Publications by authors named "Jean Claude Reubi"

191 Publications

Pitfalls in the Detection of Insulinomas With Glucagon-Like Peptide-1 Receptor Imaging.

Clin Nucl Med 2020 Sep;45(9):e386-e392

From the Clinic of Radiology and Nuclear Medicine.

Purpose: Physiological pancreaticoduodenal uptake of radiolabeled exendin-4 in Brunner glands of the proximal duodenum is the most common pitfall for false interpretation of glucagon-like peptide-1 receptor (GLP-1R) imaging. The aim of this study was to analyze the pancreaticoduodenal uptake in GLP-1R PET/CT and SPECT/CT images and to identify additional potential reading pitfalls in patients with suspected insulinoma.

Methods: A post hoc analysis of a prospective study, including 52 consecutive patients, was performed. All patients underwent 1 Ga-exendin-4 PET/CT and 2 In-exendin-4 SPECT/CT scans (4 and 72 hours postinjection) in a randomized crossover order. Three board-certified nuclear medicine physicians read all scans independently. They were unaware of other results. Reference standard was surgery with histopathological confirmation of an insulinoma/nesidioblastosis and normalization of blood glucose levels after surgery.

Results: There were no false-positive readings. However, there were a number of false-negative PET/CT and SPECT/CT readings, respectively: (1) due to false interpretation of uptake in the pancreaticoduodenal region (falsely interpreted as physiological uptake in Brunner glands instead of an insulinoma in 0.6% vs 9.0%), (2) due to ectopic insulinoma (0% vs 2.6%), (3) due to small insulinoma (1.9% vs 5.1%), (4) due to insulinoma overlap with kidneys (1.9% vs 4.5%), and (5) due to nesidioblastosis (0.6% and 1.9%). Pitfalls were identified in all GLP-1R PET/CT and SPECT/CT scans.

Conclusions: Peripancreatic uptake, small size of an insulinoma, insulinoma overlap with kidneys, and presence of nesidioblastosis are potential pitfalls in GLP-1R imaging, which can lead to false reading results.
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http://dx.doi.org/10.1097/RLU.0000000000003124DOI Listing
September 2020

Brunner's Gland Hyperplasia in a Patient after Roux-Y Gastric Bypass: An Important Pitfall in GLP-1 Receptor Imaging.

Case Rep Endocrinol 2020 3;2020:4510910. Epub 2020 Apr 3.

Division of Endocrinology, Diabetology and Metabolism, University Hospital Basel, Petersgraben 4, 4053 Basel, Switzerland.

Severe cases of postprandial hypoglycaemia after bariatric surgery can be a diagnostic and therapeutic challenge. The diagnostic role of Ga-DOTA-Exendin-4 PET/CT in postbariatric hypoglycaemia for further treatment decisions is unclear. We present a case of a 50-year-old woman with frequent and severe postprandial hypoglycaemic (≤2.5 mmol/L) episodes starting three years after Roux-Y gastric bypass. Despite strict dietary adherence and several medical therapies, the patient remained severely affected, and Ga-DOTA-Exendin-4 PET/CT was performed to exclude atypical presentation of an insulinoma or nesidioblastosis. No pancreatic abnormalities were found, but intensive tracer accumulation in the first and second part of the duodenum was detected, which proved to be hyperplastic Brunner's glands on histology and were strongly positive for the glucagon-like peptide-1 receptor. This case provides histopathological verification that duodenal Ga-DOTA-Exendin-4 uptake is caused by uptake in Brunner's glands and points to a potential relationship between bariatric surgery and Brunner's glands.
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http://dx.doi.org/10.1155/2020/4510910DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7160728PMC
April 2020

GIP receptor: Expression in neuroendocrine tumours, internalization, signalling from endosomes and structure-function relationship studies.

Peptides 2020 03 16;125:170229. Epub 2019 Dec 16.

LPCNO, ERL 1226 INSERM, Université De Toulouse, CNRS, INSA, UPS, 135 Avenue De RAngueil, 31077 Toulouse, France. Electronic address:

GIP is well known as a peptide regulating metabolic functions. In this review paper, we summarize a series of data on GIP receptor (GIPR). First, expression study of GIPR in human neuroendocrine tumours showed a very high incidence (nearly 100%) and a high density in both functional and non functional pancreatic tumours, ileal tumours, bronchial tumours and medullary thyroid carcinomas. Then, data on internalization of GIPR following stimulation by GIP are reported. Rapid and abundant internalization of GIPR also found in tumor pancreatic endocrine cells opens the possibility of tumor imaging and eradication using radiolabeled GIP. Interestingly, internalized GIPR continues to signal in early endosomes stimulating production of cAMP and activation of PKA, thus, supporting the view that GIPR signals from both plasma membrane and vesicles of internalization. At last, we summarize data from studies using in synergy molecular modeling and site-directed mutagenesis, which identified crucial amino acids of transmembrane domains of GIPR involved in GIPR binding site of GIP and/or in its activation and coupling to Gs protein. All together, these last molecular data may help to better understand structure-activity relationship data on GIP and GIPR.
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http://dx.doi.org/10.1016/j.peptides.2019.170229DOI Listing
March 2020

68Ga-Exendin-4 PET/CT Detects Insulinomas in Patients With Endogenous Hyperinsulinemic Hypoglycemia in MEN-1.

J Clin Endocrinol Metab 2019 12;104(12):5843-5852

Center for Neuroendocrine and Endocrine Tumors, University Hospital Basel, Basel, Switzerland.

Context: Surgical intervention is advised in patients with multiple endocrine neoplasia type-1 (MEN-1) and nonfunctioning pancreatic neuroendocrine tumors (PanNETs) with a size ≥20 mm. Functioning PanNETs, such as in patients with endogenous hyperinsulinemic hypoglycemia (EHH) due to (one or multiple) insulinomas, should be treated surgically independent of size. Preoperative localization of insulinomas is critical for surgery.

Objective: To evaluate the feasibility and sensitivity of 68Ga-DOTA-exendin-4 positron emission tomography (PET)/CT in the detection of clinically relevant lesions in patients with MEN-1 and EHH in combination with MRI.

Design: Post hoc subgroup analysis of a larger prospective imaging study with 52 patients with EHH.

Patients: Six of 52 consecutive patients with EHH and genetically proven MEN-1 mutation were included.

Interventions: All patients received one 68Ga-DOTA-exendin-4 PET/CT and one MRI scan within 3 to 4 days. Thereafter, surgery was performed based on all imaging results.

Main Outcome Measures: Lesion-based sensitivity of PET/CT and MRI for detection of clinically relevant lesions was calculated. Readers were unaware of other results. The reference standard was surgery with histology and treatment outcome. True positive (i.e., clinically relevant lesions) was defined as PanNETs ≥20 mm or insulinoma.

Results: In six patients, 37 PanNETs were confirmed by histopathology. Sensitivity (95% CI) in the detection of clinically relevant lesions for combined PET/CT plus MRI, MRI, and PET/CT was 92.3% (64% to 99.8%), 38.5% (13.9% to 68.4%), and 84.6% (54.6% to 98.1%), respectively (P = 0.014 for the comparison of PET/CT plus MRI vs MRI). Postsurgery, EHH resolved in all patients.

Conclusion: 68Ga-DOTA-exendin-4 PET/CT is feasible in patients with MEN-1 and EHH. The combination with MRI is superior to MRI alone in the detection of insulinomas and may guide the surgical strategy.
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http://dx.doi.org/10.1210/jc.2018-02754DOI Listing
December 2019

Localization of Tc-GRP Analogs in GRPR-Expressing Tumors: Effects of Peptide Length and Neprilysin Inhibition on Biological Responses.

