Hyperpolarized Pyruvate MR Spectroscopy Depicts Glycolytic Inhibition in a Mouse Model of Glioma

The Impact of Glycolysis and Its Inhibitors on the Immune Response to Inflammation and Autoimmunity

Glucose metabolism is a crucial biological pathway maintaining the activation of extra- and intracellular signaling pathways involved in the immune response. Immune cell stimulation via various environmental factors results in their activation and metabolic reprogramming to aerobic glycolysis. Different immune cells exhibit cell-type-specific metabolic patterns when performing their biological functions. Numerous published studies have shed more light on the importance of metabolic reprogramming in the immune system. Moreover, this knowledge is crucial for revealing new ways to target inflammatory pathologic states, such as autoimmunity and hyperinflammation. Here, we discuss the role of glycolysis in immune cell activity in physiological and pathological conditions, and the potential use of inhibitors of glycolysis for disease treatment.

Histone lactylation bridges metabolic reprogramming and epigenetic rewiring in driving carcinogenesis: Oncometabolite fuels oncogenic transcription

Heightened lactate production in cancer cells has been linked to various cellular mechanisms such as angiogenesis, hypoxia, macrophage polarisation and T-cell dysfunction. The lactate-induced lactylation of histone lysine residues is noteworthy, as it functions as an epigenetic modification that directly augments gene transcription from chromatin. This epigenetic modification originating from lactate effectively fosters a reliance on transcription, thereby expediting tumour progression and development. Herein, this review explores the correlation between histone lactylation and cancer characteristics, revealing histone lactylation as an innovative epigenetic process that enhances the vulnerability of cells to malignancy. Moreover, it is imperative to acknowledge the paramount importance of acknowledging innovative therapeutic methodologies for proficiently managing cancer by precisely targeting lactate signalling. This comprehensive review illuminates a crucial yet inadequately investigated aspect of histone lactylation, providing valuable insights into its clinical ramifications and prospective therapeutic interventions centred on lactylation.

Hyperpolarized Carbon 13 MRI: Clinical Applications and Future Directions in Oncology

Hyperpolarized carbon 13 MRI (13C MRI) is a novel imaging approach that can noninvasively probe tissue metabolism in both normal and pathologic tissues. The process of hyperpolarization increases the signal acquired by several orders of magnitude, allowing injected 13C-labeled molecules and their downstream metabolites to be imaged in vivo, thus providing real-time information on kinetics. To date, the most important reaction studied with hyperpolarized 13C MRI is exchange of the hyperpolarized 13C signal from injected [1-13C]pyruvate with the resident tissue lactate pool. Recent preclinical and human studies have shown the role of several biologic factors such as the lactate dehydrogenase enzyme, pyruvate transporter expression, and tissue hypoxia in generating the MRI signal from this reaction. Potential clinical applications of hyperpolarized 13C MRI in oncology include using metabolism to stratify tumors by grade, selecting therapeutic pathways based on tumor metabolic profiles, and detecting early treatment response through the imaging of shifts in metabolism that precede tumor structural changes. This review summarizes the foundations of hyperpolarized 13C MRI, presents key findings from human cancer studies, and explores the future clinical directions of the technique in oncology. Keywords: Hyperpolarized Carbon 13 MRI, Molecular Imaging, Cancer, Tissue Metabolism © RSNA, 2023.

MR-Nucleomics: The study of pathological cellular processes with multinuclear magnetic resonance spectroscopy and imaging in vivo

Clinical medicine has experienced a rapid development in recent decades, during which therapies targeting specific cellular signaling pathways, or specific cell surface receptors, have been increasingly adopted. While these developments in clinical medicine call for improved precision in diagnosis and treatment monitoring, modern medical imaging methods are restricted mainly to anatomical imaging, lagging behind the requirements of precision medicine. Although positron emission tomography and single photon emission computed tomography have been used clinically for studies of metabolism, their applications have been limited by the exposure risk to ionizing radiation, the subsequent limitation in repeated and longitudinal studies, and the incapability in assessing downstream metabolism. Magnetic resonance spectroscopy (MRS) or spectroscopic imaging (MRSI) are, in theory, capable of assessing molecular activities in vivo, although they are often limited by sensitivity. Here, we review some recent developments in MRS and MRSI of multiple nuclei that have potential as molecular imaging tools in the clinic.

The Antiviral Effects of 2-Deoxy-D-glucose (2-DG), a Dual D-Glucose and D-Mannose Mimetic, against SARS-CoV-2 and Other Highly Pathogenic Viruses

Viral infection almost invariably causes metabolic changes in the infected cell and several types of host cells that respond to the infection. Among metabolic changes, the most prominent is the upregulated glycolysis process as the main pathway of glucose utilization. Glycolysis activation is a common mechanism of cell adaptation to several viral infections, including noroviruses, rhinoviruses, influenza virus, Zika virus, cytomegalovirus, coronaviruses and others. Such metabolic changes provide potential targets for therapeutic approaches that could reduce the impact of infection. Glycolysis inhibitors, especially 2-deoxy-D-glucose (2-DG), have been intensively studied as antiviral agents. However, 2-DG's poor pharmacokinetic properties limit its wide clinical application. Herein, we discuss the potential of 2-DG and its novel analogs as potent promising antiviral drugs with special emphasis on targeted intracellular processes.

