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The cannabinoid receptor type 2 (CB2R) is an attractive target for diagnosis and therapy of neurodegenerative diseases and cancer. Recently, we reported a novel naphthyrid-2-one based positron-emission tomography (PET) radioligand for imaging of the CB2R in the brain ([18F]5). In this study we aimed at the development of a novel 18F-labeled CB2R radioligand with improved binding properties and metabolic stability. Starting from the structure of 5, we developed a novel series of fluorinated derivatives by modifying the substituents at the naphthyrid-2-one subunit. Compound 28 (LU13) was identified with the highest binding affinity and selectivity versus CB1R (CB2RKi = 0.6 nM; CB1RKi/CB2RKi > 1000) and was selected for radiolabeling with 18F and biological characterization. The radiofluorination was performed starting from the corresponding bromo-precursor (31) bearing a fully deuterated N-alkyl chain to protect against defluorination. The in vitro evaluation of [18F]LU13 proved the high binding affinity of the radioligand towards rat (rCB2RKD = 0.2 nM) and human (hCB2RKD = 1.1 nM) CB2R. Metabolism studies in mice revealed a metabolic stability at 30 min p.i. with fractions of parent compound of >80% in the brain and 90% in the spleen with only trace of defluorination products detected in plasma. PET imaging in a rat model of vector-based/related overexpression in the striatum revealed a high signal to background ratio, demonstrating the ability of [18F]LU13 to reach and selectively label the hCB2R in the brain. Thus, [18F]LU13 is a novel and highly promising PET radioligand for the imaging of up regulated CB2R expression under pathological conditions in the brain.

Objectives: The cyclic nucleotide phosphodiesterase 2A is an intracellular enzyme which hydrolyzes the second messengers cAMP and cGMP and therefore plays an important role in signaling processes. It is highly expressed in distinct brain areas associated with emotion, memory and learning. Therefore, it is assumed that the PDE2A is involved in the pathophysiology of neurodegenerative and neuropsychiatric diseases. To enable a specific imaging of this enzyme in the brain by PET, we are developing fluorine-18 labeled radioligands with high inhibitory potency and selectivity toward other phosphodiesterases, in particular the PDE10A, which is also located in typical PDE2A-rich brain regions. Methods: Out of a series of 12 tricyclic triazolopyridopyrazine-based derivatives with high inhibitory potency toward PDE2A and selectivity vs. PDE10A [1], the most promising candidate 1 was selected for radiofluorination. The radiolabeling was performed in a two-step one-pot procedure via nucleophilic aromatic substitution of the nitro group (precursor 2) by [18F]fluoride followed by the reduction of the activating ketone function to obtain the desired radiotracer [18F]1 (Figure 1). The product was isolated using semi-preparative HPLC followed by final purification with solid-phase extraction and formulation in isotonic saline containing 10% ethanol. In vitro autoradiography studies with cryosections of rat brain and PET studies in female Sprague-Dawley rats (30 min dynamic PET imaging after intravenous injection, nanoScan® PET/MRI, MEDISO, Budapest, Hungary) were performed. The in vivo metabolism of [18F]1 was investigated by radio-HPLC analysis of extracts obtained from blood plasma and homogenized brain of rats at 30 min p.i. Results: The new derivative 1 inhibits PDE2A with high potency (IC50 PDE2A3 = 1.99 nM) and superior selectivity against PDE10A (IC50 PDE10A1 = 1910 nM). [18F]1 was obtained with a radiochemical yield of 2.1 ± 0.7% (EOB), molar activities of 10–20 GBq/µmol (E

Zyklotrone bilden als Ressource medizinischer Radionuklide eine zentrale Infrastruktur für die Entwicklung neuer und die Produktion klinisch etablierter Radiotracer zur molekularen Hybridbildgebung. Da die letzte umfassende Veröffentlichung zu Zyklotronen ca. 15 Jahre alt ist, wurde eine Statuserhebung zu den für die Nuklearmedizin und Radiopharmazie in Deutschland, Österreich und der Schweiz (D-A-CH-Länder) betriebenen Zyklotronen angestrebt.

Objectives: During the last 15 years several PSMA PET ligands for prostate cancer imaging have been developed resulting in the recent approvals of 68Ga-PSMA-11, 18F-PSMA-1007 and 18F-DCFPyL.[1,2] However, 99mTc remains a popular radiometal for SPECT imaging due to its longer half-life and availability from 99Mo/99mTc generators especially in outpatient imaging centers. Due to the widespread availability of SPECT cameras PSMA SPECT ligands have the potential to substantially extend the availability of PSMA-based imaging, but currently no PSMA SPECT ligand is approved. MIP-1404, PSMA-I&S and HYNIC-iPSMA are rare examples of PSMA SPECT tracers in clinical development. Accordingly, the aim of our study was to develop a PSMA ligand for 99mTc SPECT imaging of prostate cancer based on an N2S2 chelator, which enables reliable radiolabeling to form stable 99mTc complexes.[3] Methods: A number of compounds, which contain the PSMA binding motif Glu-urea-Lys, a varying linker and a bisaminothiol (BAT)-type N2S2 chelator, were synthesized. Selected compounds were radiolabeled with 99mTc, followed by assessment of in vitro stability of the formed complexes via radio-HPLC. The specific binding affinity towards PSMA and the internalization of the radioligands were examined in LNCaP cells, supplemented by autoradiographic studies. Tissue distribution and tumor accumulation were evaluated in LNCaP-tumor bearing mice via quantitative SPECT/CT imaging, benchmarked with [99mTc]Tc-PSMA-I&S[4] and [68Ga]Ga-PSMA-11. Results: Among the six 99mTc radioligands synthesized and examined, [99mTc]TcO-ABX474 showed most favorable properties. Radiolabeling of ABX474 (50 µg) was achieved starting from [99mTc]NaTcO4 (0.2-2 GBq) in saline (1.4 mL) using SnCl2 (1 µg in 0.01 M HCl) as reducing agent, in presence of calcium-D-heptagluconate (10 µg) and D-mannitol (1 mg) at pH 5-6. Incubation at r.t. for 20 min followed by heating at 80°C for 20 min afforded the product-containing solution with a radioche

´Objectives: The emerging significance of the tumor microenvironment (TME) as a new frontier for cancer diagnosis and therapy can be primarily attributed to its unique features, such as the interconnection between stromal and cancer cells.1 Cancer-associated fibroblasts (CAFs) within the TME are identified by biomarkers such as fibroblast activation protein alpha (FAP), which are expressed on their surfaces. Targeting FAP using small molecule 18F-labeled inhibitors (FAPIs) have recently garnered significant attention for noninvasive tumor visualization using PET.2 Currently, the predominant 18F-fluorination method for radiolabeling FAPIs involves chelation-based radiofluorination strategies using aluminum [18F]fluoride ([18F]AlF). Herein, a powerful radiofluorination protocol for the preparation of an 18F-labeled FAPI via the sulfur [18F]fluoride exchange ([18F]SuFEx) reaction is disclosed.3 Methods: The incorporation of the aryl fluorosulfate motif into the linker of the FAPI core structure (2) via amide bond formation allowed the radiolabeling precursor 3 to be accessed in moderate yield (Scheme 1 A, 46%). The radiosynthesis commenced with [18F]fluoride loading onto a QMA-cartridge which was eluted with a methanolic solution containing Et4NHCO3, followed by evaporation of the solvent under reduced pressure at 70 oC for 5 min (Scheme 1 B). Thereafter, the precursor 3 (100 µg, 145 nmol) in MeCN was added to the reaction vial, and allowed to react by [18F]SuFEx at room temperature for 5 min. The reaction was quenched by water dilution followed by SPE-based purification using a C18 cartridge. [18F]3 was isolated by elution from the cartridge with EtOH and the identity of the product was confirmed by UHPLC. Results The optimized radiosynthesis of 18F-labeled FAPI ([18F]3) was obtained with non-decay corrected isolated activity yields (AY) of 54 ± 3% (n = 3) and >99% RCP in 25 min. The automated radiosynthesis afforded [18F]3 in an unoptimized 11% AY, with >95% RCP an

