Differential expression of somatostatin receptor subtypes in human peripheral blood mononuclear cell subsets

BACKGROUND: Somatostatin (SS)-binding sites have been demonstrated in human lymphoid tissues and peripheral blood cells. However, not much is known with respect to the SS receptor subtype (sst) expression pattern and the expression of SS itself in the immune system. OBJECTIVE: The aim of this study was to evaluate the mRNA expression of the five known sst (sst(1-5)) in peripheral blood mononuclear cell (sub)populations. Moreover, the expression of the mRNAs encoding SS and the SS-like peptide cortistatin (CST) in immune cell subsets was studied. METHODS: RT-PCR and quantitative PCR were performed to evaluate sst, SS and CST mRNA expression in cells in the basal or activated state. Fluorescence-activated cell sorter (FACS) analysis using fluorescent SS was performed to visualize sst protein on cell membranes. RESULTS: B- and T-lymphocytes selectively expressed sst(3) mRNA. sst(3) expression in B-lymphocytes was significantly lower compared with T-lymphocytes. Unstimulated, freshly isolated monocytes did not express any sst mRNA. Upon activation, monocytes selectively expressed sst(2) mRNA, whereas T-lymphocyte activation upregulated sst(3) expression. sst(2) mRNA expression on monocytes was confirmed by FACS analysis. B- and T-lymphocytes did not express SS mRNA, while both cell types expressed CST mRNA. CST mRNA expression was downregulated following T-lymphocyte activation. CONCLUSION: We demonstrate for the first time unequivocally that human peripheral blood B- and T-lymphocytes selectively express sst(3), whereas monocytes do not express sst. However, upon activation, monocytes are induced to express sst(2A). No expression of SS mRNA was detected in any cell type, whereas all cell types expressed CST mRNA. The differential expression of sst and CST mRNA in lymphocytes and monocytes s

Effects of Somatostatin Analogs and Dopamine Agonists on Insulin-Like Growth Factor 2-Induced Insulin Receptor Isoform-A Activation by Gastroenteropancreatic Neuroendocrine Tumor Cells

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The role of mTOR inhibitors in the inhibition of growth and cortisol secretion in human adrenocortical carcinoma cells

Patients with adrenocortical carcinoma (ACC) need new treatment options. The aim of this study was to evaluate the effects of the mTOR inhibitors sirolimus and temsirolimus on human ACC cell growth and cortisol production. In H295, HAC15, and SW13 cells, we have evaluated mTOR, IGF2, and IGF1 receptor expressions; the effects of sirolimus and temsirolimus on cell growth; and the effects of sirolimus on apoptosis, cell cycle, and cortisol production. Moreover, the effects of sirolimus on basal and IGF2-stimulated H295 cell colony growth and on basal and IGF1-stimulated phospho-AKT, phospho-S6K1, and phospho-ERK in H295 and SW13 were studied. Finally, we have evaluated the effects of combination treatment of sirolimus with an IGF2-neutralizing antibody. We have found that H295 and HAC15 expressed IGF2 at a >1800-fold higher level than SW13. mTOR inhibitors suppressed cell growth in a dose-/time-dependent manner in all cell lines. SW13 were the most sensitive to these effects. Sirolimus inhibited H295 colony surviving fraction and size. These effects were not antagonized by IGF2, suggesting the involvement of other autocrine regulators of mTOR pathways. In H295, sirolimus activated escape pathways. The blocking of endogenously produced IGF2 increased the antiproliferative effects of sirolimus on H295. Cortisol production by H295 and HAC15 was inhibited by sirolimus. The current study demonstrates that mTOR inhibitors inhibit the proliferation and cortisol production in ACC cells. Different ACC cells have different sensitivity to the mTOR inhibitors. mTOR could be a target for the treatment of human ACCs, but variable responses might be expected. In selected cases of ACC, the combined targeting of mTOR and IGF2 coul

Mifepristone effects on tumor somatostatin receptor expression in two patients with Cushing's syndrome due to ectopic adrenocorticotropin secretion

