Somatostatin and dopamine receptors as targets for medical treatment of Cushing's Syndrome

Integrative Clinical, Radiological, and Molecular Analysis for Predicting Remission and Recurrence of Cushing Disease

CONTEXT

Adrenocorticotropin (ACTH)-secreting pituitary tumors (ACTHomas) are associated with severe comorbidities and increased mortality. Current treatments mainly focus on remission and prevention of persistent disease and recurrence. However, there are still no useful biomarkers to accurately predict the clinical outcome after surgery, long-term remission, or disease relapse.

OBJECTIVES

This work aimed to identify clinical, biochemical, and molecular markers for predicting long-term clinical outcome and remission in ACTHomas.

METHODS

A retrospective multicenter study was performed with 60 ACTHomas patients diagnosed between 2004 and 2018 with at least 2 years' follow-up. Clinical/biochemical variables were evaluated yearly. Molecular expression profile of the somatostatin/ghrelin/dopamine regulatory systems components and of key pituitary factors and proliferation markers were evaluated in tumor samples after the first surgery.

RESULTS

Clinical variables including tumor size, time until diagnosis/first surgery, serum prolactin, and postsurgery cortisol levels were associated with tumor remission and relapsed disease. The molecular markers analyzed were distinctly expressed in ACTHomas, with some components (ie, SSTR1, CRHR1, and MKI67) showing instructive associations with recurrence and/or remission. Notably, an integrative model including selected clinical variables (tumor size/postsurgery serum cortisol), and molecular markers (SSTR1/CRHR1) can accurately predict the clinical evolution and remission of patients with ACTHomas, generating a receiver operating characteristic curve with an area under the curve of 1 (P < .001).

CONCLUSION

This study demonstrates that the combination of a set of clinical and molecular biomarkers in ACTHomas is able to accurately predict the clinical evolution and remission of patients. Consequently, the postsurgery molecular profile represents a valuable tool for clinical evaluation and follow-up of patients with ACTHomas.

Current and Emerging Medical Therapies in Pituitary Tumors

Pituitary tumors (PT) represent in, the majority of cases, benign tumors for which surgical treatment still remains, except for prolactin-secreting PT, the first-line therapeutic option. Nonetheless, the role played by medical therapies for the management of such tumors, before or after surgery, has evolved considerably, due in part to the recent development of well-tolerated and highly efficient molecules. In this review, our aim was to present a state-of-the-art of the current medical therapies used in the field of PT and the benefits and caveats for each of them, and further specify their positioning in the therapeutic algorithm of each phenotype. Finally, we discuss the future of PT medical therapies, based on the most recent studies published in this field.

The Mechanisms Underlying Autonomous Adrenocorticotropic Hormone Secretion in Cushing's Disease

Cushing’s disease caused due to adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas (ACTHomas) leads to hypercortisolemia, resulting in increased morbidity and mortality. Autonomous ACTH secretion is attributed to the impaired glucocorticoid negative feedback (glucocorticoid resistance) response. Interestingly, other conditions, such as ectopic ACTH syndrome (EAS) and non-neoplastic hypercortisolemia (NNH, also known as pseudo-Cushing’s syndrome) also exhibit glucocorticoid resistance. Therefore, to differentiate between these conditions, several dynamic tests, including those with desmopressin (DDAVP), corticotrophin-releasing hormone (CRH), and Dex/CRH have been developed. In normal pituitary corticotrophs, ACTH synthesis and secretion are regulated mainly by CRH and glucocorticoids, which are the ACTH secretion-stimulating and -suppressing factors, respectively. These factors regulate ACTH synthesis and secretion through genomic and non-genomic mechanisms. Conversely, glucocorticoid negative feedback is impaired in ACTHomas, which could be due to the overexpression of 11β-HSD2, HSP90, or TR4, or loss of expression of CABLES1 or nuclear BRG1 proteins. Genetic analysis has indicated the involvement of several genes in the etiology of ACTHomas, including USP8, USP48, BRAF, and TP53. However, the association between glucocorticoid resistance and these genes remains unclear. Here, we review the clinical aspects and molecular mechanisms of ACTHomas and compare them to those of other related conditions.

A Novel Mechanism Regulating Dopamine Receptor Type 2 Signal Transduction in Pituitary Tumoral Cells: The Role of cAMP/PKA-Induced Filamin A Phosphorylation

The actin binding protein filamin A (FLNA) is required for somatostatin receptor 2 (SSTR2) and dopamine receptor 2 (DRD2) expression and signaling in GH- and PRL-secreting PitNETs, respectively, playing a role in tumor responsiveness to somatostatin receptors ligands and dopaminergic drugs. FLNA functions are regulated by several mechanisms, including phosphorylation. It has been shown that in GH-secreting PitNETs FLNA phosphorylation on Ser2152 (P-FLNA) switches FLNA function from a scaffold that allows SSTR2 signal transduction, to a signal termination protein that hampers SSTR2 antitumoral effects. Aims of the present study were to evaluate in PRL- and ACTH-secreting PitNETs cell lines MMQ and AtT-20 the effects of cAMP pathway activation and DRD2 agonist on P-FLNA and the impact of P-FLNA on DRD2 signal transduction. We found that forskolin increased (+2.2 ± 0.8-fold, p < 0.01 in MMQ; +1.9 ± 0.58-fold, p < 0.05 in AtT-20), and DRD2 agonist BIM53097 reduced (-49.4 ± 25%, p < 0.001 in MMQ; -45.8 ± 28%, p < 0.05 in AtT-20), P-FLNA on Ser2152. The overexpression of a phosphomimetic (S2152D) FLNA mutant in both cell lines prevented DRD2 antiproliferative effects, that were comparable in cells transfected with empty vector, wild-type FLNA as well as phosphodeficient FLNA mutant (S2152A) (-20.6 ± 5% cell proliferation, p < 0.001 in MMQ; -36.6 ± 12%, p < 0.01 in AtT-20). Accordingly, S2152D FLNA expression abolished the expected ability of BIM53097 to increase or decrease, in MMQ and in AtT20 respectively, ERK phosphorylation, an effect that was maintained in S2152A FLNA expressing cells (+1.8 ± 0.65-fold, p < 0.05 in MMQ; -55 ± 13%, p < 0.01 in AtT-20). In addition, the inhibitory effects of DRD2 on hormone secretion (-34.3 ± 6% PRL, p < 0.05 in MMQ; -42.8 ± 22% ACTH, p < 0.05 in AtT-20, in cells expressing S2152A FLNA) were completely lost in S2152D FLNA transfected cells. In conclusion, our data demonstrated that cAMP pathway and DRD2 agonist regulated FLNA activity by increasing or decreasing, respectively, its phosphorylation. Moreover, we found that P-FLNA prevented DRD2 signaling in PRL- and ACTH-secreting tumoral pituitary cell lines, suggesting that this FLNA modification might represent a new regulatory mechanism shared by different GPCRs. In PitNETs expressing DRD2, modulation of P-FLNA might suggest new pharmacological strategies to overcome drug resistance, and P-FLNA might represent a new biomarker for tumor responsiveness to dopaminergic agents.

