Immunohistochemical detection of somatostatin receptor (SSTR) subtypes 2A and 5 in pituitary adenoma from acromegalic patients: good correlation with preoperative response to octreotide

Drug resistance in pituitary tumours: from cell membrane to intracellular signalling

The pharmacological treatment of pituitary tumours is based on the use of stable analogues of somatostatin and dopamine. The analogues bind to somatostatin receptor types 2 and 5 (SST2 and SST5) and dopamine receptor type 2 (DRD2), respectively, and generate signal transduction cascades in cancerous pituitary cells that culminate in the inhibition of hormone secretion, cell growth and invasion. Drug resistance occurs in a subset of patients and can involve different steps at different stages, such as following receptor activation by the agonist or during the final biological responses. Although the expression of somatostatin and dopamine receptors in cancer cells is a prerequisite for these drugs to reach a biological effect, their presence does not guarantee the success of the therapy. Successful therapy also requires the proper functioning of the machinery of signal transduction and the finely tuned regulation of receptor desensitization, internalization and intracellular trafficking. The present Review provides an updated overview of the molecular factors underlying the pharmacological resistance of pituitary tumours. The Review discusses the experimental evidence that supports a role for receptors and intracellular proteins in the function of SSTs and DRD2 and their clinical importance.

Machine Learning-based Prediction Model for Treatment of Acromegaly With First-generation Somatostatin Receptor Ligands

CONTEXT

Artificial intelligence (AI), in particular machine learning (ML), may be used to deeply analyze biomarkers of response to first-generation somatostatin receptor ligands (fg-SRLs) in the treatment of acromegaly.

OBJECTIVE

To develop a prediction model of therapeutic response of acromegaly to fg-SRL.

METHODS

Patients with acromegaly not cured by primary surgical treatment and who had adjuvant therapy with fg-SRL for at least 6 months after surgery were included. Patients were considered controlled if they presented growth hormone (GH) <1.0 ng/mL and normal age-adjusted insulin-like growth factor (IGF)-I levels. Six AI models were evaluated: logistic regression, k-nearest neighbor classifier, support vector machine, gradient-boosted classifier, random forest, and multilayer perceptron. The features included in the analysis were age at diagnosis, sex, GH, and IGF-I levels at diagnosis and at pretreatment, somatostatin receptor subtype 2 and 5 (SST2 and SST5) protein expression and cytokeratin granulation pattern (GP).

RESULTS

A total of 153 patients were analyzed. Controlled patients were older (P = .002), had lower GH at diagnosis (P = .01), had lower pretreatment GH and IGF-I (P < .001), and more frequently harbored tumors that were densely granulated (P = .014) or highly expressed SST2 (P < .001). The model that performed best was the support vector machine with the features SST2, SST5, GP, sex, age, and pretreatment GH and IGF-I levels. It had an accuracy of 86.3%, positive predictive value of 83.3% and negative predictive value of 87.5%.

CONCLUSION

We developed a ML-based prediction model with high accuracy that has the potential to improve medical management of acromegaly, optimize biochemical control, decrease long-term morbidities and mortality, and reduce health services costs.

Clinical, biological, radiological, and pathological comparison of sparsely and densely granulated somatotroph adenomas: a single center experience from a cohort of 131 patients with acromegaly

PURPOSE

Growth hormone-producing pituitary adenomas are divided into two clinically relevant histologic subtypes, densely (DG-A) and sparsely (SG-A) granulated. Histologic subtype was evaluated in a large cohort of patients with acromegaly, separating DG-A and SG-A, and correlated with clinicopathological characteristics.

METHODS

Patients with acromegaly undergoing surgery as initial therapy between 1995 and 2015 were identified. Histologic subtype was determined by keratin expression pattern with CAM5.2 and correlated with clinical and imaging parameters, somatostatin receptor subtype 2 (SST2) expression, post-surgical remission rate, and application of a prognostic scoring system incorporating proliferation and invasiveness.

RESULTS

One hundred thirty-one patients were included. Tumors were classified as DG-A (75, 57.3%), SG-A (29, 22.1%), intermediate (I-A) (9, 6.9%), and unclassified (18, 13.7%) when CAM5.2 was negative. DG-A and I-A were combined for analysis (DG/I-A) and compared to SG-A. Age, gender, proliferation, and post-surgical remission did not differ. SG-A were larger [2 vs. 1.5 cm (median), p = 0.03], more frequently invasive [65.5% vs. 32.9%, p = 0.004], associated with higher MRI T2-weighted signal ratio [1.01 vs. 0.82 (median), p = 0.01], showed lower SST2 expression (p < 0.0001), and scored higher in the prognostic classification (p = 0.004). Surgical remission occurred in 41.7% DG/I-A and 41.4% SG-A (p = 1.0). On multivariate analysis, absence of invasion (p = 0.009) and lower pre-operative IGF-1 index (p = 0.0002) were associated with post-surgical remission.

