Evaluation of the 177mLu-concentration in in-house produced 177Lu-radiopharmaceuticals and commercially available Lutathera®.

BACKGROUND: 177Lu-radiopharmaceuticals can contain the metastable impurity [177mLu]lutetium with a physical half-life of 160.4 days, in varying concentrations depending on the route of production of the radionuclidic precursor [177Lu]lutetium. Due to the long half-life of [177mLu]lutetium, difficulties with waste disposal or sterility testing could arise. Here, we analyzed several 177Lu-samples of different origins and suppliers regarding their 177mLu-concentration. RESULTS: All samples tested showed a 177mLu-concentration in the range that was stated on the certificate of analysis from the supplier which is in accordance with the European Pharmacopoeia. CONCLUSIONS: Although all 177mLu-concentrations were in accordance with the European Pharmacopoeia, we need to take into account the respective national legislation regarding radioactivity release limits. With regard to the German legislation, several probes for sterility testing in external laboratories could not be released for transport due to the concentration of [177mLu]lutetium. Moreover, waste water tanks should specifically be monitored for 177mLu-concentration, when e.g. Lutathera® is administered in the clinic.

Metallacages with 2,6-dipicolinoylbis(N,N-dialkylthioureas) as novel platforms in nuclear medicine for 68Ga, 177Lu and 198Au.

BACKGROUND: Heterometallic gold metallacages are of great interest for the incorporation of several cations. Especially in nuclear medicine, those metallacages can serve as a platform for radionuclides relevant for imaging or therapy (e.g. 68Ga or 177Lu). Moreover, the radionuclide 198Au is an attractive beta emitter, for potential application in nuclear medicine. Here, we aim to synthesize a new set of gold metallacages and to study their ability to coordinate to 68Ga, 177Lu and 198Au. RESULTS: New heterometallic gold metallacages of composition [M{Au(Lmorph-κS)}3] (M = La3+, Tb3+, Lu3+ or Y3+) and [Ga{Au(Lmorph-κS)}2]NO3 have been synthesized from 2,6-dipicolinoylbis(N,N-morpholinylthiourea) (H2Lmorph) with [AuCl(THT)] and the target M3+ metal ions in yields ranging from 33 (Lu) to 62% (Tb). The characterization of the compounds bases on ESI-MS, 1H NMR, IR, EA and single-crystal X-ray diffraction techniques (all except the Ga derivative). Selected gold cages derived from H2Lmorph were compared to previously reported gold cages that were derived from 2,6-dipicolinoylbis(N,N-diethylthiourea) (H2Ldiethyl). The tested metallacages show similar IC50 values close to that of auranofin in four different cancer cell lines (MCF-7, PC-3, U383, U343), e.g. 4.5 ± 0.7 µM for [Ga{Au(Ldiethyl)}2]NO3 on PC-3. The radiolabeling experiments thereof show high radiochemical purities with 68Ga and 198Au and low radiochemical purity with 177Lu. CONCLUSIONS: The results indicate that these gold metallacages could serve as a novel platform for inclusion of different (radio)nuclides with potential theranostic applications in nuclear medicine.

Highlight selection of radiochemistry and radiopharmacy developments by editorial board.

BACKGROUND: The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biannual highlight commentary to update the readership on trends in the field of radiopharmaceutical development. MAIN BODY: This selection of highlights provides commentary on 21 different topics selected by each coauthoring Editorial Board member addressing a variety of aspects ranging from novel radiochemistry to first-in-human application of novel radiopharmaceuticals. CONCLUSION: Trends in radiochemistry and radiopharmacy are highlighted. Hot topics cover the entire scope of EJNMMI Radiopharmacy and Chemistry, demonstrating the progress in the research field in many aspects.

Gold-Based Coronands as Hosts for M3+ Metal Ions: Ring Size Matters.

