Martin Gotthardt

A new technique for in vivo imaging of specific GLP-1 binding sites: First results in small rodents

EXPERIMENTAL OBJECTIVESnIn vivo imaging of GLP-1 receptor-positive tissues may allow examination of physiologic and pathophysiologic processes. Based on the GLP-1 analog Exendin 4, we have developed a radiolabeled compound specifically targeting the GLP-1 receptor (DTPA-Lys40-Exendin 4). This work aims to detect GLP-1 receptor-positive tissues by biodistribution studies and in vivo small animal imaging studies. For in vivo imaging, a high-resolution multi-pinhole SPECT (single photon emission computed tomography) system was used in conjunction with an MRI (magnetic resonance imaging) system for image fusion.nnnRESULTSnDTPA-Lys40-Exendin 4 can be labeled with 111In to high specific activity (40 GBq/micromol). The radiochemical purity reliably exceeded 95%. Using this compound for in vivo small animal imaging of rats and mice as well as for biodistribution studies, specific GLP-1 binding sites could be detected in stomach, pancreas, lung, adrenals, and pituitary. Receptor-positive tissues were visualized with a high-resolution SPECT system with a resolution of less than 1 mm.nnnCONCLUSIONSnThe new technique using DTPA-Lys40-Exendin 4 allows highly sensitive imaging of GLP-1 receptor-positive tissues in vivo. Therefore, intra-individual follow-up studies of GLP-1 receptor-positive tissue could be conducted in vivo.

Non-invasive quantification of the beta cell mass by SPECT with 111In-labelled exendin

AbstractAims/hypothesisA reliable method for in vivo quantification of pancreatic beta cell mass (BCM) could lead to further insight into the pathophysiology of diabetes. The glucagon-like peptide 1 receptor, abundantly expressed on beta cells, may be a suitable target for imaging. We investigated the potential of radiotracer imaging with the GLP-1 analogue exendin labelled with indium-111 for determination of BCM in vivo in a rodent model of beta cell loss and in patients with type 1 diabetes and healthy individuals.MethodsThe targeting of 111In-labelled exendin was examined in a rat model of alloxan-induced beta cell loss. Rats were injected with 15xa0MBq 111In-labelled exendin and single photon emission computed tomography (SPECT) acquisition was performed 1xa0h post injection, followed by dissection, biodistribution and ex vivo autoradiography studies of pancreatic sections. BCM was determined by morphometric analysis after staining with an anti-insulin antibody. For clinical evaluation SPECT was acquired 4, 24 and 48xa0h after injection of 150xa0MBq 111In-labelled exendin in five patients with type 1 diabetes and five healthy individuals. The tracer uptake was determined by quantitative analysis of the SPECT images.ResultsIn rats, 111In-labelled exendin specifically targets the beta cells and pancreatic uptake is highly correlated with BCM. In humans, the pancreas was visible in SPECT images and the pancreatic uptake showed high interindividual variation with a substantially lower uptake in patients with type 1 diabetes.Conclusions/interpretationThese studies indicate that 111In-labelled exendin may be suitable for non-invasive quantification of BCM.n Trial registration ClinicalTrials.gov NCT01825148, EudraCT: 2012-000619-10

Improved tumour detection by gastrin receptor scintigraphy in patients with metastasised medullary thyroid carcinoma