Ziel: Der Programmed Cell Death Ligand 1 (PD-L1) ist auf verschiedenen Tumorentitäten überexprimiert und hemmt die Immunantwort durch Bindung an PD-1 auf T-Zellen. Immuncheckpoint-Inhibitoren können diese Blockade aufbrechen und die Immunantwort reaktivieren. Da nur ca. 30% der Patienten auf eine solche Therapie ansprechen, besteht klinisch ein dringender Bedarf an einem nicht-invasiven PET/SPECT-Radioliganden, um die Ansprechrate der Patienten auf diese Therapie abzuschätzen.[1] Methoden: Basierend auf den Strukturen von nicht-peptidischen PD-L1-Inhibitoren, wurden sechs verschiedene Radioliganden synthetisiert und mit [64Cu]Cu2+ markiert (HZDR, 30 MeV TR-FLEX-Zyklotron). Bindungsaffinitäten wurden auf stabil hPD-L1 überexprimierenden PC3 Zellen bestimmt. In vivo wurden qualitative PET/CT-Bilder (nanoSCAN PET/CT, Mediso) an NMRI-FoxN1-Nacktmäusen mit PC3-hPD-L1- und mock-Tumoren aufgenommen. Ergebnisse: Zwei PD-L1-Inhibitoren wurden synthetisch mit stark wasserlöslichen Säuregruppen, hydrophilen Linkern und NODAGA modifiziert (Abb. 1a).[2] Die LogD7.4-Werte der [64Cu]Cu-Radioliganden lagen zwischen –3,17 und –4,15 und die Bindungsaffinitäten (KD) zwischen 80,5 und 532,8 nM. Abhängig von der Zahl und dem Substitutionsmuster der Sulfon- und Phosphonsäuregruppen, zeigte sich in vivo eine stark unterschiedliche Pharmakokinetik. Der Radioligand mit R1 = SO2Me, R2 = PO3H2 und n = 0 zeigte in vivo eine kurze Zirkulationszeit, renale Ausscheidung, gute Tumoraufnahme (SUVmax = 3.5) und einen deutlichen Kontrast zwischen hPD-L1- und mock-Tumor (Abb. 1b). Schlussfolgerungen: Der PD-L1-Radioligand mit je einer Sulfon- und Phosphonsäuregruppe wies das beste pharmakokinetische Profil auf. Um die Bindungsaffinität und die Tumoraufnahme zu verbessern, wird das Leitmotiv derzeit weiter modifiziert. Referenzen: [1] Postow M. A., Callahan M. K., Wolchok J. D. J. Clin. Oncol. 2015, 33, 1974-1982. [2] Stadlbauer S., Krutzek F., Kopka K. EP21212444.0, 2021.

Bispidines (3,7-diazabicyclo[3.3.1]nonane) and their derivatives act as bifunctional chelators (BFC), combining the advantages of multidentate macrocyclic and acyclic ligands (e.g., high kinetic inertness, rapid radiolabelling under mild conditions) [1]. This bicyclic chelator system shows a great diversity in terms of its denticity and type of functional groups, yielding a wide range of multidentate ligands that can bind a variety of different metal ions [1-3]. In addition, they allow a facile functionalisation of targeting molecules such as peptides, peptidomimetics, and bispecific antibodies which can also be used as target modules for adapter CAR T-cell cross-linkage [1, 4]. Herein, we present a nonadentate bispidine ligand labelled with [177Lu]Lu3+ and [225Ac]Ac3+ at mild conditions. The radiometal complexes have been obtained with high radiochemical yields (99%) and are stable in human serum [3]. This is unique so far, as many chelators are not able to bind both LuIII and AcIII under mild conditions (physiological pH, T<40°C) with fast complexation kinetics and high molar activities (>100 MBq/nmol for [177Lu]Lu3+ and ~0.2 MBq/nmol for [225Ac]Ac3+). For targeting, the chelator was functionalised with a peptidic somatostatin analogue (Tyr3 -octreotate), which addresses the somatostatin subtype receptor 2 in neuroendocrine tumours. Both 177Lu(III)- and 225Ac(III)-labelled conjugates were investigated towards their binding affinity and internalization in a murine pheochromocytoma (MPC) and human pancreatic carcinoid (BON1) tumour cell line and were compared with [177Lu]Lu(III)- and [ 225Ac]Ac(III)-DOTA-TATE. The presented 177Lu(III)- and 225Ac(III)-labelled bispidine-conjugates show favourable labelling kinetics and high radiostabilities in human serum. The radioconjugates exhibited dissociation constants in the lower nanomolar range (<10 nM) and high internalisation rates (>95 %) in both cell lines. In comparison to the corresponding DOTA-radioconjugates, milder

The prostate-specific membrane antigen (PSMA) is expressed in approx. 80% of prostate cancer at considerably higher levels in tumor cells compared to healthy tissues. Its upregulation occurs in all stages of the disease. Therefore, PSMA has emerged as an attractive target for molecular imaging and especially targeted radionuclide therapy (endoradiotherapy) of metastatic castration-resistant prostate cancer (mCRPC). Due to its favorable nuclear physical properties, actinium-225 belongs to the clinically applied alpha emitters for therapeutic applications. More than ten clinical trials are displayed for actinium-225-DOTA-based conjugates. A trial using [225Ac]Ac-PSMA-617 as the IMP in men with PSMA-positive prostate cancer is projected to start. Actinium-225 can be chelated with the standard DOTA chelator, but requires rather harsh labeling conditions such as high temperatures (80–95°C) or microwave assistance. Alternatively, with the complexing agent macropa mild labeling conditions, low reaction temperature and high in vivo stability can be realized owing to its perfect characteristics for Ac3+ chelation. Moreover, to further improve the tumor uptake for future targeted alpha therapy, albumin binding units based on 4-iodophenylbutyrate were introduced to increase the tumor uptake. Two 225Ac-radioconjugates with albumin binders were prepared, either containing one or two PSMA-binding units (based on PSMA-617), the second one to raise the binding affinity to the PSMA receptor. The synthetic approach consisted of the functionalization of one or two picolinic side arms with a clickable reactive site for the connection of the vector molecules. The azide-functionalized PSMA derivative, which also contains the albumin binder, was prepared using standard peptide coupling conditions. Cell culture-based studies regarding radioligand affinity and clonogenicity were performed using PSMA-positive LNCaP cells and the biodistribution of the radioconjugates wa

Aim/Introduction The programmed cell death ligand 1 (PD-L1) is expressed by several cancer types and leads to a downregulation of the local immune response, therefore enabling tumour cells to evade the immune response.[1] So-called immune checkpoint inhibitors (ICI) are able to reactivate the immune system, however, only 30% of the patients respond to an ICI monotherapy.[2] Since PD-L1 is heterogeneously expressed within and across tumour sites, there is an urgent clinical need for a diagnostic, non-invasive imaging probe to support therapy decision. Small molecule-based radiotracers for PD-L1 PET or SPECT imaging fulfil these requirements due to their fast clearance, low risk of side effects and highly sensitive imaging at the molecular level.[3] Materials & Methods Based on a published small molecule PD-L1 inhibitor, six different radioligands were synthesized and radiolabelled with copper-64 (HZDR, 30 MeV TR-FLEX cyclotron). Binding affinities were determined on PC3 cells stably overexpressing human PD-L1 which were kindly provided by the Department of Radioimmunology. For in vivo evaluation, qualitative PET/CT imaging experiments (nanoSCAN PET/CT scanner, Mediso) were performed in NMRI-FoxN1-nude mice bearing PC3-hPD-L1 xenografted tumours. Results We designed six radioligands by modifying the PD-L1 binding motif with strongly water-solubilizing sulfonate and phosphonate groups, hydrophilic linker units and a NODAGA-chelator in 21 – 25 organic synthesis steps (12-13 longest linear sequence).[4] The copper-64 labelled radiotracers exhibited log(D) values between –3.17 and –4.15. Binding affinities (Kd) were between 80.5 and 532.8 nmol/L. Depending on the number and pattern of sulfonate and phosphonate groups, the in vivo experiments showed drastically different pharmacokinetic profiles: The radiotracer containing three sulfonates showed long circulation times of 24 h due to albumin binding, renal clearance but low tumour uptake (SUVmax = 1.4). Substitution of one

