Bromocriptine Induces Autophagy-Dependent Cell Death in Pituitary Adenomas

Autophagy inhibition suppresses hormone production and cell growth in pituitary tumor cells: A potential approach to pituitary tumors

Pituitary tumors (PTs) represent about 10% of all intracranial tumors, and most are benign. However, some PTs exhibit continued growth despite multimodal therapies. Although temozolomide (TMZ), an alkylating chemotherapeutic agent, is a first-line medical treatment for aggressive PTs, some PTs are resistant to TMZ. Existing literature indicated the involvement of autophagy in cell growth in several types of tumors, including PTs, and autophagy inhibitors have anti-tumor effects. In this study, the expression of several autophagy-inducible genes, including Atg3, Beclin1, Map1lc3A, Map1lc3b, Ulk1, Wipi2, and Tfe3 in two PT cell lines, the mouse corticotroph AtT-20 cells and the rat mammosomatotroph GH4 cells were identified. Down regulation of Tfe3, a master switch of basal autophagy, using RNA interference, suppressed cell proliferation in AtT-20 cells, suggesting basal autophagy contributes to the maintenance of cellular functions in PT cells. Expectedly, treatment with bafilomycin A1, an autophagy inhibitor, suppressed cell proliferation, increased the cleavage of PARP1, and reduced ACTH production in AtT-20 cells. Treatment with two additional autophagy inhibitors, chloroquine (CQ) and monensin, demonstrated similar effects on cell proliferation, apoptosis, and ACTH production in AtT-20 cells. Also, treatment with CQ suppressed cell proliferation and growth hormone production in GH4 cells. Moreover, the combination of CQ and TMZ had an additive effect on the inhibition of cell proliferation in AtT-20 and GH4 cells. The additive effect of anti-cancer drugs such as CQ alone or in combination with TMZ may represent a novel therapeutic approach for PTs, in particular tumors with resistance to TMZ.

Intranasal 15d-PGJ2 inhibits the growth of rat lactotroph pituitary neuroendocrine tumors by inducing PPARγ-dependent apoptotic and autophagic cell death

PPARγ agonists have been reported to induce cell death in pituitary neuroendocrine tumor (PitNET) cell cultures. However, the therapeutic effects of PPARγ agonists in vivo remain unclear. In the present study, we found that intranasal 15d-PGJ2, an endogenous PPARγ agonist, resulted in growth suppression of Fischer 344 rat lactotroph PitNETs induced by subcutaneous implantation with a mini-osmotic pump containing estradiol. Intranasal 15d-PGJ2 reduced the volume and weight of the pituitary gland and the level of serum prolactin (PRL) in rat lactotroph PitNETs. 15d-PGJ2 treatment attenuated pathological changes and significantly decreased the ratio of PRL/pituitary-specific transcription factor 1 (Pit-1) and estrogen receptor α (ERα)/Pit-1 double-positive cells. Moreover, 15d-PGJ2 treatment induced apoptosis in the pituitary gland characterized by an increased ratio of TUNEL-positive cells, cleavage of caspase-3, and elevated activity of caspase-3. 15d-PGJ2 treatment decreased the levels of cytokines, including TNF-α, IL-1β, and IL-6. Furthermore, 15d-PGJ2 treatment markedly increased the protein expression of PPARγ and blocked autophagic flux, as evidenced by the accumulation of LC3-II and SQSTM1/p62 and the decrease in LAMP-1 expression. Importantly, all these effects mediated by 15d-PGJ2 were abolished by cotreatment with the PPARγ antagonist GW9662. In conclusion, intranasal 15d-PGJ2 suppressed the growth of rat lactotroph PitNETs by inducing PPARγ-dependent apoptotic and autophagic cell death. Therefore, 15d-PGJ2 may be a potential new drug for lactotroph PitNETs.

Current and Emerging Medical Therapies in Pituitary Tumors

Pituitary tumors (PT) represent in, the majority of cases, benign tumors for which surgical treatment still remains, except for prolactin-secreting PT, the first-line therapeutic option. Nonetheless, the role played by medical therapies for the management of such tumors, before or after surgery, has evolved considerably, due in part to the recent development of well-tolerated and highly efficient molecules. In this review, our aim was to present a state-of-the-art of the current medical therapies used in the field of PT and the benefits and caveats for each of them, and further specify their positioning in the therapeutic algorithm of each phenotype. Finally, we discuss the future of PT medical therapies, based on the most recent studies published in this field.

