Pseudohypoxia in paraganglioma and pheochromocytoma is associated with an immunosuppressive phenotype

Single-cell chromosome and bulk transcriptome analysis as a diagnostic tool to differentiate between localized and metastatic pheochromocytoma and sympathetic paraganglioma

Approximately 10-20% of patients with pheochromocytoma or sympathetic paraganglioma (PPGL) develop metastatic disease, most often as metachronous lesions. Unfortunately, there is a lack of accurate biomarkers that can predict the biologic behavior of a PPGL at the initial diagnosis. We investigated tumor samples from patients with PPGL and a diagnosis of either localized or metastatic disease with synchronous or metachronous metastases and performed a comprehensive molecular analysis through application of single-cell whole-genome sequencing and bulk transcriptome analysis, including variant detection analysis of RNA sequences. We found that PPGL displayed complex karyotypes with recurrent aneuploidies and substantial cell-to-cell karyotype variability, indicating ongoing chromosomal instability (CIN) in both localized and metastatic tumors. Transcriptome analysis on the other hand revealed several differences between localized and metastatic PPGL including TNFα and TGFβ signaling in metastatic PPGL that were already detectable in primary tumor samples of initially non-metastatic-appearing PPGLs that developed metachronous metastases. Altogether our findings indicate that while localized and metastatic PPGL in general have comparable genomic landscapes, they do show transcriptional differences that are already detectable in primary tumor PPGL before development of metastases. This finding could provide an important tool for improvement of patient stratification at initial diagnosis.

Prognosis and tumor microenvironment in pseudohypoxic pheochromocytoma/paraganglioma

Pheochromocytoma and paraganglioma (PPGL) are rare tumors that occur in the adrenal medulla and extra-adrenal tissues, respectively. The prognosis and tumor microenvironment (TME) of pseudohypoxic PPGL as a major entity have not been fully described. Based on the clinical database of 65 patients with PPGL, we assessed the morphological features as well as the immunohistochemistry of pseudohypoxia-related proteins (SDHB and CAIX) and TME-related immune cell markers. Furthermore, we compared the relapse-free survival (RFS) rates in localized patients between the pathological subgroups. Among 50 available specimens, 84% and 30% of the cases exhibited at least one morphological adverse feature including vascular/capsular invasion and a Ki-67 index > 3%, respectively. The SDHB and CAIX positivity rates were 81% and 51%. Concerning the immune cell markers, the CD163-positive cell numbers were higher in hypoxia-associated PPGL composed of SDHB-negative or CAIX-positive cases than in non-hypoxia PPGL (median 66 vs. 23/mm2). Concerning prognosis, RFS rates were significantly lower in cases with Ki-67 indices > 3% and SDHB-negativity than in those with Ki-67 indices ≤ 3% and SDHB-positivity (3-year rate: 64% vs. 100%, P < 0.001; 57% vs. 100%, P = 0.03). In contrast, RFS was comparable between CAIX-positive and CAIX-negative PPGL cases. Our analyses suggested that SDHB-deficient PPGL exhibited a higher incidence of relapse. Furthermore, M2 macrophage infiltration in TME might be crucial in pseudohypoxic PPGL pathogenesis.

A blood-based liquid biopsy analyzing soluble immune checkpoints and cytokines identifies distinct neuroendocrine tumors

BACKGROUND

Neuroendocrine neoplasms (NENs) comprise a group of rare tumors originating from neuroendocrine cells, which are present in both endocrine glands and scattered throughout the body. Due to their scarcity and absence of specific markers, diagnosing NENs remains a complex challenge. Therefore, new biomarkers are required, ideally, in easy-to-obtain blood samples.

METHODS

A panel of blood soluble immune checkpoints (sPD-L1, sPD-L2, sPD-1, sCD25, sTIM3, sLAG3, Galectin-9, sCD27, sB7.2 and sSIGLEC5) and cytokines (IL4, IL6, IP10 and MCP1) was quantified in a cohort of 139 NENs, including 29 pituitary NENs, 46 pheochromocytomas and paragangliomas, and 67 gastroenteropancreatic and pulmonary (GEPP) NENs, as well as in 64 healthy volunteers (HVs). The potential of these circulating immunological parameters to distinguish NENs from HVs, differentiate among various NENs subtypes, and predict their prognosis was evaluated using mathematical regression models. These immunological factors-based models generated scores that were evaluated by Receiver Operating Characteristic (ROC) and Area Under the Curve (AUC) analyses. Correlations between these scores and clinical data were performed. From these analyses, a minimal signature emerged, comprising the five shared immunological factors across the models: sCD25, sPD-L2, sTIM3, sLAG3, and Galectin-9. This refined signature was evaluated, validated, and checked for specificity against non-neuroendocrine tumors, demonstrating its potential as a clinically relevant tool for identifying distinct NENs.

