15 YEARS OF PARAGANGLIOMA: Metabolism and pheochromocytoma/paraganglioma

Hormonally Silent Multifocal Pheochromocytoma in the Setting of a Well-Differentiated Neuroendocrine Tumor of the Appendix: A Case Report

Pheochromocytomas (PCCs) and paragangliomas (PGLs) represent tumors arising from chromaffin cells of the adrenal medulla and extra-adrenal sympathetic paraganglia, respectively. PCCs commonly produce one or more catecholamines (epinephrine, norepinephrine, and dopamine), but rarely are they biochemically silent. PGLs on the other hand, generally do not produce catecholamines. They have the highest heritability of all adrenal tumors and are known to be associated with genetic mutations. Patients with hereditary tumors typically present at a younger age and with multifocal disease when compared to sporadic disease. Specific genetic mutations have been well established with hereditary syndromes involving PCC/PGLs. Further research has aimed to identify other mutations and delineate specific phenotypes associated with these mutations. A 34-year-old woman presented for evaluation following a laparoscopic appendectomy that identified a 4-cm well-differentiated neuroendocrine tumor on final pathology. Further work-up included a repeat CT scan followed by a Dotatate PET CT scan which revealed a large (7.3 x 5.8 cm) periaortic mass related to the left adrenal gland. Functional adrenal work-up was negative and her Chromogranin A level was 679 ng/mL. She did report intermittent chest tightness and palpitations but was otherwise asymptomatic. The patient subsequently underwent an exploratory laparotomy with left adrenalectomy and adjacent tumor resection as well as completion of right hemicolectomy with ileocolonic anastomosis. Surgical pathology revealed two distinct masses consistent with multifocal PCC. No residual tumor was found in the colectomy specimen and 24 lymph nodes were negative. She had an uneventful recovery and genetic testing showed a variant of uncertain significance for the POLE and VHL genes. She has received genetic counseling and will be enrolled in an appropriate surveillance protocol.

The connection between tricarboxylic acid cycle enzyme mutations and pseudohypoxic signaling in pheochromocytoma and paraganglioma

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors originating from chromaffin cells, holding significant clinical importance due to their capacity for excessive catecholamine secretion and associated cardiovascular complications. Roughly 80% of cases are associated with genetic mutations. Based on the functionality of these mutated genes, PPGLs can be categorized into distinct molecular clusters: the pseudohypoxia signaling cluster (Cluster-1), the kinase signaling cluster (Cluster-2), and the WNT signaling cluster (Cluster-3). A pivotal factor in the pathogenesis of PPGLs is hypoxia-inducible factor-2α (HIF2α), which becomes upregulated even under normoxic conditions, activating downstream transcriptional processes associated with pseudohypoxia. This adaptation provides tumor cells with a growth advantage and enhances their ability to thrive in adverse microenvironments. Moreover, pseudohypoxia disrupts immune cell communication, leading to the development of an immunosuppressive tumor microenvironment. Within Cluster-1a, metabolic perturbations are particularly pronounced. Mutations in enzymes associated with the tricarboxylic acid (TCA) cycle, such as succinate dehydrogenase (SDHx), fumarate hydratase (FH), isocitrate dehydrogenase (IDH), and malate dehydrogenase type 2 (MDH2), result in the accumulation of critical oncogenic metabolic intermediates. Notable among these intermediates are succinate, fumarate, and 2-hydroxyglutarate (2-HG), which promote activation of the HIFs signaling pathway through various mechanisms, thus inducing pseudohypoxia and facilitating tumorigenesis. SDHx mutations are prevalent in PPGLs, disrupting mitochondrial function and causing succinate accumulation, which competitively inhibits α-ketoglutarate-dependent dioxygenases. Consequently, this leads to global hypermethylation, epigenetic changes, and activation of HIFs. In FH-deficient cells, fumarate accumulation leads to protein succination, impacting cell function. FH mutations also trigger metabolic reprogramming towards glycolysis and lactate synthesis. IDH1/2 mutations generate D-2HG, inhibiting α-ketoglutarate-dependent dioxygenases and stabilizing HIFs. Similarly, MDH2 mutations are associated with HIF stability and pseudohypoxic response. Understanding the intricate relationship between metabolic enzyme mutations in the TCA cycle and pseudohypoxic signaling is crucial for unraveling the pathogenesis of PPGLs and developing targeted therapies. This knowledge enhances our comprehension of the pivotal role of cellular metabolism in PPGLs and holds implications for potential therapeutic advancements.

