Mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene have been linked to predisposition to pituitary adenomas. However, the mechanism by which this occurs remains unknown. AIP interacts with a number of interesting proteins, including members of the cAMP signalling pathway that has been shown to be consistently altered in pituitary tumours. The functional role of Aip was investigated using both over-expression and knock down of Aip in GH3 cells. cAMP signalling and its downstream effectors, including GH secretion, were then investigated. cAMP signalling was analysed using cAMP assays, cAMP-response element-promoter luciferase reporter assays, real-time PCR and finally secreted GH quantification. Over-expression of wild-type (WT)-Aip reduced forskolin-induced cAMP signalling at the total cAMP level, luciferase reporter activity and target gene expression, when compared with empty vector and the non-functional R304X mutant. Additionally, GH secretion was reduced in WT-Aip over-expressing GH3 cells treated with forskolin. Knock down of endogenous Aip resulted in increased cAMP signalling but a decrease in GH secretion was also noted. Inhibition of phosphodiesterase activity using general and selective inhibitors did not completely ablate the effect of Aip on forskolin-augmented cAMP signalling. A mechanism by which Aip acts as a tumour suppressor, by maintaining a low cAMP signalling and concentration, is suggested. Mutations of Aip render the protein incapable of such activity. This effect appears not to be mediated by the AIP–PDE interaction, suggesting the involvement of other interacting partners in mediating this outcome.
R Formosa, A Xuereb-Anastasi, and J Vassallo
Anna Angelousi, Georgios K Dimitriadis, Georgios Zografos, Svenja Nölting, Gregory Kaltsas, and Ashley Grossman
Tumourigenesis is a relatively common event in endocrine tissues. Currently, specific guidelines have been developed for common malignant endocrine tumours, which also incorporate advances in molecular targeted therapies (MTT), as in thyroid cancer and in gastrointestinal neuroendocrine malignancies. However, there is little information regarding the role and efficacy of MTT in the relatively rare malignant endocrine tumours mainly involving the adrenal medulla, adrenal cortex, pituitary, and parathyroid glands. Due to the rarity of these tumours and the lack of prospective studies, current guidelines are mostly based on retrospective data derived from surgical, locoregional and ablative therapies, and studies with systemic chemotherapy. In addition, in many of these malignancies the prognosis remains poor with individual patients responding differently to currently available treatments, necessitating the development of new personalised therapeutic strategies. Recently, major advances in the molecular understanding of endocrine tumours based on genomic, epigenomic, and transcriptome analysis have emerged, resulting in new insights into their pathogenesis and molecular pathology. This in turn has led to the use of novel MTTs in increasing numbers of patients. In this review, we aim to present currently existing and evolving data using MTT in the treatment of adrenal, pituitary and malignant parathyroid tumours, and explore the current utility and effectiveness of such therapies and their future evolution.
Ben C Whitelaw
Temozolomide is an oral chemotherapy used to treat aggressive pituitary tumours since 2006. It is inexpensive and well tolerated, the main side effects are fatigue, nausea and cytopenia. Overall the studies demonstrate approximately 70% response rate for temozolomide, if response is defined radiologically as complete, partial response or stable disease. Using the more stringent criteria of complete or partial response, the success rate is near 40%. Functioning tumours respond more frequently than non-functioning tumours. Tumours which are depleted of methyl guanine methyltransferase (MGMT), as assessed by immunohistochemistry, also are more likely to respond. Temozolomide has an established role in treating pituitary tumours which have demonstrated metastases or which are refractory and progressing, despite all conventional treatment (so-called salvage treatment). The challenge is to offer temozolomide earlier in the pathway if appropriate. Tumours which demonstrate aggressive clinical behaviour (defined as clinically relevant growth despite optimal treatment) should be considered for temozolomide. One common situation when this might occur is tumour progression after surgery and radiotherapy. It is unnecessary to wait until salvage treatment is required. Anticipated (but not yet demonstrated) aggressive behaviour can be regarded as a potential indication for temozolomide, but there is currently insufficient evidence to recommend this. Ideally a trial should assess this potential indication. Early treatment could be considered in selected cases when high levels of proliferation and invasion were demonstrated, causing significant clinical concern.
K A S Al-Shoumer, S A Beshyah, and D G Johnston
R C F Leonard, A Ray, L Lee, T Leonard, and P Hopwood
Thomas J Giordano
The classification of human cancers represents one of the cornerstones of modern pathology. Over the last century, surgical pathologists established the current taxonomy of neoplasia using traditional histopathological parameters, which include tumor architecture, cytological features and cellular proliferation. This morphological classification is efficient and robust with high reproducibility and has served patients and health care providers well. The most recent decade has witnessed an explosion of genome-wide molecular genetic and epigenetic data for most cancers, including tumors of endocrine organs. The availability of this expansive multi-dimensional genomic data, collectively termed the cancer genome, has catalyzed a re-examination of the classification of endocrine tumors. Here, recent cancer genome studies of various endocrine tumors, including those of the thyroid, pituitary and adrenal glands, pancreas, small bowel, lung and skin, are presented with special emphasis on how genomic insights are impacting endocrine tumor classification.
Simona Grozinsky-Glasberg, Ilan Shimon, Márta Korbonits, and Ashley B Grossman
Neuroendocrine tumours (NETs) represent a heterogeneous family of neoplasms, which may develop from different endocrine glands (such as the pituitary, the parathyroid or the neuroendocrine adrenal glands), endocrine islets (within the thyroid or pancreas) as well as from endocrine cells dispersed between exocrine cells throughout the digestive and respiratory tracts. The development of somatostatin analogues (SSA) as important diagnostic and treatment tools has revolutionised the clinical management of patients with NETs. However, although symptomatic relief and stabilisation of tumour growth for various periods of time are observed in many patients treated with SSA, tumour regression is rare. Possible mechanisms when this does occur include antagonism of local growth factor release and effects, probably including activation of tyrosine and serine–threonine phosphatases, and indirect effects via anti-angiogenesis. The development of new SSA, new drug combination therapies and chimaeric molecules should further improve the clinical management of these patients, as should a more complete understanding of their mode of action.