Pharmaceuticals (Basel) 2019 Mar 20;12(1). Epub 2019 Mar 20.

Molecular Radiopharmacy, INRASTES, NCSR "Demokritos", 15310 Athens, Greece.

The overexpression of gastrin-releasing peptide receptors (GRPRs) in frequently occurring human tumors has provided the opportunity to use bombesin (BBN) analogs as radionuclide carriers to cancer sites for diagnostic and therapeutic purposes. We have been alternatively exploring human GRP motifs of higher GRPR selectivity compared to frog BBN sequences aiming to improve pharmacokinetic profiles. In the present study, we compared two differently truncated human endogenous GRP motifs: GRP(14⁻27) and GRP(18⁻27). An acyclic tetraamine was coupled at the N-terminus to allow for stable binding of the SPECT radionuclide Tc. Their biological profiles were compared in PC-3 cells and in mice without or with coinjection of phosphoramidon (PA) to induce transient neprilysin (NEP) inhibition in vivo. The two Tc-N₄-GRP(14/18⁻27) radioligands displayed similar biological behavior in mice. Coinjection of PA exerted a profound effect on in vivo stability and translated into notably improved radiolabel localization in PC-3 experimental tumors. Hence, this study has shown that promising Tc-radiotracers for SPECT imaging may indeed derive from human GRP sequences. Radiotracer bioavailability was found to be of major significance. It could be improved during in situ NEP inhibition resulting in drastically enhanced uptake in GRPR-expressing lesions.
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http://dx.doi.org/10.3390/ph12010042DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6469168PMC
March 2019

AIP-mutated acromegaly resistant to first-generation somatostatin analogs: long-term control with pasireotide LAR in two patients.

Endocr Connect 2019 Apr;8(4):367-377

Department of Endocrinology, Centre Hospitalier Universitaire (CHU) de Liège, Liège Université, Domaine Universitaire du Sart-Tilman, Liège, Belgium.

Acromegaly is a rare disease due to chronic excess growth hormone (GH) and IGF-1. Aryl hydrocarbon receptor interacting protein (AIP) mutations are associated with an aggressive, inheritable form of acromegaly that responds poorly to SST2-specific somatostatin analogs (SSA). The role of pasireotide, an SSA with affinity for multiple SSTs, in patients with AIP mutations has not been reported. We studied two AIP mutation positive acromegaly patients with early-onset, invasive macroadenomas and inoperable residues after neurosurgery. Patient 1 came from a FIPA kindred and had uncontrolled GH/IGF-1 throughout 10 years of octreotide/lanreotide treatment. When switched to pasireotide LAR, he rapidly experienced hormonal control which was associated with marked regression of his tumor residue. Pasireotide LAR was stopped after >10 years due to low IGF-1 and he maintained hormonal control without tumor regrowth for >18 months off pasireotide LAR. Patient 2 had a pituitary adenoma diagnosed when aged 17 that was not cured by surgery. Chronic pasireotide LAR therapy produced hormonal control and marked tumor shrinkage but control was lost when switched to octreotide. Tumor immunohistochemistry showed absent AIP and SST2 staining and positive SST5. Her AIP mutation positive sister developed a 2.5 cm follicular thyroid carcinoma aged 21 with tumoral loss of heterozygosity at the AIP locus and absent AIP staining. Patients 1 and 2 required multi-modal therapy to control diabetes. On stopping pasireotide LAR after >10 years of treatment, Patient 1's glucose metabolism returned to baseline levels. Long-term pasireotide LAR therapy can be beneficial in some AIP mutation positive acromegaly patients that are resistant to first-generation SSA.
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http://dx.doi.org/10.1530/EC-19-0004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6454377PMC
April 2019

The tetraamine chelator outperforms HYNIC in a new technetium-99m-labelled somatostatin receptor 2 antagonist.

EJNMMI Res 2018 Aug 2;8(1):75. Epub 2018 Aug 2.

Divisions of Radiopharmaceutical Chemistry and Nuclear Medicine, University Hospital Basel, Petersgraben 4, 4031, Basel, Switzerland.

Background: Somatostatin receptor targeting radiopeptides are successfully being used to image, stage, and monitor patients with neuroendocrine tumours. They are exclusively agonists that internalise upon binding to the relevant receptor. According to recent reports, antagonists may be preferable to agonists. To date, Tc-labelled somatostatin receptor antagonists have attracted little attention. Here, we report on a new somatostatin receptor subtype 2 (sst2) antagonist, SS-01 (p-Cl-Phe-cyclo(D-Cys-Tyr-D-Trp-Lys-Thr-Cys)D-Tyr-NH), with the aim of developing Tc-labelled ligands for SPECT/CT imaging. SS-01 was prepared using Fmoc solid-phase synthesis and subsequently coupled to the chelators 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), 6-carboxy-1,4,8,11-tetraazaundecane (N4), and 6-hydrazinonicotinic acid (HYNIC) to form the corresponding peptide-chelator conjugates SS-03, SS-04, and SS-05, respectively. SS-04 and SS-05 were radiolabelled with Tc and SS-03 with Lu. Binding affinity and antagonistic properties were determined using autoradiography and immunofluorescence microscopy. Biodistribution and small animal SPECT/CT studies were performed on mice bearing HEK293-rsst2 xenografts.

Results: The conjugates showed low nanomolar sst2 affinity and antagonistic properties. Lu-DOTA-SS-01 (Lu-SS-03) and Tc-N4-SS-01 (Tc-SS-04) demonstrated high cell binding and low internalisation, whereas Tc-HYNIC/edda-SS-01 (Tc-SS-05) showed practically no cellular uptake in vitro. The Tc-SS-04 demonstrated impressive tumour uptake at early time points, with 47% injected activity per gram tumour (%IA/g) at 1 h post-injection. The tumour uptake persisted after 4 h and was 32.5 %IA/g at 24 h. The uptake in all other organs decreased much more rapidly leading to high tumour-to-normal organ ratios, which was reflected in high-contrast SPECT/CT images.

Conclusions: These data indicate a very promising Tc-labelled sst2-targeting antagonist. The results demonstrate high sensitivity of the Tc-labelling strategy, which was shown to strongly influence the receptor affinity, contrary to corresponding agonists. Tc-SS-04 exhibits excellent pharmacokinetics and imaging properties and appears to be a suitable candidate for SPECT/CT clinical translation.
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http://dx.doi.org/10.1186/s13550-018-0428-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6070450PMC
August 2018

New Gastrin Releasing Peptide Receptor-Directed [Tc]Demobesin 1 Mimics: Synthesis and Comparative Evaluation.

J Med Chem 2018 04 19;61(7):3138-3150. Epub 2018 Mar 19.

Molecular Radiopharmacy, INRASTES , National Center for Scientific Research "Demokritos" , GR-153 10 Athens , Greece.

