Aims/hypothesis A reliable method for in vivo quantification of pancreatic beta cell mass (BCM) could lead to further insight into the pathophysiology of diabetes. The glucagonlike 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 111 In-labelled exendin was examined in a rat model of alloxan-induced beta cell loss. Rats were injected with 15 MBq 111 In-labelled exendin and single photon emission computed tomography (SPECT) acquisition was performed 1 h 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 48 h after injection of 150 MBq 111 In-labelled exendin in five patients with type 1 Maarten Brom and Wietske Woliner-van der Weg contributed equally to this study. Diabetologia (2014) 57:950-959 DOI 10.1007 diabetes and five healthy individuals. The tracer uptake was determined by quantitative analysis of the SPECT images. Results In rats, 111 In-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/interpretation These studies indicate that 111 Inlabelled exendin may be suitable for non-invasive quantification of BCM.

Purpose:To investigate the physiological origins responsible for the varying blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) responses to carbogen (95% O 2 /5% CO 2 ) breathing observed with different tumor types. Materials and Methods:Susceptibility contrast-enhanced MRI using the exogenous blood pool contrast agent NC100150 to determine blood volume and vessel size, and immunohistochemical-derived morphometric parameters, were determined in GH3 prolactinomas and RIF-1 fibrosarcomas, both grown in mice, which exhibited very different BOLD responses to carbogen.Results: Administration of NC100150 increased the R 2 * and R 2 rates of both tumor types, and indicated a significant four-fold larger blood volume in the GH3 tumor. The ratio ⌬R 2 */⌬R 2 showed that the capillaries in the GH3 were two-fold larger than those in the RIF-1, in agreement with morphometric analysis. Carbogen breathing induced a significant 25% decrease in R 2 * in the GH3 prolactinoma, whereas the response in the RIF-1 fibrosarcoma was negligible. Conclusion:Low blood volume and small vessel size (and hence reduced hematocrit) are two reasons for the lack of R 2 * change in the RIF-1 with carbogen breathing. BOLD MRI is sensitive to erythrocyte-perfused vessels, whereas exogenous contrast agents interrogate the total perfused vascular volume. BOLD MRI, coupled with a carbogen challenge, provides information on functional, hemodynamic tumor vasculature.

A semiautomatic method based on a computerized digital image analysis system was developed to quantitate the perfused fraction of blood vessels and the relative vascular area in cross-sections of human glioma xenografts, implanted subcutaneously in athymic mice or intracerebrally in nude rats. The fluorescent dye Hoechst 33342 was injected intravenously to detect perfused tumor vessels. An immunofluorescent staining of Collagen type IV visualized the vascular structures in the same tumor section. Whole tumor sections were automatically scanned twice on a computercontrolled motorized stage of a fluorescence microscope under two different settings of the image analysis system. At the beginning of a scanning session an interactive routine was used to determine the threshold value for segmentation of vascular structures from the darker background. After the first scan a composite image was created, from the individually processed microscopic images, containing the detected vascular structures. The second scan yielded another composite image with objects representing the perfused areas. When both composite images were combined the overlapping structures showed the perfused vessels. Differences in perfused fractions and relative vascular areas were found between different tumors. The reproducibility of this analysis system was tested and evaluated. The method developed here provides a fast and accurate technique for simultaneous quantitative analysis of tumor perfusion and vasculature.

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Hypoxic tumor cells are resistant to radiotherapy and various chemotherapeutic agents. The pretherapeutic assessment of intratumoral hypoxia may allow selection of patients for intensified treatment regimens. Carbonic anhydrase IX (CAIX) is an endogenous hypoxia-related protein involved in pH regulation and is upregulated in many tumor types. Radionuclide imaging using a monoclonal antibody against CAIX, such as cG250, may allow noninvasive PET of hypoxia in these tumor types. The aims of this study were to investigate whether 89 Zr-labeled cG250-F(ab9) 2 allowed visualization of tumor hypoxia using small-animal PET and whether the tracer showed spatial correlation to the microscopic distribution of CAIX-expressing cells in a human head and neck xenograft tumor model. Methods: Athymic mice with subcutaneous human head and neck carcinoma xenografts (SCCNij3) were imaged with small-animal PET after injection of 89 Zr-cG250-F(ab9) 2 . PET images were parameterized in terms of standardized uptake values (SUVs). After injection with the nitroimidazole hypoxia marker pimonidazole and the perfusion marker Hoechst 33342, the animals were sacrificed, tumors excised, and CAIX-and pimonidazole-marked hypoxia and blood perfusion were analyzed immunohistochemically. 89 Zr-cG250-F(ab9) 2 tumor uptake was analyzed by ex vivo activity counting and by autoradiography of tumor sections. Results: As early as 4 h after administration, accumulation of 89 Zr-cG250-F(ab9) 2 in the tumor had occurred and tumors were clearly visualized by PET, with reduced uptake by 24 h after injection. Pixel-bypixel analysis showed a significant positive spatial correlation between CAIX expression and 89 Zr-cG250-F(ab9) 2 localization (r 5 0.57-0.74; P , 0.0001). Also, significant correlations were found between pimonidazole staining intensity and 89 ZrcG250-F(ab9) 2 activity concentration, although less strong (r 5 0.46-0.68; P , 0.0001). Tumor maximum SUV correlated significantly with tumor uptake determined ex vivo (r 5 0.93; P 5 0.0067), as did fractions of CAIX and pimonidazole in tumor sections (r 5 0.75; P 5 0.03 and r 5 0.78; P 5 0.02, respectively). Conclusion: 89 Zr-labeled cG250-F(ab9) 2 small-animal PET showed rapid accumulation in a head and neck xenograft tumor model with good correlation to CAIX expression on a microscopic level.