Novel pathway for somatostatin analogs in patients with acromegaly

A Novel Mutation of Aryl Hydrocarbon Receptor Interacting Protein Gene Associated with Familial Isolated Pituitary Adenoma Mediates Tumor Invasion and Growth Hormone Hypersecretion

BACKGROUND

Germline mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene were identified in nearly 20% of families with familial isolated pituitary adenoma. Some variants of AIP have been confirmed to induce tumor cell proliferation and invasiveness; however, the mechanism is still unclear.

METHODS

A novel missense mutation (c.512C>T, p.T171I) was discovered in 3 patients from a Chinese family with familial isolated pituitary adenoma. In silico and multiplex ligation-dependent probe amplification analysis predicted the mutation to be pathogenic. GH3 and 293FT cell lines were used to verify the variant's effect on cell proliferation (Cell Counting Kit-8), invasiveness (Transwell) and growth hormone (GH) secretion (enzyme-linked immunosorbent assay) by transfection with different vectors: control, blank vector, wild-type AIP, p.T171I variant (experimental group), p.Q315* variant, and AIP small interfering RNA. Furthermore, Zac1, Sstr2, interleukin (IL)-6, and Stat3/phosphorylation-Stat3 expression (reverse transcription polymerase chain reaction, Western blot) in each group was also evaluated.

RESULTS

The experimental group, p.Q315* variant group, and AIP small interfering RNA-overexpressing group promoted cell proliferation at 24 and 48 hours, respectively (compared with the control group; P < 0.01 for both). Similarly, the cells in the experimental group manifested more invasion and GH secretion compared with the control group (P < 0.01 and P < 0.05, respectively). Furthermore, the experimental group cells expressed less Sstr2 (a prerequisite for the responsiveness to somatostatin analogues) and Zac1 (tumor suppressor gene), but more IL-6 and phosphorylated-Stat3 (GH-secretion related).

CONCLUSIONS

The novel AIP mutation c.512C>T (p.T171I) is a pathogenic variant that promoted cell proliferation, invasiveness, and GH secretion through regulation of Sstr2, Zac1, and IL-6/phosphorylated-Stat3 expression.

Impact of preoperative pasireotide therapy on invasive octreotide-resistant acromegaly

A 43-year-old woman with an 8-year history of diabetes, hypertension, and dyslipidemia presented with amenorrhea and convulsion. Her MRI scan revealed a 3.5-cm T2-hyperintense pituitary macroadenoma with suprasellar extension to the frontal lobe and bilateral cavernous sinus invasion. Her serum levels of GH and insulin-like growth factor-I (IGF-I) were elevated to 9.08 ng/mL (normal range: <2.1 ng/mL) and 1,000 ng/mL (normal range: 90-233 ng/mL, SD score +10.6), respectively. Bromocriptine insufficiently suppressed her GH levels, while octreotide paradoxically increased her GH levels. Together with her characteristic features, she was diagnosed with acromegaly caused by an invasive GH-producing pituitary macroadenoma. As performing a one-stage operation would have been extremely difficult, she was first treated with pasireotide long-acting release (40 mg monthly) for 5 months followed by a successful transsphenoidal surgery. One month after the first injection, biochemical control was achieved (IGF-I, 220 ng/mL; GH, 1.26 ng/mL), and tumor shrinkage of approximately 50% was observed. The resected tumor was histologically diagnosed as a sparsely granulated somatotroph adenoma, with higher expression of somatostatin receptor subtype 5 (SSTR5) than that of SSTR2A. The germline aryl hydrocarbon receptor interacting protein (AIP) mutation was negative, and several tumor cells were weakly immunoreactive for AIP. Despite the presence of a residual tumor postoperatively, biochemical control was achieved 6 months after the final injection of pasireotide. In conclusion, this case suggests that pasireotide may be an option for preoperative first-line therapy in invasive and octreotide-resistant sparsely granulated somatotroph adenomas.

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.

Giant pituitary adenoma: histological types, clinical features and therapeutic approaches

Giant pituitary adenomas comprise about 6-10% of all pituitary tumors. They are mostly clinically non-functioning adenomas and occur predominantly in males. The presenting symptoms are usually secondary to compression of neighboring structures, but also due to partial or total hypopituitarism. Functioning adenomas give rise to specific symptoms of hormonal hypersecretion. The use of dopamine agonists is considered a first-line treatment in patients with giant macroprolactinomas. Somatostatin analogs can also be used as primary treatment in cases of growth hormone and thyrotropin producing giant adenomas, although remission of the disease is not achieved in the vast majority of these patients. Neurosurgical treatment, either through transsphenoidal or transcranial surgery, continues to be the treatment of choice in the majority of patients with giant pituitary adenomas. The intrinsic complexity of these tumors requires the use of different therapies in a combined or sequential way. A multimodal approach and a therapeutic strategy involving a multidisciplinary team of expert professionals form the basis of the therapeutic success in these patients.

Germline mutations of aryl hydrocarbon receptor-interacting protein (AIP) gene and somatostatin receptor 1-5 and AIP immunostaining in patients with sporadic acromegaly with poor versus good response to somatostatin analogues

OBJECTIVE

To determine aryl hydrocarbon interacting protein (AIP) gene variations and AIP and somatostatin receptor (SSTR) 1-5 immunostaining in patients with apparently sporadic acromegaly with poor versus good response to somatostatin analogues (SRLs).

METHODS

A total of 94 patients (66 with poor and 28 with good response to SRLs) were screened for the AIP gene variations using Sanger sequencing. Immunostaining was performed in 60 tumors.

RESULTS

Several variations, albeit some with undetermined significance, were detected, especially in poor responder patients. The prevalence of AIP mutation was 2.1% in the whole group and 1.5% in patients with poor response to SRLs. AIP, SSTR2A, and SSTR2B immunostainings were decreased in patients with poor response (p < 0.05 for all), and other SSTRs did not differ between the groups (p > 0.05 for all). Patients with low AIP had decreased levels of SSTR2A and SSTR3 (p < 0.05 for all). AIP and SSTR2A immunostainings were positively correlated to the treatment response and age at diagnosis was negatively correlated (p < 0.05 for all). In poor responder patients with high SSTR2A immunostaining, SSTR2B immunostaining and preoperative tumor size were positively and negatively correlated, respectively, to SRL response (p < 0.05 for all).

CONCLUSIONS

Lack of response to SRLs does not necessarily increase the risk of harboring AIP mutations. The finding of decreased AIP, SSTR2A, and SSTR2B immunostaining in patients with poor response to SRLs and decreased SSTR2A and SSTR3 level in those with low AIP immunostaining suggests a possible interaction between AIP and some SSTR subtypes that might alter SRL sensitivity.