We have previously reported on the gastrin releasing peptide receptor (GRPR) antagonist [Tc]1, ([Tc]demobesin 1, Tc-[N'-diglycolate-dPhe,Leu-NHEt]BBN(6-13)). [Tc]1 has shown superior biological profile compared to analogous agonist-based Tc-radioligands. We herein present a small library of [Tc]1 mimics generated after structural modifications in (a) the linker ([Tc]2, [Tc]3, [Tc]4), (b) the peptide chain ([Tc]5, [Tc]6), and (c) the C-terminus ([Tc]7 or [Tc]8). The effects of above modifications on the biological properties of analogs were studied in PC-3 cells and tumor-bearing SCID mice. All analogs showed subnanomolar affinity for the human GRPR, while most receptor-affine 4 and 8 behaved as potent GRPR antagonists in a functional internalization assay. In mice bearing PC-3 tumors, [Tc]1-[Tc]6 exhibited GRPR-specific tumor uptake, rapidly clearing from normal tissues. [Tc]4 displayed the highest tumor uptake (28.8 ± 4.1%ID/g at 1 h pi), which remained high even after 24 h pi (16.3 ± 1.8%ID/g), well surpassing that of [Tc]1 (5.4 ± 0.7%ID/g at 24 h pi).
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http://dx.doi.org/10.1021/acs.jmedchem.8b00177DOI Listing
April 2018

Safety, Biodistribution, and Radiation Dosimetry of Ga-OPS202 in Patients with Gastroenteropancreatic Neuroendocrine Tumors: A Prospective Phase I Imaging Study.

J Nucl Med 2018 06 12;59(6):909-914. Epub 2017 Oct 12.

Division of Nuclear Medicine, University Hospital Basel, Basel, Switzerland

Preclinical and preliminary clinical evidence indicates that radiolabeled somatostatin (sst) receptor antagonists perform better than agonists in detecting neuroendocrine tumors (NETs). We performed a prospective phase I/II study to evaluate the sst receptor antagonist Ga-OPS202 (Ga-NODAGA-JR11; NODAGA = 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid and JR11 = Cpa-c(dCys-Aph(Hor)-dAph(Cbm)-Lys-Thr-Cys)-dTyr-NH)) for PET imaging. Here, we report the results of phase I of the study. Patients received 2 single 150-MBq intravenous injections of Ga-OPS202 3-4 wk apart (15 μg of peptide at visit 1 and 50 μg at visit 2). At visit 1, a dynamic PET/CT scan over the kidney was obtained during the first 30 min after injection, and static whole-body scans were obtained at 0.5, 1, 2, and 4 h after injection; at visit 2, a static whole-body scan was obtained at 1 h. Blood samples and urine were collected at regular intervals to determine Ga-OPS202 pharmacokinetics. Safety, biodistribution, radiation dosimetry, and the most appropriate imaging time point for Ga-OPS202 were assessed. Twelve patients with well-differentiated gastroenteropancreatic (GEP) NETs took part in the study. Ga-OPS202 cleared rapidly from the blood, with a mean residence time of 2.4 ± 1.1 min/L. The organs with the highest mean dose coefficients were the urinary bladder wall, kidneys, and spleen. The calculated effective dose was 2.4E-02 ± 0.2E-02 mSv/MBq, corresponding to 3.6 mSv, for a reference activity of 150 MBq. Based on total numbers of detected malignant lesions, the optimal time window for the scan was between 1 and 2 h. For malignant liver lesions, the time point at which most patients had the highest mean tumor contrast was 1 h. Ga-OPS202 was well tolerated; adverse events were grade 1 or 2, and there were no signals of concern from laboratory blood or urinalysis tests. Ga-OPS202 showed favorable biodistribution and imaging properties, with optimal tumor contrast between 1 and 2 h after injection. Dosimetry analysis revealed that the dose delivered by Ga-OPS202 to organs is similar to that delivered by other Ga-labeled sst analogs. Further evaluation of Ga-OPS202 for PET/CT imaging of NETs is therefore warranted.
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http://dx.doi.org/10.2967/jnumed.117.199737DOI Listing
June 2018

In Vitro Evaluation of Molecular Tumor Targets in Nuclear Medicine: Immunohistochemistry Is One Option, but Under Which Conditions?

J Nucl Med 2017 12 14;58(12):1885-1887. Epub 2017 Sep 14.

Institute of Pathology, University of Berne, Berne, Switzerland

The identification of new molecular targets for diagnostic and therapeutic applications using in vitro methods is an important challenge in nuclear medicine. One such method is immunohistochemistry, increasingly popular because it is easy to perform. This review presents the case for conducting receptor immunohistochemistry to evaluate potential molecular targets in human tumor tissue sections. The focus is on the immunohistochemistry of G-protein-coupled receptors, one of the largest families of cell surface proteins, representing a major class of drug targets and thus playing an important role in nuclear medicine. This review identifies common pitfalls and challenges and provides guidelines on performing such immunohistochemical studies. An appropriate validation of the target is a prerequisite for developing robust and informative new molecular probes.
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http://dx.doi.org/10.2967/jnumed.117.197582DOI Listing
December 2017

Approaches to Multireceptor Targeting: Hybrid Radioligands, Radioligand Cocktails, and Sequential Radioligand Applications.

J Nucl Med 2017 09;58(Suppl 2):10S-16S

Department of Nuclear Medicine, University Hospital Freiburg, Freiburg, Germany

Modern drug discovery highly depends on the identification and validation of the drug targets. Using the method of in vitro quantitative receptor autoradiography, we demonstrated that-for instance, in neuroendocrine tumors-up to 3 receptors can be coexpressed at a relatively high density. In addition, nonendocrine tumors such as breast, prostate, and brain tumors concomitantly express several G protein-coupled receptors at a high density. We propose 3 strategies for exploiting these findings for multireceptor targeting in vivo: use of heterobivalent or heteromultivalent ligands, which may bind simultaneously or monovalently to their different molecular targets; coinjection of a cocktail of radioligands; and sequential injection of different radioligands. Any of these strategies may help to remedy some of the major problems in cancer targeting: heterogeneity, change in phenotype during disease progression, and resistance.
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http://dx.doi.org/10.2967/jnumed.116.186882DOI Listing
September 2017

A Critical Evaluation of sst3 and sst5 Immunohistochemistry in Human Pituitary Adenomas.

Neuroendocrinology 2018 7;106(2):116-127. Epub 2017 Apr 7.

Background: Somatostatin receptor (sst) overexpression in neuroendocrine tumors allows sst-targeted tumor imaging and therapy with long-acting, cold, or radioactive somatostatin analogs. sst2 has been most important, owing to its wide overexpression and high affinity for somatostatin analogs, but other sst subtypes become of increasing clinical interest due to drug development. Immunohistochemistry is the preferred method to detect sst in resected tumor tissues. While it is established for sst2 using the antibody UMB-1, there is less experience for other sst subtypes.

Methods: sst3 and sst5 immunohistochemistry using the antibodies UMB-5 and UMB-4 was evaluated in 60 pituitary adenomas and compared with in vitro sst autoradiography (ARG), the in vitro gold standard method to assess sst.

Results: UMB-4 immunohistochemistry for sst5 yielded membranous staining of tumor cells. It correlated fairly well with ARG, results matching in 80% of tumors. UMB-5 immunohistochemistry for sst3 showed not only a membranous, but also cytoplasmic background staining. Agreement with ARG was limited. All tumors showed UMB-5 staining, while only 57% were positive by ARG. In comparison, UMB-1 staining levels showed a highly significant correlation with autoradiographic sst2 density levels (R2 = 0.797). Not only tumor cells, but also intratumoral blood vessels were immunohistochemically positive for sst2, 3, and 5.

Conclusion: UMB-1 immunohistochemistry for sst2 is excellent. sst3 immunohistochemistry using UMB-5 is not yet optimal, with suspected limited specificity, and should be applied with caution. UMB-4 immunohistochemistry for sst5 appears to be equivalent to sst5-ARG and suitable for diagnostic applications.
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http://dx.doi.org/10.1159/000472563DOI Listing
January 2019

PET/CT Imaging of Unstable Carotid Plaque with Ga-Labeled Somatostatin Receptor Ligand.