PurposeRadiopeptide imaging is a valuable imaging method in the management of patients with neuroendocrine tumours (NET). To determine the clinical performance of gastrin receptor scintigraphy (GRS), it was compared with somatostatin receptor scintigraphy (SRS), computed tomography (CT) and 18F-FDG positron emission tomography (PET) in patients with metastasised/recurrent medullary thyroid carcinoma (MTC).MethodsTwenty-seven consecutive patients underwent imaging with GRS, SRS (19 patients), CT and PET (26 patients). GRS and SRS were compared with respect to tumour detection and uptake. CT, PET, magnetic resonance imaging (MRI), ultrasound (US) and follow-up were used for verification of findings. In addition, GRS, CT and PET were directly compared with each other to determine which method performs best.ResultsNineteen patients underwent both GRS and SRS. Among these, GRS showed a tumour detection rate of 94.2% as compared to 40.7% for SRS [mean number of tumour sites (±SD) and 95% confidence intervals (CI): GRS 4.3±3.1/2.8–5.7, SRS 1.8±1.6/1.1–2.6]. In 26 patients, GRS, CT and PET were compared. Here, GRS showed a tumour detection rate of 87.3% (CT 76.1%, PET 67.2%; mean number of tumour sites and 95% CI: GRS 4.5±4.0/2.9–6.1, CT 3.9±3.5/2.5–5.3, PET 3.5±3.3/2.1–4.8). If GRS and CT were combined, they were able to detect 96.7% of areas of tumour involvement.ConclusionGRS had a higher tumour detection rate than SRS and PET in our study. GRS in combination with CT was most effective in the detection of metastatic MTC.

Correlation Between In Vivo 18F-FDG PET and Immunohistochemical Markers of Glucose Uptake and Metabolism in Pheochromocytoma and Paraganglioma

Pheochromocytomas and paragangliomas (PPGLs) can be localized by 18F-FDG PET. The uptake is particularly high in tumors with an underlying succinate dehydrogenase (SDH) mutation. SDHx-related PPGLs are characterized by compromised oxidative phosphorylation and a pseudohypoxic response, which mediates an increase in aerobic glycolysis, also known as the Warburg effect. The aim of this study was to explore the hypothesis that increased uptake of 18F-FDG in SDHx-related PPGLs is reflective of increased glycolytic activity and is correlated with expression of different proteins involved in glucose uptake and metabolism through the glycolytic pathway. Methods: Twenty-seven PPGLs collected from patients with hereditary mutations in SDHB (n = 2), SDHD (n = 3), RET (n = 5), neurofibromatosis 1 (n = 1), and myc-associated factor X (n = 1) and sporadic patients (n = 15) were investigated. Preoperative 18F-FDG PET/CT studies were analyzed; mean and maximum standardized uptake values (SUVs) in manually drawn regions of interest were calculated. The expression of proteins involved in glucose uptake (glucose transporters types 1 and 3 [GLUT-1 and -3, respectively]), phosphorylation (hexokinases 1, 2, and 3 [HK-1, -2, and -3, respectively]), glycolysis (monocarboxylate transporter type 4 [MCT-4]), and angiogenesis (vascular endothelial growth factor [VEGF], CD34) were examined in paraffin-embedded tumor tissues using immunohistochemical staining with peroxidase-catalyzed polymerization of diaminobenzidine as a read-out. The expression was correlated with corresponding SUVs. Results: Both maximum and mean SUVs for SDHx-related tumors were significantly higher than those for sporadic and other hereditary tumors (P < 0.01). The expression of HK-2 and HK-3 was significantly higher in SDHx-related PPGLs than in sporadic PPGLs (P = 0.022 and 0.025, respectively). The expression of HK-2 and VEGF was significantly higher in SDHx-related PPGLs than in other hereditary PPGLs (P = 0.039 and 0.008, respectively). No statistical differences in the expression were observed for GLUT-1, GLUT-3, and MCT-4. The percentage anti-CD 34 staining and mean vessel perimeter were significantly higher in SDHx-related PPGLs than in sporadic tumors (P = 0.050 and 0.010, respectively). Mean SUVs significantly correlated with the expression of HK-2 (P = 0.027), HK-3 (P = 0.013), VEGF (P = 0.049), and MCT-4 (P = 0.020). Conclusion: The activation of aerobic glycolysis in SDHx-related PPGLs is associated with increased 18F-FDG accumulation due to accelerated glucose phosphorylation by hexokinases rather than increased expression of glucose transporters.

