SDHB and SDHD silenced pheochromocytoma spheroids respond differently to tumour microenvironment and their aggressiveness is inhibited by impairing stroma metabolism

The Immune Landscape of Pheochromocytoma and Paraganglioma: Current Advances and Perspectives

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors derived from neural crest cells from adrenal medullary chromaffin tissues and extra-adrenal paraganglia, respectively. Although the current treatment for PPGLs is surgery, optimal treatment options for advanced and metastatic cases have been limited. Hence, understanding the role of the immune system in PPGL tumorigenesis can provide essential knowledge for the development of better therapeutic and tumor management strategies, especially for those with advanced and metastatic PPGLs. The first part of this review outlines the fundamental principles of the immune system and tumor microenvironment, and their role in cancer immunoediting, particularly emphasizing PPGLs. We focus on how the unique pathophysiology of PPGLs, such as their high molecular, biochemical, and imaging heterogeneity and production of several oncometabolites, creates a tumor-specific microenvironment and immunologically "cold" tumors. Thereafter, we discuss recently published studies related to the reclustering of PPGLs based on their immune signature. The second part of this review discusses future perspectives in PPGL management, including immunodiagnostic and promising immunotherapeutic approaches for converting "cold" tumors into immunologically active or "hot" tumors known for their better immunotherapy response and patient outcomes. Special emphasis is placed on potent immune-related imaging strategies and immune signatures that could be used for the reclassification, prognostication, and management of these tumors to improve patient care and prognosis. Furthermore, we introduce currently available immunotherapies and their possible combinations with other available therapies as an emerging treatment for PPGLs that targets hostile tumor environments.

Animal and Cell Culture Models of PPGLs - Achievements and Limitations

Research on rare tumors heavily relies on suitable models for basic and translational research. Paragangliomas (PPGL) are rare neuroendocrine tumors (NET), developing from adrenal (pheochromocytoma, PCC) or extra-adrenal (PGL) chromaffin cells, with an annual incidence of 2-8 cases per million. While most PPGL cases exhibit slow growth and are primarily treated with surgery, limited systemic treatment options are available for unresectable or metastatic tumors. Scarcity of appropriate models has hindered PPGL research, preventing the translation of omics knowledge into drug and therapy development. Human PPGL cell lines are not available, and few animal models accurately replicate the disease's genetic and phenotypic characteristics. This review provides an overview of laboratory models for PPGLs, spanning cellular, tissue, organ, and organism levels. We discuss their features, advantages, and potential contributions to diagnostics and therapeutics. Interestingly, it appears that in the PPGL field, disease models already successfully implemented in other cancers have not been fully explored.

Tumour microenvironment in pheochromocytoma and paraganglioma

Pheochromocytomas and Paragangliomas (Pheo/PGL) are rare catecholamine-producing tumours derived from adrenal medulla or from the extra-adrenal paraganglia respectively. Around 10-15% of Pheo/PGL develop metastatic forms and have a poor prognosis with a 37% of mortality rate at 5 years. These tumours have a strong genetic determinism, and the presence of succinate dehydrogenase B (SDHB) mutations are highly associated with metastatic forms. To date, no effective treatment is present for metastatic forms. In addition to cancer cells, the tumour microenvironment (TME) is also composed of non-neoplastic cells and non-cellular components, which are essential for tumour initiation and progression in multiple cancers, including Pheo/PGL. This review, for the first time, provides an overview of the roles of TME cells such as cancer-associated fibroblasts (CAFs) and tumour-associated macrophages (TAMs) on Pheo/PGL growth and progression. Moreover, the functions of the non-cellular components of the TME, among which the most representatives are growth factors, extracellular vesicles and extracellular matrix (ECM) are explored. The importance of succinate as an oncometabolite is emerging and since Pheo/PGL SDH mutated accumulate high levels of succinate, the role of succinate and of its receptor (SUCNR1) in the modulation of the carcinogenesis process is also analysed. Further understanding of the mechanism behind the complicated effects of TME on Pheo/PGL growth and spread could suggest novel therapeutic targets for further clinical treatments.

Effects of metabolic cancer therapy on tumor microenvironment

Targeting tumor metabolism for cancer therapy is an old strategy. In fact, historically the first effective cancer therapeutics were directed at nucleotide metabolism. The spectrum of metabolic drugs considered in cancer increases rapidly - clinical trials are in progress for agents directed at glycolysis, oxidative phosphorylation, glutaminolysis and several others. These pathways are essential for cancer cell proliferation and redox homeostasis, but are also required, to various degrees, in other cell types present in the tumor microenvironment, including immune cells, endothelial cells and fibroblasts. How metabolism-targeted treatments impact these tumor-associated cell types is not fully understood, even though their response may co-determine the overall effectivity of therapy. Indeed, the metabolic dependencies of stromal cells have been overlooked for a long time. Therefore, it is important that metabolic therapy is considered in the context of tumor microenvironment, as understanding the metabolic vulnerabilities of both cancer and stromal cells can guide new treatment concepts and help better understand treatment resistance. In this review we discuss recent findings covering the impact of metabolic interventions on cellular components of the tumor microenvironment and their implications for metabolic cancer therapy.

Metformin Treatment Induces Different Response in Pheochromocytoma/Paraganglioma Tumour Cells and in Primary Fibroblasts

Simple Summary

Pheochromocytoma/paragangliomas (PPGLs) are neuroendocrine tumours and are often non-metastatic. However, no effective treatment is available for their metastatic form. Recent studies have shown that metformin exhibits antiproliferative activity in many human cancers, including PPGLs. Nevertheless, no data are available concerning whether metformin is also able to inhibit PPGL metastatic spread. A tumour is a very complex system, comprising not only cancer cells, but also other cells that all together form the so-called tumour microenvironment. Cancer-associated fibroblasts are residential or recruited fibroblasts, transformed by cancer cells, to promote tumour growth and spread. Therefore, the interplay between tumour cells and cancer-associated fibroblasts has become an interesting target for cancer therapy. Here, we demonstrate that metformin has different effects on cancer cells and fibroblasts, providing evidence that metformin may hold promise for altering tumour microenvironment homeostasis. Improving our knowledge on malignant tumour microenvironment properties could lead to develop complementary strategies to target tumour spread and progression.

Abstract

Pheochromocytoma/paragangliomas (PPGLs) are neuroendocrine tumours, often non-metastatic, but without available effective treatment for their metastatic form. Recent studies have shown that metformin exhibits antiproliferative activity in many human cancers, including PPGLs. Nevertheless, no data are available on the role of metformin on PPGL cells (two-dimension, 2D) and spheroids (three-dimension, 3D) migration/invasion. In this study, we observed that metformin exerts an antiproliferative effect on 2D and 3D cultures of pheochromocytoma mouse tumour tissue (MTT), either silenced or not for the SDHB subunit. However, metformin did not affect MTT migration. On the other hand, metformin did not have a short-term effect on the proliferation of mouse primary fibroblasts, but significantly decreased their ability to migrate. Although the metabolic changes induced by metformin were similar between MTT and fibroblasts (i.e., an overall decrease of ATP production and an increase in intracellular lactate concentration) the activated signalling pathways were different. Indeed, after metformin administration, MTT showed a reduced phosphorylation of Akt and Erk1/2, while fibroblasts exhibited a downregulation of N-Cadherin and an upregulation of E-Cadherin. Herein, we demonstrated that metformin has different effects on cell growth and spread depending on the cell type nature, underlining the importance of the tumour microenvironment in dictating the drug response.