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Jahn U, Garske-Román U, Sandström M, Lubberink M, Sundin A. Impact of administered amount of peptide on tumor dosimetry at the first cycle of peptide receptor radionuclide therapy (PRRT) in relation to total tumor somatostatin receptor expression. EJNMMI Res 2023; 13:45. [PMID: 37204528 DOI: 10.1186/s13550-023-00997-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2023] [Accepted: 05/08/2023] [Indexed: 05/20/2023] Open
Abstract
BACKGROUND The accumulation of 177Lu-DOTATATE might be influenced by the amount of administered peptide in relation to the tumor somatostatin receptor expression. The effect of the administered peptide mass on the resulting absorbed dose in tumors and normal organs has not previously been assessed in relation to the patients' tumor load. METHOD Patients with small intestinal (n = 141) and pancreatic (n = 62) neuroendocrine tumors (NETs) who underwent PRRT were selected for retrospective evaluation. All patients had received 7.4 GBq 177Lu-DOTATATE, and the amount of administered peptide in the preparation varied from 93 to 456 µg. The absorbed dose in tumors and normal tissue at the first PRRT cycle was calculated, based on SPECT-measurements at day 1, 4, and 7 post-infusion. The total tumor somatostatin receptor expression (tTSSTRE) was calculated on SPECT after 24 h by multiplying the functional tumor volume, delineated by 42% cut-off VOIs of the highest activity, with the SUVmean for the respective tumor VOIs. Spearman's rank correlation analyzed any relationship between the administered amount of peptide and the absorbed dose in tumors and normal organs, in relation to the patients' tTSSTRE. RESULTS There was no correlation between the amount of peptide and any of the tested parameters in relation to tTSSTRE. CONCLUSION In this retrospective analysis, no correlation between the amount of administered peptide in the 177Lu-DOTATATE preparation and the absorbed radiation doses in tumors and normal tissues was demonstrated in relation to the total tumor SSTR expression.
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Affiliation(s)
- Ulrika Jahn
- Department of Surgical Sciences, Nuclear Medicine and PET, Uppsala University Hospital, 751 85, Uppsala, Sweden.
- Medical Imaging Centre, Uppsala University Hospital, Uppsala, Sweden.
| | - Ulrike Garske-Román
- Department of Blood and Tumor Diseases, Uppsala University Hospital, Uppsala, Sweden
- Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - Mattias Sandström
- Department of Surgical Sciences, Nuclear Medicine and PET, Uppsala University Hospital, 751 85, Uppsala, Sweden
- Department of Medical Physics, Uppsala University Hospital, Uppsala, Sweden
| | - Mark Lubberink
- Department of Surgical Sciences, Nuclear Medicine and PET, Uppsala University Hospital, 751 85, Uppsala, Sweden
- Department of Medical Physics, Uppsala University Hospital, Uppsala, Sweden
| | - Anders Sundin
- Department of Surgical Sciences, Nuclear Medicine and PET, Uppsala University Hospital, 751 85, Uppsala, Sweden
- Medical Imaging Centre, Uppsala University Hospital, Uppsala, Sweden
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A Physiologically Based Pharmacokinetic Model for In Vivo Alpha Particle Generators Targeting Neuroendocrine Tumors in Mice. Pharmaceutics 2021; 13:pharmaceutics13122132. [PMID: 34959413 PMCID: PMC8703774 DOI: 10.3390/pharmaceutics13122132] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 12/04/2021] [Accepted: 12/07/2021] [Indexed: 12/13/2022] Open
Abstract
In vivo alpha particle generators have great potential for the treatment of neuroendocrine tumors in alpha-emitter-based peptide receptor radionuclide therapy (α-PRRT). Quantitative pharmacokinetic analyses of the in vivo alpha particle generator and its radioactive decay products are required to address concerns about the efficacy and safety of α-PRRT. A murine whole-body physiologically based pharmacokinetic (PBPK) model was developed for 212Pb-labeled somatostatin analogs (212Pb-SSTA). The model describes pharmacokinetics of 212Pb-SSTA and its decay products, including specific and non-specific glomerular and tubular uptake. Absorbed dose coefficients (ADC) were calculated for bound and unbound radiolabeled SSTA and its decay products. Kidneys received the highest ADC (134 Gy/MBq) among non-target tissues. The alpha-emitting 212Po contributes more than 50% to absorbed doses in most tissues. Using this model, it is demonstrated that α-PRRT based on 212Pb-SSTA results in lower absorbed doses in non-target tissue than α-PRRT based on 212Bi-SSTA for a given kidneys absorbed dose. In both approaches, the energies released in the glomeruli and proximal tubules account for 54% and 46%, respectively, of the total energy absorbed in kidneys. The 212Pb-SSTA-PBPK model accelerates the translation from bench to bedside by enabling better experimental design and by improving the understanding of the underlying mechanisms.
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Distinct In Vitro Binding Profile of the Somatostatin Receptor Subtype 2 Antagonist [ 177Lu]Lu-OPS201 Compared to the Agonist [ 177Lu]Lu-DOTA-TATE. Pharmaceuticals (Basel) 2021; 14:ph14121265. [PMID: 34959665 PMCID: PMC8706879 DOI: 10.3390/ph14121265] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Revised: 12/01/2021] [Accepted: 12/02/2021] [Indexed: 01/14/2023] Open
Abstract
Treatment of neuroendocrine tumours with the radiolabelled somatostatin receptor subtype 2 (SST2) peptide agonist [177Lu]Lu-DOTA-TATE is effective and well-established. Recent studies suggest improved therapeutic efficacy using the SST2 peptide antagonist [177Lu]Lu-OPS201. However, little is known about the cellular mechanisms that lead to the observed differences. In the present in vitro study, we compared kinetic binding, saturation binding, competition binding, cellular uptake and release of [177Lu]Lu-OPS201 versus [177Lu]Lu-DOTA-TATE using HEK cells stably transfected with the human SST2. While [177Lu]Lu-OPS201 and [177Lu]Lu-DOTA-TATE exhibited comparable affinity (KD, 0.15 ± 0.003 and 0.08 ± 0.02 nM, respectively), [177Lu]Lu-OPS201 recognized four times more binding sites than [177Lu]Lu-DOTA-TATE. Competition assays demonstrated that a high concentration of the agonist displaced only 30% of [177Lu]Lu-OPS201 bound to HEK-SST2 cell membranes; an indication that the antagonist binds to additional sites that are not recognized by the agonist. [177Lu]Lu-OPS201 showed faster association and slower dissociation than [177Lu]Lu-DOTA-TATE. Whereas most of [177Lu]Lu-OPS201 remained at the cell surface, [177Lu]Lu-DOTA-TATE was almost completely internalised inside the cell. The present data identified distinct differences between [177Lu]Lu-OPS201 and [177Lu]Lu-DOTA-TATE regarding the recognition of receptor binding sites (higher for [177Lu]Lu-OPS201) and their kinetics (faster association and slower dissociation of [177Lu]Lu-OPS201) that explain, to a great extent, the improved therapeutic efficacy of [177Lu]Lu-OPS201 compared to [177Lu]Lu-DOTA-TATE.
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Jahn U, Ilan E, Velikyan I, Fröss-Baron K, Lubberink M, Sundin A. Receptor depletion and recovery in small-intestinal neuroendocrine tumors and normal tissues after administration of a single intravenous dose of octreotide measured by 68Ga-DOTATOC PET/CT. EJNMMI Res 2021; 11:118. [PMID: 34822040 PMCID: PMC8617112 DOI: 10.1186/s13550-021-00860-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Accepted: 11/03/2021] [Indexed: 01/04/2023] Open
Abstract
BACKGROUND Low-grade neuroendocrine tumors (NETs) are characterized by an abundance of somatostatin receptors (SSTR) that can be targeted with somatostatin analogs (SSA). When activated with a single dose of SSA, the receptor-ligand complex is internalized, and the receptor is by default recycled within 24 h. Ongoing medication with long-acting SSAs at 68Ga-DOTA-SSA-PET has been shown to increase the tumor-to-normal organ contrast. This study was performed to investigate the time-dependent extended effect (7 h) of a single intravenous dose of 400 µg short-acting octreotide on the tumor versus normal tissue uptake of 68Ga-DOTATOC. METHODS Patients with small-intestinal NETs received a single intravenous dose of 400 µg octreotide and underwent dynamic abdominal 68Ga-DOTATOC-PET/CT at three sessions (0, 3 and 6 h) plus static whole-body (WB) PET/CT (1, 4 and 7 h), starting each PET/CT session by administering 167 ± 21 MBq, 23.5 ± 4.2 µg (mean ± SD, n = 12) of 68Ga-DOTATOC. A previously acquired clinical whole-body 68Ga-DOTATOC scan was used as baseline. SUV and net uptake rate Ki were calculated in tumors, and SUV in healthy organs. RESULTS Tumor SUV decreased significantly from baseline to 1 h post-injection but subsequently increased over time and became similar to baseline at 4 h and 7 h. The tumor net uptake rate, Ki, similarly increased significantly over time and showed a linear correlation both with SUV and tumor-to-blood ratio. By contrast, the uptake in liver, spleen and pancreas remained significantly below baseline levels also at 7 h and the receptor turn-over in tumors thus exceeded that in the normal tissue, with restitution of tumor 68Ga-DOTATOC uptake mainly completed at 7 h. These results however differed depending on tumor size, with significant increases in Ki and SUV between the 1st and 2nd PET, in large tumors (≥ 4 mL) but not in small (> 1 to < 4 mL) tumors. CONCLUSION SSTR recycling is faster in small-intestinal NETs than in liver, spleen and pancreas. This opens the possibility to protect normal tissues during PRRT by administering a single dose of cold peptide hours before peptide receptor radionuclide therapy (PRRT), and most likely additionally improve the availability and uptake of the therapeutic preparation in the tumors.
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Affiliation(s)
- Ulrika Jahn
- Radiology and Molecular Imaging, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden. .,Uppsala University Hospital, 75185, Uppsala, Sweden.
| | - Ezgi Ilan
- Radiology and Molecular Imaging, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.,Uppsala University Hospital, 75185, Uppsala, Sweden.,Medical Physics, Uppsala University Hospital, Uppsala, Sweden
| | - Irina Velikyan
- Radiology and Molecular Imaging, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.,Uppsala University Hospital, 75185, Uppsala, Sweden.,Medical Imaging Centre, Uppsala University Hospital, Uppsala, Sweden
| | - Katarzyna Fröss-Baron
- Radiology and Molecular Imaging, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.,Uppsala University Hospital, 75185, Uppsala, Sweden.,Medical Imaging Centre, Uppsala University Hospital, Uppsala, Sweden
| | - Mark Lubberink
- Radiology and Molecular Imaging, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.,Uppsala University Hospital, 75185, Uppsala, Sweden.,Medical Physics, Uppsala University Hospital, Uppsala, Sweden
| | - Anders Sundin
- Radiology and Molecular Imaging, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.,Uppsala University Hospital, 75185, Uppsala, Sweden.,Medical Imaging Centre, Uppsala University Hospital, Uppsala, Sweden
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Combination treatments to enhance peptide receptor radionuclide therapy of neuroendocrine tumours. Eur J Nucl Med Mol Imaging 2019; 47:907-921. [DOI: 10.1007/s00259-019-04499-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2019] [Accepted: 08/21/2019] [Indexed: 12/11/2022]
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6
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Endothelin-converting enzyme-1 regulates glucagon-like peptide-1 receptor signalling and resensitisation. Biochem J 2019; 476:513-533. [PMID: 30626614 DOI: 10.1042/bcj20180853] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Revised: 01/07/2019] [Accepted: 01/08/2019] [Indexed: 02/08/2023]
Abstract
Following nutrient ingestion, glucagon-like peptide 1 (GLP-1) is secreted from intestinal L-cells and mediates anti-diabetic effects, most notably stimulating glucose-dependent insulin release from pancreatic β-cells but also inhibiting glucagon release, promoting satiety and weight reduction and potentially enhancing or preserving β-cell mass. These effects are mediated by the GLP-1 receptor (GLP-1R), which is a therapeutic target in type 2 diabetes. Although agonism at the GLP-1R has been well studied, desensitisation and resensitisation are perhaps less well explored. An understanding of these events is important, particularly in the design and use of novel receptor ligands. Here, using either HEK293 cells expressing the recombinant human GLP-1R or the pancreatic β-cell line, INS-1E with endogenous expressesion of the GLP-1R, we demonstrate GLP-1R desensitisation and subsequent resensitisation following removal of extracellular GLP-1 7-36 amide. Resensitisation is dependent on receptor internalisation, endosomal acidification and receptor recycling. Resensitisation is also regulated by endothelin-converting enzyme-1 (ECE-1) activity, most likely through proteolysis of GLP-1 in endosomes and the facilitation of GLP-1R dephosphorylation and recycling. Inhibition of ECE-1 activity also increases GLP-1-induced activation of extracellular signal-regulated kinase and generation of cAMP, suggesting processes dependent upon the lifetime of the internalised ligand-receptor complex.
