The MIF promoter SNP rs755622 is associated with immune activation in glioblastoma

Intratumoral heterogeneity is a defining hallmark of glioblastoma, driving drug resistance and ultimately recurrence. Many somatic drivers of microenvironmental change have been shown to affect this heterogeneity and, ultimately, the treatment response. However, little is known about how germline mutations affect the tumoral microenvironment. Here, we find that the single-nucleotide polymorphism (SNP) rs755622 in the promoter of the cytokine macrophage migration inhibitory factor (MIF) is associated with increased leukocyte infiltration in glioblastoma. Furthermore, we identified an association between rs755622 and lactotransferrin expression, which could also be used as a biomarker for immune-infiltrated tumors. These findings demonstrate that a germline SNP in the promoter region of MIF may affect the immune microenvironment and further reveal a link between lactotransferrin and immune activation.

GAP43-dependent mitochondria transfer from astrocytes enhances glioblastoma tumorigenicity

The transfer of intact mitochondria between heterogeneous cell types has been confirmed in various settings, including cancer. However, the functional implications of mitochondria transfer on tumor biology are poorly understood. Here we show that mitochondria transfer is a prevalent phenomenon in glioblastoma (GBM), the most frequent and malignant primary brain tumor. We identified horizontal mitochondria transfer from astrocytes as a mechanism that enhances tumorigenesis in GBM. This transfer is dependent on network-forming intercellular connections between GBM cells and astrocytes, which are facilitated by growth-associated protein 43 (GAP43), a protein involved in neuron axon regeneration and astrocyte reactivity. The acquisition of astrocyte mitochondria drives an increase in mitochondrial respiration and upregulation of metabolic pathways linked to proliferation and tumorigenicity. Functionally, uptake of astrocyte mitochondria promotes cell cycle progression to proliferative G2/M phases and enhances self-renewal and tumorigenicity of GBM. Collectively, our findings reveal a host-tumor interaction that drives proliferation and self-renewal of cancer cells, providing opportunities for therapeutic development.

TMIC-82. LIPOCALIN-2 MEDIATES CELL-INTRINSIC AND CELL-EXTRINSIC FUNCTIONS IN GLIOBLASTOMA

Glioblastoma (GBM) is the most common primary brain tumor with a median survival of 17-20 months. Despite therapeutic treatments including surgery, radiation, chemotherapy, a subset of GBM clones, termed cancer stem cells (CSCs) are radio-resistant and chemo-resistant, leading to mortality of the patient. CSCs also have altered metabolic profiles and have an enhanced capacity to scavenge nutrients from their microenvironment, including iron. Lipocalin-2 (LCN2) functions to sequester iron and is traditionally considered an inflammatory marker through its function of limiting iron for bacterial usage. LCN2 has been described to have both a pro and anti-tumorigenic and has context-dependent functions depending on iron status. LCN2 has been shown to be important in brain metastasis, but its role in GBM is still largely unknown. To investigate how LCN2 plays a role in the GBM microenvironment, we orthotopically implanted syngeneic mouse GBM cells into male and female LCN2 knockout and wild-type mice. Female LCN2 knockout mice succumbed to tumors faster compared to males, revealing another example of sex differences in the tumor microenvironment. To assess a cell-intrinsic function for LNC2, we added recombinant LCN2 to mouse GBM cell lines and saw that proliferation also increased. When we probed for receptor expression in our knockdown cell lines, we saw that the LCN2 canonical receptor, SLC22a17, was upregulated in response. Furthermore, in a subset of slow-cycling cells of CSCs, LCN2 was shown to be up-regulated. Taken together, these data suggest that LCN2 functions in an iron-dependent manner to affect proliferation and sex-specific tumorigenesis. Given the fact that males have more iron than females, it is worth investigating the role of iron in GBM sex difference progression and therapeutic targets.

