Combined PET Imaging of the Inflammatory Tumor Microenvironment Identifies Margins of Unique Radiotracer Uptake

Imaging Macrophage-associated Inflammation

Macrophages belong to the mononuclear phagocyte system comprising closely related cells of bone marrow origin. Activated macrophages are critical in several diseases such as tuberculosis, sarcoidosis, Crohn's disease, and atherosclerosis. Noninvasive imaging techniques that can specifically image activated macrophages could therefore help in differentiating various forms of inflammatory diseases and to monitor therapeutic responses.

Precision Medicine in Pediatric Neurooncology: A Review

Central nervous system tumors are the leading cause of cancer related death in children. Despite much progress in the field of pediatric neurooncology, modern combination treatment regimens often result in significant late effects, such as neurocognitive deficits, endocrine dysfunction, secondary malignancies, and a host of other chronic health problems. Precision medicine strategies applied to pediatric neurooncology target specific characteristics of individual patients' tumors to achieve maximal killing of neoplastic cells while minimizing unwanted adverse effects. Here, we review emerging trends and the current literature that have guided the development of new molecularly based classification schemas, promising diagnostic techniques, targeted therapies, and delivery platforms for the treatment of pediatric central nervous system tumors.

The Effect of MCM3AP-AS1/miR-211/KLF5/AGGF1 Axis Regulating Glioblastoma Angiogenesis

Glioblastoma (GBM) is the most aggressive and malignant primary tumor. Angiogenesis plays a critical role in the progression of GBM. Previous studies have indicated that long non-coding RNAs (lncRNAs) are abnormally expressed in various cancers and participate in the regulation of the malignant behaviors of tumors. The present study demonstrated that lncRNA antisense 1 to Micro-chromosome maintenance protein 3-associated protein (MCM3AP-AS1) was upregulated whereas miR-211 was downregulated in glioma-associated endothelial cells (GECs). Knockdown of MCM3AP-AS1 suppressed the cell viability, migration, and tube formation of GECs and played a role in inhibiting angiogenesis of GBM in vitro. Furthermore, knockdown of MCM3AP-AS1 increased the expression of miR-211. Luciferase reporter assay implicated that miR-211 targeted KLF5 3'-UTR and consequently inhibited KLF5 expression. Besides, in this study we found that MCM3AP-AS1 knockdown decreased KLF5 and AGGF1 expression by upregulating miR-211. In addition, KLF5 was associated with the promoter region of AGGF1. Knockdown of KLF5 decreased AGGF1 expression by transcriptional repression, and also inhibited the activation of PI3K/AKT and ERK1/2 signaling pathways. Overall, this study reveals that MCM3AP-AS1/miR-211/KLF5/AGGF1 axis plays a prominent role in the regulation of GBM angiogenesis and also serves as new therapeutic target for the anti-angiogenic therapy of glioma.

Metformin and temozolomide, a synergic option to overcome resistance in glioblastoma multiforme models

Glioblastoma multiforme (GBM) is the most aggressive primary brain tumor with poor survival. Cytoreduction in association with radiotherapy and temozolomide (TMZ) is the standard therapy, but response is heterogeneous and life expectancy is limited. The combined use of chemotherapeutic agents with drugs targeting cell metabolism is becoming an interesting therapeutic option for cancer treatment. Here, we found that metformin (MET) enhances TMZ effect on TMZ-sensitive cell line (U251) and overcomes TMZ-resistance in T98G GBM cell line. In particular, combined-treatment modulated apoptosis by increasing Bax/Bcl-2 ratio, and reduced Reactive Oxygen Species (ROS) production. We also observed that MET associated with TMZ was able to reduce the expression of glioma stem cells (GSC) marker CD90 particularly in T98G cells but not that of CD133. In vivo experiments showed that combined treatment with TMZ and MET significantly slowed down growth of TMZ-resistant tumors but did not affect overall survival of TMZ-sensitive tumor bearing mice. In conclusion, our results showed that metformin is able to enhance TMZ effect in TMZ-resistant cell line suggesting its potential use in TMZ refractory GBM patients. However, the lack of effect on a GBM malignancy marker like CD133 requires further evaluation since it might influence response duration.