J Nucl Med 2017 05 8;58(5):774-780. Epub 2016 Dec 8.

Institute of Nuclear Medicine, University College London, London, United Kingdom.

Ga-labeled somatostatin receptor ligand PET imaging has recently been shown in preclinical and early human studies to have a potential role in the evaluation of vulnerable arterial plaques. We prospectively evaluated carotid plaque Ga-DOTATATE uptake in patients with recent carotid events, assessed inter- and intraobserver variability of such measurements, and explored the mechanism of any plaque DOTATATE activity with immunohistochemistry in resected specimens. Twenty consecutively consenting patients with recent symptomatic carotid events (transient ischemic attack, stroke, or amaurosis fugax), due for carotid endarterectomy, were prospectively recruited. Ga-DOTATATE PET/CT of the neck was performed before surgery. Ga-DOTATATE uptake was measured by drawing regions of interest along the carotid plaques and contralateral plaques/carotid arteries by an experienced radionuclide radiologist and radiographer. Two PET quantification methods with inter- and intraobserver variability were assessed. Resected carotid plaques were retrieved for somatostatin receptor subtype-2 (sst2) immunohistochemical staining. The median time delay between research PET and surgery was 2 d. SUVs and target-to-background ratios for the symptomatic plaques and the asymptomatic contralateral carotid arteries/plaques showed no significant difference ( = 19, > 0.10), regardless of quantification method. The intraclass correlation coefficient was greater than 0.8 in all measures of carotid artery/plaque uptake (SUV) and greater than 0.6 in almost all measures of target-to-background ratio. None of the excised plaques was shown to contain cells (macrophages, lymphocytes, vessel-associated cells) expressing sst2 on their cell membrane. Ga-DOTATATE activity on PET in recently symptomatic carotid plaques is not significantly different from contralateral carotids/plaques. Any activity seen on PET is not shown to be from specific sst2 receptor-mediated uptake in vitro. It is therefore unlikely that sst2 PET/CT imaging will have a role in the detection and characterization of symptomatic carotid plaques.
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http://dx.doi.org/10.2967/jnumed.116.181438DOI Listing
May 2017

Approaches to improve metabolic stability of a statine-based GRP receptor antagonist.

Nucl Med Biol 2017 02 4;45:22-29. Epub 2016 Nov 4.

Department of Nuclear Medicine, University Hospital Freiburg, Germany; German Cancer Consortium (DKTK), Heidelberg, Germany; German Cancer Research Center (DKFZ), Heidelberg, Germany,. Electronic address:

The bombesin receptor family, in particular the gastrin-releasing peptide receptor (GRPr), is an attractive target in the field of nuclear oncology due to the high density of these receptors on the cell surface of several human tumors. The successful clinical implementation of Cu-CB-TE2A-AR06, Ga-RM2 and Ga-NODAGA-MJ9, prompted us to continue the development of GRPr-antagonists. The aim of the present study was to assess if N-terminal modulations of the statine-based GRPr-antagonist influence the binding affinity, the pharmacokinetic performance and the in vivo metabolic stability.

Methods: The GRPr-antagonist (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH) was functionalized with the chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) via the spacer 4-amino-1-carboxymethyl-piperidine (Pip) and the amino acid N-Methyl-β-Ala, to obtain NMe-RM2 and labeled with Ga and Lu. The GRPr affinity of the corresponding metalloconjugates determined using [I-Tyr]-BN as radioligand. In vitro evaluation included internalization studies using PC3 cells. The Ga-conjugate was evaluated in PC3 xenografts by biodistribution and PET studies, while investigations on the metabolic stability and plasma protein binding were performed.

Results: The half maximum inhibitory concentrations (IC) of the metalloconjugates, using [I-Tyr]-BN, are in the low nanomolar range. PC3-cell culture binding studies of both metallated NMe-RM2 and RM2 show high GRPr-bound activity and low internalization. Metabolic studies showed that Ga-NMe-RM2 and Ga-RM2 are being cleaved in a similar fashion into three metabolites, with a good proportion of about 50% of the remaining blood activity at 15min post injection (p.i.) being represented by the intact radiotracer. Ga-NMe-RM2 was shown to target specifically PC3 xenografts, with high and sustained tumor uptake of about 13% IA/g within a time frame of 3h. The PET images clearly visualized the tumor.

Conclusions: The relatively high percentage of the remaining intact radiotracer in blood 15min post injection sufficiently enables in vivo targeting of GRPr positive tumors, finding which has been also shown in clinical trials.
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http://dx.doi.org/10.1016/j.nucmedbio.2016.11.004DOI Listing
February 2017

Highly Increased 125I-JR11 Antagonist Binding In Vitro Reveals Novel Indications for sst2 Targeting in Human Cancers.

J Nucl Med 2017 02 25;58(2):300-306. Epub 2016 Aug 25.

The Salk Institute for Biological Studies, La Jolla, California.

There is recent in vitro and in vivo evidence that somatostatin receptor subtype 2 (sst) antagonists are better tools to target neuroendocrine tumors (NETs) than sst agonists. Indeed, antagonists bind to a greater number of sst sites than agonists. Whether sst antagonists could be used successfully to target non-NETs, expressing low sst density, is unknown. Here, we compare quantitatively I-JR11 sst antagonist binding in vitro with that of the sst agonist I-Tyr-octreotide in large varieties of non-NET and NET.

Methods: In vitro receptor autoradiography was performed with I-JR11 and I-Tyr-octreotide in cancers from prostate, breast, colon, kidney, thyroid, and lymphoid tissues as well as NETs as reference.

Results: In general, I-JR11 binds to many more sst sites than I-Tyr-octreotide. In 13 breast cancers, 8 had a low binding (mean density, 844 ± 168 dpm/mg of tissue) with the agonist whereas 12 had a high binding (mean density, 4,447 ± 1,128 dpm/mg of tissue) with the antagonist. All 12 renal cell cancers showed a low binding of sst with the agonist (mean density, 348 ± 49 dpm/mg of tissue) whereas all cases had a high sst binding with the antagonist (mean density, 3,777 ± 582 dpm/mg of tissue). One of 5 medullary thyroid cancers was positive with the agonist, whereas 5 of 5 were positive with the antagonist. In 15 non-Hodgkin lymphomas, many more sst sites were labeled with the antagonist than with the agonist. In 14 prostate cancers, none had sst binding with the agonist and only 4 had a weak binding with the antagonist. None of 17 colon cancers showed sst sites with the agonist, and only 3 cases were weakly positive with the antagonist. In the various tumor types, adjacent sst-expressing tissues such as vessels, lymphocytes, nerves, mucosa, or stroma were more strongly labeled with the antagonist than with the agonist. The reference NET cases, incubated with a smaller amount of tracer, were also found to have many more sst sites measured with the antagonist.

Conclusion: All renal cell cancers and most breast cancers, non-Hodgkin lymphomas, and medullary thyroid cancers represent novel indications for the in vivo radiopeptide targeting of sst by sst antagonists, comparable to NET radiotargeting with sst agonists.
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http://dx.doi.org/10.2967/jnumed.116.177733DOI Listing
February 2017

Approaches to Improve the Pharmacokinetics of Radiolabeled Glucagon-Like Peptide-1 Receptor Ligands Using Antagonistic Tracers.

J Nucl Med 2016 08 28;57(8):1282-8. Epub 2016 Apr 28.

Department of Nuclear Medicine, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.

