A Step-by-Step Guide for the Novel Radiometal Production for Medical Applications: Case Studies with 68Ga, 44Sc, 177Lu and 161Tb.

The production of novel radionuclides is the first step towards the development of new effective radiopharmaceuticals, and the quality thereof directly affects the preclinical and clinical phases. In this review, novel radiometal production for medical applications is briefly elucidated. The production status of the imaging nuclide 44Sc and the therapeutic ß--emitter nuclide 161Tb are compared to their more established counterparts, 68Ga and 177Lu according to their targetry, irradiation process, radiochemistry, and quality control aspects. The detailed discussion of these significant issues will help towards the future introduction of these promising radionuclides into drug manufacture for clinical application under Good Manufacturing Practice (GMP).

Targeted Radiotherapeutics from 'Bench-to-Bedside'.

The concept of targeted radionuclide therapy (TRT) is the accurate and efficient delivery of radiation to disseminated cancer lesions while minimizing damage to healthy tissue and organs. Critical aspects for successful development of novel radiopharmaceuticals for TRT are: i) the identification and characterization of suitable targets expressed on cancer cells; ii) the selection of chemical or biological molecules which exhibit high affinity and selectivity for the cancer cell-associated target; iii) the selection of a radionuclide with decay properties that suit the properties of the targeting molecule and the clinical purpose. The Center for Radiopharmaceutical Sciences (CRS) at the Paul Scherrer Institute in Switzerland is privileged to be situated close to unique infrastructure for radionuclide production (high energy accelerators and a neutron source) and access to C/B-type laboratories including preclinical, nuclear imaging equipment and Swissmedic-certified laboratories for the preparation of drug samples for human use. These favorable circumstances allow production of non-standard radionuclides, exploring their biochemical and pharmacological features and effects for tumor therapy and diagnosis, while investigating and characterizing new targeting structures and optimizing these aspects for translational research on radiopharmaceuticals. In close collaboration with various clinical partners in Switzerland, the most promising candidates are translated to clinics for 'first-in-human' studies. This article gives an overview of the research activities at CRS in the field of TRT by the presentation of a few selected projects.

Neuroimaging with Radiopharmaceuticals Targeting the Glutamatergic System.

Radiopharmacy at ETH has worked on the development of novel PET tracers for neuro-, cardiac- and tumor imaging for many years. In this paper, our efforts on targeting the glutamatergic system of the metabotropic glutamate receptor subtype 5 (mGluR5) and the ionotropic N-methyl-D-aspartate (NMDA) receptor are summarized. We briefly described the principles of positron emission tomography (PET) tracer development for the central nervous system (CNS) and the radiolabeling methods used in our laboratory. To assess the radioligands, results of in vitro autoradiography, biodistribution, and metabolite studies as well as PET imaging data are discussed. Furthermore, key PET parameters for kinetic modeling and quantification methods are provided. Two mGluR5 PET tracers, [11C]ABP688 and [18F]PSS232, were translated in our GMP labs and evaluated in human subjects. The newly developed GluN2B PET tracer [11C]Me-NB1 is currently being investigated in a first-in-human PET study and several F-18 labeled tracers are being evaluated in non-human primates in which the first-in-class will be translated for human studies.

A first-in-man PET study of [18F]PSS232, a fluorinated ABP688 derivative for imaging metabotropic glutamate receptor subtype 5.

PURPOSE: Non-invasive imaging of metabotropic glutamate receptor 5 (mGlu5) in the brain using PET is of interest in e.g., anxiety, depression, and Parkinson's disease. Widespread application of the most widely used mGlu5 tracer, [11C]ABP688, is limited by the short physical half-life of carbon-11. [18F]PSS232 is a fluorinated analog with promising preclinical properties and high selectivity and specificity for mGlu5. In this first-in-man study, we evaluated the brain uptake pattern and kinetics of [18F]PSS232 in healthy volunteers. METHODS: [18F]PSS232 PET was performed with ten healthy male volunteers aged 20-40 years. Seven of the subjects received a bolus injection and the remainder a bolus/infusion protocol. Cerebral blood flow was determined in seven subjects using [15O]water PET. Arterial blood activity was measured using an online blood counter. Tracer kinetics were evaluated by compartment modeling and parametric maps were generated for both tracers. RESULTS: At 90 min post-injection, 59.2 ± 11.1% of total radioactivity in plasma corresponded to intact tracer. The regional first pass extraction fraction of [18F]PSS232 ranged from 0.41 ± 0.06 to 0.55 ± 0.03 and brain distribution pattern matched that of [11C]ABP688. Uptake kinetics followed a simple two-tissue compartment model. The volume of distribution of total tracer (V T, ml/cm3) ranged from 1.18 ± 0.20 for white matter to 2.91 ± 0.51 for putamen. The respective mean distribution volume ratios (DVR) with cerebellum as the reference tissue were 0.88 ± 0.06 and 2.12 ± 0.10, respectively. The tissue/cerebellum ratios of a bolus/infusion protocol (30/70 dose ratio) were close to the DVR values. CONCLUSIONS: Brain uptake of [18F]PSS232 matched the distribution of mGlu5 and followed a two-tissue compartment model. The well-defined kinetics and the possibility to use reference tissue models, obviating the need for arterial blood sampling, make [18F]PSS232 a promising fluorine-18 labeled radioligand for measuring mGlu5 density in humans.