CONCLUSION

CAM5.2 allowed distinction between DG/I-A and SG-A in most but not all cases. Histologic subtype did not predict surgical outcome. Absence of invasion and lower pre-operative IGF-1 index were the only significant predictors of post-surgical remission in this cohort.

Up-regulation of sex-determining region Y-box 9 (SOX9) in growth hormone-secreting pituitary adenomas

BACKGROUND

Pituitary adenomas are benign brain tumors that cause considerable morbidity and neurological symptoms. SOX9 as a regulatory transcriptional mediator affects normal and tumor cell growth with an undefined role in pituitary adenomas pathogenesis. Thus, in the present study, the expression pattern of SOX9 in GH-secreting pituitary tumors and normal pituitary tissues is investigated.

METHODS

The SOX9 gene expression level was evaluated in 60 pituitary tissues including different types of GH-secreting adenomas and normal pituitary tissues through Real-Time PCR. The protein level of SOX9 was assessed using immunohistochemistry. The correlations of SOX9 gene and protein expression level with the patient's clinical and pathological features were considered.

RESULTS

The SOX9 over-expression was detected in GH-secreting adenomas tumor tissues compared to normal pituitary tissues which were accompanied by overexpression of SOX9 protein in tumor tissues. The over-expression of SOX9 had a significant impact on GH-secreting adenomas tumor incidence with the odds ratio of 8.4 and the diagnostic value of SOX9 was considerable. The higher level of SOX9 expression was associated with invasive and macro tumors in GH-secreting pituitary adenoma patients. The positive correlation of SOX9 gene and protein level was observed and the tumor size and tumor invasive features were valuable in predicting SOX9 expression level in GH-producing pituitary tumors.

CONCLUSION

The study provided the first shreds of evidence regarding the expression pattern of SOX9 in the GH- secreting pituitary adenomas at both gene and protein levels which may emphasize the possible involvement of SOX9 as a mediator in pituitary adenoma tumor formation also open up new intrinsic molecular mechanism regarding pituitary adenoma pathogenesis.

Multicenter, Observational Study of Lanreotide Autogel for the Treatment of Patients with Acromegaly in Routine Clinical Practice in Germany, Austria and Switzerland

BACKGROUND

Evidence from controlled trials has shown that lanreotide autogel is effective in achieving biochemical and symptom control in patients with acromegaly. However, it is important to better understand the real-world patient population receiving lanreotide autogel treatment.

METHODS

In this non-interventional study the long-term treatment response to lanreotide autogel in adult patients with acromegaly from office-based centers or clinics in Germany, Austria and Switzerland was studied. Assessments included growth hormone and insulin-like growth factor-I levels, symptoms, quality of life, lanreotide plasma levels and tumor somatostatin receptor subtype expression. The primary endpoint was achievement of full biochemical control, defined as growth hormone ≤2.5 µg/L and insulin-like growth factor I normalization at month 12.

RESULTS

76 patients were enrolled from 21 sites. 7/51 (13.7%) patients of the efficacy population had full biochemical control at baseline, 15/33 (45.5%) at month 12 and 10/26 (38.5%) at month 24 of treatment. At 12 months of treatment higher rates of biochemical control were observed in the following subgroups: older patients (>53 years [median]), females, treatment-naïve patients, and patients with a time since diagnosis of longer than 1.4 years (median). No clinically relevant differences in acromegaly symptoms or quality of life scores were observed. Median fasting blood glucose and glycated hemoglobin levels remained unchanged throughout the study. No new safety signals were observed. Overall tolerability of treatment with lanreotide autogel was judged by 80.8% of the enrolled patients at month 12 as 'very good' or 'good'.

CONCLUSION

Treatment with lanreotide autogel in a real-world setting showed long-term effectiveness and good tolerability in patients with acromegaly.

Follicle-stimulating Hormone-secreting Pituitary Adenoma Accompanied by Painful Thyroiditis

A 30-year-old woman with multiple ovarian cysts presented with high serum estradiol levels. She had a pituitary adenoma, but the follicle-stimulating hormone (FSH) concentration was within the normal range. The patient complained of neck pain and palpitations during the disease course, and laboratory results revealed thyrotoxicosis and a systemic inflammatory response with negative findings for anti-thyroid stimulating hormone (TSH) receptor antibody and positive findings for anti-thyroglobulin and anti-thyroid peroxidase antibodies. Prednisolone improved the symptoms and the thyroid function and was discontinued after two months. A histological examination of the pituitary tumor confirmed it to be FSH-producing pituitary adenoma, with subsequent normalization of the serum estradiol concentration.

Pasireotide-LAR in acromegaly patients treated with a combination therapy: a real-life study

PURPOSE

Little data are available regarding the safety and efficacy of switching to Pasireotide-LAR monotherapy in acromegaly patients with partial resistance to first-generation somatostatin agonists (1gSRL) who require combination treatment with cabergoline or pegvisomant.

