Stress Response Leading to Resistance in Glioblastoma-The Need for Innovative Radiotherapy (iRT) Concepts

miR-3059-3p Regulates Glioblastoma Multiforme Radiosensitivity Enhancement through the Homologous Recombination Pathway of DNA Repair

Background

Glioblastoma multiforme (GBM) is one of the most deadly and recalcitrant illnesses of the neurocentral nervous system in humans. MicroRNAs (miRNAs) are a class of noncoding RNAs that play important roles in the regulation of gene expression and biological processes, including radiosensitivity. In this study, we demonstrated the relationship between miR-3059-3p and radiation in GBM.

Materials and Methods

Radioresistant (RR) cells were obtained by exposing GBM8401 cells to 80 Gy radiation in 20 weekly 4 Gy fractions. miR-3059-3p mRNA and DNA replication helicase/nuclease 2 (DNA2) protein expressions were detected using real-time polymerase chain reaction and immunoblotting. Using flow cytometry, colony formation and apoptosis were identified using miR-3059-3p mimic, miR-3059-3p inhibitor, DNA2 siRNA, and DNA2 plasmid. Immunoblotting was used to detect DNA repair proteins.

Results

Low levels of miR-3059-3p and high levels of DNA2 were observed in RR cells. Colony formation and apoptosis assays revealed that miR-3059-3p targeted DNA2 to regulate radioresistance. Immunoblotting revealed that miR-3059-3p regulated the homologous recombination (HR) pathway (Rad51 and Rad52) but not the nonhomologous end joining pathway (ku70 and ku80).

Conclusion

Downregulation of DNA2 via miR-3059-3p enhanced the radiosensitivity of GBM cells through the inhibition of the HR pathway.

Progression Patterns in Non-Contrast-Enhancing Gliomas Support Brain Tumor Responsiveness to Surgical Lesions

Purpose: The overall benefit of surgical treatments for patients with glioma is undisputed. We have shown preclinically that brain tumor cells form a network that is capable of detecting damage to the tumor, and repair itself. The aim of this study was to determine whether a similar mechanism might contribute to local recurrence in the clinical setting.

Methods: We evaluated tumor progression patterns of 24 initially non-contrast-enhancing gliomas that were partially resected or biopsied. We measured the distance between the new contrast enhancement developing over time, and prior surgical lesioning, and evaluated tumor network changes in response to sequential resections by quantifying tumor cells and tumor networks with specific stainings against IDH1-R132H.

Results: We found that new contrast enhancement appeared within the residual, non-enhancing tumor mass in 21/24 patients (87.5%). The location of new contrast enhancement within the residual tumor region was non-random; it occurred adjacent to the wall of the resection cavity in 12/21 patients (57.1%). Interestingly, the density of the glioma cell network increased in all patient tumors between initial resection or biopsy and recurrence. In line with the histological and radiological malignization, Ki67 expression increased from initial to final resections in 14/17 cases.

Conclusion: The non-random distribution of glioma malignization in patients and unidirectional increase of anatomical tumor networks after surgical procedures provides evidence that surgical lesions, in the presence of residual tumor cells, can stimulate local tumor progression and tumor cell network formation. This argues for the development of intraoperative treatments increasing the benefits from surgical resection by specifically disrupting the mechanisms of local recurrence, particularly tumor cell network functionality.

Glioblastoma Relapses Show Increased Markers of Vulnerability to Ferroptosis

Background

Despite the availability of various therapy options and being a widely focused research area, the prognosis of glioblastoma (GBM) still remains very poor due to therapy resistance, genetic heterogeneity and a diffuse infiltration pattern. The recently described non-apoptotic form of cell death ferroptosis may, however, offer novel opportunities for targeted therapies. Hence, the aim of this study was to investigate the potential role of ferroptosis in GBM, including the impact of treatment on the expression of the two ferroptosis-associated players glutathione-peroxidase 4 (GPX4) and acyl-CoA-synthetase long-chain family number 4 (ACSL4). Furthermore, the change in expression of the recently identified ferroptosis suppressor protein 1 (FSP1) and aldehyde dehydrogenase (ALDH) 1A3 was investigated.