The controlled, self-assembled synthesis of multinuclear coordination compounds can be performed via different approaches. Frequently, steric, geometric and/or electronic factors located at the ligand systems predefine the way in which metal ions can assemble them to large aggregates. For the compounds in the present paper, also the Pearson's acidities and preferred coordination geometries of the metal ions were used as organization principles. The ligand under study, 2,6-dipicolinoylbis(N,N-diethylthiourea), H2L1ethyl, possesses 'soft' sulfur and 'hard' nitrogen and oxygen donors. One-pot reactions of this compound with [AuCl(tht)] (tht = tetrahydrothiophene) and M3+ salts (M = Sc, Y, La, Ln, Ga, In) give products with gold-based {Au3(L1ethyl)3}3+ or {Au2(L1ethyl)2}2+ coronands, which host central M3+ ions. The formation of such units is templated by the M3+ ions and the individual size of the coronand rings is dependent on the ionic radii of the central ions in a way that small ions such as Ga3+ form a [Ga⊂{Au2(L1ethyl)2}]+ assembly, while larger ions (starting from Sc3+/In3+) establish neutral [M⊂{Au3(L1ethyl)3}] units with nine-coordinate central ions.

Technetium Complexes with an Isocyano-alkyne Ligand and Its Reaction Products.

The attachment of an ethyne substituent in the para position of phenylisocyanide, CNPhpC≡CH, enables the isocyanide to replace carbonyl ligands in the coordination sphere of common technetium(I) starting materials such as (NBu4)[Tc2(µ-Cl)3(CO)6]. The ligand exchange proceeds under thermal conditions and finally forms the corresponding hexakis(isocyanide)technetium(I) complex. The product undergoes a copper-catalyzed cycloaddition ("Click" reaction), e.g., with benzyl azide, which gives the [Tc(CNPhazole)6]+ cation. The free, uncoordinated "Click" product is obtained from a reaction of the corresponding tetrakis(CNPhazole)copper(I) complex and NaCN. It readily reacts with mer-[Tc(CO)3(tht)(PPh3)2](BF4) (tht = tetrahydrothiophene) under exchange of the thioether ligand. Alternatively, [Cu(CNPhazole)4]+ can be used as a transmetalation reagent for the synthesis of the hexakis(isocyanide)technetium(I) complex, which is the preferable approach for the synthesis of the technetium complex with the short-lived nuclear isomer 99mTc, and a corresponding protocol for [99mTc(CNPhazole)6]+ is reported. The 99Tc and copper complexes have been studied by single-crystal X-ray diffraction and/or spectroscopic methods including IR and multinuclear NMR spectroscopy.

Optimization of 177Lu-labelling of DOTA-TOC, PSMA-I&T and FAPI-46 for clinical application.

BACKGROUND: 177Lu-radiopharmaceuticals are routinely used for the treatment of various tumor entities. The productions of radiopharmaceuticals follow strict good-manufacturing practice guidelines and synthesis optimizations thereof have a strong impact on e.g. the quality of the product, radiation safety and costs. The purpose of this study is to optimize the precursor load of three radiopharmaceuticals. For that, different precursor loads were evaluated and compared to previously reported findings. RESULTS: All three radiopharmaceuticals were successfully synthesized in high radiochemical purities and yields on the ML Eazy. The precursor load was optimized for [177Lu]Lu-FAPI-46 from 27.0 to 9.7 µg/GBq, for [177Lu]Lu-DOTATOC from 11 to 10 µg/GBq and for [177Lu]Lu-PSMA-I&T from 16.3 to 11.6 µg/GBq. CONCLUSIONS: We successfully reduced the precursor load for all three radiopharmaceuticals while maintaining their quality.

[Is there an unmet need to establish a young talent section "Young DGN" within the German Society of Nuclear Medicine (DGN)? - Results of a 2021/2022 web-based survey among German Nuclear Medicine professionals]. / Besteht der Bedarf zur Gründung einer Nachwuchsorganisation "Young DGN" innerhalb der Deutschen Gesellschaft für Nuklearmedizin (DGN)? Ergebnisse einer webbasierten Umfrage in der deutschen Nuklearmedizin 2021/2022.