Molecular evidence and clinical importance of β-arrestins expression in patients with acromegaly

β-arrestins seem to have a role in endocytosis and desensitization of somatostatin receptor subtype 2 (sst2) and could be associated with the responsiveness to somatostatin receptor ligands (SRL) in patients with acromegaly. To investigate the in vivo correlation between β-arrestins 1 and 2 with sst2, sst5 and dopamine receptor subtype 2 (D2) expressions, and the association of β-arrestins with response to first-generation SRL and invasiveness in somatotropinomas. β-arrestins 1 and 2, sst2, sst5 and D2 mRNA expressions were evaluated by quantitative real-time RT-PCR on tumoral tissue of 96 patients. Moreover, sst2 and sst5 protein expressions were also evaluated in 40 somatotropinomas by immunohistochemistry. Response to SRL, defined as GH <1 μg/l and normal IGF-I levels, was assessed in 40 patients. The Knosp-Steiner criteria were used to define invasiveness. Median β-arrestin 1, β-arrestin 2, sst2, sst5 and D2 mRNA copy numbers were 478; 9375; 731; 156; and 3989, respectively. There was a positive correlation between β-arrestins 1 and 2 (R = 0.444, P < 0.001). However, no correlation between β-arrestins and sst2, sst5 (mRNA and protein levels) or D2 was found. No association was found between β-arrestins expression and SRL responsiveness or tumour invasiveness. Although previous data suggest a putative correlation between β-arrestins and sst2, our data clearly indicated that no association existed between β-arrestins and sst2, sst5 or D2 expression, nor with response to SRL or tumour invasiveness. Therefore, further studies are required to clarify whether β-arrestins have a role in the response to treatment with SRL in acromegaly.

Cyclic 3',5'-adenosine monophosphate (cAMP) signaling in the anterior pituitary gland in health and disease

The cyclic 3',5'-adenosine monophosphate (cAMP) was the first among the so-called "second messengers" to be described. It is conserved in most organisms and functions as a signal transducer by mediating the intracellular effects of multiple hormones and neurotransmitters. In this review, we first delineate how different members of the cAMP pathway ensure its correct compartmentalization and activity, mediate the terminal intracellular effects, and allow the crosstalk with other signaling pathways. We then focus on the pituitary gland, where cAMP exerts a crucial function by controlling the responsiveness of the cells to hypothalamic hormones, neurotransmitters and peripheral factors. We discuss the most relevant physiological functions mediated by cAMP in the different pituitary cell types, and summarize the defects affecting this pathway that have been reported in the literature. We finally discuss how a deregulated cAMP pathway is involved in the pathogenesis of pituitary disorders and how it affects the response to therapy.

MANAGEMENT OF ENDOCRINE DISEASE: Personalized medicine in the treatment of acromegaly

Acromegaly is associated with high morbidity and elevated mortality when not adequately treated. Surgery is the first-line treatment for most patients as it is the only one that can lead to immediate cure. In patients who are not cured by surgery, treatment is currently based on a trial-and-error approach. First-generation somatostatin receptor ligands (fg-SRL) are initiated for most patients, although approximately 25% of patients present resistance to this drug class. Some biomarkers of treatment outcome are described in the literature, with the aim of categorizing patients into different groups to individualize their treatments using a personalized approach. In this review, we will discuss the current status of precision medicine for the treatment of acromegaly and future perspectives on the use of personalized medicine for this purpose.

AIP and the somatostatin system in pituitary tumours

Classic somatostatin analogues aimed at somatostatin receptor type 2, such as octreotide and lanreotide, represent the mainstay of medical treatment for acromegaly. These agents have the potential to decrease hormone secretion and reduce tumour size. Patients with a germline mutation in the aryl hydrocarbon receptor-interacting protein gene, AIP, develop young-onset acromegaly, poorly responsive to pharmacological therapy. In this review, we summarise the most recent studies on AIP-related pituitary adenomas, paying special attention to the causes of somatostatin resistance; the somatostatin receptor profile including type 2, type 5 and truncated variants; the role of G proteins in this pathology; the use of first and second generation somatostatin analogues; and the role of ZAC1, a zinc-finger protein with expression linked to AIP in somatotrophinoma models and acting as a key mediator of octreotide response.

Suppression of Extrapancreatic Glucagon by Octreotide May Reduce the Fasting and Postprandial Glucose Levels in a Diabetic Patient after Total Pancreatectomy

A 52-year-old woman was treated with sensor augmented pump therapy after undergoing total pancreatectomy for a nonfunctional pancreatic neuroendocrine tumor (NET). The secretion of both endogenous insulin and pancreatic glucagon were completely depleted. Octreotide long acting repeatable (Oct-LAR) was administered for the treatment of liver metastasis of NET. Both the fasting and postprandial glucagon levels decreased immediately after the administration of Oct-LAR. In a continuous glucose monitoring analysis, episodes of nocturnal hypoglycemia was found to increase and an improvement of postprandial hyperglycemia was observed. This case suggests that octreotide may reduce the glucose level in both the fasting and postprandial states, in part by the suppression of extrapancreatic glucagon.

Effects of environmental pollutants on signaling pathways in rat pituitary GH3 adenoma cells

An increased rate of acromegaly was reported in industrialized areas, suggesting an involvement of environmental pollutants in the pathogenesis and behavior of GH-secreting pituitary adenomas. Based on these premises, the aim of the study was to evaluate the effects of some widely diffused pollutants (i.e. benzene, BZ; bis(2-ethylhexyl) phthalate, DEHP and polychlorinated biphenyls, PCB) on growth hormone secretion, the somatostatin and estrogenic pathways, viability and proliferation of rat GH-producing pituitary adenoma (GH3) cells. All the pollutants induced a statistically significant increase in GH secretion and interfered with cell signaling. They all modulated the expression of SSTR2 and ZAC1, involved in the somatostatin signaling, and the expression of the transcription factor FOXA1, involved in the estrogen receptor signaling. Moreover, all the pollutants increased the expression of the CYP1A1, suggesting AHR pathway activation. None of the pollutants impacted on cell proliferation or viability. Present data demonstrate that exposure to different pollutants, used at in vivo relevant concentrations, plays an important role in the behavior of GH3 pituitary adenoma cells, by increasing GH secretion and modulating several cellular signaling pathways. These observations support a possible influence of different pollutants in vivo on the GH-adenoma aggressiveness and biological behavior.

Remarkable Shrinkage of a Growth Hormone (GH)-secreting Macroadenoma Induced by Somatostatin Analogue Administration: A Case Report and Literature Review

Acromegaly is caused by excessive growth hormone secretion, usually from pituitary adenomas. Somoatostatin analogues are widely used as primary or adjunctive therapy in the management of acromegaly. In this report, we present a case with remarkable shrinkage of a tumor after relatively short-term octreotide long-acting release (LAR) administration. During the 30-month follow-up after starting octreotide LAR, there was no recurrence of acromegaly with remarkable shrinkage of the tumor on pituitary magnetic resonance imaging. A literature review of the predictors for tumor shrinkage after the administration of somatostatin analogues in patients with acromegaly is also discussed in relation to this case.

Successful management of octreotide-insensitive thyrotropin-secreting pituitary adenoma with bromocriptine and surgery: A case report and literature review

RATIONALE

Case reports concerning the value of dopamine agonists in the treatment of patients with thyrotropin-secreting pituitary adenoma (TSHoma) are limited. Herein, we present a rare case of octreotide-insensitive TSHoma responding to bromocriptine therapy.

PATIENT CONCERNS

A 45-year-old Chinese man was admitted to Peking Union Medical College Hospital with marked clinical manifestations of hyperthyroidism.