Unlabelled: The glucagon-like peptide-1 (GLP-1) receptors are important biomarkers for imaging pancreatic β-cell mass and detection of benign insulinomas. Using GLP-1 receptor antagonists, we aimed to eliminate the insulin-related side effects reported for all GLP-1 receptor agonists. Additionally, using a nonresidualizing tracer, (125)I-Bolton-Hunter-Exendin(9-39)NH2 ((125)I-BH-Ex(9-39)NH2), we aimed to reduce the high kidney uptake, enabling a better detection of insulinomas in the tail and head of the pancreas.

Methods: The affinity and biodistribution of Ex(9-39)NH2-based antagonists, modified with DOTA or NODAGA chelators at positions Lys(27) and Lys(40) and labeled with (68)Ga and (125)I-BH-Ex(9-39)NH2, were compared with the reference GLP-1 receptor agonist [Nle(14),Lys(40)(Ahx-DOTA-(68)Ga)NH2]Ex-4. The inhibitory concentration of 50% (IC50) values were determined using autoradiography on human tissues with (125)I-GLP-1(7-36)NH2 as a radioligand. Pharmacokinetics and PET imaging were studied in nude mice bearing rat Ins-1E tumors.

Results: Conjugation of DOTA and NODAGA chelators at positions Lys(27) and Lys(40) of Ex(9-39)NH2 resulted in a distinct loss of affinity toward GLP-1 receptor in vitro. Among the studied antagonists, [Lys(40)(NODAGA-(nat)Ga)NH2]Ex(9-39) showed the lowest IC50 value (46.7 ± 16.3 nM). The reference agonist [Nle(14),Lys(40)(Ahx-DOTA)NH2]Ex-4 demonstrated the highest affinity (IC50 = 0.9 ± 0.3 nM). Biodistribution of [Nle(14),Lys(40)(Ahx-DOTA-(68)Ga)NH2]Ex-4 at 1 h after injection demonstrated 40.2 ± 8.2 percentage injected activity per gram (%IA/g) uptake in Ins-1E tumor, 12.5 ± 2.2 %IA/g in the pancreas, and 235.8 ± 17.0 %IA/g in the kidney, with tumor-to-blood and tumor-to-kidney ratios of 100.52 and 0.17, respectively. Biodistribution of [Lys(40)(NODAGA-(68)Ga)NH2]Ex(9-39) showed only 2.2 ± 0.2 %IA/g uptake in Ins-1E tumor, 1.0 ± 0.1 %IA/g in the pancreas, and 78.4 ± 8.5 %IA/g in the kidney at 1 h after injection, with tumor-to-blood and tumor-to-kidney ratios of 7.33 and 0.03, respectively. In contrast, (125)I-BH-Ex(9-39)NH2 showed tumor uptake (42.5 ± 8.1 %IA/g) comparable to the agonist and 28.8 ± 5.1 %IA/g in the pancreas at 1 h after injection. As we hypothesized, the kidney uptake of (125)I-BH-Ex(9-39)NH2 was low, only 12.1 ± 1.4 %IA/g at 1 h after injection. The tumor-to-kidney ratio of (125)I-BH-Ex(9-39)NH2 was improved 20-fold.

Conclusion: Our results suggest that iodinated Ex(9-39)NH2 may be a promising tracer for imaging GLP-1 receptor expression in vivo. Because of the 20-fold improved tumor-to-kidney ratio (125)I-BH-Ex(9-39)NH2 may offer higher sensitivity in the detection of insulinomas and imaging of β-cell mass in diabetic patients. Further studies with (124)I-BH-Ex(9-39)NH2 are warranted.
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http://dx.doi.org/10.2967/jnumed.115.168948DOI Listing
August 2016

Copper-64 Labeled Macrobicyclic Sarcophagine Coupled to a GRP Receptor Antagonist Shows Great Promise for PET Imaging of Prostate Cancer.

Mol Pharm 2015 Aug 15;12(8):2781-90. Epub 2015 Jul 15.

‡Department of Nuclear Medicine, University Hospital Freiburg, Freiburg 79106, Germany.

The gastrin-releasing peptide receptor (GRPr) is an important molecular target for the visualization and therapy of tumors and can be targeted with radiolabeled bombesin derivatives. The present study aims to develop statine-based bombesin receptor antagonists suitable for labeling with 64Cu for imaging by positron emission tomography (PET). The potent GRPr antagonist D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 was conjugated to the sarcophagine (3,6,10,13,16,19-hexaazabicyclo[6.6.6] icosane=Sar) derivative 5-(8-methyl-3,6,10,13,16,19-hexaaza-bicyclo[6.6.6]icosan-1-ylamino)-5-oxopentanoic acid (MeCOSar) via PEG4 (LE1) and PEG2 (LE2) spacers and radiolabeled with 64Cu2+ with >95% yield and specific activities of about 100 MBq/nmol. Both Cu(II) conjugates have high affinity for GRPr (IC50: natCu-LE1, 1.4±0.1 nM; natCu-LE2, 3.8±0.6 nM). The antagonistic properties of both conjugates were confirmed by Ca2+-flux measurements. Biodistribution studies of Cu-64-LE1 exhibited specific targeting of the tumor (19.6±4.7% IA/g at 1 h p.i.) and GRPr-positive organs. Biodistribution and PET images at 4 and 24 h postinjection showed increasing tumor-to-background ratios with time. This was illustrated by the acquisition of PET images showing high tumor-to-normal tissue contrast. This study demonstrates the high affinity of the MeCOSar-PEGx-bombesin conjugates to GRPr. The stability of 64Cu complexes of MeCOSar, the long half-life of 64Cu, and the suitable biodistribution profile of the 64Cu-labeled peptides lead to PET images of high contrast suitable for potential translation into the clinic.
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http://dx.doi.org/10.1021/mp500671jDOI Listing
August 2015

Preoperative localization of adult nesidioblastosis using ⁶⁸Ga-DOTA-exendin-4-PET/CT.

Endocrine 2015 Dec 23;50(3):821-3. Epub 2015 May 23.

Division of Experimental Pathology, Department of Pathology, Institute of Pathology, University of Bern, 3010, Bern, Switzerland.

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http://dx.doi.org/10.1007/s12020-015-0633-7DOI Listing
December 2015

Localization of Hidden Insulinomas with ⁶⁸Ga-DOTA-Exendin-4 PET/CT: A Pilot Study.

J Nucl Med 2015 Jul 21;56(7):1075-8. Epub 2015 May 21.

Clinic of Radiology and Nuclear Medicine, University of Basel Hospital, Basel, Switzerland

Unlabelled: (111)In-DOTA-exendin-4 SPECT/CT has been shown to be highly efficient in the detection of insulinomas. We aimed at determining whether novel PET/CT imaging with [Nle(14),Lys(40)(Ahx-DOTA-(68)Ga)NH2]exendin-4 ((68)Ga-DOTA-exendin-4) is feasible and sensitive in detecting benign insulinomas.

Methods: (68)Ga-DOTA-exendin-4 PET/CT and (111)In-DOTA-exendin-4 SPECT/CT were performed in a randomized cross-over order on 5 patients with endogenous hyperinsulinemic hypoglycemia. The gold standard for comparison was the histologic diagnosis after surgery.

Results: In 4 patients histologic diagnosis confirmed a benign insulinoma, whereas one patient refused surgery despite a positive (68)Ga-DOTA-exendin-4 PET/CT scan. In 4 of 5 patients, previously performed conventional imaging (CT or MR imaging) was not able to localize the insulinoma. (68)Ga-DOTA-exendin-4 PET/CT correctly identified the insulinoma in 4 of 4 patients, whereas (111)In-DOTA-exendin-4 SPECT/CT correctly identified the insulinoma in only 2 of 4 patients.