Objectives: An upregulation of cannabinoid receptors type 2 (CB2) has been reported in association with inflammation processes, traumatic brain injury, neurodegeneration and cancer.[1] The activation of CB2 leads to an anti-inflammatory action. Therefore, the non-invasive assessment of the CB2 availability with PET could improve the decision-making for CB2-directed therapies. We developed a series of fluorinated naphthyridine-2-one-carboxamides as CB2 ligands, of which [18F]LU14[2] and [18F]LU13 were radiosynthesized and biologically evaluated. Methods: The two radioligands [18F]LU14[2] and [18F]LU13 were developed starting from appropriate precursor compounds.The fraction of radiometabolites was quantified in isolated plasma and brain samples at 30 min p.i. The CB2 binding affinities selectivities (expressed and determined from KD and Ki values of both radioligands were determined in vitro. PET studies were performed to evaluate the radioligand uptake into the brains of rats overexpressing the hCB2(D80N) in the right striatum[3]. Results: Favourable properties where achieved for [18F]LU14, which could be further improved for [18F]LU13 (AM, affinity, selectivity and metabolic stability). In rats bearing the local overexpression of the hCB2 a target-specific and reversible uptake for both radioligands was demonstrated. [18F]LU14 reached a TAC peak SUV of 3.3 ± 0.6 at 7.4 ± 2.8 min p.i., and the SUVr (target region–to–cerebellum) was stable between 6.6 and 7.0 after 30 min p.i. For [18F]LU13 a stable SUV of 3.6 ± 0.9 after 26 min p.i. was reached and a close to linearly increasing SUVr (target region–to–cerebellum) up to 8.8 ± 4.3 at 60 min p.i. was determined (slope = 0.15 SUV/min; R² =.0.8). Conclusion: [18F]LU14 and [18F]LU13 showed an excellent ability to image the CB2 receptors in vivo. Additionally, [18F]LU14 revealed a faster washout from the non-target regions in the brain, compared to [18F]LU13. References: [1] Stasiulewicz et al. IJMS, 2020, 21, 2778; [2] Te

Introduction The cannabinoid receptor 2 (CB2R) is involved in inflammatory processes [1], whereby an increased expression correlates with malignancy in various cancer types like human epidermal growth receptor 2 positive (HER2+) or triple negative breast cancer (TNBC) [2]. Hence, the CB2R is suggested as a pharmacological target and prognostic marker for stratification and staging of patients [3]. In the present in vitro studies, we investigated the expression of the CB2R in HER2+ and TNBC models, as well as the potential of our novel radioligand [18F]JHU94620-d8 to assess the CB2R availability in TNBC models. Methods The colocalisation of CB2R with Iba1 (macrophages) and CD31 (blood vessels) in cryosections of mouse TNBC 4T1 tumours heterotopically implanted in both NMRI-nude and Balb/c mice was investigated by immunofluorescence staining (IF). The CB2R expression in 4T1, the human HER2+ cell lines HCC1954 (HCC and LCC2) and human TNBC cell lines MDA-MB-231 (MDA and BrM2) was determined by IF. Competitive radioligand binding assays with the CB2R-specific ligands [3H]WIN55,212-2 and [3H]A-836339 were performed vs. 10 µM JHU94620-d8, GW405833 and WIN55,212-2, and A 836339 as competitor (n=1). Autoradiography with the CB2R-specific [18F]JHU94620-d8 vs. 10 µM competitor was performed with cryosections obtained from 4T1 tumours (n=3) as well as rat brains harbouring a local overexpression of the human CB2R (AAV-hCB2R, n=1) [4]. Results A high correlation between the heterogeneously distributed CB2R and Iba1, and a weak correlation between CB2R and CD31 was found in 4T1 tumours. Colocalisation of CB2R and Iba1 (Balb/c: Pearson’s coefficient r=0.69±0.03, Manders’ coefficient M1: 0.7±0.12; NMRI-nude: r=0.7±0.12, M1=0.71±0.15) or CD31 (Balb/c: r=0.35±0.09, M1=0.15±0.02; NMRI-nude: r=0.35±0.11; M1=0.19±0.09) was independent of the mouse breed (CB2R/Iba1: pr=0.9, pM1=0.972; CB2R/CD31: pr=0.41, pM1=0.52). By IF the expression of CB2R and HER2 was confirmed in HCC and LCC2, but

Objective: The programmed cell death-ligand 1 (PD-L1) is upregulated on many different cancers and allows the tumor cells to evade immune response through binding to the PD-1 receptor.[1] Monoclonal antibodies, i.e. checkpoint inhibitors, are able to break this blockade and thus reactivate the immune system.[2] However, only 30% of the patients respond to antibody-based immunotherapy. Because PD-L1 is heterogeneously expressed within and across tumor sites, there is an urgent clinical need for a non-invasive, diagnostic imaging approach helping for therapy decision. Radiotracers for PET and SPECT imaging are able to meet these requirements. Especially small molecules are favourable, because of their short clearance times and for providing high imaging contrast.[3] Methods: Modification of two literature known small molecule PD-L1 inhibitors with water-solubilizing groups, different linkers and a DOTA chelator resulted in six different radioligands. Labeling was performed with Cu-64 (HZDR, 30 MeV TR-FLEX cyclotron) and binding affinities to PD-L1 were determined in vitro on transduced PC3 cells stably overexpressing human PD-L1. Qualitative PET scans (nanoSCAN PET/CT scanner, Mediso) were performed in NMRI-FoxN1-nude mice bearing PC3-hPD-L1 xenografted tumors. Results: Organic synthesis started from biaryl building blocks (R1 = H, R2 = Br and R1 = R2 = Me), which underwent a Mitsunobu reaction with the central chloroaryl moiety. The bis(sulfonic acid) group was attached via a sarcosine spacer. Three different linker structures were synthesized and attached by Cu(I)-catalyzed click reaction. Synthesis was finished with DOTA conjugation and subsequent quantitative labeling with Cu-64 under standard labeling conditions was achieved. Using the shake flask method, log(D) values ranging from –1.5 to –2.5 were obtained. Saturation binding assays revealed that biphenyl compounds with R1 = R2 = Me showed promising binding affinities to PD-L1 (KD between 60 and 123 nM). In mic

Introduction The cannabinoid receptor 2 (CB2R) is involved in inflammatory processes [1], whereby an increased expression correlates with malignancy in various cancer types like human epidermal growth receptor 2 positive (HER2+) or triple negative breast cancer (TNBC) [2]. Hence, the CB2R is suggested as a pharmacological target and prognostic marker for stratification and staging of patients [3]. In the present in vitro studies, we investigated the expression of the CB2R in HER2+ and TNBC models, as well as the potential of our novel radioligand [18F]JHU94620-d8 to assess the CB2R availability in TNBC models. Methods The colocalisation of CB2R with Iba1 (macrophages) and CD31 (blood vessels) in cryosections of mouse TNBC 4T1 tumours heterotopically implanted in both NMRI-nude and Balb/c mice was investigated by immunofluorescence staining (IF). The CB2R expression in 4T1, the human HER2+ cell lines HCC1954 (HCC and LCC2) and human TNBC cell lines MDA-MB-231 (MDA and BrM2) was determined by IF. Competitive radioligand binding assays with the CB2R-specific ligands [3H]WIN55,212-2 and [3H]A-836339 were performed vs. 10 µM JHU94620-d8, GW405833 and WIN55,212-2, and A 836339 as competitor (n=1). Autoradiography with the CB2R-specific [18F]JHU94620-d8 vs. 10 µM competitor was performed with cryosections obtained from 4T1 tumours (n=3) as well as rat brains harbouring a local overexpression of the human CB2R (AAV-hCB2R, n=1) [4]. Results A high correlation between the heterogeneously distributed CB2R and Iba1, and a weak correlation between CB2R and CD31 was found in 4T1 tumours. Colocalisation of CB2R and Iba1 (Balb/c: Pearson’s coefficient r=0.69±0.03, Manders’ coefficient M1: 0.7±0.12; NMRI-nude: r=0.7±0.12, M1=0.71±0.15) or CD31 (Balb/c: r=0.35±0.09, M1=0.15±0.02; NMRI-nude: r=0.35±0.11; M1=0.19±0.09) was independent of the mouse breed (CB2R/Iba1: pr=0.9, pM1=0.972; CB2R/CD31: pr=0.41, pM1=0.52). By IF the expression of CB2R and HER2 was confirmed in HCC and LCC2, but