DIAGNOSES

Thyroid function tests demonstrated elevated concentrations of free thyroid hormones in the presence of normal thyrotropin. Magnetic resonance imaging findings showed a pituitary microadenoma on the right side of the sellar region. Based on characteristic endocrine results and neuroimaging findings, the patient was diagnosed with TSHoma.

INTERVENTIONS

Most patients with TSHomas are significantly responsive to somatostatin analog treatment. However, our patient was orally administered with bromocriptine to normalize thyroid function as assessed by suppression tests conducted prior to surgery. A transsphenoidal surgery was performed by an experienced neurosurgeon for tumor removal.

OUTCOMES

The pituitary lesion was totally resected. Following the operation, the results of thyroid function tests were immediately within reference limits. During the follow-up, there was no residual or recurrent tumor.

LESSONS

Attention should be paid to the role of dopamine agonists such as bromocriptine and cabergoline as adjuvant therapy for TSHomas that are insensitive to traditional medical treatment by somatostatin analogs.

Efficacy and safety of long-acting pasireotide in Japanese patients with acromegaly or pituitary gigantism: results from a multicenter, open-label, randomized, phase 2 study

A multicenter, open-label, phase 2 study was conducted to investigate the efficacy and safety of long-acting pasireotide formulation in Japanese patients with acromegaly or pituitary gigantism. Medically naïve or inadequately controlled patients (on somatostatin analogues or dopamine agonists) were included. Primary end point was the proportion of all patients who achieved biochemical control (mean growth hormone [GH] levels<2.5μg/L and normalized insulin-like growth factor-1 [IGF-1]) at month 3. Thirty-three patients (acromegaly, n=32; pituitary gigantism, n=1) were enrolled and randomized 1:1:1 to receive open-label pasireotide 20mg, 40mg, or 60mg. The median age was 52 years (range, 31-79) and 20 patients were males. At month 3, 18.2% of patients (6/33; 90% confidence interval: 8.2%, 32.8%) had biochemical control (21.2% [7/33] when including a patient with mean GH<2.5μg/L and IGF-1< lower limit of normal). Reductions in the median GH and IGF-1 levels observed at month 3 were maintained up to month 12; the median percent change from baseline to month 12 in GH and IGF-1 levels were -74.71% and -59.33%, respectively. Twenty-nine patients completed the 12-month core phase, 1 withdrew consent, and 3 discontinued treatment due to adverse events (AEs; diabetes mellitus, hyperglycemia, liver function abnormality, n=1 each). Almost all patients (97%; 32/33) experienced AEs; the most common AEs were nasopharyngitis (48.5%), hyperglycemia (42.4%), diabetes mellitus (24.2%), constipation (18.2%), and hypoglycemia (15.2%). Serious AEs were reported in 7 patients with the most common being hyperglycemia (n=2). Long-acting pasireotide demonstrated clinically relevant efficacy and was well tolerated in Japanese patients with acromegaly or pituitary gigantism.

Genetic Aspects of Pituitary Adenomas

Although most of pituitary adenomas are benign, they may cause significant burden to patients. Sporadic adenomas represent the vast majority of the cases, where recognized somatic mutations (eg, GNAS or USP8), as well as altered gene-expression profile often affecting cell cycle proteins have been identified. More rarely, germline mutations predisposing to pituitary adenomas -as part of a syndrome (eg, MEN1 or Carney complex), or isolated to the pituitary (AIP or GPR101) can be identified. These alterations influence the biological behavior, clinical presentations and therapeutic responses, and their full understanding helps to provide appropriate care for these patients.

Role of Phosphodiesterases on the Function of Aryl Hydrocarbon Receptor-Interacting Protein (AIP) in the Pituitary Gland and on the Evaluation of AIP Gene Variants

Familial isolated pituitary adenoma (FIPA) is caused in about 20% of cases by loss-of-function germline mutations in the AIP gene. Patients harboring AIP mutations usually present with somatotropinomas resulting either in gigantism or young-onset acromegaly. AIP encodes for a co-chaperone protein endowed with tumor suppressor properties in somatotroph cells. Among other mechanisms proposed to explain this function, a regulatory effect over the 3',5'-cyclic adenosine monophosphate (cAMP) signaling pathway seems to play a prominent role. In this setting, the well-known interaction between AIP and 2 different isoforms of phosphodiesterases (PDEs), PDE2A3 and PDE4A5, is of particular interest. While the interaction with over-expressed AIP does not seem to affect PDE2A3 function, the reported effect on PDE4A5 is, in contrast, reduced enzymatic activity. In this review, we explore the possible implications of these molecular interactions for the function of somatotroph cells. In particular, we discuss how both PDEs and AIP could act as negative regulators of the cAMP pathway in the pituitary, probably both by shared and independent mechanisms. Moreover, we describe how the evaluation of the AIP-PDE4A5 interaction has proven to be a useful tool for testing AIP mutations, complementing other in silico, in vitro, and in vivo analyses. Improved assessment of the pathogenicity of AIP mutations is indeed paramount to provide adequate guidance for genetic counseling and clinical screening in AIP mutation carriers, which can lead to prospective diagnosis of pituitary adenomas.

Somatostatin receptor ligands in acromegaly: clinical response and factors predicting resistance

INTRODUCTION

Somatostatin (SST) receptor ligands (SRL), in particular those of first generation (Octreotide and Lanreotide), are widely used in medical treatment of acromegaly, but they assure biochemical control of disease (and the possibility of an improvement of clinical symptoms and tumor shrinkage), only in a subset of patients.

DISCUSSION

The mechanisms underlying the so called "SRL resistance" are various and involve in particular SST receptor expression and molecular pathways of signal transduction. Different predictors of SRL response have been reported, including clinical and biochemical features (gender, age, growth hormone and insulin-like growth factor-I levels at diagnosis), and tumor characteristic (both at preoperative magnetic resonance imaging study and histopathology) as well as expression of SST receptors. In some cases, only a "partial resistance" to SST can be detected, probably due to the presence of other impaired molecular mechanisms involved in signal transduction, which compromise specific pathways and not others. This may explain some cases of dissociated response between biochemical control and tumor shrinkage.

The genetic background of acromegaly

Acromegaly is caused by a somatotropinoma in the vast majority of the cases. These are monoclonal tumors that can occur sporadically or rarely in a familial setting. In the last few years, novel familial syndromes have been described and recent studies explored the landscape of somatic mutations in sporadic somatotropinomas. This short review concentrates on the current knowledge of the genetic basis of both familial and sporadic acromegaly.