Conclusion: These preliminary data suggest that the use of (68)Ga-DOTA-exendin-4 PET/CT in detecting hidden insulinomas is feasible.
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http://dx.doi.org/10.2967/jnumed.115.157768DOI Listing
July 2015

Stereochemistry of amino acid spacers determines the pharmacokinetics of (111)In-DOTA-minigastrin analogues for targeting the CCK2/gastrin receptor.

Bioconjug Chem 2015 Jun 20;26(6):1113-9. Epub 2015 May 20.

‡Division of Radiological Chemistry, University Hospital Basel, Petersgraben 4, CH-4031 Basel, Switzerland.

The metabolic instability and high kidney retention of minigastrin (MG) analogues hamper their suitability for use in peptide-receptor radionuclide therapy of CCK2/gastrin receptor-expressing tumors. High kidney retention has been related to N-terminal glutamic acids and can be substantially reduced by coinjection of polyglutamic acids or gelofusine. The aim of the present study was to investigate the influence of the stereochemistry of the N-terminal amino acid spacer on the enzymatic stability and pharmacokinetics of (111)In-DOTA-(d-Glu)6-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2 ((111)In-PP11-D) and (111)In-DOTA-(l-Glu)6-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2 ((111)In-PP11-L). Using circular dichroism measurements, we demonstrate the important role of secondary structure on the pharmacokinetics of the two MG analogues. The higher in vitro serum stability together with the improved tumor-to-kidney ratio of the (d-Glu)6 congener indicates that this MG analogue might be a good candidate for further clinical study.
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http://dx.doi.org/10.1021/acs.bioconjchem.5b00187DOI Listing
June 2015

Neurotensin receptors in pancreatic ductal carcinomas.

EJNMMI Res 2015 24;5:17. Epub 2015 Mar 24.

Cell Biology and Experimental Cancer Research, Institute of Pathology, University of Berne, PO Box 62, Murtenstrasse 31, CH-3010 Berne, Switzerland.

Background: The frequent expression of neurotensin receptors (NT-R) in primaries of pancreatic ductal carcinomas has triggered the development of radioactive neurotensin analogs for possible in vivo targeting of these tumors. However, the complete lack of information regarding NT-R in liver metastases of pancreatic cancer and pancreatic intraepithelial neoplasia (PanIN) makes an in vitro study of NT-R in these tissues indispensable.

Methods: Using in vitro receptor autoradiography with (125)I-[Tyr(3)]-neurotensin, NT-R were investigated in 18 primaries and 23 liver metastases of pancreatic ductal carcinomas as well as in 19 PanIN lesions.

Results: We report here that 13 of 18 ductal carcinoma primaries and 14 of 23 liver metastases expressed NT-R. Moreover, none of the six PanIN 1B cases expressed NT-R, while two of six PanIN 2 and five of seven PanIN 3 expressed NT-R. Binding was fully displaced by the type 1 NT-R-selective antagonist SR48692, indicating that the NT-R in the tumors are of the type 1 NT-R subtype.

Conclusions: These in vitro data extend the currently available information on NT-R in invasive and non-invasive pancreatic ductal tumors. They suggest that type 1 NT-R may be a novel, specific marker of PanIN of higher degree. The high expression of NT-R in primaries and metastases of invasive cancer strongly support the need to develop radioactive neurotensin analogs for the diagnosis and therapy of this tumor type.
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http://dx.doi.org/10.1186/s13550-015-0094-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4388205PMC
April 2015

Triple-peptide receptor targeting in vitro allows detection of all tested gut and bronchial NETs.

J Nucl Med 2015 Apr 19;56(4):613-5. Epub 2015 Feb 19.

Cell Biology and Experimental Cancer Research, Institute of Pathology, University of Berne, Berne, Switzerland.

Unlabelled: A high proportion of gut and bronchial neuroendocrine tumors (NETs) overexpresses somatostatin receptors, especially the sst2 subtype. It has also recently been observed that incretin receptors, namely glucagonlike peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) receptors, can be overexpressed in gut and bronchial NETs. However, because not all tumors can express these receptors in sufficient amounts, in vivo imaging with a single radioligand may not always be successful. We therefore evaluated with in vitro methods whether a cocktail of radioligands targeting these 3 receptors would improve tumor labeling.

Methods: In vitro receptor autoradiography was performed on 55 NETs, comparing in each successive section of tumor the binding with a single radioligand, either (125)I-Tyr(3)-octreotide, (125)I-GLP-1(7-36)amide, or (125)I-GIP(1-30), with the binding using a cocktail of all 3 radioligands, given concomitantly under identical experimental conditions.

Results: Using the cocktail of radioligands, all tumors without exception showed moderate to very high binding, with a receptor density corresponding to 1,000-10,000 dpm/mg of tissue; conversely, single-ligand binding, although identifying most tumors as receptor-positive, failed to detect receptors or measured only a low density of receptors below 1,000 dpm/mg in a significant number of tumors. In addition, the cocktail of radioligands always provided a homogeneous labeling of the whole tumor, whereas single radioligands occasionally showed heterogeneous labeling.

Conclusion: The study suggests that the use of a cocktail of 3 radioligands binding to somatostatin receptors, GLP-1 receptors, and GIP receptors would allow detecting virtually all NETs and labeling them homogeneously in vivo, representing a significant improvement for imaging and therapy in NETs.
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http://dx.doi.org/10.2967/jnumed.114.153189DOI Listing
April 2015

Does somatostatin or gastric inhibitory peptide receptor expression correlate with tumor grade and stage in gut neuroendocrine tumors?

Neuroendocrinology 2015 12;101(1):45-57. Epub 2015 Jan 12.

Division of Cell Biology and Experimental Cancer Research, Institute of Pathology, University of Bern, Bern, Switzerland.

Background/aims: Important characteristics of neuroendocrine neoplasms (NEN) for prognosis and therapeutic decisions are the MIB-1 proliferative index (tumor grade) and tumor stage. Moreover, these tumors express peptide hormone receptors like somatostatin and gastric inhibitory peptide (GIP) receptors which represent important established and potential future targets, respectively, for molecular imaging and radiotherapy. However, the interrelation between tumor proliferation, stage, and peptide receptor amounts has never been assessed.

Methods: In 114 gastrointestinal and bronchopulmonary NEN, the proliferative rate assessed with MIB-1 immunohistochemistry and tumor stage were compared with the somatostatin type 2 receptor (sst2) and GIP receptor expression measured quantitatively with in vitro receptor autoradiography.

Results: NEN generally showed high sst2 and GIP receptor expression. GIP receptor but not sst2 expression correlated with the MIB-1 index. GIP receptor levels gradually increased in a subset of insulinomas and nonfunctioning pancreatic NEN, and decreased in ileal and bronchopulmonary NEN with increasing MIB-1 rate. MIB-1 levels were identified, above which GIP receptor levels were consistently high or low. These MIB-1 levels were clearly different from those defining tumor grade. In grade 3 NEN, GIP receptor levels were always low, while sst2 levels were variable and sometimes extremely high. Conversely, sst2 expression correlated more frequently with tumor stage than GIP receptor expression, with metastasized NEN showing higher sst2 levels than localized tumors.