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Synthesis and preclinical investigation of 99mTc-p-SCN-Bzl-DTPA-cetuximab for targeting EGFR using head and neck squamous cell carcinoma (HNSCC) xenografts. Mol Biol Rep 2019; 46:1675-1682. [DOI: 10.1007/s11033-019-04616-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Accepted: 01/18/2019] [Indexed: 02/06/2023]
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Treppiedi D, Jobin ML, Peverelli E, Giardino E, Sungkaworn T, Zabel U, Arosio M, Spada A, Mantovani G, Calebiro D. Single-Molecule Microscopy Reveals Dynamic FLNA Interactions Governing SSTR2 Clustering and Internalization. Endocrinology 2018; 159:2953-2965. [PMID: 29931263 DOI: 10.1210/en.2018-00368] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Accepted: 06/14/2018] [Indexed: 11/19/2022]
Abstract
The cytoskeletal protein filamin A (FLNA) has been suggested to play an important role in the responsiveness of GH-secreting pituitary tumors to somatostatin receptor subtype 2 (SSTR2) agonists by regulating SSTR2 expression and signaling. However, the underlying mechanisms are unknown. In this study, we use fast multicolor single-molecule microscopy to image individual SSTR2 and FLNA molecules at the surface of living cells with unprecedented spatiotemporal resolution. We find that SSTR2 and FLNA undergo transient interactions, which occur preferentially along actin fibers and contribute to restraining SSTR2 diffusion. Agonist stimulation increases the localization of SSTR2 along actin fibers and, subsequently, SSTR2 clustering and recruitment to clathrin-coated pits (CCPs). Interfering with FLNA-SSTR2 binding with a dominant-negative FLNA fragment increases SSTR2 mobility, hampers the formation and alignment of SSTR2 clusters along actin fibers, and impairs both SSTR2 recruitment to CCPs and SSTR2 internalization. These findings indicate that dynamic SSTR2-FLNA interactions critically control the nanoscale localization of SSTR2 at the plasma membrane and are required for coupling SSTR2 clustering to internalization. These mechanisms explain the critical role of FLNA in the control of SSTR2 expression and signaling and suggest the possibility of targeting SSTR2-FLNA interactions for the therapy of pharmacologically resistant GH-secreting pituitary tumors.
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Affiliation(s)
- Donatella Treppiedi
- Endocrinology Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
- Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
| | - Marie-Lise Jobin
- Institute of Pharmacology and Toxicology, University of Würzburg, Würzburg, Germany
- Bio-Imaging Center/Rudolf Virchow Center, University of Würzburg, Würzburg, Germany
| | - Erika Peverelli
- Endocrinology Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
- Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
| | - Elena Giardino
- Endocrinology Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
- Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
| | - Titiwat Sungkaworn
- Institute of Pharmacology and Toxicology, University of Würzburg, Würzburg, Germany
- Bio-Imaging Center/Rudolf Virchow Center, University of Würzburg, Würzburg, Germany
| | - Ulrike Zabel
- Institute of Pharmacology and Toxicology, University of Würzburg, Würzburg, Germany
- Bio-Imaging Center/Rudolf Virchow Center, University of Würzburg, Würzburg, Germany
| | - Maura Arosio
- Endocrinology Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
- Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
| | - Anna Spada
- Endocrinology Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
- Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
| | - Giovanna Mantovani
- Endocrinology Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
- Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
| | - Davide Calebiro
- Institute of Pharmacology and Toxicology, University of Würzburg, Würzburg, Germany
- Bio-Imaging Center/Rudolf Virchow Center, University of Würzburg, Würzburg, Germany
- Institute of Metabolism and Systems Research, University of Birmingham, Birmingham, United Kingdom
- Centre of Membrane Proteins and Receptors (COMPARE), Universities of Birmingham and Nottingham, Birmingham, United Kingdom
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Treppiedi D, Peverelli E, Giardino E, Ferrante E, Calebiro D, Spada A, Mantovani G. Somatostatin Receptor Type 2 (SSTR2) Internalization and Intracellular Trafficking in Pituitary GH-Secreting Adenomas: Role of Scaffold Proteins and Implications for Pharmacological Resistance. Horm Metab Res 2017; 49:259-268. [PMID: 27632151 DOI: 10.1055/s-0042-116025] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
AbstractSomatostatin receptor type 2 (SSTR2), together with SSTR5, represents the main
target of medical treatment for growth hormone (GH)-secreting pituitary tumors,
since it is expressed in most of these tumors and exerts both antiproliferative
and cytostatic effects, and reduces hormone secretion, as well. However,
clinical practice indicates a great variability in the frequency and entity of
favorable responses of acromegalic patients to long-acting somatostatin
analogues (SSAs), but the molecular mechanisms regulating this pharmacological
resistance are not completely understood. So far, several potentially implied
mechanisms have been suggested, including impaired expression of SSTRs, or
post-receptor signal transduction alterations. More recently, new studies
exploited the molecular factors involved in SSTRs intracellular trafficking
regulation, this being a critical point for the modulation of the available
active G-coupled receptors (GPCRs) amount at the cell surface. In this respect,
the role of the scaffold proteins such as β-arrestins, and the cytoskeleton
protein Filamin A (FLNA), have become of relevant importance for GH-secreting
pituitary tumors. In fact, β-arrestins are linked to SSTR2 desensitization and
internalization, and FLNA is able to regulate SSTR2 trafficking and stability at
the plasma membrane. Therefore, the present review will summarize emerging
evidence highlighting the role of β-arrestins and FLNA, as possible novel
players in the modulation of agonist activated-SSTR2 receptor trafficking and
response in GH-secreting pituitary tumors.
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Affiliation(s)
- D Treppiedi
- Endocrine Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico; Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
| | - E Peverelli
- Endocrine Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico; Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
| | - E Giardino
- Endocrine Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico; Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
| | - E Ferrante
- Endocrine Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico; Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
| | - D Calebiro
- Institute of Pharmacology and Toxicology, University of Würzburg, and Rudolf Virchow Center, Bio-Imaging Center, Würzburg, Germany
| | - A Spada
- Endocrine Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico; Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
| | - G Mantovani
- Endocrine Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico; Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
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Physiologically based pharmacokinetic modeling of (18)F-SiFAlin-Asp3-PEG1-TATE in AR42J tumor bearing mice. Nucl Med Biol 2016; 43:243-6. [PMID: 27067044 DOI: 10.1016/j.nucmedbio.2016.01.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2015] [Accepted: 01/04/2016] [Indexed: 11/21/2022]
Abstract
PURPOSE Peptide receptor radionuclide therapy (PRRT) is commonly performed in the treatment of neuroendocrine tumors (NET), where somatostatin analogs (DOTATATE) are radiolabeled with (90)Y, (68)Ga or (111)In for pre-therapeutic and therapeutic purposes. Quantitative evaluation of the biokinetic data can be performed by using physiologically based pharmacokinetic (PBPK) models. Knowledge about the biodistribution in a pre-clinical setting would allow optimizing the translation from bench to bedside. The aim of this study was to develop a PBPK model to describe the biodistribution of a novel sst2-targeting radiotracer. METHODS Biokinetic data of six mice after injection of (18)F-SiFAlin-Asp3-PEG1-TATE were investigated using two PBPK models. The PBPK models describe the biodistribution of the tracer in the tumor, kidneys, liver, remainder and whole body via blood flow to these organs via absorption, distribution, metabolism and excretion. A recently published sst2 PBPK model for humans (model 1) was used to describe the data. Physiological information in this model was adapted to that of a mouse. Model 1 was further modified by implementing receptor-mediated endocytosis (model 2). Model parameters were fitted to the biokinetic data of each mouse. Model selection was performed by calculating Akaike weights wi using the corrected Akaike Information Criterion (AICc). RESULTS The implementation of receptor-mediated endocytosis considerably improved the description of the biodistribution (Akaike weights w1=0% and w2=100% for model 1 and 2, respectively). The resulting time-integrated activity coefficients determined by model 2 were for tumor (0.05 ± 0.02) h, kidneys (0.11 ± 0.01) h and liver (0.02 ± 0.01) h. CONCLUSION Simply downscaling a human PBPK model does not allow for an accurate description of (18)F-SiFAlin-Asp3-PEG1-TATE in mice. Biokinetics of this tracer can be accurately and adequately described using a physiologically based pharmacokinetic model including receptor-mediated endocytosis. Thus, an optimized translation from bench to bedside is possible.
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Kuan SL, Wang T, Raabe M, Liu W, Lamla M, Weil T. Programming Bioactive Architectures with Cyclic Peptide Amphiphiles. Chempluschem 2015; 80:1347-1353. [PMID: 31973290 DOI: 10.1002/cplu.201500218] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2015] [Indexed: 01/06/2023]
Abstract
We present a versatile approach for the synthesis of cyclic peptide amphiphiles of the hormone somatostatin (SST) with tunable lipophilic tails to program bioactive nanoarchitectures. A novel bis-alkylation reagent is synthesized that facilitates the functionalization of SST with a thiol anchor. Different hydrophobic moieties are introduced inspired by a biomimetic palmitoylation approach which opens access to cyclic peptide amphiphiles that display rich self-organization and cell membrane interactions.
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Affiliation(s)
- Seah Ling Kuan
- Institute of Organic Chemistry III-Macromolecular Chemistry & Biomaterials, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm (Germany)
| | - Tao Wang
- Institute of Organic Chemistry III-Macromolecular Chemistry & Biomaterials, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm (Germany)
| | - Marco Raabe
- Institute of Organic Chemistry III-Macromolecular Chemistry & Biomaterials, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm (Germany)
| | - Weina Liu
- Institute of Organic Chemistry III-Macromolecular Chemistry & Biomaterials, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm (Germany)
| | - Markus Lamla
- Institute of Organic Chemistry III-Macromolecular Chemistry & Biomaterials, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm (Germany)
| | - Tanja Weil
- Institute of Organic Chemistry III-Macromolecular Chemistry & Biomaterials, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm (Germany)
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Paterson BM, Roselt P, Denoyer D, Cullinane C, Binns D, Noonan W, Jeffery CM, Price RI, White JM, Hicks RJ, Donnelly PS. PET imaging of tumours with a 64Cu labeled macrobicyclic cage amine ligand tethered to Tyr3-octreotate. Dalton Trans 2013; 43:1386-96. [PMID: 24202174 DOI: 10.1039/c3dt52647j] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The use of copper radioisotopes in cancer diagnosis and radionuclide therapy is possible using chelators that are capable of binding Cu(II) with sufficient stability in vivo to provide high tumour-to-background contrast. Here we report the design and synthesis of a new bifunctional chelator, 5-(8-methyl-3,6,10,13,16,19-hexaaza-bicyclo[6.6.6]icosan-1-ylamino)-5-oxopentanoic acid (MeCOSar), that forms copper complexes of exceptional stability by virtue of a cage amine (sarcophagine) ligand and a new conjugate referred to as SarTATE, obtained by the conjugation of MeCOSar to the tumour-targeting peptide Tyr(3)-octreotate. Radiolabeling of SarTATE with (64)Cu(II), a radioisotope suitable for positron emission tomography (PET), was fast (~20 min), easily performed at room temperature and consistently resulted in high radiochemical purity (>99%). In vitro and in vivo evaluation of (64)CuSarTATE demonstrated its high selectivity for tumour cells expressing somatostatin receptor 2 (sstr2). Biodistribution and PET imaging comparisons were made between (64)CuSarTATE and (64)Cu-labeled DOTA-Tyr(3)-octreotate ((64)CuDOTATATE). Both radiopharmaceuticals showed excellent uptake in sstr2-positive tumours at 2 h post-injection. While tumour uptake of (64)CuDOTATATE decreased significantly at 24 h, (64)CuSarTATE activity was retained, improving contrast at later time points. (64)CuSarTATE accumulated less than (64)CuDOTATATE in the non-target organs, liver and lungs. The uptake of (64)CuSarTATE in the kidneys was high at 2 h but showed significant clearance by 24 h. The new chemistry and pre-clinical evaluation presented here demonstrates that MeCOSar is a promising bifunctional chelator for Tyr(3)-octreotate that could be applied to a combined imaging and therapeutic regimen using a combination of (64)Cu- and (67)CuSarTATE complexes, owing to improved tumour-to-non-target organ ratios compared to (64)CuDOTATATE at longer time points.
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Affiliation(s)
- Brett M Paterson
- School of Chemistry, The University of Melbourne, Parkville, VIC, Australia.