Somatostatin receptor ligands in the treatment of acromegaly

First-generation somatostatin receptors ligands (SRL) are the mainstay in the medical treatment of acromegaly, however the percentage of patients controlled with these drugs significantly varies in the different studies. Many factors are involved in the resistance to SRL. In this review, we update the physiology of somatostatin and its receptors (sst), the use of SRL in the treatment of acromegaly and the factors involved in the response to these drugs. The SRL act through interaction with the sst, which up to now have been characterized as five subtypes. The first-generation SRL, octreotide and lanreotide, are considered sst2 specific and have biochemical response rates varying from 20 to 70%. Tumor volume reduction can be found in 36-75% of patients. Several factors may determine the response to these drugs, such as sst, AIP, E-cadherin, ZAC1, filamin A and β-arrestin expression in the somatotropinomas. In patients resistant to first-generation SRL, alternative medical treatment options include: SRL high dose regimens, SRL in combination with cabergoline or pegvisomant, or the use of pasireotide. Pasireotide is a next-generation SRL with a broader pattern of interaction with sst. In the light of the recent increase of treatment options in acromegaly and the deeper knowledge of the determinants of response to the current first-line therapy, a shift from a trial-and-error treatment to a personalized one could be possible.

Somatotroph-Specific Aip-Deficient Mice Display Pretumorigenic Alterations in Cell-Cycle Signaling

Patients with familial isolated pituitary adenoma are predisposed to pituitary adenomas, which in a subset of cases is due to germline inactivating mutations of the aryl hydrocarbon receptor–interacting protein (AIP) gene. Using Cre/lox and Flp/Frt technology, a conditional mouse model was generated to examine the loss of the mouse homolog, Aip, in pituitary somatotrophs. By 40 weeks of age, >80% of somatotroph specific Aip knockout mice develop growth hormone (GH) secreting adenomas. The formation of adenomas results in physiologic effects recapitulating the human syndrome of acromegaly, including increased body size, elevated serum GH and insulin-like growth factor 1 levels, and glucose intolerance. The pretumorigenic Aip-deficient somatotrophs secrete excess GH and exhibit pathologic hyperplasia associated with cytosolic compartmentalization of the cyclin-dependent kinase (CDK) inhibitor p27^kip1 and perinuclear accentuation of CDK-4. Following tumor formation, the Aip-deficient somatotrophs display reduced expression of somatostatin receptor subtype 5 with impaired response to octreotide. The delayed tumor emergence, even with loss of both copies of Aip, implies that additional somatic events are required for adenoma formation. These findings suggest that pituitary hyperplasia precedes adenomatous transformation in somatotroph-specific Aip-deficient mice and reveal potential mechanisms involved in the pretumorigenic state that ultimately contribute to transformation.

Expression of Somatostatin Receptor 2 in Somatotropinoma Correlated with the Short-Term Efficacy of Somatostatin Analogues

The expression of somatostatin receptor subtypes (SSTRs) in pituitary growth hormone- (GH-) secreting adenomas may predict the response to somatostatin analogues (SSA). Our aim was to evaluate the value of the immunohistochemical (IHC) scores of 2 subtypes, SSTR2 and SSTR5, in predicting the short-term efficacy of SSA therapy in patients with active acromegaly. Ninety-three newly diagnosed acromegalic patients were included in our study. These patients were categorized into either a SSA-pretreated group (SA, n = 63) or a direct-surgery group (DS, n = 30), depending on whether or not presurgical SSA treatment was received. IHC analysis, using a 12-grade scoring system, with rabbit monoclonal antibodies against SSTR2 and SSTR5, was performed on all adenoma tissues. The reduction of GH, IGF-1, and tumor size after treatment with SSA for 3 months was measured. Compared with that in the DS group, SSTR2 expression was lower in the SA group. Additionally, in the SA group, SSTR2 expression was positively correlated with the reduction of IGF-1 and tumor volume. However, there was no correlation between the SSTR5 score and the efficacy of SSA. In conclusion, the protein expression of SSTR2, but not of SSTR5, is a valuable indicator in predicting biochemical and tumor size response to short-term SSA treatment in acromegalic patients.

Somatostatin analogues in acromegaly and gastroenteropancreatic neuroendocrine tumours: past, present and future

Acromegaly is a hormonal disorder that arises when the pituitary gland secretes excess growth hormone (GH), which in turn stimulates a concomitant increase in serum insulin-like growth factor 1 (IGF-1) levels. Gastroenteropancreatic neuroendocrine tumours (GEP-NET) constitute a heterogeneous group of tumours that can secrete serotonin and a variety of peptide hormones that may cause characteristic symptoms known as carcinoid syndrome or other symptoms and hormonal hypersecretion syndromes depending on the tumour's site of origin. Current medical therapy for the treatment of acromegaly and GEP-NET involves the administration of somatostatin analogues that effectively suppress excess hormone secretion. After its discovery in 1979, octreotide became the first synthetic biologically stable somatostatin analogue with a short-acting formulation of octreotide introduced into clinical practice in the late 1980s. Lanreotide, another somatostatin analogue, became available in the mid-1990s initially as a prolonged-release formulation administered every 10 or 14 days. Long-acting release formulations of both octreotide (Sandostatin LAR and Novartis) and lanreotide (Somatuline Autogel, Ipsen), based on microparticle and nanoparticle drug-delivery technologies, respectively, were later developed, which allowed for once-monthly administration and improved convenience. First-generation somatostatin analogues remain one of the cornerstones of medical therapy in the management of pituitary and GEP-NET hormone hypersecretion, with octreotide having the longest established efficacy and safety profile of the somatostatin analogue class. More recently, pasireotide (Signifor), a next-generation multireceptor-targeted somatostatin analogue, has emerged as an alternative therapeutic option for the treatment of acromegaly. This review summarizes the development and clinical success of somatostatin analogues.

Genetic and clinical characteristics of Japanese patients with sporadic somatotropinoma

Most of acromegaly is caused by a sporadic somatotropinoma and a couple of novel gene mutations responsible for somatotropinoma have recently been reported. To determine the cause of sporadic somatotropinoma in Japanese patients, we analyzed 61 consecutive Japanese patients with somatotropinoma without apparent family history. Comprehensive genetic analysis revealed that 31 patients harbored guanine nucleotide-binding protein, alpha stimulating (GNAS) mutations (50.8%) and three patients harbored aryl hydrocarbon receptor interacting protein (AIP) mutations (4.9%). No patients had G protein-coupled receptor 101 (GPR101) mutations. The patients in this cohort study were categorized into three groups of AIP, GNAS, and others and compared the clinical characteristics. The AIP group exhibited significantly younger age at diagnosis, larger tumor, and higher nadir GH during oral glucose tolerance test. In all patients with AIP mutation, macro- and invasive tumor was detected and repetitive surgery or postoperative medical therapy was needed. One case showed a refractory response to postoperative somatostatin analogue (SSA) but after the addition of cabergoline as combined therapy, serum IGF-I levels were controlled. The other case showed a modest response to SSA and the switching to cabergoline monotherapy was also effective. These data suggest that although resistance to SSA has been reported in patients with AIP mutations, the response to dopamine agonist (DA) may be retained. In conclusion, the cause of sporadic somatotropinoma in Japanese patients was comparable with the previous reports in Caucasians, patients with AIP mutations showed unique clinical characteristics, and DA may be a therapeutic option for patients with AIP mutations.