Safety and Efficacy of Subcutaneous Pasireotide in Patients With Cushing's Disease: Results From an Open-Label, Multicenter, Single-Arm, Multinational, Expanded-Access Study

Introduction: The efficacy and safety of subcutaneous (sc) pasireotide have been evaluated in a Phase III trial. Here, we report safety and efficacy results from a multinational, expanded-access study of pasireotide sc in patients with Cushing's disease (CD) in a real-world setting (clinicaltrials.gov, identifier: NCT01582061). Methods: Adults with active CD previously untreated with pasireotide were enrolled; pasireotide sc was initiated at 600 μg twice daily (bid; EU countries) or 900 μg bid (non-EU countries; 600 μg bid in patients with impaired glucose metabolism). Pasireotide dose could be adjusted in 300 μg increments/decrements to a maximum of 900 μg bid or minimum of 300 μg bid for sustained urinary free cortisol (UFC) normalization/tolerability issues. Primary objective: document the safety of pasireotide sc in patients with CD. Key secondary objectives: assess the proportion of patients with mean UFC (mUFC) not exceeding the upper limit of normal (ULN) and changes from baseline in clinical signs/symptoms and quality of life (QoL) to weeks 12, 24, and 48. Results: One hundred and four patients received pasireotide: female, n = 84 (80.8%); median duration of pasireotide exposure, 25.1 weeks; median (range) baseline mUFC, 321.2 nmol/24 h (142-10,920; 2.3 × ULN [1.0-79.2]). Forty (38.5%) patients completed the study. The most common reasons for premature discontinuation of pasireotide were unsatisfactory therapeutic effect (n = 26, 25.0%) and adverse events (AEs; n = 20, 19.2%). Drug-related grade 3/4 AEs or drug-related serious AEs (primary endpoint) were documented in 42 (40.4%) patients, most commonly diabetes mellitus (n = 12, 11.5%) and hyperglycemia (n = 8, 7.7%). All patients experienced ≥1 AE and most (n = 102; 98.1%) reported ≥1 drug-related AE; six (5.8%) patients discontinued treatment because of hyperglycemia-related AEs. At weeks 12, 24, and 48, respectively, 36/66 (54.5%), 22/46 (47.8%), and 9/21 (42.9%) evaluable patients had normalized mUFC levels. Clinical signs/symptoms and QoL were also improved. Conclusions: In an international, real-world, clinical-practice setting, pasireotide sc was generally well-tolerated (no new safety signals were identified), effectively reduced UFC (normalization in ~50% of evaluable patients) and improved clinical signs and QoL in patients with CD. While hyperglycemia-related AEs were common, consistent with previous studies, most were manageable, with <6% of patients discontinuing treatment because of these events.

The Ectopic Adrenocorticotropic Hormone Syndrome: Rarely Easy, Always Challenging

Despite modern imaging techniques, differentiating ectopic adrenocorticotropic hormone (ACTH) syndrome from pituitary-dependent Cushing's syndrome, Cushing's disease, is especially difficult when well-differentiated carcinoids are the source of ACTH secretion, particularly pulmonary carcinoid tumors. ACTH-secreting pulmonary carcinoids, like the corticotroph adenomas causing Cushing's disease, are often small and difficult to detect, and patients present with a gradual onset of the classical signs and symptoms of Cushing's syndrome, indistinguishable from the presentation of Cushing's disease. Hence, the differential diagnosis relies on a combination of clinical assessment, dynamic biochemical tests, inferior petrosal sinus sampling, and multimodal imaging, each with its own caveats and pitfalls.

Protein expression of somatostatin receptor 2, somatostatin receptor 5 and dopamine D2 receptor in normal pituitary gland and ACTH-secreting pituitary adenoma in dogs

PURPOSE

To evaluate the protein expression of somatostatin receptor (SSTR) 2, SSTR5 and dopamine D2 receptor (DA2R)-targets of somatostatin analogs and dopamine agonists-in normal canine pituitary and canine adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas.

METHODS

Six normal canine pituitary glands and 14 canine ACTH-secreting pituitary adenoma cases were included in this study. The protein expression of SSTR2, SSTR5 and DA2R was determined by double-label immunofluorescence staining of these receptors and ACTH.

RESULTS

SSTR2, SSTR5, and DA2R proteins were expressed in the anterior and intermediate lobes of normal canine pituitary glands. In the anterior pituitary lobes, the percentages of SSTR2-, SSTR5-, and DA2R-positive cells among the ACTH-positive population were 27.0 ± 8.6%, 27.9 ± 5.9%, and 34.0 ± 9.4%, respectively. In contrast, the corresponding percentages in the intermediate pituitary lobes were 97.8 ± 1.5%, 94.1 ± 4.4%, and 96.1 ± 6.6%, respectively. Of the 14 ACTH-secreting pituitary adenoma cases, 11, 12, and 6 cases expressed SSTR2, SSTR5, and DA2R, respectively. Additionally, four cases showed strong positive staining for both SSTR2 and SSTR5. Two of these were ACTH-secreting pituitary adenomas likely derived from the intermediate pituitary lobe, because these are α-Melanocyte-stimulation hormone (α-MSH)-positive stains.

CONCLUSION

Immunohistological detection and characterization of SSTR2, SSTR5 and DA2R may provide useful additional information for determining treatment options when an ACTH-secreting pituitary adenoma cannot be completely resected, or in the case of recurrence.

Efficacy and safety of once-monthly pasireotide in Cushing's disease: a 12 month clinical trial

BACKGROUND

Cushing's disease is a rare debilitating endocrine disorder for which few prospective interventional studies have been done. We report results of the first phase 3 trial assessing long-acting intramuscular pasireotide in patients with Cushing's disease.

METHODS

In this phase 3 clinical trial we recruited patients aged 18 years or older with persistent, recurrent, or de-novo (non-surgical candidates) Cushing's disease who had a mean urinary free cortisol (mUFC) concentration (from three 24 h samples) of 1·5-5·0 times the upper limit of normal (ULN), a normal or greater than normal morning plasma adrenocorticotropic hormone concentration, and a pituitary source of Cushing's syndrome, from 57 sites across 19 countries. Exclusion criteria included previous pasireotide treatment, mitotane therapy within 6 months, and pituitary irradiation within 10 years. We randomly allocated patients 1:1 (block size of four) using an interactive-response-technology system to intramuscular pasireotide 10 mg or 30 mg every 4 weeks for 12 months (in the core phase). We stratified randomisation by screening mUFC concentration (1·5 to <2·0 × ULN and 2·0-5·0 × ULN). The dose could be uptitrated (from 10 mg to 30 mg or from 30 mg to 40 mg) at month 4 if the mUFC concentration was greater than 1·5 × ULN, and at month 7, month 9, or month 12 if the mUFC concentration was greater than 1·0 × ULN. Investigators, patients, site personnel, and those assessing outcomes were masked to dose group allocation. The primary endpoint was the proportion of patients in each group with an mUFC concentration of less than or equal to the ULN at month 7. Efficacy analyses were based on intention to treat. This trial is registered with ClinicalTrials.gov, number NCT01374906.

