Comparative Measurements of Hypoxia in Human Brain Tumors Using Needle Electrodes and EF5 Binding

Automated glioblastoma patient classification using hypoxia levels measured through magnetic resonance images

INTRODUCTION

The challenge of treating Glioblastoma (GBM) tumors is due to various mechanisms that make the tumor resistant to radiation therapy. One of these mechanisms is hypoxia, and therefore, determining the level of hypoxia can improve treatment planning and initial evaluation of its effectiveness in GBM. This study aimed to design an intelligent system to classify glioblastoma patients based on hypoxia levels obtained from magnetic resonance images with the help of an artificial neural network (ANN).

MATERIAL AND METHOD

MR images and PET measurements were available for this study. MR images were downloaded from the Cancer Imaging Archive (TCIA) database to classify glioblastoma patients based on hypoxia. The images in this database were prepared from 27 patients with glioblastoma on T1W + Gd, T2W-FLAIR, and T2W. Our designed algorithm includes various parts of pre-processing, tumor segmentation, feature extraction from images, and matching these features with quantitative parameters related to hypoxia in PET images. The system's performance is evaluated by categorizing glioblastoma patients based on hypoxia.

RESULTS

The results of classification with the artificial neural network (ANN) algorithm were as follows: the highest sensitivity, specificity, and accuracy were obtained at 86.71, 85.99 and 83.17%, respectively. The best specificity was related to the T2W-EDEMA image with the tumor to blood ratio (TBR) as a hypoxia parameter. T1W-NECROSIS image with the TBR parameter also showed the highest sensitivity and accuracy.

CONCLUSION

The results of the present study can be used in clinical procedures before treating glioblastoma patients. Among these treatment approaches, we can mention the radiotherapy treatment design and the prescription of effective drugs for the treatment of hypoxic tumors.

Clinical relevance and therapeutic predictive ability of hypoxia biomarkers in head and neck cancer tumour models

Tumour hypoxia promotes poor patient outcomes, with particularly strong evidence for head and neck squamous cell carcinoma (HNSCC). To effectively target hypoxia, therapies require selection biomarkers and preclinical models that can accurately model tumour hypoxia. We established 20 patient-derived xenograft (PDX) and cell line-derived xenograft (CDX) models of HNSCC that we characterised for their fidelity to represent clinical HNSCC in gene expression, hypoxia status and proliferation and that were evaluated for their sensitivity to hypoxia-activated prodrugs (HAPs). PDX models showed greater fidelity in gene expression to clinical HNSCC than cell lines, as did CDX models relative to their paired cell lines. PDX models were significantly more hypoxic than CDX models, as assessed by hypoxia gene signatures and pimonidazole immunohistochemistry, and showed similar hypoxia gene expression to clinical HNSCC tumours. Hypoxia or proliferation status alone could not determine HAP sensitivity across our 20 HNSCC and two non-HNSCC tumour models by either tumour growth inhibition or killing of hypoxia cells in an ex vivo clonogenic assay. In summary, our tumour models provide clinically relevant HNSCC models that are suitable for evaluating hypoxia-targeting therapies; however, additional biomarkers to hypoxia are required to accurately predict drug sensitivity.

Tetralol derivative NNC-55-0396 targets hypoxic cells in the glioblastoma microenvironment: an organ-on-chip approach

Glioblastoma (GBM) is a highly malignant brain tumour characterised by limited treatment options and poor prognosis. The tumour microenvironment, particularly the central hypoxic region of the tumour, is known to play a pivotal role in GBM progression. Cells within this region adapt to hypoxia by stabilising transcription factor HIF1-α, which promotes cell proliferation, dedifferentiation and chemoresistance. In this study we sought to examine the effects of NNC-55-0396, a tetralol compound which overactivates the unfolded protein response inducing apoptosis, using the organ-on-chip technology. We identified an increased sensitivity of the hypoxic core of the chip to NNC, which correlates with decreasing levels of HIF1-α in vitro. Moreover, NNC blocks the macroautophagic process that is unleashed by hypoxia as revealed by increased levels of autophagosomal constituent LC3-II and autophagy chaperone p62/SQSTM1. The specific effects of NNC in the hypoxic microenvironment unveil additional anti-cancer abilities of this compound and further support investigations on its use in combined therapies against GBM.

Wnt Signaling in Brain Tumors: A Challenging Therapeutic Target

The involvement of Wnt signaling in normal tissue homeostasis and disease has been widely demonstrated over the last 20 years. In particular, dysregulation of Wnt pathway components has been suggested as a relevant hallmark of several neoplastic malignancies, playing a role in cancer onset, progression, and response to treatments. In this review, we summarize the current knowledge on the instructions provided by Wnt signaling during organogenesis and, particularly, brain development. Moreover, we recapitulate the most relevant mechanisms through which aberrant Wnt pathway activation may impact on brain tumorigenesis and brain tumor aggressiveness, with a particular focus on the mutual interdependency existing between Wnt signaling components and the brain tumor microenvironment. Finally, the latest anti-cancer therapeutic approaches employing the specific targeting of Wnt signaling are extensively reviewed and discussed. In conclusion, here we provide evidence that Wnt signaling, due to its pleiotropic involvement in several brain tumor features, may represent a relevant target in this context, although additional efforts will be needed to: (i) demonstrate the real clinical impact of Wnt inhibition in these tumors; (ii) overcome some still unsolved concerns about the potential systemic effects of such approaches; (iii) achieve efficient brain penetration.

Advances in PET and MRI imaging of tumor hypoxia

Tumor hypoxia is a complex and evolving phenomenon both in time and space. Molecular imaging allows to approach these variations, but the tracers used have their own limitations. PET imaging has the disadvantage of low resolution and must take into account molecular biodistribution, but has the advantage of high targeting accuracy. The relationship between the signal in MRI imaging and oxygen is complex but hopefully it would lead to the detection of truly oxygen-depleted tissue. Different ways of imaging hypoxia are discussed in this review, with nuclear medicine tracers such as [¹⁸F]-FMISO, [¹⁸F]-FAZA, or [⁶⁴Cu]-ATSM but also with MRI techniques such as perfusion imaging, diffusion MRI or oxygen-enhanced MRI. Hypoxia is a pejorative factor regarding aggressiveness, tumor dissemination and resistance to treatments. Therefore, having accurate tools is particularly important.

A2B Adenosine Receptor Enhances Chemoresistance of Glioblastoma Stem-Like Cells under Hypoxia: New Insights into MRP3 Transporter Function

Glioblastoma is the most common and aggressive primary brain tumor, characterized by its high chemoresistance and the presence of a cell subpopulation that persists under hypoxic niches, called glioblastoma stem-like cells (GSCs). The chemoresistance of GSCs is mediated in part by adenosine signaling and ABC transporters, which extrude drugs outside the cell, such as the multidrug resistance-associated proteins (MRPs) subfamily. Adenosine promotes MRP1-dependent chemoresistance under normoxia. However, adenosine/MRPs-dependent chemoresistance under hypoxia has not been studied until now. Transcript and protein levels were determined by RT-qPCR and Western blot, respectively. MRP extrusion capacity was determined by intracellular 5 (6)-Carboxyfluorescein diacetate (CFDA) accumulation. Cell viability was measured by MTS assays. Cell cycle and apoptosis were determined by flow cytometry. Here, we show for the first time that MRP3 expression is induced under hypoxia through the A2B adenosine receptor. Hypoxia enhances MRP-dependent extrusion capacity and the chemoresistance of GSCs. Meanwhile, MRP3 knockdown decreases GSC viability under hypoxia. Downregulation of the A_2B receptor decreases MRP3 expression and chemosensibilizes GSCs treated with teniposide under hypoxia. These data suggest that hypoxia-dependent activation of A_2B adenosine receptor promotes survival of GSCs through MRP3 induction.