Role of Translocator 18 KDa Ligands in the Activation of Leukotriene B4 Activated G-Protein Coupled Receptor and Toll Like Receptor-4 Pathways in Neutrophils

TSPO (Translocator 18 KDa; tryptophan-rich sensory protein oxygen sensor) is a constitutive outer mitochondrial membrane protein overexpressed in inflammatory cells during local or systemic processes. Despite its expression is characterized, role of TSPO in inflammation remains elusive. For this study, we investigated the role of TSPO ligands on neutrophil functions elicited by two different inflammatory pathways. Peritoneal neutrophils were isolated from male Balb-C mice, treated with TSPO ligand diazepam, Ro5-4864 or PK11195 (1,100 or 1000 nM; 2 h) and further stimulated with lipopolysaccharide from Escherichia coli (LPS), a binding for Toll-Like Receptor-4 (TLR4), or leukotriene B4 (LTB4), a G-protein coupled receptor (GPCR) ligand. LPS treatment did not lead to overexpression of TSPO on neutrophils, and pre-treatment with any TSPO ligand did not alter cytokine expression, adhesion molecule expression, or the production of reactive oxygen and nitrogen species caused by LPS stimulation. Conversely, all TSPO ligands impaired LTB4’s actions, as visualized by reductions in L-selectin shedding, β2 integrin overexpression, neutrophil chemotaxis, and actin filament assembly. TSPO ligands showed distinct intracellular effects on LTB4-induced neutrophil locomotion, with diazepam enhancing cofilin but not modifying Arp2/3 expression, and Ro5-4864 and PK11195 reducing both cofilin and Arp2/3 expression. Taken together, our data exclude a direct role of TSPO ligands in TLR4-elicited pathways, and indicate that TSPO activation inhibits GPCR inflammatory pathways in neutrophils, with a relevant role in neutrophil influx into inflammatory sites.

Tumor Microenvironment in Treatment of Glioma

Glioma is one of the most malignant and fatal tumors in adults. Researchers and physicians endeavor to improve clinical efficacy towards it but made little achievement. In recent years, people have made advances in understanding characteristics and functions of tumor microenvironment and its role in different processes of tumor. In this paper, we describe the effects of tumor microenvironment on glioma proliferation, invasion and treatments. By explaining underlying mechanisms and enumerating new therapy strategies employing tumor microenvironment, we aim to provide novel ideas to improve clinical outcomes of glioma.

Nanoparticle-Based Magnetic Resonance Imaging on Tumor-Associated Macrophages and Inflammation

The inflammatory response, mediated by tissue-resident or newly recruited macrophages, is an underlying pathophysiological condition for many diseases, including diabetes, obesity, neurodegeneration, atherosclerosis, and cancer. Paradoxically, inflammation is a double-edged sword in oncology. Macrophages are, generally speaking, the major drivers of inflammatory insult. For many solid tumors, high density of cells expressing macrophage-associated markers have generally been found in association with a poor clinical outcome, characterized by inflamed microenvironment, a high level of dissemination and resistance to conventional chemotherapies. On another hand, radiation treatment also triggers an inflammatory response in tumors (often referred to as pseudoprogression), which can be associated with a positive treatment response. As such, non-invasive imaging of cancer inflammation and tumor-associated macrophages (TAMs) provides a revolutionary diagnostic tool and monitoring strategy for anti-inflammatory, immuno- and radiotherapies. Recently, quantitative T2-weighted magnetic resonance imaging (qT2wMRI), using injection of superparamagnetic iron oxide nanoparticles (SPIONs), has been reported for the assessment of TAMs non-invasively in animal models and in human trials. The SPIONs are magnetic resonance imaging (MRI) contrast agents that significantly decrease T2 MR relaxation times in inflamed tissues due to the macrophage-specific uptake and retention. It has been shown that macrophage-populated tumors and metastases will accumulate iron oxide nanoparticles and decrease T2-relaxation time that will result in a negative (dark) contrast in qT2wMRI. Non-invasive imaging of TAMs using SPION holds a great promise for staging the inflammatory microenvironment of primary and metastatic tumors as well monitoring the treatment response of cancer patients treated with radiation and immunotherapy.

