated Method

Background: Glucagon-like peptide 1 receptor (GLP-1R) is preferentially expressed in pancreatic islets, especially in β-cells, and highly expressed in human insulinomas and gastrinomas. In recent years several GLP-1R-avid radioligands have been developed to image insulin-secreting tumors or to provide a tentative quantitative in vivo biomarker of pancreatic β-cell mass. Exendin-4, a 39-amino acid peptide with high binding affinity to GLP-1R, has been labeled with Ga-68 for imaging with positron emission tomography (PET). Preparation conditions may influence the quality and in vivo behavior of tracers. Starting from a published synthesis and quality controls (QCs) procedure, we have developed and validated a new rapid and simple UV-Radio-HPLC method to test the chemical and radiochemical purity of [68Ga]Ga-NODAGA-exendin-4, to be used in the clinical routine. Methods: Ga-68 was obtained from a 68Ge/68Ga Generator (GalliaPharma®) and purified using a cationic-exchange cartridge on an automated synthesis module (Scintomics GRP®). NODAGA-exendin-4 contained in the reactor (10 µg) was reconstituted with HEPES and ascorbic acid. The reaction mixture was incubated at 100 °C. The product was purified through HLB cartridge, diluted, and sterilized. To validate the proposed UV-Radio-HPLC method, a stepwise approach was used, as defined in the guidance document released by the International Conference on Harmonization of Technical Requirements of Pharmaceuticals for Human Use (ICH), adopted by the European Medicines Agency (CMP/ICH/381/95 2014). The assessed parameters are specificity, linearity, precision (repeatability), accuracy, and limit of quantification. Therefore, a range of concentrations of Ga-NODAGA-exendin-4, NODAGA-exendin-4 (5, 4, 3.125, 1.25, 1, and 0.75 μg/mL) and [68Ga]Ga-NODAGA-exendin-4 were analyzed. To validate the entire production process, three consecutive batches of [68Ga]Ga-NODAGA-exendin-4 were tested. Results: Excellent linearity was found between 5-0.75 μg/mL for both the analytes (NODAGA-exendin-4 and 68Ga-NODAGA-exendin-4), with a correlation coefficient (R2) for calibration curves equal to 0.999, average coefficients of variation (CV%) < 2% (0.45% and 0.39%) and average per cent deviation value of bias from 100%, of 0.06% and 0.04%, respectively. The calibration curve for the determination of [68Ga]Ga-NODAGA-exendin-4 was linear with a R2 of 0.993 and CV% < 2% (1.97%), in accordance to acceptance criteria. The intra-day and inter-day precision of our method was statistically confirmed using 10 μg of peptide. The mean radiochemical yield was 45 ± 2.4% in all the three validation batches of [68Ga]Ga-NODAGA-exendin-4. The radiochemical purity of [68Ga]Ga-NODAGA-exendin-4 was >95% (97.05%, 95.75% and 96.15%) in all the three batches. Conclusions: The developed UV-Radio-HPLC method to assess the radiochemical and chemical purity of [68Ga]Ga-NODAGA-exendin-4 is rapid, accurate and reproducible like its fully automated production. It allows the routine use of this PET tracer as a diagnostic tool for PET imaging of GLP-1R expression in vivo, ensuring patient safety.

In Vivo Evaluation of Gallium-68-Labeled IRDye800CW as a Necrosis Avid Contrast Agent in Solid Tumors

Necrosis only occurs in pathological situations and is directly related to disease severity and, therefore, is an important biomarker. Tumor necrosis occurs in most solid tumors due to improperly functioning blood vessels that cannot keep up with the rapid growth, especially in aggressively growing tumors. The amount of necrosis per tumor volume is often correlated to rapid tumor proliferation and can be used as a diagnostic tool. Furthermore, efficient therapy against solid tumors will directly or indirectly lead to necrotic tumor cells, and detection of increased tumor necrosis can be an early marker for therapy efficacy. We propose the application of necrosis avid contrast agents to detect therapy-induced tumor necrosis. Herein, we advance gallium-68-labeled IRDye800CW, a near-infrared fluorescent dye that exhibits excellent necrosis avidity, as a potential PET tracer for in vivo imaging of tumor necrosis. We developed a reliable labeling procedure to prepare [68Ga]Ga-DOTA-PEG4-IRDye800CW ([68Ga]Ga-1) with a radiochemical purity of >96% (radio-HPLC). The prominent dead cell binding of fluorescence and radioactivity from [68Ga]Ga-1 was confirmed with dead and alive cultured 4T1-Luc2 cells. [68Ga]Ga-1 was injected in 4T1-Luc2 tumor-bearing mice, and specific fluorescence and PET signal were observed in the spontaneously developing tumor necrosis. The ip injection of D-luciferin enabled simultaneous bioluminescence imaging of the viable tumor regions. Tumor necrosis binding was confirmed ex vivo by colocalization of fluorescence uptake with TUNEL dead cell staining and radioactivity uptake in dichotomized tumors and frozen tumor sections. Our presented study shows that [68Ga]Ga-1 is a promising PET tracer for the detection of tumor necrosis.