Targeting of a CCK 2 receptor splice variant with 111 In-labelled cholecystokinin-8 (CCK8) and 111 In-labelled minigastrin

PurposeRadiolabelled cholecystokinin (CCK) and gastrin-derived peptides potentially can be used for peptide receptor radionuclide therapy (PRRT). Recently, a splice variant version of the CCK2R has been identified, designated CCK2i4svR. Constitutive expression of this receptor has been demonstrated in human colorectal cancer and in pancreatic cancer, but not in normal tissue. So far, it has never been shown whether radiolabelled peptides can target the CCK2i4svR in vivo. In this paper, we investigated the potential of sulfated 111In-labelled DOTA-CCK8 (sCCK8), a pan-CCKR-binding peptide, and [111In]DOTA-minigastrin (MG0), a CCK2R selective peptide, for the targeting of the CCK2i4svR.Materials and methodsThe receptor binding affinity of [111In]DOTA-sCCK8 and [111In]DOTA-MG0 for the CCK2R and CCK2i4svR was determined using stably transfected HEK293 cell lines, expressing either CCK2R or CCK2i4svR. Tumour targeting was studied in HEK293-CCK2i4svR tumour-bearing athymic mice.Results[111In]DOTA-sCCK8 as well as [111In]DOTA-MG0 specifically bound both CCK2R and CCK2i4svR with affinities in the low nanomolar range. In vivo experiments revealed that accumulation of both peptides in CCK2i4svR-positive tumours was similar (3.21u2009±u20090.77 and 3.01u2009±u20090.67%ID/g, sCCK8 and MG0, respectively, 24xa0h p.i.). Kidney retention of [111In]DOTA-MG0 (32.4u2009±u20097.5%ID/g, 24xa0h p.i.) was markedly higher than that of [111In]DOTA-sCCK8 (2.75u2009±u20090.31%ID/g, 24xa0h p.i.).ConclusionWe demonstrated that the CCK2i4svR is a potential target for PRRT using a radiolabelled sulfated CCK8 peptide. As this receptor is expressed on colorectal and pancreatic tumours, but not in normal tissue, these tumours are potentially new targets for PRRT with CCK8 and gastrin analogs.

Amplitude-based optimal respiratory gating in positron emission tomography in patients with primary lung cancer

AbstractObjectivesRespiratory motion during PET imaging introduces quantitative and diagnostic inaccuracies, which may result in non-optimal patient management. This study investigated the effects of respiratory gating on image quantification using an amplitude-based optimal respiratory gating (ORG) algorithm.MethodsWhole body FDG-PET/CT was performed in 66 lung cancer patients. The respiratory signal was obtained using a pressure sensor integrated in an elastic belt placed around the patient’s thorax. ORG images were reconstructed with 50xa0%, 35xa0%, and 20xa0% of acquired PET data (duty cycle). Lesions were grouped into anatomical locations. Differences in lesion volume between ORG and non-gated images, and mean FDG-uptake (SUVmean) were calculated.ResultsLesions in the middle and lower lobes demonstrated a significant SUVmean increasexa0for all duty cycles and volume decrease for duty cycles of 35 % and 20 %. Significant increase in SUVmean and decrease in volume for lesions in the upper lobes were observed for a 20xa0% duty cycle. The SUVmean increase for central lesions was significant forxa0all duty cycles, whereas a significant volume decrease was observed for a duty cycle of 20xa0%.ConclusionsThis study implies that ORG could influence clinical PET imaging with respect to response monitoring and radiotherapy planning.Key Points• Quantifying lesion volume and uptake in PET is important for patient managementn • Respiratory motion artefacts introduce inaccuracies in quantification of PET imagesn • Amplitude-based optimal respiratory gating maintains image quality through selection of duty cyclen • The effect of respiratory gating on lesion quantification depends on anatomical location

Beta cell imaging - a key tool in optimized diabetes prevention and treatment

The prevalence of diabetes is 382 million worldwide, and is expected to rise to 592 million in 2035 (http://www.idf.org/diabetesatlas); 2.5-15% of national annual healthcare budgets are related to diabetes care, potentially increasing to 40% in high-prevalence countries. Beta cell dysfunction and death are central events in diabetes pathogenesis, but the natural history of beta cell loss remains unknown. Clinical imaging of beta cells will play a pivotal role in developing strategies for optimized diabetes prevention and treatment.