METHOD

In this monocentric prospective study within a tertiary university hospital, 15 consecutive acromegalic adults partially resistant to 1gSRL treated with octreotide LAR or lanreotide SR, and cabergoline (n = 4, 3.5 mg/week) or pegvisomant (n = 11, median dose 100 mg/week), were switched to Pasireotide-LAR (8 with 40 mg/month; 7 with 60 mg/month). Immunohistochemical expression level of SSTR5 and the granulation pattern of nine somatotroph adenomas were retrospectively determined to test for a correlation with the therapeutic efficacy of Pasireotide-LAR.

RESULTS

Median IGF-1 concentration at the first evaluation (median 3 months) was similar to baseline (1.0 vs 1.1 ULN). 11/15 patients had IGF-1 levels ≤1.3 ULN before and after the switch but individual changes were variable. Hyperglycemia was frequent and greater in diabetic patients. 7/15 patients stopped Pasireotide-LAR due to lack of control of IGF-1 or intolerance. 8/15 patients received Pasireotide-LAR for a median of 29 months with IGF-1 levels ≤1.3 ULN and acceptable glucose tolerance (median HbA1c 6.1%). Two patients required initiation of oral antidiabetic treatment. The intensity of SSTR5 expression and the granulation pattern of adenomas were of limited value for the prediction of Pasireotide-LAR effectiveness.

CONCLUSION

Pasireotide-LAR may represent a suitable therapeutic alternative in a subset of acromegalic patients requiring combination therapy involving a 1gSRL.

PREDICTIVE MARKERS FOR POSTSURGICAL MEDICAL MANAGEMENT OF ACROMEGALY: A SYSTEMATIC REVIEW AND CONSENSUS TREATMENT GUIDELINE

Objective: To clarify the selection of medical therapy following transsphenoidal surgery in patients with acromegaly, based on growth hormone (GH)/insulin-like growth factor 1 (IGF-1) response and glucometabolic control. Methods: We carried out a systematic literature review on three of the best studied and most practical predictive markers of the response to somatostatin analogues (SSAs): somatostatin receptor (SSTR) expression, tumor morphologic classification, and T2-weighted magnetic resonance imaging (MRI) signal intensity. Additional analyses focused on glucose metabolism in treated patients. Results: The literature survey confirmed significant associations of all three factors with SSA responsiveness. SSTR expression appears necessary for the SSA response; however, it is not sufficient, as approximately half of SSTR2-positive tumors failed to respond clinically to first-generation SSAs. MRI findings (T2-hypo-intensity) and a densely granulated phenotype also correlate with SSA efficacy, and are advantageous as predictive markers relative to SSTR expression alone. Glucometabolic control declines with SSA monotherapy, whereas GH receptor antagonist (GHRA) monotherapy may restore normoglycemia. Conclusion: We propose a decision tree to guide selection among SSAs, dopamine agonists (DAs), and GHRA for medical treatment of acromegaly in the postsurgical setting. This decision tree employs three validated predictive markers and other clinical considerations, to determine whether SSAs are appropriate first-line medical therapy in the postsurgical setting. DA treatment is favored in patients with modest IGF-1 elevation. GHRA treatment should be considered for patients with T2-hyperintense tumors with a sparsely granulated phenotype and/or low SSTR2 staining, and may also be favored for individuals with diabetes. Prospective analyses are required to test the utility of this therapeutic paradigm. Abbreviations: DA = dopamine agonist; DG = densely granulated; GH = growth hormone; GHRA = growth hormone receptor antagonist; HbA1c = glycated hemoglobin; IGF-1 = insulin-like growth factor-1; MRI = magnetic resonance imaging; SG = sparsely granulated; SSA = somatostatin analogue; SSTR = somatostatin receptor.

International Union of Basic and Clinical Pharmacology. CV. Somatostatin Receptors: Structure, Function, Ligands, and New Nomenclature

Somatostatin, also known as somatotropin-release inhibitory factor, is a cyclopeptide that exerts potent inhibitory actions on hormone secretion and neuronal excitability. Its physiologic functions are mediated by five G protein-coupled receptors (GPCRs) called somatostatin receptor (SST)1-5. These five receptors share common structural features and signaling mechanisms but differ in their cellular and subcellular localization and mode of regulation. SST₂ and SST₅ receptors have evolved as primary targets for pharmacological treatment of pituitary adenomas and neuroendocrine tumors. In addition, SST₂ is a prototypical GPCR for the development of peptide-based radiopharmaceuticals for diagnostic and therapeutic interventions. This review article summarizes findings published in the last 25 years on the physiology, pharmacology, and clinical applications related to SSTs. We also discuss potential future developments and propose a new nomenclature.

Is receptor profiling useful for predicting pituitary therapy?

