Generation of novel single-chain antibodies by phage-display technology to direct imaging agents highly selective to pancreatic beta- or alpha-cells in vivo.
OBJECTIVE
Noninvasive determination of pancreatic beta-cell mass in vivo has been hampered by the lack of suitable beta-cell-specific imaging agents. This report outlines an approach for the development of novel ligands homing selectively to islet cells in vivo.


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 beta- or alpha-cells. These SCAs are internalized by target cells, disappear rapidly from the vasculature, and exert no toxicity in vivo. Specific binding to beta- or alpha-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 strongly predicted the beta-cell mass and was inversely related to the glucose excursions during an intraperitoneal glucose tolerance test.


CONCLUSIONS
Our data provide strong evidence that the presented SCAs are highly specific for pancreatic beta-cells and enable imaging and quantification in vivo.
Ueberberg
Sandra
S
Department of Internal Medicine I, Division of Endocrinology and Metabolism, Berufsgenossenschaftliches University Hospital Bergmannsheil, Ruhr-University Bochum, Bochum, Germany.
Meier
Juris J
JJ
Waengler
Carmen
C
Schechinger
Wolfgang
W
Dietrich
Johannes W
JW
Tannapfel
Andrea
A
Schmitz
Inge
I
Schirrmacher
Ralf
R
Köller
Manfred
M
Klein
Harald H
HH
Schneider
Stephan
S
D000818:Animals; D000906:Antibodies / Q000032:analysis; D000918:Antibody Specificity; D017209:Apoptosis; D002460:Cell Line; D002470:Cell Survival; D003921:Diabetes Mellitus, Experimental / Q000473:pathology / Q000503:physiopathology*; D004721:Endoplasmic Reticulum / Q000276:immunology; D005260:Female; D050416:Glucagon-Secreting Cells / Q000276:immunology / Q000473:pathology / Q000648:ultrastructure*; D005951:Glucose Tolerance Test; D006801:Humans; D007150:Immunohistochemistry; D050417:Insulin-Secreting Cells / Q000276:immunology / Q000473:pathology / Q000648:ultrastructure*; D008854:Microscopy, Electron; D051381:Rats; D022142:Secretory Vesicles / Q000276:immunology / Q000473:pathology
D000906:Antibodies