RESULTS

Most of the immunological factors analyzed showed specific expression patterns among different NENs. Scores based on signatures of these factors identified NENs with high efficiency, showing AUCs ranging between 0.948 and 0.993 depending on the comparison, and accuracies between 92.52% and 95.74%. These scores illustrated biological features of NENs including the similarity between pheochromocytomas and paragangliomas, the divergence between gastrointestinal and pulmonary NENs, and correlated with clinical features. Furthermore, the models demonstrated strong performance in distinguishing metastatic and exitus GEPP NENs, achieving sensitivities and specificities ranging from 80.95% to 88.89%. Additionally, an easy-to-implement minimal signature successfully identified all analyzed NENs with AUC values exceeding 0.900, and accuracies between 84.11% and 93.12%, which was internally validated by a discovery and validation randomization strategy. These findings highlight the effectiveness of the models and minimal signature in accurately diagnosing and differentiating NENs.

CONCLUSIONS

The analysis of soluble immunological factors in blood presents a promising liquid biopsy approach for identifying NENs, delivering critical insights for both prognosis and diagnosis. This study serves as a proof-of-concept for an innovative clinical tool that holds the potential to transform the management of these rare malignancies, providing a non-invasive and effective method for early detection and disease monitoring.

Copper-enriched automotive brake wear particles perturb human alveolar cellular homeostasis

BACKGROUND

Airborne fine particulate matter with diameter < 2.5 μm (PM2.5), can reach the alveolar regions of the lungs, and is associated with over 4 million premature deaths per year worldwide. However, the source-specific consequences of PM2.5 exposure remain poorly understood. A major, but unregulated source is car brake wear, which exhaust emission reduction measures have not diminished.

METHODS

We used an interdisciplinary approach to investigate the consequences of brake-wear PM2.5 exposure upon lung alveolar cellular homeostasis using diesel exhaust PM as a comparator. This involved RNA-Seq to analyse global transcriptomic changes, metabolic analyses to investigate glycolytic reprogramming, mass spectrometry to determine PM composition, and reporter assays to provide mechanistic insight into differential effects.

RESULTS

We identified brake-wear PM from copper-enriched non-asbestos organic, and ceramic brake pads as inducing the greatest oxidative stress, inflammation, and pseudohypoxic HIF activation (a pathway implicated in diseases associated with air pollution exposure, including cancer, and pulmonary fibrosis), as well as perturbation of metabolism, and metal homeostasis compared with brake wear PM from low- or semi-metallic pads, and also, importantly, diesel exhaust PM. Compositional and metal chelator analyses identified that differential effects were driven by copper.

CONCLUSIONS

We demonstrate here that brake-wear PM may perturb cellular homeostasis more than diesel exhaust PM. Our findings demonstrate the potential differences in effects, not only for non-exhaust vs exhaust PM, but also amongst different sources of non-exhaust PM. This has implications for our understanding of the potential health effects of road vehicle-associated PM. More broadly, our findings illustrate the importance of PM composition on potential health effects, highlighting the need for targeted legislation to protect public health.

[Advance in HIF expression and immune microenvironment in pseudohypoxic HNPGL]

This article systematically reviewed the pathological features, molecular mechanisms, and tumor microenvironment of head and neck paraganglioma（HNPGL）, with a focus on pseudohypoxic HNPGL. It was demonstrated that pseudohypoxic HNPGL mainly involves multiple gene mutations, such as SDHx and VHL/EPAS1, which affect the stability and activity of HIF protein and exacerbate the development of the tumor. Meanwhile, the paper also analyzed the expression patterns of HIF-1α and HIF-2α in HNPGL, and found that differences in HIF activation may have an impact on the therapeutic response of specific subtypes. In addition, the paper explored the tumor microenvironment of HNPGL and found that immune cells such as macrophages, CD4⁺T cells, and CD8⁺T cells play an important role in the tumor, and the heterogeneity of the immune microenvironment also affects the choice of therapeutic approaches and responsiveness. Through comprehensive analysis, these findings not only contribute to a deeper understanding of the pathogenesis and developmental process of HNPGL, but also provide clues for future personalized treatments for specific subtypes.

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.

