Prevalence of Gs alpha mutations in Korean patients with pituitary adenomas

Genomics, Transcriptomics, and Epigenetics of Sporadic Pituitary Tumors

Pituitary tumors (PT) are highly heterogeneous neoplasms, comprising functioning and nonfunctioning lesions. Functioning PT include prolactinomas, causing amenorrhea-galactorrhea in women and sexual dysfunction in men; GH-secreting adenomas causing acromegaly-gigantism; ACTH-secreting corticotrophinomas causing Cushing disease (CD); and the rare TSH-secreting thyrotrophinomas that result in central hyperthyroidism. Nonfunctioning PT do not result in a hormonal hypersecretion syndrome and most of them are of gonadotrope differentiation; other non-functioning PT include null cell adenomas and silent ACTH-, GH- and PRL-adenomas. Less than 5% of PT occur in a familial or syndromic context whereby germline mutations of specific genes account for their molecular pathogenesis. In contrast, the more common sporadic PT do not result from a single molecular abnormality but rather emerge from several oncogenic events that culminate in an increased proliferation of pituitary cells, and in the case of functioning tumors, in a non-regulated hormonal hypersecretion. In recent years, important advances in the understanding of the molecular pathogenesis of PT have been made, including the genomic, transcriptomic, epigenetic, and proteomic characterization of these neoplasms. In this review, we summarize the available molecular information pertaining the oncogenesis of PT.

Proteogenomic landscape and clinical characterization of GH-producing pituitary adenomas/somatotroph pituitary neuroendocrine tumors

The clinical characteristics of growth hormone (GH)-producing pituitary adenomas/somatotroph pituitary neuroendocrine tumors (GHomas/somatotroph PitNETs) vary across patients. In this study, we aimed to integrate the genetic alterations, protein expression profiles, transcriptomes, and clinical characteristics of GHomas/somatotroph PitNETs to identify molecules associated with acromegaly characteristics. Targeted capture sequencing and copy number analysis of 36 genes and nontargeted proteomics analysis were performed on fresh-frozen samples from 121 sporadic GHomas/somatotroph PitNETs. Targeted capture sequencing revealed GNAS as the only driver gene, as previously reported. Classification by consensus clustering using both RNA sequencing and proteomics revealed many similarities between the proteome and the transcriptome. Gene ontology analysis was performed for differentially expressed proteins between wild-type and mutant GNAS samples identified by nontargeted proteomics and involved in G protein-coupled receptor (GPCR) pathways. The results suggested that GNAS mutations impact endocrinological features in acromegaly through GPCR pathway induction. ATP2A2 and ARID5B correlated with the GH change rate in the octreotide loading test, and WWC3, SERINC1, and ZFAND3 correlated with the tumor volume change rate after somatostatin analog treatment. These results identified a biological connection between GNAS mutations and the clinical and biochemical characteristics of acromegaly, revealing molecules associated with acromegaly that may affect medical treatment efficacy.

Genetic and Epigenetic Pathogenesis of Acromegaly

Simple Summary

Various genetic and epigenetic factors are involved in the pathogenesis of somatotroph tumors. Although GNAS mutations are the most prevalent cause of somatotroph tumors, the cause of half of all pathogenesis occurrences remains unclarified. However, recent findings including the pangenomic analysis, such as genome, transcriptome, and methylome approaches, and histological characteristics of pituitary tumors, the involvement of AIP and GPR101, the mechanisms of genomic instability, and possible involvement of miRNAs have gradually unveiled the whole landscape of underlying mechanisms of somatotroph tumors. In this review, we will focus on the recent advances in the pathogenesis of somatotroph tumors.

Abstract

Acromegaly is caused by excessive secretion of GH and IGF-I mostly from somatotroph tumors. Various genetic and epigenetic factors are involved in the pathogenesis of somatotroph tumors. While somatic mutations of GNAS are the most prevalent cause of somatotroph tumors, germline mutations in various genes (AIP, PRKAR1A, GPR101, GNAS, MEN1, CDKN1B, SDHx, MAX) are also known as the cause of somatotroph tumors. Moreover, recent findings based on multiple perspectives of the pangenomic approach including genome, transcriptome, and methylome analyses, histological characterization, genomic instability, and possible involvement of miRNAs have gradually unveiled the whole landscape of the underlying mechanisms of somatotroph tumors. In this review, we will focus on the recent advances in genetic and epigenetic pathogenesis of somatotroph tumors.

gsp Mutation Is Not a Molecular Biomarker of Long-Term Response to First-Generation Somatostatin Receptor Ligands in Acromegaly

Simple Summary

Acromegaly treatment consists of surgical, medical, and radiation therapy. First-generation somatostatin receptor ligands are the mainstay of medical therapy, with approximately 40% disease control rate. Several parameters have been evaluated as predictors of response to these drugs, including mutations in the stimulatory G-protein α subunit (gsp mutation), which is still controversial. In this study, we aimed to evaluate in a large series of patients whether gsp mutation predicts long-term response to medical treatment and to characterize the gsp mutated population. The ability to predict response to medical therapy would help to choose a therapy that presents higher odds of controlling the disease, which ultimately would reduce treatment costs and disease morbi-mortality.