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Sreenivasan VKA, Kim EJ, Goodchild AK, Connor M, Zvyagin AV. Targeting somatostatin receptors using in situ-bioconjugated fluorescent nanoparticles. Nanomedicine (Lond) 2012; 7:1551-60. [DOI: 10.2217/nnm.12.42] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Aim: The author’s group report, for the first time, on the development of a quantum dot (QD)-based fluorescent somatostatin (somatotropin release-inhibiting factor [SRIF]) probe that enables specific targeting of somatostatin receptors. Receptor-mediated endocytosis of SRIF was imaged using this probe. Materials & methods: Biotinylated SRIF-analog (SRIF-B) and streptavidin (Sav)-coated QDs were used for the probe synthesis. A dye-labeled streptavidin complex was used to evaluate the effect of Sav binding on the activity of SRIF-B. Results: A preconjugated probe of the form SRIF-B:Sav-QD, was inactive and unable to undergo receptor-mediated endocytosis. An alternative in situ bioconjugation strategy, where SRIF-B and Sav-QD were added in two consecutive steps, enabled visualization of the receptor-mediated endocytosis. The process of Sav binding appeared to be responsible for the inactivity in the first case. Conclusion: The in situ two-step bioconjugation strategy allowed QDs to be targeted to somatostatin receptors. This strategy should enable flexible fluorescent tagging of SRIF for the investigation of molecular trafficking in cells and targeted delivery in live animals. Original submitted 14 November 2011; Revised submitted 27 February 2012; Published online 20 July 2012
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Affiliation(s)
| | - Eun J Kim
- Department of Science Education – Chemical Education Major, Daegu University, Gyeonbuk, Republic of Korea
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Guo Y, Ferdani R, Anderson CJ. Preparation and biological evaluation of (64)Cu labeled Tyr(3)-octreotate using a phosphonic acid-based cross-bridged macrocyclic chelator. Bioconjug Chem 2012; 23:1470-7. [PMID: 22663248 DOI: 10.1021/bc300092n] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Somatostatin receptors (SSTr) are overexpressed in a wide range of neuroendocrine tumors, making them excellent targets for nuclear imaging and therapy, and radiolabeled somatostatin analogues have been investigated for positron emission tomography imaging and radionuclide therapy of SSTr-positive tumors, especially of the subtype-2 (SSTr2). The aim of this study was to develop a somatostatin analogue, Tyr(3)-octreotate (Y3-TATE), conjugated to a novel cross-bridged macrocyclic chelator, 11-carboxymethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane-4-methanephosphonic acid (CB-TE1A1P). Unlike traditional cross-bridged macrocycles, such as 4,11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (CB-TE2A), CB-TE1A1P-Y3-TATE was radiolabeled with (64)Cu in high purity and high specific activity using mild conditions. Saturation binding assays revealed that (64)Cu-CB-TE1A1P-Y3-TATE had comparable binding affinity but bound to more binding sites in AR42J rat pancreatic tumor cell membranes than (64)Cu-CB-TE2A-Y3-TATE. Both radiopharmaceuticals showed comparable uptake in SSTr2 positive tissues in AR42J tumor-bearing rats. (64)Cu-CB-TE1A1P-Y3-TATE demonstrated improved blood clearance compared to (64)Cu-CB-TE2A-Y3-TATE, as the tumor/blood ratios of (64)Cu-CB-TE1A1P-Y3-TATE were shown to be significantly higher than those of (64)Cu-CB-TE2A-Y3-TATE at 4 and 24 h postinjection. (64)Cu-CB-TE1A1P-Y3-TATE, in spite of a relatively high kidney uptake, accumulated less in nontarget organs such as liver, lung, and bone. Small animal PET/CT imaging of (64)Cu-CB-TE1A1P-Y3-TATE in AR42J tumor bearing rats validated significant uptake and good contrast in the tumor. This study suggests that CB-TE1A1P is a promising bifunctional chelator for (64)Cu-labeled for Y3-TATE, owing to high binding affinity and target tissue uptake, the ability to radiolabel the agent at lower temperatures, and improved tumor/nontarget organ ratios over (64)Cu-CB-TE2A-Y3-TATE.
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Affiliation(s)
- Yunjun Guo
- Mallinckrodt Institute of Radiology, Washington University, St. Louis, MO, USA
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Mohan ML, Vasudevan NT, Gupta MK, Martelli EE, Naga Prasad SV. G-protein coupled receptor resensitization-appreciating the balancing act of receptor function. Curr Mol Pharmacol 2012:CMP-EPUB-20120530-2. [PMID: 22697395 PMCID: PMC4607669] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2011] [Revised: 11/22/2011] [Accepted: 11/28/2011] [Indexed: 06/01/2023]
Abstract
G-protein coupled receptors (GPCRs) are seven transmembrane receptors that are pivotal regulators of cellular responses including vision, cardiac contractility, olfaction, and platelet activation. GPCRs have been a major target for drug discovery due to their role in regulating a broad range of physiological and pathological responses. GPCRs mediate these responses through a cyclical process of receptor activation (initiation of downstream signals), desensitization (inactivation that results in diminution of downstream signals), and resensitization (receptor reactivation for next wave of activation). Although these steps may be of equal importance in regulating receptor function, significant advances have been made in understanding activation and desensitization with limited effort towards resensitization. Inadequate importance has been given to resensitization due to the understanding that resensitization is a homeostasis maintaining process and is not acutely regulated. Evidence indicates that resensitization is a critical step in regulating GPCR function and may contribute towards receptor signaling and cellular responses. In light of these observations, it is imperative to discuss resensitization as a dynamic and mechanistic regulator of GPCR function. In this review we discuss components regulating GPCR function like activation, desensitization, and internalization with special emphasis on resensitization. Although we have used β-adrenergic receptor as a proto-type GPCR to discuss mechanisms regulating receptor function, other GPCRs are also described to put forth a view point on the universality of such mechanisms.
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Affiliation(s)
- Maradumane L Mohan
- Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH, 44195.
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Evaluation of copper-64-labeled somatostatin agonists and antagonist in SSTr2-transfected cell lines that are positive and negative for p53: implications for cancer therapy. Nucl Med Biol 2011; 39:187-97. [PMID: 22056254 DOI: 10.1016/j.nucmedbio.2011.08.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2011] [Revised: 08/10/2011] [Accepted: 08/14/2011] [Indexed: 12/19/2022]
Abstract
OBJECTIVES Radiolabeled somatostatin analogs have become important agents for molecular imaging and targeted radiotherapy of somatostatin receptor-positive tumors. Here we determine the effect of the tumor suppressor protein, p53, on trafficking (64)Cu to tumor cell nuclei from DOTA vs. CB-TE2A-conjugated agonist Y3-TATE and the antagonist (64)Cu-CB-TE2A-sst2-ANT in cell lines that are positive or negative for p53. METHODS Receptor binding, internalization, cyclic adenosine monophosphate (cAMP) and nuclear localization studies were performed with the somatostatin receptor subtype 2 (SSTr2) agonists, (64)Cu-CB-TE2A-Y3-TATE and (64)Cu-DOTA-Y3-TATE vs. antagonist, (64)Cu-CB-TE2A-sst2-ANT, in SSTr2-transfected p53 +/+ and -/- HCT116 colorectal carcinoma cells. RESULTS The antagonist, (64)Cu-CB-TE2A-sst2-ANT, bound 8-9-fold more SSTr2 binding sites than did the (64)Cu-labeled agonists. (64)Cu-CB-TE2A-Y3-TATE was more efficiently internalized than (64)Cu-DOTA-Y3-TATE, while (64)Cu-CB-TE2A-sst2-ANT showed lower yet significant levels of internalization. CB-TE2A-Y3-TATE acted as a full agonist, inhibiting cAMP production, whereas CB-TE2A-sst2-ANT showed no inhibition of cAMP production. The (64)Cu from agonists (64)Cu-DOTA-Y3-TATE and (64)Cu-CB-TE2A-Y3-TATE showed greater nuclear localization at 24 h in p53 +/+ vs. -/- cells; however, there was no difference in the levels of (64)Cu from the antagonist based on p53 status. Surprisingly, the DOTA and CB-TE2A-conjugated agonists showed similar nuclear localization in the p53 +/+ and -/- cells, suggesting no difference in (64)Cu release from these chelators in the HCT116 cell lines. CONCLUSION Based on these in vitro data, the agonist (64)Cu-CB-TE2A-Y3-TATE demonstrates the most promise as an agent for targeted radiotherapy in p53 positive, SSTr2-positive tumors.
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Sreenivasan VKA, Stremovskiy OA, Kelf TA, Heblinski M, Goodchild AK, Connor M, Deyev SM, Zvyagin AV. Pharmacological characterization of a recombinant, fluorescent somatostatin receptor agonist. Bioconjug Chem 2011; 22:1768-75. [PMID: 21823634 DOI: 10.1021/bc200104u] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Somatostatin (SST) is a peptide neurotransmitter/hormone found in several mammalian tissue types. Apart from its natural importance, labeled SST/analogues are utilized in clinical applications such as targeting/diagnosis of neuroendocrine tumors. We report on the development and characterization of a novel, recombinant, fluorescent somatostatin analogue that has potential to elucidate somatostatin-activated cell signaling. SST was genetically fused with a monomeric-red fluorescent protein (mRFP) as the fluorescent label. The attachment of SST to mRFP had no detectable effect on its fluorescent properties. This analogue's potency to activate the endogenous and transfected somatostatin receptors was characterized using assays of membrane potential and Ca(2+) mobilization and immunocytochemistry. SST-mRFP was found to be an effective somatostatin receptor agonist, able to trigger the membrane hyperpolarization, mobilization of the intracellular Ca(2+) and receptor-ligand internalization in cells expressing somatostatin receptors. This complex represents a novel optical reporter due to its red emission spectral band suitable for in vivo imaging and tracking of the somatostatin receptor signaling pathways, affording higher resolution and sensitivity than those of the state-of-the-art radiolabeling bioassays.
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Demaegdt H, Gard P, De Backer JP, Lukaszuk A, Szemenyei E, Tóth G, Tourwé D, Vauquelin G. Binding of "AT4 receptor" ligands to insulin regulated aminopeptidase (IRAP) in intact Chinese hamster ovary cells. Mol Cell Endocrinol 2011; 339:34-44. [PMID: 21457753 DOI: 10.1016/j.mce.2011.03.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Revised: 03/17/2011] [Accepted: 03/22/2011] [Indexed: 01/03/2023]
Abstract
Insulin regulated aminopeptidase (IRAP) recognises "AT(4)-receptor" ligands like angiotensin IV (Ang IV) and peptidomimetics like AL-11. The metabolic stability and high affinity of [(3)H]AL-11 for catalytically active IRAP allowed its detection in Chinese hamster ovary (CHO-K1) cell membranes in the absence of chelators (Demaegdt et al., 2009). Here, we show that, contrary to [(3)H]Ang IV, [(3)H]AL-11 displays high affinity and specificity for IRAP in intact CHO-K1 cells as well. After binding to IRAP at the surface, [(3)H]AL-11 is effectively internalized by an endocytotic process. Unexpectedly, surface binding and internalization of [(3)H]AL-11 was not affected by pretreating the cells with Ang IV but declined with AL-11. In the latter case surface expression of IRAP even increased. After elimination of simpler explanations, it is proposed that metabolically stable "AT(4)-receptor" ligands undergo semi-continuous cycling between the cell surface and endosomal compartments. The in vivo efficacy of stable and unstable "AT(4)-receptor" ligands could therefore differ.
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Affiliation(s)
- Heidi Demaegdt
- Department of Molecular and Biochemical Pharmacology, Research Group of Experimental Pharmacology, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
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Hoeben BAW, Molkenboer-Kuenen JDM, Oyen WJG, Peeters WJM, Kaanders JHAM, Bussink J, Boerman OC. Radiolabeled cetuximab: dose optimization for epidermal growth factor receptor imaging in a head-and-neck squamous cell carcinoma model. Int J Cancer 2010; 129:870-8. [PMID: 20957635 DOI: 10.1002/ijc.25727] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2010] [Accepted: 09/21/2010] [Indexed: 12/26/2022]
Abstract
Noninvasive imaging of the epidermal growth factor receptor (EGFR) in head-and-neck squamous cell carcinoma could be of value to select patients for EGFR-targeted therapy. We assessed dose optimization of (111) Indium-DTPA-cetuximab ((111) In-cetuximab) for EGFR imaging in a head-and-neck squamous cell carcinoma xenograft model. (111) In-cetuximab slowly internalized into FaDu cells in vitro, amounting to 1.0 × 10(4) molecules cetuximab per cell after 24 hr (15.8% of added activity). In nude mice with subcutaneous FaDu xenograft tumors, a protein dose escalation study with (111) In-cetuximab showed highest specific accumulation in tumors at protein doses between 1 and 30 μg per mouse (mean tumor uptake 33.1 ± 3.1%ID/g, 3 days postinjection (p.i.)). The biodistribution of (111) In-cetuximab and (125) I-cetuximab was determined at 1, 3 and 7 days p.i. at optimal protein dose. Tumor uptake was favorable for (111) In-cetuximab compared to (125) I-cetuximab. With pixel-by-pixel analysis, good correlations were found between intratumoral distribution of (111) In-cetuximab as determined by autoradiography and EGFR expression in the same tumor sections as determined immunohistochemically (mean r = 0.74 ± 0.14; all correlations p < 0.0001). Micro Single Photon Emission Computed Tomography (MicroSPECT) scans clearly visualized FaDu tumors from 1 day p.i. onward and tumor-to-background contrast increased until 7 days p.i. (tumor-to-liver ratios 0.58 ± 0.24, 3.42 ± 0.66, 8.99 ± 4.66 and 16.33 ± 11.56, at day 0, day 1, day 3 and day 7 p.i., respectively). Our study suggests that, at optimal cetuximab imaging dose, (111) In-cetuximab can be used for visualization of EGFR expression in head-and-neck squamous cell carcinoma using SPECT.