Synergistic Anticancer Effect of Glycolysis and Histone Deacetylases Inhibitors in a Glioblastoma Model

Over the last decade, we have seen tremendous progress in research on 2-deoxy-D-glucose (2-DG) and its analogs. Clinical trials of 2-DG have demonstrated the challenges of using 2-DG as a monotherapy, due to its poor drug-like characteristics, leading researchers to focus on improving its bioavailability to tissue and organs. Novel 2-DG analogs such as WP1122 and others have revived the old concept of glycolysis inhibition as an effective anticancer strategy. Combined with other potent cytotoxic agents, inhibitors of glycolysis could synergistically eliminate cancer cells. We focused our efforts on the development of new combinations of anticancer agents coupled with 2-DG and its derivatives, targeting glioblastoma, which is in desperate need of novel approaches and therapeutic options and is particularly suited to glycolysis inhibition, due to its reliance on aerobic glycolysis. Herein, we present evidence that a combined treatment of 2-DG analogs and modulation of histone deacetylases (HDAC) activity via HDAC inhibitors (sodium butyrate and sodium valproate) exerts synergistic cytotoxic effects in glioblastoma U-87 and U-251 cells and represents a promising therapeutic strategy.

Measuring the Metabolic Evolution of Glioblastoma throughout Tumor Development, Regression, and Recurrence with Hyperpolarized Magnetic Resonance

Rapid diagnosis and therapeutic monitoring of aggressive diseases such as glioblastoma can improve patient survival by providing physicians the time to optimally deliver treatment. This research tested whether metabolic imaging with hyperpolarized MRI could detect changes in tumor progression faster than conventional anatomic MRI in patient-derived glioblastoma murine models. To capture the dynamic nature of cancer metabolism, hyperpolarized MRI, NMR spectroscopy, and immunohistochemistry were performed at several time-points during tumor development, regression, and recurrence. Hyperpolarized MRI detected significant changes of metabolism throughout tumor progression whereas conventional MRI was less sensitive. This was accompanied by aberrations in amino acid and phospholipid lipid metabolism and MCT1 expression. Hyperpolarized MRI can help address clinical challenges such as identifying malignant disease prior to aggressive growth, differentiating pseudoprogression from true progression, and predicting relapse. The individual evolution of these metabolic assays as well as their correlations with one another provides context for further academic research.

Characterization of Distinctive In Vivo Metabolism between Enhancing and Non-Enhancing Gliomas Using Hyperpolarized Carbon-13 MRI

The development of hyperpolarized carbon-13 (¹³C) metabolic MRI has enabled the sensitive and noninvasive assessment of real-time in vivo metabolism in tumors. Although several studies have explored the feasibility of using hyperpolarized ¹³C metabolic imaging for neuro-oncology applications, most of these studies utilized high-grade enhancing tumors, and little is known about hyperpolarized ¹³C metabolic features of a non-enhancing tumor. In this study, ¹³C MR spectroscopic imaging with hyperpolarized [1-¹³C]pyruvate was applied for the differential characterization of metabolic profiles between enhancing and non-enhancing gliomas using rodent models of glioblastoma and a diffuse midline glioma. Distinct metabolic profiles were found between the enhancing and non-enhancing tumors, as well as their contralateral normal-appearing brain tissues. The preliminary results from this study suggest that the characterization of metabolic patterns from hyperpolarized ¹³C imaging between non-enhancing and enhancing tumors may be beneficial not only for understanding distinct metabolic features between the two lesions, but also for providing a basis for understanding ¹³C metabolic processes in ongoing clinical trials with neuro-oncology patients using this technology.

Differentiating Radiation Necrosis from Brain Tumor Using Hyperpolarized Carbon-13 MR Metabolic Imaging

PURPOSE

Differentiation between radiation-induced necrosis and tumor recurrence is crucial to determine proper management strategies but continues to be one of the central challenges in neuro-oncology. We hypothesized that hyperpolarized ¹³C MRI, a unique technique to measure real-time in vivo metabolism, would distinguish radiation necrosis from tumor on the basis of cell-intrinsic metabolic differences. The purpose of this study was to explore the feasibility of using hyperpolarized [1-¹³C]pyruvate for differentiating radiation necrosis from brain tumors.