The value of an acute octreotide suppression test in predicting short-term efficacy of somatostatin analogues in acromegaly

Predicting the efficacy of long-acting somatostatin analogues (SSA) remains a challenge. We aim to quantitatively evaluate the predictive value of the octreotide suppression test (OST) in short-term efficacy of SSA in active acromegaly. Sixty-seven newly diagnosed acromegaly patients were assessed with OST. Subsequently, all patients were treated with long-acting SSA for 3 months, followed by reassessment. Nine parameters were tested, including GH_n (the nadir GH during OST), ΔGH1 (= [GH_0h-GH_n]/GH_0h, GH_0h was the baseline GH during OST), ΔGH2 (= [GH_m-GH_n]/GH_m, GH_m was the mean GH on day curve), AUC_(0-6h) (the GH area under the curve during OST) , ΔAUC1 (= [GH_0h-AUC_(0-6h)]/GH_0h), ΔAUC2 (=[GH_m-AUC_(0-6h)]/GH_m), AUC_(m-6h) (the GH AUC during OST where GH_m was used instead of GH_0h), ΔAUC1' (=[GH_0h-AUC_(m-6h)]/GH_0h) and ΔAUC2' (=[GH_m-AUC_(m-6h)]/GH_m). The Youden indices were calculated to determine the optimal cutoffs to predict the short-term efficacy of SSA. ΔGH2 more than 86.83%, ΔAUC2 more than -57.48% and ΔAUC2' more than -57.98% provided the best predictors of a good GH response (sensitivity 93.8%, specificity 85.7%). ΔGH2 more than 90.51% provided the best predictor of a good tumor size response (sensitivity 84.8%, specificity 87.5%). The percentage fall of GH_n (ΔGH) was a better predictive parameter than GH_n. OST showed higher efficiency in predicting the efficacy of octreotide LAR than lanreotide SR. In conclusion, OST is a valid tool to predict both GH and tumor size response to short-term efficacy of SSA in acromegaly, especially for octreotide LAR. GH_m is better to be used as basal GH than GH₀ during OST.

Anatomy, Physiology, and Laboratory Evaluation of the Pituitary Gland

The pituitary gland functions prominently in the control of most endocrine systems in the body. Diverse processes such as metabolism, growth, reproduction, and water balance are tightly regulated by the pituitary in conjunction with the hypothalamus and various downstream endocrine organs. Benign tumors of the pituitary gland are the primary cause of pituitary pathology and can result in inappropriate secretion of pituitary hormones or loss of pituitary function. First-line management of clinically significant tumors often involves surgical resection. Understanding of normal pituitary physiology and basic testing strategies to assess for pituitary dysfunction should be familiar to any skull base surgeon.

Predictive value of T2 relative signal intensity for response to somatostatin analogs in newly diagnosed acromegaly

INTRODUCTION

The difficulty of predicting the efficacy of somatostatin analogs (SSA) is not fully resolved. Here, we quantitatively evaluated the predictive value of relative signal intensity (rSI) on T1- and T2-weighted magnetic resonance imaging (MRI) for the short-term efficacy (3 months) of SSA therapy in patients with active acromegaly and assessed the correlation between MRI rSI and expression of somatostatin receptors (SSTR).

METHODS

This was a retrospective review of prospectively recorded data. Ninety-two newly diagnosed patients (37 males and 55 females) with active acromegaly were recruited. All patients were treated with pre-surgical SSA, followed by reassessment and transspenoidal surgery. rSI values were generated by calculating the ratio of SI in the tumor to the SI of normal frontal white matter. The Youden indices were calculated to determine the optimal cutoff of rSI to determine the efficacy of SSA. The correlation between rSI and expression of SSTR2/5 was analyzed by the Spearman rank correlation coefficient.

RESULTS

T2 rSI was strongly correlated with biochemical sensitivity to SSA. The cutoff value of T2 rSI to distinguish biochemical sensitivity was 1.205, with a positive predictive value (PPV) of 81.5 % and a negative predictive value (NPV) of 77.3 %. No correlation was found between MRI and tumor size sensitivity. Moreover, T2 rSI was negatively correlated with the expression of SSTR5.

CONCLUSION

T2 rSI correlates with the expression of SSTR5 and quantitatively predicts the biochemical efficacy of SSA in acromegaly.

Advancing Treatment of Pituitary Adenomas through Targeted Molecular Therapies: The Acromegaly and Cushing Disease Paradigms

The current treatment of pituitary adenomas requires a balance of conservative management, surgical resection, and in select tumor types, molecular therapy. Acromegaly treatment is an evolving field where our understanding of molecular targets and drug therapies has improved treatment options for patients with excess growth hormone levels. We highlight the use of molecular therapies in this disease process and advances in this field, which may represent a paradigm shift for the future of pituitary adenoma treatment.

Interpreting biochemical control response rates with first-generation somatostatin analogues in acromegaly

CONTEXT

The somatostatin analogues octreotide LAR and lanreotide Autogel have been evaluated for the treatment of acromegaly in numerous clinical trials, with considerable heterogeneity in reported biochemical response rates. This review examines and attempts to account for these differences in response rates reported in the literature.

EVIDENCE ACQUISITION

PubMed was searched for English-language studies of a minimum duration of 24 weeks that evaluated ≥10 patients with acromegaly treated with octreotide LAR or lanreotide Autogel from 1990 to March 2015 and reported GH and/or IGF-1 data as the primary objective of the study.

EVIDENCE SYNTHESIS

Of the 190 clinical trials found, 18 octreotide LAR and 15 lanreotide Autogel studies fulfilled the criteria for analysis. It is evident from the protocols of these studies that multiple factors are capable of impacting on reported response rates. Prospective studies reporting an intention-to-treat analysis that evaluated medically naïve patients and used the composite endpoint of both GH and IGF-1 control were associated with lower response rates. The use of non-composite biochemical control endpoints, heterogeneous patient populations, analyses that exclude treatment non-responders, assay variability and prior responsiveness to medical therapy are just a few of the factors identified that likely contribute to higher success rates.

CONCLUSIONS

The wide range of reported response rates with somatostatin analogues may be confusing and could lead to misinterpretation by both the patient and the physician in certain situations. Understanding the factors that potentially drive the variation in response rates should allow clinicians to better gauge treatment expectations in specific patients.

Low beta-arrestin expression correlates with the responsiveness to long-term somatostatin analog treatment in acromegaly

OBJECTIVE

The high expression of somatostatin receptor subtype 2 (SSTR2 also known as sst2) usually present in growth hormone (GH)-secreting adenomas is the rationale for therapy with somatostatin analogs (SSAs) in acromegaly. Although SSTR2 expression is a good predictor for biochemical response to SSA treatment, we still face tumors resistant to SSAs despite high SSTR2 expression. Recently, beta-arrestins (β-arrestins) have been highlighted as key players in the regulation of SSTR2 function.

DESIGN

To investigate whether β-arrestins might be useful predictors of responsiveness to long-term SSA treatment in acromegaly, we retrospectively evaluated 35 patients with acromegaly who underwent adenomectomy in two referral centers in The Netherlands.

METHODS

β-arrestin mRNA levels were evaluated in adenoma samples, together with SSTR2 (and SSTR5) mRNA and protein expression. Biochemical response to long-term SSA treatment (median 12 months) was assessed in 32 patients.