Objectives Bispidines (3,7-diazabicyclo[3.3.1]nonanes) are of great interest for the use in radiopharmaceutical applications. Combining the advantages of highly preorganised rigid macrocyclic ligands and the flexibility of open-chain ligands, they are able to form highly stable complexes at mild reaction conditions with a broad range of di- and trivalent metal ions.1,2 Here, we present a nonadentate bispidine ligand (Fig. 1) labelled with [177Lu]LuCl3, [225Ac]AcCl3 and [111In]InCl3 at mild conditions and report their stability and inertness in aqueous solution and human serum.3 The results in terms of radiolabelling conditions and serum stabilities are compared with the “gold standard” DOTA, which requires harsh radiolabelling conditions, and the octadentate bispidine ligand H2bispa.2,4 Methods The bispidine ligand was synthesised according to literature on a multigram scale, with an overall yield of 5% over 9 steps.2 Radiolabelling experiments of the nonadentate bispidine ligand with [177Lu]Lu3+ and [225Ac]Ac3+ were carried out at 40 °C using 150 mM NH4OAc buffer (pH 6). Radiolabelling with [111In]In3+ was performed in the same buffer at room temperature. For comparison, the DOTA and the octadentate bispidine ligand H2bispa2 were labelled with the trivalent radiometals as well. The radiochemical yields and purities were monitored via radio-TLC and radio-HPLC for different ligand concentrations after 5 min, 30 min and 60 min. Radiostabilities in human serum were studied by radio-TLC and radio-SEC after 1 h, 1 d, 3 d and 7 d. Results Radiolabelling experiments gave quantitative yields for the formation of both 177Lu- and 225Ac‑complexes at 40 °C after 5 minutes for ligand concentrations of 10-6 mol/L. With [111In]In3+ a quantitative conversion was obtained even at room temperature after 60 minutes with a ligand concentration of 5·10-6 mol/L. For [177Lu]Lu3+, a molar activity of >100 MBq/nmol, for [225Ac]Ac3+ 0.2 MBq/nmol and for [111In]In3+ >20 MBq/nmol was found at

Bispidines (3,7-diazabicyclo[3.3.1]nonane) and their derivatives act as bifunctional chelating agents (BFCAs). Combining the advantages of highly preorganised rigid macrocyclic ligands and the flexibility of open-chain ligands, bispidines are able to form highly stable complexes at mild reaction conditions with a broad range of di- and trivalent metal ions. Of particular interest, they allow the coupling to biological targeting vectors such as peptides, peptidomimetics, T cell receptor derivatives as well as any kind of natural and recombinant antibody derivatives to construct effective radiopharmaceuticals for diagnostic and therapeutic purposes. Here, we present a nonadentate bispidine ligand (Figure 1), which forms stable and inert complexes with [177Lu]LuCl3, [225Ac]AcCl3 and [111In]InCl3 at mild conditions. This is unique so far, as few chelators are able to tightly bind both Lu(III) and Ac(III) under mild conditions (physiological pH, T<40°C) with fast complexation kinetics. We investigated the thermodynamic and kinetic properties of the radio-complexes. For targeting, the chelator was functionalised with a peptidic somatostatin analogue (Tyr3-octreotate, TATE), which addresses the somatostatin subtype receptor 2 in neuroendocrine tumors. The bispidine-TATE conjugate was labelled with 177Lu(III) and 225Ac(III) and investigated in SSTR2-positive mouse pheochromocytoma (MPC) and human pancreatic carcinoid tumour (BON-SSTR2) cell lines. Moreover, quantitative small animal SPECT imaging showed specific uptake of the [177Lu]Lu-conjugate in vivo in naturally SSTR2-positve MPC tumour allografts. Some structural optimisation will be required to further reduce off-target accumulation. However, the bispidine chelator shows a promising potential for a broad application in nuclear medicine, both in imaging and radionuclide therapy.

Aim: The programmed cell death ligand 1 (PD-L1) is overexpressed by various cancers, resulting in a downregulation of the local immune response and therefore enabling further tumor growth.[1] Immune checkpoint inhibitors (ICIs) can reactivate the immune system, however, only 30% of the patients respond to an ICI monotherapy.[2] Since PD-L1 is heterogeneously expressed within and across tumor sites, there is an urgent clinical need for non-invasive diagnostic tools to support the therapeutic decision process. Small molecule-based radiotracers for noninvasive molecular PD-L1 imaging offer improved tissue penetration, fast blood clearance and low immunogenicity over radiolabeled antibodies. Methods: Based on a published small molecule PD-L1 inhibitor, 10 different radioligands were synthesized and radiolabeled with copper-64 (HZDR, 30 MeV TR-FLEX cyclotron). Binding affinities were determined on PC3 cells stably overexpressing human PD-L1. For in vivo evaluation, qualitative PET/CT imaging (nanoSCAN PET/CT, Mediso) was performed in NMRI-FoxN1-nude mice bearing PC3-hPD-L1 xenografted tumors. Results: Modification of the PD-L1 binding motif with strongly water-solubilizing sulfonate and phosphonate groups, different linker units and a NODAGA-chelator in 21-25 organic synthesis steps (12-13 longest linear sequence) yielded 10 different ligands [3]. The 64Cu-labelled radiotracers exhibited logD values between -3.17 and -4.15 for six ligands of the first series, with dissociation constants (Kd) between 80.5 and 532.8 nM, as determined by saturation binding assays. Depending on the number and pattern of sulfonate and phosphonate groups, the in vivo experiments showed drastically different pharmacokinetic profiles: Compounds bearing a less hydrophilic linker showed improved tumor uptake. Three sulfonates resulted in increased blood circulation times of up to 24 h due to albumin binding increased renal clearance but also low tumor uptake (SUVmax = 1.4). Substitution of one sul

Objectives The prostate-specific membrane antigen (PSMA) is expressed in most cases of prostate cancer at considerably higher levels in tumor cells compared to healthy tissues [1-3] and its upregulation occurs in all stage of the disease [4, 5]. Therefore, PSMA has emerged as an attractive target for molecular imaging and especially targeted radionuclide therapy (endoradiotherapy) of metastatic castration-resistant prostate cancer (mCRPC), given the example of [177Lu]Lu-PSMA-617. We recently described the synthesis and in-depth characterization of PSMA radioligands for targeted alpha therapy with actinium-225 [6]. Our present study aimed at the design, synthesis and preclinical evaluation of albumin-binding PSMA ligands in order to optimize their tissue distribution profile and to improve their pharmacokinetic properties. Methods Two novel compounds were prepared by combining a macropa chelator with one or two lysine-ureido-glutamate–based PSMA-binding entities equipped with 4-(p-iodophenyl)butyrate residues. The albumin-binding properties of the 225Ac-labeled conjugates were investigated in vitro using mouse, rat and human serum. The specific interaction of both compounds with human serum albumin was confirmed by microscale thermophoresis. Cell culture-based studies regarding radioligand affinity and clonogenicity were performed on PSMA-positive LNCaP cells. The biodistribution of the radioconjugates was analyzed in LNCaP tumor-bearing mice with ensuing investigation of tissue toxicity by histological examinations. Results Radiolabeling of both PSMA ligands with 225Ac was achieved at up to 5 MBq/nmol with >99% radiochemical purity. In vitro assays confirmed considerable binding of the radioligands to mouse, rat and human serum proteins. Cell binding and survival studies revealed a higher cell binding affinity and an improved cell killing efficiency for the radioconjugate with two PSMA-binding entities compared to the derivative with only one targeting motif. Biodis

Introduction Isocitrate dehydrogenase mutation 1 (mIDH1, IDH1R132H) is commonly reported in gliomas and is proposed as an interesting target for the diagnosis, prognosis and therapy for patients with gliomas. Some preclinical evaluations of 125I- or 18F-labeled mIDH1 ligands are reported for non-invasive imaging of mIDH1-bearing gliomas,1-3 however, to date, no radiotracers for PET imaging of mIDH1 are clinically available owing to hitherto low potency, selectivity and metabolic stability. Herein, the efforts to develop a novel mIDH1 selective PET radiotracer for imaging gliomas with mIDH1 are reported. Methods Compound GSK321 bearing the absolute configuration 3-R, 27-S (Fig.1) has been selected as the starting point to develop an 18F-labelled PET radioligand for imaging of mIDH1 due to the high potency (IC50 mIDH1 = 4.6 nM).4 A non-enantioselective synthesis of GSK321 was envisaged to get access to all stereoisomers for biological evaluation. The separation of the four stereoisomers of GSK321 was attempted via isocratic semi-preparative chiral HPLC using a CHIRALPAK IA column (10*250mm, 5µm) and an eluent mixture of ACN/H2O (1/1, v/v) at a flow rate of 3 mL/min. The IC50 values of separated stereoisomers of GSK321 were measured by enzymatic assays for wildtype IDH1 and IDH1R132H coupled to diaphorase. The introduction of the 18F-label into the most potent and selective stereoisomer of GSK321 will be performed via the copper-mediated radiofluorination of the corresponding boronic acid pinacol ester. Results The stereoisomeric mixture of GSK321 was synthesized from N-boc-protected piperidone with an overall yield of 22 % over seven steps. In a first attempt to separate the stereoisomers by semi-preparative chiral HPLC, only one enantiomeric pair [(3-R,27-S)- and (3-S,27-R)-GSK321)]was obtained in pure form which was further characterized by NMR spectroscopy. For the isolation of other enantiomeric pair [(3-R,27-S)- and (3-S,27-R)-GSK321], further chiral HPLC methods