AIM: In various medical societies, dedicated young talent sections provide an important basis for promoting young members. However, the German Society of Nuclear Medicine (DGN) had not yet implemented such a section. Therefore, the aim of this work was to assess the opinion of nuclear medicine professionals in Germany on establishing a young talent section within the DGN ("Young DGN"). METHODS: An initiative group of young DGN members developed a survey questionnaire comprising 18 questions. The questionnaire was initially sent as a PDF to the members of the DGN University Committee (Hochschulausschuss) by e-mail on 10/12/2021. As an online survey, the questionnaire was then emailed at four additional time points between 12/23/2021 and 3/18/2022 via the DGN eBrief and on 2/23/2022 to the members of the mailing list of the Berufsverband Deutscher Nuklearmediziner (BDN). RESULTS: The survey closed on 3/31/2022 with 111 responses (n=104 online surveys, n=7 PDFs). The median age of participants was 32.5 years (range, 20-80). 86% of participants indicated that they were interested in a Young DGN section, of which 67% were willing to participate. 79% indicated that nuclear medicine was an exciting field for them. 96% expressed interest in additional education offers and 60% in the establishment of a mentoring program. 75% believed that Young DGN would improve the visibility of the specialty. CONCLUSION: The survey results indicate strong support for the establishment of a young talent section within the DGN among nuclear medicine professionals in Germany. A large proportion of those who participated in the survey would envision active involvement. There was a particular consensus on the desire to expand the range of education and training activities.

Good practices for 68Ga radiopharmaceutical production.

BACKGROUND: The radiometal gallium-68 (68Ga) is increasingly used in diagnostic positron emission tomography (PET), with 68Ga-labeled radiopharmaceuticals developed as potential higher-resolution imaging alternatives to traditional 99mTc agents. In precision medicine, PET applications of 68Ga are widespread, with 68Ga radiolabeled to a variety of radiotracers that evaluate perfusion and organ function, and target specific biomarkers found on tumor lesions such as prostate-specific membrane antigen, somatostatin, fibroblast activation protein, bombesin, and melanocortin. MAIN BODY: These 68Ga radiopharmaceuticals include agents such as [68Ga]Ga-macroaggregated albumin for myocardial perfusion evaluation, [68Ga]Ga-PLED for assessing renal function, [68Ga]Ga-t-butyl-HBED for assessing liver function, and [68Ga]Ga-PSMA for tumor imaging. The short half-life, favourable nuclear decay properties, ease of radiolabeling, and convenient availability through germanium-68 (68Ge) generators and cyclotron production routes strongly positions 68Ga for continued growth in clinical deployment. This progress motivates the development of a set of common guidelines and standards for the 68Ga radiopharmaceutical community, and recommendations for centers interested in establishing 68Ga radiopharmaceutical production. CONCLUSION: This review outlines important aspects of 68Ga radiopharmacy, including 68Ga production routes using a 68Ge/68Ga generator or medical cyclotron, standardized 68Ga radiolabeling methods, quality control procedures for clinical 68Ga radiopharmaceuticals, and suggested best practices for centers with established or upcoming 68Ga radiopharmaceutical production. Finally, an outlook on 68Ga radiopharmaceuticals is presented to highlight potential challenges and opportunities facing the community.

Highlight selection of radiochemistry and radiopharmacy developments by editorial board.

BACKGROUND: The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biyearly highlight commentary to update the readership on trends in the field of radiopharmaceutical development. RESULTS: This commentary of highlights has resulted in 21 different topics selected by each member of the Editorial Board addressing a variety of aspects ranging from novel radiochemistry to first in man application of novel radiopharmaceuticals. Also the first contribution in relation to MRI-agents is included. CONCLUSIONS: Trends in (radio)chemistry and radiopharmacy are highlighted demonstrating the progress in the research field being the scope of EJNMMI Radiopharmacy and Chemistry.

Are radiopharmaceuticals self-sterilizing? Radiation effect of gallium-68 and lutetium-177 on bacillus pumilus and staphylococcus succinus.

