Monoclonal Antibodies against the Human Somatostatin Receptor Subtypes 1–5: Development and Immunohistochemical Application in Neuroendocrine Tumors

Abstract

Background: Activation of somatostatin receptors (sstr1–5) by somatostatin and its analogues exerts an inhibitory effect on hormone secretion and provides the basis for the treatment of a range of endocrine diseases such as acromegaly, Cushing’s disease and neuroendocrine tumors (NET). The lack of well-characterized commercially available sstr subtype-specific antibodies prevents routine identification of the sstr expression profile in patients. Methods: We generated and characterized new mouse monoclonal antibodies (mAbs) targeting the five human sstr subtypes using ELISA and immunohistochemistry, and tested their suitability in formalin-fixed and paraffin-embedded (FFPE) human tissues and archival samples of normal pancreatic tissue and NET. Results: All mAbs were highly specific with no cross-reactivity. The sstr1–5 immunoreactivity in gastrointestinal NET (n = 67) was correlated with clinicopathologic data. With the exception of sstr3, NET were highly positive for all receptor subtypes (42, 63, 6, 32 and 65% of tumors were positive for sstr1, sstr2a, sstr3, sstr4 and sstr5, respectively). sstr1, sstr2a and sstr5 were present at the plasma membrane and in the cytoplasm of tumor cells, whereas sstr3 and sstr4 were almost exclusively cytoplasmic. Immunoreactivity of sstr1, sstr2a and sstr4 tended to decrease as tumor aggressiveness increased. sstr5 showed an opposite pattern, with higher staining in well-differentiated carcinomas compared with well-differentiated tumors. sstr5 immunoreactivity was correlated with the presence of metastases and angioinvasion, suggesting a possible association with more aggressive behavior. Conclusion: Determination of the sstr1–5 by immunohistochemistry using subtype-specific mAbs is feasible in FFPE tissue and may provide a tool for routine clinical practice.

Molecular and functional properties of densely and sparsely granulated GH-producing pituitary adenomas

“…The monoclonal mouse antibody for SSTR2 (clone #402038) was purchased from R&D Systems, Wiesbaden, Germany (30). The mouse MABs for SSTR1, 3, 4 and 5 were provided by Novartis, and their specificity has recently been described in detail (31). The SSTR5 antibody was raised against amino acids 350-363 at the very C-terminus of the human SSTR5 (31) and therefore does not recognise recently described truncated SSTR5 variants that arise from alternative splicing at the C-terminus (32,33).…”

“…Intensity of staining was graded in comparison to control samples from normal pituitary tissue (for SSTR1, 2, 3 and 5) and to pancreas tissue (SSTR4) (no staining, (C) barely detectable, C weakly positive below the intensity of control sample, CC same intensity as controls, CCC stronger than controls). The absolute intensity was clearly higher for membrane than for cytoplasmic staining (30,31). Samples were scored positive when they showed a CC or CCC staining in more than 50% of tumour cells as described elsewhere (34).…”

Medical therapy for advanced gastro-entero-pancreatic and bronchopulmonary neuroendocrine tumors

“…[29] SSTR2 is usually expressed in NENs, and its loss could be highly correlated with the dysregulation of tumor proliferation, consequently promoting tumor growth. [30,31] SSTR1 and SSTR5 are less expressed in NENs and correlate with a major risk of angioinvasion and distant metastasis. SSTR3 is even less present, and SSTR4 is almost absent.…”

Neuroendocrine tumors of the digestive system: pathologic and molecular characteristics

“…В настоящее время описано 5 подтипов SSTR, которые принадлежат к семейству рецепторов, сопряженных с G-белками. Показано, что аналоги соматостатина обладают наи-большей специфичностью связывания с рецепторами 2-го подтипа [71][72][73]. Поскольку показатели экспрес-сии рецепторов значительно отличаются в разных опу-холях, ИГХ-особенности их выявления являются клю-чевыми параметрами, позволяющими назначить обо-снованную лекарственную терапию аналогами соматостатина и, кроме того, оценить прогноз течения заболевания.…”