TMIC-69. MITOCHONDRIAL TRANSFER FROM ASTROCYTES ENHANCES METABOLISM AND DRIVES PROLIFERATION OF GLIOBLASTOMA

Mitochondrial transfer occurs both in stroke (central nervous system) and inflammatory pain (peripheral nerves). However, its role in glioblastoma (GBM) remains poorly understood. We hypothesized that mitochondrial transfer from non-malignant to GBM cells supports tumor metabolism and growth. Using transgenic mice expressing fluorophore-tagged mitochondria, we found that ~50% of orthotopically-implanted mouse GBM cells acquire mitochondria. Brain-resident cells, especially astrocytes, were the primary mitochondrial donors in vitro and in vivo. Mitochondrial transfer also occurred from immortalized human astrocytes to patient-derived xenograft (PDX) models in vitro at rates of 15-35%. GBM cells that acquired mitochondria expressed higher levels of the ATP-synthase subunit ATP5A and produced more ATP, while metabolomics revealed multiple upregulated pathways in recipient cells. These data point to increased metabolic activity in recipient cells. In vivo, mouse GBM cells that acquired mitochondria were more likely to be in S/G2/M cell cycle phases. We observed a similar effect in PDX that acquired astrocyte mitochondria in vitro, suggesting that transfer drives GBM proliferation. Using sorted mouse and human GBM cells with/without in vitro astrocyte mitochondrial acquisition, we found that mitochondrial transfer promoted in vitro self-renewal and in vivo tumorigenicity, leading to significant reduction in survival and increased penetrance in orthotopic GBM models. Transfer in mouse and human systems was contact-dependent and was abrogated by physical separation of donor and recipient cells by transwell inserts. Pharmacologic inhibition of cytoskeleton and gap junctions did not affect transfer rate, while blocking growth-associated protein 43 (GAP43) function by c-Jun N-terminus kinase inhibition decreased transfer rate by 15-30%, suggesting a potential role of GAP43. Taken together, mitochondrial transfer comprises a fundamental, protumorigenic mechanism of GBM, enhancing metabolic activity and driving tumor cell proliferation. Elucidating the molecular machinery regulating astrocyte mitochondrial transfer and its downstream protumorigenic effects will lead to therapeutic opportunities targeting this understudied tumor microenvironment interaction.

Abstract 2430: The role of cellular iron and the homeostatic iron regulator (HFE) in high-grade brain tumor cell migration

High-grade brain tumors such as grade III astrocytoma and glioblastoma represent among the most difficult to manage malignancies facing oncological practice. Diffuse migration and invasion into adjacent healthy brain tissue yields complete surgical resection of these tumors unfeasible. As a result, despite receiving maximal surgical resection and an aggressive course of chemoradiation, the majority of high-grade brain tumor patients suffer from recurrent disease. Increased expression levels of the homeostatic iron regulator gene (HFE) in high-grade brain tumors have been correlated with poorer outcomes. HFE is known to influence cellular iron metabolism by inhibiting transferrin-mediated iron uptake yet little is known regarding how HFE or iron impact the migratory capabilities of high-grade brain tumor cells. In order to better understand how HFE expression and cellular iron metabolism influence cell migration in high grade brain tumors, we utilized brain tumor cell lines that had been genetically manipulated to express different levels of HFE. We observed that knocking down HFE in KR158 or LN229 glioma cell lines resulted in significantly decreased migratory capacity. Since HFE is known to inhibit transferrin mediated iron uptake, we studied how directly modulating the iron status of glioma cells impacted their ability to migrate. Treatment of a panel of glioma cell lines: LN229, T98G, U87, KR158, with iron in the form of hemin or ferric ammonium citrate resulted in significantly reduced migration. Furthermore, the iron-induced reduction in migration could be rescued by the addition of deferoxamine, an iron chelator. Cell viability in response to the iron treatments was assayed and found to not be significantly altered - suggesting that cellular iron status was influencing migratory capacity independent of cell viability. To gain mechanistic insights into HFE and iron-induced effects on cell migration, we analyzed the Chinese Glioma Genome Atlas (CGGA) for correlations between HFE and the Rho GTPases RHOA, RAC1, and CDC42 – genes which are known to play a crucial role in determining the migratory capacity of cancer cells. Interestingly, we found statistically significant correlations between the Rho GTPases RHOA, RAC1, CDC42 and HFE in both grade III astrocytoma and glioblastoma patient cohorts. Immunoblotting of iron treated glioma cell lines demonstrated that expression of RhoA and Cdc42 was reduced suggesting that alterations in Rho GTPase expression and signaling may play a role in iron-induced effects on cell migration. Our results demonstrate that targeting cancer cell iron metabolism as an addition to existing treatment regimens may be a promising avenue for further investigation.