FINDINGS

Between Dec 28, 2011, and Dec 9, 2014, we randomly allocated 150 patients to receive pasireotide 10 mg (74 [49%] patients) or 30 mg (76 [51%] patients). The primary efficacy endpoint was met by 31 (41·9% [95% CI 30·5-53·9]) of 74 patients in the 10 mg group and 31 (40·8% [29·7-52·7]) of 76 in the 30 mg group. The most common adverse events were hyperglycaemia (36 [49%] in the 10 mg group and 36 [47%] in the 30 mg group), diarrhoea (26 [35%] and 33 [43%]), cholelithiasis (15 [20%] and 34 [45%]), diabetes mellitus (14 [19%] and 18 [24%]), and nausea (15 [20%] and 16 [21%]). Serious adverse events suspected to be study drug related were reported in eight (11%) patients in the 10 mg group and four (5%) in the 30 mg group. Two (3%) patients in the 30 mg group died during the study (pulmonary artery thrombosis and cardiorespiratory failure); neither death was judged to be related to the study drug.

INTERPRETATION

Long-acting pasireotide normalised mUFC concentration in about 40% of patients with Cushing's disease at month 7 and had a similar safety profile to that of twice-daily subcutaneous pasireotide. Long-acting pasireotide is an efficacious treatment option for some patients with Cushing's disease who have persistent or recurrent disease after initial surgery or are not surgical candidates, and provides a convenient monthly administration schedule.

FUNDING

Novartis Pharma AG.

Pituitary-Directed Therapies for Cushing's Disease

Cushing's disease (CD) is caused by a pituitary corticotroph neuroendocrine tumor inducing uncontrolled hypercortisolism. Transsphenoidal surgery is the first-line treatment in most cases. Nonetheless, some patients will not achieve cure even in expert hands, others may not be surgical candidates and a significant percentage will experience recurrence. Many patients will thus require medical therapy to achieve disease control. Pharmacologic options to treat CD have increased in recent years, with an explosion in knowledge related to pathophysiology at the molecular level. In this review, we focus on medications targeting specifically pituitary adrenocorticotropic hormone-secreting tumors. The only medication in this group approved for the treatment of CD is pasireotide, a somatostatin receptor ligand. Cabergoline and temozolomide may also be used in select cases. Previously studied and abandoned medical options are briefly discussed, and emphasis is made on upcoming medications. Mechanism of action and available data on efficacy and safety of cell cycle inhibitor roscovitine, epidermal growth factor receptor inhibitor gefitinib, retinoic acid, and silibinin, a heat shock protein 90 inhibitor are also presented.

Therapeutic Strategies for the Treatment of Severe Cushing's Syndrome

Severe Cushing's syndrome presents an acute emergency and is defined by massively elevated random serum cortisol [more than 36 μg/dL (1000 nmol/L)] at any time or a 24-h urinary free cortisol more than fourfold the upper limit of normal and/or severe hypokalaemia (<3.0 mmol/L), along with the recent onset of one or more of the following: sepsis, opportunistic infection, intractable hypokalaemia, uncontrolled hypertension, heart failure, gastrointestinal haemorrhage, glucocorticoid-induced acute psychosis, progressive debilitating myopathy, thromboembolism or uncontrolled hyperglycaemia and ketocacidosis. Treatment focuses on the management of the severe metabolic disturbances followed by rapid resolution of the hypercortisolaemia, and subsequent confirmation of the cause. Emergency lowering of the elevated serum cortisol is most rapidly achieved with oral metyrapone and/or ketoconazole; if parenteral therapy is required then intravenous etomidate is rapidly effective in almost all cases, but all measures require careful supervision. The optimal order and combination of drugs to treat severe hypercortisolaemia-mostly in the context of ectopic ACTH-secreting syndrome, adrenocortical carcinoma or an ACTH-secreting pituitary adenoma (mainly macroadenomas)-is not yet established. Combination therapy may be useful not only to rapidly control cortisol excess but also to lower individual drug dosages and consequently the possibility of adverse effects. If medical treatments fail, bilateral adrenalectomy should be performed in the shortest possible time span to prevent the debilitating complications of uncontrolled hypercortisolaemia.

Currently used and investigational drugs for Cushing´s disease

INTRODUCTION

Cushing's disease (CD) is caused by a corticotroph adenoma of the pituitary gland that secretes excess adrenocorticotropic hormone (ACTH) causing increased morbidity and mortality. Surgery is the treatment of choice, but is not always successful. Alternatives include radiotherapy, adrenal surgery, and pharmaceutical therapy. The latter is increasingly gaining momentum due to the recent development of compounds that reduce hypercortisolaemia or its symptoms, acting through different mechanisms. Areas covered: In this article, the authors provide a complete overview of the treatment options for Cushing´s disease, including adrenal-directed, tumor-targeted, and peripheral therapies that are currently used or in development, and discuss their potential advantages and limitations. Expert opinion: Considering the lack of long-term remission in up to half of the patients after surgery, and the delayed response to radiotherapy along with potential side effects, there is a strong need for an effective pharmaceutical treatment. Pasireotide, mifepristone, ketoconazole and metyrapone have been approved by regulatory authorities but their use remains limited due to considerable costs and side effects. Research in this field has focused recently on the improvement of pre-existing drugs and the development of safe new ones. However, few approaches aim at targeting the source of the disease, the ACTH-secreting adenoma.

Update on medical treatment for Cushing's disease

Cushing's disease (CD) is the most common cause of endogenous Cushing's syndrome (CS). The goal of treatment is to rapidly control cortisol excess and achieve long-term remission, to reverse the clinical features and reduce long-term complications associated with increased mortality. While pituitary surgery remains first line therapy, pituitary radiotherapy and bilateral adrenalectomy have traditionally been seen as second-line therapies for persistent hypercortisolism. Medical therapy is now recognized to play a key role in the control of cortisol excess. In this review, all currently available medical therapies are summarized, and novel medical therapies in phase 3 clinical trials, such as osilodrostat and levoketoconazole are discussed, with an emphasis on indications, efficacy and safety. Emerging data suggests increased efficacy and better tolerability with these novel therapies and combination treatment strategies, and potentially increases the therapeutic options for treatment of CD. New insights into the pathophysiology of CD are highlighted, along with potential therapeutic applications. Future treatments on the horizon such as R-roscovitine, retinoic acid, epidermal growth factor receptor inhibitors and somatostatin-dopamine chimeric compounds are also described, with a focus on potential clinical utility.

Emerging Histopathological and Genetic Parameters of Pituitary Adenomas: Clinical Impact and Recommendation for Future WHO Classification

The review assesses immunohistochemical findings of somatostatin receptors and of metalloproteinases in different pituitary adenoma types and the significance of molecular genetic data. Current evidence does not support routine immunohistochemical assessment of somatostatin or dopamine receptor subtype expression on hormone-secreting or nonfunctioning pituitary adenomas. Further prospective studies are needed to define its role for clinical decision making. Until then we suggest to restrict membrane receptor profiling to individual cases or for study purposes. The problems of adenoma expansion and invasion are discussed. Despite partially contradictory publications, proteases clearly play a major role in permission of infiltrative growth of pituitary adenomas. Therefore, detection of at least MMP-2, MMP-9, TIMP-2, and uPA seems to be justified. Molecular characterization is important for familial adenomas, adenomas in MEN, Carney complex, and McCune-Albright syndrome and can gain insight into pathogenesis of sporadic adenomas.

Bilateral adrenalectomy in the 21st century: when to use it for hypercortisolism?