Abstract

Background: It is still controversial if activating mutations in the stimulatory G-protein α subunit (gsp mutation) are a biomarker of response to first generation somatostatin receptor ligands (fg-SRL) treatment in acromegaly. Thus, we aimed to evaluate whether gsp mutation predicts long-term response to fg-SRL treatment and to characterize the phenotype of patients harboring gsp mutations. Methods: GNAS1 sequencing was performed by Sanger. SST2 and SST5 were analyzed by immunohistochemistry (IHC) and real-time RT-PCR. The cytokeratin granulation pattern was evaluated by IHC. Biochemical control was defined as GH < 1.0 ng/mL and normal age-adjusted IGF-I levels. Results: gsp mutation was found in 54 out of 136 patients evaluated. Biochemical control with fg-SRL treatment was similar in gsp+ and gsp- patients (37% vs. 25%, p = 0.219). Tumors harboring gsp mutation were smaller (p = 0.035) and had a lower chance of invading cavernous sinuses (p = 0.001). SST5 protein (p = 0.047) and mRNA (p = 0.013) expression levels were higher in wild-type tumors. Conclusions: In this largest series available in the literature, we concluded that gsp is not a molecular biomarker of response to fg-SRL treatment in acromegaly. However, the importance of its negative association with cavernous sinus invasion and SST5 expression needs to be further investigated.

GH/PRL-secreting pituitary macroadenoma associated with GNAS p.Gln227Leu mutation: pediatric case report and review

GH-secreting pituitary adenomas (GHomas) are rare in the pediatric population. Guanine nucleotide-binding protein, alpha stimulating (GNAS) somatic mutations are often found in patients with GHoma. Here, we report an 8-year-old girl with GH-secreting pituitary adenoma successfully treated by operative tumor resection and postoperative treatment with octreotide long-acting release (LAR). Tumor DNA sequence analysis revealed a somatic heterozygous c.680A>T (p.Gln227Leu) mutation in GNAS. We reviewed 1,084 cases of GHomas, 409 (37.7%) of which harbored GNAS mutations. In pediatrics cases, aged 15 years or younger, 11 harbored a GNAS mutation, and GNAS p.Arg201Cys was identified in five cases. No other cases of codon 227 mutation were detected. These cases suggest that, in pediatric patients, the clinical features of GHoma may differ from those observed in adults. This is possibly related to octreotide or dopamine agonist resistance. Of six patients with surgical resistance, only one was reactive when treated with octreotide. Our case shows that octreotide LAR is an effective choice for treating GNAS-induced GHoma. This is the first report detailing the effectiveness of octreotide LAR in a GNAS codon 227 mutation-induced GHoma in a pediatric case. Examination of the relationship between genetic variation and clinical features in pediatric patients will enable us to assess the long-term effects of surgical and medical treatment of GHomas.

MEG3 is associated with gsp oncogene regulation of growth hormone hypersecretion, proliferation and invasiveness of human GH-secreting adenomas

Overactivation of the Gs-mediated pathway by mutations of the G-protein α subunit (Gsα), a gsp oncogene, results in increased growth hormone (GH) hypersecretion and reduced tumor volume in patients with GH-secreting pituitary tumors. However, the mechanism underlying the clinical characteristics of gsp oncogene requires further investigation. Cyclic adenosine monophosphate-responsive element binding (CREB), as a downstream target gene of gsp oncogene, is implicated in activating maternally expressed gene 3 (MEG3). The present study proposes that gsp oncogene mediates MEG3-regulating GH hypersecretion, resulting in the small tumor size of GH-secreting tumors. Therefore, the present study detected Gsα mutations by polymerase chain reaction in GH-secreting tumors, and revealed that Gsα mutations were observed in 7/25 (28%) GH-secreting tumors. Gsp-positive tumors indicated significantly increased levels of phosphorylated p-CREB (P<0.0001) and MEG3 (P=0.039), compared with gsp-negative tumors. The results indicated that MEG3 levels were positively correlated with GH and IGF-1 levels, and negatively correlated with the tumor volume of GH-secreting tumors. The group with gsp-positive or with high MEG3 expression indicated a significantly reduced proportion of invasiveness and lower Ki-67 index, compared with the gsp-negative or low MEG3 expression group. In conclusion, gsp oncogene may mediate MEG3 by promoting GH hypersecretion, resulting in smaller tumors, as well as suppressing proliferation and invasiveness of GH-secreting pituitary tumors.

