Objective: Currently, there is no effective medical treatment for patients with pituitary-dependent Cushing’s disease. A novel somatostatin (SS) analogue, named SOM230, with high binding affinity to SS receptor subtypes sst₁, sst₂, sst₃ and sst₅ was recently introduced. We compared the in vitro effects of the sst₂-preferring SS analogue octreotide (OCT) and the multi-ligand SOM230 on ACTH release by human and mouse corticotroph tumour cells. Methods: By quantitative RT-PCR the sst subtype expression level was determined in human corticotroph adenomas. In vitro, the inhibitory effect of OCT and SOM230 on ACTH release by dispersed human corticotroph adenoma cells and mouse AtT20 corticotroph adenoma cells was determined. In addition, the influence of dexamethasone on the responsiveness to OCT and SOM230 was studied. Results: Corticotroph adenomas expressed predominantly sst₅ mRNA (six out of six adenomas), whereas sst₂ mRNA expression was detected at significantly lower levels. In a 72 h incubation with 10 nmol/l SOM230, ACTH release was inhibited in three out of five cultures (range −30 to −40%). Ten nmol/l OCT slightly inhibited ACTH release in only one of five cultures (− 28%). In AtT20 cells, expressing sst₂, sst₃ and sst₅, SOM230 inhibited ACTH secretion with high potency (IC₅₀ 0.2 nmol/l). Dexamethasone (10 nmol/l) pre-treatment did not influence the sensitivity of the cells to the inhibitory effect of SOM230, suggesting that sst₅ is relatively resistant to negative control by glucocorticoids. Conclusions: The selective expression of sst₅ receptors in corticotroph adenomas and the preferential inhibition of ACTH release by human corticotroph adenoma cells by SOM230 in vitro, suggest that SOM230 may have potential in the treatment of patients with pituitary-dependent Cushing’s disease.

Increasing evidence suggests that neuropeptides play a role in the regulatory mechanisms between the neuroendocrine and immune systems. A differential expression of the five known somatostatin (SS) receptors (sst_1–5) has been demonstrated in human immune cells and tissues. However, little is known concerning regulation and expression of sst_1–5and the peptide SS. Therefore, we investigated the expression and the time-dependent regulation of sst_1–5, SS, and cortistatin (CST), a novel SS-like peptide, in human monocytes (MO), monocyte-derived macrophages (MP), and dendritic cells (DC) in the basal and lipopolysaccharide (LPS)-activated state. MO, MP, and DC selectively expressed sst₂mRNA. SS mRNA was not detectable, whereas all samples expressed CST mRNA. Expression levels of sst₂and CST mRNA showed marked differences and were in the rank order of MP>>DC>>>MO. LPS stimulation did not induce expression of SS or sst_1,3,4,5. However, sst₂mRNA expression was upregulated significantly by stimulation with LPS. CST mRNA was upregulated as well. During differentiation of MO in MP or DC, time-dependent, significantly increasing sst₂and CST mRNA levels were found. By confocal microscopy, the presence of sst₂receptors was demonstrated on MP, but not on DC. This study demonstrates for the first time a selective and inducible expression of the recently discovered CST, as well as sst₂, in human monocyte-derived cells, suggesting a role for a CST-sst₂system rather than a SS-sst₂system in these immune cell types.