Therapeutic options available for the treatment of Cushing's syndrome (CS) have expanded over the last 5 years. For instance, the efficient management of severe hypercortisolism using a combination of fast-acting steroidogenesis inhibitors has been reported. Recent publications on the long-term efficacy of drugs or radiation techniques have also demonstrated low toxicity. These data should encourage endocrinologists to reconsider the place of bilateral adrenalectomy in patients with ACTH-dependent aetiologies of CS; similarly, the indication of bilateral adrenalectomy is reassessed in primary bilateral macronodular adrenal hyperplasia. The objective of this review is to compare the efficacy and side effects of the various therapeutic options of hypercortisolism with those of bilateral adrenalectomy, in order to better define its indications in the 21st century.

Current strategies for the treatment of severe Cushing's syndrome

Severe Cushing's syndrome may present an acute emergency in patients diagnosed with Cushing's syndrome with recent onset of at least one of the following: sepsis, opportunistic infection; intractable hypokalaemia, uncontrolled hypertension; heart failure; gastrointestinal hemorrhage; acute psychosis; progressive debilitating myopathy; thromboembolism; uncontrolled hyperglycemia and ketoacidosis. The biochemical definition includes serum cortisol ≥41μg/dl (1100 nmol/l) and/or severe hypokalemia (<3.0 mmol/l) or urine free cortisol fivefold the upper limit of normal. Treatment focuses on the management of severe metabolic disturbances followed by rapid resolution of the hypercortisolemia and subsequent confirmation of the cause. We emphasize the control of the hypokalemia, hypertension, diabetes and any psychotic state, anti-coagulation, monitoring and vigorous therapy of opportunistic infections. The ideal first-line therapies include metyrapone and ketoconazole, followed by parenteral etomidate; if all else fails life-saving bilateral adrenalectomy should be considered.

Treatment of Cushing's Syndrome: An Endocrine Society Clinical Practice Guideline

OBJECTIVE

The objective is to formulate clinical practice guidelines for treating Cushing's syndrome.

PARTICIPANTS

Participants include an Endocrine Society-appointed Task Force of experts, a methodologist, and a medical writer. The European Society for Endocrinology co-sponsored the guideline.

EVIDENCE

The Task Force used the Grading of Recommendations, Assessment, Development, and Evaluation system to describe the strength of recommendations and the quality of evidence. The Task Force commissioned three systematic reviews and used the best available evidence from other published systematic reviews and individual studies.

CONSENSUS PROCESS

The Task Force achieved consensus through one group meeting, several conference calls, and numerous e-mail communications. Committees and members of The Endocrine Society and the European Society of Endocrinology reviewed and commented on preliminary drafts of these guidelines.

CONCLUSIONS

Treatment of Cushing's syndrome is essential to reduce mortality and associated comorbidities. Effective treatment includes the normalization of cortisol levels or action. It also includes the normalization of comorbidities via directly treating the cause of Cushing's syndrome and by adjunctive treatments (eg, antihypertensives). Surgical resection of the causal lesion(s) is generally the first-line approach. The choice of second-line treatments, including medication, bilateral adrenalectomy, and radiation therapy (for corticotrope tumors), must be individualized to each patient.

Inhibition of heat shock protein 90 decreases ACTH production and cell proliferation in AtT-20 cells

PURPOSE

Cushing's disease is primarily caused by adrenocorticotropic hormone (ACTH)-producing pituitary adenomas. If excision of the tumor from the pituitary, which is the primary treatment for Cushing's disease, is unsuccessful, further medical therapy is needed to treat the resultant hypercortisolism. Some of the drugs used to treat this condition have shown potential therapeutic benefits, but a more effective treatment should be explored for the treatment of Cushing's disease. In the present study, we determined the effect of heat shock protein 90 inhibitors on ACTH production and cell proliferation of AtT-20 corticotroph tumor cells.

METHODS

AtT-20 pituitary corticotroph tumor cells were cultured. The expression levels of mouse proopiomelanocortin (POMC) and pituitary tumor transforming gene 1 (PTTG1) mRNA were evaluated using quantitative real-time PCR. Cellular DNA content was analyzed with fluorescence-activated cell sorting (FACS) analysis. The protein levels were determined by Western blot analysis.

RESULTS

Both 17-allylamino-17-demethoxygeldanamycin and CCT018159 decreased POMC mRNA levels in AtT-20 cells and ACTH levels in the culture medium of these cells, suggesting that both drugs suppress ACTH synthesis and secretion in corticotroph tumor cells. Both drugs also decreased cell proliferation and induced apoptosis. FACS analyses revealed that both agents increased the percentage of AtT-20 cells in the G2/M phase. These drugs decreased cell proliferation, presumably due to the induction of cell death and arrest of the cell cycle in AtT-20 cells. Tumor weight in mice xenografted with AtT-20 cells and treated with CCT018159 was lower than in AtT-20-xenografted control mice. CCT018159 also decreased plasma ACTH levels, and POMC and PTTG1 mRNA levels in the tumor cells.

CONCLUSIONS

CCT018159 inhibits ACTH production and corticotroph tumor cell proliferation in vitro and in vivo.

The Treatment of Cushing's Disease

Cushing's disease (CD), or pituitary-dependent Cushing's syndrome, is a severe endocrine disease caused by a corticotroph pituitary tumor and associated with increased morbidity and mortality. The first-line treatment for CD is pituitary surgery, which is followed by disease remission in around 78% and relapse in around 13% of patients during the 10-year period after surgery, so that nearly one third of patients experience in the long-term a failure of surgery and require an additional second-line treatment. Patients with persistent or recurrent CD require additional treatments, including pituitary radiotherapy, adrenal surgery, and/or medical therapy. Pituitary radiotherapy is effective in controlling cortisol excess in a large percentage of patients, but it is associated with a considerable risk of hypopituitarism. Adrenal surgery is followed by a rapid and definitive control of cortisol excess in nearly all patients, but it induces adrenal insufficiency. Medical therapy has recently acquired a more important role compared to the past, due to the recent employment of novel compounds able to control cortisol secretion or action. Currently, medical therapy is used as a presurgical treatment, particularly for severe disease; or as postsurgical treatment, in cases of failure or incomplete surgical tumor resection; or as bridging therapy before, during, and after radiotherapy while waiting for disease control; or, in selected cases, as primary therapy, mainly when surgery is not an option. The adrenal-directed drug ketoconazole is the most commonly used drug, mainly because of its rapid action, whereas the glucocorticoid receptor antagonist, mifepristone, is highly effective in controlling clinical comorbidities, mainly glucose intolerance, thus being a useful treatment for CD when it is associated with diabetes mellitus. Pituitary-directed drugs have the advantage of acting at the site responsible for CD, the pituitary tumor. Among this group of drugs, the dopamine agonist cabergoline and the somatostatin analog pasireotide result in disease remission in a consistent subgroup of patients with CD. Recently, pasireotide has been approved for the treatment of CD when surgery has failed or when surgery is not an option, and mifepristone has been approved for the treatment of Cushing's syndrome when associated with impairment of glucose metabolism in case of the lack of a surgical indication. Recent experience suggests that the combination of different drugs may be able to control cortisol excess in a great majority of patients with CD.