RESULTS

β-arrestin 1 and 2 mRNA was significantly lower in adenoma tissues from patients who achieved insulin-like growth factor 1 normalization (P = 0.024 and P = 0.047) and complete biochemical control (P = 0.047 and P = 0.039). The SSTR2 mRNA was higher in SSA responder patients compared with the resistant ones (P = 0.026). This difference was more evident when analyzing the SSTR2/β-arrestin 1 and SSTR2/β-arrestin 2 ratio (P = 0.011 and P = 0.010). β-arrestin 1 and 2 expression showed a significant trend of higher median values from full responders, partial responders to resistant patients (P = 0.045 and P = 0.021, respectively). Interestingly, SSTR2 protein expression showed a strong inverse correlation with both β-arrestin 1 and 2 mRNA (ρ = -0.69, P = 0.0011 and ρ = -0.67, P = 0.0016).

CONCLUSIONS

Low β-arrestin expression and high SSTR2/β-arrestin ratio correlate with the responsiveness to long-term treatment with SSAs in patients with acromegaly.

Genetic Predictors of Response to Different Medical Therapies in Acromegaly

In the era of predictive medicine, management of diseases is evolving into a more personal and individualized approach, as more data are available regarding clinical, biochemical, radiological, molecular, histopathological, and genetic aspects. In the particular setting of acromegaly, which is a rare, chronic, debilitating, and disfiguring disease, an optimized approach deems even more necessary, especially because of an associated increased morbidity and mortality, the impact on patients' quality of life, and the increased cost of frequently necessary life-long treatments. In this paper, we review the available studies that address potential genetic influences on acromegaly, their role in the outcome, and response to treatments, as well as their contribution to the risk of developing side effects. We focus mainly on pharmacogenetic factors involved during treatment with dopamine agonists, somatostatin analogs, and pegvisomant. Specifically, mutations in dopamine receptors, somatostatin receptors, growth hormone receptors, and metabolic pathways involved in growth hormone action; polymorphisms in the insulin-like growth factor and the insulin-like growth factor binding proteins; and polymorphisms in other genes that may determine differences in the frequency of developing adverse events.

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.

Combining Cadherin Expression with Molecular Markers Discriminates Invasiveness in Growth Hormone and Prolactin Pituitary Adenomas

Although growth hormone (GH)- and prolactin (PRL)-secreting pituitary adenomas are considered benign, in many patients, tumour growth and/or invasion constitute a particular challenge. In other tumours, progression relies in part on dysfunction of intercellular adhesion mediated by the large family of cadherins. In the present study, we have explored the contribution of cadherins in GH and PRL adenoma pathogenesis, and evaluated whether this class of adherence molecules was related to tumour invasiveness. We have first established, by quantitative polymerase chain reaction and immunohistochemistry, the expression profile of classical cadherins in the normal human pituitary gland. We show that the cadherin repertoire is restricted and cell-type specific. Somatotrophs and lactotrophs express mainly E-cadherin and cadherin 18, whereas N-cadherin is present in the other endocrine cell types. This repertoire undergoes major differential modification in GH and PRL tumours: E-cadherin is significantly reduced in invasive GH adenomas, and this loss is associated with a cytoplasmic relocalisation of cadherin 18 and catenins. In invasive prolactinomas, E-cadherin distribution is altered and is accompanied by a mislocalisation of cadherin 18, β-catenin and p120 catenin. Strikingly, de novo expression of N-cadherin is present in a subset of adenomas and cells exhibit a mesenchymal phenotype exclusively in invasive tumours. Binary tree analysis, performed by combining the cadherin repertoire with the expression of a subset of known molecular markers, shows that cadherin/catenin complexes play a significant role in discrimination of tumour invasion.

Pasireotide: a novel treatment for patients with acromegaly

Morbidity and mortality rates in patients with active acromegaly are higher than the general population. Adequate biochemical control restores mortality to normal rates. Now, medical therapy has an increasingly important role in the treatment of patients with acromegaly. Somatostatin receptor ligands (SRLs) are considered the standard medical therapy, either after surgery or as a first-line therapy when surgery is deemed ineffective or is contraindicated. Overall, octreotide and lanreotide are first-generation SRLs and are effective in ~20%-70% of patients. Pegvisomant, a growth hormone receptor antagonist, controls insulin-like growth factor 1 in 65%-90% of cases. Consequently, a subset of patients (nonresponders) requires other treatment options. Drug combination therapy offers the potential for more efficacious disease control. However, the development of new medical therapies remains essential. Here, emphasis is placed on new medical therapies to control acromegaly. There is a focus on pasireotide long-acting release (LAR) (Signifor LAR®), which was approved in 2014 by the US Food and Drug Administration and the European Medicine Agency for the treatment of acromegaly. Pasireotide LAR is a long-acting somatostatin multireceptor ligand. In a Phase III clinical trial in patients with acromegaly (naïve to medical therapy or uncontrolled on a maximum dose of first-generation SRLs), 40 and 60 mg of intramuscular pasireotide LAR achieved better biochemical disease control than octreotide LAR, and tumor shrinkage was noted in both pasireotide groups. Pasireotide LAR tolerability was similar to other SRLs, except for a greater frequency and degree of hyperglycemia and diabetes mellitus. Baseline glucose may predict hyperglycemia occurrence after treatment, and careful monitoring of glycemic status and appropriate treatment is required. A precise definition of patients with acromegaly who will derive the greatest therapeutic benefit from pasireotide LAR remains to be established. Lastly, novel therapies and new potential delivery modalities (oral octreotide) are summarized.

Clinical importance of achieving biochemical control with medical therapy in adult patients with acromegaly

In acromegaly, achieving biochemical control (growth hormone [GH] level <1.0 ng/mL and age- and sex-normalized levels of insulin-like growth factor 1 [IGF-1]) through timely diagnosis and appropriate treatment provides an opportunity to improve patient outcomes. Diagnosis of acromegaly is challenging because it is rooted in observing subtle clinical manifestations, and it is typical for acromegaly to evolve for up to 10 years before it is recognized. This results in chronic exposure to elevated levels of GH and IGF-1 and delay in patients receiving appropriate treatment, which consequently increases mortality risk. In this review, the clinical impact of elevated GH and IGF-1 levels, the effectiveness of current therapies, and the potential role of novel treatments for acromegaly will be discussed. Clinical burden of acromegaly and benefits associated with management of GH and IGF-1 levels will be reviewed. Major treatment paradigms in acromegaly include surgery, medical therapy, and radiotherapy. With medical therapies, such as somatostatin analogs, dopamine agonists, and GH receptor antagonists, a substantial proportion of patients achieve reduced GH and normalized IGF-1 levels. In addition, signs and symptoms, quality of life, and comorbidities have also been reported to improve to varying degrees in patients who achieve biochemical control. Currently, there are several innovative therapies in development to improve patient outcomes, patient use, and access. Timely biochemical control of acromegaly ensures that the patient can ultimately improve morbidity and mortality from this disease and its extensive consequences.

Differential somatostatin receptor (SSTR) 1-5 expression and downstream effectors in histologic subtypes of growth hormone pituitary tumors

PURPOSE

The aim of this study was to examine whether differential expression of somatostatin receptors (SSTR) 1-5 and downstream effectors are different in densely (DG) and sparsely (SG) granulated histological growth hormone (GH) pituitary tumor subtypes.