Mutation of the Cell Cycle Regulator p27kip1 Drives Pseudohypoxic Pheochromocytoma Development

Simple Summary

Pheochromocytomas and paragangliomas (PPGLs) can be subdivided into at least three different subgroups associated with different clinical manifestations and depending on the risk to metastasize. A shortage in human tumor material, the lack of a functional human cell line and very limited animal models were major drawbacks for PPGL research and consequently for the development of patient-tailored targeted therapies. We have previously reported that the MENX rat model develops pheochromocytoma with a full penetrance at the age of 8–10 months, however, it was unclear which human group the rat tumors modeled best. In order to characterize the rat pheochromocytomas, we analyzed gene expression, the catecholamine profile, TCA-cycle metabolism, methylation, angiogenesis, histology and mitochondrial ultrastructure. In all aspects, rat MENX pheochromocytomas resemble the features of the human pseudohypoxia group, the most aggressive one and in need of effective therapeutic approaches.

Abstract

Background: Pseudohypoxic tumors activate pro-oncogenic pathways typically associated with severe hypoxia even when sufficient oxygen is present, leading to highly aggressive tumors. Prime examples are pseudohypoxic pheochromocytomas and paragangliomas (p-PPGLs), neuroendendocrine tumors currently lacking effective therapy. Previous attempts to generate mouse models for p-PPGLs all failed. Here, we describe that the rat MENX line, carrying a Cdkn1b (p27) frameshift-mutation, spontaneously develops pseudohypoxic pheochromocytoma (p-PCC). Methods: We compared rat p-PCCs with their cognate human tumors at different levels: histology, immunohistochemistry, catecholamine profiling, electron microscopy, transcriptome and metabolome. The vessel architecture and angiogenic potential of pheochromocytomas (PCCs) was analyzed by light-sheet fluorescence microscopy ex vivo and multi-spectral optoacoustic tomography (MSOT) in vivo. Results: The analysis of tissues at various stages, from hyperplasia to advanced grades, allowed us to correlate tumor characteristics with progression. Pathological changes affecting the mitochrondrial ultrastructure where present already in hyperplasias. Rat PCCs secreted high levels of norepinephrine and dopamine. Transcriptomic and metabolomic analysis revealed changes in oxidative phosphorylation that aggravated over time, leading to an accumulation of the oncometabolite 2-hydroxyglutarate, and to hypermethylation, evident by the loss of the epigenetic mark 5-hmC. While rat PCC xenografts showed high oxygenation, induced by massive neoangiogenesis, rat primary PCC transcriptomes possessed a pseudohypoxic signature of high Hif2a, Vegfa, and low Pnmt expression, thereby clustering with human p-PPGL. Conclusion: Endogenous rat PCCs recapitulate key phenotypic features of human p-PPGLs. Thus, MENX rats emerge as the best available animal model of these aggressive tumors. Our study provides evidence of a link between cell cycle dysregulation and pseudohypoxia.

Natural History and Management of Familial Paraganglioma Syndrome Type 1: Long-Term Data from a Large Family

Head and neck paragangliomas are the most common clinical features of familial paraganglioma syndrome type 1 caused by succinate dehydrogenase complex subunit D (SDHD) mutation. The clinical management of this syndrome is still unclear. In this study we propose a diagnostic algorithm for SDHD mutation carriers based on our family case series and literature review. After genetic diagnosis, first evaluation should include biochemical examination and whole-body imaging. In case of lesion detection, nuclear medicine examination is required for staging and tumor characterization. The study summarizes the diagnostic accuracy of different functional imaging techniques in SDHD mutation carriers. 18F-3,4-dihydroxyphenylalanine (18F-DOPA) positron emission tomography (PET)-computed tomography (CT) is considered the gold standard. If it is not available, 123I-Metaiodobenzylguanidine (MIBG) could be used also for predicting response to radiometabolic therapy. 18F-fluoro-2-deoxy-D-glucose (18F-FDG) PET-CT has a prognostic role since high uptake identifies more aggressive cases. Finally, 68Ga-peptides PET-CT is a promising diagnostic technique, demonstrating the best diagnostic accuracy in our and in other published case series, even if this finding still needs to be confirmed in larger studies. Periodic follow-up should consist of annual biochemical and ultrasonographic screening and biannual magnetic resonance examination to identify biochemical silent tumors early.

Metabolic Regulation of Epithelial to Mesenchymal Transition: Implications for Endocrine Cancer

The last few decades have witnessed an outstanding advancement in our understanding of the hallmarks of endocrine cancers. This includes the epithelial to mesenchymal transition (EMT), a process that alters the morphology and functional characteristics of carcinoma cells. The mesenchymal stem cell like phenotype produced by EMT allows the dislocation of cancer cells from the primary tumor site with inheritance of motility, metastatic and invasive properties. A fundamental driver thought to initiate and propagate EMT is metabolic reprogramming that occur during these transitions. Though there remains a paucity of data regarding the alterations that occur during EMT in endocrine cancers, the contribution of deregulated metabolism is a prominent feature. This mini review focuses on metabolic reprogramming events that occur in cancer cells and in particular those of endocrine origin. It highlights the main metabolic reprogramming outcomes of EMT, encompassing glycolysis, mitochondria oxidative phosphorylation and function, glutamine and lipid metabolism. Comprehending the metabolic changes that occur during EMT will help formulate potential bioenergetic targets as therapies for endocrine cancer metastasis.