Temozolomide-Induced Shrinkage of Invasive Pituitary Adenoma in Patient with Nelson's Syndrome: A Case Report and Review of the Literature

Introduction. Invasive tumours in Nelson's syndrome need aggressive therapy. Recent reports have documented the efficacy of temozolomide (TMZ) in the treatment of adenomas resistant to conventional management. Objective. The review of the literature concerning TMZ treatment of atypical corticotroph adenomas and a case study of 56-year-old woman who developed Nelson's syndrome. Treatment Proceeding. The patient with Cushing's disease underwent transsphenoidal adenomectomy followed by a 27-month-long period of remission. Due to a regrowth of the tumor, she underwent two reoperations followed by stereotactic radiotherapy. Because of treatment failures, bilateral adrenalectomy was performed. Then she developed Nelson's syndrome. A fourth transsphenoidal adenomectomy was performed, but there was a rapid recurrence. Five months later, she underwent a right frontotemporal craniotomy. Due to a rapid regrowth of the tumour, the patient did not receive gamma-knife therapy and was treated with cabergoline and somatostatin analogue for some time. Only TMZ therapy resulted in marked clinical, biochemical, and radiological improvement. To date, this is the first case of invasive corticotroph adenoma in Nelson's syndrome treated with temozolomide in Poland. Conclusion. In our opinion, temozolomide can be an effective treatment option of invasive adenomas in Nelson's syndrome.

Pituitary-directed medical therapy in Cushing's disease

Transsphenoidal surgery remains the first line therapy in Cushing's disease, but a large number of patients will not be cured or disease will recur over time. Repeat pituitary surgery, bilateral adrenalectomy, and radiation have limitations with respect to efficacy and/or side effects. Therefore, there is a clear need for an effective medical treatment. The studies reviewed here suggest a role for pituitary-directed therapies, applying multireceptor ligand somatostatin analogs like pasireotide or second-generation dopamine agonists. Retinoic acid has been also studied in a small prospective study. These compounds target ACTH-secretion at the pituitary level and possibly inhibit corticotrope proliferation. Specific side effects of these compounds need to be considered, especially when used as long-term therapy. These novel approaches could provide options for treatment of patients in whom surgery has failed or is not possible, and while awaiting effects of radiation therapy. Preoperative use to decrease cortisol excess, potentially reducing perioperative complications, needs to be further studied.

Treatment of Cushing's disease: a mechanistic update

Cushing's disease (CD) is characterized by an ACTH-producing anterior corticotrope pituitary adenoma. If hypothalamus-pituitary-adrenal (HPA) axis physiology is disrupted, ACTH secretion increases, which in turn stimulates adrenocortical steroidogenesis and cortisol production. Medical treatment plays an important role for patients with persistent disease after surgery, for those in whom surgery is not feasible, or while awaiting effects of radiation. Multiple drugs, with different mechanisms of action and variable efficacy and tolerability for controlling the deleterious effects of chronic glucocorticoid excess, are available. The molecular basis and clinical data for centrally acting drugs, adrenal steroidogenesis inhibitors, and glucocorticoid receptor antagonists are reviewed, as are potential novel molecules and future possible targets for CD treatment. Although progress has been made in the understanding of specific corticotrope adenoma receptor physiology and recent clinical studies have detected improved effects with a combined medical therapy approach, there is a clear need for a more efficacious and better-tolerated medical therapy for patients with CD. A better understanding of the molecular mechanisms in CD and of HPA axis physiology should advance the development of new drugs in the future.

Managing Cushing's disease: the state of the art

Cushing's disease is a rare chronic disease caused by a pituitary adenoma, which leads to excess secretion of adrenocorticotropic hormone (ACTH). The over-production of ACTH leads to hyperstimulation of the adrenal glands and a chronic excess of cortisol, resulting in the signs and symptoms of a severe clinical state (Cushing's syndrome) that leads to significant morbidity, negative impacts on the patient's quality of life, and, if untreated, increased mortality. The management of patients with Cushing's disease is complicated by the heterogeneity of the condition, with signs and symptoms that overlap with those of other diseases, and high subclinical incidence rates. Controversies surrounding the tests used for screening and identifying patients with Cushing's disease add to the challenge of patient management. Surgical intervention to remove the adenoma is the first-line treatment for patients with Cushing's disease, but medical therapies are useful in patients who relapse or are unsuitable for surgery. The recent introduction of pasireotide, the first pituitary-directed medical therapy, expands the number of treatment options available for patients with Cushing's disease. This state-of-the-art review aims to provide an overview of the most recent scientific research and clinical information regarding Cushing's disease. Continuing research into improving the diagnosis and treatment of Cushing's disease will help to optimize patient management.

Inhibitory effects of SOM230 on adrenocorticotropic hormone production and corticotroph tumor cell proliferation in vitro and in vivo

Adrenocorticotropic hormone (ACTH) production by pituitary corticotroph adenomas is the main cause of Cushing's disease. A drug that targets pituitary ACTH-secreting adenomas would aid treatment of Cushing's disease. Octreotide, a somatostatin receptor type 2 (SSTR2)-preferring somatostatin analogue, has no effect on ACTH secretion in patients with Cushing's disease. The multiligand SOM230 (pasireotide) displays a much higher affinity for SSTR1 and SSTR5 than octreotide and suppresses ACTH secretion in cultures of human corticotroph tumors to a greater extent than octreotide. In the present in vitro and in vivo study, we determined the effect of SOM230 on ACTH production and cell proliferation of AtT-20 corticotroph tumor cells. SOM230 decreased proopiomelanocortin (POMC) mRNA levels in AtT-20 cells and ACTH levels in the culture medium of these cells, suggesting that SOM230 suppresses ACTH synthesis and secretion in corticotroph tumor cells. SOM230 also decreased cell proliferation and both cyclic adenosine monophosphate response element-binding protein and Akt phosphorylation in AtT-20 cells. SSTR5 knockdown inhibited the SOM230-induced decreases in cell proliferation. Fluorescence-activated cell sorting analyses revealed that SOM230 did not attenuate cell cycle progression. Tumor weight in mice xenografted with AtT-20 cells and treated with SOM230 was significantly lower than in AtT-20-xenografted control mice. SOM230 also significantly decreased plasma ACTH levels, and POMC and pituitary tumor transforming gene mRNA levels in the tumor cells. Thus, SOM230 inhibits ACTH production and corticotroph tumor cell proliferation in vitro and in vivo.

Systemic therapy of Cushing's syndrome

Cushing’s disease (CD) in a stricter sense derives from pathologic adrenocorticotropic hormone (ACTH) secretion usually triggered by micro- or macroadenoma of the pituitary gland. It is, thus, a form of secondary hypercortisolism. In contrast, Cushing’s syndrome (CS) describes the complexity of clinical consequences triggered by excessive cortisol blood levels over extended periods of time irrespective of their origin. CS is a rare disease according to the European orphan regulation affecting not more than 5/10,000 persons in Europe. CD most commonly affects adults aged 20–50 years with a marked female preponderance (1:5 ratio of male vs. female). Patient presentation and clinical symptoms substantially vary depending on duration and plasma levels of cortisol. In 80% of cases CS is ACTH-dependent and in 20% of cases it is ACTH-independent, respectively. Endogenous CS usually is a result of a pituitary tumor. Clinical manifestation of CS, apart from corticotropin-releasing hormone (CRH-), ACTH-, and cortisol-producing (malign and benign) tumors may also be by exogenous glucocorticoid intake. Diagnosis of hypercortisolism (irrespective of its origin) comprises the following: Complete blood count including serum electrolytes, blood sugar etc., urinary free cortisol (UFC) from 24 h-urine sampling and circadian profile of plasma cortisol, plasma ACTH, dehydroepiandrosterone, testosterone itself, and urine steroid profile, Low-Dose-Dexamethasone-Test, High-Dose-Dexamethasone-Test, after endocrine diagnostic tests: magnetic resonance imaging (MRI), ultra-sound, computer tomography (CT) and other localization diagnostics. First-line therapy is trans-sphenoidal surgery (TSS) of the pituitary adenoma (in case of ACTH-producing tumors). In patients not amenable for surgery radiotherapy remains an option. Pharmacological therapy applies when these two options are not amenable or refused. In cases when pharmacological therapy becomes necessary, Pasireotide should be used in first-line in CD. CS patients are at an overall 4-fold higher mortality rate than age- and gender-matched subjects in the general population. The following article describes the most prominent substances used for clinical management of CS and gives a systematic overview of safety profiles, pharmacokinetic (PK)-parameters, and regulatory framework.