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Affiliation(s)
- Bianca A W Hoeben
- Department of Radiation Oncology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
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Naqvi SAR, Sosabowski JK, Nagra SA, Ishfaq MM, Mather SJ, Matzow T. Radiopeptide internalisation and externalization assays: cell viability and radioligand integrity. Appl Radiat Isot 2010; 69:68-74. [PMID: 20880713 DOI: 10.1016/j.apradiso.2010.09.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2009] [Revised: 08/19/2010] [Accepted: 09/02/2010] [Indexed: 10/19/2022]
Abstract
Various aspects of radiopeptide receptor-mediated cell internalisation and externalization assays were assessed, including the integrity of externalized peptides and the effect of varying the pH and incubation time of the acid wash step (to remove surface receptor-bound ligand) on efficacy and cell viability. The observed intact proportion of externalized peptide was 5-10%, and acid wash buffers with pH 2.8 or below were found to be detrimental to cell viability and integrity, particularly following prolonged incubation times.
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Affiliation(s)
- Syed Ali Raza Naqvi
- Centre for Molecular Oncology and Imaging, Institute of Cancer, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, Charterhouse Square, London EC1M 6BQ, United Kingdom
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21
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Magainin 2 in action: distinct modes of membrane permeabilization in living bacterial and mammalian cells. Biophys J 2008; 95:5757-65. [PMID: 18835901 DOI: 10.1529/biophysj.108.133488] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Interactions of cationic antimicrobial peptides with living bacterial and mammalian cells are little understood, although model membranes have been used extensively to elucidate how peptides permeabilize membranes. In this study, the interaction of F5W-magainin 2 (GIGKWLHSAKKFGKAFVGEIMNS), an equipotent analogue of magainin 2 isolated from the African clawed frog Xenopus laevis, with unfixed Bacillus megaterium and Chinese hamster ovary (CHO)-K1 cells was investigated, using confocal laser scanning microscopy. A small amount of tetramethylrhodamine-labeled F5W-magainin 2 was incorporated into the unlabeled peptide for imaging. The influx of fluorescent markers of various sizes into the cytosol revealed that magainin 2 permeabilized bacterial and mammalian membranes in significantly different ways. The peptide formed pores with a diameter of approximately 2.8 nm (< 6.6 nm) in B. megaterium, and translocated into the cytosol. In contrast, the peptide significantly perturbed the membrane of CHO-K1 cells, permitting the entry of a large molecule (diameter, >23 nm) into the cytosol, accompanied by membrane budding and lipid flip-flop, mainly accumulating in mitochondria and nuclei. Adenosine triphosphate and negatively charged glycosaminoglycans were little involved in the magainin-induced permeabilization of membranes in CHO-K1 cells. Furthermore, the susceptibility of CHO-K1 cells to magainin was found to be similar to that of erythrocytes. Thus, the distinct membrane-permeabilizing processes of magainin 2 in bacterial and mammalian cells were, to the best of our knowledge, visualized and characterized in detail for the first time.
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Roosterman D, Kempkes C, Cottrell GS, Padilla BE, Bunnett NW, Turck CW, Steinhoff M. Endothelin-converting enzyme-1 degrades internalized somatostatin-14. Endocrinology 2008; 149:2200-7. [PMID: 18276747 PMCID: PMC2329273 DOI: 10.1210/en.2007-1628] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Agonist-induced internalization of somatostatin receptors (ssts) determines subsequent cellular responsiveness to peptide agonists and influences sst receptor scintigraphy. To investigate sst2A trafficking, rat sst2A tagged with epitope was expressed in human embryonic kidney cells and tracked by antibody labeling. Confocal microscopical analysis revealed that stimulation with sst and octreotide induced internalization of sst2A. Internalized sst2A remained sequestrated within early endosomes, and 60 min after stimulation, internalized sst2A still colocalized with beta-arrestin1-enhanced green fluorescence protein (EGFP), endothelin-converting enzyme-1 (ECE-1), and rab5a. Internalized (125)I-Tyr(11)-SST-14 was rapidly hydrolyzed by endosomal endopeptidases, with radioactive metabolites being released from the cell. Internalized (125)I-Tyr(1)-octreotide accumulated as an intact peptide and was released from the cell as an intact peptide ligand. We have identified ECE-1 as one of the endopeptidases responsible for inactivation of internalized SST-14. ECE-1-mediated cleavage of SST-14 was inhibited by the specific ECE-1 inhibitor, SM-19712, and by preventing acidification of endosomes using bafilomycin A(1). ECE-1 cleaved SST-14 but not octreotide in an acidic environment. The metallopeptidases angiotensin-1 converting enzyme and ECE-2 did not hydrolyze SST-14 or octreotide. Our results show for the first time that stimulation with SST-14 and octreotide induced sequestration of sst2A into early endosomes and that endocytosed SST-14 is degraded by endopeptidases located in early endosomes. Furthermore, octreotide was not degraded by endosomal peptidases and was released as an intact peptide. This mechanism may explain functional differences between octreotide and SST-14 after sst2A stimulation. Moreover, further investigation of endopeptidase-regulated trafficking of neuropeptides may result in novel concepts of neuropeptide receptor inactivation in cancer diagnosis.
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Affiliation(s)
- Dirk Roosterman
- Department of Dermatology, Interdisziplinäres Zentrum für Klinische Forschung Münster, and Ludwig Bolzmann Institute for Cell and Immunobiology of the Skin, University Münster, D-48149 Münster, Germany.
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Wieder H, Beer AJ, Poethko T, Meisetschlaeger G, Wester HJ, Rummeny E, Schwaiger M, Stahl AR. PET/CT with Gluc-Lys-([(18)F]FP)-TOCA: correlation between uptake, size and arterial perfusion in somatostatin receptor positive lesions. Eur J Nucl Med Mol Imaging 2007; 35:264-71. [PMID: 17912524 DOI: 10.1007/s00259-007-0576-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2007] [Accepted: 08/27/2007] [Indexed: 11/29/2022]
Abstract
PURPOSE Somatostatin receptor (sstr) positive tumours vary widely in uptake of radiolabelled somatostatin (sst) analogues. This study determinates variability in lesion uptake of the glycosylated sst analogon N(alpha)-(1-deoxy-D-fructosyl)-N(epsilon)-(2-[(18)F]fluoropropionyl)-Lys(0)-Tyr(3)-octreotate (Gluc-Lys([(18)F]FP)-TOCA) and correlates it with lesion size and arterial perfusion as measured on computed tomography (CT). METHODS Ten patients with metastasized neuroendocrine carcinomas were investigated with positron emission tomography PET/CT (Biograph 16, Siemens, Germany). Lesion standardized uptake values (SUVs) were determined at approximately 50 min post tracer injection according to a 60% isocontour volume of interest around each lesion. Lesion size and enhancement in the arterial phase (hounsfield units, HUs) were derived from CT. RESULTS 114 lesions in the upper abdomen had a correlate on both, PET and CT. Variability in lesion SUVs was high (SUV(mean) 22 +/- 13). Intraindividually, there was a sigmoid positive correlation between lesion SUV and lesion diameter indicating partial volume effects. Residual variability in lesions > or =3 cm (> or =2.5 cm) ranged down to about half (third) of the maximum lesion uptake and remained unexplained by partial volume effects. No correlation with measured HU in the arterial phase was found, neither intraindividually nor interindividually. CONCLUSION Partial volume effects were a major source of intraindividual variability in tumour tracer uptake. Lesions below 2.5 to 3 cm should thus be used with caution when performing dose calculations. In larger lesions residual variability in uptake must be considered; it may be due to variable sstr2 expression on the tumours' cell surfaces.
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Affiliation(s)
- Hinrich Wieder
- Department of Nuclear Medicine, Technische Universität München, Klinikum Rechts der Isar, Munich, Germany
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Abstract
The experimental data reviewed in the present paper deal with the molecular events underlying the agonist-dependent regulation of the distinct somatostatin receptor subtypes and may suggest important clues about the clinical use of somatostatin analogs with different pattern of receptor specificity for the in vivo targeting of tumoral somatostatin receptors. Somatostatin receptor subtypes are characterized by differential beta-arrestin trafficking and endosomal sorting upon agonist binding due, at least in part, to the differences in their C-terminal tails. Moreover, the subcellular expression pattern of somatostatin receptor subtypes and their activity in response to agonist treatment are affected by intracellular complements, such as proteins involved in intracellular vesicle trafficking. Different somatostatin analogs may induce distinct conformations of the receptor/ligand complex, preferentially coupled to either receptor signaling or receptor endocytosis.
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Durán-Prado M, Bucharles C, Gonzalez BJ, Vázquez-Martínez R, Martínez-Fuentes AJ, García-Navarro S, Rhodes SJ, Vaudry H, Malagón MM, Castaño JP. Porcine somatostatin receptor 2 displays typical pharmacological sst2 features but unique dynamics of homodimerization and internalization. Endocrinology 2007; 148:411-21. [PMID: 17053026 DOI: 10.1210/en.2006-0920] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Somatostatin (SRIF) exerts its multiple actions, including inhibition of GH secretion and of tumoral growth, through a family of five receptor subtypes (sst1-sst5). We recently reported that an sst2-selective agonist markedly decreases GH release from pig somatotropes, suggesting important roles for this scarcely explored receptor, psst2. Here, functional expression of psst2 in Chinese hamster ovary-K1 and human embryonic kidney-293-AD cell lines was employed to determine its pharmacological features and functional ability to reduce cAMP, and to examine its homodimerization and internalization dynamics in real time in single living cells. Results show that psst2 is a high-affinity receptor (dissociation constant = 0.27 nM) displaying a typical sst2 profile (nM affinity for SRIF-14> or =SRIF-28>cortistatin>MK678>octreotide) and high selectivity (EC(50) = 1.1 nM) for the sst2 agonist l-779,976, but millimolar or undetectable affinity to other sst-specific agonists (sst3>sst1>sst5>>>sst4). Accordingly, SRIF dose-dependently inhibited forskolin-stimulated cAMP with high potency (EC(50) = 6.55 pm) and modest efficacy (maximum 29.1%) via psst2. Cotransfection of human embryonic kidney-293 and Chinese hamster ovary-K1 cells with two receptor constructs modified with distinct fluorescent tags (psst2-YFP/psst2-CFP) enabled fluorescence resonance energy transfer measurement of physical interaction between psst2 receptors and also receptor internalization in single living cells. This revealed that under basal conditions, psst2 forms constitutive homodimers/homomultimers, which dissociate immediately (11 sec) upon SRIF binding. Interestingly, contrary to human sst2, psst2 rapidly reassociates (110.5 sec) during a subsequent process that temporally overlaps with receptor internalization (half-maximal = 95.1 sec). Therefore, psst2 is a potent inhibitory receptor displaying a unique set of interrelated dynamic features of agonist-dependent dimerization, dissociation, internalization, and reassociation, a cascade of events that might be critical for receptor function.
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Affiliation(s)
- Mario Durán-Prado
- Department of Cell Biology, University of Córdoba, E-14014 Córdoba, Spain
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Roosterman D, Goerge T, Schneider SW, Bunnett NW, Steinhoff M. Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ. Physiol Rev 2006; 86:1309-79. [PMID: 17015491 DOI: 10.1152/physrev.00026.2005] [Citation(s) in RCA: 403] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.