PET data, mice; i.v. administration of [18F]FLUDA with and without pre-administration of istradefylline

The data publication contain: 1) Radiosynthesis data (Scheme of the synthesis module; RP-HPLC chromatograms of formulated [18F]BA3; MLC chromatograms of in vivo metabolism studies) 2) Biological data (Baseline TAC of CD-1 mice brain, biodistribution after i.v. injection of [18F]BA3) 3) Analytical data (1H, 13C, 19F NMR spectra; LC-MS chromatograms for final products)

Objectives: During the last 15 years several PSMA PET ligands for prostate cancer imaging have been developed resulting in the recent approvals of 68Ga-PSMA-11, 18F-PSMA-1007 and 18F-DCFPyL.[1,2] However, 99mTc remains a popular radiometal for SPECT imaging due to its longer half-life and availability from 99Mo/99mTc generators especially in outpatient imaging centers. Due to the widespread availability of SPECT cameras PSMA SPECT ligands have the potential to substantially extend the availability of PSMA-based imaging, but currently no PSMA SPECT ligand is approved. MIP-1404, PSMA-I&S and HYNIC-iPSMA are rare examples of PSMA SPECT tracers in clinical development. Accordingly, the aim of our study was to develop a PSMA ligand for 99mTc SPECT imaging of prostate cancer based on an N2S2 chelator, which enables reliable radiolabeling to form stable 99mTc complexes.[3] Methods: A number of compounds, which contain the PSMA binding motif Glu-urea-Lys, a varying linker and a bisaminothiol (BAT)-type N2S2 chelator, were synthesized. Selected compounds were radiolabeled with 99mTc, followed by assessment of in vitro stability of the formed complexes via radio-HPLC. The specific binding affinity towards PSMA and the internalization of the radioligands were examined in LNCaP cells, supplemented by autoradiographic studies. Tissue distribution and tumor accumulation were evaluated in LNCaP-tumor bearing mice via quantitative SPECT/CT imaging, benchmarked with [99mTc]Tc-PSMA-I&S[4] and [68Ga]Ga-PSMA-11. Results: Among the six 99mTc radioligands synthesized and examined, [99mTc]TcO-ABX474 showed most favorable properties. Radiolabeling of ABX474 (50 µg) was achieved starting from [99mTc]NaTcO4 (0.2-2 GBq) in saline (1.4 mL) using SnCl2 (1 µg in 0.01 M HCl) as reducing agent, in presence of calcium-D-heptagluconate (10 µg) and D-mannitol (1 mg) at pH 5-6. Incubation at r.t. for 20 min followed by heating at 80°C for 20 min afforded the product-containing solution with a radioche

Objectives The prostate-specific membrane antigen (PSMA) is expressed in most cases of prostate cancer at considerably higher levels in tumor cells compared to healthy tissues [1-3] and its upregulation occurs in all stage of the disease [4, 5]. Therefore, PSMA has emerged as an attractive target for molecular imaging and especially targeted radionuclide therapy (endoradiotherapy) of metastatic castration-resistant prostate cancer (mCRPC), given the example of [177Lu]Lu-PSMA-617. We recently described the synthesis and in-depth characterization of PSMA radioligands for targeted alpha therapy with actinium-225 [6]. Our present study aimed at the design, synthesis and preclinical evaluation of albumin-binding PSMA ligands in order to optimize their tissue distribution profile and to improve their pharmacokinetic properties. Methods Two novel compounds were prepared by combining a macropa chelator with one or two lysine-ureido-glutamate–based PSMA-binding entities equipped with 4-(p-iodophenyl)butyrate residues. The albumin-binding properties of the 225Ac-labeled conjugates were investigated in vitro using mouse, rat and human serum. The specific interaction of both compounds with human serum albumin was confirmed by microscale thermophoresis. Cell culture-based studies regarding radioligand affinity and clonogenicity were performed on PSMA-positive LNCaP cells. The biodistribution of the radioconjugates was analyzed in LNCaP tumor-bearing mice with ensuing investigation of tissue toxicity by histological examinations. Results Radiolabeling of both PSMA ligands with 225Ac was achieved at up to 5 MBq/nmol with >99% radiochemical purity. In vitro assays confirmed considerable binding of the radioligands to mouse, rat and human serum proteins. Cell binding and survival studies revealed a higher cell binding affinity and an improved cell killing efficiency for the radioconjugate with two PSMA-binding entities compared to the derivative with only one targeting motif. Biodis

The cannabinoid receptor type 2 (CB2R) is an attractive target for diagnosis and therapy of neurodegenerative diseases and cancer. Recently, we reported a novel naphthyrid-2-one based positron-emission tomography (PET) radioligand for imaging of the CB2R in the brain ([18F]5). In this study we aimed at the development of a novel 18F-labeled CB2R radioligand with improved binding properties and metabolic stability. Starting from the structure of 5, we developed a novel series of fluorinated derivatives by modifying the substituents at the naphthyrid-2-one subunit. Compound 28 (LU13) was identified with the highest binding affinity and selectivity versus CB1R (CB2RKi = 0.6 nM; CB1RKi/CB2RKi > 1000) and was selected for radiolabeling with 18F and biological characterization. The radiofluorination was performed starting from the corresponding bromo-precursor (31) bearing a fully deuterated N-alkyl chain to protect against defluorination. The in vitro evaluation of [18F]LU13 proved the high binding affinity of the radioligand towards rat (rCB2RKD = 0.2 nM) and human (hCB2RKD = 1.1 nM) CB2R. Metabolism studies in mice revealed a metabolic stability at 30 min p.i. with fractions of parent compound of >80% in the brain and 90% in the spleen with only trace of defluorination products detected in plasma. PET imaging in a rat model of vector-based/related overexpression in the striatum revealed a high signal to background ratio, demonstrating the ability of [18F]LU13 to reach and selectively label the hCB2R in the brain. Thus, [18F]LU13 is a novel and highly promising PET radioligand for the imaging of up regulated CB2R expression under pathological conditions in

We recognize 131Ba as a SPECT radionuclide, which provides a diagnostic match for the therapeutic alpha-emitting radionuclides 223Ra and 224Ra. The gamma-emitter barium-131 (t½ = 11.5 d) decays with an energy of 123.8 keV (30% intensity) of the first decay via cesium-131 (t½ = 9.7 d) to stable xenon-131, each by electron capture. Our aim was to develop of a straightforward resin-based radiochemical separation to yield 131Ba with high radionuclide purity. Furthermore, the radiolabeling of the complexing agent macropa with [131Ba]Ba2+ using mild labeling conditions was intended. For this purpose, different TLC systems as reaction control were utilized. The radiopharma-cological characterization of 131Ba-labeled macropa in comparison to uncomplexed [131Ba]Ba2+ was carried out in healthy mice, including biodistribution and small animal SPECT/CT experiments.