BACKGROUND: For radiopharmaceuticals, aseptic preparation in combination with filtration is the most commonly used sterilizing method. In general, the production of radiopharmaceuticals needs to fulfil the requirements of good manufacturing practice. In the scope of this work, we focused on the positron emitter gallium-68 and on the therapeutically used beta- and gamma-emitter lutetium-177, as they are routinely used for in-house synthesis of radiopharmaceuticals in nuclear medicine departments. Our hypothesis is, that radiopharmaceuticals might be self-sterilizing due to a high radioactivity concentration and high-energy radionuclides in the preparation for intravenous injections. RESULTS: Incubation with gallium-68 and lutetium-177 for both 30 minutes and 5 hours post-dispensing did not cause any significant effect on bacteria growth. As the theoretical dose is only 0.1-0.6 % of the Ph. Eur. recommended dose of 25 kGy, we conclude that the beta and positron energy of lutetium-177 and gallium-68 as used for standard radiopharmaceutical in-house production is not sufficient to decrease the number of colony forming units compared to the control values. CONCLUSIONS: Based on these findings, gallium-68 and lutetium-177 labeled radiopharmaceuticals are not self-sterilizing under the tested conditions with respect to bacillus pumilus and staphylococcus succinus. Consequently, strict aseptic preparation conditions in addition to end-sterilization of the radiopharmaceutical e.g. through membrane filtration are strongly advised for in-house productions.

Fully-automated production of [68Ga]Ga-FAPI-46 for clinical application.

BACKGROUND: [68Ga]Ga-FAPI-46 is a promising radiopharmaceutical for in vivo detection of the fibroblast activation protein by positron emission tomography. Until now, the synthesis of [68Ga]Ga-FAPI-46 has been only performed manually. Our aim was to evaluate the automated synthesis of this radiopharmaceutical on two different commercially available synthesis modules in order to make the tracer readily available for clinical application. RESULTS: The synthesis of [68Ga]Ga-FAPI-46 with different amounts of precursor (10-50 µg) on the Modular Lab PharmTracer (MLPT) and Modular Lab eazy (ML eazy) from Eckert & Ziegler with a customized synthesis template and a customized single-use cassette yielded best results with 50 µg FAPI-46 for clinical multi-dose application. All relevant quality control parameters tested (e.g. sterility, stability and radiochemical purity) were in accordance with the European Pharmacopoeia. CONCLUSIONS: [68Ga]Ga-FAPI-46 was successfully synthesized fully-automated on the synthesis modules Modular Lab PharmTracer and ML eazy and is, thus, available for multi-dose application in clinical settings.

Thorium chelators for targeted alpha therapy: Rapid chelation of thorium-226.

One of the main challenges in targeted alpha therapy is assuring delivery of the α-particle dose to the targeted cells. Thus, it is critical to identify ligands for α-emitting radiometals that will form complexes that are very stable, both in vitro and in vivo. In this investigation, thorium-227 (t1/2 = 18.70 days) chelation of ligands containing hydroxypyridinonate (HOPO) or picolinic acid (pa) moieties and the stability of the resultant complexes were studied. Chelation reactions were followed by reversed-phased HPLC and gamma spectroscopy. Studies revealed that high 227 Th chelation yields could be obtained within 2.5 h or less with ligands containing four Me-3,2-HOPO moieties, 1 (83%) and 2 (65%), and also with ligands containing pa moieties, H4 octapa 3 (65%) and H4 py4pa 6 (87%). No reaction occurred with H4 neunpa-p-Bn-NO2 4, and the chelation reaction with another pa ligand H4 pypa 5 gave inconsistent yields with a very broad radio-HPLC peak. The ligands spermine-(Me-3,2-HOPO)4 1, H4 octapa 3, and H4 py4pa 6 had high stability (i.e., 87% of 227 Th still bound to the ligand) in phosphate-buffered saline at room temperature over a 6-day period. Preliminary studies with ligand 6 demonstrated efficient chelation of thorium-226 (t1/2 = 30.57 min) when heated to 80°C for 5 min.

Fully-automated production of [68Ga]Ga-PentixaFor on the module Modular Lab-PharmTracer.

BACKGROUND: PentixaFor is a promising radiopharmaceutical for positron emission tomography in the detection of different tumor entities and other diseases. Until now, the synthesis of [68Ga]Ga-PentixaFor was reported for the automated synthesis module from Scintomics® only. Our aim was to evaluate the automated synthesis of this radiopharmaceutical on a different module in order to make it available for a broader community. RESULTS: The synthesis of [68Ga]Ga-PentixaFor with different amounts of PentixaFor (50 µg, 30 µg and 20 µg) on the Modular Lab PharmTracer (MLPT) from Eckert & Ziegler with the already established synthesis template for [68Ga]Ga-DOTATOC yielded best results with 50 µg PentixaFor for clinical multi-dose application. All different quality control parameters tested (e.g. sterility, stability and radiochemical purity) were in accordance with the European Pharmacopoeia. CONCLUSIONS: [68Ga]Ga-PentixaFor was successfully synthesized fully-automated on the synthesis module Modular Lab PharmTracer and can be used for multi-dose application in clinical settings.