Medical treatment of pituitary tumours may present important challenges in the presence of resistance to first line therapy. In this setting, the availability of specific markers of responsiveness/resistance could be helpful to provide tailored patients' treatment. Pituitary receptor profiling has emerged as a potentially useful tool for predicting the response to specific pituitary-directed medical therapy, mainly somatostatin analogues and dopamine agonists. However, its utility is not always straightforward. In fact, agonist-receptor coupling to the consequent biological response is complex and sometimes jeopardizes the understanding of the molecular basis of pharmacological resistance. Defective expression of pituitary receptors, genetic alterations, truncated variants, impaired signal transduction or involvement of other proteins, such as cytoskeleton proteins or the Aryl hydrocarbon receptor interacting protein amongst others, have been linked to differential tumour phenotype or treatment responsiveness with conflicting results, keeping the debate on the utility of pituitary receptor profiling open. Why does this occur? How can we overcome the difficulties? Is there a true role for pituitary receptor profiling in the near future? All authors of this debate article agree on the need of prospective studies using standardized methods in order to assess the efficacy of receptor profiling as a reliable clinical predictive factor.

Factors predicting pasireotide responsiveness in somatotroph pituitary adenomas resistant to first-generation somatostatin analogues: an immunohistochemical study

AIM

To gather data regarding factors predicting responsiveness to pasireotide in acromegaly.

PATIENTS AND METHODS

SSTR2a, SSTR3, SSTR5, AIP, Ki-67 and the adenoma subtype were evaluated in somatotroph adenomas from 39 patients treated post-operatively with somatostatin analogues (SSAs). A standardized SSTR scoring system was applied (scores 0-3). All patients received first-generation SSAs, and 11 resistant patients were subsequently treated with pasireotide LAR.

RESULTS

None of the patients with negative or cytoplasmic-only SSTR2a expression (scores 0-1) were responsive to first-generation SSAs, as opposed to 20% (score 2) and 50% of patients with a score of 3 (P=0.04). None of the patients with an SSTR5 score of 0-1 were responsive to pasireotide, as opposed to 5/7 cases with a score of 2 or 3 (P=0.02). SSTR3 expression did not influence first-generation SSAs or pasireotide responsiveness. Tumours with low AIP were resistant to first-generation SSAs (100 vs 60%; P=0.02), while they had similar responsiveness to pasireotide compared to tumours with conserved AIP expression (50 vs 40%; P=0.74). Tumours with low AIP displayed reduced SSTR2 (SSTR2a scores 0-1 44.4 vs 6.7%; P=0.006) while no difference was seen in SSTR5 (SSTR5 scores 0-1 33.3 vs 23.3%; P=0.55). Sparsely granulated adenomas responded better to pasireotide compared to densely granulated ones (80 vs 16.7%; P=0.04).

CONCLUSION

The expression of SSTR5 might predict responsiveness to pasireotide in acromegaly. AIP deficient and sparsely granulated adenomas may benefit from pasireotide treatment. These results need to be confirmed in larger series of pasireotide-treated patients.

Expression of somatostatin receptor subtype 2 in growth hormone-secreting pituitary adenoma and the regulation of miR-185

INTRODUCTION

Long-acting somatostatin analogs (SSAs) are most widely used to treat growth hormone (GH)-secreting pituitary adenoma. However, approximately 30 % of treated patients show resistance to SSAs, which may be associated with the reduction of somatostatin receptor subtype 2 (SSTR2) mRNA and protein expression.

MATERIALS AND METHODS

The present study used immunohistochemistry to detect the expression of SSTR2 and SSTR5 in twenty human GH-secreting adenoma samples treated with SSAs and seven normal pituitary samples.

RESULTS

The staining intensities of SSTR2 and SSTR5 were stronger in most adenoma samples than in normal pituitary. The expression of SSTR2 tended to be lower in the SSA non-responder group than in responders. A search of the Bioinformatics data bank and the miRCURY™ LNA array confirmed miR-185 as the putative mircoRNA (miRNA) regulating the expression of SSTR2. An in vitro study using Dual Luciferase reporter assay demonstrated that miR-185 likely targets the 3'-UTR of SSTR2 mRNA in the rat pituitary adenoma GH3 cell line. MiR-185 also downregulated or upregulated the expression of SSTR2 mRNA and SSTR2 protein, following transfection with miR-185 mimics or inhibitors, respectively.

CONCLUSION

MiR-185 enhanced the cell proliferation and inhibited the apoptosis of GH3 cells.