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Sprague JE, Peng Y, Sun X, Weisman GR, Wong EH, Achilefu S, Anderson CJ. Preparation and biological evaluation of copper-64-labeled tyr3-octreotate using a cross-bridged macrocyclic chelator. Clin Cancer Res 2005; 10:8674-82. [PMID: 15623652 DOI: 10.1158/1078-0432.ccr-04-1084] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE Somatostatin receptors (SSTr) are expressed on many neuroendocrine tumors, and several radiotracers have been developed for imaging these types of tumors. For this reason, peptide analogues of somatostatin have been well characterized. Copper-64 (t(1/2) = 12.7 hours), a positron emitter suitable for positron emission tomography (PET) imaging, was shown recently to have improved in vivo clearance properties when chelated by the cross-bridged tetraazamacrocycle 4,11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo(6.6.2)hexadecane (CB-TE2A) compared with 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA). EXPERIMENTAL DESIGN CB-TE2A and TETA were conjugated to the somatostatin analogue tyrosine-3-octreotate (Y3-TATE) for evaluation of CB-TE2A as a bifunctional chelator of 64Cu. The in vitro affinity of each compound for SSTr was determined using a homologous competitive binding assay. In vivo characteristics of both radiolabeled compounds were examined in biodistribution and microPET studies of AR42J tumor-bearing rats. RESULTS Cu-CB-TE2A-Y3-TATE (Kd = 1.7 nmol/L) and Cu-TETA-Y3-TATE (Kd = 0.7 nmol/L) showed similar affinities for AR42J derived SSTr. In biodistribution studies, nonspecific uptake in blood and liver was lower for 64Cu-CB-TE2A-Y3-TATE. Differences increased with time such that, at 4 hours, blood uptake was 4.3-fold higher and liver uptake was 2.4-fold higher for 64Cu-TETA-Y3-TATE than for 64Cu-CB-TE2A-Y3-TATE. In addition, 4.4-times greater tumor uptake was detected with 64Cu-CB-TE2A-Y3-TATE than with 64Cu-TETA-Y3-TATE at 4 hours postinjection. MicroPET imaging yielded similar results. CONCLUSIONS CB-TE2A appears to be a superior in vivo bifunctional chelator of 64Cu for use in molecular imaging by PET or targeted radiotherapy due to both improved nontarget organ clearance and higher target organ uptake of 64Cu-CB-TE2A-Y3-TATE compared with 64Cu-TETA-Y3-TATE.
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Affiliation(s)
- Jennifer E Sprague
- Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Stahl A, Meisetschläger G, Schottelius M, Bruus-Jensen K, Wolf I, Scheidhauer K, Schwaiger M. [123I]Mtr-TOCA, a radioiodinated and carbohydrated analogue of octreotide: scintigraphic comparison with [111In]octreotide. Eur J Nucl Med Mol Imaging 2005; 33:45-52. [PMID: 16151771 DOI: 10.1007/s00259-005-1872-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2005] [Accepted: 05/19/2005] [Indexed: 11/28/2022]
Abstract
PURPOSE Scintigraphy with maltotriose-[123I]Tyr3-octreotate ([123I]Mtr-TOCA) is compared with [111In]DTPA-Phe1-octreotide ([111In]OC) to assess the differences in pharmacokinetics and imaging properties as well as to estimate the therapeutic potential of the corresponding [131I]Mtr-TOCA. METHODS Six patients with somatostatin receptor (sstr)-positive tumours were assessed using a dual-head gamma camera. After injection of 137 +/- 28 MBq [123I]Mtr-TOCA, dynamic data acquisition of the upper abdomen (30 min) was performed followed by whole-body scans at 0.5 h, 1 h, 3 h and 20 h as well as by SPECT imaging (tumour) at 2 h. [111In]OC scintigraphy was performed by acquiring whole-body scans (4 h, 24 h) and SPECT (24 h). Using a region of interest (ROI) method, tissue and tumour bound activity was assessed and dosimetry performed. RESULTS [123I]Mtr-TOCA shows rapid tumour uptake. Up to 4 h, tumour/organ (tu/org) ratios are stable and generally higher than with [111In]OC. From 3 h to 20 h, tu/org ratios increase for spleen, remain stable for liver and decrease significantly for all other tissues. In contrast, with [111In]OC, tu/org ratios decrease slightly between 4 h and 24 h for liver, spleen and kidney and increase for all other tissues. On [123I]Mtr-TOCA scintigraphy, a total of 27 lesions are detected, whereas 33 lesions are detected on [111In]OC scintigraphy (p=0.50). Effective patient absorbed dose is 1.9 +/- 0.9 mSv per 100 MBq [123I]Mtr-TOCA. CONCLUSION Compared with [111In]OC, [123I]Mtr-TOCA enables faster imaging of sstr-positive tumours with a lower radiation burden to the patient. [123I]Mtr-TOCA and [111In]OC allow for tumour imaging with almost identical contrast and diagnostic yield. As regards peptide receptor radionuclide therapy, radioiodinated Mtr-TOCA is hampered by limited intratumoural activity retention
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Affiliation(s)
- Alexander Stahl
- Department of Nuclear Medicine, Technische Universität München, Klinikum rechts der Isar, Ismaninger Strasse 22, 81675 Munich, Germany.
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van der Hoek J, van der Lelij AJ, Feelders RA, de Herder WW, Uitterlinden P, Poon KW, Boerlin V, Lewis I, Krahnke T, Hofland LJ, Lamberts SW. The somatostatin analogue SOM230, compared with octreotide, induces differential effects in several metabolic pathways in acromegalic patients. Clin Endocrinol (Oxf) 2005; 63:176-84. [PMID: 16060911 DOI: 10.1111/j.1365-2265.2005.02322.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
OBJECTIVE Recently, our first clinical study with the novel multiligand somatostatin (SRIF) analogue SOM230 in acromegalic patients showed that SOM230, due to its beneficial inhibitory effects on GH levels compared with octreotide (OCT), might increase the number of patients that can be biochemically controlled. Since SRIF analogues are also known to interact with other metabolic pathways, IGF-I, IGFBP-1, glucose and insulin concentrations on the control day (CD) and on treatment days following a single s.c. injection SOM230 100 and 250 microg, were compared to those following OCT 100 microg. DESIGN AND PATIENTS Randomized, cross-over, double-blinded proof-of-concept trial in 12 patients with active acromegaly. RESULTS Free IGF-I levels were suppressed after 24 h by OCT, SOM230 250 and 100 microg, whereas at 48 h only both SOM230 dosages still induced these inhibitory effects. Circulating IGFBP-1 levels (AUC; 0830-1430 h) compared with CD, increased sharply after OCT (from 48 to 237 microg/l/h; P < 0.001 vs. CD), while SOM230 250 and 100 microg elicited a lower and dose-dependent effect (163 and 90 microg/l/h, respectively, P < 0.05 vs. CD and OCT). Neither insulin nor GH levels showed statistically significant correlation with IGFBP-1 levels either after SOM230 or OCT. An early rise in glucose levels 1 h postinjection with SOM230 250 microg compared with OCT and CD was observed 8.3 +/- 0.8, 4.4 +/- 0.5 and 4.9 +/- 0.4 mmol/l, respectively: P < 0.05). SOM230 250 microg (19 +/- 4 vs. 46 +/- 3 mU/l on CD: P < 0.05), although clearly less potent than OCT (5.4 +/- 0.4 mU/l: P < 0.01 vs. CD), inhibited insulin release. Since these corresponding absolute insulin levels cannot entirely explain this hyperglycaemic effect of SOM230, other mechanisms seem involved in this glucose rise. If SOM230 would influence glucose homeostasis in peripheral target tissues of insulin action, expression of SS-receptors (sst) seems a logical necessity. In normal human liver tissues, analysed by quantitative polymerase chain reaction (PCR), the average sst1 mRNA expression level appeared significantly higher compared with sst2 (n = 6, relative copy number 161 +/- 46 vs. 57 +/- 6; P < 0.05). Fat tissue expressed both sst1 and sst2 mRNA, whereas in muscle only sst2 mRNA was found. CONCLUSION Both dosages of SOM230 inhibit free IGF-I in a more sustained fashion compared to OCT, implying longer duration of action. The superior action of OCT compared with SOM230 in stimulating IGFBP-1 levels, suggests direct regulation of IGFBP-1 by SRIF analogues via sst2. Finally, expression of only sst1 and sst2 in target tissues of insulin action, might point towards additional modulatory effects by SOM230 on glucose homeostasis.
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Affiliation(s)
- Joost van der Hoek
- Department of Internal Medicine, Section Endocrinology, Erasmus MC, Dr Molewaterplein 40, 3015 GD Rotterdam, The Netherlands.
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Liu Q, Cescato R, Dewi DA, Rivier J, Reubi JC, Schonbrunn A. Receptor Signaling and Endocytosis Are Differentially Regulated by Somatostatin Analogs. Mol Pharmacol 2005; 68:90-101. [PMID: 15855408 DOI: 10.1124/mol.105.011767] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Upon hormone stimulation, the sst2 somatostatin receptor couples to adenylyl cyclase through G(i/o) proteins and undergoes rapid endocytosis via clathrin-coated pits. In this study, we determined the relationship between the ability of ligands to induce sst2 receptor internalization and inhibit adenylyl cyclase. Immunocytochemical studies demonstrated that peptide agonists [such as somatostatin-14, cortistatin-17, octreotide, vapreotide, KE108 (Tyr0-cyclo[d-diaminobutyric acid-Arg-Phe-Phe-d-Trp-Lys-Thr-Phe]), and SOM230 (cyclo[diaminoethylcarbamoyl-hydroxyproline-phenylglycine-d-Trp-Lys-(4-O-benzyl)-l-Tyr-Phe])] and nonpeptide agonists (such as L-779,976), stimulated the rapid endocytosis of sst2 receptors in human embryonic kidney 293 and CHO-K1 cells. In contrast, two antagonists did not induce receptor endocytosis by themselves and completely blocked agonist stimulation. Using a quantitative enzyme-linked immunosorbent assay to measure sst2 receptor sequestration, we found that peptide agonists varied by more than 100-fold in their potencies but exhibited the same efficacy as somatostatin14. In contrast, L-779,976 did not induce maximal receptor internalization. It is interesting that although betaarrestin-2 was recruited to cell surface sst2 receptors after stimulation with either somatostatin14 or L-779,976, the betaarrestin-receptor complex dissociated earlier in the endocytic pathway with the nonpeptide ligand. Although all agonists, including L-779,976, produced the same maximal inhibition of cyclic AMP, the potency ratio for inhibition of cyclic AMP and stimulation of receptor endocytosis varied by 15-fold. In general, native peptides showed similar potencies for cyclic AMP inhibition and receptor endocytosis, whereas short therapeutic analogs were substantially more potent at inhibiting cyclic AMP synthesis. These results demonstrate that the activity of somatostatin analogs to regulate receptor endocytosis and signaling are not tightly linked and provide compelling evidence for the induction of agonist specific states of the sst2 receptor.
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Affiliation(s)
- Qisheng Liu
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center-Houston, TX 77225, USA
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Schottelius M, Reubi JC, Eltschinger V, Schwaiger M, Wester HJ. N-Terminal Sugar Conjugation and C-Terminal Thr-for-Thr(ol) Exchange in Radioiodinated Tyr3-octreotide: Effect on Cellular Ligand Trafficking in Vitro and Tumor Accumulation in Vivo. J Med Chem 2005; 48:2778-89. [PMID: 15828816 DOI: 10.1021/jm040794i] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
For effective targeting of somatostatin receptor (sst) expressing tumors by radiolabeled octreotide analogues, high ligand uptake into sst-positive cells is mandatory. To optimize it, two modifications have been introduced into [(125)I]Tyr(3)-octreotide ([(125)I]TOC): C-terminal Thr-for-Thr(ol) exchange (leading to Tyr(3)-octreotate (TOCA)) and N-terminal derivatization with different carbohydrates. Both have significant impact on radioligand uptake into sst(2)-expressing cells in vitro and in vivo. Glucose conjugation via Amadori reaction by itself led to improved tumor uptake of [(123)I]Gluc-TOC in vivo, which is based on an enhancement of peptide internalization despite a reduction in receptor affinity. In the case of the doubly modified analogues [(123)I]Gluc-TOCA, [(123)I]Gluc-S-TOCA, and [(123)I]Gal-S-TOCA, a cumulative effect of both structural modifications was observed, leading up to a 5-fold increased uptake of these compounds in sst-expressing tumors compared to [(125)I]TOC. Thus, glycosylation with small carbohydrates was found to be a suitable tool to enhance receptor-mediated uptake of radiolabeled octreotide analogues into sst-positive malignancies, leading to tracers with excellent characteristics for in vivo sst-imaging applications.
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Affiliation(s)
- Margret Schottelius
- Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, 81675 München, Germany.
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Ginj M, Chen J, Walter MA, Eltschinger V, Reubi JC, Maecke HR. Preclinical Evaluation of New and Highly Potent Analogues of Octreotide for Predictive Imaging and Targeted Radiotherapy. Clin Cancer Res 2005. [DOI: 10.1158/1078-0432.1136.11.3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Purpose: Molecular imaging and targeted radiotherapy are emerging fields in nuclear oncology. Five human somatostatin receptors (hsstr1-hsstr5) are known to be overexpressed to some degree on various tumors, sstr2 being the most important one. Clinically used somatostatin based radiopeptides target exclusively sstr2. The aim of this study was to develop novel analogues with a broader sstr profile for diagnostic (positron emission tomography and single-photon emission computed tomography) and radiotherapeutic applications.