METHODS

The study included 33 acromegalic patients with 23 DG and 10 SG tumors. SSTR1-5 were measured by qPCR and immunoblotting. Signaling candidates downstream of SSTR2 were also assessed.

RESULTS

SSTR2 mRNA and protein levels were significantly higher in DG compared to SG tumors. Downstream of SSTR2, p27(kip1) was decreased (2.6-fold) in SG compared to DG tumors, suggesting a potential mechanism of SSA resistance in SG tumors with intact SSTR2 expression. Re-expression of E-cadherin in GH pituitary cell increased p27(kip1) levels.

CONCLUSIONS

Histological subtyping correlated with SSTR2, E cadherin and p27(kip) protein levels and these may serve as useful biomarkers in GH tumors to predict behavior and response to therapy with SSA.

Impact of gsp mutations in somatotroph pituitary adenomas on growth hormone response to somatostatin analogs: a meta-analysis

OBJECTIVE

Somatic mutations in the GNAS1 gene, which encodes the alpha-subunit of G stimulatory proteins (gsp), are frequently detected in somatotroph pituitary tumors and have been associated to specific clinical and histopathological characteristics. However, the question whether the presence of a somatic gsp mutation affects the response to somatostatin analog treatment remains unresolved.

DESIGN

Following a literature search, we performed a meta-analysis, including 8 eligible studies, in order to estimate the effect of gsp mutation on the percent reduction of growth hormone (GH) levels during an acute octreotide suppression test (OST). A total of 310 patients with acromegaly [126 gsp (+) and 184 gsp (-)] were included in the analysis.

RESULTS

The presence of the gsp mutation was related with a greater reduction in GH levels on OST [Weighted Mean Difference (WMD): 9.08 % (95 % CI, 2.73, 15.42); p = 0.005; random effects model]. There was significant heterogeneity for this effect estimate (I(2) = 58 %, p value for heterogeneity = 0.02). A sensitivity analysis after exclusion of a study with different methodology of OST provided similar estimates [WMD: 6.93 % (95 % CI, 1.40, 12.46); p = 0.01], albeit with no significant heterogeneity (I(2) = 35 %, p value for heterogeneity = 0.16).

CONCLUSIONS

The present meta-analysis suggests a role for gsp mutation as a prognostic factor of treatment response to somatostatin analogs.

Truncated somatostatin receptor 5 may modulate therapy response to somatostatin analogues--Observations in two patients with acromegaly and severe headache

BACKGROUND

Somatotropinomas have unique "fingerprints" of somatostatin receptor (sst) expression, which are targets in treatment of acromegaly with somatostatin analogues (SSAs). However, a significant expression of sst is not always related to the biochemical response to SSAs. Headache is a common complaint in acromegaly and considered a clinical marker of disease activity. SSAs are reported to have an own analgesic effect, but the sst involved are unknown.

PATIENTS AND METHODS

We investigated sst expression in two acromegalic patients with severe headache and no biochemical effects of octreotide, but a good response to pasireotide. We searched the literature for determinants of biochemical and analgesic effects of SSAs in somatotropinomas.

RESULTS

Case 1 had no biochemical or analgesic effects of octreotide, a semi-selective SSA, but a rapid and significant effect of pasireotide, a pan-SSA. Case 2 demonstrated discordance between analgesic and biochemical effects of octreotide, in that headache disappeared, but without biochemical improvement. In contrast, pasireotide normalized insulin-like growth factor 1. Both adenomas were sparsely granulated and had strong membranous expressions of sst2a in 50-75% and sst5 in 75-100% of tumor cells. The truncated sst5 variant TMD4 (sst5TMD4) showed expression in 20-57% of tumor cells.

CONCLUSIONS

A poor biochemical response to octreotide may be associated with tumor expression of a truncated sst5 variant, despite abundant sst2a expression, suggesting an influence from variant sst5 on common sst signaling pathways. Furthermore, unrelated analgesic and biochemical effects of SSAs supported a complex pathogenesis of acromegaly-associated headache. Finally, assessment of truncated sst5 in addition to full length sst could be important for a choice of postoperative SSA treatment in somatotropinomas.

Update on prognostic factors in acromegaly: Is a risk score possible?

Certain clinical conditions and markers have recently been demonstrated to modify the natural history of acromegaly in affected patients. Thus, some clinical, histological, radiological and molecular factors are associated with more aggressive pituitary tumors that have higher biochemical activity, higher tumor volumes and decreased tumoral and biochemical responses to current therapies. However, these factors do not seem to have an equal influence on the prognosis of patients with acromegaly. We present a review of the factors that influence the clinical course of patients with acromegaly and propose a risk value for each factor that will allow prognostic scoring for affected patients by considering a combination of these factors.

Truncated somatostatin receptor variant sst5TMD4 confers aggressive features (proliferation, invasion and reduced octreotide response) to somatotropinomas

The GH/IGF1 response of somatotropinomas to somatostatin analogues (SSA) is associated with their pattern of somatostatin receptor (sst1-sst5) expression. Recently, we demonstrated that expression of a truncated sst5-variant (sst5TMD4) can influence the secretory response of somatotropinomas to SSA-therapy; however, its potential relationship with aggressive features (e.g. invasion/proliferation) is still unknown. Here, we show that sst5TMD4 is present in 50% of non-functioning pituitary-adenomas (NFPA) (n = 30) and 89% of somatotropinomas (n = 36), its expression levels being highest in somatotropinomas > > NFPAs > > > normal pituitaries (negligible expression; n = 8). In somatotropinomas, sst5TMD4 mRNA and protein levels correlated positively, and its expression was directly associated with tumor invasiveness (cavernous/sphenoid sinus), and inversely correlated with age and GH/IGF1 reduction after 3-6 months with octreotide-LAR therapy. GNAS+ somatotropinomas expressed lower sst5TMD4 levels. ROC analysis revealed sst5TMD4 expression as the only marker, within all sst-subtypes, capable to predict tumor invasiveness in somatotropinomas. sst5TMD4 overexpression increased cell viability in cultured somatotropinoma (n = 5). Hence, presence of sst5TMD4 associates with increased aggressive features and worse prognosis in somatotropinomas, thereby providing a potentially useful tool to refine somatotropinoma diagnosis, predict outcome of clinical response to SSA-therapy and develop new therapeutic targets.

Regulation of aryl hydrocarbon receptor interacting protein (AIP) protein expression by MiR-34a in sporadic somatotropinomas

INTRODUCTION

Patients with germline AIP mutations or low AIP protein expression have large, invasive somatotroph adenomas and poor response to somatostatin analogues (SSA).

METHODS

To study the mechanism of low AIP protein expression 31 sporadic somatotropinomas with low (n = 13) or high (n = 18) AIP protein expression were analyzed for expression of AIP messenger RNA (mRNA) and 11 microRNAs (miRNAs) predicted to bind the 3'UTR of AIP. Luciferase reporter assays of wild-type and deletion constructs of AIP-3'UTR were used to study the effect of the selected miRNAs in GH3 cells. Endogenous AIP protein and mRNA levels were measured after miRNA over- and underexpression in HEK293 and GH3 cells.