The curious case of Gαs gain-of-function in neoplasia

BACKGROUND

Mutations activating the α subunit of heterotrimeric Gs protein are associated with a number of highly specific pathological molecular phenotypes. One of the best characterized is the McCune Albright syndrome. The disease presents with an increased incidence of neoplasias in specific tissues.

MAIN BODY

A similar repertoire of neoplasms can develop whether mutations occur spontaneously in somatic tissues during fetal development or after birth. Glands are the most "permissive" tissues, recently found to include the entire gastrointestinal tract. High frequency of activating Gαs mutations is associated with precise diagnoses (e.g., IPMN, Pyloric gland adenoma, pituitary toxic adenoma). Typically, most neoplastic lesions, from thyroid to pancreas, remain well differentiated but may be a precursor to aggressive cancer.

CONCLUSIONS

Here we propose the possibility that gain-of-function mutations of Gαs interfere with signals in the microenvironment of permissive tissues and lead to a transversal neoplastic phenotype.

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.

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.

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.

Pituitary MRI characteristics in 297 acromegaly patients based on T2-weighted sequences

Responses of GH-secreting adenomas to multimodal management of acromegaly vary widely between patients. Understanding the behavioral patterns of GH-secreting adenomas by identifying factors predictive of their evolution is a research priority. The aim of this study was to clarify the relationship between the T2-weighted adenoma signal on diagnostic magnetic resonance imaging (MRI) in acromegaly and clinical and biological features at diagnosis. An international, multicenter, retrospective analysis was performed using a large population of 297 acromegalic patients recently diagnosed with available diagnostic MRI evaluations. The study was conducted at ten endocrine tertiary referral centers. Clinical and biochemical characteristics, and MRI signal findings were evaluated. T2-hypointense adenomas represented 52.9% of the series, were smaller than their T2-hyperintense and isointense counterparts (P<0.0001), were associated with higher IGF1 levels (P=0.0001), invaded the cavernous sinus less frequently (P=0.0002), and rarely caused optic chiasm compression (P<0.0001). Acromegalic men tended to be younger at diagnosis than women (P=0.067) and presented higher IGF1 values (P=0.01). Although in total, adenomas had a predominantly inferior extension in 45.8% of cases, in men this was more frequent (P<0.0001), whereas in women optic chiasm compression of macroadenomas occurred more often (P=0.0067). Most adenomas (45.1%) measured between 11 and 20 mm in maximal diameter and bigger adenomas were diagnosed at younger ages (P=0.0001). The T2-weighted signal differentiates GH-secreting adenomas into subgroups with particular behaviors. This raises the question of whether the T2-weighted signal could represent a factor in the classification of acromegalic patients in future studies.

Genetic analysis of a patient with coexisting acromegaly, thyroid papillary carcinoma and subcutaneous fibroma

The aim of the present study was to analyze the MEN1 and gsα gene mutations in a Chinese patient with growth hormone-producing pituitary tumors causing acromegaly, papillary thyroid carcinoma and subcutaneous fibroma. Genomic DNA was isolated from the patient and 10 healthy controls, and prepared for polymerase chain reaction (PCR) analysis. Numerous pairs of primers were designed to amplify exons 1–10 of the MEN1 gene and exons 8 and 9 of the gsα gene, and the PCR products were sequenced to detect mutations. In the study patient, a heterozygous G→A mutation was detected at nucleotide 7848 within exon 10 of the MEN1 gene; the missense mutation caused the substitution of alanine with threonine at amino acid 541 (A541T) in the menin protein. In addition, a G→A mutation at nucleotide 7997 within exon 10 of the MEN1 gene was identified; the mutation was synonymous, therefore, the proline at amino acid 590 of the menin protein (P590P) did not change. No other mutations were observed in exons 8 and 9 of the gsα gene, therefore, the G7848A mutation within exon 10 of the MEN1 gene may represent the molecular pathology underlying pituitary somatotroph adenomas and papillary thyroid carcinoma. Furthermore, the pituitary adenomas, thyroid carcinoma and subcutaneous fibroma of the present patient may be considered as early manifestations of multiple endocrinologic neoplasia syndrome 1 as opposed to pure endocrine tumors, however, a long-term follow-up study is required to clarify this.

Gsp mutation in acromegaly and its influence on TRH-induced paradoxical GH response

OBJECTIVE

We recently reported that paradoxical GH response to TRH administration reflects biological characteristics in patients with acromegaly. The aim of this study is to elucidate the relationship between gsp mutations and the paradoxical GH response to TRH.

PATIENTS

Sixty-seven patients with acromegaly were included for analysis. Paradoxical increase in serum GH level to TRH, GH suppression by octreotide and bromocriptine, radiological profiles and histopathological findings were analysed with respect to tumour gsp-mutation status.