Methods

Immunohistochemistry was performed on sample pairs of primary and relapse GBM of 24 patients who had received standard adjuvant treatment with radiochemotherapy. To identify cell types generally prone to undergo ferroptosis, co-stainings of ferroptosis susceptibility genes in combination with cell-type specific markers including glial fibrillary acidic protein (GFAP) for tumor cells and astrocytes, as well as the ionized calcium-binding adapter molecule 1 (Iba1) for microglial cells were performed, supplemented by double stains combining GPX4 and ACSL4.

Results

While the expression of GPX4 decreased significantly during tumor relapse, ACSL4 showed a significant increase. These results were confirmed by analyses of data sets of the Cancer Genome Atlas. These profound changes indicate an increased susceptibility of relapsed tumors towards oxidative stress and associated ferroptosis, a cell death modality characterized by unrestrained lipid peroxidation. Moreover, ALDH1A3 and FSP1 expression also increased in the relapses with significant results for ALDH1A3, whereas for FSP1, statistical significance was not reached. Results obtained from double staining imply that ferroptosis occurs more likely in GBM tumor cells than in microglial cells.

Conclusion

Our study implies that ferroptosis takes place in GBM tumor cells. Moreover, we show that recurrent tumors have a higher vulnerability to ferroptosis. These results affirm that utilizing ferroptosis processes might be a possible novel therapy option, especially in the situation of recurrent GBM.

Metabolic Tumor Microenvironment Characterization of Contrast Enhancing Brain Tumors Using Physiologic MRI

The tumor microenvironment is a critical regulator of cancer development and progression as well as treatment response and resistance in brain neoplasms. The available techniques for investigation, however, are not well suited for noninvasive in vivo characterization in humans. A total of 120 patients (59 females; 61 males) with newly diagnosed contrast-enhancing brain tumors (64 glioblastoma, 20 brain metastases, 15 primary central nervous system (CNS) lymphomas (PCNSLs), and 21 meningiomas) were examined with a previously established physiological MRI protocol including quantitative blood-oxygen-level-dependent imaging and vascular architecture mapping. Six MRI biomarker maps for oxygen metabolism and neovascularization were fused for classification of five different tumor microenvironments: glycolysis, oxidative phosphorylation (OxPhos), hypoxia with/without neovascularization, and necrosis. Glioblastoma showed the highest metabolic heterogeneity followed by brain metastasis with a glycolysis-to-OxPhos ratio of approximately 2:1 in both tumor entities. In addition, glioblastoma revealed a significant higher percentage of hypoxia (24%) compared to all three other brain tumor entities: brain metastasis (7%; p < 0.001), PCNSL (8%; p = 0.001), and meningioma (8%; p = 0.003). A more aggressive biological brain tumor behavior was associated with a higher percentage of hypoxia and necrosis and a lower percentage of remaining vital tumor tissue and aerobic glycolysis. The proportion of oxidative phosphorylation, however, was rather similar (17–26%) for all four brain tumor entities. Tumor microenvironment (TME) mapping provides insights into neurobiological differences of contrast-enhancing brain tumors and deserves further clinical cancer research attention. Although there is a long roadmap ahead, TME mapping may become useful in order to develop new diagnostic and therapeutic approaches.

Pulsed low-dose rate radiotherapy has an improved therapeutic effect on abdominal and pelvic malignancies

Until now, there has been a lack of standard and effective treatments for patients with recurrent malignant tumors or abdominal and pelvic malignancies with extensive invasion (Morris, 2000). Generally, these patients face problems such as inability to undergo surgery or chemotherapy resistance (Combs et al., 2016). Re-radiotherapy has achieved a prominent place in the treatment of patients who have received radiotherapy previously and developed in-field recurrences (Straube et al., 2018). However, re-radiotherapy is very complicated, requiring comprehensive consideration of appropriate radiation dose, interval from first radiotherapy, boundary of the radiotherapy target area, and damage to surrounding normal tissues (Straube et al., 2019). In other words, it is necessary to focus on the protection of surrounding normal tissues while maximizing the efficacy of re-radiotherapy in such patients.