Molecular basis of pharmacological therapy in Cushing's disease

Cushing's disease (CD) is a severe endocrine condition caused by an adrenocorticotropin (ACTH)-producing pituitary adenoma that chronically stimulates adrenocortical cortisol production and with potentially serious complications if not or inadequately treated. Active CD may produce a fourfold increase in mortality and is associated with significant morbidities. Moreover, excess mortality risk may persist even after CD treatment. Although predictors of risk in treated CD are not fully understood, the importance of early recognition and adequate treatment is well established. Surgery with resection of a pituitary adenoma is still the first line therapy, being successful in about 60-70 % of patients; however, recurrence within 2-4 years may often occur. When surgery fails, medical treatment can reduce cortisol production and ameliorate clinical manifestations while more definitive therapy becomes effective. Compounds that target hypothalamic-pituitary axis, glucocorticoid synthesis or adrenocortical function are currently used to control the deleterious effects of chronic glucocorticoid excess. In this review we describe and analyze the molecular basis of the drugs targeting the disease at central level, suppressing ACTH secretion, as well as at peripheral level, acting as adrenal inhibitors, or glucocorticoid receptor antagonists. Understanding of the underlying molecular mechanisms in CD and of glucocorticoid biology should promote the development of new targeted and more successful therapies in the future. Indeed, most of the drugs discussed have been tested in limited clinical trials, but there is potential therapeutic benefit in compounds with better specificity for the class of receptors expressed by ACTH-secreting tumors. However, long-term follow-up with management of persistent comorbidities is needed even after successful treatment of CD.

Does somatostatin have a role in the regulation of cortisol secretion in primary pigmented nodular adrenocortical disease (ppnad)? a clinical and in vitro investigation

CONTEXT

Somatostatin (SST) receptors (SSTRs) are expressed in a number of tissues, including the adrenal cortex, but their role in cortisol secretion has not been well characterized.

OBJECTIVES

The objective of the study was to investigate the expression of SSTRs in the adrenal cortex and cultured adrenocortical cells from primary pigmented nodular adrenocortical disease (PPNAD) tissues and to test the effect of a single injection of 100 μg of the SST analog octreotide on cortisol secretion in patients with PPNAD.

SETTING AND DESIGN

The study was conducted at an academic research laboratory and clinical research center. Expression of SSTRs was examined in 26 PPNAD tissues and the immortalized PPNAD cell line CAR47. Ten subjects with PPNAD underwent a randomized, single-blind, crossover study of their cortisol secretion every 30 minutes over 12 hours (6:00 pm to 6:00 am) before and after the midnight administration of octreotide 100 μg sc.

METHODS

SSTRs expression was investigated by quantitative PCR and immunohistochemistry. The CAR47 and primary cell lines were studied in vitro. The data of the 10 patients were analyzed before and after the administration of octreotide.

RESULTS

All SSTRs, especially SSTR1-3, were expressed in PPNAD at significantly higher levels than in normal adrenal. SST was found to differentially regulate expression of its own receptors in the CAR47 cell line. However, the administration of octreotide to patients with PPNAD did not significantly affect cortisol secretion.

CONCLUSIONS

SSTRs are overexpressed in PPNAD tissues in comparison with normal adrenal cortex. Octreotide did not exert any significant effect on cortisol secretion in a short clinical pilot study in a small number of patients with PPNAD, but long-acting SST analogs targeting multiple SSTRs may be worth investigating in this condition.

Medical management of Cushing's disease

Cushing's disease (CD), caused by excess adrenocorticotropin secretion from tumorous pituitary corticotrophs, is associated with substantial morbidity and mortality. The primary, definitive therapy for patients with CD is selective pituitary adenomectomy, generally performed via a transsphenoidal approach. Medical therapy has an important adjunctive role in the management of patients with CD, including preoperative patient preparation in patients with severe disease, and temporizing management of hypercortisolism while awaiting the effects of radiation therapy to occur in patients who are not in remission postoperatively. Medical therapy can also be used in patients with hypercortisolism of unclear origin or in the few patients who decline or are unfit for surgery. Available medical options for patients with CD include centrally acting agents (cabergoline and pasireotide), steroidogenesis inhibitors (ketoconazole, metyrapone, mitotane and etomidate) and a glucocorticoid receptor antagonist (mifepristone). Pasireotide and mifepristone have been recently granted regulatory approval in some countries for use in patients with CD, whereas other medications are used "off label" in this patient population. As clinical trials using comparator agents have not been reported, the choice between different medications is based on patient characteristics and preference. Despite impressive advances in pharmacotherapy for patients with CD, much remains to be done. The long term efficacy and safety of medical therapies for hypercortisolism need to be evaluated and the role of combination therapy must be further characterized. As the pathogenesis of CD becomes better understood at the molecular level, it is likely that novel, targeted medical therapies will be developed to treat CD.

New avenues in the medical treatment of Cushing's disease: corticotroph tumor targeted therapy

Cushing's disease (CD) is a condition of chronic hypercortisolism caused by an adrenocorticotropic hormone-secreting pituitary adenoma. First-line transsphenoidal surgery is not always curative and disease sometimes recurs. Radiotherapy often requires months or years to be effective, and is also not curative in many cases. Consequently, effective medical therapies for patients with CD are needed. Corticotroph adenomas frequently express both dopamine (D2) and somatostatin receptors (predominantly sstr5). Pasireotide, a somatostatin analog with high sstr5 binding affinity, has shown urinary free cortisol (UFC) reductions in most patients with CD in a large phase 3 trial, with UFC normalization and tumor shrinkage in a subset of patients. Adverse events were similar to other somatostatin analogs, with the exception of the degree and severity of hyperglycemia. Two small trials (one prospective and one retrospective) have suggested that cabergoline, a D2 receptor agonist, could be effective in normalizing UFC, but current long-term data results are conflicting. Combination treatment with pasireotide plus cabergoline and the adrenal steroidogenesis inhibitor ketoconazole has been successful, but further investigation in larger trials is necessary. Retinoic acid also showed interesting results in a recent very small prospective study. Glucocorticoid receptor blockade with mifepristone has recently demonstrated improvement in signs and symptoms of Cushing's and glycemic control; however, this modality does not address the etiology of the disease and has inherent adverse events related to its mechanism of action. Pituitary-targeted medical therapies will soon play a more prominent role in treating CD, and may potentially become first-line medical therapy when surgery fails or is contraindicated.