Citation Format: Ganesh Shenoy, Katie Troike, Kondaiah Palsa, Madison Kuhn, Quinn Wade, Becky Slagle-Webb, Amanda Snyder, Chachrit Khunsriraksakul, Justin D. Lathia, Dhimant Desai, Hong-Gang Wang, Elizabeth Proctor, James R. Connor. The role of cellular iron and the homeostatic iron regulator (HFE) in high-grade brain tumor cell migration [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2430.

Unexplored Functions of Sex Hormones in Glioblastoma Cancer Stem Cells

Biological sex impacts a wide array of molecular and cellular functions that impact organismal development and can influence disease trajectory in a variety of pathophysiological states. In nonreproductive cancers, epidemiological sex differences have been observed in a series of tumors, and recent work has identified previously unappreciated sex differences in molecular genetics and immune response. However, the extent of these sex differences in terms of drivers of tumor growth and therapeutic response is less clear. In glioblastoma (GBM), the most common primary malignant brain tumor, there is a male bias in incidence and outcome, and key genetic and epigenetic differences, as well as differences in immune response driven by immune-suppressive myeloid populations, have recently been revealed. GBM is a prototypic tumor in which cellular heterogeneity is driven by populations of therapeutically resistant cancer stem cells (CSCs) that underlie tumor growth and recurrence. There is emerging evidence that GBM CSCs may show a sex difference, with male tumor cells showing enhanced self-renewal, but how sex differences impact CSC function is not clear. In this mini-review, we focus on how sex hormones may impact CSCs in GBM and implications for other cancers with a pronounced CSC population. We also explore opportunities to leverage new models to better understand the contribution of sex hormones vs sex chromosomes to CSC function. With the rising interest in sex differences in cancer, there is an immediate need to understand the extent to which sex differences impact tumor growth, including effects on CSC function.

The evolution of the cancer stem cell state in glioblastoma: emerging insights into the next generation of functional interactions

Cellular heterogeneity is a hallmark of advanced cancers and has been ascribed in part to a population of self-renewing, therapeutically resistant cancer stem cells (CSCs). Glioblastoma (GBM), the most common primary malignant brain tumor, has served as a platform for the study of CSCs. In addition to illustrating the complexities of CSC biology, these investigations have led to a deeper understanding of GBM pathogenesis, revealed novel therapeutic targets, and driven innovation towards the development of next-generation therapies. While there continues to be an expansion in our knowledge of how CSCs contribute to GBM progression, opportunities have emerged to revisit this conceptual framework. In this review, we will summarize the current state of CSCs in GBM using key concepts of evolution as a paradigm (variation, inheritance, selection, and time) to describe how the CSC state is subject to alterations of cell intrinsic and extrinsic interactions that shape their evolutionarily trajectory. We identify emerging areas for future consideration, including appreciating CSCs as a cell state that is subject to plasticity, as opposed to a discrete population. These future considerations will not only have an impact on our understanding of this ever-expanding field but will also provide an opportunity to inform future therapies to effectively treat this complex and devastating disease.