Growth hormone granulation pattern and somatostatin receptor subtype 2A correlate with postoperative somatostatin receptor ligand response in acromegaly: a large single center experience

Acromegaly is associated with serious morbidity and mortality, if not well controlled. Approved somatostatin receptor ligands (SRLs) are a mainstay of medical therapy and exhibit preferential affinity for somatostatin receptor (SSTR) subtype 2. Our objective was to assess whether characteristic features of individual growth hormone (GH)-secreting adenomas at diagnosis, correlated with SRL sensitivity, using defined tumor markers. A retrospective review of 86 consecutive acromegaly surgeries (70 patients) performed between January 2006 and December 2011 was undertaken. Patients with any preoperative medical treatment were excluded. Response to SRL therapy was defined as normalization of insulin-like growth factor 1 (IGF1) and random GH < 1.0 ng/dl. Immunohistochemical staining pattern: sparsely granulated, densely granulated, mixed growth hormone-prolactin (GH/PRL) and SSRT2 positivity (+) were correlated with clinicopathologic features, adenoma recurrence, and SRL treatment response. Two-tailed t test, univariate ANOVA, Kruskal-Wallis and bivariate correlation were performed using PAWS 18. The cohort eligible for analysis comprised 59 patients (41 female and 18 male). Based on pre-surgery adenoma imaging dimensions, 81.3% (48) were macroadenomas and average maximum tumor diameter was 18.1 ± 9.9 mm. Patients on SRLs were followed for 13.4 ± 15.8 (mean ± SD) months. Sparsely granulated adenomas were significantly larger at diagnosis, exhibited lower SSTR2 positivity and had a lower rate of biochemical normalization to SRLs. Densely granulated adenomas were highly responsive to SRLs. Overall, patients with SSTR2A+ adenomas responded more favorably to SRL treatment than those with SSTR2A- adenomas. Eighty-one percent of patients with SSTR2A+ adenomas were biochemically controlled (both GH and IGF1) on SRL treatment, e.g. a much higher normalization rate than that reported in the unselected acromegaly population (20-30%). Detailed knowledge of adenoma GH granularity and the immunohistochemical SSTR2A+ status is a predictor of SRL response. These immunoreactive markers should be assessed routinely on surgical specimens to assess subsequent SRL responsiveness and potential need for adjunctive therapy after surgery.

Granulation pattern, but not GSP or GHR mutation, is associated with clinical characteristics in somatostatin-naive patients with somatotroph adenomas

OBJECTIVE

Somatotroph adenomas causing acromegaly are histologically classified into densely granulated (DG) and sparsely granulated (SG) subtypes with different morphology, clinical characteristics and treatment outcomes. Granulation pattern has been reported to co-segregate with a recurrent mutation at codon 49 in growth hormone receptor (GHR) and GSP oncogene. This study examines response to the octreotide suppression test (OST) in relation to granulation pattern and mutation in GHR and GSP.

DESIGN

This is a retrospective, single-centre study of 52 patients with pathologically confirmed somatotroph adenoma who were naïve to medical therapy presenting between January 2001 and October 2010.

METHODS

Clinical, radiological and hormonal data at diagnosis were recorded. GHR and GSP were genotyped, granulation pattern determined and response to the OST measured.

RESULTS

SG adenomas were larger (P=0.038), occurred in younger patients (P=0.029), were more common in females (P=0.026) and were more invasive (P<0.0001 and P=0.001), with diminished responses to the OST (P=0.007) compared with DG adenomas. GSP mutation was unrelated to granulation pattern but associated with smaller tumours (P=0.027), producing more GH (P=0.048) that responded better to the OST (P=0.022). Codon 49 of GHR was not mutated.

CONCLUSIONS

Adenoma histological phenotype, not genotype, corresponds to clinical and biochemical characteristics and response to the OST. SG adenomas constitute a clinically more unfavourable subtype but are not associated with GHR mutations in our series. Ascertainment of the adenoma subtype may become an important consideration in the management of acromegaly.

Low somatostatin receptor subtype 2, but not dopamine receptor subtype 2 expression predicts the lack of biochemical response of somatotropinomas to treatment with somatostatin analogs

OBJECTIVES

To evaluate somatostatin receptor 2A (SSTR2A) and dopamine receptor 2 (DR2) protein expression in somatotropinomas and to relate it to response to somatostatin analogues (SA).

DESIGN AND PATIENTS

SSTR2A and DR2 expression was analyzed by immunohistochemistry in 88 somatotropinomas from patients submitted to either pre-surgical or adjuvant SA treatment. Tumors were scored according to percentage of immunostained cells: 0 (< 25%), 1 (25-50%), and 2 (> 50%). Relation between protein expression and response to SA was performed in 66 patients. Response to SA was assessed by percent IGF-I reduction, being considered as an IGF-I per cent reduction higher than 50%. Disease control was also assessed (GH < 1.0 ng/ml and normal IGF-I).