A rare case of Cushing syndrome by cyclic ectopic-ACTH

ACTH-dependent Cushing syndrome (CS) due to ectopic ACTH production is most times difficult to manage. The identification of the source of ACTH may take many years. Surgery or chemotherapy for the primary tumor is not always possible. Control of Cushing symptoms is many times achieved using medication, or bilateral adrenalectomy in refractory cases. This case presents a Brazilian male who showed severe hypertension, mood changes, muscle weakness, darkening of skin, and increased abdominal fat. An investigation for Cushing syndrome was carried out and, after a four-year follow-up, a carotid glomus tumor (chemodectoma) was confirmed, a rare ectopic ACTH-producing tumor. Besides, the patient presented cyclic Cushing syndrome that was exacerbated by diverticulitis episodes. This case presents interesting pitfalls on diagnosis and management of ACTH-dependent CS. This is the only report of a chemodectoma that produced ACTH in the literature.

Somatostatin receptor pathophysiology in the neuroendocrine system

The actions of somatostatin (SRIF) are mediated by specific G protein-coupled receptors, named SRIF receptor (SSTR) subtypes 1, 2, 3 and 5. SRIF binding to SSTR activates a series of second messenger systems, resulting in the inhibition of calcium channels and adenylate cyclase activity, ultimately leading to inhibition of hormone secretion, while stimulation of other second messengers, such as phosphotyrosine phosphatases play a role in the control of cell growth. The SSTR and dopamine receptor families share a 30% sequence homology and appear to be structurally related. The knowledge on the pathophysiology of these two families of G protein-coupled receptors in neuroendocrine tumors has progressively increased due to the new insights in receptor dimerization, internalization and trafficking. Depending on the expression of different SSTRs in tissues, their combinations and interactions affect the functionality of the subtypes expressed and the influence of the microenvironment, the response to ligands and, by consequence, the response to treatment can be very different.

Detection of paranasal ectopic adrenocorticotropic hormone-secreting pituitary adenoma by Ga-68-DOTANOC positron-emission tomography-computed tomography

Ectopic adrenocorticotropic hormone (ACTH)-secreting tumors account for approximately 10% of Cushing's syndrome (CS). We present an extremely rare case of a patient with CS caused by an ectopic ACTH-secreting pituitary adenoma (EAPA) of the ethmoid sinus. The tumor was identified by positron-emission tomography-computed tomography (PET/CT) using the somatostatin receptor analogue Ga-68-DOTANOC. Transnasal endoscopic resection was performed and the patient showed significant clinical improvement with normalization of the endocrine pituitary axis. Immunostaining showed a somatostatin receptor 2 and 5-positive ACTH-producing adenoma. In patients with ectopic ACTH secretion, Ga-68-DOTANOC-PET/CT may play an important role in the localization of EAPA. Transnasal endoscopic resection is the therapy of choice.

G Protein-Coupled Receptors in cancer: biochemical interactions and drug design

G Protein-Coupled Receptors (GPCRs) share the same topology made of seven-transmembrane segments and represent the largest family of membrane receptors. Initially associated with signal transduction in differentiated cells, GPCRs and heterotrimeric G proteins were shown to behave as proto-oncogenes whose overexpression or activating mutations confer transforming properties. The first part of this review focuses on the link between biochemical interactions of a GPCR with other receptors, such as dimerization or multiprotein complexes, and their oncogenic properties. Alteration of these interactions or deregulation of transduction cascades can promote uncontrolled cell proliferation or cell transformation that leads to tumorigenicity and malignancy. The second part concerns the design of drugs specifically targeting these complex interactions and their promise in cancer therapy.

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 ((111)In-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 (sst(2)) 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 sst(2) preferring analog) and cabergoline (D(2) agonist) both decreased the ACTH levels in the cultured tumor cells of patient 1.

CONCLUSION

We describe two patients with ACTH-producing bronchial carcinoids, in whom a direct down-regulatory effect of glucocorticoid levels on tumoral sst(2) 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.

Treatment Options in Cushing's Disease

Endogenous Cushing’s syndrome is a grave disease that requires a multidisciplinary and individualized treatment approach for each patient. Approximately 80% of all patients harbour a corticotroph pituitary adenoma (Cushing’s disease) with excessive secretion of adrenocorticotropin-hormone (ACTH) and, consecutively, cortisol. The goals of treatment include normalization of hormone excess, long-term disease control and the reversal of comorbidities caused by the underlying pathology. The treatment of choice is neurosurgical tumour removal of the pituitary adenoma. Second-line treatments include medical therapy, bilateral adrenalectomy and radiation therapy. Drug treatment modalities target at the hypothalamic/pituitary level, the adrenal gland and at the glucocorticoid receptor level and are commonly used in patients in whom surgery has failed. Bilateral adrenalectomy is the second-line treatment for persistent hypercortisolism that offers immediate control of hypercortisolism. However, this treatment option requires a careful individualized evaluation, since it has the disadvantage of permanent hypoadrenalism which requires lifelong glucocorticoid and mineralocorticoid replacement therapy and bears the risk of developing Nelson’s syndrome. Although there are some very promising medical therapy options it clearly remains a second-line treatment option. However, there are numerous circumstances where medical management of CD is indicated. Medical therapy is frequently used in cases with severe hypercortisolism before surgery in order to control the metabolic effects and help reduce the anestesiological risk. Additionally, it can help to bridge the time gap until radiotherapy takes effect. The aim of this review is to analyze and present current treatment options in Cushing’s disease.

The role of somatostatin and dopamine D2 receptors in endocrine tumors

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 D(2) receptor (D(2)) 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 D(2) 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 D(2) pathophysiology and the future perspectives for treatment with SSA, DA agonists, and SS/DA chimeric compounds are discussed.

Management of Cushing disease

Cushing disease is caused by a corticotroph tumor of the pituitary gland. Patients with Cushing disease are usually treated with transsphenoidal surgery, as this approach leads to remission in 70-90% of cases and is associated with low morbidity when performed by experienced pituitary gland surgeons. Nonetheless, among patients in postoperative remission, the risk of recurrence of Cushing disease could reach 20-25% at 10 years after surgery. Patients with persistent or recurrent Cushing disease might, therefore, benefit from a second pituitary operation (which leads to remission in 50-70% of cases), radiation therapy to the pituitary gland or bilateral adrenalectomy. Remission after radiation therapy occurs in ∼85% of patients with Cushing disease after a considerable latency period. Interim medical therapy is generally advisable after patients receive radiation therapy because of the long latency period. Bilateral adrenalectomy might be considered in patients who do not improve following transsphenoidal surgery, particularly patients who are very ill and require rapid control of hypercortisolism, or those wishing to avoid the risk of hypopituitarism associated with radiation therapy. Adrenalectomized patients require lifelong adrenal hormone replacement and are at risk of Nelson syndrome. The development of medical therapies with improved efficacy might influence the management of this challenging condition.