Hypoxia Transcriptomic Modifications Induced by Proton Irradiation in U87 Glioblastoma Multiforme Cell Line

In Glioblastoma Multiforme (GBM), hypoxia is associated with radioresistance and poor prognosis. Since standard GBM treatments are not always effective, new strategies are needed to overcome resistance to therapeutic treatments, including radiotherapy (RT). Our study aims to shed light on the biomarker network involved in a hypoxic (0.2% oxygen) GBM cell line that is radioresistant after proton therapy (PT). For cultivating cells in acute hypoxia, GSI’s hypoxic chambers were used. Cells were irradiated in the middle of a spread-out Bragg peak with increasing PT doses to verify the greater radioresistance in hypoxic conditions. Whole-genome cDNA microarray gene expression analyses were performed for samples treated with 2 and 10 Gy to highlight biological processes activated in GBM following PT in the hypoxic condition. We describe cell survival response and significant deregulated pathways responsible for the cell death/survival balance and gene signatures linked to the PT/hypoxia configurations assayed. Highlighting the molecular pathways involved in GBM resistance following hypoxia and ionizing radiation (IR), this work could suggest new molecular targets, allowing the development of targeted drugs to be suggested in association with PT.

Inhibition of HSP90 as a Strategy to Radiosensitize Glioblastoma: Targeting the DNA Damage Response and Beyond

Radiotherapy is an essential component of multi-modality treatment of glioblastoma (GBM). However, treatment failure and recurrence are frequent and give rise to the dismal prognosis of this aggressive type of primary brain tumor. A high level of inherent treatment resistance is considered to be the major underlying reason, stemming from constantly activated DNA damage response (DDR) mechanisms as a consequence of oncogene overexpression, persistent replicative stress, and other so far unknown reasons. The molecular chaperone heat shock protein 90 (HSP90) plays an important role in the establishment and maintenance of treatment resistance, since it crucially assists the folding and stabilization of various DDR regulators. Accordingly, inhibition of HSP90 represents a multi-target strategy to interfere with DDR function and to sensitize cancer cells to radiotherapy. Using NW457, a pochoxime-based HSP90 inhibitor with favorable brain pharmacokinetic profile, we show here that HSP90 inhibition at low concentrations with per se limited cytotoxicity leads to downregulation of various DNA damage response factors on the protein level, distinct transcriptomic alterations, impaired DNA damage repair, and reduced clonogenic survival in response to ionizing irradiation in glioblastoma cells in vitro. In vivo, HSP90 inhibition by NW457 improved the therapeutic outcome of fractionated CBCT-based irradiation in an orthotopic, syngeneic GBM mouse model, both in terms of tumor progression and survival. Nevertheless, in view of the promising in vitro results the in vivo efficacy was not as strong as expected, although apart from the radiosensitizing effects HSP90 inhibition also reduced irradiation-induced GBM cell migration and tumor invasiveness. Hence, our findings identify the combination of HSP90 inhibition and radiotherapy in principle as a promising strategy for GBM treatment whose performance needs to be further optimized by improved inhibitor substances, better formulations and/or administration routes, and fine-tuned treatment sequences.

microRNAs: Potential glioblastoma radiosensitizer by targeting radiation-related molecular pathways