RESULTS

Twenty-six (38·8%) gsp mutations were detected, and the number of paradoxical GH responders to TRH, defined as an increase of 100% or more in GH after TRH, was 49 (73·1%). Among the paradoxical GH responders to TRH, 21 patients (42·9%) had a gsp mutation and 28 patients (57·1%) did not. The percentage of paradoxical GH responders to TRH in gsp-positive and gsp-negative patients was not significantly different (80·8% and 68·3%, respectively). The gsp-positive group showed a significantly higher paradoxical increase in serum GH level by TRH administration (1830% vs 650% GH increase, P = 0·045) and greater GH suppression by octreotide (88·7% vs 75·4% GH decrease, P = 0·003) than the gsp-negative group.

CONCLUSION

Paradoxical GH response to TRH was observed regardless of gsp mutation, although the rate of increase was significantly higher in gsp-positive patients. These results suggest that gsp mutation is not sufficient to cause the paradoxical GH response to TRH, while other unidentified factors have a strong influence on paradoxical GH response to TRH in patients with acromegaly.

Adenoma granulation pattern correlates with clinical variables and effect of somatostatin analogue treatment in a large series of patients with acromegaly

CONTEXT

Somatotroph adenomas have been classified into densely granulated (DG) and sparsely granulated (SG) tumours with a transitional, intermediate group. Gsp oncogenes are activating mutations in the Gsα subunit gene, found in approximately 40% of somatotroph adenomas.

OBJECTIVES

To explore granulation pattern and presence of gsp oncogene in acromegaly with correlations to clinical and biochemical variables and to the effect of treatment with somatostatin analogues (SA), as well as to describe granulation pattern in adenomas with and without SA pretreatment.

DESIGN/SETTINGS/PATIENTS

Seventy-eight patients with active acromegaly were included. Long-term SA efficacy was evaluated in 29 patients treated preoperatively and in ten treated postoperatively. Granulation pattern was examined, as were immunohistochemical analyses for E-cadherin and SSTR2a. Protein levels of E-cadherin and SSTR2a were measured (Western blot). Gsp mutation analysis was available for 74 adenomas.

RESULTS

DG adenomas and the transitional group had higher serum levels of IGF-1 per tumour volume than SG (P = 0·009; P = 0·005). Acute and long-term SA responses were lower in SG (P = 0·001; P = 0·043). No correlation between gsp mutation and granulation was found, and no difference in granulation pattern according to preoperative SA treatment was demonstrated. A significant correlation between granulation and E-cadherin was found, where SG had lowest immunohistochemical expression, substantiated by protein levels, and a highly significant gradient was observed from DG, through the transitional group, to SG.

CONCLUSIONS

Densely granulated adenomas were highly responsive to somatostatin analogues in contrast to SG adenomas. The transitional group behaved clinically more like DG adenomas. However, based on E-cadherin, a marker of dedifferentiation, the transitional group seemed to be a true intermediate.

Impact of gsp oncogene on the mRNA content for somatostatin and dopamine receptors in human somatotropinomas

INTRODUCTION

It has been reported in some series that gsp+ somatotropinomas are more sensitive to somatostatin analogues (SA) and dopamine's actions which may be related to their somatostatin receptor (SSTR) and dopamine receptor (DR) profile. No previous studies have been undertaken to evaluate the SSTR and DR profile related with the gsp status in somatotropinomas.

OBJECTIVES

To determine if (1) gsp status is correlated with response to octreotide LAR (LAR) and tumor expression patterns of SSTR1-5 and DR1-5 and (2) cAMP level can directly modulate SSTR and DR mRNA levels.

METHODS

Response to SA was evaluated by GH and IGF-I percent reduction after 3 and 6 months of treatment with LAR. Conventional PCR and sequencing were used to identify gsp+ tumors. Quantitative real-time PCR was used to determine SSTR and DR tumor expression. Primary pituitary cell cultures of primates were used to study whether SSTR and DR expression is regulated by forskolin.

RESULTS

The response to LAR did not significantly differ between patients with gsp+ and gsp- tumors; however, gsp+ tumors expressed higher levels of SSTR1, SSTR2, DR2 and a lower level of SSTR3. Forskolin increased SSTR1, SSTR2, DR1 and DR2 expression in cell cultures.

CONCLUSION

Elevated SSTR1, SSTR2, and DR2 tumor expression may help improve responsiveness to SA and DA therapy; however, this study may not have been appropriately powered to observe significant effects in the clinical response. Elevated cAMP levels could be directly responsible for the upregulation in SSTR1, SSTR2 and DR2 mRNA levels observed in gsp+ patients.