In-vivo inhibition of neutral endopeptidase 1 results in higher absorbed tumor doses of [177Lu]Lu-PP-F11N in humans: the lumed phase 0b study.

BACKGROUND: A new generation of radiolabeled minigastrin analogs delivers low radiation doses to kidneys and are considered relatively stable due to less enzymatic degradation. Nevertheless, relatively low tumor radiation doses in patients indicate limited stability in humans. We aimed at evaluating the effect of sacubitril, an inhibitor of the neutral endopeptidase 1, on the stability and absorbed doses to tumors and organs by the cholecystokinin-2 receptor agonist [177Lu]Lu-PP-F11N in patients. In this prospective phase 0 study eight consecutive patients with advanced medullary thyroid carcinoma and a current somatostatin receptor subtype 2 PET/CT scan were included. Patients received two short infusions of ~ 1 GBq [177Lu]Lu-PP-F11N in an interval of ~ 4 weeks with and without Entresto® pretreatment in an open-label, randomized cross-over order. Entresto® was given at a single oral dose, containing 48.6 mg sacubitril. Adverse events were graded and quantitative SPECT/CT and blood sampling were performed. Absorbed doses to tumors and relevant organs were calculated. RESULTS: Pretreatment with Entresto® showed no additional toxicity and increased the stability of [177Lu]Lu-PP-FF11N in blood significantly (p < 0.001). Median tumor-absorbed doses were 2.6-fold higher after Entresto® pretreatment (0.74 vs. 0.28 Gy/GBq, P = 0.03). At the same time, an increase of absorbed doses to stomach, kidneys and bone marrow was observed, resulting in a tumor-to-organ absorbed dose ratio not significantly different with and without Entresto®. CONCLUSIONS: Premedication with Entresto® results in a relevant stabilization of [177Lu]Lu-PP-FF11N and consecutively increases radiation doses in tumors and organs. Trial registration clinicaltrails.gov, NCT03647657. Registered 20 August 2018.

161Tb-DOTATOC Production Using a Fully Automated Disposable Cassette System: A First Step Toward the Introduction of 161Tb into the Clinic.

161Tb is an interesting radionuclide for application in the treatment of neuroendocrine neoplasms' small metastases and single cancer cells because of its conversion and Auger-electron emission. Tb has coordination chemistry similar to that of Lu; therefore, like 177Lu, it can stably radiolabel DOTATOC, one of the leading peptides used for the treatment of neuroendocrine neoplasms. However, 161Tb is a recently developed radionuclide that has not yet been specified for clinical use. Therefore, the aim of the current work was to characterize and specify 161Tb and to develop a protocol for the synthesis and quality control of 161Tb-DOTATOC with a fully automated process conforming to good-manufacturing-practice guidelines, in view of its clinical use. Methods: 161Tb, produced by neutron irradiation of 160Gd in high-flux reactors followed by radiochemical separation from its target material, was characterized regarding its radionuclidic purity, chemical purity, endotoxin level, and radiochemical purity (RCP) in analogy to what is described in the European Pharmacopoeia for no-carrier-added 177Lu. In addition, 161Tb was introduced into a fully automated cassette-module synthesis to produce 161Tb-DOTATOC, as used for 177Lu-DOTATOC. The quality and stability of the produced radiopharmaceutical in terms of identity, RCP, and ethanol and endotoxin content were assessed by means of high-performance liquid chromatography, gas chromatography, and an endotoxin test, respectively. Results: 161Tb produced under the described conditions showed, as the no-carrier-added 177Lu, a pH of 1-2, radionuclidic purity and RCP of more than 99.9%, and an endotoxin level below the permitted range (175 IU/mL), indicating its appropriate quality for clinical use. In addition, an efficient and robust procedure for the automated production and quality control of 161Tb-DOTATOC with clinically applicable specifications and activity levels, that is, 1.0-7.4 GBq in 20 mL, was developed. The radiopharmaceutical's quality control was also developed using chromatographic methods, which confirmed the product's stability (RCP ≥ 95%) over 24 h. Conclusion: The current study demonstrated that 161Tb has appropriate features for clinical use. The developed synthesis protocol guarantees high yields and safe preparation of injectable 161Tb-DOTATOC. The investigated approach could be translated to other DOTA-derivatized peptides; thus, 161Tb could be successfully applied in clinical practice for radionuclide therapy.

