The successful peptide receptor imaging of tumors, as exemplified for somatostatin receptors, is based on the overexpression of peptide receptors in selected tumors and the high-affinity binding to these tumors of agonist radioligands that are subsequently internalized into the tumor cells in which they accumulate. Although in vitro studies have shown ample evidence that the ligand-receptor complex is internalized, in vivo evidence of agonist-induced internalization of peptide receptors, such as somatostatin receptors, is missing. Methods: Rats subcutaneously transplanted with the somatostatin receptor subtype 2 (sst 2 )-expressing AR42J tumor cells were treated with intravenous injections of various doses of the sst 2 agonist [Tyr 3 , Thr 8 ]-octreotide (TATE) or of the sst 2 antagonist 1,4,7,10-tetraazacyclododecane-N,N9,N$,N9$,-tetraacetic acid (DOTA)-Bass and were sacrificed at various times ranging from 2.5 min to 24 h after injection. The tumors and pancreas were then removed from each animal. All tissue samples were processed for sst 2 immunohistochemistry using sst 2 -specific antibodies. Results: Compared with the sst 2 receptors in untreated animals, which localized at the plasma membrane in pancreatic and AR42J tumor cells, the sst 2 receptors in treated animals are detected intracellularly after an intravenous injection of the agonist TATE. Internalization is fast, as the receptors are already internalizing 2.5 min after TATE injection. The process is extremely efficient, as most of the cell surface receptors internalize into the cell and are found in endosomelike structures after TATE injection. The internalization is most likely reversible, because 24 h after injection the receptors are again found at the cell surface. The process is also agonist-dependent, because internalization is seen with high-affinity sst 2 agonists but not with high-affinity sst 2 antagonists. The same internalization properties are seen in pancreatic and AR42J tumor cells. They can further be confirmed in vitro in human embryonic kidneysst 2 cells, with an immunofluorescence microscopy-based sst 2 internalization assay. Conclusion: These animal data strongly indicate that the process of in vivo sst 2 internalization after agonist stimulation is fast, extremely efficient, and fully functional under in vivo conditions in neoplastic and physiologic sst 2 target tissues. This molecular process is, therefore, likely to be responsible for the high and long-lasting uptake of sst 2 radioligands seen in vivo in sst 2 -expressing tumors.

Lung cancer is the leading cause of cancer death worldwide. The overall 5-year survival after therapy is about 16% and there is a clear need for better treatment options, such as therapies targeting specific molecular structures. G-protein coupled receptors (GPCRs), as the largest family of cell surface receptors, represent an important group of potential targets for diagnostics and therapy. We therefore used laser capture microdissection and GPCR-focused Affymetrix microarrays to examine the expression of 929 GPCR transcripts in tissue samples of 10 patients with squamous cell carcinoma and 7 with adenocarcinoma in order to identify novel targets in non-small cell lung carcinoma (NSCLC). The relative gene expression levels were calculated in tumour samples compared to samples of the neighbouring alveolar tissue in every patient. Based on this unique study design, we identified 5 significantly overexpressed GPCRs in squamous cell carcinoma, in the following decreasing order of expression: GPR87 > CMKOR1 > FZD10 > LGR4 > P2RY11. All are non-olfactory and GRAFS (glutamate, rhodopsin, adhesion, frizzled/taste2, secretin family) classified. GPR87, LGR4 and CMKOR1 are orphan receptors. GPR87 stands out as a candidate for further target validation due to its marked overexpression and correlation on a mutation-based level to squamous cell carcinoma.

. Role of the different isoforms of cyclooxygenase and nitric oxide synthase during gastric ulcer healing in cyclooxygenase-1 and -2 knockout mice.

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