A role for ceruloplasmin in the control of human glioblastoma cell responses to radiation

Background

Glioblastoma (GB) is the most common and most aggressive malignant brain tumor. In understanding its resistance to conventional treatments, iron metabolism and related pathways may represent a novel avenue. As for many cancer cells, GB cell growth is dependent on iron, which is tightly involved in red-ox reactions related to radiotherapy effectiveness. From new observations indicating an impact of RX radiations on the expression of ceruloplasmin (CP), an important regulator of iron metabolism, the aim of the present work was to study the functional effects of constitutive expression of CP within GB lines in response to beam radiation depending on the oxygen status (21% O₂ versus 3% O₂).

Methods and results

After analysis of radiation responses (Hoechst staining, LDH release, Caspase 3 activation) in U251-MG and U87-MG human GB cell lines, described as radiosensitive and radioresistant respectively, the expression of 9 iron partners (TFR1, DMT1, FTH1, FTL, MFRN1, MFRN2, FXN, FPN1, CP) were tested by RTqPCR and western blots at 3 and 8 days following 4 Gy irradiation. Among those, only CP was significantly downregulated, both at transcript and protein levels in the two lines, with however, a weaker effect in the U87-MG, observable at 3% O₂. To investigate specific role of CP in GB radioresistance, U251-MG and U87-MG cells were modified genetically to obtain CP depleted and overexpressing cells, respectively. Manipulation of CP expression in GB lines demonstrated impact both on cell survival and on activation of DNA repair/damage machinery (γH2AX); specifically high levels of CP led to increased production of reactive oxygen species, as shown by elevated levels of superoxide anion, SOD1 synthesis and cellular Fe2 + .

Conclusions

Taken together, these in vitro results indicate for the first time that CP plays a positive role in the efficiency of radiotherapy on GB cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09808-6.

Tumor Microenvironment in Glioma Invasion

A major malignant trait of gliomas is their remarkable infiltration capacity. When glioma develops, the tumor cells have already reached the distant part. Therefore, complete removal of the glioma is impossible. Recently, research on the involvement of the tumor microenvironment in glioma invasion has advanced. Local hypoxia triggers cell migration as an environmental factor. The transcription factor hypoxia-inducible factor (HIF) -1α, produced in tumor cells under hypoxia, promotes the transcription of various invasion related molecules. The extracellular matrix surrounding tumors is degraded by proteases secreted by tumor cells and simultaneously replaced by an extracellular matrix that promotes infiltration. Astrocytes and microglia become tumor-associated astrocytes and glioma-associated macrophages/microglia, respectively, in relation to tumor cells. These cells also promote glioma invasion. Interactions between glioma cells actively promote infiltration of each other. Surgery, chemotherapy, and radiation therapy transform the microenvironment, allowing glioma cells to invade. These findings indicate that the tumor microenvironment may be a target for glioma invasion. On the other hand, because the living body actively promotes tumor infiltration in response to the tumor, it is necessary to reconsider whether the invasion itself is friend or foe to the brain.

Adapt to Persist: Glioblastoma Microenvironment and Epigenetic Regulation on Cell Plasticity

Glioblastoma (GBM) is the most frequent and aggressive brain tumor, characterized by great resistance to treatments, as well as inter- and intra-tumoral heterogeneity. GBM exhibits infiltration, vascularization and hypoxia-associated necrosis, characteristics that shape a unique microenvironment in which diverse cell types are integrated. A subpopulation of cells denominated GBM stem-like cells (GSCs) exhibits multipotency and self-renewal capacity. GSCs are considered the conductors of tumor progression due to their high tumorigenic capacity, enhanced proliferation, invasion and therapeutic resistance compared to non-GSCs cells. GSCs have been classified into two molecular subtypes: proneural and mesenchymal, the latter showing a more aggressive phenotype. Tumor microenvironment and therapy can induce a proneural-to-mesenchymal transition, as a mechanism of adaptation and resistance to treatments. In addition, GSCs can transition between quiescent and proliferative substates, allowing them to persist in different niches and adapt to different stages of tumor progression. Three niches have been described for GSCs: hypoxic/necrotic, invasive and perivascular, enhancing metabolic changes and cellular interactions shaping GSCs phenotype through metabolic changes and cellular interactions that favor their stemness. The phenotypic flexibility of GSCs to adapt to each niche is modulated by dynamic epigenetic modifications. Methylases, demethylases and histone deacetylase are deregulated in GSCs, allowing them to unlock transcriptional programs that are necessary for cell survival and plasticity. In this review, we described the effects of GSCs plasticity on GBM progression, discussing the role of GSCs niches on modulating their phenotype. Finally, we described epigenetic alterations in GSCs that are important for stemness, cell fate and therapeutic resistance.

Spatial immune heterogeneity of hypoxia-induced exhausted features in high-grade glioma

The tumor immune microenvironment (TIME) in high-grade glioma (HGG) exhibits high spatial heterogeneity. Though the tumor core and peripheral regions have different biological features, the cause of this spatial heterogeneity has not been clearly elucidated. Here, we examined the spatial heterogeneity of HGG using core and peripheral regions obtained separately from the patients with HGG. We analyzed infiltrating immune cells by flow cytometry from 34 patients with HGG and the transcriptomes by RNA-seq analysis from 18 patients with HGG. Peripheral region-infiltrating immune cells were in vitro cultured in hypoxic conditions and their immunophenotypes analyzed. We analyzed whether the frequencies of exhausted CD8⁺ T cells and immunosuppressive cells in the core or peripheral regions are associated with the survival of patients with HGG. We found that terminally exhausted CD8⁺ T cells and immunosuppressive cells, including regulatory T (T_REG) cells and M2 tumor-associated macrophages (TAMs), are more enriched in the core regions than the peripheral regions. Terminally exhausted and immunosuppressive profiles in the core region significantly correlated with the hypoxia signature, which was enriched in the core region. Importantly, in vitro culture of peripheral region-infiltrating immune cells in hypoxic conditions resulted in an increase in terminally exhausted CD8⁺ T cells, CTLA-4⁺ T_REG cells, and M2 TAMs. Finally, we found that a high frequency of PD-1⁺CTLA-4⁺CD8⁺ T cells in the core regions was significantly associated with decreased progression-free survival of patients with HGG. The hypoxic condition in the core region of HGG directly induces an immunosuppressive TIME, which is associated with patient survival.

First-In-Human Study in Cancer Patients Establishing the Feasibility of Oxygen Measurements in Tumors Using Electron Paramagnetic Resonance With the OxyChip

OBJECTIVE

The overall objective of this clinical study was to validate an implantable oxygen sensor, called the 'OxyChip', as a clinically feasible technology that would allow individualized tumor-oxygen assessments in cancer patients prior to and during hypoxia-modification interventions such as hyperoxygen breathing.