Architects of Pituitary Tumour Growth

The pituitary is a master gland responsible for the modulation of critical endocrine functions. Pituitary neuroendocrine tumours (PitNETs) display a considerable prevalence of 1/1106, frequently observed as benign solid tumours. PitNETs still represent a cause of important morbidity, due to hormonal systemic deregulation, with surgical, radiological or chronic treatment required for illness management. The apparent scarceness, uncommon behaviour and molecular features of PitNETs have resulted in a relatively slow progress in depicting their pathogenesis. An appropriate interpretation of different phenotypes or cellular outcomes during tumour growth is desirable, since histopathological characterization still remains the main option for prognosis elucidation. Improved knowledge obtained in recent decades about pituitary tumorigenesis has revealed that this process involves several cellular routes in addition to proliferation and death, with its modulation depending on many signalling pathways rather than being the result of abnormalities of a unique proliferation pathway, as sometimes presented. PitNETs can display intrinsic heterogeneity and cell subpopulations with diverse biological, genetic and epigenetic particularities, including tumorigenic potential. Hence, to obtain a better understanding of PitNET growth new approaches are required and the systematization of the available data, with the role of cell death programs, autophagy, stem cells, cellular senescence, mitochondrial function, metabolic reprogramming still being emerging fields in pituitary research. We envisage that through the combination of molecular, genetic and epigenetic data, together with the improved morphological, biochemical, physiological and metabolically knowledge on pituitary neoplastic potential accumulated in recent decades, tumour classification schemes will become more accurate regarding tumour origin, behaviour and plausible clinical results.

Treatment Strategies for Dopamine Agonist-Resistant and Aggressive Prolactinomas: A Comprehensive Analysis of the Literature

Despite most of the prolactinomas can be treated with endocrine therapy and/or surgery, a significant percentage of these tumors can be resistant to endocrine treatments and/or recur with prominent invasion into the surrounding anatomical structures. Hence, clinical, pathological, and molecular definitions of aggressive prolactinomas are important to guide for classical and novel treatment modalities. In this review, we aimed to define molecular endocrinological features of dopamine agonist-resistant and aggressive prolactinomas for designing future multimodality treatments. Besides surgery, temozolomide chemotherapy and radiotherapy, peptide receptor radionuclide therapy, estrogen pathway modulators, progesterone antagonists or agonists, mTOR/akt inhibitors, pasireotide, gefitinib/lapatinib, everolimus, and metformin are tested in preclinical models, anecdotal cases, and in small case series. Moreover, chorionic gonadotropin, gonadotropin releasing hormone, TGFβ and PRDM2 may seem like possible future targets for managing aggressive prolactinomas. Lastly, we discussed our management of a unique prolactinoma case by asking which tumors' proliferative index (Ki67) increased from 5-6% to 26% in two subsequent surgeries performed in a 2-year period, exerted massive invasive growth, and secreted huge levels of prolactin leading up to levels of 1 605 671 ng/dl in blood.

Genomic and transcriptomic analysis of pituitary adenomas reveals the impacts of copy number variations on gene expression and clinical prognosis among prolactin-secreting subtype

Pituitary adenomas (PAs) are slow growing and benign primary intracranial tumors that often cause occupying effects or endocrine symptoms. PAs can be classified into various subtypes according to hormone secretion. Although widespread transcriptional alterations that cause aberrant hormone secretion have been characterized, the impact of genomic variations on transcriptional alterations is unclear due to the rare occurrence of single-nucleotide variations in PA. In this study, we performed whole-genome sequencing (WGS) on 76 PA samples across three clinical subtypes (PRL-PAs; GH-PAs, and NFPAs); transcriptome sequencing (RNA-seq) of 54 samples across these subtypes was also conducted. Nine normal pituitary tissues were used as controls. Common and subtype-specific transcriptional alterations in PAs were identified. Strikingly, widespread genomic copy number amplifications were discovered for PRL-PAs, which are causally involved in transcriptomic changes in this subtype. Moreover, we found that the high copy number variations (CNVs) in PRL-PA cause increased prolactin production, drug resistance and proliferative capacity, potentially through key genes with copy number amplification and transcriptional activation, such as BCAT1. This study provides insight into how genomic CNVs affect the transcriptome and clinical outcomes of PRL-PA and sheds light on the development of potential therapeutics for aberrantly activated targets.

Autophagy and Pituitary Adenoma

Pituitary adenomas (PAs) are common, benign intracranial tumors that are usually effectively controlled with surgery, pharmacotherapy or radiotherapy. Some PAs against which conventional treatment is ineffective are great clinical challenges at present. Autophagy is a widespread physiological process in cells. Through autophagy, cells can degrade damaged or redundant proteins and organelles and achieve the recycling of intracellular substances to maintain the homeostasis of the intracellular environment. An increasing number of studies have demonstrated the importance of autophagy in tumor therapy. Both radiotherapy and chemotherapy can induce autophagy, which plays different roles in the course of therapy. In recent years, there has been growing interest in the role of autophagy during the treatment of PAs. This chapter reviews the recent progress of research on autophagy in PA and the autophagic mechanisms in the treatment of PA.