Glioblastoma (GBM) is the most lethal type of primary brain tumor. Currently, even with optimal and multimodal cancer therapies, the survival rate of GBM patients remains poor. One reason for inadequate response of GBM tumors to radiotherapy is radioresistance (RR). Thus, there is a critical need for new insights about GBM treatment to increase the chance of treatment. microRNAs (miRNAs) are important regulatory molecules that can effectively control GBM radiosensitivity (RS) by affecting radiation-related signal transduction pathways such as apoptosis, proliferation, DNA repair and cell cycle regulation. miRNAs provide new clinical perspectives for developing effective GBM treatments. A growing body of literature has demonstrated that GBM RS can be modified by modulating the expression of miRNAs such as miR-7, miR-10b, miR-124, miR-128, miR-320, miR-21, miR-203, and miR-153. This paper highlights the miRNAs and the underlying molecular mechanisms that are involved in the RS of GBM. Besides highlighting the role of miRNAs in different signaling pathways, we explain the mechanisms that affect RS of GBM for modulating radiation response at the clinical level.

Proton Therapy and Src Family Kinase Inhibitor Combined Treatments on U87 Human Glioblastoma Multiforme Cell Line

Glioblastoma Multiforme (GBM) is the most common of malignant gliomas in adults with an exiguous life expectancy. Standard treatments are not curative and the resistance to both chemotherapy and conventional radiotherapy (RT) plans is the main cause of GBM care failures. Proton therapy (PT) shows a ballistic precision and a higher dose conformity than conventional RT. In this study we investigated the radiosensitive effects of a new targeted compound, SRC inhibitor, named Si306, in combination with PT on the U87 glioblastoma cell line. Clonogenic survival assay, dose modifying factor calculation and linear-quadratic model were performed to evaluate radiosensitizing effects mediated by combination of the Si306 with PT. Gene expression profiling by microarray was also conducted after PT treatments alone or combined, to identify gene signatures as biomarkers of response to treatments. Our results indicate that the Si306 compound exhibits a radiosensitizing action on the U87 cells causing a synergic cytotoxic effect with PT. In addition, microarray data confirm the SRC role as the main Si306 target and highlights new genes modulated by the combined action of Si306 and PT. We suggest, the Si306 as a new candidate to treat GBM in combination with PT, overcoming resistance to conventional treatments.

Cytosolic Hsp70 as a biomarker to predict clinical outcome in patients with glioblastoma

INTRODUCTION

The major stress-inducible heat shock protein 70 (Hsp70) is induced after different stress stimuli. In tumors, elevated intracellular Hsp70 levels were associated on the one hand with radio- and chemotherapy resistance and on the other hand with a favorable outcome for patients. This study was undertaken to investigate cytosolic Hsp70 (cHsp70) as a potential biomarker for progression free (PFS) and overall survival (OS) in patients with primary glioblastomas (GBM).

METHODS

The cHsp70 expression in tumor tissue of 60 patients diagnosed with primary GBM was analyzed by immunohistochemistry. The cHsp70 expression was correlated to the PFS and OS of the patients.

RESULTS

A high cHsp70 expression was associated with a prolonged PFS (hazard ratio = 0.374, p = 0.001) and OS (hazard ratio = 0.416, p = 0.014) in GBM patients treated according to the standard Stupp protocol with surgery, radiotherapy and temozolomide.

CONCLUSIONS

These data suggest that the intracellular Hsp70 expression might serve as a prognostic marker in patients with primary GBM.

Rosmarinic acid and siRNA combined therapy represses Hsp27 (HSPB1) expression and induces apoptosis in human glioma cells