Preliminary Study of New Gallium-68 Radiolabeled Peptide Targeting NRP-1 to Detect Brain Metastases by Positron Emission Tomography

Due to their very poor prognosis and a fatal outcome, secondary brain tumors are one of the biggest challenges in oncology today. From the point of view of the early diagnosis of these brain micro- and macro-tumors, the sensitivity and specificity of the diagnostic tools constitute an obstacle. Molecular imaging, such as Positron Emission Tomography (PET), is a promising technique but remains limited in the search for cerebral localizations, given the commercially available radiotracers. Indeed, the [18F]FDG PET remains constrained by the physiological fixation of the cerebral cortex, which hinders the visualization of cerebral metastases. Tumor angiogenesis is recognized as a crucial phenomenon in the progression of malignant tumors and is correlated with overexpression of the neuropilin-1 (NRP-1) receptor. Here, we describe the synthesis and the photophysical properties of the new gallium-68 radiolabeled peptide to target NRP-1. The KDKPPR peptide was coupled with gallium-68 anchored into a bifunctional NODAGA chelating agent, as well as Cy5 for fluorescence detection. The Cy5 absorbance spectra did not change, whereas the molar extinction coefficient (ε) decreased drastically. An enhancement of the fluorescence quantum yield (φF) could be observed due to the better water solubility of Cy5. [68Ga]Ga-NODAGA-K(Cy5)DKPPR was radiosynthesized efficiently, presented hydrophilic properties (log D = -1.86), and had high in vitro stability (>120 min). The molecular affinity and the cytotoxicity of this new chelated radiotracer were evaluated in vitro on endothelial cells (HUVEC) and MDA-MB-231 cancer cells (hormone-independent and triple-negative line) and in vivo on a brain model of metastasis in a nude rat using the MDA-MB-231 cell line. No in vitro toxicity has been observed. The in vivo preliminary experiments showed promising results, with a high contrast between the healthy brain and metastatic foci for [68Ga]Ga-NODAGA-K(Cy5)DKPPR.

Advances in Radiopharmaceutical Sciences for Vascular Inflammation Imaging: Focus on Clinical Applications

Biomedical imaging technologies offer identification of several anatomic and molecular features of disease pathogenesis. Molecular imaging techniques to assess cellular processes in vivo have been useful in advancing our understanding of several vascular inflammatory diseases. For the non-invasive molecular imaging of vascular inflammation, nuclear medicine constitutes one of the best imaging modalities, thanks to its high sensitivity for the detection of probes in tissues. 2-[¹⁸F]fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) is currently the most widely used radiopharmaceutical for molecular imaging of vascular inflammatory diseases such as atherosclerosis and large-vessel vasculitis. The combination of [¹⁸F]FDG and positron emission tomography (PET) imaging has become a powerful tool to identify and monitor non-invasively inflammatory activities over time but suffers from several limitations including a lack of specificity and avid background in different localizations. The use of novel radiotracers may help to better understand the underlying pathophysiological processes and overcome some limitations of [¹⁸F]FDG PET for the imaging of vascular inflammation. This review examines how [¹⁸F]FDG PET has given us deeper insight into the role of inflammation in different vascular pathologies progression and discusses perspectives for alternative radiopharmaceuticals that could provide a more specific and simple identification of pathologies where vascular inflammation is implicated. Use of these novel PET tracers could lead to a better understanding of underlying disease mechanisms and help inform the identification and stratification of patients for newly emerging immune-modulatory therapies. Future research is needed to realize the true clinical translational value of PET imaging in vascular inflammatory diseases.