A chemical genomics-aggrephagy integrated method studying functional analysis of autophagy inducers

Macroautophagy/autophagy plays a critical role in the pathogenesis of various human diseases including neurodegenerative disorders such as Parkinson disease (PD) and Huntington disease (HD). Chemical autophagy inducers are expected to serve as disease-modifying agents by eliminating cytotoxic/damaged proteins. Although many autophagy inducers have been identified, their precise molecular mechanisms are not fully understood because of the complicated crosstalk among signaling pathways. To address this issue, we performed several chemical genomic analyses enabling us to comprehend the dominancy among the autophagy-associated pathways followed by an aggresome-clearance assay. In a first step, more than 400 target-established small molecules were assessed for their ability to activate autophagic flux in neuronal PC12D cells, and we identified 39 compounds as autophagy inducers. We then profiled the autophagy inducers by testing their effect on the induction of autophagy by 200 well-established signal transduction modulators. Our principal component analysis (PCA) and clustering analysis using a dataset of "autophagy profiles" revealed that two Food and Drug Administration (FDA)-approved drugs, memantine and clemastine, activate endoplasmic reticulum (ER) stress responses, which could lead to autophagy induction. We also confirmed that SMK-17, a recently identified autophagy inducer, induced autophagy via the PRKC/PKC-TFEB pathway, as had been predicted from PCA. Finally, we showed that almost all of the autophagy inducers tested in this present work significantly enhanced the clearance of the protein aggregates observed in cellular models of PD and HD. These results, with the combined approach, suggested that autophagy-activating small molecules may improve proteinopathies by eliminating nonfunctional protein aggregates.Abbreviations: ADK: adenosine kinase; AMPK: AMP-activated protein kinase; ATF4: activating transcription factor 4; BECN1: beclin-1; DDIT3/CHOP: DNA damage inducible transcript 3; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; EIF2S1/eIF2α: eukaryotic translation initiation factor 2 subunit alpha; ER: endoplasmic reticulum; ERN1/IRE1α: endoplasmic reticulum to nucleus signaling 1; FDA: Food and Drug Administration; GSH: glutathione; HD: Huntington disease; HSPA5/GRP78: heat shock protein family A (Hsp70) member 5; HTT: huntingtin; JAK: Janus kinase, MAP1LC3B/LC3: microtubule associated protein 1 light chain 3 beta; MAP2K/MEK: mitogen-activated protein kinase kinase; MAP3K8/Tpl2: mitogen-activated protein kinase kinase kinase 8; MAPK: mitogen-activated protein kinase; MPP⁺: 1-methyl-4-phenylpyridinium; MTOR: mechanistic target of rapamycin kinase; MTORC: MTOR complex; NAC: N-acetylcysteine; NGF: nerve growth factor 2; NMDA: N-methyl-D-aspartate; PCA: principal component analysis; PD: Parkinson disease; PDA: pancreatic ductal adenocarcinoma; PIK3C3: phosphatidylinositol 3-kinase catalytic subunit type 3; PMA: phorbol 12-myristate 13-acetate; PRKC/PKC: protein kinase C; ROCK: Rho-associated coiled-coil protein kinase; RR: ribonucleotide reductase; SIGMAR1: sigma non-opioid intracellular receptor 1; SQSTM1/p62: sequestosome 1; STK11/LKB1: serine/threonine kinase 11; TFEB: Transcription factor EB; TGFB/TGF-β: Transforming growth factor beta; ULK1: unc-51 like autophagy activating kinase 1; XBP1: X-box binding protein 1.

Treatment of Pituitary and Other Tumours with Cabergoline: New Mechanisms and Potential Broader Applications

Cabergoline is a dopamine agonist that has been used as the first-line treatment option for prolactin-secreting pituitary adenomas for several decades. It not only suppresses hormone production from these prolactinomas, but also causes tumour shrinkage. Recent studies revealed some novel mechanisms by which cabergoline suppresses tumour cell proliferation and induces cell death. In this article, we review the most recent findings in cabergoline studies, focusing on its anti-tumour function. These studies suggest the potential broader clinical use of cabergoline in the treatment of other tumours such as breast cancer, pancreatic neuroendocrine tumours, and lung cancer.