PROCEDURES

Radiation necrosis was initiated by employing a CT-guided 80-Gy single-dose irradiation of a half cerebrum in mice (n = 7). Intracerebral tumor was modeled with two orthotopic mouse models: GL261 glioma (n = 6) and Lewis lung carcinoma (LLC) metastasis (n = 7). ¹³C 3D MR spectroscopic imaging data were acquired following hyperpolarized [1-¹³C]pyruvate injection approximately 89 and 14 days after treatment for irradiated and tumor-bearing mice, respectively. The ratio of lactate to pyruvate (Lac/Pyr), normalized lactate, and pyruvate in contrast-enhancing lesion was compared between the radiation-induced necrosis and brain tumors. Histopathological analysis was performed from resected brains.

RESULTS

Conventional MRI exhibited typical radiographic features of radiation necrosis and brain tumor with large areas of contrast enhancement and T2 hyperintensity in all animals. Normalized lactate in radiation necrosis (0.10) was significantly lower than that in glioma (0.26, P = .004) and LLC metastatic tissue (0.25, P = .00007). Similarly, Lac/Pyr in radiation necrosis (0.18) was significantly lower than that in glioma (0.55, P = .00008) and LLC metastasis (0.46, P = .000008). These results were consistent with histological findings where tumor-bearing brains were highly cellular, while irradiated brains exhibited pathological markers consistent with reparative changes from radiation necrosis.

CONCLUSION

Hyperpolarized ¹³C MR metabolic imaging of pyruvate is a noninvasive imaging method that differentiates between radiation necrosis and brain tumors, providing a groundwork for further clinical investigation and translation for the improved management of patients with brain tumors.

Glycolytic metabolism of pathogenic T cells enables early detection of GVHD by 13C-MRI

Graft-versus-host disease (GVHD) is a prominent barrier to allogeneic hematopoietic stem cell transplantation (AHSCT). Definitive diagnosis of GVHD is invasive, and biopsies of involved tissues pose a high risk of bleeding and infection. T cells are central to GVHD pathogenesis, and our previous studies in a chronic GVHD mouse model showed that alloreactive CD4+ T cells traffic to the target organs ahead of overt symptoms. Because increased glycolysis is an early feature of T-cell activation, we hypothesized that in vivo metabolic imaging of glycolysis would allow noninvasive detection of liver GVHD as activated CD4+ T cells traffic into the organ. Indeed, hyperpolarized 13C-pyruvate magnetic resonance imaging detected high rates of conversion of pyruvate to lactate in the liver ahead of animals becoming symptomatic, but not during subsequent overt chronic GVHD. Concomitantly, CD4+ T effector memory cells, the predominant pathogenic CD4+ T-cell subset, were confirmed to be highly glycolytic by transcriptomic, protein, metabolite, and ex vivo metabolic activity analyses. Preliminary data from single-cell sequencing of circulating T cells in patients undergoing AHSCT also suggested that increased glycolysis may be a feature of incipient acute GVHD. Metabolic imaging is being increasingly used in the clinic and may be useful in the post-AHSCT setting for noninvasive early detection of GVHD.

Emerging Techniques in Imaging of Glioma Microenvironment

Magnetic resonance imaging (MRI) has been the cornerstone of imaging of brain tumors in the past 4 decades. Conventional MRI remains the workhorse for neuro-oncologic imaging, not only for basic information such as location, extent, and navigation but also able to provide information regarding proliferation and infiltration, angiogenesis, hemorrhage, and more. More sophisticated MRI sequences have extended the ability to assess and quantify these features; for example, permeability and perfusion acquisitions can assess blood-brain barrier disruption and angiogenesis, diffusion techniques can assess cellularity and infiltration, and spectroscopy can address metabolism. Techniques such as fMRI and diffusion fiber tracking can be helpful in diagnostic planning for resection and radiation therapy, and more sophisticated iterations of these techniques can extend our understanding of neurocognitive effects of these tumors and associated treatment responses and effects. More recently, MRI has been used to go beyond such morphological, physiological, and functional characteristics to assess the tumor microenvironment. The current review highlights multiple recent and emerging approaches in MRI to characterize the tumor microenvironment.

2-Deoxy-d-Glucose and Its Analogs: From Diagnostic to Therapeutic Agents

The ability of 2-deoxy-d-glucose (2-DG) to interfere with d-glucose metabolism demonstrates that nutrient and energy deprivation is an efficient tool to suppress cancer cell growth and survival. Acting as a d-glucose mimic, 2-DG inhibits glycolysis due to formation and intracellular accumulation of 2-deoxy-d-glucose-6-phosphate (2-DG6P), inhibiting the function of hexokinase and glucose-6-phosphate isomerase, and inducing cell death. In addition to glycolysis inhibition, other molecular processes are also affected by 2-DG. Attempts to improve 2-DG’s drug-like properties, its role as a potential adjuvant for other chemotherapeutics, and novel 2-DG analogs as promising new anticancer agents are discussed in this review.