Molecular Characterization of Growth Hormone-producing Tumors in the GC Rat Model of Acromegaly

Additive effects of ALXN2420, a GH receptor antagonist, and octreotide on IGF1 suppression in vivo

OBJECTIVE

Acromegaly is an endocrine disorder caused by the hypersecretion of growth hormone (GH) by a benign tumor of the pituitary that leads to insulin-like growth factor-1 (IGF1) overproduction. In most patients, somatostatin analogs (SSAs), the current first-line medical therapy for acromegaly, do not normalize IGF1 levels. This study aims to investigate the pre-clinical efficacy of ALXN2420, a novel, small peptide antagonist of the growth hormone receptor (GHR), being developed as a combination therapy to SSAs to further suppress and normalize IGF1 levels.

DESIGN

In vitro and in vivo experiments were performed to investigate the efficacy of ALXN2420 in antagonizing the GHR and in reducing circulating IGF1 levels.

METHODS

The binding affinity of ALXN2420 to GHR was determined by Surface Plasmon Resonance (SPR), and inhibition of GH-induced GHR activation was investigated in vitro in primary hepatocytes. The efficacy of ALXN2420 in suppressing IGF1 levels was evaluated in rats and dogs. The ability of ALXN2420 to reduce growth was determined in the juvenile rat model. Ultimately, the effect of combining ALXN2420 with a SSA in suppressing IGF1 was examined in rats.

RESULTS

ALXN2420 bound to the human GHR and inhibited its activation by GH in vitro. In vivo, ALXN2420 administration efficiently reduced IGF1 levels, which was associated with reduced growth in juvenile rats. Importantly, when combined with a SSA, ALXN2420 demonstrated an additive effect on IGF1 reduction.

CONCLUSION

These results support the investigation of ALXN2420 as a combination therapy for the treatment of patients with acromegaly inadequately controlled by SSAs.

The molecular biology of sporadic acromegaly

GH-secreting tumors represent 15 % to 20 % of all pituitary neuroendocrine tumors (pitNETs), of which 95 % occur in a sporadic context, without an identifiable inherited cause. Recent multi-omic approaches have characterized the epigenomic, genomic, transcriptomic, proteomic and kynomic landscape of pituitary tumors. Transcriptomic analysis has allowed us to discover specific transcription factors driving the differentiation of pituitary tumors and gene expression patterns. GH-secreting, along with PRL- and TSH-secreting pitNETs are driven by POU1F1; ACTH-secreting tumors are determined by TBX19; and non-functioning tumors, which are predominantly of gonadotrope differentiation are conditioned by NR5A1. Upregulation of certain miRNAs, such as miR-107, is associated with tumor progression, while downregulation of others, like miR-15a and miR-16-1, correlates with tumor size reduction. Additionally, miRNA expression profiles are linked to treatment resistance and clinical outcomes, providing insights into potential therapeutic targets. Specific somatic mutations in GNAS, PTTG1, GIPR, HGMA2, MAST and somatic variants associated with cAMP, calcium signaling, and ATP pathways have also been associated with the development of acromegaly. This review focuses on the oncogenic mechanisms by which sporadic acromegaly can develop, covering a complex series of molecular alterations that ultimately alter the balance between proliferation and apoptosis, and dysregulated hormonal secretion.

Acromegalic Rat Model Presented Cognitive Impairments and Tau Hyperphosphorylation in the Hippocampus

INTRODUCTION

Acromegaly patients, in addition to the most prominent physical and endocrine changes, also exhibit a higher risk of cognitive dysfunction. However, the reasons and mechanisms underlying cognitive impairments in acromegaly patients remain unknown.

METHODS

Acromegalic rats were induced by subcutaneous injection of tumor cells, with continuous monitoring of the body weight and hormones to confirm the occurrence of acromegaly. Behavioral assessments, including open field test, novel object recognition test, and Barnes maze test, were conducted to evaluate the animals' cognitive function. Western blotting, immunohistochemistry, and immunofluorescence techniques were employed to examine changes in the hippocampal tau protein, Aβ, and associated signaling pathways.

RESULTS

The tumor cells secreting growth hormone increased the secretion of growth hormone, resulting in changes in body size and endocrine functions, thus causing acromegaly. The acromegaly model showed deficiencies in working memory and spatial memory. Hyperphosphorylation of tau protein was observed in the hippocampus of the acromegaly model, but no Aβ deposition was observed. The acromegaly model exhibits hippocampal growth hormone (GH) resistance, decreased expression of GH receptors, and subsequently reduced expression activity of the PI3K-Akt-GSK3β signaling pathway, which is responsible for the hyperphosphorylation of tau protein.