S K Khoo, R Pendek, R Nickolov, D C Luccio-Camelo, T L Newton, A Massie, D Petillo, J Menon, D Cameron, B T Teh, and S-P Chan
Isolated familial somatotropinoma (IFS) accounts for 18% of familial isolated pituitary adenoma (FIPA) cases. Recently, germline mutations of the aryl hydrocarbon receptor-interacting protein gene (AIP) have been found in families with pituitary adenoma predisposition, FIPA, and IFS. In this study, we investigate the AIP mutation status and perform a genome-wide scan to search for the modifier regions of acromegalic phenotypes in an IFS family of 31 aborigines from Borneo. Complete endocrine diagnosis and data could not be collected due to logistical and cultural reasons. AIP mutation screening was carried out by direct sequencing and the genome-wide scan was performed using 400 microsatellites. Non-parametric linkage analysis was performed to obtain the logarithm of odds (LOD) scores. A novel AIP frameshift mutation in exon 4 (c.500delC) (p.P167HfsX3) was identified in all members with acromegalic features, as well as in 15 members without acromegalic features, revealing incomplete penetrance of AIP. The data showed that patients with the same mutation may express acromegalic features of differing severity, suggesting the existence of modifier genes. The highest LOD score of 2.2 was obtained near D19S571 (19q13.41). We also found weak linkages on chromosomes 3q28, 8q12.1, and 21q22.13, with LOD scores of 1.1, 1.8, and 1.4 respectively. Our results show the first genome-wide scan that identifies novel modifier loci for acromegalic phenotypes in an IFS family. Identification of modifier loci may provide further insight into the disease mechanism and explain the clinical variability observed in its patients.
Federico Gatto and Leo J Hofland
Somatostatin (SS) and dopamine (DA) receptors have been highlighted as two critical regulators in the negative control of hormonal secretion in a wide group of human endocrine tumors. Both families of receptors belong to the superfamily of G protein-coupled receptors and share a number of structural and functional characteristics. Because of the generally reported high expression of somatostatin receptors (SSTRs) in neuroendocrine tumors (NET), somatostatin analogs (SSA) have a pronounced role in the medical therapy for this class of tumors, especially pituitary adenomas and well-differentiated gastroenteropancreatic NET (GEP NET). Moreover, NET express not only SSTR but also frequently dopamine receptors (DRs), and DA agonists targeting the D2 receptor (D2) have been demonstrated to be effective in controlling hormone secretion and cell proliferation in in vivo and in vitro studies. The treatment with SSAs combined with DA agonists has already been demonstrated efficacious in a subgroup of patients with GH-secreting pituitary adenomas and few reported cases of carcinoids. The recent availability of new selective and universal SSA and DA agonists, as well as the chimeric SS/DA compounds, may shed new light on the potential role of SSTR and D2 as combined targets for biotherapy in NET. This review provides an overview of the latest studies evaluating the expression of SSTR and DR in NET, focusing on their co-expression and the possible clinical implications of such co-expression. Moreover, the most recent insights in SSTR and D2 pathophysiology and the future perspectives for treatment with SSA, DA agonists, and SS/DA chimeric compounds are discussed.
Maria Chiara Zatelli, Daniela Piccin, Cristina Vignali, Federico Tagliati, Maria Rosaria Ambrosio, Marta Bondanelli, Vincenzo Cimino, Antonio Bianchi, Herbert A Schmid, Massimo Scanarini, Alfredo Pontecorvi, Laura De Marinis, Giulio Maira, and Ettore C degli Uberti
Somatostatin (SRIF) analogs have been employed in medical therapy of non-functioning pituitary adenomas (NFA), with contrasting results. Previous evidence showed that SRIF can exert its antiproliferative effects by reducing vascular endothelial growth factor (VEGF) secretion and action, and that VEGF expression may be related to pituitary tumor growth. The aim of our study was to clarify the possible effects of a multireceptor SRIF ligand on VEGF secretion and cell proliferation in human NFA primary cultures. We assessed the expression of SRIF receptors (SSTR1–5), the in vitro effects on VEGF secretion, and on cell viability of SRIF and of the stable SRIF analog pasireotide (SOM230), which activates SSTR1, 2, 3, and 5. Twenty-five NFA were examined by RT-PCR for expression of α-subunit, SSTR, VEGF, and VEGF receptors 1 (VEGF-R1) and 2 (VEGF-R2). Primary cultures were tested with SRIF and with pasireotide. All NFA samples expressed α-sub, VEGF and VEGFR-1 and 2, while SSTR expression pattern was highly variable. Two different groups were identified according to VEGF secretion inhibition by SRIF. VEGF secretion and cell viability were reduced by SRIF and pasireotide in the ‘responder’ group, but not in the ‘non-responder’ group, including NFA expressing SSTR5. SRIF and pasireotide completely blocked forskolin-induced VEGF secretion. In addition, SRIF and pasireotide completely abrogated the promoting effects of VEGF on NFA cell viability. Our data demonstrate that pasireotide can inhibit NFA cell viability by inhibiting VEGF secretion, and suggest that the multireceptor-SSTR agonist pasireotide might be useful in medical therapy of selected NFA.