METHODS

Patients with any solid tumor at ≤3-cm depth from the skin-surface scheduled to undergo surgical resection (with or without neoadjuvant therapy) were considered eligible for the study. The OxyChip was implanted in the tumor and subsequently removed during standard-of-care surgery. Partial pressure of oxygen (pO2) at the implant location was assessed using electron paramagnetic resonance (EPR) oximetry.

RESULTS

Twenty-three cancer patients underwent OxyChip implantation in their tumors. Six patients received neoadjuvant therapy while the OxyChip was implanted. Median implant duration was 30 days (range 4-128 days). Forty-five successful oxygen measurements were made in 15 patients. Baseline pO2 values were variable with overall median 15.7 mmHg (range 0.6-73.1 mmHg); 33% of the values were below 10 mmHg. After hyperoxygenation, the overall median pO2 was 31.8 mmHg (range 1.5-144.6 mmHg). In 83% of the measurements, there was a statistically significant (p ≤ 0.05) response to hyperoxygenation.

CONCLUSIONS

Measurement of baseline pO2 and response to hyperoxygenation using EPR oximetry with the OxyChip is clinically feasible in a variety of tumor types. Tumor oxygen at baseline differed significantly among patients. Although most tumors responded to a hyperoxygenation intervention, some were non-responders. These data demonstrated the need for individualized assessment of tumor oxygenation in the context of planned hyperoxygenation interventions to optimize clinical outcomes.

Hypoxia and pH co-triggered oxidative stress amplifier for tumor therapy

To keep fast proliferation, tumor cells are exposed to higher oxidative stress than normal cells and they upregulate the amount of some antioxidants such as glutathione (GSH) against reactive oxygen species to maintain the balance. This phenomenon is severe in hypoxic tumor cells. Although researchers have proposed a series of treatment strategies based on regulating the intracellular reactive oxygen species level, few of them are related to the hypoxic tumor. Herein, a novel organic compound (PLC) was designed by using lysine as a bridge to connect two functional small molecules, a hypoxia-responsive nitroimidazole derivative (pimonidazole) and a pH-responsive cinnamaldehyde (CA) derivative. Then, the oxidative stress amplifying ability of PLC in hypoxic tumor cells was evaluated. The acidic microenvironment of tumor can trigger the release of CA to produce reactive oxygen species. Meanwhile, large amount of nicotinamide adenine dinucleotide phosphate (NADPH) can be consumed to decrease the synthesis of GSH during the bio-reduction process of the nitro group in PLC under hypoxic conditions. Therefore, the lethal effect of CA can be amplified for the decrease of GSH. Our results prove that this strategy can significantly enhance the therapeutic effect of CA in the hypoxic tumor cells.

Next Generation Imaging Techniques to Define Immune Topographies in Solid Tumors

In recent years, cancer immunotherapy experienced remarkable developments and it is nowadays considered a promising therapeutic frontier against many types of cancer, especially hematological malignancies. However, in most types of solid tumors, immunotherapy efficacy is modest, partly because of the limited accessibility of lymphocytes to the tumor core. This immune exclusion is mediated by a variety of physical, functional and dynamic barriers, which play a role in shaping the immune infiltrate in the tumor microenvironment. At present there is no unified and integrated understanding about the role played by different postulated models of immune exclusion in human solid tumors. Systematically mapping immune landscapes or "topographies" in cancers of different histology is of pivotal importance to characterize spatial and temporal distribution of lymphocytes in the tumor microenvironment, providing insights into mechanisms of immune exclusion. Spatially mapping immune cells also provides quantitative information, which could be informative in clinical settings, for example for the discovery of new biomarkers that could guide the design of patient-specific immunotherapies. In this review, we aim to summarize current standard and next generation approaches to define Cancer Immune Topographies based on published studies and propose future perspectives.

Hypoxia and the phenomenon of immune exclusion

Over the last few years, cancer immunotherapy experienced tremendous developments and it is nowadays considered a promising strategy against many types of cancer. However, the exclusion of lymphocytes from the tumor nest is a common phenomenon that limits the efficiency of immunotherapy in solid tumors. Despite several mechanisms proposed during the years to explain the immune excluded phenotype, at present, there is no integrated understanding about the role played by different models of immune exclusion in human cancers. Hypoxia is a hallmark of most solid tumors and, being a multifaceted and complex condition, shapes in a unique way the tumor microenvironment, affecting gene transcription and chromatin remodeling. In this review, we speculate about an upstream role for hypoxia as a common biological determinant of immune exclusion in solid tumors. We also discuss the current state of ex vivo and in vivo imaging of hypoxic determinants in relation to T cell distribution that could mechanisms of immune exclusion and discover functional-morphological tumor features that could support clinical monitoring.

WNK3 promotes the invasiveness of glioma cell lines under hypoxia by inducing the epithelial-to-mesenchymal transition

Background

The primary features of malignant glioma include high rates of mortality and recurrence, uncontrollable invasiveness, strong angiogenesis, and widespread hypoxia. The hypoxic microenvironment is an important factor affecting the malignant progression of glioma. However, the molecular mechanisms underlying glioma adaption in hypoxic microenvironments are poorly understood.

Objective

The work presented in this paper focuses on the role of WNK3 gene in glioma invasion under hypoxic conditions. Furthermore, we aim to explore its role in epithelial-to-mesenchymal transition (EMT).

Methods

ShRNA targeting WNK3 transfection was used to knockdown the WNK3 expression in U87 cells. We used western blot analysis to detect the relative expression of proteins in U87 cells. The effect of WNK3 on cell migration was explored using a transwell assay in the U87 cell line. We also evaluated WNK3 expression levels in glioma samples by immunohistochemistry analysis.

Results

WNK3 expression was significantly higher in high-grade (III and IV) gliomas than in low-grade (I and II) gliomas. WNK3 expression was up-regulated in U87 cells when cultured in a hypoxic environment in addition; WNK3 knockdown inhibited the invasion of U87 glioma cells by regulating the EMT, especially under hypoxic conditions.

Conclusion

These findings suggested that WNK3 plays an important role in the hypoxic microenvironment of glioma and might also be a candidate for therapeutic application in the treatment of glioma.

In vivo hypoxia characterization using blood oxygen level dependent magnetic resonance imaging in a preclinical glioblastoma mouse model

PURPOSE

Hypoxia measurements can provide crucial information regarding tumor aggressiveness, however current preclinical approaches are limited. Blood oxygen level dependent (BOLD) Magnetic Resonance Imaging (MRI) has the potential to continuously monitor tumor pathophysiology (including hypoxia). The aim of this preliminary work was to develop and evaluate BOLD MRI followed by post-image analysis to identify regions of hypoxia in a murine glioblastoma (GBM) model.

METHODS

A murine orthotopic GBM model (GL261-luc2) was used and independent images were generated from multiple slices in four different mice. Image slices were randomized and split into training and validation cohorts. A 7 T MRI was used to acquire anatomical images using a fast-spin-echo (FSE) T2-weighted sequence. BOLD images were taken with a T2*-weighted gradient echo (GRE) and an oxygen challenge. Thirteen images were evaluated in a training cohort to develop the MRI sequence and optimize post-image analysis. An in-house MATLAB code was used to evaluate MR images and generate hypoxia maps for a range of thresholding and ΔT2* values, which were compared against respective pimonidazole sections to optimize image processing parameters. The remaining (n = 6) images were used as a validation group. Following imaging, mice were injected with pimonidazole and collected for immunohistochemistry (IHC). A test of correlation (Pearson's coefficient) and agreement (Bland-Altman plot) were conducted to evaluate the respective MRI slices and pimonidazole IHC sections.