G protein inactive and active forms investigated by simulation methods

Molecular dynamics and computational alanine scanning techniques have been used to investigate G proteins in their inactive state (the Galpha(i1)beta(1)gamma(2) heterotrimer) as well as in their empty and monomeric active states (Galpha(i1) subunit). We find that: (i) the residue Q204 of Galpha(i1) plays a key role for binding Gbeta(1)gamma(2) and is classified among the most relevant in the interaction with a key cellular partner, the so-called regulator of G protein signaling protein. The mutation of this residue to L, which is observed in a variety of diseases, provides still fair stability to the inactive state because of the formation of van der Waals interactions. (ii) The empty state turns out to adopt some structural features of the active one, including a previously unrecognized rearrangement of a key residue (K46). (iii) The so-called Switch IV region increases its mobility on passing from the empty to the active state, and, even more, to the inactive state. Such change in mobility could be important for its several structural and functional roles. (iv) A large scale motion of the helical domain in the inactive state might be important for GDP release upon activation by GPCR, consistently with experimental data.

Prevalence of gsp oncogene in somatotropinomas and clinically non-functioning pituitary adenomas: our experience

The purpose of the present study is to evaluate the prevalence of the gsp oncogene in Brazilian patients harboring somatotropinomas and non-functioning pituitary adenomas (NFPA). Patients and methods Deoxyribonucleic acid was extracted from 54 somatotropinomas and 14 NFPA. Exons 8 and 9 (including codons 201 and 227, respectively) of the GNAS gene were amplified by polymerase chain reaction (PCR). The PCR products were then purified and sequenced using the same primers. Results The gsp oncogene was found in nine tumors (eight somatotropinomas). The prevalence among somatotropinomas was 15% and among NFPA was 7%. The mutation was found in codon 201 in eight tumors and in codon 227 in one tumor (a somatotropinoma). No differences were found in age, sex, GH, and IGF-I levels or tumor volume at diagnosis between gsp+ and gsp- patients. Conclusion We found a lower than expected prevalence of gsp mutations in somatotropinomas and a similar prevalence in NFPA compared to previous studies from other countries.

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.

The clinical response to somatostatin analogues in acromegaly correlates to the somatostatin receptor subtype 2a protein expression of the adenoma

OBJECTIVE

Reduced expression of the somatostatin receptor subtype 2 (SSTR2) has been suggested as an explanation for the poor response to octreotide in acromegaly, but studies correlating levels of SSTR2 mRNA to octreotide efficacy have been contradictory. Some studies have found better responses to somatostatin analogues in G-protein alpha subunit (Gsalpha) mutation (gsp oncogene)-positive adenomas. The aim of this study was to determine adenoma SSTR2a protein expression and gsp status in a large group of patients with acromegaly, and relate this to the clinical effect of octreotide.

PATIENTS

Seventy-one patients were included. All underwent transsphenoidal surgery, 23 patients after preoperative octreotide treatment.

MEASUREMENTS

The adenoma SSTR2a expression was examined by immunohistochemistry and Western blot analysis, and gsp status determined. An acute octreotide test was performed, and the change in IGF-1 level after 6 months preoperative octreotide treatment was recorded.

RESULTS

The acute octreotide response in non-pretreated patients and the preoperative long-term octreotide response were significantly better in patients with adenomas containing a large proportion of cells that stained positively for SSTR2a by immunohistochemistry. However, the SSTR2a protein level assessed by Western blot did not correlate with the octreotide response. The preoperatively treated group had lower SSTR2a protein levels and fewer adenomas with a large percentage of positively stained cells. The gsp oncogene was detected in 43% of the adenomas but did not correlate to the octreotide response.

CONCLUSION

The clinical effect of octreotide correlates with the proportion of cells positive for SSTR2a in immunohistochemical staining, rather than the adenoma SSTR2a protein level. There may be a down-regulation of SSTR2a during octreotide treatment.

A prospective, multicentre study to investigate the efficacy, safety and tolerability of octreotide LAR (long-acting repeatable octreotide) in the primary therapy of patients with acromegaly

OBJECTIVE

To evaluate the efficacy, safety and tolerability of octreotide LAR (long-acting repeatable octreotide) in the primary therapy of acromegaly.

DESIGN AND PATIENTS

Ninety-eight previously untreated acromegalics were recruited into this prospective multicentre study. A total of 68 patients successfully completed 48 weeks of the study period, received 12 doses of octreotide LAR 10-30 mg every 4 weeks, and constituted the population used for this analysis.