To determine the inhibitory profile of the novel somatostatin (SRIF) analog SOM230 with broad SRIF receptor binding, we compared the in vitro effects of SOM230, octreotide (OCT), and SRIF-14 on hormone release by cultures of different types of secreting pituitary adenomas. OCT (10 nm) significantly inhibited GH release in seven of nine GH-secreting pituitary adenoma cultures (range, −26 to −73%), SOM230 (10 nm) in eight of nine cultures (range, −22 to −68%), and SRIF-14 (10 nm) in six of six cultures (range, −30 to −75%). The sst analysis showed predominant but variable levels of somatostatin receptor (sst)₂ and sst₅ mRNA expression. In one culture completely resistant to OCT, SOM230 and SRIF-14 significantly inhibited GH release in a dose-dependent manner with an IC₅₀ value in the low nanomolar range. In the other cultures, SOM230 showed a lower potency of GH release inhibition (IC₅₀, 0.5 nm), compared with OCT (IC₅₀, 0.02 nm) and SRIF-14 (IC₅₀, 0.02 nm). A positive correlation was found between sst₂ but not sst₅ mRNA levels in the adenoma cells and the inhibitory potency of OCT on GH release in vivo and in vitro, and the effects of SOM230 and SRIF-14 in vitro. In three prolactinoma cultures, 10 nm OCT weakly inhibited prolactin (PRL) release in only one (−28%), whereas 10 nm SOM230 significantly inhibited PRL release in three of three cultures (−23, −51, and −64.0%). The inhibition of PRL release by SOM230 was related to the expression level of sst₅ but not sst₂ mRNA. Several conclusions were reached. First, SOM230 has a broad profile of inhibition of tumoral pituitary hormone release in the low nanomolar range, probably mediated via both sst₂ and sst₅ receptors. The higher number of responders of GH-secreting pituitary adenoma cultures to SOM230, compared with OCT, suggest that SOM230 has the potency to increase the number of acromegalic patients which can be biochemically controlled. Second, compared with OCT, SOM230 is more potent in inhibiting PRL release by mixed GH/PRL-secreting adenoma and prolactinoma cells.

The mTOR-inhibitor everolimus improves progression-free survival in advanced pancreatic neuroendocrine tumours (PNETs). However, adaptive resistance to mTOR inhibition is described. QGP-1 and BON-1, two human PNET cell lines, were cultured with increasing concentrations of everolimus up to 22 weeks to reach a dose of 1 μM everolimus, respectively, 1000-fold and 250-fold initial IC₅₀. Using total DNA content as a measure of cell number, growth inhibitory dose–response curves of everolimus were determined at the end of resistance induction and over time after everolimus withdrawal. Response to ATP-competitive mTOR inhibitors OSI-027 and AZD2014, and PI3K-mTOR inhibitor NVP-BEZ235 was studied. Gene expression of 10 PI3K-Akt-mTOR pathway-related genes was evaluated using quantitative real-time PCR (RT–qPCR). Long-term everolimus-treated BON-1/R and QGP-1/R showed a significant reduction in everolimus sensitivity. During a drug holiday, gradual return of everolimus sensitivity in BON-1/R and QGP-1/R led to complete reversal of resistance after 10–12 weeks. Treatment with AZD2014, OSI-027 and NVP-BEZ235 had an inhibitory effect on cell proliferation in both sensitive and resistant cell lines. Gene expression in BON-1/R revealed downregulation of MTOR, RICTOR, RAPTOR, AKT and HIF1A, whereas 4EBP1 was upregulated. In QGP-1/R, a downregulation of HIF1A and an upregulation of ERK2 were observed. Long-term everolimus resistance was induced in two human PNET cell lines. Novel PI3K-AKT-mTOR pathway-targeting drugs can overcome everolimus resistance. Differential gene expression profiles suggest different mechanisms of everolimus resistance in BON-1 and QGP-1.