RESULTS

For the training cohort, the optimized parameters of "thresholding" (20 ≤ T2* ≤ 35 ms) and ΔT2* (±4 ms) yielded a Pearson's correlation of 0.697. These parameters were applied to the validation cohort confirming a strong Pearson's correlation (0.749) when comparing the respective analyzed MR and pimonidazole images.

CONCLUSION

Our preliminary study supports the hypothesis that BOLD MRI is correlated with pimonidazole measurements of hypoxia in an orthotopic GBM mouse model. This technique has further potential to monitor hypoxia during tumor development and therapy.

Hypoxia induced ferritin light chain (FTL) promoted epithelia mesenchymal transition and chemoresistance of glioma

Background

Hypoxia, a fundamental characteristic of glioma, is considered to promote tumor malignancy by inducing process of epithelial mesenchymal transition (EMT). Ferritin Light Chain (FTL) is one of the iron metabolism regulators and is overexpressed in glioma. However, relationship between hypoxia and FTL expression and its role in regulating EMT remains unclear.

Methods

Immunohistochemistry (IHC), western blot and public datasets were used to evaluate FTL level in glioma. Wound healing, transwell assays, CCK8, annexin V staining assay were used to measure migration, invasion, proliferation and apoptosis of glioma cells in vitro. Interaction between HIF1A and FTL was assessed by luciferase reporter and Chromatin immunoprecipitation (ChIP) assays. Subcutaneous xenograft model was established to investigate in vivo growth.

Results

FTL expression was enriched in high grade glioma (HGG) and its expression significantly associated with IDH1/2 wildtype and unfavorable prognosis of glioma patients. FTL expression positively correlated with HIF1A in glioma tissues and obviously increased in U87 and U251 cells under hypoxia in a time-dependent manner. Mechanistically, HIF-1α regulates FTL expression by directly binding to HRE-3 in FTL promoter region. Furthermore, we found that knockdown FTL dramatically repressed EMT and reduced migration and invasion of glioma by regulating AKT/GSK3β/ β-catenin signaling both in vitro and in vivo. Moreover, our study found downregulation FTL decreased the survival rate and increased the apoptosis of glioma cells treated with temozolomide (TMZ). FTL expression segregated glioma patients who were treated with TMZ or with high MGMT promoter methylation into survival groups in TCGA dataset. Patients with methylated MGMT who had high FTL expression presented similar prognosis with patients with unmethylated MGMT.

Conclusion

Our study strongly suggested that hypoxia-inducible FTL was a regulator of EMT and acted not only as a prognostic marker but also a novel biomarker of response to TMZ in glioma.

Hypoxia, metabolism, and the circadian clock: new links to overcome radiation resistance in high-grade gliomas

Radiotherapy is the cornerstone of treatment of high-grade gliomas (HGGs). It eradicates tumor cells by inducing oxidative stress and subsequent DNA damage. Unfortunately, almost all HGGs recur locally within several months secondary to radioresistance with intricate molecular mechanisms. Therefore, unravelling specific underlying mechanisms of radioresistance is critical to elucidating novel strategies to improve the radiosensitivity of tumor cells, and enhance the efficacy of radiotherapy. This review addresses our current understanding of how hypoxia and the hypoxia-inducible factor 1 (HIF-1) signaling pathway have a profound impact on the response of HGGs to radiotherapy. In addition, intriguing links between hypoxic signaling, circadian rhythms and cell metabolism have been recently discovered, which may provide insights into our fundamental understanding of radioresistance. Cellular pathways involved in the hypoxic response, DNA repair and metabolism can fluctuate over 24-h periods due to circadian regulation. These oscillatory patterns may have consequences for tumor radioresistance. Timing radiotherapy for specific times of the day (chronoradiotherapy) could be beneficial in patients with HGGs and will be discussed.

Serine-dependent redox homeostasis regulates glioblastoma cell survival

Background

The amino acid serine is an important substrate for biosynthesis and redox homeostasis. We investigated whether glioblastoma (GBM) cells are dependent on serine for survival under conditions of the tumour microenvironment.

Methods

Serine availability in GBM cells was modulated pharmacologically, genetically and by adjusting serine and glycine concentrations in the culture medium. Cells were investigated for regulation of serine metabolism, proliferation, sensitivity to hypoxia-induced cell death and redox homeostasis.

Results

Hypoxia-induced expression of phosphoglycerate dehydrogenase (PHGDH) and the mitochondrial serine hydroxymethyltransferase (SHMT2) was observed in three of five tested glioma cell lines. Nuclear factor erythroid 2-related factor (Nrf) 2 activation also induced PHGDH and SHMT2 expression in GBM cells. Low levels of endogenous PHGDH as well as PHGDH gene suppression resulted in serine dependency for cell growth. Pharmacological inhibition of PHGDH with CBR-5884 reduced proliferation and sensitised cells profoundly to hypoxia-induced cell death. This effect was accompanied by an increase in reactive oxygen species and a decrease in the NADPH/NADP⁺ ratio. Similarly, hypoxia-induced cell death was enhanced by PHGDH gene suppression and reduced by PHGDH overexpression.

Conclusions

Serine facilitates adaptation of GBM cells to conditions of the tumour microenvironment and its metabolism could be a plausible therapeutic target.

64Cu-ATSM/64Cu-Cl2 and their relationship to hypoxia in glioblastoma: a preclinical study

Background

Diacetyl-bis(N4-methylthiosemicarbazone), labeled with 64Cu (⁶⁴Cu-ATSM) has been suggested as a promising tracer for imaging hypoxia. However, various controversial studies highlighted potential pitfalls that may disable its use as a selective hypoxic marker. They also highlighted that the results may be tumor location dependent. Here, we first analyzed uptake of Cu-ATSM and its less lipophilic counterpart Cu-Cl₂ in the tumor over time in an orthotopic glioblastoma model. An in vitro study was also conducted to investigate the hypoxia-dependent copper uptake in tumor cells. We then further performed a comprehensive ex vivo study to compare ⁶⁴Cu uptake to hypoxic markers, specific cellular reactions, and also transporter expression.

Methods

μPET was performed 14 days (¹⁸F-FMISO), 15 days (⁶⁴Cu-ATSM and ⁶⁴Cu-Cl2), and 16 days (⁶⁴Cu-ATSM and ⁶⁴Cu-Cl₂) after C6 cell inoculation. Thereafter, the brains were withdrawn for further autoradiography and immunohistochemistry. C6 cells were also grown in hypoxic workstation to analyze cellular uptake of Cu complexes in different oxygen levels.

Results

In vivo results showed that Cu-ASTM and Cu-Cl2 accumulated in hypoxic areas of the tumors. Cu-ATSM also stained, to a lesser extent, non-hypoxic regions, such as regions of astrogliosis, with high expression of copper transporters and in particular DMT-1 and CTR1, and also characterized by the expression of elevated astrogliosis. In vitro results show that 64Cu-ATSM showed an increase in the uptake only in severe hypoxia at 0.5 and 0.2% of oxygen while for ⁶⁴Cu-Cl2, the cell retention was significantly increased at 5% and 1% of oxygen with no significant rise at lower oxygen percentages.

