Generation of Novel Single-Chain Antibodies by Phage-Display Technology to Direct Imaging Agents Highly Selective to Pancreatic β- or α-Cells In Vivo

Generation of Novel Single-Chain Antibodies by Phage-Display Technology to Direct Imaging Agents Highly Selective to Pancreatic β- or α-Cells In Vivo Sandra Ueberberg 1 , Juris J. Meier 2 , Carmen Waengler 3 , 4 , Wolfgang Schechinger 1 , Johannes W. Dietrich 1 , Andrea Tannapfel 5 , Inge Schmitz 5 , Ralf Schirrmacher 4 , Manfred Köller 6 , Harald H. Klein 1 and Stephan Schneider 1 1 Department of Internal Medicine I, Division of Endocrinology and Metabolism, Berufsgenossenschaftliches University Hospital Bergmannsheil, Ruhr-University Bochum, Bochum, Germany; 2 Department of Internal Medicine I, St. Josef-Hospital, Ruhr-University Bochum, Bochum, Germany; 3 Department of Nuclear Medicine, Hospital of the Ludwig-Maximilians-University, Munich, Germany; 4 Department of Neurology & Neurosurgery, Lady Davis Institute for Medical Research, McGill University, Montreal, Canada; 5 Institute for Pathology, Ruhr-University Bochum, Bochum, Germany; 6 Chirurgische Forschung, Berufsgenossenschaftliches Universitätsklinikum Bergmannsheil, Ruhr-Universität Bochum, Bochum, Germany. Corresponding author: Stephan Schneider, stephan.schneider{at}ruhr-unibochum.de . Abstract OBJECTIVE Noninvasive determination of pancreatic β-cell mass in vivo has been hampered by the lack of suitable β-cell–specific imaging agents. This report outlines an approach for the development of novel ligands homing selectively to islet cells in vivo. RESEARCH DESIGN AND METHODS To generate agents specifically binding to pancreatic islets, a phage library was screened for single-chain antibodies (SCAs) on rat islets using two different approaches. 1 ) The library was injected into rats in vivo, and islets were isolated after a circulation time of 5 min. 2 ) Pancreatic islets were directly isolated, and the library was panned in the islets in vitro. Subsequently, the identified SCAs were extensively characterized in vitro and in vivo. RESULTS We report the generation of SCAs that bind highly selective to either β- or α-cells. These SCAs are internalized by target cells, disappear rapidly from the vasculature, and exert no toxicity in vivo. Specific binding to β- or α-cells was detected in cell lines in vitro, in rats in vivo, and in human tissue in situ. Electron microscopy demonstrated binding of SCAs to the endoplasmatic reticulum and the secretory granules. Finally, in a biodistribution study the labeling intensity derived from [ 125 I]-labeled SCAs after intravenous administration in rats strongl