Cholecystokinin 2 Receptor Agonist 177Lu-PP-F11N for Radionuclide Therapy of Medullary Thyroid Carcinoma: Results of the Lumed Phase 0a Study.

Treatment of patients with advanced medullary thyroid carcinoma (MTC) is still a challenge. For more than 2 decades, it has been known that the cholecystokinin 2 receptor is a promising target for the treatment of MTC with radiolabeled minigastrin analogs. Unfortunately, kidney toxicity has precluded their therapeutic application so far. In 6 consecutive patients, we evaluated with advanced 3-dimensional dosimetry whether improved minigastrin analog 177Lu-DOTA-(d-Glu)6-Ala-Tyr-Gly-Trp-Nle-Asp-PheNH2 (177Lu-PP-F11N) is a suitable agent for the treatment of MTC. Methods: Patients received 2 injections of about 1 GBq (∼80 µg) of 177Lu-PP-F11N with and without a solution of succinylated gelatin (SG, a plasma expander used for nephroprotection) in a random crossover sequence to evaluate biodistribution, pharmacokinetics, and tumor and organ dosimetry. An electrocardiogram was obtained and blood count and blood chemistry were measured up to 12 wk after the administration of 177Lu-PP-F11N to assess safety. Results: In all patients, 177Lu-PP-F11N accumulation was visible in tumor tissue, stomach, and kidneys. Altogether, 13 tumors were eligible for dosimetry. The median absorbed doses for tumors, stomach, kidneys, and bone marrow were 0.88 (interquartile range [IQR]: 0.85-1.04), 0.42 (IQR: 0.25-1.01), 0.11 (IQR: 0.07-0.13), and 0.028 (IQR: 0.026-0.034) Gy/GBq, respectively. These doses resulted in median tumor-to-kidney dose ratios of 11.6 (IQR: 8.11-14.4) without SG and 13.0 (IQR: 10.2-18.6) with SG; these values were not significantly different (P = 1.0). The median tumor-to-stomach dose ratio was 3.34 (IQR: 1.14-4.70). Adverse reactions (mainly hypotension, flushing, and hypokalemia) were self-limiting and not higher than grade 1. Conclusion:177Lu-PP-F11N accumulates specifically in MTC at a dose that is sufficient for a therapeutic approach. With a low kidney and bone marrow radiation dose, 177Lu-PP-F11N shows a promising biodistribution. The dose-limiting organ is most likely the stomach. Further clinical studies are necessary to evaluate the maximum tolerated dose and the efficacy of 177Lu-PP-F11N.

Targeting of the Cholecystokinin-2 Receptor with the Minigastrin Analog 177Lu-DOTA-PP-F11N: Does the Use of Protease Inhibitors Further Improve In Vivo Distribution?