Conclusion

In the present study, we show that Cu-complexes undoubtedly accumulate in hypoxic areas of the tumors. This uptake may be the reflection of a direct dependency to a redox metabolism and also a reflection of hypoxic-induced overexpression of transporters. We also show that Cu-ATSM also stained non-hypoxic regions such as astrogliosis.

The Binding of PD-L1 and Akt Facilitates Glioma Cell Invasion Upon Starvation via Akt/Autophagy/F-Actin Signaling

Glioma, especially glioblastoma, is pathologically characterized by high aggressiveness, which largely contributed to the ineffectiveness of current therapies. It has been recently reported that intrinsic PD-L1 can regulate tumor malignancy, whereas underlying mechanisms remain mostly unclear. Here, we report a novel mechanism by which PD-L1 promotes glioma cell infiltration. In orthotopic glioma models, PD-L1 expression was up-regulated predominantly in glioma cells in the infiltrating front. For PD-L1-overexpressed glioma cells, PI3K/Akt and actin regulations were among the top six most altered signaling pathways as detected by RNA-sequencing. PD-L1 significantly activated Akt/F-actin signaling while suppressed autophagic signaling upon cell starvation. Mechanistically, PD-L1 preferentially bound to Akt among various PI3K/Akt signaling proteins. Serial truncation identified the interaction between the 128-237aa fragment of PD-L1 and the 112-480aa fragment of Akt, which facilitates the membrane translocation/activation of Akt, and was unaffected by Perifosin (specific p-Akt inhibitor targeting Akt PH-domain). Taken together, our data indicate that in glioma cells, PD-L1 is induced to prevent autophagic cytoskeleton collapse via Akt binding/activation, facilitating glioma cell invasion upon starvation stress.

Chemotherapeutic Stress Induces Transdifferentiation of Glioblastoma Cells to Endothelial Cells and Promotes Vascular Mimicry

Glioblastoma (GBM) is the most common and aggressive primary malignant brain tumor affecting adults, with a median survival of approximately 21 months. One key factor underlying the limited efficacy of current treatment modalities is the remarkable plasticity exhibited by GBM cells, which allows them to effectively adapt to changes induced by anticancer therapeutics. Moreover, GBM tumors are highly vascularized with aberrant vessels that complicate the delivery of antitumor agents. Recent research has demonstrated that GBM cells have the ability to transdifferentiate into endothelial cells (ECs), illustrating that GBM cells may use plasticity in concert with vascularization leading to the creation of tumor-derived blood vessels. The mechanism behind this transdifferentiation, however, remains unclear. Here, we show that treatment with temozolomide (TMZ) chemotherapy induces time-dependent expression of markers for glioma stem cells (GSCs) and immature and mature ECs. In addition, GBM tumors growing as orthotopic xenografts in nude mice showed increased expression of GSC and EC markers after TMZ treatment. Ex vivo FACS analysis showed the presence of immature and mature EC populations. Furthermore, immunofluorescence analysis revealed increased tumor-derived vessels in TMZ-recurrent tumors. Overall, this study identifies chemotherapeutic stress as a new driver of transdifferentiation of tumor cells to endothelial cells and highlights cellular plasticity as a key player in therapeutic resistance and tumor recurrence.

Diagnostic Clinical Trials in Breast Cancer Brain Metastases: Barriers and Innovations

Optimal treatment of breast cancer brain metastases (BCBM) is often hampered by limitations in diagnostic abilities. Developing innovative tools for BCBM diagnosis is vital for early detection and effective treatment. In this study we explored the advances in trial for the diagnosis of BCBM, with review of the literature. On May 8, 2019, we searched ClinicalTrials.gov for interventional and diagnostic clinical trials involving BCBM, without limiting for date or location. Information on trial characteristics, experimental interventions, results, and publications were collected and analyzed. In addition, a systematic review of the literature was conducted to explore published studies related to BCBM diagnosis. Only 9 diagnostic trials explored BCBM. Of these, 1 trial was withdrawn because of low accrual numbers. Three trials were completed; however, none had published results. Modalities in trial for BCBM diagnosis entailed magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET), PET-CT, nanobodies, and circulating tumor cells (CTCs), along with a collection of novel tracers and imaging biomarkers. MRI continues to be the diagnostic modality of choice, whereas CT is best suited for acute settings. Advances in PET and PET-CT allow the collection of metabolic and functional information related to BCBM. CTC characterization can help reflect on the molecular foundations of BCBM, whereas cell-free DNA offers new genetic material for further exploration in trials. The integration of machine learning in BCBM diagnosis seems inevitable as we continue to aim for rapid and accurate detection and better patient outcomes.

A faster PISTOL for 1 H MR-based quantitative tissue oximetry

Quantitative mapping of oxygen tension (pO₂ ), noninvasively, could potentially be beneficial in cancer and stroke therapy for monitoring therapy and predicting response to certain therapies. Intracellular pO₂ measurements may also prove useful in tracking the health of labeled cells and understanding the dynamics of cell therapy in vivo. Proton Imaging of Siloxanes to map Tissue Oxygenation Levels (PISTOL) is a relatively new oximetry technique that measures the T₁ of administered siloxanes such as hexamethyldisiloxane (HMDSO), to map the tissue pO₂ at various locations with a temporal resolution of 3.5 minutes. We have now developed a siloxane-selective Look-Locker imaging sequence equipped with an echo planar imaging (EPI) readout to accelerate PISTOL acquisitions. The new tissue oximetry sequence, referred to as PISTOL-LL, enables the mapping of HMDSO T₁ , and hence tissue pO₂ in under one minute. PISTOL-LL was tested and compared with PISTOL in vitro and in vivo. Both sequences were used to record dynamic changes in pO₂ of the rat thigh muscle (healthy Fischer rats, n = 6), and showed similar results (P > 0.05) as the other, with each sequence reporting a significant increase in pO₂ (P < 0.05) under hyperoxia compared with steady state normoxia. This study demonstrates the ability of the new sequence in rapidly and accurately mapping the pO₂ changes and accelerating quantitative ¹ H MR tissue oximetry by approximately 4-fold. The faster PISTOL-LL technique could enable dynamic ¹ H oximetry with higher temporal resolution for assesing tissue oxygentation and tracking the health of transplanted cells labeled with siloxane-based probes. With minor modifications, this sequence can be useful for ¹⁹ F applications as well.

Glioblastoma Unique Features Drive the Ways for Innovative Therapies in the Trunk-branch Era

Glioblastoma multiforme is a solid tumor with particular aspects due to its organ of origin and its development modalities. The brain is very sensitive to oxygen and glucose deprivation and it is the only organ that cannot be either transplanted or entirely removed. Furthermore, many clues and recent indirect experimental evidence indicate that the micro-infiltration of the whole brain parenchyma occurs in very early stages of tumor bulk growth or likely even before. As a consequence, the primary glioblastoma (IDH-wildtype, WHO 2016) is the only tumor where the malignant (i.e. distantly infiltrating the organ of origin) and deadly (i.e. leading cause to patient’s death) phases coincide and overlap in one single phase of its natural history. To date, the prognosis of optimally treated glioblastoma patients remains dismal despite recent fundamental progress in neurosurgical techniques which are enabling better maximal safe resection and survival outcome. Intratumor variegated heterogeneity of glioblastoma bulk due to trunk-branch evolution and very early micro-infiltration and settlement of neoplastic cells in the entire brain parenchyma are the reasons for resistance to current therapeutic treatments. With the aim of future innovative and effective therapies, this paper deals with the unique glioblastoma features, the appropriate research methods as well as the strategies to follow to overcome current causes of resistance.