CONCLUSION

The prolonged elevation of GH and insulin-like growth factor 1 caused by acromegaly may lead to abnormalities in the SD rat's PI3K-Akt-GSK3β signaling pathway, subsequently resulting in hyperphosphorylation of the hippocampal tau protein and cognitive impairment.

Mechanisms of ageing: growth hormone, dietary restriction, and metformin

Tackling the mechanisms underlying ageing is desirable to help to extend the duration and improve the quality of life. Life extension has been achieved in animal models by suppressing the growth hormone-insulin-like growth factor 1 (IGF-1) axis and also via dietary restriction. Metformin has become the focus of increased interest as a possible anti-ageing drug. There is some overlap in the postulated mechanisms of how these three approaches could produce anti-ageing effects, with convergence on common downstream pathways. In this Review, we draw on evidence from both animal models and human studies to assess the effects of suppression of the growth hormone-IGF-1 axis, dietary restriction, and metformin on ageing.

RET signalling provides tumorigenic mechanism and tissue specificity for AIP-related somatotrophinomas

It is unclear how loss-of-function germline mutations in the widely-expressed co-chaperone AIP, result in young-onset growth hormone secreting pituitary tumours. The RET receptor, uniquely co-expressed in somatotrophs with PIT1, induces apoptosis when unliganded, while RET supports cell survival when it is bound to its ligand. We demonstrate that at the plasma membrane, AIP is required to form a complex with monomeric-intracellular-RET, caspase-3 and PKCδ resulting in PIT1/CDKN2A-ARF/p53-apoptosis pathway activation. AIP-deficiency blocks RET/caspase-3/PKCδ activation preventing PIT1 accumulation and apoptosis. The presence or lack of the inhibitory effect on RET-induced apoptosis separated pathogenic AIP variants from non-pathogenic ones. We used virogenomics in neonatal rats to demonstrate the effect of mutant AIP protein on the RET apoptotic pathway in vivo. In adult male rats altered AIP induces elevated IGF-1 and gigantism, with pituitary hyperplasia through blocking the RET-apoptotic pathway. In females, pituitary hyperplasia is induced but IGF-1 rise and gigantism are blunted by puberty. Somatotroph adenomas from pituitary-specific Aip-knockout mice overexpress the RET-ligand GDNF, therefore, upregulating the survival pathway. Somatotroph adenomas from patients with or without AIP mutation abundantly express GDNF, but AIP-mutated tissues have less CDKN2A-ARF expression. Our findings explain the tissue-specific mechanism of AIP-induced somatotrophinomas and provide a previously unknown tumorigenic mechanism, opening treatment avenues for AIP-related tumours.

Chronic adult-onset of growth hormone/IGF-I hypersecretion improves cognitive functions and LTP and promotes neuronal differentiation in adult rats

AIM

Besides their metabolic and endocrine functions, the growth hormone (GH) and its mediated factor, the insulin-like growth factor I (IGF-I), have been implicated in different brain functions, including neurogenesis. Long-lasting elevated GH and IGF-I levels result in non-reversible somatic, endocrine and metabolic morbidities. However, the subcutaneous implantation of the GH-secreting (GH-S) GC cell line in rats leads to the controllable over-secretion of GH and elevated IGF-I levels, allowing the experimental study of their short-term effects on brain functions.

METHODS

Adult rats were implanted with GC cells and checked 10 weeks later, when a GH/IGF-I-secreting tumour was already formed.

RESULTS

Tumour-bearing rats acquired different operant conditioning tasks faster and better than controls and tumour-resected groups. They also presented better retentions of long-term memories in the passive avoidance test. Experimentally evoked long-term potentiation (LTP) in the hippocampus was also larger and longer lasting in the tumour bearing than in the other groups. Chronic adult-onset of GH/IGF-I hypersecretion caused an acceleration of early progenitors, facilitating a faster neural differentiation, maturation and integration in the dentate gyrus, and increased the complexity of dendritic arbours and spine density of granule neurons.

CONCLUSION

Thus, adult-onset hypersecretion of GH/IGF-I improves neurocognitive functions, long-term memories, experimental LTP and neural differentiation, migration and maturation.

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.

The oncogenic role of the In1-ghrelin splicing variant in prostate cancer aggressiveness

Background

The Ghrelin-system is a complex, pleiotropic family composed of several peptides, including native-ghrelin and its In1-ghrelin splicing variant, and receptors (GHSR 1a/b), which are dysregulated in various endocrine-related tumors, where they associate to pathophysiological features, but the presence, functional role, and mechanisms of actions of In1-ghrelin splicing variant in prostate-cancer (PCa), is completely unexplored. Herein, we aimed to determine the presence of key ghrelin-system components (native-ghrelin, In1-ghrelin, GHSR1a/1b) and their potential pathophysiological role in prostate cancer (PCa).