Conclusions: sst2, a clinically crucial molecular target, shows variable and unpredictable expression in NEN irrespective of tumor grade. Therefore, each NEN should be tested for sst2 if clinical applications with somatostatin analogs are considered. Conversely, the potential future role of GIP receptors as molecular targets in NEN may be dependent on the MIB-1 level.
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http://dx.doi.org/10.1159/000371804DOI Listing
December 2015

Evaluation of three different families of bombesin receptor radioantagonists for targeted imaging and therapy of gastrin releasing peptide receptor (GRP-R) positive tumors.

J Med Chem 2015 Jan 17;58(2):682-91. Epub 2014 Dec 17.

Division of Radiological Chemistry, University Hospital Basel , Petersgraben 4, CH-4031 Basel, Switzerland.

Two new classes of radiolabeled GRP receptor antagonists are studied and compared with the well-established statine-based receptor antagonist DOTA-4-amino-1-carboxymethylpiperidine-d-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 (RM2, 1; DOTA:1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid; Sta:(3S,4S)-4-amino-3-hydroxy-6-methylheptanoic acid). The bombesin-based pseudopeptide DOTA-4-amino-1-carboxymethylpiperidine-d-Phe-Gln-Trp-Ala-Val-Gly-His-Leuψ(CHOH-CH2)-(CH2)2-CH3 (RM7, 2), and the methyl ester DOTA-4-amino-1-carboxymethylpiperidine-d-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-OCH3 (ARBA05, 3) analogues are labeled with (111)In and evaluated in vitro in PC-3 cell line and in vivo in PC-3 tumor-bearing nude mice. Antagonist potency was assessed by immunofluorescence-based receptor internalization and Ca(2+) mobilization assays. The conjugates showed good binding affinity, the IC50 value of 2 (3.2 ± 1.8 nM) being 2 and 10 times lower than 1 and 3. Compared to (111)In-1, (111)In-2 showed higher uptake in target tissues such as pancreas (1.5 ± 0.5%IA/g and 39.8 ± 9.3%IA/g at 4 h, respectively), whereas the compounds had similar tumor uptake (11.5 ± 2.4%IA/g and 11.8 ± 3.9%IA/g at 4h, respectively). The displacement of the radioligand in vivo was different in different receptor positive organs and depended on the displacing peptide.
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http://dx.doi.org/10.1021/jm5012066DOI Listing
January 2015

N-terminal modifications improve the receptor affinity and pharmacokinetics of radiolabeled peptidic gastrin-releasing peptide receptor antagonists: examples of 68Ga- and 64Cu-labeled peptides for PET imaging.

J Nucl Med 2014 Oct 21;55(10):1719-25. Epub 2014 Aug 21.

Department of Nuclear Medicine, University Hospital Freiburg, Freiburg, Germany

Unlabelled: Gastrin-releasing peptide receptors (GRPrs) are overexpressed on a variety of human cancers, providing the opportunity for peptide receptor targeting via radiolabeled bombesin-based peptides. As part of our ongoing investigations into the development of improved GRPr antagonists, this study aimed at verifying whether and how N-terminal modulations improve the affinity and pharmacokinetics of radiolabeled GRPr antagonists.

Methods: The potent GRPr antagonist MJ9, Pip-d-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH(2) (Pip, 4-amino-1-carboxymethyl-piperidine), was conjugated to 1,4,7-triazacyclononane, 1-glutaric acid-4,7 acetic acid (NODAGA), and 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) and radiolabeled with (68)Ga and (64)Cu. The GRPr affinity of the corresponding metalloconjugates was determined using (125)I-Tyr(4)-BN as a radioligand. The labeling efficiency of (68)Ga(3+) was compared between NODAGA-MJ9 and NOTA-MJ9 in acetate buffer, at room temperature and at 95°C. The (68)Ga and (64)Cu conjugates were further evaluated in vivo in PC3 tumor xenografts by biodistribution and PET imaging studies.

Results: The half maximum inhibitory concentrations of all the metalloconjugates are in the high picomolar-low nanomolar range, and these are the most affine-radiolabeled GRPr antagonists we have studied so far in our laboratory. NODAGA-MJ9 incorporates (68)Ga(3+) nearly quantitatively (>98%) at room temperature within 10 min and at much lower peptide concentrations (1.4 × 10(-6) M) than NOTA-MJ9, for which the labeling yield was approximately 45% under the same conditions and increased to 75% at 95°C for 5 min. Biodistribution studies showed high and specific tumor uptake, with a maximum of 23.3 ± 2.0 percentage injected activity per gram of tissue (%IA/g) for (68)Ga-NOTA-MJ9 and 16.7 ± 2.0 %IA/g for (68)Ga-NODAGA-MJ9 at 1 h after injection. The acquisition of PET images with the (64)Cu-MJ9 conjugates at later time points clearly showed the efficient clearance of the accumulated activity from the background already at 4 h after injection, whereas tumor uptake still remained high. The high pancreas uptake for all radiotracers at 1 h after injection was rapidly washed out, resulting in an increased tumor-to-pancreas ratio at later time points.

Conclusion: We have developed 2 GRPr antagonistic radioligands, which are improved in terms of binding affinity and overall biodistribution profile. Their promising in vivo pharmacokinetic performance may contribute to the improvement of the diagnostic imaging of tumors overexpressing GRPr.
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http://dx.doi.org/10.2967/jnumed.114.141242DOI Listing
October 2014

[111In-DOTA]LTT-SS28, a first pansomatostatin radioligand for in vivo targeting of somatostatin receptor-positive tumors.

J Med Chem 2014 Aug 23;57(15):6564-71. Epub 2014 Jul 23.

Molecular Radiopharmacy, INRASTES, National Center for Scientific Research "Demokritos" , GR-153 10 Athens, Greece.

Radiolabeled pansomatostatin-like analogues are expected to enhance the diagnostic sensitivity and to expand the clinical indications of currently applied sst2-specific radioligands. In this study, we present the somatostatin mimic [DOTA]LTT-SS28 {[(DOTA)Ser1,Leu8,D-Trp22,Tyr25]SS28} and its 111In radioligand. [DOTA]LTT-SS28 exhibited a pansomatostatin-like profile binding with high affinity to all five hsst1-hsst5 subtypes (IC50 values in the lower nanomolar range). Furthermore, [DOTA]LTT-SS28 behaved as an agonist at hsst2, hsst3, and hsst5, efficiently stimulating internalization of the three receptor subtypes. Radioligand [111In-DOTA]LTT-SS28 showed good stability in the mouse bloodstream. It displayed strong and specific uptake in AR42J tumors 4 h postinjection (9.3±1.6% ID/g vs 0.3±0.0% ID/g during sst2 blockade) in mice. Significant and specific uptake was also observed in HEK293-hsst2-, HEK293-hsst3-, and HEK293-hsst5-expressing tumors (4.43±1.5, 4.88±1.1, and <3% ID/g, respectively, with values of <0.5% ID/g during receptor blockade). In conclusion, the somatostatin mimic [111In-DOTA]LTT-SS28 specifically localizes in sst2-, sst3-, and sst5-expressing xenografts in mice showing promise for multi-sst1-sst5 targeted tumor imaging.
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http://dx.doi.org/10.1021/jm500581dDOI Listing
August 2014

Comparison of somatostatin receptor agonist and antagonist for peptide receptor radionuclide therapy: a pilot study.

J Nucl Med 2014 Aug 24;55(8):1248-52. Epub 2014 Jun 24.

Department of Nuclear Medicine, University Hospital Freiburg, Freiburg, Germany German Cancer Consortium (DKTK), Freiburg, Germany; and Department of Radiology, Sloan-Kettering Cancer Center, New York, New York.