Comparative evaluation of [18F]DiFA and its analogs as novel hypoxia positron emission tomography and [18F]FMISO as the standard

INTRODUCTION

Hypoxia, a common feature of most solid tumors, is an important predictor of tumor progression and resistance to radiotherapy. We developed a novel hypoxia imaging probe with optimal biological characteristics for use in clinical settings.

METHODS

We designed and synthesized several new hypoxia probes with additional hydrophilic characteristics compared to [¹⁸F]fluoromisonidazole ([¹⁸F]FMISO). These were 1-(2,2-Dihydroxy-methyl-3-[¹⁸F]-Fluoropropyl) azomycin ([¹⁸F]DiFA, formerly [¹⁸F]HIC101) and its analogs ([¹⁸F]F1 and [¹⁸F]F2). Biodistribution studies with EMT6 mammary carcinoma cell-bearing mice were performed 1 and 2 h after injection of each probe. Small-animal positron emission tomography (PET) imaging studies were conducted using [¹⁸F]DiFA and [¹⁸F]FMISO in the same mice. Tumoral hypoxia was confirmed via pimonidazole staining. Ex vivo digital autoradiographs were obtained for confirming the co-localization of [¹⁸F]DiFA and pimonidazole in the tumor tissues.

RESULTS

The EMT6 tumors used had pimonidazole-positive regions. In biodistribution studies, the tumor-to-blood ratio and tumor-to-muscle ratio of [¹⁸F]DiFA was significantly higher than the respective [¹⁸F]FMISO ratios 1 h after injection. Hence, we selected [¹⁸F]DiFA as the best hypoxia probe among those tested. Small-animal PET imaging studies showed time-dependent increases in the tumor-to-normal tissue ratio of [¹⁸F]DiFA uptake. Rapid clearance from the rest of the body was observed primarily via the renal system. Ex vivo autoradiography showed a positive correlation between [¹⁸F]DiFA uptake and the regions of pimonidazole distribution, indicating that [¹⁸F]DiFA selectively accumulated in the tumor tissue's hypoxic region.

CONCLUSIONS

A better contrast image and a shorter waiting time may be obtained with [¹⁸F]DiFA than with [¹⁸F]FMISO.

ADVANCES IN KNOWLEDGE

By optimizing LogP based on the [¹⁸F]FMISO structure, we demonstrated that [¹⁸F]DiFA could detect tumor hypoxia regions at an early time point. IMPLICATIONS FOR PATIENT CARE: [¹⁸F]DiFA imaging facilitates the evaluation of various cancer hypoxic states due to the lower uptake of normal tissues and could contribute to novel treatment development.

Glioblastoma's Next Top Model: Novel Culture Systems for Brain Cancer Radiotherapy Research

Glioblastoma (GBM), the most common and aggressive primary brain tumor in adults, remains one of the least treatable cancers. Current standard of care—combining surgical resection, radiation, and alkylating chemotherapy—results in a median survival of only 15 months. Despite decades of investment and research into the development of new therapies, most candidate anti-glioma compounds fail to translate into effective treatments in clinical trials. One key issue underlying this failure of therapies that work in pre-clinical models to generate meaningful improvement in human patients is the profound mismatch between drug discovery systems—cell cultures and mouse models—and the actual tumors they are supposed to imitate. Indeed, current strategies that evaluate the effects of novel treatments on GBM cells in vitro fail to account for a wide range of factors known to influence tumor growth. These include secreted factors, the brain’s unique extracellular matrix, circulatory structures, the presence of non-tumor brain cells, and nutrient sources available for tumor metabolism. While mouse models provide a more realistic testing ground for potential therapies, they still fail to account for the full complexity of tumor-microenvironment interactions, as well as the role of the immune system. Based on the limitations of current models, researchers have begun to develop and implement novel culture systems that better recapitulate the complex reality of brain tumors growing in situ. A rise in the use of patient derived cells, creative combinations of added growth factors and supplements, may provide a more effective proving ground for the development of novel therapies. This review will summarize and analyze these exciting developments in 3D culturing systems. Special attention will be paid to how they enhance the design and identification of compounds that increase the efficacy of radiotherapy, a bedrock of GBM treatment.

Pericytes in Glioblastomas: Multifaceted Role Within Tumor Microenvironments and Potential for Therapeutic Interventions

Glioblastoma (GBM) is an aggressive and lethal disease that often results in a poor prognosis. Unlike most solid tumors, GBM is characterized by diffuse infiltrating margins, extensive angiogenesis, hypoxia, necrosis, and clonal heterogeneity. Recurrent disease is an unavoidable consequence for many patients as standard treatment options such as surgery, radiotherapy, and chemotherapy have proven to be insufficient in causing long-term survival benefits. Systemic delivery of promising drugs is hindered due to the blood-brain barrier and non-uniform perfusion within GBM tissue. In recent years, many investigations have highlighted the role of GBM stem cells (GSCs) and their microenvironment in the initiation and maintenance of tumor tissue. Preclinical and early clinical studies to target GSCs and microenvironmental components are currently underway. Of these strategies, immunotherapy using checkpoint inhibitors and redirected cytotoxic T cells have shown promising results in early investigations. But, GBM microenvironment is heterogenous and recent investigations have shown cell populations within this microenvironment to be plastic. These studies underline the importance of identifying the role of and targeting multiple cell populations within the GBM microenvironment which could have a synergistic effect when combined with novel therapies. Pericytes are multipotent perivascular cells that play a vital role within the GBM microenvironment by assisting in tumor initiation, survival, and progression. Due to their role in regulating the blood-brain barrier permeability, promoting angiogenesis, tumor growth, clearing extracellular matrix for infiltrating GBM cells and in helping GBM cells evade immune surveillance, pericytes could be ideal therapeutic targets for stymieing or exploiting their role within the GBM microenvironment. This chapter will introduce hallmarks of GBM and elaborate on the contributions of pericytes to these hallmarks by examining recent findings. In addition, the chapter also highlights the therapeutic value of targeting pericytes, while discussing conventional and novel GBM therapies and obstacles to their efficacy.

Induction and Assessment of Hypoxia in Glioblastoma Cells In Vitro

To simulate and study the hypoxic microenvironment associated with intracerebral glioma in vivo, simple and reproducible methods are described and discussed for inducing hypoxia or chemical pseudohypoxia in glioma cell cultures and assessing their effects on the expression and nuclear translocation of hypoxia-inducible factor (HIF)-1α, a key transcriptional factor of oxygen homeostasis, by Western blot analysis and immunocytochemistry.