Context: Two patients presented with Cushing's syndrome due to ectopic ACTH secretion. Initial localization studies included computed tomography, magnetic resonance imaging, and octreoscans (111In-pentreotide scintigraphy), which were negative in both patients. They were treated with the glucocorticoid receptor antagonist mifepristone, with improvement in their clinical symptoms. Follow-up octreoscans after, respectively, 6 and 12 months showed the unequivocal presence of a bronchial carcinoid in both patients. Objective: The objective of the study was to correlate in vivo and in vitro findings in patients with ectopic ACTH-producing syndrome. Methods: We determined the expression of somatostatin and dopamine receptors by immunohistochemistry (patients 1 and 2), quantitative PCR, and in vitro culturing of tumor cells (patient 1 only). In Vitro Results: Both tumors were strongly positive for somatostatin receptor type 2 (sst2) on immunohistochemistry, whereas one of the tumors (patient 1) was also dopamine receptor subtype 2 (D 2) positive on both immunohistochemistry and quantitative PCR. Octreotide (a sst2preferring analog) and cabergoline (D2 agonist) both decreased the ACTH levels in the cultured tumor cells of patient 1. Conclusion:Wedescribe two patients with ACTH-producing bronchial carcinoids, inwhoma direct down-regulatory effect of glucocorticoid levels on tumoral sst2 receptor expression is suggested by a remarkable change in octreoscan status after successful mifepristone therapy. Further studies will have to demonstrate whether glucocorticoid lowering or antagonizing therapy may be used to improve the diagnostic accuracy of somatostatin receptor scintigraphy in patients with ectopic ACTH production of unknown primary origin. Copyrigh

Immunoreactivity score using an anti-sst2A receptor monoclonal antibody strongly predicts the biochemical response to adjuvant treatment with somatostatin analogs in acromegaly

Context: Somatostatin receptor subtype 2 (sst2A) protein expression has been demonstrated to positively correlate with somatostatin analog treatment outcome in GH-secreting adenomas. Recently, a new rabbit monoclonal anti-sst2A antibody (clone UMB-1) has been validated as a reliable method to selectively detect sst2A protein levels in formalin-fixed tissues. Objective: The aim of the study was to establish whether the evaluation of sst2A protein levels, assessed with a routine reproducible immunohistochemistry protocol using UMB-1 antibody, may predict the successful adjuvant therapy with somatostatin analogs in acromegalic patients. Design, Setting, and Patients: Thirty-six acromegalic patients from our referral hospital were evaluated retrospectively. Sst2A expression analysis was performed by immunohistochemistry in 25 patients and by quantitative RT-PCR in 26 patients. Sst2A immunoreactivity was evaluated using an immunoreactivity score (IRS), which takes into account both the percentage of positive cells and staining intensity. Interventions: Patients with persistent disease after surgery (n = 26) were treated with somatostatin analogs for a median duration of 6 months. Main Outcome Measure: GH and IGF-I levels were measured before and after postoperative treatment. Results: Sst2A IRS showed a significant positive correlation with both GH (P = 0.039) and IGF-I (P = 0.001) suppression by octreotide. Sst2A IRS was negatively associated with IGF-I levels reached after treatment (P = 0.001), and patients that achieved IGF-I normalization showed significantly higher sst2A IRS compared to the group that was not normalized (P = 0.002). A sst2A IRS of at least 5 showed a sensitivity of 86% and a specificity of 91% in predicting IGF-I normalization during adjuvant octreotide treatment. Conclusion: Sst2A IRS with the anti-sst2A antibody UMB-1 represents a valid tool in the clinical practice to identify acromegalic patients likely to be responders to adjuvant the

Preoperative normalization of cortisol levels in cushing's disease after medical treatment: Consequences for somatostatin and dopamine receptor subtype expression and in vitro response to somatostatin analogs and dopamine agonists

Context: Corticotroph pituitary adenomas often highly express the dopamine 2 receptor (D2R) and somatostatin receptor subtype 5 (sst5). The sst2 expression is relatively low, likely resulting from downregulating effects of high cortisol levels. This may explain why the sst2-preferring somatostatin analog octreotide, compared with the multi-receptor-targeting somatostatin analog pasireotide, is generally ineffective in Cushing's disease. Objective: Our objective was to compare sst and D2R expression levels between adenomas from patients with elevated and normalized preoperative urinary free cortisol excretion. Patients and Design: Corticotroph adenoma tissue was examined from patients from group 1 (n = 22; elevated preoperative urinary free cortisol) and group 2 (n = 11;meanduration of preoperative normocortisolism 10 weeks). Somatotroph adenoma tissue from 10 acromegalic patients was examined to compare receptor expression profiles. Main Outcome Measures: We evaluated receptor mRNA and protein expression levels and effects of octreotide,p