Immunohistochemical Profiling of SSTR2 and HIF-2α with the Tumor Microenvironment in Pheochromocytoma and Paraganglioma

Metastatic pheochromocytomas and paragangliomas (PPGLs) are rare endocrine malignancies with limited effective treatment options. The association between the tumor microenvironment (TME) with somatostatin receptor 2 (SSTR2) and hypoxia-induced factor-2α (HIF-2α) in PPGLs, critical for optimizing combination therapeutic strategies with immunotherapy, remains largely unexplored. To evaluate the association of SSTR2 and HIF-2α immunoreactivity with the TME in patients with PPGLs, we analyzed the expression of SSTR2A, HIF-2α, and TME components, including tumor-infiltrating lymphocytes (CD4 and CD8), tumor-associated macrophages (CD68 and CD163), and PD-L1, using immunohistochemistry in patients with PPGLs. The primary outcome was to determine the association of the immune profiles with SSTR2A and HIF-2α expression. Among 45 patients with PPGLs, SSTR2A and HIF2α were positively expressed in 21 (46.7%) and 14 (31.1%) patients, respectively. The median PD-L1 immunohistochemical score (IHS) was 2.0 (interquartile range: 0-30.0). Positive correlations were observed between CD4, CD8, CD68, and CD163 levels. A negative correlation was found between the CD163/CD68 ratio (an indicator of M2 polarization) and SSTR2A expression (r = -0.385, p = 0.006). HIF-2α expression showed a positive correlation with PD-L1 IHS (r = 0.348, p = 0.013). The co-expression of PD-L1 (HIS > 10) and HIF-2α was found in seven patients (15.6%). No associations were observed between SDHB staining results and the CD163/CD68 ratio, PD-L1, or SSTR2A expression. Our data suggest the potential of combination therapy with immunotherapy and peptide receptor radionuclide therapy or HIF-2α inhibitors as a treatment option in selected PPGL populations.

Genetic variants in hypoxia-inducible factor pathway are associated with colorectal cancer risk and immune infiltration

Hypoxia-inducible factor (HIF) pathway genes influence tumorigenesis and immune status. However, the associations between genetic variants in hypoxia-related genes and colorectal cancer risk and the immune status of hypoxia-associated genes in colorectal cancer have not been systematically characterized. The associations between genetic variants and colorectal cancer risk were evaluated in Chinese, Japanese and European populations using logistic regression analysis. The relationships between target genes and tumour immune infiltration were predicted by Tumour Immune Estimation Resource (TIMER). We found that rs34533650 in EPAS1 was associated with colorectal cancer risk (OR = 1.43, 95% CI = 1.20-1.70, P(FDR)  = 8.35 × 10-4 ), and this finding was validated in two independent populations (Japanese: OR = 1.07, 95% CI = 1.01-1.15, p = 3.38 × 10-2 ; European: OR = 1.11, 95% CI = 1.03-1.19, p = 6.04 × 10-3 ). EPAS1-associated genes were enriched in immune-related pathways. In addition, we found that EPAS1 copy number variation (CNV) was associated with the degree of infiltration of immune cells and observed correlations between EPAS1 expression and immune cell infiltration levels in colorectal cancer. These results highlight that genetic variants of hypoxia-related genes play roles in colorectal cancer risk and provide new insight that EPAS1 might be a promising predictor of colorectal cancer susceptibility and immune status.

Hypoxia as a potential inducer of immune tolerance, tumor plasticity and a driver of tumor mutational burden: Impact on cancer immunotherapy

In cancer patients, immune cells are often functionally compromised due to the immunosuppressive features of the tumor microenvironment (TME) which contribute to the failures in cancer therapies. Clinical and experimental evidence indicates that developing tumors adapt to the immunological environment and create a local microenvironment that impairs immune function by inducing immune tolerance and invasion. In this context, microenvironmental hypoxia, which is an established hallmark of solid tumors, significantly contributes to tumor aggressiveness and therapy resistance through the induction of tumor plasticity/heterogeneity and, more importantly, through the differentiation and expansion of immune-suppressive stromal cells. We and others have provided evidence indicating that hypoxia also drives genomic instability in cancer cells and interferes with DNA damage response and repair suggesting that hypoxia could be a potential driver of tumor mutational burden. Here, we reviewed the current knowledge on how hypoxic stress in the TME impacts tumor angiogenesis, heterogeneity, plasticity, and immune resistance, with a special interest in tumor immunogenicity and hypoxia targeting. An integrated understanding of the complexity of the effect of hypoxia on the immune and microenvironmental components could lead to the identification of better adapted and more effective combinational strategies in cancer immunotherapy. Clearly, the discovery and validation of therapeutic targets derived from the hypoxic tumor microenvironment is of major importance and the identification of critical hypoxia-associated pathways could generate targets that are undeniably attractive for combined cancer immunotherapy approaches.