MEASUREMENTS AND RESULTS

A clinically relevant reduction (i.e. to < or = 5 microg/l) in mean GH (mGH) was recorded in 72% of patients after 24 weeks of treatment, and 42% reached a 'safe' GH value (< or = 2.5 microg/l). At week 48, 16 more patients were considered partial GH responders (GH > 2.5 microg/l and < or = 5 microg/l) and 44% had reached a GH level < or = 2.5 microg/l. IGF-1 levels normalized in 38% and 34% of patients after 24 and 48 weeks of treatment, respectively. At study completion, 10 patients (14.7%) who had not normalized their IGF-1 levels had achieved at least a 50% decrement in this marker. In eight microadenoma patients, tumour volume decreased from a mean baseline level of 298 +/- 145 mm3 to 139 +/- 94 mm3 after 24 weeks and to 99 +/- 70 mm3 after 48 weeks of therapy. In 60 patients with macroadenoma, the corresponding values were 3885 +/- 5077 mm3 at baseline and 2723 +/- 3435 and 2406 +/- 3207 mm3 after 24 and 48 weeks, respectively. At weeks 24 and 48, a significant (> 20%) tumour volume reduction was reported in 63% and 75% of patients, respectively. A reduction in the severity of symptoms of acromegaly was observed early in treatment and was maintained throughout the study period.

CONCLUSION

Octreotide LAR represents a viable alternative to surgery for primary treatment of acromegaly leading to a progressive regression of tumour volume, a sustained control of biochemical abnormalities and an adequate relief of symptoms of the disease.

Analysis of GNAS mutations in 60 growth hormone secreting pituitary tumors: correlation with clinical and pathological characteristics and surgical outcome based on highly sensitive GH and IGF-I criteria for remission

Although the molecular mechanisms underlying GH secreting pituitary tumor formation are not well understood, mutations in the alpha-subunit of the stimulatory G gene, GNAS, have been identified in up to 40%. As these mutations could play a role in tumor growth, we screened 60 GH secreting tumors for GNAS mutations and assessed whether mutation status correlated with their clinical and pathological characteristics. Tumor specimens obtained at surgery were snap frozen. Tumor DNA was extracted, and PCR was used to amplify regions containing 2 sites of recurrent activating somatic mutations in codons 201 and 227 in GNAS. Amplicons were bi-directionally sequenced and analyzed. GNAS mutations were present in 24/60 (40%) of tumors; these were arg201cys(n = 15), arg201ser(n = 2), arg201his(n = 2), gln227leu(n = 4), gln227arg(n = 1). Preoperative IGF-I levels (age-adjusted) were higher (p = 0.01), but GH levels were slightly higher (p = 0.18) in mutation positive vs. negative groups. Mutation positive tumors were somewhat smaller than negative tumors (p = 0.07). The proportion of tumors >2 cm was somewhat less among positive (8.3%) vs. negative tumors (25%) (p = 0.10). Neither mib proliferation index, the proportion of invasive tumors nor surgical remission rates differed in the groups. IGF-I normalization rate with somatostatin analog therapy was similar in positive (3 of 6) vs. negative (3 of 7) patients. GH secreting tumors harboring GNAS mutations had higher preoperative IGF-I levels, somewhat higher preoperative GH levels and tended to be smaller than tumors without mutations. Presence of a GNAS mutation did not predict a difference in a proliferation marker, surgical remission or response to somatostatin analog therapy.

Pituitary tumor transforming gene overexpression facilitates pituitary tumor development

Intrinsic and extrinsic stimuli result in profound pituitary growth changes ranging from hypoplasia to hyperplasia. Pituitary tumor transforming gene (PTTG) abundance correlates with pituitary trophic status. Mice with Pttg inactivation exhibit pituitary hypoplasia, whereas targeted pituitary PTTG overexpression driven by alpha-subunit glycoprotein (alphaGSU) promoter results in focal pituitary hyperplasia. To test the impact of pituitary hyperplasia on tumor development, we crossbred alphaGSU.PTTG with Rb+/- mice, which develop pituitary tumors with high penetrance. Pituitary glands of resulting bitransgenic alphaGSU.PTTGxRb+/- mice were compared with monotransgenic alphaGSU.PTTG, Rb+/-, and wild-type mice. Confocal microscopy showed that PTTG-overexpressing cells have enlarged nuclei and marked redistribution of chromatin, and electron microscopy of alphaGSU.PTTG pituitaries showed enlarged gonadotrophs with prominent Golgi complexes and numerous secretory granules. These morphological findings were even more remarkable in alphaGSU.PTTGxRb+/- pituitaries. Mice from all four genotypes were sequentially imaged by magnetic resonance imaging to evaluate pituitary volume, and glands from alphaGSU.PTTGxRb+/- mice were the largest as early as 2 months of age (P = 0.0003). Cumulative incidence of pituitary tumors visualized by magnetic resonance imaging did not differ between Rb+/- and alphaGSU.PTTGxRb+/- mice. However, anterior lobe tumors determined after necropsy were 3.5 times more frequent in alphaGSU.PTTGxRb+/- than in Rb+/- mice (P = 0.0036), whereas the frequency of intermediate lobe tumors was similar. In summary, alphaGSU.PTTGxRb+/- pituitary glands exhibit enhanced cellular activity, increased volume, and higher prevalence of anterior pituitary tumors, indicating that changes in pituitary PTTG content directly relate to both pituitary trophic status and tumorigenic potential.