Relevance of Copper and Organic Cation Transporters in the Activity and Transport Mechanisms of an Anticancer Cyclometallated Gold(III) Compound in Comparison to Cisplatin.

The molecular mechanisms of toxicity and cellular transport of anticancer metallodrugs, including platinum-based agents, have not yet been fully elucidated. The aim of our study was to investigate the relevance of copper transporters (CTR1 and ATP7A/B), organic cation transporters (OCT2) and the multidrug and toxin extrusion proteins (MATE) in the intracellular accumulation of a novel organometallic cytotoxic Au(III) compound in cancer cells in comparison to cisplatin. Specifically, the synthesis and characterization of the gold complex [Au(pyb-H)(PPh2Ar)Cl]PF6 (PPh2Ar = 3-[4-(diphenylphosphino)phenyl]-7-methoxy-2H-chromen-2-one] (1), featuring a coumarin ligand endowed with "smart" fluorescence properties, have been achieved. Initially, the cytotoxic effects of both cisplatin and 1 were studied in a small panel of human cancer cells, and against a non-tumorigenic cell line in vitro. Thus, the human ovarian cancer cell line A2780 and its cisplatin resistant variant A2780cisR, were selected, being most sensitive to the treatment of the gold complex. Co-incubation of the metallodrugs with CuCl2 (a CTR1 substrate) increased the cytotoxic effects of both the Au(III) complex and cisplatin; while co-incubation with cimetidine (inhibitor of OCT2 and MATE) showed some effect only after 72 h incubation. ICP-MS (Inductively Coupled Plasma Mass Spectrometry) analysis of the cell extracts showed that co-incubation with CuCl2 increases Au and Cu accumulation in both cancer cell lines, in accordance with the enhanced antiproliferative effects. Conversely, for cisplatin, no increase in Pt content could be observed in both cell lines after co-incubation with either CuCl2 or cimetidine, excluding the involvement of CTR1, OCT2, and MATE in drug accumulation and overall anticancer effects. This result, together with the evidence for increased Cu content in A2780 cells after cisplatin co-treatment with CuCl2, suggests that copper accumulation is the reason for the observed enhanced anticancer effects in this cell line. Moreover, metal uptake studies in the same cell lines indicate that both 1 and cisplatin are not transported intracellularly by CTR1 and OCT2. Finally, preliminary fluorescence microscopy studies enabled the visualization of the sub-cellular distribution of the gold compound in A2780 cells, suggesting accumulation in specific cytosolic components/organelles.

On the toxicity and transport mechanisms of cisplatin in kidney tissues in comparison to a gold-based cytotoxic agent.

Mechanisms of toxicity and cellular transport of anticancer metallodrugs, including platinum-based agents, have not yet been fully elucidated. Here, we studied the toxic effects and accumulation mechanisms of cisplatin in healthy rat kidneys ex vivo, using the Precision Cut Tissue Slices (PCTS) method. In addition, for the first time, we investigated the nephrotoxic effects of an experimental anticancer cyclometallated complex [Au(pyb-H)(PTA)Cl]PF6 (PTA = 1,3,5-triazaphosphaadamantane). The viability of the kidney slices after metallodrug treatment was evaluated by ATP content determination and histomorphology analysis. A concentration dependent decrease in viability of PCKS was observed after exposure to cisplatin or the Au(iii) complex, which correlated with the increase in slice content of Pt and Au, respectively. Metal accumulation in kidney slices was analysed by ICP-MS. The involvement of OCTs and MATE transporters in the accumulation of both metal compounds in kidneys was evaluated co-incubating the tissues with cimitedine, inhibitor of OCT and MATE. Studies of mRNA expression of the markers KIM-1, villin, p53 and Bax showed that cisplatin damages proximal tubules, whereas the Au(iii) complex preferentially affects the distal tubules. However, no effect of cimetidine on the toxicity or accumulation of cisplatin and the Au(iii) complex was observed. The effect of temperature on metallodrug accumulation in kidneys suggests the involvement of a carrier-mediated uptake process, other than OCT2, for cisplatin; while carrier-mediated excretion was suggested in the cases of the Au(iii) complex.

p-NO2-Bn-H4neunpa and H4neunpa-Trastuzumab: Bifunctional Chelator for Radiometalpharmaceuticals and 111In Immuno-Single Photon Emission Computed Tomography Imaging.