Somatostatin (SS) and dopamine (DA) receptors have been highlighted as two critical regulators in the negative control of hormonal secretion in a wide group of human endocrine tumors. Both families of receptors belong to the superfamily of G protein-coupled receptors and share a number of structural and functional characteristics. Because of the generally reported high expression of somatostatin receptors (SSTRs) in neuroendocrine tumors (NET), somatostatin analogs (SSA) have a pronounced role in the medical therapy for this class of tumors, especially pituitary adenomas and well-differentiated gastroenteropancreatic NET (GEP NET). Moreover, NET express not only SSTR but also frequently dopamine receptors (DRs), and DA agonists targeting the D₂ receptor (D₂) have been demonstrated to be effective in controlling hormone secretion and cell proliferation in in vivo and in vitro studies. The treatment with SSAs combined with DA agonists has already been demonstrated efficacious in a subgroup of patients with GH-secreting pituitary adenomas and few reported cases of carcinoids. The recent availability of new selective and universal SSA and DA agonists, as well as the chimeric SS/DA compounds, may shed new light on the potential role of SSTR and D₂ as combined targets for biotherapy in NET. This review provides an overview of the latest studies evaluating the expression of SSTR and DR in NET, focusing on their co-expression and the possible clinical implications of such co-expression. Moreover, the most recent insights in SSTR and D₂ pathophysiology and the future perspectives for treatment with SSA, DA agonists, and SS/DA chimeric compounds are discussed. Abstract Somatostatin (SS) and dopamine (DA) receptors have been highlighted as two critical regulators in the negative control of hormonal secretion in a wide group of human endocrine tumors. Both families of receptors belong to the superfamily of G protein-coupled receptors and share a number of structural and functional characteristics. Because of the generally reported high expression of somatostatin receptors (SSTRs) in neuroendocrine tumors (NET), somatostatin analogs (SSA) have a pronounced role in the medical therapy for this class of tumors, especially pituitary adenomas and well-differentiated gastroenteropancreatic NET (GEP NET). Moreover, NET express not only SSTR but also frequently dopamine receptors (DRs), and DA agonists targeting the D₂ receptor (D₂) have been demonstrated to be effective in controlling hormone secretion and cell proliferation in in vivo and in vitro studies. The treatment with SSAs combined with DA agonists has already been demonstrated efficacious in a subgroup of patients with GH-secreting pituitary adenomas and few reported cases of carcinoids. The recent availability of new selective and universal SSA and DA agonists, as well as the chimeric SS/DA compounds, may shed new light on the potential role of SSTR and D₂ as combined targets for biotherapy in NET. This review provides an overview of the latest studies evaluating the expression of SSTR and DR in NET, focusing on their co-expression and the possible clinical implications of such co-expression. Moreover, the most recent insights in SSTR and D₂ pathophysiology and the future perspectives for treatment with SSA, DA agonists, and SS/DA chimeric compounds are discussed.

Context Metyrapone and ketoconazole, frequently used steroidogenesis inhibitors for treatment of Cushing’s syndrome, can be associated with side effects and limited efficacy. Osilodrostat is a CYP11B1 and CYP11B2 inhibitor, with unknown effects on other steroidogenic enzymes. Objective To compare the effects of osilodrostat, metyrapone, and ketoconazole on adrenal steroidogenesis, and pituitary adenoma cells in vitro. Methods HAC15 cells, seventeen primary human adrenocortical cell cultures, and pituitary adenoma cells were incubated with osilodrostat, metyrapone, or ketoconazole (0.01-10 µM). Cortisol and ACTH were measured using chemiluminescence immunoassays, and steroid profiles by liquid chromatography-mass spectrometry. Results In HAC15 cells, osilodrostat inhibited cortisol production more potently (IC₅₀: 0.035 µM) than metyrapone (0.068 µM; P<0.0001), and ketoconazole (0.621 µM; P<0.0001). IC₅₀ values of osilodrostat and metyrapone for basal cortisol production varied with a 25-fold and 18-fold difference, respectively, with comparable potency. Aldosterone production was inhibited more potently by osilodrostat versus metyrapone and ketoconazole. Osilodrostat and metyrapone treatment resulted in strong inhibition of corticosterone and cortisol, 11-deoxycortisol accumulation, and modest effects on adrenal androgens. No pituitary-directed effects of osilodrostat were observed. Conclusions Under our study conditions, osilodrostat is a potent cortisol production inhibitor in human adrenocortical cells, comparable with metyrapone. All steroidogenesis inhibitors showed large variability in sensitivity between primary adrenocortical cultures. Osilodrostat might inhibit CYP11B1 and CYP11B2, in some conditions to a lesser extent CYP17A1 activity, and a proximal step in the steroidogenesis. Osilodrostat is a promising novel treatment option for Cushing’s syndrome, and in vivo differences with metyrapone are potentially driven by pharmacokinetic differences.