Patients with metastatic medullary thyroid cancer (MTC) have limited systemic treatment options. The use of radiolabeled gastrin analogs targeting the cholecystokinin-2 receptor (CCK2R) is an attractive approach. However, their therapeutic efficacy is presumably decreased by their enzymatic degradation in vivo. We aimed to investigate whether the chemically stabilized analog 177Lu-DOTA-PP-F11N (177Lu-DOTA-(dGlu)6-Ala-Tyr-Gly-Trp-Nle-Asp-Phe-NH2) performs better than reference analogs with varying in vivo stability, namely 177Lu-DOTA-MG11 (177Lu-DOTA-dGlu-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2) and 177Lu-DOTA-PP-F11 (177Lu-DOTA-(dGlu)6-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2), and whether the use of protease inhibitors further improves CCKR2 targeting. First human data on 177Lu-DOTA-PP-F11N are also reported. Methods: In vitro stability of all analogs was assessed against a panel of extra- and intracellular endoproteases, whereas their in vitro evaluation was performed using the human MTC MZ-CRC-1 and the transfected A431-CCK2R(+) cell lines. Biodistribution without and with the protease inhibitors phosphoramidon and thiorphan was assessed 4 h after injection in MZ-CRC-1 and A431-CCK2R(+) dual xenografts. Autoradiography of 177Lu-DOTA-PP-F11N (without and with phosphoramidon) and NanoSPECT/CT were performed. SPECT/CT images of 177Lu-DOTA-PP-F11N in a metastatic MTC patient were also acquired. Results:natLu-DOTA-PP-F11N is less of a substrate for neprilysins than the other analogs, whereas intracellular cysteine proteases, such as cathepsin-L, might be involved in the degradation of gastrin analogs. The uptake of all radiotracers was higher in MZ-CRC-1 tumors than in A431-CCK2R(+), apparently because of the higher number of binding sites on MZ-CRC-1 cells. 177Lu-DOTA-PP-F11N had the same biodistribution as 177Lu-DOTA-PP-F11; however, uptake in the MZ-CRC-1 tumors was almost double (20.7 ± 1.71 vs. 11.2 ± 2.94 %IA [percentage injected activity]/g, P = 0.0002). Coadministration of phosphoramidon or thiorphan increases 177Lu-DOTA-MG11 uptake significantly in the CCK2R(+) tumors and stomach. Less profound was the effect on 177Lu-DOTA-PP-F11, whereas no influence or even reduction was observed for 177Lu-DOTA-PP-F11N (20.7 ± 1.71 vs. 15.6 ± 3.80 [with phosphoramidon] %IA/g, P < 0.05 in MZ-CRC-1 tumors). The first clinical data show high 177Lu-DOTA-PP-F11N accumulation in tumors, stomach, kidneys, and colon. Conclusion: The performance of 177Lu-DOTA-PP-F11N without protease inhibitors is as good as the performance of 177Lu-DOTA-MG11 in the presence of inhibitors. The human application of single compounds without unessential additives is preferable. Preliminary clinical data spotlight the stomach as a potential dose-limiting organ besides the kidneys.

Radiation dosimetry of [18F]-PSS232-a PET radioligand for imaging mGlu5 receptors in humans.

PURPOSE: (E)-3-(pyridin-2-ylethynyl)cyclohex-2-enone O-(3-(2-[18F]-fluoroethoxy)propyl) oxime ([18F]-PSS232) is a new PET tracer for imaging of metabotropic glutamate receptor subtype 5 (mGlu5), and has shown promising results in rodents and humans. The aim of this study was to estimate the radiation dosimetry and biodistribution in humans, to assess dose-limiting organs, and to demonstrate safety and tolerability of [18F]-PSS232 in healthy volunteers. METHODS: PET/CT scans of six healthy male volunteers (mean age 23.5 ± 1.7; 21-26 years) were obtained after intravenous administration of 243 ± 3 MBq of [18F]-PSS232. Serial whole-body (vertex to mid-thigh) PET scans were assessed at ten time points, up to 90 min after tracer injection. Calculation of tracer kinetics and cumulated organ activities were performed using PMOD 3.7 software. Dosimetry estimates were calculated using the OLINDA/EXM software. RESULTS: Injection of [18F]-PSS232 was safe and well tolerated. Organs with highest absorbed doses were the gallbladder wall (0.2295 mGy/MBq), liver (0.0547 mGy/MBq), and the small intestine (0.0643 mGy/MBq). Mean effective dose was 3.72 ± 0.12 mSv/volunteer (range 3.61-3.96 mSv; 0.0153 mSv/MBq). CONCLUSION: [18F]-PSS232, a novel [18F]-labeled mGlu5 tracer, showed favorable dosimetry values. Additionally, the tracer was safe and well tolerated.

[Tibetan medicine in Europe: historical, practical and regulatory aspects]. / Tibetische Arzneimittel in Europa: Historische, praktische und regulatorische Aspekte.

Being one of the great medicine systems of the world, Tibetan Medicine developed in the 8th century AD and spread throughout central Asia over the intervening centuries. The first European contact with Tibetan remedies started around 1850 in Russia. By and by, they made their way as far a Switzerland where, in the meantime, they have been produced for more than 30 years and licensed by the health authorities. During the last years, comprehensive clinical and experimental research material has been generated on several formulas, especially on Padma 28 and Padma Lax. At the same time, a genuine European pool of experience was gained. Tibetan remedies are multicomponent mixtures. Special requirements on quality assessment, efficacy and safety arise on the path to a modern Tibetan multicompound. The production of such elaborately formulated com-positions has to take into account modern demands of GMPas well as traditional sources. In recent years, a rising popularity of Asian medicine can be observed. This need of patients, physicians and therapists also demands answers from the regulatory part. Aspects such as the justification of the composition (rationale of combination) and certain quality standards have to be newly defined by the authorities in this context. Only with adapted regulatory frameworks Tibetan medicines can find their place in Europe and, together with other medical traditions and biomedical research, integratively enrich the arsenal of intervention and prevention of Western industrial societies.