Potentially nonadentate (N5O4) bifunctional chelator p-SCN-Bn-H4neunpa and its immunoconjugate H4neunpa-trastuzumab for 111In radiolabeling are synthesized. The ability of p-SCN-Bn-H4neunpa and H4neunpa-trastuzumab to quantitatively radiolabel 111InCl3 at an ambient temperature within 15 or 30 min, respectively, is presented. Thermodynamic stability determination with In3+, Bi3+, and La3+ resulted in high conditional stability constant (pM) values. In vitro human serum stability assays have demonstrated both 111In complexes to have high stability over 5 days. Mouse biodistribution of [111In][In(p-NO2-Bn-neunpa)]-, compared to that of [111In][In(p-NH2-Bn-CHX-A″-diethylenetriamine pentaacetic acid (DTPA))]2-, at 1, 4, and 24 h shows fast clearance of both complexes from the mice within 24 h. In a second mouse biodistribution study, the immunoconjugates 111In-neunpa-trastuzumab and 111In-CHX-A″-DTPA-trastuzumab demonstrate a similar distribution profile but with slightly lower tumor uptake of 111In-neunpa-trastuzumab compared to that of 111In-CHX-A″-DTPA-trastuzumab. These results were also confirmed by immuno-single photon emission computed tomography (immuno-SPECT) imaging in vivo. These initial investigations reveal the acyclic bifunctional chelator p-SCN-Bn-H4neunpa to be a promising chelator for 111In (and other radiometals) with high in vitro stability and also show H4neunpa-trastuzumab to be an excellent 111In chelator with promising biodistribution in mice.

Rhodium(I) N-Heterocyclic Carbene Bioorganometallics as in Vitro Antiproliferative Agents with Distinct Effects on Cellular Signaling.

Organometallics with N-heterocyclic carbene (NHC) ligands have triggered major interest in inorganic medicinal chemistry. Complexes of the type Rh(I)(NHC)(COD)X (where X is Cl or I, COD is cyclooctadiene, and NHC is a dimethylbenzimidazolylidene) represent a promising type of new metallodrugs that have been explored by advanced biomedical methods only recently. In this work, we have synthesized and characterized several complexes of this type. As observed by mass spectrometry, these complexes remained stable over at least 3 h in aqueous solution, after which hydrolysis of the halido ligands occurred and release of the NHC ligand was evident. Effects against mitochondria and general cell tumor metabolism were noted at higher concentrations, whereas phosphorylation of HSP27, p38, ERK1/2, FAK, and p70S6K was induced substantially already at lower exposure levels. Regarding the antiproliferative activity in tumor cells, a clear preference for iodido over chlorido secondary ligands was noted, as well as effects of the substituents of the NHC ligand.

Cellular transport mechanisms of cytotoxic metallodrugs: an overview beyond cisplatin.

The field of medicinal inorganic chemistry has grown consistently during the past 50 years; however, metal-containing coordination compounds represent only a minor proportion of drugs currently on the market, indicating that research in this area has not yet been thoroughly realized. Although platinum-based drugs as cancer chemotherapeutic agents have been widely studied, exact knowledge of the mechanisms governing their accumulation in cells is still lacking. However, evidence suggests active uptake and efflux mechanisms are involved; this may be involved also in other experimental metal coordination and organometallic compounds with promising antitumor activities in vitro and in vivo, such as ruthenium and gold compounds. Such knowledge would be necessary to elucidate the balance between activity and toxicity profiles of metal compounds. In this review, we present an overview of the information available on the cellular accumulation of Pt compounds from in vitro, in vivo and clinical studies, as well as a summary of reports on the possible accumulation mechanisms for different families of experimental anticancer metal complexes (e.g., Ru Au and Ir). Finally, we discuss the need for rationalization of the investigational approaches available to study metallodrug cellular transport.