High expression of Hsp27 in glioma cells has been closely associated with tumor cell proliferation and apoptosis inhibition. The aim of the present study was to asses the effects of rosmarinic acid (RA) on Hsp27 expression and apoptosis in non-transfected and transfected human U-87 MG cells. The effect of rosmarinic acid was compared to quercetin, which is known to be a good Hsp27 inhibitor. In order to block the expression of Hsp27 gene (HSPB1), transfection with specific siRNAs was performed. Western blotting technique was used to assess the Hsp27 expression, and caspase-3 colorimetric activity assay was performed to determine apoptosis induction. According to the results, it was found that RA and quercetin effectively silenced Hsp27 and both agents induced apoptosis by activating the caspase-3 pathway. Eighty and 215 μM RA decreased the level of Hsp27 by 28.8 and 46.7% and induced apoptosis by 30 and 54%, respectively. For the first time, we reported that rosmarinic acid has the ability to trigger caspase-3 induced apoptosis in human glioma cells. As a result of siRNA transfection, the Hsp27 gene was silenced by ~ 50% but did not cause a statistically significant change in caspase-3 activation. It was also observed that apoptosis was induced at a higher level as a result of Hsp27 siRNA and subsequent quercetin or RA treatment. siRNA transfection and 215 μM RA treatment suppressed Hsp27 expression level by 90.5% and increased caspase-3 activity by 58%. Herein, we demonstrated that RA administered with siRNA seems to be a potent combination for glioblastoma therapy.

Duocarmycin SA, a potent antitumor antibiotic, sensitizes glioblastoma cells to proton radiation

New treatment modalities for glioblastoma multiforme (GBM) are urgently needed. Proton therapy is considered one of the most effective forms of radiation therapy for GBM. DNA alkylating agents such as temozolomide (TMZ) are known to increase the radiosensitivity of GBM to photon radiation. TMZ is a fairly impotent agent, while duocarmycin SA (DSA) is an extremely potent cytotoxic agent capable of inducing a sequence-selective alkylation of duplex DNA. Here, the effects of sub-nM concentrations of DSA on the radiosensitivity of a human GBM cell line (U-138) to proton irradiation were examined. Radiation sensitivity was determined by viability, apoptosis, necrosis and clonogenic assays. DSA concentrations as low as 0.001 nM significantly sensitized U-138 cells to proton irradiation. DSA demonstrates synergistic cytotoxicity against GBM cells treated with proton radiation in vitro, which may represent a novel therapeutic alternative for the treatment of GBM.

Adjuvant stereotactic fractionated radiotherapy to the resection cavity in recurrent glioblastoma - the GlioCave study (NOA 17 - ARO 2016/3 - DKTK ROG trial)

Background

Glioblastoma relapses in the vast majority of cases within 1 year. Maximum safe resection of the recurrent glioblastoma can be offered in some cases. Re-irradiation has been established for the treatment of recurrent glioblastoma, too. In both cases, adjuvant treatment, mostly using temozolomide, can improve PFS and OS after these interventions. However, combining gross tumor resection and adjuvant re-radiotherapy to the resection cavity has not been tested so far.

Methods/Design

In the multicenter two-armed randomized Phase II GlioCave Study, fractionated stereotactic radiotherapy to the resection cavity, after gross tumor resection of recurrent glioblastoma, will be compared to observation. Depending on the size of the target volume, a total dose of 46 Gy in 2 Gy per fraction or a total dose if 36 Gy in 3 Gy per fraction will be applied. Progression free survival will be the primary endpoint of the study.

Discussion

Adjuvant treatment after gross tumor resection of recurrent glioblastoma is currently deemed to be limited to chemotherapy. However, re-irradiation has proven safety and tolerability in the treatment of macroscopic disease. Performing re-irradiation as an adjuvant measure after gross tumor resection has not been tested so far. The GlioCave Study will investigate the efficacy and the safety profile of this approach.

Trial registration

The trial was prospectively registered at clinicaltrials.gov (NCT02715297, registration date February 29th, 2016). The protocol presented hereby refers to the version 1.2 of the protocol (January 11^th, 2017).