Oxygen Regulation in Development: Lessons from Embryogenesis towards Tissue Engineering

Oxygen is a vital source of energy necessary to sustain and complete embryonic development. Not only is oxygen the driving force for many cellular functions and metabolism, but it is also involved in regulating stem cell fate, morphogenesis, and organogenesis. Low oxygen levels are the naturally preferred microenvironment for most processes during early development and mainly drive proliferation. Later on, more oxygen and also nutrients are needed for organogenesis and morphogenesis. Therefore, it is critical to maintain oxygen levels within a narrow range as required during development. Modulating oxygen tensions is performed via oxygen homeostasis mainly through the function of hypoxia-inducible factors. Through the function of these factors, oxygen levels are sensed and regulated in different tissues, starting from their embryonic state to adult development. To be able to mimic this process in a tissue engineering setting, it is important to understand the role and levels of oxygen in each developmental stage, from embryonic stem cell differentiation to organogenesis and morphogenesis. Taking lessons from native tissue microenvironments, researchers have explored approaches to control oxygen tensions such as hemoglobin-based, perfluorocarbon-based, and oxygen-generating biomaterials, within synthetic tissue engineering scaffolds and organoids, with the aim of overcoming insufficient or nonuniform oxygen levels and nutrient supply.

Effects of hypoxic preconditioning on neuroblastoma tumour oxygenation and metabolic signature in a chick embryo model

Hypoxia episodes and areas in tumours have been associated with metastatic dissemination and poor prognosis. Given the link between tumour tissue oxygen levels and cellular metabolic activity, we hypothesised that the metabolic profile between metastatic and non-metastatic tumours would reveal potential new biomarkers and signalling cues. We have used a previously established chick embryo model for neuroblastoma growth and metastasis, where the metastatic phenotype can be controlled by neuroblastoma cell hypoxic preconditioning (3 days at 1% O₂). We measured, with fibre-optic oxygen sensors, the effects of the hypoxic preconditioning on the tumour oxygenation, within tumours formed by SK-N-AS cells on the chorioallantoic membrane (CAM) of chick embryos. We found that the difference between the metastatic and non-metastatic intratumoural oxygen levels was small (0.35% O₂), with a mean below 1.5% O₂ for most tumours. The metabolomic profiling, using NMR spectroscopy, of neuroblastoma cells cultured in normoxia or hypoxia for 3 days, and of the tumours formed by these cells showed that the effects of hypoxia in vitro did not compare with in vivo tumours. One notable difference was the high levels of the glycolytic end-products triggered by hypoxia in vitro, but not by hypoxia preconditioning in tumours, likely due to the very high basal levels of these metabolites in tumours compared with cells. In conclusion, we have identified high levels of ketones (3-hydroxybutyrate), lactate and phosphocholine in hypoxic preconditioned tumours, all known to fuel tumour growth, and we herein point to the poor relevance of in vitro metabolomic experiments for cancer research.

Longitudinal PET imaging of tumor hypoxia during the course of radiotherapy

Hypoxia results from an imbalance between oxygen supply and consumption. It is a common phenomenon in solid malignant tumors such as head and neck cancer. As hypoxic cells are more resistant to therapy, tumor hypoxia is an indicator for poor prognosis. Several techniques have been developed to measure tissue oxygenation. These are the Eppendorf O2 polarographic needle electrode, immunohistochemical analysis of endogenous (e.g., hypoxia-inducible factor-1α (HIF-1a)) and exogenous markers (e.g., pimonidazole) as well as imaging methods such as functional magnetic resonance imaging (e.g., blood oxygen level dependent (BOLD) imaging, T1-weighted imaging) and hypoxia positron emission tomography (PET). Among the imaging modalities, only PET is sufficiently validated to detect hypoxia for clinical use. Hypoxia PET tracers include 18F-fluoromisonidazole (FMISO), the most commonly used hypoxic marker, 18F-flouroazomycin arabinoside (FAZA), 18Ffluoroerythronitroimidazole (FETNIM), 18F-2-nitroimidazolpentafluoropropylacetamide (EF5) and 18F-flortanidazole (HX4). As technical development provides the opportunity to increase the radiation dose to subregions of the tumor, such as hypoxic areas, it has to be ensured that these regions are stable not only from imaging to treatment but also through the course of radiotherapy. The aim of this review is therefore to characterize the behavior of tumor hypoxia during radiotherapy for the whole tumor and for subregions by using hypoxia PET tracers, with focus on head and neck cancer patients.

Clinical trials targeting hypoxia

The concept of tumour hypoxia as a cause of radiation resistance has been prevalent for over 100 years. During this time, our understanding of tumour hypoxia has matured with the recognition that oxygen tension within a tumour is influenced by both diffusion and perfusion mechanisms. In parallel, clinical strategies to modify tumour hypoxia with the expectation that this will improve response to radiation have been developed and tested in clinical trials. Despite many disappointments, meta-analysis of the data on hypoxia modification confirms a significant impact on both tumour control and survival. Early trials evaluated hyperbaric oxygen followed by a generation of studies testing oxygen mimetics such as misonidazole, pimonidazole and etanidazole. One highly significant result stands out from the use of nimorazole in advanced laryngeal cancer with a significant advantage seen for locoregional control using this radiosensitiser. More recent studies have evaluated carbogen and nicotinamide targeting both diffusion related and perfusion related hypoxia. A significant survival advantage is seen in muscle invasive bladder cancer and also for locoregional control in hypopharygeal cancer associated with a low haemoglobin. New developments include the recognition that mitochondrial complex inhibitors reducing tumour oxygen consumption are potential radiosensitising agents and atovaquone is currently in clinical trials. One shortcoming of past hypoxia modifying trials is the failure to identify oxygenation status and select those patient with significant hypoxia. A range of biomarkers are now available including histological necrosis, immunohistochemical intrinsic markers such as CAIX and Glut 1 and hypoxia gene signatures which have been shown to predict outcome and will inform the next generation of hypoxia modifying clinical trials.

Glioblastoma Stem Cells and Their Microenvironment

Glioblastoma (GBM) is the most common primary malignant astrocytoma associated with a poor patient survival. Apart from arising de novo, GBMs also occur due to progression of slower growing grade III astrocytomas. GBM is characterized by extensive hypoxia, angiogenesis, proliferation and invasion. Standard treatment options such as surgical resection, radiation therapy and chemotherapy have increased median patient survival to 14.6 months in adults but recurrent disease arising from treatment resistant cancer cells often results in patient mortality. These treatment resistant cancer cells have been found to exhibit stem cell like properties. Strategies to identify or target these Glioblastoma Stem Cells (GSC) have proven to be unsuccessful so far. Studies on cancer stem cells (CSC) within GBM and other cancers have highlighted the importance of paracrine signaling networks within their microenvironment on the growth and maintenance of CSCs. The study of GSCs and their communication with various cell populations within their microenvironment is therefore not only important to understand the biology of GBMs but also to predict response to therapies and to identify novel targets which could stymy support to treatment resistant cancer cells and prevent disease recurrence. The purpose of this chapter is to introduce the concept of GSCs and to detail the latest findings indicating the role of various cellular subtypes within their microenvironment on their survival, proliferation and differentiation.

Radiotherapy and Glioma Stem Cells: Searching for Chinks in Cellular Armor

Purpose of the review

Radiation became a pillar of oncologic treatment in the last century and provided a powerful and effective locoregional treatment of solid malignancies. After achieving some of the first cures in lymphomas and skin cancers, it assumed a key role in curative treatment of epithelioid malignancies. Despite success across a variety of histologic types, glioblastoma (GBM), the most common primary brain tumor afflicting adults, remains ultimately resistant to current radiation strategies. While GBMs demonstrate an initial response, recurrence is essentially universal and fatal, and typically reoccur in the areas that received the most intense radiation.