Experimental Design: The following promising structures emerged from a parallel synthetic approach: [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA0),1-Nal3,Thr8]-octreotide (1, DOTA-NOC-ATE) and [DOTA0,BzThi3,Thr8]-octreotide (2, DOTA-BOC-ATE). The conjugates were labeled with cold and radioactive 111In. Pharmacologic properties were compared with [111In-DOTA,Tyr3]-octreotide ([111In-DOTA]-TOC).
Results: The receptor affinity profile showed high affinity of both peptides to hsstr2, hsstr3, and hsstr5 and some intermediate affinity to hsstr4, whereas [111In-DOTA]-TOC shows affinity only to sstr2. The internalization is fast in sstr2 expressing AR4-2J and in transfected sstr3 expressing human embryonic kidney 293 cells. Both radiopeptides internalize much more efficiently than [111In-DOTA]-TOC. Animal biodistribution studies showed very high and specific uptake of [111In]-1 and [111In]-2 in s.c. implanted AR4-2J tumors (Lewis rats) and in somatostatin receptor expressing normal tissues. The uptake was at least 2-fold higher in these tissues and in the tumor compared with [111In-DOTA]-TOC. In addition, the kidney uptake was significantly lower for both radiopeptides.
Conclusions: These data suggest that the novel radiopeptides are superior to [111In/90Y-DOTA]-TOC and show great promise for the clinical application in the imaging of somatostatin receptor–positive tumors and their targeted radiotherapy.
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Affiliation(s)
- Mihaela Ginj
- 1Division of Radiological Chemistry, Department of Radiology, University Hospital Basel, Basel, Switzerland and
| | - Jianhua Chen
- 1Division of Radiological Chemistry, Department of Radiology, University Hospital Basel, Basel, Switzerland and
| | - Martin A. Walter
- 1Division of Radiological Chemistry, Department of Radiology, University Hospital Basel, Basel, Switzerland and
| | | | | | - Helmut R. Maecke
- 1Division of Radiological Chemistry, Department of Radiology, University Hospital Basel, Basel, Switzerland and
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Schottelius M, Poethko T, Herz M, Reubi JC, Kessler H, Schwaiger M, Wester HJ. First (18)F-labeled tracer suitable for routine clinical imaging of sst receptor-expressing tumors using positron emission tomography. Clin Cancer Res 2004; 10:3593-606. [PMID: 15173065 DOI: 10.1158/1078-0432.ccr-03-0359] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE Despite excellent radionuclide characteristics, no (18)F-labeled peptides are available for quantitative peptide receptor mapping using positron emission tomography (PET) so far, mainly due to time-consuming multistep radiosyntheses with limited overall yields. A newly developed two-step chemoselective conjugation method allows rapid and high-yield [(18)F]fluorination of peptides via oxime formation and was applied for the synthesis of new (18)F-labeled carbohydrated Tyr(3)-octreotate (TOCA) analogs with optimized pharmacokinetics suitable for clinical routine somatostatin-receptor (sst) imaging. EXPERIMENTAL DESIGN (18)F-labeled glucose (Gluc-S-) and cellobiose (Cel-S-) derivatives of aminooxy-functionalized TOCA were synthesized via oxime formation with 4-[(18)F]fluorobenzaldehyde ([(18)F]FBOA-peptides). Both the in vitro internalization profile of Gluc-S-Dpr([(18)F]FBOA)TOCA and Cel-S-Dpr([(18)F]FBOA)TOCA in hsst(2)-expressing Chinese hamster ovary cells (dual tracer protocol) and their biodistribution in AR42J tumor-bearing mice were investigated and compared with two [(18)F]fluoropropionylated ([(18)F]FP) analogs, Gluc-Lys([(18)F]FP)TOCA and Gluc-S-Dpr([(18)F]FP)TOCA. RESULTS In contrast to [(18)F]FP-labeling (3 h), chemo-selective [(18)F]FBOA-formation (50 min) afforded the respective radiopeptides in high yields (65-85%). In vitro, Gluc-S-Dpr([(18)F]FBOA)TOCA and Cel-S-Dpr([(18)F]FBOA)-TOCA showed high internalization (139 +/- 2 and 163 +/- 8 of the reference [(125)I]Tyr(3)-octreotide, respectively), which was reflected by high tumor accumulation in vivo [21.8 +/- 1.4 and 24.0 +/- 2.5% of injected dose/g (1 h), respectively]. How-ever, only Cel-S-Dpr([(18)F]FBOA)TOCA and Gluc-S-Dpr([(18)F]FP)TOCA (tumor: 15.1 +/- 1.5% of injected dose/g) with its very low accumulation in all of the nontarget organs showed improved tumor:organ ratios compared with Gluc-Lys([(18)F]FP)TOCA. For Cel-S-Dpr([(18)F]FBOA)TOCA,tumor:organ ratios (1 h) were 42:1, 27:1, 15:1, 3:1, and 208:1 for blood, liver, intestine, kidney, and muscle, respectively. CONCLUSION Due to the fast and high-yield chemoselective radiofluorination strategy and to its excellent pharmacokinetics, Cel-S-Dpr([(18)F]FBOA)TOCA represents the first tracer suitable for routine clinical application in PET somatostatin receptor imaging.
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Affiliation(s)
- Margret Schottelius
- Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, München, Germany
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Kuhnast B, Bodenstein C, Haubner R, Wester HJ, Senekowitsch-Schmidtke R, Schwaiger M, Weber WA. Targeting of gelatinase activity with a radiolabeled cyclic HWGF peptide. Nucl Med Biol 2004; 31:337-44. [PMID: 15028246 DOI: 10.1016/j.nucmedbio.2003.10.011] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/18/2003] [Indexed: 11/20/2022]
Abstract
Matrix metalloproteinases (MMPs) are a family of proteinases that play an important role in cancer as well as in numerous diseases. In this article, we describe the labeling of a phage display selected cyclic decapeptide containing the HWGF (histidine-tryptophane-glycine-phenylalanine) sequence to target MMP-2 and MMP-9. To evaluate the ability of this labeled peptide to monitor non invasively MMP-2 and MMP-9 activity, in vitro studies, biodistribution, competition studies and plasma metabolites analyses in Lewis Lung cancer tumor bearing mice were performed.
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Affiliation(s)
- B Kuhnast
- Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universitaet Muenchen, 81675 Munich, Germany.
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Morinville A, Martin S, Lavallée M, Vincent JP, Beaudet A, Mazella J. Internalization and trafficking of neurotensin via NTS3 receptors in HT29 cells. Int J Biochem Cell Biol 2004; 36:2153-68. [PMID: 15313463 DOI: 10.1016/j.biocel.2004.04.013] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2003] [Revised: 03/17/2004] [Accepted: 04/14/2004] [Indexed: 11/16/2022]
Abstract
The neurotensin receptor-3, originally identified as sortilin, is unique among neuropeptide receptors in that it is a single trans-membrane domain, type I receptor. To gain insight into the functionality of neurotensin receptor-3, we examined the neurotensin-induced intracellular trafficking of this receptor in the human carcinoma cell line HT29, which expresses both neurotensin receptor-1 and -3 sub-types. At steady state, neurotensin receptor-3 was found by sub-cellular fractionation and electron microscopic techniques to be predominantly associated with intracellular elements. A small proportion (approximately 10%) was associated with the plasma membrane, but a significant amount (approximately 25%) was observed inside the nucleus. Following stimulation with neurotensin (NT), neurotensin/neurotensin receptor-3 complexes were internalized via the endosomal pathway. This internalization entailed no detectable loss of cell surface receptors, suggesting compensation through either recycling or intracellular receptor recruitment mechanisms. Internalized ligand and receptors were both sorted to the pericentriolar recycling endosome/Trans-Golgi Network (TGN), indicating that internalized neurotensin is sorted to this compartment via neurotensin receptor-3. Furthermore, within the Trans-Golgi Network, neurotensin was bound to a lower molecular form of the receptor than at the cell surface or in early endosomes, suggesting that signaling and transport functions of neurotensin receptor-3 may be mediated through different molecular forms of the protein. In conclusion, the present work suggests that the neurotensin receptor-3 exists in two distinct forms in HT29 cells: a high molecular weight, membrane-associated form responsible for neurotensin endocytosis from the cell surface and a lower molecular weight, intracellular form responsible for the sorting of internalized neurotensin to the Trans-Golgi Network.
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Affiliation(s)
- Anne Morinville
- Montreal Neurological Institute, McGill University, 3801 University Street, Montreal, Que., Canada H3A 2B4
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González-Maeso J, Wise A, Green A, Koenig JA. Agonist-induced desensitization and endocytosis of heterodimeric GABAB receptors in CHO-K1 cells. Eur J Pharmacol 2004; 481:15-23. [PMID: 14637170 DOI: 10.1016/j.ejphar.2003.09.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
gamma-Aminobutyric acid B (GABA(B)) receptor is the first discovered G protein-coupled receptor that requires two subunits, GB1 and GB2, to form a functional receptor. Whereas the molecular and functional characteristics of GABA(B) receptors have been recently extensively studied, the mechanisms underlying receptor desensitization and endocytosis are still poorly understood. We have investigated the effect of continuous agonist exposure on the human GABA(B) receptor functional response and redistribution when expressed in Chinese hamster ovary (CHO-K1) cells. The wild-type GABA(B) receptor-mediated inhibition of the adenylate cyclase activity appeared desensitized after 2 h in the presence of GABA (100 microM). Fusion proteins were generated by attachment of cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP) to GB1 and GB2, respectively, and confocal microscopy experiments in intact living cells semi-stably expressing the constructs were performed. Incubation of co-expressing CFP-GB1 and YFP-GB2 cells in the presence of GABA (100 microM) for 2 h induced a profound receptor internalization, and CFP-GB1 and YFP-GB2 appeared co-localized in the endosome (labelled with Cy3-transferrin). The internalization was blocked by a selective GABA(B) receptor antagonist. These results represent the first clear visualization of agonist-induced internalization of the unique heterodimeric GABA(B) receptor.
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Affiliation(s)
- Javier González-Maeso
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QJ, UK.
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Nyitrai G, Kékesi KA, Emri Z, Szárics E, Juhász G, Kardos J. GABA(B) receptor antagonist CGP-36742 enhances somatostatin release in the rat hippocampus in vivo and in vitro. Eur J Pharmacol 2004; 478:111-9. [PMID: 14575795 DOI: 10.1016/j.ejphar.2003.08.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Here, we show the modulation of somatostatin functions in the hippocampus by the orally active 'cognition enhancer' GABA(B) receptor antagonist, (3-aminopropyl)n-butylphosphinic acid (CGP-36742), both in vivo and in vitro. Using high-pressure liquid chromatography-coupled electrospray mass spectrometry, we measured a two-fold increase in the extracellular level of somatostatin to CGP-36742 application in the hippocampus of anaesthetised rats. The basal release of [125I]somatostatin in the synaptosomal fraction was increased by CGP-36742 in concentrations lower than 1 muM. Simultaneous measurement of [14C]Glu and [3H]gamma-aminobutyric-acid ([3H]GABA) showed that CGP-36742 increased their basal release. However, prior [125I]somatostatin application suppressed the increase in the basal release of [14C]Glu and induced a net decrease in the basal release of [3H]GABA. Somatostatin application had a similar effect. In slices, CGP-36742 increased the postsynaptic effect of somatostatin on CA1 pyramidal cells. These results suggest a pre- and postsynaptic functional 'cross-talk' between coexisting GABA(B) and somatostatin receptors in the rat hippocampus.
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Affiliation(s)
- Gabriella Nyitrai
- Department of Neurochemistry, Chemical Research Center, Hungarian Academy of Sciences, H-1025 Budapest, Pusztaszeri út 59-67, Hungary.