In vivo imaging of beta cells with radiotracers: state of the art, prospects and recommendations for development and use

Radiotracer imaging is characterised by high in vivo sensitivity, with a detection limit in the lower picomolar range. Therefore, radiotracers represent a valuable tool for imaging pancreatic beta cells. High demands are made of radiotracers for in vivo imaging of beta cells. Beta cells represent only a small fraction of the volume of the pancreas (usually 1–3%) and are scattered in the tiny islets of Langerhans throughout the organ. In order to be able to measure a beta cell-specific signal, one has to rely on highly specific tracer molecules because current in vivo imaging technologies do not allow the resolution of single islets in humans non-invasively. Currently, a considerable amount of preclinical data are available for several radiotracers and three are under clinical evaluation. We summarise the current status of the evaluation of these tracer molecules and put forward recommendations for their further evaluation.

111In-exendin uptake in the pancreas correlates with the beta cell mass and not with the alpha cell mass

Targeting of the GLP-1 receptor with 111In-labeled exendin is an attractive approach to determine the β-cell mass (BCM). Preclinical studies as well as a proof-of-concept study in type 1 diabetic patients and healthy subjects showed a direct correlation between BCM and radiotracer uptake. Despite these promising initial results, the influence of α-cells on the uptake of the radiotracer remains a matter of debate. In this study, we determined the correlation between pancreatic tracer uptake and β- and α-cell mass in a rat model for β-cell loss. The uptake of 111In-exendin (% ID/g) showed a strong positive linear correlation with the BCM (Pearson r = 0.82). The fraction of glucagon-positive cells in the total endocrine mass was increased after alloxan treatment (26% ± 4%, 43% ± 8%, and 69% ± 21% for 0, 45, and 60 mg/kg alloxan, respectively). The uptake of 111In-exendin showed a negative linear correlation with the α-cell fraction (Pearson r = −0.76). These data clearly indicate toward specificity of 111In-exendin for β-cells and that the influence of the α-cells on 111In-exendin uptake is negligible.

Combined PET/MRI: from Status Quo to Status Go. Summary Report of the Fifth International Workshop on PET/MR Imaging; February 15–19, 2016; Tübingen, Germany

This article provides a collaborative perspective of the discussions and conclusions from the fifth international workshop of combined positron emission tomorgraphy (PET)/magnetic resonance imaging (MRI) that was held in Tübingen, Germany, from February 15 to 19, 2016. Specifically, we summarise the second part of the workshop made up of invited presentations from active researchers in the field of PET/MRI and associated fields augmented by round table discussions and dialogue boards with specific topics. This year, this included practical advice as to possible approaches to moving PET/MRI into clinical routine, the use of PET/MRI in brain receptor imaging, in assessing cardiovascular diseases, cancer, infection, and inflammatory diseases. To address perceived challenges still remaining to innovatively integrate PET and MRI system technologies, a dedicated round table session brought together key representatives from industry and academia who were engaged with either the conceptualisation or early adoption of hybrid PET/MRI systems. Discussions during the workshop highlighted that emerging unique applications of PET/MRI such as the ability to provide multi-parametric quantitative and visual information which will enable not only overall disease detection but also disease characterisation would eventually be regarded as compelling arguments for the adoption of PET/MR. However, as indicated by previous workshops, evidence in favour of this observation is only growing slowly, mainly due to the ongoing inability to pool data cohorts from independent trials as well as different systems and sites. The participants emphasised that moving from status quo to status go entails the need to adopt standardised imaging procedures and the readiness to act together prospectively across multiple PET/MRI sites and vendors.