Recent Findings

Glioma stem cells (GSCs), a subpopulation of tumor cells with expression profiles similar to neural stem cells and marked self-renewal capacities, have been shown to drive tumor recurrence and preclude curative radiotherapy. Recent research has shown that these cells have enhanced DNA repair capacity, elevated resistance to cytotoxic ion fluxes and escape multi-modality therapies.

Summary

We will analyze the current understanding of GSCs and radiation by highlighting key discoveries probing their ability to withstand radiotherapy. We then speculate on novel mechanisms by which GSC can be made sensitive to or specifically targeted by radiation therapy.

Classifying the evolutionary and ecological features of neoplasms

Neoplasms change over time through a process of cell-level evolution, driven by genetic and epigenetic alterations. However, the ecology of the microenvironment of a neoplastic cell determines which changes provide adaptive benefits. There is widespread recognition of the importance of these evolutionary and ecological processes in cancer, but to date, no system has been proposed for drawing clinically relevant distinctions between how different tumours are evolving. On the basis of a consensus conference of experts in the fields of cancer evolution and cancer ecology, we propose a framework for classifying tumours that is based on four relevant components. These are the diversity of neoplastic cells (intratumoural heterogeneity) and changes over time in that diversity, which make up an evolutionary index (Evo-index), as well as the hazards to neoplastic cell survival and the resources available to neoplastic cells, which make up an ecological index (Eco-index). We review evidence demonstrating the importance of each of these factors and describe multiple methods that can be used to measure them. Development of this classification system holds promise for enabling clinicians to personalize optimal interventions based on the evolvability of the patient's tumour. The Evo- and Eco-indices provide a common lexicon for communicating about how neoplasms change in response to interventions, with potential implications for clinical trials, personalized medicine and basic cancer research.

Regulation of hypoxia-induced autophagy in glioblastoma involves ATG9A

BACKGROUND

Hypoxia is negatively associated with glioblastoma (GBM) patient survival and contributes to tumour resistance. Anti-angiogenic therapy in GBM further increases hypoxia and activates survival pathways. The aim of this study was to determine the role of hypoxia-induced autophagy in GBM.

METHODS

Pharmacological inhibition of autophagy was applied in combination with bevacizumab in GBM patient-derived xenografts (PDXs). Sensitivity towards inhibitors was further tested in vitro under normoxia and hypoxia, followed by transcriptomic analysis. Genetic interference was done using ATG9A-depleted cells.

RESULTS

We find that GBM cells activate autophagy as a survival mechanism to hypoxia, although basic autophagy appears active under normoxic conditions. Although single agent chloroquine treatment in vivo significantly increased survival of PDXs, the combination with bevacizumab resulted in a synergistic effect at low non-effective chloroquine dose. ATG9A was consistently induced by hypoxia, and silencing of ATG9A led to decreased proliferation in vitro and delayed tumour growth in vivo. Hypoxia-induced activation of autophagy was compromised upon ATG9A depletion.

CONCLUSIONS

This work shows that inhibition of autophagy is a promising strategy against GBM and identifies ATG9 as a novel target in hypoxia-induced autophagy. Combination with hypoxia-inducing agents may provide benefit by allowing to decrease the effective dose of autophagy inhibitors.

Perfluorocarbon emulsions radiosensitise brain tumors in carbogen breathing mice with orthotopic GL261 gliomas

Background

Tumour hypoxia limits the effectiveness of radiation therapy. Delivering normobaric or hyperbaric oxygen therapy elevates pO₂ in both tumour and normal brain tissue. However, pO2 levels return to baseline within 15 minutes of stopping therapy.

Aim

To investigate the effect of perfluorocarbon (PFC) emulsions on hypoxia in subcutaneous and intracranial mouse gliomas and their radiosensitising effect in orthotopic gliomas in mice breathing carbogen (95%O₂ and 5%CO₂).

Results

PFC emulsions completely abrogated hypoxia in both subcutaneous and intracranial GL261 models and conferred a significant survival advantage orthotopically (Mantel Cox: p = 0.048) in carbogen breathing mice injected intravenously (IV) with PFC emulsions before radiation versus mice receiving radiation alone. Carbogen alone decreased hypoxia levels substantially and conferred a smaller but not statistically significant survival advantage over and above radiation alone.

Conclusion

IV injections of PFC emulsions followed by 1h carbogen breathing, radiosensitises GL261 intracranial tumors.

GBM radiosensitizers: dead in the water…or just the beginning?

The finding that most GBMs recur either near or within the primary site after radiotherapy has fueled great interest in the development of radiosensitizers to enhance local control. Unfortunately, decades of clinical trials testing a wide range of novel therapeutic approaches have failed to yield any clinically viable radiosensitizers. However, many of  the previous radiosensitizing strategies were not based on clear pre-clinical evidence, and in many cases blood-barrier penetration was not considered. Furthermore, DNA repair inhibitors have only recenly arrived in the clinic, and likely represent potent agents for glioma radiosensitization. Here, we present recent progress in the use of small molecule DNA damage response inhibitors as GBM radiosensitizers. In addition, we discuss the latest progress in targeting hypoxia and oxidative stress for GBM radiosensitization.

Cyclooxygenase-2 Induction by Amino Acid Deprivation Requires p38 Mitogen-Activated Protein Kinase in Human Glioma Cells

Glioblastomas (GBMs) are malignant brain tumors that can outstrip nutrient supplies due to rapid growth. Cyclooxygenase-2 (COX-2) has been linked to GBMs and may contribute to their aggressive phenotypes. Amino acid starvation results in COX-2 mRNA and protein induction in multiple human glioma cell lines in a process requiring p38 mitogen-activated protein kinase (p38-MAPK) and the Sp1 transcription factor. Increased vascular endothelial growth factor expression results from starvation-dependent COX-2 induction. These data suggest that COX-2 induction with amino acid deprivation may be a part of the adaptation of glioma cells to these conditions, and potentially alter cellular response to anti-neoplastic therapy.

Multidrug resistance in glioblastoma stem-like cells: Role of the hypoxic microenvironment and adenosine signaling

Glioblastoma multiforme (GBM) is considered the most common and aggressive tumour of the central nervous system and is characterized for being highly chemoresistant. This property is mainly due to the activation of Multiple Drug Resistance (MDR) mechanisms that protect cancer cells from structurally and morphologically different drugs. Overexpression and increased ABC transporters activity is one of the most important MDR mechanisms at the clinical level, and both its expression and activity are elevated in GBM cells. Within the tumour, there is a subpopulation called glioblastoma stem-like cells (GSCs), which due to its high tumourigenic capacity and chemoresistance, have been postulated as the main responsible for tumour recurrence. The GSCs inhabit hypoxic tumour zones, niches that apart from maintaining and promoting stem phenotype have also been correlated with high chemoresistance. Of the signalling pathways activated during hypoxia, purinergic signalling has been highly associated to the induction of MDR mechanisms. Through its receptors, the nucleoside adenosine has been shown to promotes the chemoresistance mediated by ABC transporters. Therefore, targeting its components is a promising alternative for GBM treatment. In this review, we will discuss chemoresistance in GSCs and the effect of the hypoxic microenvironment and adenosine on MDR mechanisms.

Selective turn-on near-infrared fluorescence probe for hypoxic tumor cell imaging

In this study, we designed a new selective turn on near-infrared fluorescence probe by conjugating (1-methyl-2-nitro-1H-imidazol-5-yl)methanol to DCPO with ether linkage for hypoxic tumor cell imaging.