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GLP-1 Receptor Expression in Human Tumors and Human Normal Tissues: Potential for In Vivo Targeting

Division of Cell Biology and Experimental Cancer Research, Institute of Pathology, University of Bern, Bern, Switzerland

View larger version (54K): [in this window] [in a new window]   FIGURE 1.  Representative in vitro receptor autoradiography to assess 125I-GLP-1(7–36)amide binding to human tumor tissue. (A) Hematoxylin- and eosin-stained (HE) tissue section shows pheochromocytoma. Bar = 1 mm. (B) Autoradiogram shows total binding of 125I-GLP-1(7–36)amide. There is very strong labeling of the entire tumor tissue. Inset shows autoradiogram with nonspecific (ns) binding of 125I-GLP-1(7–36)amide: complete displacement of 125I-GLP-1(7–36)amide in presence of 100 nM unlabeled (cold) GLP-1(7–36)amide.

View larger version (29K): [in this window] [in a new window]   FIGURE 2.  In vitro receptor autoradiography on human pancreas. (A) Immunohistochemistry for synaptophysin staining islets (arrowheads) surrounded by acini. Bar = 1 mm. (B) Autoradiogram shows total binding of 125I-GLP-1(7–36)amide: strong binding to islets, weak binding to acini. (C) Autoradiogram shows nonspecific binding of 125I-GLP-1(7–36)amide in presence of 100 nM unlabeled (cold) GLP-1(7–36)amide.

View larger version (96K): [in this window] [in a new window]   FIGURE 3.  In vitro receptor autoradiography on human normal tissues. (A and C) Hematoxylin- and eosin-stained (HE) tissue sections show the following: (A) duodenum with Brunner's glands (arrowhead) and overlying mucosa (m) and (C) colon with myenteric nerve plexus (arrowheads), muscularis propria (mp), and mucosa (m). Bars = 1 mm. (B and D) Autoradiograms show total binding of 125I-GLP-1(7–36)amide. (B) Duodenum with very strong specific binding to Brunner's glands (arrowhead). Note that labeling observed in mucosa (m) is nonspecific. (D) Colon with specific binding to myenteric plexus (arrowheads). As in the duodenum, labeling observed in mucosa (m) is nonspecific.

View larger version (85K): [in this window] [in a new window]   FIGURE 4.  Comparison of in vitro GLP-1 receptor autoradiography of lung in rat and human. (A and C) Hemotoxylin- and eosin-stained (HE) tissue sections show the following: (A) rat lung with alveolar septa (stars) and large blood vessels (arrows) and (C) human lung with alveolar septa (stars) and small blood vessels (arrows). Bars = 1 mm. (B and D) Autoradiograms show total binding of 125I-GLP-1(7–36)amide. (B) Rat lung with very strong and diffuse binding to alveolar septa (stars) and no binding to large blood vessels (arrows). (D) Human lung with topically restricted binding, partly to small blood vessels (arrows) but not to alveolar septa (stars). Complete displacement of 125I-GLP-1(7–36)amide by 100 nM unlabeled (cold) GLP-1(7–36)amide provides proof of specific GLP-1 receptor binding (not shown).

View larger version (19K): [in this window] [in a new window]   FIGURE 5.  Representative competition experiments in human tumor and normal tissues—namely, pheochromocytoma (A), pancreatic islets (B), duodenal Brunner's glands (C), and myenteric nerve plexus of colon (D). In all examples, high-affinity displacement of 125I-GLP-1(7–36)amide by GLP-1 receptor-selective agonists GLP-1(7–36)amide and exendin-4 and low-affinity displacement by GLP-2 receptor-selective agonist GLP-2 and glucagon receptor-selective agonist glucagon(1–29) was evident.