Sex Differences in Glioblastoma Immunotherapy Response

Glioblastoma (GBM), the most common primary malignant brain tumor, remains difficult to treat and shares phenotypes, including an aberrant immune response, with other neurological disorders. Understanding the cellular and molecular mechanisms underlying this pathological immune response remains a priority, particularly as standard of care for advanced cancers evolves to include immunotherapies, which have yet to show strong clinical efficacy in GBM. Epidemiological evidence supports a sex difference in GBM, with increased prevalence in males, and recent studies identified differences between males and females ranging from genetic aberrations to cellular programs. Sex differences have also been identified in immune response, and in this mini-review, we present these differences to highlight potential sex-specific cellular and molecular mechanisms that underly GBM growth and response to immunotherapies. These sex differences offer an opportunity to understand GBM pathogenesis and extend beyond GBM to other tumors and neurological disorders to inform the development of next-generation therapies.

CBIO-10. REDUCED IRON EXPORT FUNCTIONS IN A CELL INTRINSIC MANNER TO DRIVE GLIOBLASTOMA GROWTH

Glioblastoma (GBM), the most common primary malignant brain tumor in adults, is characterized by invasive growth and poor prognosis. Iron is a critical regulator of many cellular processes, and GBM tumor cells have been shown to modulate expression of iron-associated proteins to enhance iron uptake from the surrounding microenvironment, driving tumor initiation and growth. While iron uptake has been the central focus of previous investigations, additional mechanisms of iron regulation, such as compensatory iron efflux, have not been explored in the context of GBM. The hemochromatosis (HFE) gene encodes a transmembrane glycoprotein that aids in iron homeostasis by limiting cellular iron release, resulting in a sequestration phenotype. We find that HFE is upregulated in GBM tumors compared to non-tumor brain and that expression of HFE increases with tumor grade. Furthermore, HFE mRNA expression is associated with significantly reduced survival specifically in female patients with GBM. Based on these findings, we hypothesize that GBM tumor cells upregulate HFE expression to augment cellular iron loading and drive proliferation, ultimately leading to reduced survival of female patients. To test this hypothesis, we generated Hfe knockdown and overexpressing mouse glioma cell lines. We observed significant alterations in the expression of several iron handling genes with Hfe knockdown or overexpression, suggesting global disruption of iron homeostasis. Additionally, we show that knockdown of Hfe in these cells increases apoptosis and leads to a significant impairment of tumor growth in vivo. These findings support the hypothesis that Hfe is a critical regulator of cellular iron status and contributes to tumor aggression. Future work will include further exploration of the mechanisms that contribute to these phenotypes as well as interactions with the tumor microenvironment. Elucidating the mechanisms by which iron effulx contributes to GBM may inform the development of next-generation targeted therapies.

TAMI-12. CANCER STEM CELL ENRICHMENT AND METABOLIC SUBSTRATE ADAPTABILITY ARE DRIVEN BY HYDROGEN SULFIDE SUPPRESSION IN GLIOBLASTOMA

Glioblastoma (GBM) remains among the deadliest of human malignancies. The emergence of the cancer stem cell (CSC) phenotype represents a major challenge to disease management and durable treatment response. The extrinsic, environmental, and lifestyle factors that result in CSC enrichment are not well understood. The CSC state endows cells with a fluid metabolic profile, enabling the utilization of multiple nutrient sources. Therefore, to test the impact of diet on CSC enrichment, we evaluated disease progression in tumor-bearing mice fed an obesity-inducing high-fat diet (HFD) versus an energy-balanced, low-fat control diet. HFD consumption resulted in hyper-aggressive disease that was accompanied by CSC enrichment and shortened survival. HFD consumption also drove intracerebral accumulation of saturated fats, which in turn inhibited the production and signaling of the gasotransmitter hydrogen sulfide (H2S). H2S is an endogenously produced bio-active metabolite derived from sulfur amino acid catabolism. It functions principally through protein S-sulfhydration and regulates a variety of programs including mitochondrial bioenergetics and cellular metabolism. Inhibition of H2S synthesis resulted in increased proliferation and chemotherapy resistance, whereas treatment with H2S donors led to cytotoxicity and death of cultured GBM cells. Compared to non-cancerous controls, patient GBM specimens were reduced in overall protein S-sulfhydration, which was primarily lost from proteins regulating cellular metabolism. These findings support the hypothesis that diet-regulated H2S signaling serves to suppress GBM by restricting metabolic adaptability, while its loss triggers CSC enrichment and disease acceleration. Interventions augmenting H2S bioavailability concurrent with GBM standard of care may improve outcomes for GBM patients.