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Møller LN, Stidsen CE, Hartmann B, Holst JJ. Somatostatin receptors. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2003; 1616:1-84. [PMID: 14507421 DOI: 10.1016/s0005-2736(03)00235-9] [Citation(s) in RCA: 255] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
In 1972, Brazeau et al. isolated somatostatin (somatotropin release-inhibiting factor, SRIF), a cyclic polypeptide with two biologically active isoforms (SRIF-14 and SRIF-28). This event prompted the successful quest for SRIF receptors. Then, nearly a quarter of a century later, it was announced that a neuropeptide, to be named cortistatin (CST), had been cloned, bearing strong resemblance to SRIF. Evidence of special CST receptors never emerged, however. CST rather competed with both SRIF isoforms for specific receptor binding. And binding to the known subtypes with affinities in the nanomolar range, it has therefore been acknowledged to be a third endogenous ligand at SRIF receptors. This review goes through mechanisms of signal transduction, pharmacology, and anatomical distribution of SRIF receptors. Structurally, SRIF receptors belong to the superfamily of G protein-coupled (GPC) receptors, sharing the characteristic seven-transmembrane-segment (STMS) topography. Years of intensive research have resulted in cloning of five receptor subtypes (sst(1)-sst(5)), one of which is represented by two splice variants (sst(2A) and sst(2B)). The individual subtypes, functionally coupled to the effectors of signal transduction, are differentially expressed throughout the mammalian organism, with corresponding differences in physiological impact. It is evident that receptor function, from a physiological point of view, cannot simply be reduced to the accumulated operations of individual receptors. Far from being isolated functional units, receptors co-operate. The total receptor apparatus of individual cell types is composed of different-ligand receptors (e.g. SRIF and non-SRIF receptors) and co-expressed receptor subtypes (e.g. sst(2) and sst(5) receptors) in characteristic proportions. In other words, levels of individual receptor subtypes are highly cell-specific and vary with the co-expression of different-ligand receptors. However, the question is how to quantify the relative contributions of individual receptor subtypes to the integration of transduced signals, ultimately the result of collective receptor activity. The generation of knock-out (KO) mice, intended as a means to define the contributions made by individual receptor subtypes, necessarily marks but an approximation. Furthermore, we must now take into account the stunning complexity of receptor co-operation indicated by the observation of receptor homo- and heterodimerisation, let alone oligomerisation. Theoretically, this phenomenon adds a novel series of functional megareceptors/super-receptors, with varied pharmacological profiles, to the catalogue of monomeric receptor subtypes isolated and cloned in the past. SRIF analogues include both peptides and non-peptides, receptor agonists and antagonists. Relatively long half lives, as compared to those of the endogenous ligands, have been paramount from the outset. Motivated by theoretical puzzles or the shortcomings of present-day diagnostics and therapy, investigators have also aimed to produce subtype-selective analogues. Several have become available.
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Affiliation(s)
- Lars Neisig Møller
- Department of Medical Physiology, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark
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Wild D, Schmitt JS, Ginj M, Mäcke HR, Bernard BF, Krenning E, De Jong M, Wenger S, Reubi JC. DOTA-NOC, a high-affinity ligand of somatostatin receptor subtypes 2, 3 and 5 for labelling with various radiometals. Eur J Nucl Med Mol Imaging 2003; 30:1338-47. [PMID: 12937948 DOI: 10.1007/s00259-003-1255-5] [Citation(s) in RCA: 217] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2003] [Accepted: 05/24/2003] [Indexed: 10/26/2022]
Abstract
Earlier studies have shown that modification of the octapeptide octreotide in positions 3 and 8 may result in compounds with increased somatostatin receptor affinity that, if radiolabelled, display improved uptake in somatostatin receptor-positive tumours. The aim of a recent research study in our laboratory was to employ the parallel peptide synthesis approach by further exchanging the amino acid in position 3 of octreotide and coupling the macrocyclic chelator DOTA(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) to these peptides for labelling with radiometals like gallium-67 or -68, indium-111, yttrium-90 and lutetium-177. The purpose was to find radiopeptides with an improved somatostatin receptor binding profile in order to extend the spectrum of targeted tumours. A first peptide, [111In,90Y-DOTA]-1-Nal3-octreotide (111In,90Y-DOTA-NOC), was isolated which showed an improved profile. InIII-DOTA-NOC exhibited the following IC50 values (nM) when studied in competition with [125I][Leu8, d-Trp22, Tyr25]somatostatin-28 (values for YIII-DOTA-NOC are shown in parentheses): sstr2, 2.9 +/- 0.1 (3.3 +/- 0.2); sstr3, 8 +/- 2 (26 +/- 1.9); sstr5, 11.2 +/- 3.5 (10.4 +/- 1.6). Affinity towards sstr1 and 4 was very low or absent. InIII-DOTA-NOC is superior to all somatostatin-based radiopeptides having this particular type of binding profile, including DOTA-lanreotide, and has three to four times higher binding affinity to sstr2 than InIII,YIII-DOTA-Tyr3-octreotide (InIII,YIII-DOTA-TOC). In addition, [111In]DOTA-NOC showed a specific and high rate of internalization into AR4-2J rat pancreatic tumour cells which, after 4 h, was about two times higher than that of [111In]DOTA-TOC and three times higher than that of [111In]DOTA-octreotide ([111In]DOTA-OC). The internalized radiopeptides were externalized intact upon 2 h of internalization followed by an acid wash. After 2-3 h of externalization a plateau is reached, indicating a steady-state situation explained by reactivation of the receptors followed by re-endocytosis. Biodistribution studies in CA 20948 tumour-bearing rats showed rapid clearance from all sstr-negative tissues except the kidneys. At 4 h the uptake of [111In]DOTA-NOC in the tumour and sstr-positive tissues, such as adrenals, stomach and pancreas, was three to four times higher than that of [111In]DOTA-TOC. Differential blocking studies indicate that this is at least partially due to the uptake mediated by sstr3 and sstr5. These very promising preclinical data justify the use of this new radiopeptide for imaging and potentially internal radiotherapy studies in patients.
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Affiliation(s)
- Damian Wild
- Division of Radiological Chemistry, Institute of Nuclear Medicine, Department of Radiology, University Hospital Basel, Basel, Switzerland
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Hofland LJ, Lamberts SWJ. The pathophysiological consequences of somatostatin receptor internalization and resistance. Endocr Rev 2003; 24:28-47. [PMID: 12588807 DOI: 10.1210/er.2000-0001] [Citation(s) in RCA: 357] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Somatostatin receptors expressed on tumor cells form the rationale for somatostatin analog treatment of patients with somatostatin receptor-positive neuroendocrine tumors. Nevertheless, although somatostatin analogs effectively control hormonal hypersecretion by GH-secreting pituitary adenomas, islet cell tumors, and carcinoid tumors, significant differences are observed among patients with respect to the efficacy of treatment. This may be related to a differential expression of somatostatin receptor subtypes among tumors. In addition, the property of somatostatin receptor subtypes to undergo agonist-induced internalization has important consequences for visualizing, as well as for therapy, of receptor-positive tumors using radioisotope- or chemotherapeutic-compound-coupled somatostatin analogs. This review covers the pathophysiological role of somatostatin receptor subtypes in determining the efficacy of treatment of patients with somatostatin receptor-positive tumors using somatostatin analogs, as well as the preclinical and clinical consequences of agonist-induced receptor internalization for somatostatin receptor-targeted radio- and chemotherapy. Herein, the development and potential role of novel somatostatin analogs is discussed.
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Affiliation(s)
- Leo J Hofland
- Department of Internal Medicine, Erasmus Medical Center, 3015 GD Rotterdam, The Netherlands.
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Rogers BE, Chaudhuri TR, Reynolds PN, Della Manna D, Zinn KR. Non-invasive gamma camera imaging of gene transfer using an adenoviral vector encoding an epitope-tagged receptor as a reporter. Gene Ther 2003; 10:105-14. [PMID: 12571639 DOI: 10.1038/sj.gt.3301853] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
A model epitope-tagged receptor was constructed by fusing the hemagglutinin (HA) sequence on the extracellular N-terminus of the human somatostatin receptor subtype 2 (hSSTr2) gene. This construct was placed in an adenoviral (Ad-HAhSSTr2) vector. This study evaluated Ad-HAhSSTr2 in vitro and in vivo using FACS, fluorescent microscopy, radioactive binding assays, and gamma camera imaging techniques. Infection of A-427 non-small cell lung cancer cells with Ad-HAhSSTr2 or Ad-hSSTr2 resulted in similar expression of hSSTr2 by FACS analysis and binding assays using a (99m)Tc-labeled somatostatin analogue ((99m)Tc-P2045). HAhSSTr2 expression in A-427 cells was specific for infection with Ad-HAhSSTr2. FITC-labeled anti-HA antibody (FITC-HA) confirmed surface expression in live A-427 cells and the absence of internalization. Gamma camera imaging and gamma counter analysis of normal mice showed significantly greater (P<0.05) liver uptake of (99m)Tc-labeled anti-HA antibody ((99m)Tc-anti-HA) in mice injected i.v. 48 h earlier with Ad-HAhSSTr2 (53.6+/-6.9% ID/g) as compared to mice similarly injected with Ad-hSSTr2 (9.0+/-1.3% ID/g). In a mouse tumor model, imaging detected increased tumor localization of (99m)Tc-anti-HA due to direct intratumor injection Ad-HAhSSTr2. Gamma counter analysis confirmed significantly greater (P<0.05) uptake of (99m)Tc-anti-HA in tumors injected with Ad-HAhSSTr2 (12.5+/-4.1% ID/g) as compared to Ad-hSSTr2-infected tumors (5.1+/-1.5% ID/g). These studies demonstrate the feasibility of using an epitope-tagged reporter receptor for non-invasively imaging gene transfer.
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Affiliation(s)
- B E Rogers
- Department of Radiation Oncology, University of Alabama at Birmingham, 1825 6th Avenue South, WT1 674, Birmingham, AL 35294, USA
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Eisenwiener KP, Prata MIM, Buschmann I, Zhang HW, Santos AC, Wenger S, Reubi JC, Mäcke HR. NODAGATOC, a new chelator-coupled somatostatin analogue labeled with [67/68Ga] and [111In] for SPECT, PET, and targeted therapeutic applications of somatostatin receptor (hsst2) expressing tumors. Bioconjug Chem 2002; 13:530-41. [PMID: 12009943 DOI: 10.1021/bc010074f] [Citation(s) in RCA: 158] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A monoreactive NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) derived prochelator (1-(1-carboxy-3-carbo-tert-butoxypropyl)-4,7-(carbo-tert-butoxymethyl)-1,4,7-triazacyclononane (NODAGA(tBu)(3))) was synthesized in five steps with an overall yield of 21%. It is useful for the coupling to the N-terminus of peptides on solid phase and in solution; it was coupled to [Tyr3]-octreotide (TOC) on solid phase, and the resulting peptide, NODAGA-Tyr3-octreotide (NODAGATOC), was labeled with the radiometals 111In and 67Ga in high yields and good specific activities. [67Ga]- and [111In]-NODAGA-Tyr3-octreotide appear to be useful to visualize primary tumors and metastases which express somatostatin receptors subtype 2 (sstr2), such as neuroendocrine tumors, because of their high affinity to this receptor subtype with IC(50) = 3.5 +/- 1.6 nM and 1.7 +/- 0.2 nM, respectively. NODAGATOC could be used as a SPECT and PET tracer, when labeled with 111In, 67Ga, or 68Ga, and even for therapeutic applications. Surprisingly, [111In]-NODAGATOC shows 2 times higher binding affinity to sstr2, but also a factor of 4 higher affinity to sstr5 compared to [67Ga]-NODAGATOC. [67Ga]-NODAGATOC is very stable in serum and rat liver homogenate. There is no difference in the rate of internalization into AR4-2J rat pancreatic tumor cells; both radioligands are highly internalized, at 4 h a 3 times higher uptake compared to [111In]-DOTA-Tyr3-octreotide ([111In]-DOTATOC) was found. The biodistribution of [67Ga]-NODAGATOC in AR4-2J tumor bearing nude mice is very favorable at short times after injection; there is fast excretion from all nontarget organs except the kidneys and high uptake in sst receptor rich organs and in the AR4-2J tumor. Again it is superior to [111In]-DOTATOC in this respect. The results indicate an improved biological behavior which is likely due to the fact that an additional spacer group separates the chelate from the pharmacophoric part of the somatostatin analogue.
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Affiliation(s)
- Klaus-Peter Eisenwiener
- Division of Radiological Chemistry, Institute of Nuclear Medicine, Department of Radiology, University Hospital, Petersgraben 4, CH-4031 Basel, Switzerland
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Ohshima N, Ishii S, Izumi T, Shimizu T. Receptor-dependent metabolism of platelet-activating factor in murine macrophages. J Biol Chem 2002; 277:9722-7. [PMID: 11786559 DOI: 10.1074/jbc.m112406200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Degradation of platelet-activating factor (PAF) was examined by incubating PAF with macrophages from PAF receptor-deficient mice. The degradation rate was halved as compared with wild-type mice. The reduction of the rate was comparable with the presence of a PAF antagonist WEB 2086 in wild-type cells. PAF was internalized rapidly (t(12) approximately 1 min) into wild-type macrophages. The PAF internalization was inhibited by the treatment of 0.45 m sucrose but was not affected by phorbol 12-myristate 13-acetate, suggesting that PAF internalizes into macrophages with its receptor in a clathrin-dependent manner. Internalized PAF was degraded into lyso-PAF with a half-life of 20 min. Treatment of concanavalin A inhibited the conversion of PAF into lyso-PAF, suggesting that uptake of PAF enhances PAF degradation. Lyso-PAF was subsequently metabolized into 1-alkyl-2-acyl-phosphatidylcholine. In addition, release of PAF acetylhydrolase from macrophages was enhanced when wild-type macrophages were stimulated with PAF but not from macrophages of PAF receptor-deficient mice. Thus, the PAF stimulation of macrophages leads to its degradation through both intracellular and extracellular mechanisms.
