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.ISSN:0009-429

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 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 β--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).ISSN:1420-304

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.ISSN:0009-429

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

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 is known that cholecystokinine-2 receptor (CCK2R) is a promising target for the treatment of MTC with radiolabeled minigastrin analogues. Unfortunately, kidney toxicity precluded their therapeutic application so far. In 6 consecutive patients we evaluated with advanced 3D dosimetry whether improved minigastrin analogue 177Lu-DOTA-(DGlu)6-Ala-Tyr-Gly-Trp-Nle-Asp-PheNH2 (177Lu-PP-F11N) is a suitable agent for the treatment of MTC. Methods: Patients received two injections of about 1 GBq (~80 µg) 177Lu-PP-F11N with and without a solution of succinylated gelatin (SG, a plasma expander used for nephroprotection) in a random cross-over sequence in order to evaluate biodistribution, pharmacokinetics as well as tumor- and organ dosimetry. ECG, blood count and blood chemistry were measured up to 12 weeks after 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 (interquartile range = IQR) absorbed dose for tumors, stomach, kidneys and bone marrow was 0.88 Gy/GBq (0.85-1.04), 0.42 (0.25-1.01), 0.11 (0.07-0.13) and 0.028 (0.026-0.034). These resulted in a median (IQR) tumor-to-kidney dose ratio of 11.6 (8.11-14.4) without SG and 13.0 (10.2-18.6) with SG, which were not significantly different (P = 1.0). The median (IQR) tumor-to-stomach dose ratio was 3.34 (1.14-4.7). 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 little kidney and bone marrow radiation dose 177Lu-PP-F11N shows 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

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

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

PURPOSE (E)-3-(pyridin-2-ylethynyl)cyclohex-2-enone O-(3-(2-[F]-fluoroethoxy)propyl) oxime ([F]-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 [F]-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 [F]-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 [F]-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 [F]-PSS232, a novel [F]-labeled mGlu5 tracer, showed favorable dosimetry values. Additionally, the tracer was safe and well tolerated

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