In Vivo Molecular Imaging of Somatostatin Receptors in Pancreatic Islet Cells and Neuroendocrine Tumors by Miniaturized Confocal Laser-Scanning Fluorescence Microscopy

摘要

The aim of the study was to evaluate real time in vivo molecular imaging of somatostatin receptors (sstrs) using a handheldminiaturized confocal laser scan microscope (CLM) in conjunction with fluorescein-labeled octreotate (OcF) in healthy mice andmurine models of neuroendocrine tumors. For CLM a small rigid probe (diameter 7 mm) with an integrated single line laser (488nm) was used (optical slice thickness 7 ? m; lateral resolution 0.7 ? m). OcF was synthesized via Fmoc solid-phase peptide synthesisand purified by HPLC showing high-affinity binding to the sstr2 (IC50 6.2 nmol). For in vitro evaluation, rat and human pancreaticcancer cells were used and characterized with respect to its sstr subtype expression and functional properties. For in vivo confocalimaging,healthymousepancreaticisletandrenaltubularcellsaswellasimmunoincompetentnudemiceharboringsstr-expressingtumors were evaluated. Incubation of sstr-positive cells with OcF showed a specific time- and dose-dependent staining of sstr-positive cells. CLM showed rapid internalization and homogenous cytoplasmatic distribution. After systemic application to mice(n ? 8), specific time-dependent internalization and cytoplasmatic distribution into pancreatic islet cells and tubular cells of therenalcortexwasrecorded.Afterinjectionintumor-harboringnudemice(n?8),sstr-positivecellsselectivelydisplayedacellsurfaceand cytoplasmatic staining. CLM-targeted biopsies detected sstr-positive tumor cells with a sensitivity of 87.5% and a specificityof 100% as correlated with ex vivo immunohistochemistry. CLM with OcF permits real-time molecular, functional, and morphologicalimagingofsstr-expressingcellstructures,allowingthespecificvisualizationofpancreaticisletcellsandneuroendocrinetumorsinvivo.