PD-L1 and HIF-2α Upregulation in Head and Neck Paragangliomas after Embolization

Hypoxia activates pathways associated with tumor progression, metastatic spread, and alterations in the immune microenvironment leading to an immunosuppressive phenotype. In particular, the upregulation of PD-L1, a target for therapy with checkpoint inhibitors, is well-studied in several tumors. However, the relationship between hypoxia and PD-L1 regulation in pheochromocytomas and paragangliomas (PPGL), and especially in paragangliomas treated with embolization, is still largely unexplored. We investigated the expression of the hypoxia-marker HIF-2α and of PD-L1 in a PPGL-cohort with and without embolization as potential biomarkers that may predict the response to treatment with HIF-2α and checkpoint inhibitors. A total of 29 tumor samples from 25 patients who were operated at a single center were included and analyzed utilizing immunohistochemistry (IHC) for PD-L1 and HIF-2α. Embolization prior to surgery was performed in seven (24%) tumors. PD-L1 expression in tumor cells of head and neck paragangliomas (HNPGLs) receiving prior embolization (median PD-L1 positivity: 15%) was significantly higher as compared to PD-L1 expression in HNPGLs without prior embolization (median PD-L1 positivity: 0%) (p = 0.008). Consistently, significantly more HNPGLs with prior embolization were positive for HIF-2α (median nuclear HIF-2α positivity: 40%) as compared to HNPGLs without prior embolization (median nuclear HIF-2α positivity: 0%) (p = 0.016). Our results support the hypothesis that embolization with subsequent hypoxia leads to the upregulation of both PD-L1 and HIF-2α in HNPGLs, and could thus facilitate targeted treatment with HIF-2α and checkpoint inhibitors in the case of inoperable, locally advanced, or metastatic disease.

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.

PD-L1 Expression is Linked to Tumor-Infiltrating T-Cell Exhaustion and Adverse Pathological Behavior in Pheochromocytoma/Paraganglioma

Pheochromocytoma/paraganglioma (PPGL) is an endocrine-related tumor associated with excessive catecholamine release and has limited treatment options once metastasis occurs. Although recent phase 2 clinical trials of immune checkpoint inhibitors in the treatment of PPGL have preliminarily shown promising results, the fundamentals of immunotherapy for PPGL have not yet been established. In the early research, using bulk RNA sequencing of tumor samples from 7 PPGL patients, we found that PPGL tumor tissues exhibited high PD-L1 mRNA expression compared with adjacent normal adrenal medulla tissues, and this was related to T-cell exhaustion biomarkers. To further validate the association, in this study (n = 60), we first stratified all PPGL samples according to PD-L1 expression as determined by immunohistochemical staining, and then subjected 23 fresh PPGL tumor samples from the cohort to a quantitative polymerase chain reaction (n = 16), flow cytometry (n = 7), and multiplex-immunofluorescence staining. Subsequently, we evaluated the pathological manifestations of all 60 PPGL tumor samples and analyzed the correlation among PD-L1 expression, adverse pathological behavior, various clinicopathological data, and genotypes in PPGL. The results showed that PD-L1-positive expression correlated with the exhaustion of tumor-infiltrating T cells, preoperative abnormal elevation of plasma norepinephrine, high Ki67 index, and adverse pathological behavior in PPGL but not with genetic mutation or metastatic disease, possibly due to the limitation of the small number of patients with metastatic disease (n = 4) in the study cohort. In conclusion, our findings reveal that PD-L1 expression is associated with T-cell exhaustion and adverse pathological behavior in PPGL. These results are expected to provide a new theoretical basis and clinical guidance for the treatment of PPGL.

Platelet-Lymphocyte and Neutrophil-Lymphocyte Ratios Are Prognostic Markers for Pheochromocytomas and Paragangliomas

CONTEXT

Preoperative inflammatory markers, such as the neutrophil-lymphocyte ratio (NLR), platelet-lymphocyte ratio (PLR), and lymphocyte-monocyte ratio (LMR), have recently been proposed as prognostic markers in different tumors. However, their predictive values in patients with pheochromocytomas and paragangliomas (PPGLs) are uncertain.

OBJECTIVE

This study aimed to investigate the prognostic significance of inflammatory biomarkers in PPGL patients.

METHODS

Data from 1247 consecutive PPGL patients between 2002 and 2020 were evaluated. The preoperative inflammatory markers were evaluated. The prognostic roles were identified by X-tile software, Kaplan-Meier curves, and Cox regression models.

RESULTS

A total of 728 patients were included in the analysis, with a median follow-up of 63 months (IQR, 31-111 months); 31 individuals died, 28 patients developed metastases, and 12 patients developed recurrence. Our study showed that deaths were observed significantly more frequently in patients with high NLR(≥3.5) and high PLR (≥217.4) than those with low NLR (<3.5) (P = .003) and low PLR (<217.4) (P = .005). Elevated NLR (≥3.5) and elevated PLR (≥217.4) was significantly associated with decreased overall survival (OS) (P = .005), and elevated PLR (≥238.3) was significantly associated with decreased metastasis-free survival (MFS) (P = .021). Cox models illustrated that NLR and PLR were independent prognostic factors for OS, and PLR was an independent prognostic factor for MFS.

CONCLUSION

Both elevated NLR and PLR are associated with poor prognosis in PPGLs. They are convenient predictive markers that could be used in daily clinical practice.