Multifocal pheochromocytoma-paraganglioma in a 29-year-old woman with cyanotic congenital heart disease

BACKGROUND

Multifocal pheochromocytoma/paraganglioma presenting at an early age is commonly associated with a hereditary syndrome.

CASE REPORT

A 29-year-old woman was referred for evaluation of multifocal pheochromocytoma/paraganglioma. Interestingly, her family history did not include pheochromocytoma/paraganglioma, and comprehensive genetic testing for the well-documented pheochromocytoma/paraganglioma susceptibility genes was negative. Of note, this patient had a history of a complex cardiac defect resulting in cyanotic congenital heart disease and had never undergone operative repair. Thus she lived in a chronic hypoxic state with a baseline oxygen saturation of about 80%. Laboratory evaluation found marked increases in plasma norepinephrine and normetanephrines with normal epinephrine and metanephrines. Imaging revealed 4 aortocaval masses and a right adrenal mass. After appropriate preoperative preparation she underwent successful resection of each of the neoplasms, with pathologic testing revealing multifocal pheochromocytoma/paraganglioma.

DISCUSSION

This case highlights a growing recognition of the potential development of pheochromocytoma/paraganglioma in patients with cyanotic congenital heart disease. The underlying pathophysiology and phenotypic similarities between pheochromocytoma/paraganglioma in patients with cyanotic congenital heart disease and those with mutations that lead to cellular pseudohypoxia are reviewed.

Primary fibroblast co-culture stimulates growth and metabolism in Sdhb-impaired mouse pheochromocytoma MTT cells

Pheochromocytomas and paragangliomas (PGLs) due to mutations of succinate dehydrogenase (SDH) B, a subunit of the SDH complex with a role in the Krebs cycle and the respiratory chain, tend to be larger at diagnosis and more prone to metastatic disease than other tumors. This presentation contrasts with the behavior of some cell line models of SDHB impairment, which show reduced growth compared to wild type. We hypothesize that reduced growth of SDHB-impaired monolayer culture models might reflect lack of support from sources within the tumor microenvironment. The present study therefore investigates how the microenvironment, modeled here by fibroblast co-culture, modulates cell metabolism, growth and invasion in an Sdhb-impaired mouse pheochromocytoma cell line. We employed two different constructs of short hairpin RNA to knockdown Sdhb and compared growth in a monolayer with and without fibroblast co-culture. Sdhb-silenced cells showed functional impairment of SDH with elevated succinate to fumarate ratio and decreased oxidative capacity. Cell growth was delayed with an increase in doubling time of 2 h or 20 h. Clonogenic cell survival and viability, on the other hand, were either unchanged or increased compared to control. In standard monolayer culture, no differences in pro-metastatic features were present. Co-culture with primary mouse fibroblast reversed the difference of proliferation between control and Sdhb knockdown but was unable to significantly influence invasiveness under these culture conditions. Metabolic studies identified that lactate secreted by fibroblasts was taken up preferentially by Sdhb-silenced cells. In summary, the present study identified a potential role for the tumor microenvironment in influencing phenotypic features of SDHB-mutated PGLs, providing a basis for the use of therapies targeted towards the tumor microenvironment.

Pheochromocytoma: The First Metabolic Endocrine Cancer

Dysregulated metabolism is one of the key characteristics of cancer cells. The most prominent alterations are present during regulation of cell respiration, which leads to a switch from oxidative phosphorylation to aerobic glycolysis. This metabolic shift results in activation of numerous signaling and metabolic pathways supporting cell proliferation and survival. Recent progress in genetics and metabolomics has allowed us to take a closer look at the metabolic changes present in pheochromocytomas (PHEO) and paragangliomas (PGL). These neuroendocrine tumors often exhibit dysregulation of mitochondrial metabolism, which is driven by mutations in genes encoding Krebs cycle enzymes or by activation of hypoxia signaling. Present metabolic changes are involved in processes associated with tumorigenesis, invasiveness, metastasis, and resistance to various cancer therapies. In this review, we discuss the metabolic nature of PHEOs/PGLs and how unveiling the metabolic disturbances present in tumors could lead to identification of new biomarkers and personalized cancer therapies. Clin Cancer Res; 22(20); 5001-11. ©2016 AACR SEE ALL ARTICLES IN THIS CCR FOCUS SECTION, "ENDOCRINE CANCERS REVISING PARADIGMS".