Low prevalence of Gs alpha mutations in śomatotroph adenomas of children and adolescents

Mutations in the gene coding for the alpha-subunit of the heterotrimeric stimulatory G protein Gs are the most frequently identified molecular events in the development of somatotroph adenomas in adults. In children and adolescents, somatotroph adenomas are rare, and only two cases with the Gs alpha mutation have been reported so far. In this study, we therefore investigated the prevalence of activating Gs alpha mutations in 17 patients younger than 20 years with pituitary growth hormone-secreting adenomas and examined the characteristics of mutation-positive cases. The most common C-->T substitution in codon 201 was detected in two children. Interestingly, in contrast to the remaining cases, the adenomas positive for the Gs alpha mutation proved to be nonsporadic, but part of a syndrome associated with endocrine tumors in both individuals. Additional tests confirmed McCune-Albright syndrome in the first patient and multiple endocrine neoplasia type 1 syndrome in the second patient. In contrast to the findings in adult cases, somatotroph adenomas in young patients seem to carry somatic Gs alpha mutations at a lower frequency, and germ-line or early postzygotic mutational events may be responsible for the shortened latency of tumorigenesis.

Does the prevalence of gsp mutations in GH-secreting pituitary adenomas differ geographically or racially? Prevalence of gsp mutations in Japanese patients revisited

OBJECTIVE

The prevalence of gsp mutations in GH-secreting pituitary adenomas was thought to differ geographically or racially, given its exceptionally lower incidence among Japanese patients (4.4-9.3%) compared to other regions (30-50%). However, this notion is now being challenged after a recent paper reported a 53.3% incidence among Japanese with acromegaly. We have since re-evaluated the prevalence of gsp mutations on a larger scale.

PATIENTS

One hundred Japanese acromegaly patients with surgically confirmed GH-secreting pituitary adenomas were enrolled.

METHODS

mRNAs from primary cultured adenomas were used for reverse transcriptase-polymerase chain reaction and direct sequencing of the Gsalpha subunit. Patient data were reviewed from medical charts.

RESULTS

There were 53 gsp mutations (53%), consisting of 42 Arg201Cys, one Arg201His, one Arg201Ser, 8 Gln227Leu, and one Gln227Arg mutation. Age at operation, sex ratio, basal serum GH and IGF-I levels were no different with or without the mutations. In contrast, patients responded differently to most dynamic tests with statistical significance: serum GH levels in gsp-positive patients had blunted response to GHRH, were well suppressed by bromocriptine, and had higher rates of paradoxical response to TRH. Notably, paradoxical response to LHRH was observed exclusively in gsp-negative patients. Octreotide suppressed GH levels strongly regardless of gsp status. These clinical characteristics are similar to those of Caucasian patients.

CONCLUSION

We conclude that the prevalence of gsp mutations in Japanese acromegaly patients is comparable to those of other reports from various regions. Therefore, Japanese patients do not stand as an example for geographical or racial difference in the prevalence of gsp mutations in GH-secreting pituitary adenomas.

GSPalpha mutations in Mexican patients with acromegaly: potential impact on long term prognosis

OBJECTIVE

The frequency of activating mutations of the GSPalpha gene as the etiology of GH-secreting pituitary adenomas has been the subject of important ethnogenetic variability. Whereas up to 40% of Caucasian patients with acromegaly have tumors which harbor these somatic mutations, their prevalence among Asian populations is much lower. The correlation between the presence of these mutations and the clinical and biological behavior of these tumors has also been a matter of controversy. In the present study, we investigated the prevalence of GSPalpha mutations in GH-secreting tumors obtained from a genetically homogenous population of Mexican patients with acromegaly. We also sought to establish whether or not the presence of these mutations correlates in any way with the clinical or biochemical characteristics of the disease.

STUDY DESIGN AND METHODS

Fifty eight GH-secreting pituitary adenomas were examined for the presence of point mutations in either codon 201 or 227 of the GSPalpha gene, using PCR and direct sequencing of DNA extracted from either fresh or paraffin-embedded tissues. Patients were prospectively followed clinically and biochemically for up to nine years after pituitary surgery.

RESULTS

Heterozygous point mutations in exon 8 (codon 201) were found in 11 patients (19%), and no molecular alterations were evident in exon 9. The frequency and severity of the different clinical features of acromegaly did not differ between patients with and without GSPalpha mutations. Patients with and without mutations had pre-operative GH and IGF-I elevations of similar magnitude, and although microadenomas appeared to be more frequent among patients with GSPalpha mutations, this did not reach statistical significance. Upon short-term follow-up, biochemical cure (normal age- and gender-adjusted IGF-I and post-glucose GH below 1 ng/mL) was similarly achieved in both groups. After 3-9 years of post-operative follow up however, a significantly greater proportion of patients with the mutation achieved a "safe" basal GH value (100% vs 33%, p=0.001) as well a lower nadir post-glucose GH (0.53+/-0.5 vs 2.9+/-6.2 ng/mL, p=0.04) although the rate of IGF-1 normalization did not differ between the 2 groups.