Objectives: The combination of non-invasive molecular imaging (PET/SPECT)- and optical imaging (OI) techniques for tumor identification and resection are emerging. This powerful strategy promises to precisely differentiate between healthy and affected tumor tissues which is of most relevance for preoperative planning (prestaging) followed by R0-tumor resection via image-guided intraoperative surgery. The goal of this work is the development of radiolabeled near-infrared (NIR) fluorophores for PET/SPECT and optical imaging. The fluorophores were prepared for radiolabeling with the positron emitter fluorine-18 and with the gamma emitter iodine-123 for SPECT imaging with the aim to elucidate their potential as imaging agents for the detection of tumor tissues. Moreover, the radiolabeled dyes are intended to be bioconjugated to the PSMA-1007 binding motif, as a generic prominent tumor targeting vector for enrichment in prostate tumors (1). Methods: We have developed fluorophores belonging to the silicon rhodamine (SiR) family with optical properties in the NIR spectral range (2). The photostable fluorophores have been characterized using NMR-, UV/VIS/NIR-spectroscopy and mass spectrometry. Furthermore the SiRs were radiolabeled by using the approach for copper-mediated radiolabeling of arylboronic acids, functioning as precursors both for fluorine-18 and iodine-123 labeling (3). The radiolabeling conditions were optimized based on radiochemical conversions (RCC) as analyzed by using radio-HPLC and radio-TLC. The model and lead compound [18F]F-SiR was isolated by radio-HPLC followed by SPE for further in vitro experiments, e.g. in vitro stability was determined in human serum. Results: Novel boronic acid functionalized SiRs with chemical yields up to 68% were received via multistep organic syntheses. The blue dyes show high extinction coefficients up to 95.000 M-1cm-1, quantum yields of 0.33 and high photo stability making them useful for NIR optical imaging. After caref

Ziel/Aim Although CAR T-cell therapy has demonstrated tremendous clinical efficacy particularly in hematological malignancies, the success in solid tumors is still limited. The combination of the immunotherapeutic (Uni)CAR T-cell therapy with target modules (TM) in solid tumors and radiotherapy could be an additional treatment option. Therefore, we developed a human prostate stem cell antigen (PSCA)-specific, IgG4-based TM radiolabeled with copper-64 (Cu-64) for imaging and with actinium-225 (Ac-225) for treatment. Methodik/Methods A novel human PSCA-specific IgG4-based TM was conjugated with DOTAGA and radiolabeled with (Cu-64) and (Ac-255). The imaging and therapy were studied in NMRI Foxn1 nu/nu mice with xenotransplanted PSCA-expressing PC-3 tumors. Metabolic changes of the tumors were visualized with 18F-PSMA (PET), the physical size of the tumors and the distance between the vessels in the tumors (US) were measured. Ergebnisse/Results The radiochemical yield for the Cu-64/Ac-255 TM was 96 % and 52 % respectively, the RCP of the products were g.t. 97 %. The xenotransplanted mice were intravenously injected with the Cu-64 labeled TM given as single dose. After fast distribution, the blood activity concentration decreased very slowly. At 31 h p.i. the activity was maximal in the tumors thereby reaching the optimal tumor to background ratios and only the liver was also visible with much lower activity. The Ac-225 treatment resulted in significant lower tumor size as compared with the control group after 40 days. Doubling time of tumor volume was increased from 15.0 days (control) to 38.6 days of the treatment group. The 18F-PSMA ligand uptake was decreased in the tumor periphery. In comparison to the tumor size the vessel density decreased to a lower extent. Schlussfolgerungen/Conclusions We here present a Cu-64/Ac-225 labeled TM that allows the combination of (Uni)CAR T-cell immunotherapy with imaging with the Cu-64 labeled TM version and radiotherapy with the Ac

Objectives: Finding optimal 18F-fluorination conditions represents a critical and often time-consuming step in radiotracer development. Microfluidic or lab-on-a-chip devices are modern tools for that purpose but not accessible everywhere. Inspired by 18F-chemistry in low volumes based on a MAX/MCX-trapping technique for one complete 18F-batch,[1] we herein present an 18F-labeling approach using low volume aliquots (<100 µL) of defined QMA-eluates in HPLC vials as reaction vessels for optimizations as well as the preparation of radiotracers for preclinical studies. Methods: For optimization experiments, 1-80 MBq [18F]fluoride was eluted from QMA cartridges with defined mixtures of phase transfer catalyst (Kryptofix®222), base (such as K2CO3, KHCO3, KH2PO4), and 2-3% water in acetonitrile[2]. 25 or 50 µL aliquots of the eluates were pipetted into 1.5 mL HPLC vials and the sealed vials were consecutively dried once at 90°C for 3 min with a helium stream. After processing up to 15 vials in one batch, 25 or 50 µL precursor stock solution (1-20 mg/mL in MeCN, DMF, or DMSO) was added and the sealed vials were heated at defined temperatures (60-140°C) and times (5-15 min) by using three heaters equipped with aluminum blocks. Samples were 4-fold diluted with acetonitrile/water 50/50 for analysis by radio-TLC/radio-HPLC. 18F-trapping/elution at higher activity levels (~20 GBq [18F]fluoride) was performed by using a radiosynthesizer (Tracerlab FXFN) followed by transfer into a lead container having three small bores as inlet, vent needle and withdrawal port. A self-made pipet tip-to-cannula adapter allowed withdrawal of defined 25-100 µL aliquots at an activity level of ~13 MBq/µL for further processing under optimized conditions as described above. Results: The use of small reaction volumes and HPLC vials enabled an efficient 18F-optimization workflow to examine rapidly a variety of reaction parameters (>50 reactions/day) using minimal amounts of precursor. Utilizin

Aim/Introduction: In recent years quinoline-based small molecules targeting the fibroblast activation protein alpha (FAP) have gained interest for imaging a variety of tumor entities (1). A number of radiotracers for SPECT and PET have been developed, but so far only three FAP inhibitor (FAPI) radioligands have been reported to be radiolabeled with fluorine-18 (2,3,4). This study shows the optimization and automation of the radiofluorination of FAPI-74. Materials and Methods: (S)-(4-Carboxymethyl-7-{2-[4-(3-{4-[2-(2-cyano-pyrrolidin-1-yl)-2-oxoethylcarbamoyl]-quinolin-6-yloxy}-propyl)-piperazin-1-yl]-2-oxo-ethyl}-[1,4,7]triazonan-1-yl)-acetic acid, commonly referred to as FAPI-74, was radiolabeled using the [18F]AlF chelation method. Starting from [18F]fluoride, the reaction with AlCl3, chelate formation and subsequent purification was initially optimized by manual syntheses. Optimization included the examination of different anion exchangers (QMA light, PSHCO3) and elution solutions (NaOAc buffer pH4, 0.9% NaCl) as well as careful adjustment of the reaction parameters time (0-20 min), temperature (r.t. to 100°C), amount of AlCl3 and NaOAc buffer pH4, solvents (DMSO, EtOH), and precursor concentration (1-350 µM). Radiochemical conversion (RCC) was determined by radio-UPLC of the crude reaction mixtures. Selected reaction mixtures were analyzed after decay using UPLC-MS to identify non-radioactive byproducts. The optimized radiosynthetic procedure was transferred to a fully automated radiosynthesizer (TRACERlab FXFN) and the final product was purified and formulated using semi-preparative HPLC and SPE. Results: Under optimized conditions, RCC of [18F]AlF-FAPI-74 of > 99% was still observed at precursor concentrations as low as 12 µM FAPI-74 after reaction in a 1:1 molar ratio with AlCl3 in DMSO/sodium acetate buffer at pH 4 at 80°C for 15 minutes. Transfer of optimized conditions and upscaling was successfully achieved and delivered radiochemica

Objectives: The monocarboxylate transporters 1 and 4 (MCT1/4) are integral plasma membrane proteins that bi-directionally transport lactate as well as small monocarboxylated molecules. They are highly expressed in several tumors. BAY-8002 belongs to a class of compounds that have been identified as novel and specific MCT1 inhibitors based on functional high-throughput screening assays using a panel of cell lines highly sensitive towards MCT1 inhibition [1]. IC50 values of 1 to 12 nM and ca. 500–fold selectivity towards MCT4 have already been reported for BAY-8002 [1]. Here we designed an 18F-labeled analog of BAY-8002 ([18F]F-BAY-8002) aiming to image mainly MCT1 upregulation considering the fact that the absence of MCT4 expression in many types of cancer may not be necessarily sufficient as a single marker to predict treatment response [2]. Methods: BAY-8002 and its novel fluorinated analog (F-BAY-8002) were synthesized based on reported procedures [1]. As BAY-8002 already contains a chloro substituent which could serve as leaving group, the compound was considered as precursor for radiofluorination via a halogen-fluorine exchange approach (Figure 1A). [18F]F-BAY-8002 was radiolabeled via a one-step aromatic nucleophilic substitution reaction (SNAr) using 2-5 mg of precursor in the presence of the [18F]KF/K222/K2CO3 complex in dimethyl sulfoxide (DMSO) at 150 °C within 5 min (Figure 1B). Figure 1. (A) Synthesis of BAY-8002 and its novel fluorinated analog; (B) Radiosynthesis of [18F]F-BAY-8002. Separation of [18F]F-BAY-8002 from the chlorinated precursor was performed by semi-preparative HPLC. The tracer was finally purified via solid-phase extraction (Sep-Pak® C18 light cartridge) and formulated in 10% EtOH/saline solution to be ready for biological evaluations. Results: Despite using identical conditions [1], the novel fluorinated analog F-BAY-8002 was obtained in only 4% overall yield due to formation of by-products which have not been observed during the synthe