Hydroxypyridinones as a Very Promising Platform for Targeted Diagnostic and Therapeutic Radiopharmaceuticals

Hydroxypyridinones (HOPOs) have been used in the chelation therapy of iron and actinide metals. Their application in metal-based radiopharmaceuticals has also been increasing in recent years. This review article focuses on how multidentate HOPOs can be used in targeted radiometal-based diagnostic and therapeutic radiopharmaceuticals. The general structure of radiometal-based targeted radiopharmaceuticals, a brief description of siderophores, the basic structure and properties of bidentate HOPO, some representative HOPO multidentate chelating agents, radiopharmaceuticals based on HOPO multidentate bifunctional chelators for gallium-68, thorium-227 and zirconium-89, as well as the future prospects of HOPO multidentate bifunctional chelators in other metal-based radiopharmaceuticals are described and discussed in turn. The HOPO metal-based radiopharmaceuticals that have shown good prospects in clinical and preclinical studies are gallium-68, thorium-227 and zirconium-89 radiopharmaceuticals. We expect HOPO multidentate bifunctional chelators to be a very promising platform for building novel targeted radiometal-based diagnostic and therapeutic radiopharmaceuticals.

Hydroxypyridinones as a Very Promising Platform for Targeted Diagnostic and Therapeutic Radiopharmaceuticals

Hydroxypyridinones (HOPOs) have been used in the chelation therapy of iron and actinide metals. Their application in metal-based radiopharmaceuticals has also been increasing in recent years. This review article focuses on how multidentate HOPOs can be used in targeted radiometal-based diagnostic and therapeutic radiopharmaceuticals. The general structure of radiometal-based targeted radiopharmaceuticals, a brief description of siderophores, the basic structure and properties of bidentate HOPO, some representative HOPO multidentate chelating agents, radiopharmaceuticals based on HOPO multidentate bifunctional chelators for gallium-68, thorium-227 and zirconium-89, as well as the future prospects of HOPO multidentate bifunctional chelators in other metal-based radiopharmaceuticals are described and discussed in turn. The HOPO metal-based radiopharmaceuticals that have shown good prospects in clinical and preclinical studies are gallium-68, thorium-227 and zirconium-89 radiopharmaceuticals. We expect HOPO multidentate bifunctional chelators to be a very promising platform for building novel targeted radiometal-based diagnostic and therapeutic radiopharmaceuticals.

Hydroxypyridinones as a Very Promising Platform for Targeted Diagnostic and Therapeutic Radiopharmaceuticals

Hydroxypyridinones (HOPOs) have been used in the chelation therapy of iron and actinide metals. Their application in metal-based radiopharmaceuticals has also been increasing in recent years. This review article focuses on how multidentate HOPOs can be used in targeted radiometal-based diagnostic and therapeutic radiopharmaceuticals. The general structure of radiometal-based targeted radiopharmaceuticals, a brief description of siderophores, the basic structure and properties of bidentate HOPO, some representative HOPO multidentate chelating agents, radiopharmaceuticals based on HOPO multidentate bifunctional chelators for gallium-68, thorium-227 and zirconium-89, as well as the future prospects of HOPO multidentate bifunctional chelators in other metal-based radiopharmaceuticals are described and discussed in turn. The HOPO metal-based radiopharmaceuticals that have shown good prospects in clinical and preclinical studies are gallium-68, thorium-227 and zirconium-89 radiopharmaceuticals. We expect HOPO multidentate bifunctional chelators to be a very promising platform for building novel targeted radiometal-based diagnostic and therapeutic radiopharmaceuticals.

Synthesis and Preclinical Evaluation of [18F]SiFA-PSMA Inhibitors in a Prostate Cancer Model

Positron emission tomography (PET) imaging of prostate-specific membrane antigen (PSMA) with gallium-68 (⁶⁸Ga) and fluorine-18 (¹⁸F) radiotracers has aroused tremendous interest over the past few years. The use of organosilicon-[¹⁸F]fluoride acceptors (SiFA) conjugated to urea-based peptidomimetic PSMA inhibitors provides a "kit-like" multidose synthesis technology. Nine novel ¹⁸F-labeled SiFA-bearing PSMA inhibitors with different linker moieties were synthesized and analyzed for their in vitro binding against [¹²⁵I]I-TAAG-PSMA in LNCaP cells. IC₅₀ values ranged from 58-570 nM. Among all compounds, [¹⁸F]SiFA-Asp₂-PEG₃-PSMA (IC₅₀ = 125 nM) showed the highest tumor uptake in LNCaP tumors (SUV_60min 0.73). A substantial increase in molar activity (A_m) (from 7.5 ± 0.5 to 86 ± 3 GBq/μmol) led to a significant increase in LNCaP tumor uptake (SUV_60min 1.18; Δ 0.45 corresponding to +62%). In vivo blocking with DCFPyL resulted in -32% uptake after 60 min. The SiFA-isotopic exchange chemistry offers a method that is readily adaptable for a "kit-type" labeling procedure and clinical translation.