RESULTS

SSTR2A and DR2 were expressed in 100% and 98% of tumors, respectively. Biochemical response and disease control rates were 48% and 32%, respectively. Median IGF-I percent reduction after 3 months of SA treatment was lower in the SSTR2A score 0 than in the scores 1 and 2 (p < 0.001, both), and after 6 months in the score 0 than in the score 1 (p = 0.001) and 2 (p < 0.001). Biochemical response and disease control were associated with SSTR2 expression (p < 0.001 and p = 0.004, respectively). A negative predictive value for biochemical response of 100% was found when a SSTR2A expression < 25%of immunostained cells cut-off point was considered. No relation was found between DR2 expression and biochemical response and disease control.

CONCLUSION

SSTR2A and DR2 are highly expressed in somatotropinomas. Low SSTR2A, but not DR2, expression is a negative predictive factor to response to SA.

Validation of immunohistochemistry for somatostatin receptor subtype 2A in human somatotropinomas: comparison between quantitative real time RT-PCR and immunohistochemistry

Somatostatin receptors subtype 2 (SSTR2) expression in somatotropinomas is recognized as a predictor of response to the currently available somatostatin analogs and may be analyzed, mainly, by quantitative RT-PCR or immunohistochemistry (IHC). The former has the advantages of a higher sensitivity and of being quantitative, while the latter, although semi-quantitative, evaluates protein expression and is routinely used in the evaluation of pituitary adenomas. We aimed to evaluate the SSTR2A protein expression in somatotropinomas and to compare it to our previous data regarding mRNA expression, assessed by quantitative real time RTPCR. Thirteen somatotropinomas were analyzed by IHC and the tumors were scored according to percent of immunostained cells: 0 (<25%), 1 (25-50%) and 2 (>50%). SSTR2A immunostaining was present in all but one somatotropinoma, 4 (31%) tumors were classified as score 0, 4 (31%) as score 1, and 5 (38%) as score 2. Median SSTR2 mRNA content was significantly different among the three IHC scores (p=0.036) and was lower in the score 0 than in the score 2 (p=0.016). The finding that there is a positive correlation between RT-PCR and IHC indicates that IHC can be applied in order to assess the SSTR2A content in somatotropinomas.

Reassessment of sst(5) somatostatin receptor expression in normal and neoplastic human tissues using the novel rabbit monoclonal antibody UMB-4

OBJECTIVE

The frequent overexpression of somatostatin receptors (sst) in neuroendocrine tumors provides the molecular basis for the diagnostic and therapeutic application of stable somatostatin analogs. Whereas octreotide acts mainly via the sst(2) receptor, the novel pan-somatostatin analog pasireotide exhibits particular high affinity for the sst(5) receptor. To determine whether a patient is a candidate for octreotide or pasireotide therapy, it is important to evaluate the somatostatin receptor status. However, so far highly specific rabbit monoclonal antibodies have been developed for the sst(2) receptor only (clone UMB-1).

METHODS

Here, we have extensively characterized a novel rabbit monoclonal antibody for the human sst(5) receptor (clone UMB-4). In a comparative immunohistochemical study, the expression of sst(5) and sst(2) receptors was assessed using UMB-4 and UMB-1, respectively.

RESULTS

Western blot experiments unequivocally demonstrated that UMB-4 selectively detected its cognate sst(5) receptor and did not cross-react with other proteins present in crude tissue homogenates. UMB-4 yielded a highly effective immunostaining of distinct cell populations in formalin-fixed, paraffin-embedded human tissues with a predominance of plasma membrane staining. In the pituitary, sst(5) was present on all growth hormone (GH)- and adrenocorticotropin hormone (ACTH)-producing cells whereas sst(2) was only observed on a subpopulation of GH-positive cells. Consequently, sst(5) was detectable on the majority of GH and ACTH adenomas. In contrast, sst(2) was only seen on GH but not on ACTH adenomas.

CONCLUSIONS

The rabbit monoclonal antibodies UMB-4 and UMB-1 will facilitate the assessment of the somatostatin receptor status of human tumors during routine histopathological examinations.

The expression of E-cadherin in somatotroph pituitary adenomas is related to tumor size, invasiveness, and somatostatin analog response

CONTEXT

Appropriate cell-to-cell adhesion is fundamental for the epithelial phenotype of pituitary cells. Loss of the adhesion protein E-cadherin has been associated with invasiveness, metastasis, and poor prognosis in cancers of epithelial origin. In somatotroph adenomas, a variable and reduced expression of E-cadherin has been demonstrated. In addition, nuclear translocation of E-cadherin was found to correlate with pituitary tumor invasion.

OBJECTIVE

The objective was to examine the protein expression of E-cadherin in somatotroph pituitary adenomas in relation to adenoma size, invasiveness, and somatostatin analog (SMS) efficacy.

PATIENTS AND METHODS

Eighty-three patients were included, and 29 were treated preoperatively with SMS. Adenoma E-cadherin protein expression was analyzed by Western blot (61 patients) and immunohistochemistry (IHC) (80 patients) with antibodies directed against both extracellular and intracellular domains (IHC). The acute (direct surgery group) and long-term (preoperatively treated group) SMS responses were evaluated. Baseline tumor volume and invasiveness were measured on magnetic resonance imaging scans.