RESULTS

No significant difference was observed in AIP mRNA expression between tumors with low or high AIP protein expression suggesting post-transcriptional regulation. miR-34a was highly expressed in low AIP protein samples compared high AIP protein adenomas and miR-34a levels were inversely correlated with response to SSA therapy. miR-34a inhibited the luciferase-AIP-3'UTR construct, suggesting that miR-34a binds to AIP-3'UTR. Deletion mutants of the 3 different predicted binding sites in AIP-3'UTR identified the c.*6-30 site to be involved in miR-34a's activity. miR-34a overexpression in HEK293 and GH3 cells resulted in inhibition of endogenous AIP protein expression.

CONCLUSION

Low AIP protein expression is associated with high miR-34a expression. miR-34a can down-regulate AIP-protein but not RNA expression in vitro. miR-34a is a negative regulator of AIP-protein expression and could be responsible for the low AIP expression observed in somatotropinomas with an invasive phenotype and resistance to SSA.

Somatostatin receptor ligands and resistance to treatment in pituitary adenomas

Somatostatin (SST), an inhibitory polypeptide with two biologically active forms SST14 and SST28, inhibits GH, prolactin (PRL), TSH, and ACTH secretion in the anterior pituitary gland. SST also has an antiproliferative effect inducing cell cycle arrest and apoptosis. Such actions are mediated through five G-protein-coupled somatostatin receptors (SSTR): SSTR1-SSTR5. In GH-secreting adenomas, SSTR2 expression predominates, and somatostatin receptor ligands (SRLs; octreotide and lanreotide) directed to SSTR2 are presently the mainstays of medical therapy. However, about half of patients show incomplete biochemical remission, but the definition of resistance per se remains controversial. We summarize here the determinants of SRL resistance in acromegaly patients, including clinical, imaging features as well as molecular (mutations, SSTR variants, and polymorphisms), and histopathological (granulation pattern, and proteins and receptor expression) predictors. The role of SSTR5 may explain the partial responsiveness to SRLs in patients with adequate SSTR2 density in the cell membrane. In patients with ACTH-secreting pituitary adenomas, i.e. Cushing's disease (CD), SSTR5 is the most abundant receptor expressed and tumors show low SSTR2 density due to hypercortisolism-induced SSTR2 down-regulation. Clinical studies with pasireotide, a multireceptor-targeted SRL with increased SSTR5 activity, lead to approval of pasireotide for treatment of patients with CD. Other SRL delivery modes (oral octreotide), multireceptor-targeted SRL (somatoprim) or chimeric compounds targeting dopamine D2 receptors and SSTR2 (dopastatin), are briefly discussed.

Clinical experience in the screening and management of a large kindred with familial isolated pituitary adenoma due to an aryl hydrocarbon receptor interacting protein (AIP) mutation

CONTEXT

Germline AIP mutations usually cause young-onset acromegaly with low penetrance in a subset of familial isolated pituitary adenoma families. We describe our experience with a large family with R304* AIP mutation and discuss some of the diagnostic dilemmas and management issues.

OBJECTIVE

The aim of the study was to identify and screen mutation carriers in the family.

PATIENTS

Forty-three family members participated in the study.

SETTING

The study was performed in university hospitals.

OUTCOME

We conducted genetic and endocrine screening of family members.

RESULTS

We identified 18 carriers of the R304* mutation, three family members with an AIP-variant A299V, and two family members who harbored both changes. One of the two index cases presented with gigantism and pituitary apoplexy, the other presented with young-onset acromegaly, and both had surgery and radiotherapy. After genetic and clinical screening of the family, two R304* carriers were diagnosed with acromegaly. They underwent transsphenoidal surgery after a short period of somatostatin analog treatment. One of these two patients is in remission; the other achieved successful pregnancy despite suboptimal control of acromegaly. One of the A299V carrier family members was previously diagnosed with a microprolactinoma; we consider this case to be a phenocopy. Height of the unaffected R304* carrier family members is not different compared to noncarrier relatives.

CONCLUSIONS

Families with AIP mutations present particular problems such as the occurrence of large invasive tumors, poor response to medical treatment, difficulties with fertility and management of pregnancy, and the finding of AIP sequence variants of unknown significance. Because disease mostly develops at a younger age and penetrance is low, the timing and duration of the follow-up of carriers without overt disease requires further study. The psychological and financial impact of prolonged clinical screening must be considered. Excellent relationships between the family, endocrinologists, and geneticists are essential, and ideally these families should be managed in centers with specialist expertise.

The role of primary pharmacological therapy in acromegaly

BACKGROUND AND OBJECTIVES

Primary pharmacological therapy may be the only viable treatment option for many patients with acromegaly, especially those presenting with advanced disease with large inoperable tumors. Long-acting somatostatin analogs are currently the first-line treatment of choice in this setting, where they provide biochemical control and reduce tumor size in a significant proportion of patients. We herein present a brief overview of the role of primary pharmacological therapy in the treatment of acromegaly within the context of Latin America and support this with a representative case study.

CASE DESCRIPTION

A 20 year old male presented with clinical and biochemical evidence of acromegaly. The glucose-suppressed growth hormone (GH) was 5.3 μg/L, his insulin-like growth factor-1(IGF-1) was 3.5 times the ULN and serum prolactin greater than 4,000 μg/L. Pituitary MRI revealed a large and invasive mass, extending superiorly into the optic chiasm and laterally into the left cavernous sinus. He was treated with a combination of octreotide and cabergoline with remarkable clinical improvement, normalization of GH and IGF-1 values and striking shrinkage of the adenoma.

CONCLUSION

This case illustrates how effective the pharmacological therapy of acromegaly can be and yet at the same time, raises several important issues such as the need for life-long treatment with costly medications such as the somatostatin analogs. Access to these agents may be limited in regions where resources are restricted and clinicians face challenges in order to make the most efficient use of available options.

Familial pituitary tumors

Pituitary adenomas are benign intracranial neoplasms that present a major clinical concern due to hormone overproduction and/or tumor mass effects. The majority of pituitary adenomas occur sporadically; however, familial cases are increasingly being recognized, such as multiple endocrine neoplasia type 1 (MEN1), Carney complex (CNC), and familial isolated pituitary adenoma (FIPA). Familial pituitary tumors appear to differ from their sporadic counterparts both in their genetic basis and in clinical characteristics. Evidence suggests that, especially in MEN1 and FIPA, tumors are more aggressive and affect patients at a younger age, therefore justifying the importance of early diagnosis, while in Carney complex pituitary hyperplasia is common. The genetic alterations responsible for the formation of familial pituitary syndromes include the MEN1 gene, responsible for about 80% of MEN1 cases, the regulatory subunit of the protein kinase A, PRKAR1A, responsible for about 70% of Carney complex cases, and AIP, the gene coding the aryl hydrocarbon receptor interacting protein, responsible for about 20% of FIPA cases. Rarely other genes have also been found responsible for familial pituitary adenoma cases. McCune-Albright syndrome (MAS) also has a genetic origin due to mosaic mutations in the G protein-coupled α subunit coded by the GNAS1 gene. In this chapter, we summarize the genetic and clinical characteristics of these familial pituitary syndromes and MAS.