STEM-03. CONSUMPTION OF A HIGH-FAT DIET INHIBITS THE TUMOR SUPPRESSIVE ACTIVITY OF HYDROGEN SULFIDE, DRIVING CANCER STEM CELL ENRICHMENT AND DISEASE AGGRESSION IN GLIOBLASTOMA

Glioblastoma (GBM) remains among the deadliest of human malignancies. Effective disease management is lacking due in part to the emergence of the cancer stem cell (CSC) phenotype. The tumor cell extrinsic, environmental, and lifestyle factors that result in CSC enrichment are not well understood. Alongside other pathological features, the CSC state endows populations of tumor cells with a fluid metabolic profile that enables utilization of multiple nutrition sources. Therefore, to test the impact of diet on CSC enrichment, we interrogated disease progression in tumor-bearing mice fed either a high-fat diet (HFD), similar to the Western Pattern diet or a control low-fat diet. Compared to controls, HFD-consumption resulted in the presentation of a hyper-aggressive disease phenotype with truncated survival and tumors markedly enriched in tumor-initiating SOX2+ CSCs. To understand the underlying mechanism driving this finding, we examined tumors for the diet-regulated metabolite hydrogen sulfide (H2S). H2S is an endogenously produced bio-active gasotransmitter similar to nitric oxide. It functions principally through protein S-sulfhydration to regulate a variety of cellular programs including mitochondrial function, stress signaling and metabolism. While there is exceedingly limited information on H2S and GBM, its HFD-driven suppression has been reported in other organ systems. We discovered a significant reduction in H2S synthesis resulting from HFD-consumption in the brain of the mouse and a striking decrease in protein S-sulfhydration in human GBM tumor tissue when compared to non-cancerous control brain tissue. We demonstrated that chemical inhibition of H2S synthesis resulted in increased tumor cell viability whereas exposure to chemical H2S donors led to pronounced cell death of cultured mouse and human GBM cells. These data demonstrate for the first time, that H2S serves as a tumor suppressor for GBM. Moreover, the diet-driven suppression of H2S helps explain the hyper-aggressive in vivo phenotype that presents in response to HFD-consumption.

Increased fibrosis: A novel means by which GH influences white adipose tissue function

OBJECTIVE

White adipose tissue (WAT) fibrosis - the buildup of extracellular matrix (ECM) proteins, primarily collagen - is now a recognized hallmark of tissue dysfunction and is increased with obesity and lipodystrophy. While growth hormone (GH) is known to increase collagen in several tissues, no previous research has addressed its effect on ECM in WAT. Thus, the purpose of this study is to determine if GH influences WAT fibrosis.

DESIGN

This study examined WAT from four distinct strains of GH-altered mice (bGH and GHA transgenic mice as well as two tissue specific GH receptor gene disrupted lines, fat growth hormone receptor knockout or FaGHRKO and liver growth hormone receptor knockout or LiGHRKO mice). Collagen content and adipocyte size were studied in all cohorts and compared to littermate controls. In addition, mRNA expression of fibrosis-associated genes was assessed in one cohort (6month old male bovine GH transgenic and WT mice) and cultured 3T3-L1 adipocytes treated with GH.