RESULTS

Membranous E-cadherin was lost in several adenomas. Nine of these were nuclear E-cadherin positive. The E-cadherin protein expression correlated negatively to tumor size and positively to acute SMS response. Low E-cadherin levels (preoperatively treated group only) and loss of membranous E-cadherin correlated to tumor invasiveness. The E-cadherin level correlated positively to tumor reduction after SMS treatment, and adenomas with nuclear E-cadherin staining had lower IGF-I reduction and tumor shrinkage. Preoperatively treated adenomas had reduced E-cadherin protein levels, but the IHC expression was unaltered.

CONCLUSION

Reduced E-cadherin expression may correlate to a dedifferentiated phenotype in the somatotroph pituitary adenomas.

Pituitary somatostatin receptor signaling

Somatotropin-release inhibitory factor (SRIF) is a major regulator of pituitary function, mostly inhibiting hormone secretion and to a lesser extent pituitary cell growth. Five SRIF receptor subtypes (SSTR1-5) are ubiquitously expressed G-protein coupled receptors. In the pituitary, SSTR1, 2, 3 and 5 are expressed, with SSTR2 and SSTR5 predominating. As new SRIF analogs have recently been introduced for treatment of pituitary disease, we evaluate the current knowledge of cell-specific pituitary SRIF receptor signaling and highlight areas of future research for comprehensive understanding of these mechanisms. Elucidating pituitary SRIF receptor signaling enables understanding of pituitary hormone secretion and cell growth, and also encourages future therapeutic development for pituitary disorders.

Tumor ZAC1 expression is associated with the response to somatostatin analog therapy in patients with acromegaly

Somatostatin analogs (SSA) with their potent antisecretory and antiproliferative effects are the main medical treatment option for patients with neuroendocrine tumors, such as gastroenteropancreatic and acromegaly-associated growth hormone secreting pituitary tumors. Although a good portion of acromegalic patients gets normalized after SSA treatment, strict hormonal control is not achieved in a sizeable proportion of these patients. The reasons for this incomplete response to SSA treatment are unclear. We have found that the tumor suppressor ZAC1 (LOT1/PLAGL1) is essential for the antiproliferative effect of SSA in pituitary tumor cells. The aim of the present retrospective cohort study was to determine whether ZAC1 immunoreactivity in archival somatotrophinoma tissue derived from 45 patients with acromegaly routinely pretreated with SSA before surgery, was associated with response to SSA (normalization of GH, IGF-I and presence of tumor shrinkage). All tumors displayed ZAC1 immunoreactivity [weak (+; n = 15), moderate (++; n = 16) and strong (+++; n = 14)]. A significant positive correlation was found between strong ZAC1 immunoreactivity and IGF-I normalization and presence of tumor shrinkage after SSA treatment, which was not affected by age at diagnosis, gender or duration of SSA treatment. These in vivo data combined with the antiproliferative properties of ZAC1/Zac1 provide evidence of a mechanistic role for this transcription factor on SSA induced tumor shrinkage and hormone normalization.

Pathology, pathogenesis and therapy of growth hormone (GH)-producing pituitary adenomas: technical advances in histochemistry and their contribution

Growth hormone (GH)-producing adenomas (GHomas) are one of the most frequently-occurring pituitary adenomas. Differentiation of hormone-producing cells in the pituitary gland is regulated by transcription factors and co-factors. The transcription factors include Pit-1, Prop-1, NeuroD1, Tpit, GATA-2, SF-1. Aberrant expression of transcription factors such as Pit-1 results in translineage expression of GH in adrenocorticotropic hormone-producing adenomas (ACTHomas). This situation has been substantiated by GFP-Pit-1 transfection expression in the AtT20 cell line. Experimentally, GHomas have been induced in GH-releasing hormone (GHRH) or Prop-1 transgenic animals. Immunohistochemical detection of somatostatin receptor (SSTR2a) has recently emphasized their role in the response of GHomas to somatostatin analogue therapy. In this review, the advances in technology and their contribution to cell biology and medical practice are discussed.

Pituitary-independent effect of octreotide on IGF1 generation

BACKGROUND

Somatostatin analogues are frequently used for medical treatment of acromegaly. The rationale for their use is based on the inhibition of pituitary GH secretion; however, there is in vitro evidence that octreotide also acts to inhibit hepatic IGF1 generation.

AIM & DESIGN

We studied the pituitary-independent effects of octreotide on IGF1 generation in 11 severely GH-deficient (GHD) humans (age 38, range 23-52; seven males; body mass index 24.7+/-3 kg/m(2); peak-stimulated GH <3 microg/l; 3+/-1 pituitary hormone deficiencies) on a stable dose of GH replacement (0.4+/-0.1 mg) for at least 6 months. Patients were studied before and after 50 microg of s.c. octreotide three times a day for 7 days.