Identification of driver genes and key pathways of prolactinoma predicts the therapeutic effect of genipin

The purpose of the present study was to identify the potential targets and markers for diagnosis, therapy and prognosis in patients with prolactinoma at the molecular level and to determine the therapeutic effects of genipin in prolactinoma. The gene expression profiles of GSE2175, GSE26966 and GSE36314 were obtained from the Gene Expression Omnibus database. The differentially expressed genes (DEGs) were identified after comparing between gene expression profiles of the prolactinoma tissues and normal tissues. Then, Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and protein‑protein interaction (PPI) network analysis were conducted. In addition, in vitro, scratch assay, colony‑forming assay, Cell Counting Kit 8 (CCK8) assay and flow cytometry were performed to verify the functional effects of genipin. An aggregate of 12,695, 3,847 and 5,310 DEGs were identified from GSE2175, GSE26966 and GSE36314, respectively. The results of GO and KEGG analysis showed that the DEGs significant and important for prolactinoma were mostly involved with 'spindle pole' and 'oocyte meiosis'. A total of 20 genes were selected as hub genes with high degrees after PPI network analysis, including mitogen‑activated protein kinase 1 (MAPK1), MYC, early growth response 1 (EGR1), Bcl2 and calmodulin 1 (CALM1). CCK8 assay, colony‑forming assay and scratch assay were performed to verify the anti‑prolactinoma effect of genipin. The results of flow cytometry showed that apoptosis was increased by genipin. MAPK1, MYC, EGR1, Bcl2 and CALM1 were screened as main hub genes. Genipin upregulated the expression level of EGR1 and p21 (downstream mediator of EGR1) and EGR1, inhibited the proliferation and migration of prolactinoma cells. Genipin is a promising drug for treatment of patients with prolactinoma.

DEPTOR inhibits cell proliferation and confers sensitivity to dopamine agonist in pituitary adenoma

DEP domain-containing mechanistic target of rapamycin (mTOR)-interacting protein (DEPTOR) is an important modulator of mTOR, a highly conserved kinase whose hyperactivation is critically involved in a variety of human tumors. The role of DEPTOR playing in pituitary adenoma (PA) is largely unknown. Here, we reported that DEPTOR was downregulated in PA tissues, especially dopamine-resistant prolactinomas. Consistently, overexpression of DEPTOR inhibited pituitary tumor GH3 and MMQ cells proliferation in vitro and in vivo, and sensitized GH3 and MMQ cells to cabergoline (CAB), a dopamine agonist (DA). Conversely, knockdown of DEPTOR promoted GH3 and MMQ cells proliferation, and conferred cells resistance to CAB. Mechanistically, DEPTOR inhibited both mTOR Complex 1 (mTORC1) and 2 (mTORC2) activities in PA cells. In addition, DEPTOR expression level was increased to suppress mTOR kinase activity via decreasing E3 ubiquitin ligase, βTrCP1, in response to CAB. Furthermore, DEPTOR enhanced autophagy-dependent cell death to confer cells sensitivity to CAB. Taken together, our results suggest that DEPTOR may be a potential target for the treatment of PAs.

Clinical management of difficult to treat macroprolactinomas

INTRODUCTION

Prolactinomas represent the most common pituitary adenomas encountered in the clinic. While a majority of these tumors will be successfully treated by dopamine agonist (DA) such as cabergoline, their management becomes problematic since a resistance to DA can occur and/or if the tumor displays features of aggressiveness, two conditions that are closely related.

AREAS COVERED

Epidemiology and medical treatment of prolactinomas; resistance to DA and molecular basis of DA-resistance; therapeutical alternatives in case of DA-resistant Prolactinomas and therapies in development; summarizing conclusions.

EXPERT OPINION

The management of DA-resistant prolactinomas requires a multidisciplinary approach by an expert team. Along with discussions about surgery with or without gamma knife radiosurgery, genetic screening for multiple endocrine neoplasia type 1 (MEN1) syndrome is actively discussed in a case-by-case approach. In case of surgery, a careful analysis of the tumor sample can provide information about its aggressivity potential according to recent criteria. Ultimately, temozolomide can be indicated if the tumor is rapidly growing and/or threatening for the patient.

Impact of hyperprolactinemia in a patient with polyautoimmunity

Hyperprolactinemia has been proposed as a triggering factor for autoimmune diseases. The increased levels of prolactin could induce an abnormal immune response. Herein, we present a patient with hyperprolactinemia who developed polyautoimmunity. Patient's symptoms were associated with slightly raised levels of prolactin (20-40 ng/mL) and administration of dopaminergic agonists.

The Mechanism and Pathways of Dopamine and Dopamine Agonists in Prolactinomas

Dopamine agonists such as bromocriptine and cabergoline are the predominant treatment drugs for prolactinoma by inhibiting prolactin secretion and shrinking tumor size. However, the pathways of either dopamine or its agonists that lead to the death of cells are incompletely understood and some are even conflicting conclusions. The main aim of this paper is to review the different pathways of dopamine and its agonists in prolactinomas to help to gain a better understanding of their functions and drug resistance mechanisms.