Synthesis and Characterization of Multifunctional Nanovesicles Composed of POPC Lipid Molecules for Nuclear Imaging

The integration of nuclear imaging analysis with nanomedicine has tremendously grown and represents a valid and powerful tool for the development and clinical translation of drug delivery systems. Among the various types of nanostructures used as drug carriers, nanovesicles represent intriguing platforms due to their capability to entrap both lipophilic and hydrophilic agents, and their well-known biocompatibility and biodegradability. In this respect, here we present the development of a labelling procedure of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine)-based liposomes incorporating an ad hoc designed lipophilic NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) analogue, derivatized with an oleic acid residue, able to bind the positron emitter gallium-68(III). Based on POPC features, the optimal conditions for liposome labelling were studied with the aim of optimizing the Ga(III) incorporation and obtaining a significant radiochemical yield. The data presented in this work demonstrate the feasibility of the labelling procedure on POPC liposomes co-formulated with the ad hoc designed NOTA analogue. We thus provided a critical insight into the practical aspects of the development of vesicles for theranostic approaches, which in principle can be extended to other nanosystems exploiting a variety of bioconjugation protocols.

EANM guideline for harmonisation on molar activity or specific activity of radiopharmaceuticals: impact on safety and imaging quality

This guideline on molar activity (Am) and specific activity (As) focusses on small molecules, peptides and macromolecules radiolabelled for diagnostic and therapeutic applications. In this guideline we describe the definition of Am and As, and how these measurements must be standardised and harmonised. Selected examples highlighting the importance of Am and As in imaging studies of saturable binding sites will be given, and the necessity of using appropriate materials and equipment will be discussed. Furthermore, common Am pitfalls and remedies are described. Finally, some aspects of Am in relation the emergence of a new generation of highly sensitive PET scanners will be discussed.

Nanobody-Based Theranostic Agents for HER2-Positive Breast Cancer: Radiolabeling Strategies

The overexpression of human epidermal growth factor 2 (HER2) in breast cancer (BC) has been associated with a more aggressive tumor subtype, poorer prognosis and shorter overall survival. In this context, the development of HER2-targeted radiotracers is crucial to provide a non-invasive assessment of HER2 expression to select patients for HER2-targeted therapies, monitor response and identify those who become resistant. Antibodies represent ideal candidates for this purpose, as they provide high contrast images for diagnosis and low toxicity in the therapeutic setting. Of those, nanobodies (Nb) are of particular interest considering their favorable kinetics, crossing of relevant biological membranes and intratumoral distribution. The purpose of this review is to highlight the unique characteristics and advantages of Nb-based radiotracers in BC imaging and therapy. Additionally, radiolabeling methods for Nb including direct labeling, indirect labeling via prosthetic group and indirect labeling via complexation will be discussed, reporting advantages and drawbacks. Furthermore, the preclinical to clinical translation of radiolabeled Nbs as promising theranostic agents will be reported.

Thermodynamic Stability and Speciation of Ga(III) and Zr(IV) Complexes with High-Denticity Hydroxamate Chelators