RESULTS

At study entry, all patients had total IGF1 within age- and gender-related reference range (SDS 0.4+/-1.0). Octreotide treatment resulted in a significant decrease in total IGF1 (by 18%, 208+/-89 vs 173+/-62 microg/l, P=0.04), free IGF1 (by 13%, 0.83+/-0.36 vs 0.70+/-0.33 microg/l, P=0.01) and IGFBP3 (6%, 4475+/-745 vs 4209+/-912 microg/l, P=0.02). Octreotide suppressed fasting insulin from 8.1+/-3.4 to 6.3+/-4.1 mU/l (P=0.01) and was associated with an increase in fasting glucose from 5.2+/-0.9 to 5.8+/-0.9 mmol/l (P<0.01). IGFBP1 increased by 84% from 42+/-26 to 95+/-52 microg/l (P=0.04).

CONCLUSION

Our study demonstrates that octreotide induces a significant decrease in IGF1 in severely GHD adults on a fixed dose of GH replacement. This is the evidence for a non-pituitary action of octreotide on the GH/IGF1 axis, most likely by antagonising the action of GH on hepatic IGF1 generation and indirectly, by suppressing insulin secretion.

Analyses of factors influencing the acute effect of octreotide in growth hormone-secreting adenomas

Somatostatin analogues such as octreotide are used to treat active acromegalic patients by reducing serum growth hormone (GH) levels. However, the acute effect of octreotide on GH secretion differs among patients. To elucidate factors influencing the acute effect of octreotide, we collected data from 56 patients with somatotroph adenoma from two institutions. We analyzed the correlation of the following factors with the acute effect of octreotide: immunohistochemical staining of somatostatin receptor subtype 2A (SSTR 2A), presence of gsp mutation, proliferative potentials analyzed by Ki-67 staining index (SI). We found that the acute effect of octreotide significantly correlated with two factors: Ki-67 SI and the plasma membrane-dominant staining pattern of SSTR 2A. Monovariate analysis revealed a statistically significant inverse relation of Ki-67 SI with the reduction of GH by octreotide. We assessed the contribution of each factor on the acute effect of octreotide by multivariate analysis. Significant multiple regression was confirmed with p value of 0.003. Post-test revealed that the plasma membrane-dominant staining pattern of SSTR 2A was significantly related to the reduction of GH by octreotide. These results show that the acute effect of octreotide is positively related to SSTR 2A staining on the plasma membrane.

Somatostatin receptors subtypes 2 and 5, dopamine receptor type 2 expression and gsp status as predictors of octreotide LAR® responsiveness in acromegaly

We present two acromegalic patients in which clinical and molecular data are discussed in regard to their ability to predict long term octreotide LAR® therapy response. Case reports: Patient 1: female, 36 years old at diagnosis. Basal GH and IGF-I at diagnosis were 133 ng/mL and 181% above the upper limit of reference values (ULRV), respectively. Growth hormone during acute test with subcutaneous octreotide decreased from 133 to 13 ng/mL. Patient started on primary octreotide LAR® therapy (20mg q28 days) and achieved biochemical parameters of disease control after 6 months. Molecular analysis of tumor fragments: gsp +; quantitative analysis of SSTR (somatostatin receptor) and DR (dopamine receptor) mRNA - SSTR2 23954; SSTR5 2407; DR2 total 17016 copies. Patient 2: male, 38 years old at diagnosis. Basal GH and IGF-I at diagnosis were 120 ng/mL and 114% ULRV, respectively. Patient underwent non-curative trans-sphenoidal surgery. Post-operative GH and IGF-I were 112 ng/mL and 137% ULRV, respectively. Growth hormone during acute test with subcutaneous octreotide decreased from 112 to 7 ng/mL. Octreotide LAR® therapy (20 mg q28 days) was then initiated. After 6 months of treatment, patient did not attain biochemical control of disease and displayed increased tumor volume. Molecular analysis of tumor fragments: gsp not done; quantitative analysis of SSTR and DR mRNA - SSTR2 416; SSTR5 3767; DR2 total 3439 copies. In conclusion, these two cases illustrate how laboratory data can be conflicting as predictors of octreotide LAR® responsiveness and how molecular analysis of tumor fragments can help explain different behaviors in clinically similar patients.

Pathology of the human pituitary adenomas

This article describes pertinent aspects of histochemical and molecular changes of the human pituitary adenomas. The article outlines individual tumor groups with general, specific and molecular findings. The discussion further extends to the unusual adenomas or carcinomas. The description in this article are pertinent not only for the practicing pathologists who are in the position of making proper diagnosis, but also for the pituitary research scientists who engage in solving basic problems in pituitary neoplasms by histochemistry and molecular biology.