Unlabelled: Preclinical and clinical studies have indicated that somatostatin receptor (sst)-expressing tumors demonstrate higher uptake of radiolabeled sst antagonists than of sst agonists. In 4 consecutive patients with advanced neuroendocrine tumors, we evaluated whether treatment with (177)Lu-labeled sst antagonists is feasible.

Methods: After injection of approximately 1 GBq of (177)Lu-DOTA-[Cpa-c(DCys-Aph(Hor)-DAph(Cbm)-Lys-Thr-Cys)-DTyr-NH2] ((177)Lu-DOTA-JR11) and (177)Lu-DOTATATE, 3-dimensional voxel dosimetry analysis based on SPECT/CT was performed. A higher tumor-to-organ dose ratio for (177)Lu-DOTA-JR11 than for (177)Lu-DOTATATE was the prerequisite for treatment with (177)Lu-DOTA-JR11.

Results: Reversible minor adverse effects of (177)Lu-DOTA-JR11 were observed. (177)Lu-DOTA-JR11 showed a 1.7-10.6 times higher tumor dose than (177)Lu-DOTATATE. At the same time, the tumor-to-kidney and tumor-to-bone marrow dose ratio was 1.1-7.2 times higher. All 4 patients were treated with (177)Lu-DOTA-JR11, resulting in partial remission in 2 patients, stable disease in 1 patient, and mixed response in the other patient.

Conclusion: Treatment of neuroendocrine tumors with radiolabeled sst antagonists is clinically feasible and may have a significant impact on peptide receptor radionuclide therapy.
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http://dx.doi.org/10.2967/jnumed.114.138834DOI Listing
August 2014

Strict rules are needed for validation of G-protein-coupled receptor immunohistochemical studies in human tissues.

Endocrine 2014 Dec 10;47(3):659-61. Epub 2014 Jun 10.

Division of Cell Biology and Experimental Cancer Research, Institute of Pathology, University of Berne, Murtenstrasse 31, PO Box 62, 3010, Berne, Switzerland,

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http://dx.doi.org/10.1007/s12020-014-0320-0DOI Listing
December 2014

The glucose-dependent insulinotropic polypeptide receptor: a novel target for neuroendocrine tumor imaging—first preclinical studies.

J Nucl Med 2014 Jun 17;55(6):976-82. Epub 2014 Apr 17.

Department of Nuclear Medicine, University Hospital Freiburg, Freiburg, Germany

Unlabelled: A new family of peptide receptors, the incretin receptor family, overexpressed on many neuroendocrine tumors (NETs) is of great importance because it may enable the in vivo peptide-based receptor targeting of a category of NETs that does not express the somatostatin receptor. Impressive in vivo diagnostic data were published for glucagonlike peptide 1 receptor-targeting radiopeptides. Recently, promising in vitro data have appeared for the second member of the incretin family, the glucose-dependent insulinotropic polypeptide (GIP) receptor. This prompted us to develop and evaluate a new class of radioligands with the potential to be used for the in vivo targeting of GIP receptor-positive tumors.

Methods: GIP(1-42) was modified C-terminally, and the truncated peptides [Lys(30)(aminohexanoic acid [Ahx]-DOTA)]GIP(1-30)NH2 (EG1), [Lys(16)(Ahx-DOTA)]GIP(1-30)NH2 (EG2), and [Nle(14), Lys(30)(Ahx-DOTA)]GIP(1-30)NH2 (EG4) were conjugated with Ahx-DOTA via the Lys(16) and Lys(30) side chains. Their inhibitory concentration of 50% (IC50) was determined using [(125)I-Tyr(10)]GIP(1-30) as radioligand and GIP(1-30) as control peptide. The DOTA conjugates were labeled with (111)In and (68)Ga. In vitro evaluation included saturation and internalization studies using the pancreatic endocrine cell line INR1G9 transfected with the human GIP receptor (INR1G9-hGIPr). The in vivo evaluation consisted of biodistribution and PET imaging studies on nude mice bearing INR1G9-hGIPr tumors.

Results: Binding studies (IC50 and saturation studies) showed high affinity toward GIP receptor for the GIP conjugates. Specific in vitro internalization was found, and almost the entire cell-associated activity was internalized (>90% of the cell-bound activity), supporting the agonist potency of the (111)In-vectors. (111)In-EG4 and (68)Ga-EG4 were shown to specifically target INR1G9-hGIPr xenografts, with tumor uptake of 10.4% ± 2.2% and 17.0% ± 4.4% injected activity/g, 1 h after injection, respectively. Kidneys showed the highest uptake, which could be reduced by approximately 40%-50% with a modified-fluid-gelatin plasma substitute or an inhibitor of the serine protease dipeptidyl peptidase 4. The PET images clearly visualized the tumor.

Conclusion: The evaluation of EG4 as a proof-of-principle radioligand indicated the feasibility of imaging GIP receptor-positive tumors. These results prompt us to continue the development of this family of radioligands for imaging of a broad spectrum of NETs.
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http://dx.doi.org/10.2967/jnumed.113.133744DOI Listing
June 2014

Glucagon-like peptide-1 receptor imaging for the localisation of insulinomas: a prospective multicentre imaging study.

Lancet Diabetes Endocrinol 2013 Oct 25;1(2):115-22. Epub 2013 Jul 25.

Department of Radiology, Division of Nuclear Medicine, University of Basel Hospital, Switzerland.

Background: Small benign insulinomas are hard to localise, leading to difficulties in planning of surgical interventions. We aimed to prospectively assess the insulinoma detection rate of single-photon emission CT in combination with CT (SPECT/CT) with a glucagon-like peptide-1 receptor avid radiotracer, and compare detection rates with conventional CT/MRI techniques.

Methods: In our prospective imaging study, we enrolled adults aged 25-81 years at centres in Germany, Switzerland, and the UK. Eligible patients had proven clinical and biochemical endogenous hyperinsulinaemic hypoglycaemia and no evidence for metastatic disease on conventional imaging. CT/MRI imaging was done at referring centres according to standard protocols. At three tertiary nuclear medicine centres, we used whole body planar images and SPECT/CT of the abdomen up to 168 h after injection of (111)In-[Lys40(Ahx-DTPA-(111)In)NH2]-exendin-4 ((111)In-DTPA-exendin-4) to identify insulinomas. Consenting patients underwent surgery and imaging findings were confirmed histologically.

Findings: Between Oct 1, 2008, and Dec 31, 2011, we recruited 30 patients. All patients underwent (111)In-DTPA-exendin-4 imaging, 25 patients underwent surgery (with histological analysis), and 27 patients were assessed with CT/MRI. (111)In-DTPA-exendin-4 SPECT/CT correctly detected 19 insulinomas and four additional positive lesions (two islet-cell hyperplasia and two uncharacterised lesions) resulting in a positive predictive value of 83% (95% CI 62-94). One true negative (islet-cell hyperplasia) and one false negative (malignant insulinoma) result was identified in separate patients by (111)In-DTPA-exendin-4 SPECT/CT. Seven patients (23%) were referred to surgery on the basis of (111)In-DTPA-exendin-4 imaging alone. For 23 assessable patients, (111)In-DTPA-exendin-4 SPECT/CT had a higher sensitivity (95% [95% CI 74-100]) than did CT/MRI (47% [27-68]; p=0.011).

Interpretation: (111)In-DTPA-exendin-4 SPECT/CT could provide a good second-line imaging strategy for patients with negative results on initial imaging with CT/MRI.

Funding: Oncosuisse, the Swiss National Science Foundation, and UK Department of Health.
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http://dx.doi.org/10.1016/S2213-8587(13)70049-4DOI Listing
October 2013
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