Increasing attention has been recently devoted to ⁸⁹Zr(IV) and ⁶⁸Ga(III) radionuclides, due to their favorable decay characteristics for positron emission tomography (PET). In the present paper, a deep investigation is presented on Ga(III) and Zr(IV) complexes with a series of tri-(H₃L1, H₃L3, H₃L4 and desferrioxamine E, DFOE) and tetrahydroxamate (H₄L2) ligands. Herein, we describe the rational design and synthesis of two cyclic complexing agents (H₃L1 and H₄L2) bearing three and four hydroxamate chelating groups, respectively. The ligand structures allow us to take advantage of the macrocyclic effect; the H₄L2 chelator contains an additional side amino group available for a possible further conjugation with a biomolecule. The thermodynamic stability of Ga(III) and Zr(IV) complexes in solution has been measured using a combination of potentiometric and pH-dependent UV–vis titrations, on the basis of metal–metal competition. The Zr(IV)-H₄L2 complex is characterized by one of the highest formation constants reported to date for a tetrahydroxamate zirconium chelate (log β = 45.9, pZr = 37.0), although the complex-stability increase derived from the introduction of the fourth hydroxamate binding unit is lower than that predicted by theoretical calculations. Solution studies on Ga(III) complexes revealed that H₃L1 and H₄L2 are stronger chelators in comparison to DFOB. The complex stability obtained with the new ligands is also compared with that previously reported for other hydroxamate ligands. In addition to increasing the library of the thermodynamic stability data of Ga(III) and Zr(IV) complexes, the present work allows new insights into Ga(III) and Zr(IV) coordination chemistry and thermodynamics and broadens the selection of available chelators for ⁶⁸Ga(III) and ⁸⁹Zr(IV).

Solution equilibria studies on Ga(III) and Zr(IV) complexes with a series of tri- and tetrahydroxamate ligands are presented. For this purpose, the rational design and synthesis of two cyclic complexing agents bearing three and four hydroxamate chelating groups was performed. The thermodynamic and speciation studies allow a discussion of the structure−complex stability dependence. The Zr(IV)-tetrahydroxamate complex is characterized by one of the highest formation constants reported to date for a hydroxamate zirconium chelator.

Towards Facile Radiolabeling and Preparation of Gallium-68-/Bismuth-213-DOTA-[Thi8, Met(O2)11]-Substance P for Future Clinical Application: First Experiences

Substance P (SP) is a small peptide commonly known as a preferential endogenous ligand for the transmembrane neurokinin-1 receptor. Nuclear Medicine procedures currently involve radiolabeled SP derivatives in peptide radioligand endotherapy of inoperable glioblastoma. Promising clinical results sparked the demand for facile production strategies for a functionalized 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-[Thi⁸, Met(O₂)¹¹]-SP to allow for rapid Gallium-68 or Bismuth-213 complexation. Therefore, we provide a simple kit-like radiotracer preparation method that caters for the gallium-68 activity eluted from a SnO₂ generator matrix as well as preliminary results on the adaptability to produce [²¹³Bi]Bi-DOTA-[Thi⁸, Met(O₂)¹¹]SP from the same vials containing the same starting material. Following a phase of radioanalysis for complexation of gallium-68 to DOTA-[Thi⁸, Met(O₂)¹¹]SP and assessing the radiolabeling parameters, the vials containing appropriate kit-prototype material were produced in freeze-dried batches. The facile radiolabeling performance was tested and parameters for future human application were calculated to meet the criteria for theranostic loco-regional co-administration of activity doses comprising [⁶⁸Ga]Ga-DOTA-[Thi⁸, Met(O₂)¹¹]SP mixed with [²¹³Bi]Bi-DOTA-[Thi⁸, Met(O₂)¹¹]SP. [⁶⁸Ga]Ga-DOTA-[Thi⁸, Met(O₂)¹¹]SP was prepared quantitatively from lyophilized starting material within 25 min providing the required molar activity (18 ± 4 GBq/µmol) and activity concentration (98 ± 24 MBq/mL), radiochemical purity (>95%) and sustained radiolabeling performance (4 months at >95% LE) as well as acceptable product quality (>95% for 120 min). Additionally, vials of the same starting materials were successfully adapted to a labeling strategy available for preparation of [²¹³Bi]Bi-DOTA-[Thi⁸, Met(O₂)¹¹]SP providing sufficient activity for 1-2 human doses. The resultant formulation of [⁶⁸Ga]Ga-/[²¹³Bi]Bi-DOTA-[Thi⁸, Met(O₂)¹¹]SP activity doses was considered of adequate radiochemical quality for administration. This investigation proposes a simple kit-like formulation of DOTA-[Thi⁸, Met(O₂)¹¹]SP-a first-line investigation into a user friendly, straightforward tracer preparation that would warrant efficient clinical investigations in the future. Quantitative radiolabeling was accomplished for [⁶⁸Ga]Ga-DOTA-[Thi⁸, Met(O₂)¹¹]SP and [²¹³Bi]Bi-DOTA-[Thi⁸, Met(O₂)¹¹]SP preparations; a key requirement when addressing the specific route of catheter-assisted co-injection directly into the intratumoral cavities.