Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P61278 (somatostatin)
 22,083 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Somatostatin mediates its actions through five different somatostatin receptor subtypes, sst1-sst5. Recently, the somatostatin analogs des-AA1,2,5-[D-Trp8, IAmp9]somatostatin and des-AA1,5-[Tyr2, D-Trp8, IAmp9]somatostatin were synthesized and shown to be sst1-selective when tested in COS-7 cells transfected with each of the sst subtypes. In the present study, we tested the binding affinity and specificity of the iodinatable analog in primary human tumors expressing various sst subtypes, selected on the basis of in situ hybridization experiments. Des-AA1,5-[Tyr2, D-Trp8, IAmp9]somatostatin was found to have a high affinity, comparable to that of the natural somatostatin-28, for sst1-expressing tumors such as prostate cancers. However, it had no affinity for tumors expressing the sst2, sst3, or sst5 subtypes. For comparison, the somatostatin analogs octreotide or Tyr3-octreotide have no affinity for sst1-expressing tumors, but high affinity for sst2- and sst5-expressing tumors and intermediate affinity for sst3-expressing tumors. These data represent the first characterization of a sst1-selective analog in human tumors; it may be of potential use in the therapy of sst1-expressing tumors as an antiproliferative agent, as well as providing a lead compound for the development of more potent sst1-selective radioligands for in vivo tumor scintigraphy.
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PMID:A selective analog for the somatostatin sst1-receptor subtype expressed by human tumors. 959 1

The availability of subtype-specific agonists and antagonists for somatostatin (SS) receptors (SSTRs) will be important for elucidation of the function of each receptor isoform in vivo. A SS analog, des-AA1,2,5-[D-Trp8, IAmp9]SS (CH275), has been shown previously to bind preferentially to SSTR1. In this report, we identify structural determinants in the ligand and receptor responsible for the selective binding of CH275 to SSTR1 by modifying both the ligand and the receptor. We propose that IAmp9 in CH275, like Lys9 in SS, interacts with Asp137 in the middle of the third transmembrane domain of SSTR1 to form an ion pair, while other residues unique to SSTR1 conbribute to binding selectivity of CH275 for SSTR1. Replacement of Asp137 with Asn resulted in loss of binding of radiolabeled SS and decreased potencies of both SS and CH275 to induce a change in the extracellular acidification rate measured by microphysiometry. The structural determinants for specific binding to SSTR1 were mapped in chimeric SSTR1/SSTR2 receptors. One chimera, 2beta, with the N-terminus to second transmembrane domain (TM2) from SSTR2 and the remainder of the receptor from SSTR1, had low affinity for CH275. Furthermore, when a single residue, Leu107, in TM2 of SSTR1 was replaced with Phe, the corresponding residue in SSTR2, a 20-fold decrease in affinity for CH275 with no significant change in affinity for SS was observed. A reciprocal change from Phe to Leu in the chimeric receptor 2beta resulted in a 10-fold increase in affinity for CH275. Thus, Leu107 is an important determinant for CH275 binding to SSTR1. To identify the moiety in CH275 which could interact with Leu107, a new analog des-AA1,2,5-[D-Trp8, Amp9]SS was prepared. This analog bound to both SSTR1 and SSTR2 with similar affinities; thus, subtype selectivity was lost. Collectively, these data support a binding model for CH275 in which the positively charged IAmp interacts with the negatively charged Asp137 in TM3 of SSTR1 and the isopropyl group of IAmp forms a hydrophobic interaction with Leu107 in TM2.
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PMID:Structural basis for the binding specificity of a SSTR1-selective analog of somatostatin. 1032 47

Previously reported results suggest that the analogue of the somatostatin des-AA1,2,5[D-Trp8,IAmp9]-somatostatin (CH-275) peptide bearing chelating agents able to coordinate radioactive metals could be used for scintigraphic imaging of tumor lesions overexpressing sstr1. An efficient synthetic procedure for the preparation of the somatostatin analogue CH-275 and its conjugate DTPAGlu-Gly-CH-275, bearing the chelating agent DTPAGlu (DTPAGlu=N,N-bis[2-[bis(carboxy-ethyl)amino]ethyl]-L-glutamic acid) on the N-terminus, by solid-phase peptide synthesis and 9-fluorenylmethoxycarbonyl (Fmoc) chemistry, is here reported. Rapid and efficient labeling of DTPAGlu-Gly-CH-275 was achieved by addition of 111In(III) to the compound. Typical yields were greater than 97% as determined by reversed phase high performance liquid chromatography (HPLC) at specific activities in the range 4-9 GBq/micromol (100-250 Ci/mmol). A preliminary biological assay of the binding ability of 111In-DTPAGlu-Gly-CH-275 indicates, however, that the labeled compound does not display any specific interaction with somatostatin sstr1 receptors in the tested cell lines. To confirm this unexpected negative result, competition binding experiments were carried out, in which fixed tracer amounts of the 125I-labeled somatostatin-14 were incubated with the receptor-expressing cells in the presence of DTPAGlu-Gly-CH-275 or CH-275 at concentrations ranging from 10(-10) to 10(-3) M. While CH-275 shows a IC50 of 80 nM similar to that already found in displacement experiments on CHO-K1 sstr1-transfected cells, DTPAGlu-Gly-CH-275 displays instead very low or negligible affinity towards this receptor. The NMR solution characterization indicates that the presence of DTPAGlu does not influence the conformational and chemical features of the peptide moiety, thus suggesting that the loss in binding activity should be due to steric hindrance of either the chelating agent DTPAGlu or its indium complex.
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PMID:Peptide-chelating agent conjugate for selective targeting of somatostatin receptor type 1: synthesis and characterization. 1552 34

Endogenous neuropeptides, acting as neurotransmitters or hormones in the brain, carry out important functions including neural plasticity, metabolism and angiogenesis. Previous neuropeptide studies have focused on peptide-rich brain regions such as the striatum or hypothalamus. Here we present an investigation of peptides in the visual system, composed of brain regions that are generally less rich in peptides, with the aim of providing the first broad overview of peptides involved in mammalian visual functions. We target three important parts of the visual system: the primary visual cortex (V1), lateral geniculate nucleus (LGN) and superior colliculus (SC). Our study is performed in the tree shrew, a close relative of primates. Using a combination of data dependent acquisition and targeted LC-MS/MS based neuropeptidomics; we identified a total of 52 peptides from the tree shrew visual system. A total of 26 peptides, for example GAV and neuropeptide K were identified in the visual system for the first time. Out of the total 52 peptides, 27 peptides with high signal-to-noise-ratio (>10) in extracted ion chromatograms (EIC) were subjected to label-free quantitation. We observed generally lower abundance of peptides in the LGN compared to V1 and SC. Consistently, a number of individual peptides showed high abundance in V1 (such as neuropeptide Y or somatostatin 28) and in SC (such as somatostatin 28 AA1-12). This study provides the first in-depth characterization of peptides in the mammalian visual system. These findings now permit the investigation of neuropeptide-regulated mechanisms of visual perception.
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PMID:Broad characterization of endogenous peptides in the tree shrew visual system. 2232 62


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