Differential gene expression profiles of POMC-related enzymes, transcription factors and receptors between non-pituitary and pituitary ACTH-secreting tumors

The differential gene expression of proopiomelanocortin (POMC)-related processing enzymes, transcription factors, and receptors responsible for ACTH secretion between non-pituitary and pituitary ACTH-secreting tumors remains obscure. This study was attempted to determine the gene expression profiles of transcription factors (Tpit, NeuroD1 and IKZF1), proprotein convertase (PC) 1/3 and PC2, and several key receptors linked to ACTH secretion, including corticotrophin releasing hormone receptor (CRHR1), vasopressin receptor 1b (V1bR), somatostatin receptor (SSTR) subtype-2, -5 and dopamine receptor type 2 (D2R) in non-pituitary and pituitary ACTH-secreting tumors. Surgical tissue specimens from carcinoid tumors causing ectopic ACTH syndrome (EAS: n=4) and pituitary tumors causing Cushing's disease (CD: n=13), were subjected to real-time RT-PCR for measurements of each mRNA levels. POMC and CRHR1 mRNA levels in CD were far greater than those in EAS, whereas IKZF1, PC2, SSTR-2 and -5 mRNA levels in EAS were significantly greater than those in CD. NeuroD1, Tpit, PC1/3, V1bR and D2R mRNA levels were comparable between EAS and CD. In conclusion, differential gene expression profiles revealed more abundant mRNA expression in EAS than in CD of 1) IKZF1 with its potential implication of cell differentiation and hormone secretion, 2) PC2 with its possible enhanced processing activity of mature ACTH, and 3) SSTR-2 and -5 with their potential therapeutic application of more selective agonists in EAS patients.

Treatment of Cushing disease: overview and recent findings

Endogenous Cushing syndrome is an endocrine disease caused by excessive secretion of adrenocorticotropin hormone in approximately 80% of cases, usually by a pituitary corticotroph adenoma (Cushing disease [CD]). It is a heterogeneous disorder requiring a multidisciplinary and individualized approach to patient management. The goals of treatment of CD include the reversal of clinical features, the normalization of biochemical changes with minimal morbidity, and long-term control without recurrence. Generally, the treatment of choice is the surgical removal of the pituitary tumor by transsphenoidal approach, performed by an experienced surgeon. Considering the high recurrence rate, other treatments should be considered. Second-line treatments include more radical surgery, radiation therapy, medical therapy, and bilateral adrenalectomy. Drug treatment has been targeted at the hypothalamic or pituitary level, at the adrenal gland, and also at the glucocorticoid receptor level. Frequently, medical therapy is performed before surgery to reduce the complications of the procedure, reducing the effects of severe hypercortisolism. Commonly, in patients in whom surgery has failed, medical management is often essential to reduce or normalize the hypercortisolemia, and should be attempted before bilateral adrenalectomy is considered. Medical therapy can be also useful in patients with CD while waiting for pituitary radiotherapy to take effect, which can take up to 10 years or more. So far, results of medical treatment of CD have not been particularly relevant; however, newer tools promise to change this scenario. The aim of this review is to analyze the results and experiences with old and new medical treatments of CD and to reevaluate medical therapies for complications of CD and hypopituitarism in patients with cured CD.

The ectopic ACTH syndrome

Ectopic Cushing's syndrome usually relates to the ectopic ACTH syndrome (EAS) and represents ∼20% of ACTH-dependent and ∼10% of all types of Cushing's syndrome (CS). Nearly any neuroendocrine or non-endocrine tumours may be associated with EAS, but the more prevalent tumours are bronchial carcinoids, small cell lung carcinomas, pancreatic carcinoids, thymic carcinoids, medullary carcinomas of the thyroid, and phaeochromocytomas. Occult tumours are highly represented in all the series (12-38%) and constitute the more challenging cases of EAS, requiring long term follow-up. The lack of any completely reliable diagnostic test procedure and imaging to clearly reveal the source of EAS suggests that we should adopt a step-by-step multidisciplinary approach for their diagnosis and therapeutic management. Clinical features are often similar in ACTH-dependent CS, but the rapid onset and progress may suggest an ectopic source. A combination of biochemical tests and imaging studies seems the most appropriate approach for the prompt identification of EAS, even if there are several pitfalls to be avoided along the way. The most appropriate management for cure of EAS, when its source is identified, is surgical excision after controlling the hypercortisolaemia by inhibitors of cortisol secretion and other newer modalities alone or in combination; bilateral adrenalectomy remains an alternative option. Tumour histology, the presence of metastases and the effective control of hypercortisolaemia affect mortality and morbidity. If a source repeatedly fails to be found, the prognosis is often favourable but the identification of a malignant tumour should still be sought during life-long follow-up to avoid the calamity of misdiagnosis.

Recent trends in the treatment of well-differentiated endocrine carcinoma of the small bowel

Well-differentiated endocrine carcinomas of the small bowel are fairly rare neoplasms that present many clinical challenges. They secrete peptides and neuroamines that may cause carcinoid syndrome. However, many are clinically silent until late presentation with major effects. Initial treatment aims to control carcinoid syndrome with somatostatin analogs. Even if there is metastatic spread, surgical resection of the primitive tumor should be discussed in cases of retractile mesenteritis, small bowel ischemia or subocclusive syndrome in order to avoid any acute complication, in particular at the beginning of somatostatin analog treatment. The choice of treatment depends on the symptoms, general health of the patient, tumor burden, degree of uptake of radionuclide, histological features of the tumor, and tumor growth. Management strategies include surgery for cure (which is rarely achieved) or for cytoreduction, radiological interventions (transarterial embolization or radiofrequency ablation), and chemotherapy (interferon and somatostatin analogs). New biological agent and radionuclide targeted therapies are under investigation. Diffuse and non-evolving lesions should also be simply monitored. Finally, it has to be emphasized that it is of the utmost importance to enroll these patients with a rare disease in prospective clinical trials assessing new therapeutic strategies.

Pasireotide and octreotide stimulate distinct patterns of sst2A somatostatin receptor phosphorylation

Pasireotide (SOM230) is currently under clinical evaluation as a successor compound to octreotide for the treatment of acromegaly, Cushing's disease, and carcinoid tumors. Whereas octreotide acts primarily via the sst(2A) somatostatin receptor, pasireotide was designed to exhibit octreotide-like sst(2A) activity combined with enhanced binding to other somatostatin receptor subtypes. In the present study, we used phophosite-specific antibodies to examine agonist-induced phosphorylation of the rat sst(2A) receptor. We show that somatostatin and octreotide stimulate the complete phosphorylation of a cluster of four threonine residues within the cytoplasmic (353)TTETQRT(359) motif in a variety of cultured cell lines in vitro as well as in intact animals in vivo. This phosphorylation was mediated by G protein-coupled receptor kinases (GRK) 2 and 3 and followed by rapid cointernalization of the receptor and ss-arrestin into the same endocytic vesicles. In contrast, pasireotide failed to promote substantial phosphorylation and internalization of the rat sst(2A) receptor. In the presence of octreotide or SS-14, SOM230 showed partial agonist behavior, inhibiting phosphorylation, and internalization of sst(2A). Upon overexpression of GRK2 or GRK3, pasireotide stimulated selective phosphorylation of Thr356 and Thr359 but not of Thr353 or Thr354 within the (353)TTETQRT(359) motif. Pasireotide-mediated phosphorylation led to the formation of relatively unstable beta-arrestin-sst(2A) complexes that dissociated at or near the plasma membrane. Thus, octreotide and pasireotide are equally active in inducing classical G protein-dependent signaling via the sst(2A) somatostatin receptor. Yet, we find that they promote strikingly different patterns of sst(2A) receptor phosphorylation and, hence, stimulate functionally distinct pools of beta-arrestin.