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Affiliation(s)
- Noriyasu Ohshima
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, The University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033 Japan
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Smalley KSM, Koenig JA, Feniuk W, Humphrey PPA. Ligand internalization and recycling by human recombinant somatostatin type 4 (h sst(4)) receptors expressed in CHO-K1 cells. Br J Pharmacol 2001; 132:1102-10. [PMID: 11226141 PMCID: PMC1572639 DOI: 10.1038/sj.bjp.0703896] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2000] [Revised: 11/10/2000] [Accepted: 12/11/2000] [Indexed: 02/01/2023] Open
Abstract
There is controversy as to whether somatostatin sst(4) receptors internalize. In this study, CHO-K1 cells expressing human sst(4) receptor (CHOsst(4) cells) cells internalized [(125)I]-[(11)Tyr]-SRIF in a time-dependent manner, reaching a steady state at 60 min (1.4+/-0.1x10(4) molecules internalized per cell). Internalization was blocked by hypertonic sucrose (0.5 M), ATP depletion or by decreasing the temperature to 4 degrees C. Internalization of [(125)I]-[(11)Tyr]-SRIF was also inhibited (pIC(50) values) by increasing concentrations of SRIF (7.74), L-362855 (6.27) and NNC-296100 (6.50) with pIC(50) values approximately 10 fold lower than those obtained for inhibition of [(125)I]-[(11)Tyr]-SRIF binding to membrane homogenates. Internalized ligand recycled rapidly to the extracellular media (t(1/2) 3.9+/-0.7 min) with only 6.8+/-0.6% of internalized radioactivity remaining in the cell after 45 min. Confocal microscopy of permeabilized, HA-epitope tagged CHOsst(4) cells labelled with a Cy-3 conjugated antibody revealed little internal immunostaining after SRIF (1 microM) treatment, consistent with the small proportion of receptors (3.5%) estimated to be internalized by radioimmunoassay. In summary, CHOsst(4) cells internalized [(125)I]-[(11)Tyr]-SRIF in a clathrin- and ATP-dependent manner with subsequent rapid recycling to the extracellular medium. Rapid receptor recycling and the consequent low proportion of receptors internalized at any one time may explain the inability to visualize internalized receptors by confocal microscopy. It seems unlikely therefore that the marked receptor desensitization observed in CHOsst(4) cells following SRIF treatment can be accounted for by a decrease in cell surface receptor expression.
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Affiliation(s)
- K S M Smalley
- Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QJ
| | - J A Koenig
- Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QJ
| | - W Feniuk
- Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QJ
| | - P P A Humphrey
- Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QJ
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Abstract
Somatostatin, and the recently discovered neuropeptide cortistatin, exert their physiological actions via a family of six G protein-coupled receptors (sst1, sst2A, sst2B, sst3, sst4, sst5). Following the cloning of somatostatin receptors significant advances have been made in our understanding of their molecular, pharmacological and signaling properties although much progress remains to be done to define their physiological role in vivo. In this review, the present knowledge regarding neuroanatomical localization, signal transduction pathways, desensitization and internalization properties of somatostatin receptors is summarized. Evidence that somatostatin receptors can form homo- and heterodimers and can physically interact with members of the SSTRIP/Shank/ProSAP1/CortBP1 family is also discussed.
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Affiliation(s)
- Z Csaba
- Inserm U549, IFR Broca-Sainte Anne, Centre Paul Broca, Paris, France
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Vandenbulcke F, Nouel D, Vincent JP, Mazella J, Beaudet A. Ligand-induced internalization of neurotensin in transfected COS-7 cells: differential intracellular trafficking of ligand and receptor. J Cell Sci 2000; 113 ( Pt 17):2963-75. [PMID: 10934036 DOI: 10.1242/jcs.113.17.2963] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The neuropeptide neurotensin (NT) is known to be internalized in a receptor-mediated fashion into its target cells. To gain insight into the mechanisms underlying this process, we monitored in parallel the migration of the NT1 neurotensin receptor subtype and a fluorescent analog of NT (fluo-NT) in COS-7 cells transfected with a tagged NT1 construct. Fluo-NT internalization was prevented by hypertonic sucrose, potassium depletion and cytosol acidification, demonstrating that it proceeded via clathrin-coated pits. Within 0-30 minutes, fluo-NT accumulated together with its receptor in Acridine Orange-positive, acidic organelles. These organelles concentrated transferrin and immunostained positively for rab 5A, therefore they were early endosomes. After 30-45 minutes, the ligand and its receptor no longer colocalized. Fluo-NT was first found in rab 7-positive late endosomes and later in a nonacidic juxtanuclear compartment identified as the Trans-Golgi Network (TGN) by virtue of its staining for syntaxin 6. This juxtanuclear compartment also stained positively for rab 7 and for the TGN/pericentriolar recycling endosome marker rab 11, suggesting that the ligand could have been recruited to the TGN from either late or recycling endosomes. By that time, internalized receptors were detected in Lamp-1-immunoreactive lysosomes. These results demonstrate that neurotensin/NT1 receptor complexes follow a recycling cycle that is unique among the G protein-coupled receptors studied to date, and provide the first evidence for the targeting of a nonendogenous protein from endosomes to the TGN.
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Affiliation(s)
- F Vandenbulcke
- Montreal Neurological Institute, McGill University, Montreal, Quebec, H2A 2B4 Canada
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Drmota T, Milligan G. Kinetic analysis of the internalization and recycling of [3H]TRH and C-terminal truncations of the long isoform of the rat thyrotropin-releasing hormone receptor-1. Biochem J 2000; 346 Pt 3:711-8. [PMID: 10698698 PMCID: PMC1220904] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
The C-terminal tail of the long splice variant of the rat thyrotropin-releasing hormone (TRH) receptor-1 (TRHR-1L) comprises around 93 amino acids. A series of C-terminal truncations was constructed and expressed transiently in HEK-293 cells. The extent of steady-state internalization of these in response to [(3)H]TRH was dependent upon the degree of truncation. Little effect was produced by deletion of the C-terminal to 50 amino acids, although there was a substantial decrease in the extent of internalization by deletion to 45-46 amino acids. The rate of internalization of TRHR-1L in response to ligand was substantially decreased by the acid-wash procedures often used in the analysis of cellular distribution of receptors with peptide ligands, and thus an alternative procedure using a Mes-containing buffer was employed in the present study. Apart from a truncation anticipated to eliminate post-translational acylation of the re-ceptor, which altered both the association and dissociation rates of [(3)H]TRH, the kinetics of ligand binding were unaffected by C-terminal truncation. Equally, the rate of recycling to the plasma membrane of internalized receptors was unaffected by C-terminal truncation. Although the extent of internalization of the full-length receptor was impaired by pre-exposure of cells to TRH, this was not true of C-terminal truncation mutants, which displayed limited steady-state internalization ratios. A mutant with a substantial C-terminal deletion also displayed decreased functional desensitization compared with the full-length receptor.
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Affiliation(s)
- T Drmota
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, University of Glasgow, Glasgow G12 8QQ, Scotland, U.K
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Petrucci C, Cervia D, Buzzi M, Biondi C, Bagnoli P. Somatostatin-induced control of cytosolic free calcium in pituitary tumour cells. Br J Pharmacol 2000; 129:471-84. [PMID: 10711345 PMCID: PMC1571859 DOI: 10.1038/sj.bjp.0703075] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
1. In rat pituitary tumour cells (GC cells), spontaneous oscillations of the intracellular concentration of Ca2+ ([Ca2+]i) induce growth hormone (GH) secretion that is inhibited by octreotide, a somatostatin (SRIF) agonist which binds to SRIF subtype (sst) receptor 2. The effects of its functional activation on the control of [Ca2+]i were investigated using fluorimetric measurements of [Ca2+]i. 2. SRIF decreases the basal [Ca2+]i and the [Ca2+]i rise in response to forskolin (FSK) through the inhibition of L-type voltage-dependent Ca2+ channels. 3. Pretreatment with octreotide or with L-Tyr8++ Cyanamid 154806, a sst2 receptor antagonist, abolishes the SRIF-induced inhibition of [Ca2+]i. Octreotide is known to operate through agonist-induced desensitization, while the antagonist operates through receptor blockade. 4. sst1 and sst2 receptor-immunoreactivities (-IRs) are localized to cell membranes. sst2, but not sst1 receptor-IR, internalizes after cell exposure to octreotide. 5. SRIF-induced inhibition of basal [Ca2+]i or FSK-induced Ca2+ entry is blocked by pertussis toxin (PTX). 6. FSK-induced cyclic AMP accumulation is only partially decreased by SRIF or octreotide, indicating that sst2 receptors are coupled to intracellular pathways other than adenylyl cyclase (AC) inhibition. 7. In the presence of H-89, an inhibitor of cyclic AMP-dependent protein kinase (PKA), SRIF-induced inhibition of basal [Ca2+]i is still present, although reduced in amplitude. 8. SRIF inhibits [Ca2+]i by activating sst2 receptors. Inhibition of AC activity is only partly responsible for this effect, and other transduction pathways may be involved.
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Affiliation(s)
- Cristina Petrucci
- Department of Physiology and Biochemistry ‘G. Moruzzi', University of Pisa, Via S. Zeno, 31-56127 Pisa, Italy
| | - Davide Cervia
- Department of Physiology and Biochemistry ‘G. Moruzzi', University of Pisa, Via S. Zeno, 31-56127 Pisa, Italy
| | - Marco Buzzi
- Department of Biology, University of Ferrara, 44100 Ferrara, Italy
| | - Carla Biondi
- Department of Biology, University of Ferrara, 44100 Ferrara, Italy
| | - Paola Bagnoli
- Department of Physiology and Biochemistry ‘G. Moruzzi', University of Pisa, Via S. Zeno, 31-56127 Pisa, Italy
- Author for correspondence:
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Stroh T, Jackson AC, Sarret P, Dal Farra C, Vincent JP, Kreienkamp HJ, Mazella J, Beaudet A. Intracellular dynamics of sst5 receptors in transfected COS-7 cells: maintenance of cell surface receptors during ligand-induced endocytosis. Endocrinology 2000; 141:354-65. [PMID: 10614658 DOI: 10.1210/endo.141.1.7259] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Internalization of G protein-coupled receptors is crucial for resensitization of phosphorylation-desensitized receptors, but also for their long term desensitization through sequestration. To elucidate the mechanisms regulating cell surface availability of the somatostatin (SRIF) receptor subtype sst5, we characterized its internalization properties in transfected COS-7 cells using biochemical, confocal microscopic, and electron microscopic techniques. Our results demonstrated rapid and efficient sequestration of specifically bound [125I]Tyr0-D-Trp8-SRIF (up to 45% of bound radioactivity). Combined immunocytochemical detection of sst5 and visualization of a fluorescent SRIF analog by confocal microscopy revealed that whereas the internalized ligand progressively clustered toward the cell center with time, immunoreactive receptors remained predominantly associated with the plasma membrane. The preservation of cell surface receptors was confirmed by binding experiments on whole cells revealing a lack of saturability of [125I]Tyr0-D-Trp8-SRIF binding at 37 C. Binding was rendered saturable by the drug monensin, showing that receptor recycling played a key role in the preservation of cell surface receptors. Electron microscopy demonstrated that in addition to receptor recycling, internalization of receptor-ligand complexes triggered a massive recruitment of sst5 receptor molecules from intracellular stores to the membrane. This combination of recycling and recruitment of spare receptors may protect sst5 from long term down-regulation through sequestration and, therefore, facilitate extended SRIF signaling.
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Affiliation(s)
- T Stroh
- Montreal Neurological Institute, McGill University, Montréal, Québec, Canada
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50
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Sarret P, Nouel D, Dal Farra C, Vincent JP, Beaudet A, Mazella J. Receptor-mediated internalization is critical for the inhibition of the expression of growth hormone by somatostatin in the pituitary cell line AtT-20. J Biol Chem 1999; 274:19294-300. [PMID: 10383439 DOI: 10.1074/jbc.274.27.19294] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The inhibitory effect of the neuropeptide somatostatin on the expression of growth hormone was measured by quantitative polymerase chain reaction in the pituitary cell line AtT-20. We demonstrate that this effect is dependent on the internalization of somatostatin-receptor complexes and that it is totally independent from the peptide-induced inhibition of adenylate cyclase. Indeed, the inhibitory effect of the peptide on growth hormone mRNA levels was totally insensitive to pertussis toxin treatment but was totally abolished under conditions which block somatostatin receptor internalization. Comparative confocal microscopic imaging of fluorescent somatostatin sequestration and fluorescence immunolabeling of sst1, sst2A, and sst5 receptors suggests that sst2A is most probably responsible of the inhibitory effect of somatostatin on growth hormone expression.
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Affiliation(s)
- P Sarret
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, UPR 411, 660 Route des Lucioles, 06560 Valbonne, France
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