Development of a 18F-Labeled Radiotracer with Improved Brain Kinetics for Positron Emission Tomography Imaging of Translocator Protein (18 kDa) in Ischemic Brain and Glioma

We designed four novel acetamidobenzoxazolone compounds 7a-d as candidates for positron emission tomography (PET) radiotracers for imaging the translocator protein (18 kDa, TSPO) in ischemic brain and glioma. Among these compounds, 2-(5-(6-fluoropyridin-3-yl)-2-oxobenzo[d]oxazol-3(2H)-yl)-N-methyl-N-phenylacetamide (7d) exhibited high binding affinity (K_i = 13.4 nM) with the TSPO and moderate lipophilicity (log D = 1.92). [¹⁸F]7d was radiosynthesized by [¹⁸F]fluorination of the bromopyridine precursor 7h with [¹⁸F]F^- in 12 ± 5% radiochemical yield (n = 6, decay-corrected). In vitro autoradiography and PET studies of ischemic rat brain revealed higher binding of [¹⁸F]7d with TSPO on the ipsilateral side, as compared to the contralateral side, and improved brain kinetics compared with our previously developed radiotracers. Metabolite study of [¹⁸F]7d showed 93% of unchanged form in the ischemic brain at 30 min after injection. Moreover, PET study with [¹⁸F]7d provided a clear tumor image in a glioma-bearing rat model. We demonstrated that [¹⁸F]7d is a useful PET radiotracer for visualizing not only neuroinflammation but also glioma and will translate this radiotracer to a "first-in-human" study in our facility.

4'-Chlorodiazepam Protects Mitochondria in T98G Astrocyte Cell Line from Glucose Deprivation

The translocator protein (TSPO), formerly known as the peripheral-type benzodiazepine receptor (PBR), is considered an important regulator of steroidogenesis and a potential therapeutic target in neurological disorders. Previous evidence suggests that TSPO ligands can protect cells during injury and prevent apoptosis in central nervous system (CNS) cells. However, its actions on astrocytic cells under metabolic injury are not well understood. In this study, we explored whether 4'-chlorodiazepam (Ro5-4864), a TSPO ligand, might protect astrocyte mitochondria under glucose deprivation. Our results showed that 4'-chlorodiazepam preserved cell viability and reduced nuclear fragmentation in glucose-deprived cells. These effects were accompanied by a reduced production of free radicals and maintenance of mitochondrial functions in cells treated with 4'-chlorodiazepam. Finally, our findings suggest that TSPO might be involved in reducing oxidative stress by preserving mitochondrial functions in astrocytic cells exposed to glucose withdrawal.

Molecular Targets for PET Imaging of Activated Microglia: The Current Situation and Future Expectations

Microglia, as cellular mediators of neuroinflammation, are implicated in the pathogenesis of a wide range of neurodegenerative diseases. Positron emission tomography (PET) imaging of microglia has matured over the last 20 years, through the development of radiopharmaceuticals targeting several molecular biomarkers of microglial activation and, among these, mainly the translocator protein-18 kDa (TSPO). Nevertheless, current limitations of TSPO as a PET microglial biomarker exist, such as low brain density, even in a neurodegenerative setting, expression by other cells than the microglia (astrocytes, peripheral macrophages in the case of blood brain barrier breakdown), genetic polymorphism, inducing a variation for most of TSPO PET radiopharmaceuticals’ binding affinity, or similar expression in activated microglia regardless of its polarization (pro- or anti-inflammatory state), and these limitations narrow its potential interest. We overview alternative molecular targets, for which dedicated radiopharmaceuticals have been proposed, including receptors (purinergic receptors P2X7, cannabinoid receptors, α7 and α4β2 nicotinic acetylcholine receptors, adenosine 2A receptor, folate receptor β) and enzymes (cyclooxygenase, nitric oxide synthase, matrix metalloproteinase, β-glucuronidase, and enzymes of the kynurenine pathway), with a particular focus on their respective contribution for the understanding of microglial involvement in neurodegenerative diseases. We discuss opportunities for these potential molecular targets for PET imaging regarding their selectivity for microglia expression and polarization, in relation to the mechanisms by which microglia actively participate in both toxic and neuroprotective actions in brain diseases, and then take into account current clinicians’ expectations.