Methods

In1-ghrelin and native-ghrelin expression was evaluated by qPCR in prostate tissues from patients with high PCa-risk (n = 52; fresh-tumoral biopsies), and healthy-prostates (n = 12; from cystoprostatectomies) and correlated with clinical parameters using Spearman-test. In addition, In1-ghrelin and native-ghrelin was measured in plasma from an additional cohort of PCa-patients with different risk levels (n = 30) and control-healthy patients (n = 20). In vivo functional (proliferation/migration) and mechanistic (gene expression/signaling-pathways) assays were performed in PCa-cell lines in response to In1-ghrelin and native-ghrelin treatment, overexpression and/or silencing. Finally, tumor progression was monitored in nude-mice injected with PCa-cells overexpressing In1-ghrelin, native-ghrelin and empty vector (control).

Results

In1-ghrelin, but not native-ghrelin, was overexpressed in high-risk PCa-samples compared to normal-prostate (NP), and this expression correlated with that of PSA. Conversely, GHSR1a/1b expression was virtually absent. Remarkably, plasmatic In1-ghrelin, but not native-ghrelin, levels were also higher in PCa-patients compared to healthy-controls. Furthermore, In1-ghrelin treatment/overexpression, and to a much lesser extent native-ghrelin, increased aggressiveness features (cell-proliferation, migration and PSA secretion) of NP and PCa cells. Consistently, nude-mice injected with PC-3-cells stably-transfected with In1-ghrelin, but not native-ghrelin, presented larger tumors. These effects were likely mediated by ERK1/2-signaling activation and involved altered expression of key oncogenes/tumor suppressor genes. Finally, In1-ghrelin silencing reduced cell-proliferation and PSA secretion from PCa cells.

Conclusions

Altogether, our results indicate that In1-ghrelin levels (in tissue) and circulating levels (in plasma) are increased in PCa where it can regulate key pathophysiological processes, thus suggesting that In1-ghrelin may represent a novel biomarker and a new therapeutic target in PCa.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0713-9) contains supplementary material, which is available to authorized users.

The oncogenic role of the spliced somatostatin receptor sst5TMD4 variant in prostate cancer

sst5TMD4, a splice variant of the sst5 gene, is overexpressed and associated with aggressiveness in various endocrine-related tumors, but its presence, functional role, and mechanisms of actions in prostate cancer (PCa)-the most common cancer type in males-is completely unexplored. In this study, formalin-fixed, paraffin-embedded prostate pieces from patients with localized PCa, which included tumoral and nontumoral adjacent regions (n = 45), fresh biopsies from patients with high-risk PCa (n = 52), and healthy fresh prostates from cystoprostatectomies (n = 14) were examined. In addition, PCa cell lines and xenograft models were used to determine the presence and functional role of sst5TMD4. Results demonstrated that sst5TMD4 is overexpressed (mRNA/protein) in PCa samples, and this is especially drastic in metastatic and/or high Gleason score tumor samples. Remarkably, sst5TMD4 expression was associated with an altered frequency of 2 single-nucleotide polymorphisms: rs197055 and rs12599155. In addition, PCa cell lines and xenograft models were used to demonstrate that sst5TMD4 overexpression increases cell proliferation and migration in PCa cells and induces larger tumors in nude mice, whereas its silencing decreased proliferation and migration. Remarkably, sst5TMD4 overexpression activated multiple intracellular pathways (ERK/JNK, MYC/MAX, WNT, retinoblastoma), altered oncogenes and tumor suppressor gene expression, and disrupted the normal response to somatostatin analogs in PCa cells. Altogether, we demonstrate that sst5TMD4 is overexpressed in PCa, especially in those patients with a worse prognosis, and plays an important pathophysiologic role in PCa, which suggesting its potential as a biomarker and/or therapeutic target.-Hormaechea-Agulla, D., Jiménez-Vacas, J. M., Gómez-Gómez, E., L.-López, F., Carrasco-Valiente, J., Valero-Rosa, J., Moreno, M. M., Sánchez-Sánchez, R., Ortega-Salas, R., Gracia-Navarro, F., Culler, M. D., Ibáñez-Costa, A., Gahete, M. D., Requena, M. J., Castaño, J. P., Luque, R. M. The oncogenic role of the spliced somatostatin receptor sst5TMD4 variant in prostate cancer.