Radiolabeled fluorescent dyes are decisive for bimodal imaging as well as highly in demand for nuclear- and optical imaging. Silicon-rhodamines (SiRs) show unique near-infrared (NIR) optical properties, large quantum yields and extinction coefficients as well as high photostability. Here, we describe the synthesis, characterization and radiolabeling of novel NIR absorbing and emitting fluorophores from the silicon-rhodamine family for use in optical imaging (OI) combined with positron emission tomography (PET) or single photon emission computed tomography (SPECT), respectively. The presented photostable SiRs were characterized using NMR-, UV-Vis-NIR-spectroscopy and mass spectrometry. Moreover, the radiolabeling conditions using fluorine-18 or iodine-123 were extensively explored. After optimization, the radiofluorinated NIR imaging agents were obtained with radiochemical conversions (RCC) up to 70% and isolated radiochemical yields (RCY) up to 54% at molar activities of g.t. 70 GBq/µmol. Radioiodination delivered RCCs over 92% and allowed to isolate the 123I-labeled product in RCY of 54% at a molar activity of g.t. 7.6 TBq/µmol. The radiofluorinated SiRs exhibit in vitro stabilities g.t. 70% after two hours in human serum. The first described radiolabeled SiRs are a promising step toward their further development as multimodal PET/SPECT-NIR imaging agents for planning and subsequent imaging-guided oncological surgery.

Prostate-specific membrane antigen (PSMA) has shown to be a promising target for diagnosis and therapy (theranostics) of prostate cancer. An introducing overview on the regulatory status of PSMA-targeting radiopharmaceuticals in the US and Europe is given. We review developments in the field of radio- and fluorescence-guided surgery and targeted photodynamic therapy as well as multitargeting PSMA inhibitors also addressing albumin and GRPr. Technical and quality aspects of PSMA-targeting radiopharmaceuticals are described and new radiolabeling strategies are presented. Finally, insights are given into production, application and potential of alternatives beyond the commonly used radionuclides for radiolabeling PSMA inhibitors. An additional re-finement of radiopharmaceuticals is required in order to further improve dose-limiting factors like nephrotoxicity and salivary gland uptake during endoradiotherapy. The combination of ra-dionuclide therapy with therapy options of other disciplines shows a way to improve the treat-ment of patients.

Purpose. First-line treatment of patients with recurrent, metastatic prostate cancer involves hormone therapy with or without additional systemic therapies. Prostate-specific membrane antigen (PSMA) positron emission tomography (PET)/computed tomography (CT) allows the detection of oligometastatic disease that may be amenable to image-guided radiotherapy. The current study classifies the type and localization of metastases and the clinical outcome of PSMA-PET/CT-guided radiotherapy to selected metastases. Materials and methods. Between 2011 and 2019, 86 patients with recurrent, oligometastatic prostate carcinoma were identified by PSMA-PET/CT and were treated with image-guided radiotherapy of their metastases. Sites of relapse were characterized, and the primary endpoint overall survival (OS), biochemical progression-free survival (bPFS), and androgen deprivation therapy (ADT)-free survival were tabulated. Results In total, 37% of the metastases were bone metastases, 48% were pelvic nodalmetastases, and 15% were nodalmetastases outside of the pelvis. After PSMA-guided radiotherapy, a biochemical response was detected in 83% of the cohort. A statistically significant decrease in the standard uptake value (SUV) was seen in irradiated metastases. After a median follow-up of 26 months, the 3-year OS and bPFS were 84% and 55%, respectively. The median time of ADT-free survival was 13.5 months. A better clinical outcome was observed for patients receiving concomitant ADT or more than 24 fractions of radiation. Conclusion. PSMA-guided radiotherapy is a promising therapeutic approach with excellent infield control for men with oligorecurrent prostate carcinoma. However, prospective, randomized trials are necessary to determine if this approach confers a survival advantage.

With the exception of beryllium, every alkaline earth metal is characterized by a calcimimetic behavior. Thus, in vivo biodistribution mostly occurs in form of a massive accumulation in bone tissues, consisting of hydroxyapatite to a major extent. Apart from the lightest elements beryllium and magnesium, animal studies and human studies regarding the overall in vivo behavior were carried out by using radioisotopes of the elements calcium, strontium, barium, and radium. To date, only strontium with its radioisotopes gained importance for applications in nuclear medicine, mainly for pain-reducing and palliative treatment of bone metastases. In contrast, barium isotopes can be useful imaging agents and possible diagnostic analogues for theranostic approaches. This review focuses on the characteristic and chemical behavior of barium compounds, possible radioactive barium isotopes for future applications in nuclear medicine and radiopharmacy as well as recent results regarding barium-131 as diagnostic match for radium isotopes used in targeted alpha therapy.

Die klinische Bereitstellung von Radiopharmaka für diagnostische und therapeutische Zwecke ist eine der zentralen Aufgaben der konventionellen Radiopharmazie, denn sie ist das Herzstück einer jeden modernen Nuklearmedizin. Neben einem großen, aber planbaren, logistischen Aufwand ist die Versorgung mit Radiopharmaka sowohl mit radiochemischen als auch regulatorischen Herausforderungen verbunden. Das betrifft beispielsweise die zuverlässige Verfügbarkeit einzelner Radionuklide aufgrund ihrer Kurzlebigkeit und die Erfüllung obligatorischer Qualitätskontrollen. Daneben widmen sich die Radiopharmazeutischen Wissenschaften ihrem Forschungsauftrag, der in der Erforschung neuer Radionuklide, der Entwicklung und der (prä-)klinischen Testung neuer Radiopharmaka für Diagnose und Therapie und der Weiterentwicklung der bildgebenden Verfahren SPECT und PET sowie der hybriden Kombinationen mit MRT und CT, besteht. In diesem Sinne ist diese Ausgabe des Nuklearmediziners ganz den neuesten Entwicklungen auf dem Gebiet der Radiopharmazie gewidmet, welche sich mittlerweile über klassische Ansätze hin zu theranostischen Anwendungen in Form von diagnose-geleiteten Therapien entfaltet.

Resection of tumor tissue represents one of the standard curative treatment options for the clinical management of prostate cancer. However, intraoperative localization and precise delineation of malignant tissue from surrounding healthy structures still remain challenging. The development of PSMA-targeting hybrid molecules enabling the pre- and intraoperative detection of tumor tissue supported by both radioactivity (e.g., using DROP-IN technology) and fluorescence might help to overcome these limitations. Here, we report for the first time preoperative PET/CT imaging and subsequent fluorescence-guided surgery aided by a PSMA-11-derived peptidomimetic PSMA-targeting hybrid molecule.

With the exception of beryllium, every alkaline earth metal is characterized by a calcimimetic behavior. Thus, in vivo biodistribution mostly occurs in form of a massive accumulation in bone tissues, consisting of hydroxyapatite to a major extent. Apart from the lightest elements beryllium and magnesium, animal studies and human studies regarding the overall in vivo behavior were carried out by using radioisotopes of the elements calcium, strontium, barium, and radium. To date, only strontium with its radioisotopes gained importance for applications in nuclear medicine, mainly for pain-reducing and palliative treatment of bone metastases. In contrast, barium isotopes can be useful imaging agents and possible diagnostic analogues for theranostic approaches. This review focuses on the characteristic and chemical behavior of barium compounds, possible radioactive barium isotopes for future applications in nuclear medicine and radiopharmacy as well as recent results regarding barium-131 as diagnostic match for radium isotopes used in targeted alpha therapy.