RESULTS

Collagen stained area was increased in WAT from bGH mice, was depot-dependent, and increased with age. Furthermore, increased collagen content was associated with decreased adipocyte size in all depots but more dramatic changes in the subcutaneous fat pad. Notably, the increase in collagen was not associated with an increase in collagen gene expression or other genes known to promote fibrosis in WAT, but collagen gene expression was increased with acute GH administration in 3T3-LI cells. In contrast, evaluation of 6month old GH antagonist (GHA) male mice showed significantly decreased collagen in the subcutaneous depot. Lastly, to assess if GH induced collagen deposition directly or indirectly (via IGF-1), fat (Fa) and liver (Li) specific GHRKO mice were evaluated. Decreased fibrosis in FaGHRKO and increased fibrosis in LiGHRKO mice suggest GH is primarily responsible for the alterations in collagen.

CONCLUSIONS

Our results show that GH action is positively associated with an increase in WAT collagen content as well as a decrease in adipocyte size, particularly in the subcutaneous depot. This effect appears to be due to GH and not IGF-1 and reveals a novel means by which GH regulates WAT accumulation.

Growth hormone receptor antagonist transgenic mice are protected from hyperinsulinemia and glucose intolerance despite obesity when placed on a HF diet

Reduced GH levels have been associated with improved glucose metabolism and increased longevity despite obesity in multiple mouse lines. However, one mouse line, the GH receptor antagonist (GHA) transgenic mouse, defies this trend because it has reduced GH action and increased adiposity, but glucose metabolism and life span are similar to controls. Slight differences in glucose metabolism and adiposity profiles can become exaggerated on a high-fat (HF) diet. Thus, in this study, male and female GHA and wild-type (WT) mice in a C57BL/6 background were placed on HF and low-fat (LF) diets for 11 weeks, starting at 10 weeks of age, to assess how GHA mice respond to additional metabolic stress of HF feeding. On a HF diet, all mice showed significant weight gain, although GHA gained weight more dramatically than WT mice, with males gaining more than females. Most of this weight gain was due to an increase in fat mass with WT mice increasing primarily in the white adipose tissue perigonadal depots, whereas GHA mice gained in both the sc and perigonadal white adipose tissue regions. Notably, GHA mice were somewhat protected from detrimental glucose metabolism changes on a HF diet because they had only modest increases in serum glucose levels, remained glucose tolerant, and did not develop hyperinsulinemia. Sex differences were observed in many measures with males reacting more dramatically to both a reduction in GH action and HF diet. In conclusion, our findings show that GHA mice, which are already obese, are susceptible to further adipose tissue expansion with HF feeding while remaining resilient to alterations in glucose homeostasis.

The role of GH in adipose tissue: lessons from adipose-specific GH receptor gene-disrupted mice

GH receptor (GHR) gene-disrupted mice (GHR-/-) have provided countless discoveries as to the numerous actions of GH. Many of these discoveries highlight the importance of GH in adipose tissue. For example GHR-/- mice are insulin sensitive yet obese with preferential enlargement of the sc adipose depot. GHR-/- mice also have elevated levels of leptin, resistin, and adiponectin, compared with controls leading some to suggest that GH may negatively regulate certain adipokines. To help clarify the role that GH exerts specifically on adipose tissue in vivo, we selectively disrupted GHR in adipose tissue to produce Fat GHR Knockout (FaGHRKO) mice. Surprisingly, FaGHRKOs shared only a few characteristics with global GHR-/- mice. Like the GHR-/- mice, FaGHRKO mice are obese with increased total body fat and increased adipocyte size. However, FaGHRKO mice have increases in all adipose depots with no improvements in measures of glucose homeostasis. Furthermore, resistin and adiponectin levels in FaGHRKO mice are similar to controls (or slightly decreased) unlike the increased levels found in GHR-/- mice, suggesting that GH does not regulate these adipokines directly in adipose tissue in vivo. Other features of FaGHRKO mice include decreased levels of adipsin, a near-normal GH/IGF-1 axis, and minimal changes to a large assortment of circulating factors that were measured such as IGF-binding proteins. In conclusion, specific removal of GHR in adipose tissue is sufficient to increase adipose tissue and decrease circulating adipsin. However, removal of GHR in adipose tissue alone is not sufficient to increase levels of resistin or adiponectin and does not alter glucose metabolism.