CONCLUSIONS

Our results show that the prevalence of GSPalpha mutations in Mexican patients with acromegaly is intermediate between that found in Asian and Caucasian populations. In this well-defined genetic population the presence of codon 201 mutations appeared to be associated with a greater probability of achieving a "safe" GH value upon long-term follow-up.

GH-secreting pituitary adenomas infrequently contain inactivating mutations of PRKAR1A and LOH of 17q23-24

OBJECTIVE

The molecular events leading to the development of GH-secreting pituitary tumours remain largely unknown. Gsalpha (GNAS1) mutations are found in 27-43% of sporadic GH-secreting adenomas in the Caucasian population, but the frequency of GNAS1 mutations in Japanese and Korean acromegalic patients was reported to be lower, 4-9% and 16%, respectively. Other genes responsible for the tumourigenesis of GH-secreting pituitary adenomas have not been detected yet. PRKAR1A, which codes for the RIalpha regulatory subunit of cyclic AMP-dependent protein kinase A (PKA) on 17q23-24, was recently reported to contain inactivating mutations in some Carney complex families, which involved GH-secreting adenomas in about 10%. We re-evaluated the frequency of GNAS1 mutations and investigated PRKAR1A on the hypothesis that it might play a role in the tumourigenesis of GH-secreting adenomas.

DESIGN

We analysed exons 8 and 9 of GNAS1 and all exons and the exon-intron boundaries of PRKAR1A with the PCR and by direct sequencing using genomic DNA extracted from 32 GH-secreting pituitary adenomas (30 GH-secreting adenomas, two GH and PRL-secreting adenomas) and 28 corresponding peripheral blood samples, and performed loss of heterozygosity (LOH) analysis of 17q23-24 with four microsatellite markers and intragenic markers of PRKAR1A.

RESULTS

Seventeen of 32 (53.1%) tumours showed somatic-activating mutations of GNAS1: 16 (53.3%) of 30 GH-secreting adenomas and one of two GH and PRL-secreting adenomas. Neither inactivating somatic mutations of PRKAR1A nor LOH of 17q23-24 were detected in any of the tumours examined.

CONCLUSION

We reconfirm the important role of activating mutations of GNAS1 in GH-secreting adenomas, and conclude that PRKAR1A does not play a significant role in the tumourigenesis.

Aberrant G protein signaling in nervous system tumors

Object. Guanosine triphosphate (GTP)—binding proteins, also known as G proteins, play important roles in the regulation of cell growth and differentiation by transmitting intracellular signals from cell surface receptors. In this paper, the authors review G protein signaling in general and its aberrations in four human nervous system tumors.

Methods. In the nervous system, four tumor types have been associated with aberrant G protein signaling. The first tumor type includes astrocytomas, which have increased levels of the activated form of the small G protein, p21-ras, without primary oncogenic p21-ras mutations. The likely source for increased p21-ras activity in sporadically occurring astrocytomas is overexpressed or constitutively activated growth factor receptors, whereas in neurofibromatosis Type 1 (NF1)—associated astrocytomas, the source is a loss of expression of neurofibromin, a major inactivator of p21-ras (ras—GTPase activating protein [GAP]). The second type of tumor associated with aberrant G protein signaling includes sporadic and NF1-associated neurofibromas and malignant peripheral nerve sheath tumors, which also have increased p21-ras activity due to a loss of neurofibromin expression. The third tumor type includes subependymal giant cell astrocytomas as part of the tuberous sclerosis complex (TSC). These tumors display a loss of tuberin expression due to germline mutations in the TSC2 gene. Tuberin functions as an inactivator of the small G protein rap1B (rap1-GAP) and, hence, loss of its expression could lead to increased rap1B activity. In addition to TSC-associated tumors, the authors demonstrate that the majority of sporadically occurring astrocytomas display either loss of tuberin or overexpression of rap1B. This suggests that increased rap1B activity, which can augment p21-ras—mediated signals, also contributes to G protein—mediated aberrant signaling in sporadically occurring astrocytomas. The fourth tumor type includes a significant subset of pituitary adenomas that show constitutive activation of the Gα subunit of the large heterotrimeric Gs protein, which is involved in hormone receptor signaling. The net result of this aberrant activation is increased cyclic adenosine monophosphate and mitogenic tumor-promoting signals.

Conclusions. The authors' review of G protein signaling and aberrations in this process is made with the long-term view that increased understanding of relevant signaling pathways will eventually lead to novel biological targeted therapies against these tumors.