Targeted imaging and therapy approaches based on novel prostate-specific membrane antigen (PSMA) inhibitors have fundamentally changed the treatment regimen of prostate cancer. However, the exact mechanism of PSMA inhibitor internalization has not yet been studied, and the inhibitors' subcellular fate remains elusive. Here we investigated the intracellular distribution of peptidomimetic PSMA inhibitors and of PSMA itself by stimulated emission depletion (STED) nanoscopy, applying a novel non-standard live cell staining protocol. Imaging analysis confirmed PSMA cluster formation at the cell surface of prostate cancer cells and clathrin-dependent endocytosis of PSMA inhibitors. Following the endosomal pathway, PSMA inhibitors accumulated in prostate cancer cells at clinically relevant time points. In contrast to PSMA itself, PSMA inhibitors were found to eventually distribute homogeneously in the cytoplasm, a molecular condition that promises benefits for treatment as cytoplasmic and in particular perinuclear enrichment of the radionuclide carriers may better facilitate the radiation-mediated damage of cancerous cells. This study is the first to reveal the subcellular fate of PSMA/PSMA inhibitor complexes at the nanoscale and aims to inspire the development of new approaches in the field of prostate cancer research, diagnostics, and therapeutics.

Currently, targeted alpha therapy is one of the most investigated topics in radiopharmaceutical cancer management. Especially, the alpha emitter 225 Ac provides excellent nuclear properties and is gaining increasing popularity for the treatment of various tumor entities. We herein report on the synthesis of two universal 225Ac-chelators for mild condition radiolabeling and binding sites to conjugate biomolecules via the copper-mediated click chemistry. A convenient radiolabeling procedure was investigated as well as the complex stability proved for both chelators and two PSMA-targeting model radioconjugates. Studies regarding affinity and cell survival were per-formed on LNCaP cells followed by biodistribution studies, which were performed using LNCaP tumor-bearing mice. High efficiency radiolabeling for all conjugates was demonstrated. Cell binding studies revealed a fourfold lower cell affinity for the PSMA conjugate with one targeting vector compared to the conjugate owing two targeting vectors. Additionally, these differences were verified by in vitro cell survival evaluation and biodistribution studies, both showing a higher therapeutic efficiency for the same dose on a cellular leve, a higher tumor up-take (15%ID/g) and a rapid whole body clearance after 24 hours. The synthesized chelators will overcome obstacles of lacking stability and worse labeling needs regarding 225Ac complexation using the DOTA chelator. Moreover, the universal functionalization expands the coverage of these chelators in combination with any sensitive bio(macro)molecule, thus improving treat-ment of any addressable tumor target.

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 23 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. Conclusion: Trends in radiochemistry and radiopharmacy are highlighted demonstrating the progress in the research field being the scope of EJNMMI Radiopharmacy and Chemistry.

Background: The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biyearly highlight commentary to describe trends in the field. Results: This commentary of highlights has resulted in 19 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. Conclusion: Trends in radiochemistry and radiopharmacy are highlighted demonstrating the progress in the research field being the scope of EJNMMI Radiopharmacy and Chemistry.

Targeted imaging and therapy approaches based on novel prostate-specific membrane antigen (PSMA) inhibitors have fundamentally changed the treatment regimen of prostate cancer. However, the exact mechanism of PSMA inhibitor internalization has not yet been studied, and the inhibitors' subcellular fate remains elusive. Here we investigated the intracellular distribution of peptidomimetic PSMA inhibitors and of PSMA itself by stimulated emission depletion (STED) nanoscopy, applying a novel non-standard live cell staining protocol. Imaging analysis confirmed PSMA cluster formation at the cell surface of prostate cancer cells and clathrin-dependent endocytosis of PSMA inhibitors. Following the endosomal pathway, PSMA inhibitors accumulated in prostate cancer cells at clinically relevant time points. In contrast to PSMA itself, PSMA inhibitors were found to eventually distribute homogeneously in the cytoplasm, a molecular condition that promises benefits for treatment as cytoplasmic and in particular perinuclear enrichment of the radionuclide carriers may better facilitate the radiation-mediated damage of cancerous cells. This study is the first to reveal the subcellular fate of PSMA/PSMA inhibitor complexes at the nanoscale and aims to inspire the development of new approaches in the field of prostate cancer research, diagnostics, and therapeutics.

Von Erdalkalimetallionen außer Beryllium ist bekannt, dass sie ein calcimimetisches Verhalten zeigen. Damit ist ihr Schicksal in vivo vorgezeichnet, das in einem beträchtlichen Maße durch den Einbau in Knochengewebe, welches zum Hauptteil aus Hydroxylapatit besteht, charakterisiert ist. In diesem Sinne wurde auch die Verwendung von Radionukliden dieser Elemente als Knochensucher forciert. Mit Ausnahme von Beryllium und Magnesium wurden Tierexperimente und Humananwendungen mit Radionukliden von Calcium, Strontium, Barium und Radium durchgeführt, wobei bis heute lediglich Strontium und Radium, in der Hauptsache als Therapienuklide zur palliativen Behandlung von Knochenmetastasen, Eingang in nuklearmedizinische Routineanwendungen gefunden haben. In diesem Übersichtsartikel werden die Radionuklide des Bariums vorgestellt, sowie deren Herstellung und Verwendung. Aktuelle Forschungsergebnisse mit Radionukliden des Bariums in Radiopharmazie und Nuklearmedizin werden präsentiert.

Herein we report the design and synthesis of a series of highly selective CCR2 antagonists as 18F-labeled PET tracers. The derivatives were evaluated extensively for their off-target profile at 48 different targets. The most potent and selective candidate was applied in vivo in a biodistribution study, demonstrating a promising profile for further preclinical development. This compound represents the first potential nonpeptidic PET tracer for the imaging of CCR2 receptors.

Von Erdalkalimetallionen außer Beryllium ist bekannt, dass sie ein calcimimetisches Verhalten zeigen. Damit ist ihr Schicksal in vivo vorgezeichnet, das in einem beträchtlichen Maße durch den Einbau in Knochengewebe, welches zum Hauptteil aus Hydroxylapatit besteht, charakterisiert ist. In diesem Sinne wurde auch die Verwendung von Radionukliden dieser Elemente als Knochensucher forciert. Mit Ausnahme von Beryllium und Magnesium wurden Tierexperimente und Humananwendungen mit Radionukliden von Calcium, Strontium, Barium und Radium durchgeführt, wobei bis heute lediglich Strontium und Radium, in der Hauptsache als Therapienuklide zur palliativen Behandlung von Knochenmetastasen, Eingang in nuklearmedizinische Routineanwendungen gefunden haben. In diesem Übersichtsartikel werden die Radionuklide des Bariums vorgestellt, sowie deren Herstellung und Verwendung. Aktuelle Forschungsergebnisse mit Radionukliden des Bariums in Radiopharmazie und Nuklearmedizin werden präsentiert.

Purpose: [⁶⁸Ga]Ga-PSMA-11 is a promising radiopharmaceutical for detecting tumour lesions in prostate cancer, but knowledge of the pharmacokinetics is limited. Dynamic PET-CT was performed to investigate the tumour detection and differences in temporal distribution, as well as in kinetic modelling of [⁶⁸Ga]Ga-PSMA-11 by tissue type. Methods: Dynamic PET-CT over the lower abdomen and static whole-body PET-CT 80–90 min p.i. from 142 patients with biochemical recurrence were retrospectively analysed. Detection rates were compared to PSA levels. Average time-activity curves were calculated from tumour lesions and normal tissue. A three-compartment model and non-compartment model were used to calculate tumour kinetics. Results: Overall detection rate was 70.42%, and in patients with PSA > 0.4 ng/mL 76.67%. All tumour lesions presented the steepest standardised uptake value (SUV) incline in the first 7–8 min before decreasing to different degrees. Normal tissue presented with a low uptake, except for the bladder, which accumulated activity the steepest 15–16 min. p.i.. While all tumour lesions continuously increased, bone metastases showed the steepest decline, resulting in a significantly lower SUV than lymph node metastases (60 and 80–90 min). Transport rate from the blood and tracer binding and internalisation rate were lower in bone metastases. Heterogeneity (fractal dimension) and vascular density were significantly lower in bone metastases. Conclusion: Even at low PSA between 0.51 and 0.99 ng/mL, detection rate was 57%. Dynamic imaging showed a time window in the first 10 min where tumour uptake is high, but no bladder activity is measured, aiding accuracy in distinction of local recurrence. Kinetic modelling provided additional information for tumour characterisation by tissue type.