MicroRNA-378 enhances radiation response in ectopic and orthotopic implantation models of glioblastoma

Glioblastoma multiforme (GBM) is the most common and highly malignant primary brain tumor, which is virtually incurable due to its therapeutic resistance to radiation and chemotherapy. To develop novel therapeutic approaches for treatment of GBM, we examined the role of miR-378 on tumor growth, angiogenesis, and radiation response in ectopic and orthotopic U87 glioblastoma models. Cell and tumor growth rates, in vitro and in vivo radiation sensitivities, and tumor vascular density were evaluated in U87-GFP and U87-miR-378 tumor lines. Ectopic tumor response to radiation was evaluated under normal blood flow and clamp hypoxic conditions. Results show that in vitro, miR-378 expression moderately increased cell growth rate and plating efficiency, but did not alter radiation sensitivity. U87-miR-378 tumors exhibited a higher transplantation take rate than U87-GFP tumors. In vivo, under oxygenated condition, subcutaneous U87-miR-378 tumors receiving 25 Gy showed a tendency for longer tumor growth delay (TGD) than control U87-GFP tumors. In contrast, under hypoxic condition, U87-miR-378 xenografts exhibited substantially shorter TGD than U87-GFP tumors, indicating that under normal blood flow conditions, U87-miR-378 tumors were substantially more oxygenated than U87-GFP tumors. Intracranial multi-photon laser-scanning microscopy demonstrated increased vascular density of U87-miR-378 versus control U87-GFP tumors. Finally, miR-378 increased TGD following 12 Gy irradiation in U87 intracranial xenografts, and significantly prolonged survival of U87-miR-378 tumor-bearing mice (P = 0.04). In conclusion, higher miR-378 expression in U87-miR-378 cells promotes tumor growth, angiogenesis, radiation-induced TGD, and prolongs survival of orthotopic tumor-bearing hosts. Regulation of VEGFR2 by miR-378 significantly increased vascular density and oxygenation in U87 xenografts.

Glioma progression through the prism of heat shock protein mediated extracellular matrix remodeling and epithelial to mesenchymal transition

Glial tumor is one of the intrinsic brain tumors with high migratory and infiltrative potential. This essentially contributes to the overall poor prognosis by circumvention of conventional treatment regimen in glioma. The underlying mechanism in gliomagenesis is bestowed by two processes- Extracellular matrix (ECM) Remodeling and Epithelial to mesenchymal transition (EMT). Heat Shock Family of proteins (HSPs), commonly known as "molecular chaperons" are documented to be upregulated in glioma. A positive correlation also exists between elevated expression of HSPs and invasive capacity of glial tumor. HSPs overexpression leads to mutational changes in glioma, which ultimately drive cells towards EMT, ECM modification, malignancy and invasion. Differential expression of HSPs - a factor providing cytoprotection to glioma cells, also contributes towards its radioresistance /chemoresistance. Various evidences also display upregulation of EMT and ECM markers by various heat shock inducing proteins e.g. HSF-1. The aim of this review is to study in detail the role of HSPs in EMT and ECM leading to radioresistance/chemoresistance of glioma cells. The existing treatment regimen for glioma could be enhanced by targeting HSPs through immunotherapy, miRNA and exosome mediated strategies. This could be envisaged by better understanding of molecular mechanisms underlying glial tumorigenesis in relation to EMT and ECM remodeling under HSPs influence. Our review might showcase fresh potential for the development of next generation therapeutics for effective glioma management.

Low co-expression of epidermal growth factor receptor and its chaperone heat shock protein 90 is associated with worse prognosis in primary glioblastoma, IDH-wild-type

Epidermal growth factor receptor (EGFR) is a major oncogenic driver in glioblastoma (GBM) without mutations in the isocitrate dehydrogenase gene (IDH-wildtype). Heat shock protein 90 (HSP90) is a regulator of the stability of oncogenic proteins including EGFR, thereby acting as a molecular chaperone. We investigated the expression of EGFR and its chaperone HSP90 in GBM, IDH-wildtype. Tissue availability permitted analysis of 237/449 consecutive GBM cases, among them 214 IDH-wildtype (90.3%). The expression of EGFR and HSP90 was analysed by immunohistochemistry on a tissue microarray containing various tumour regions. The expression intensity (EI), and an expression score (ES) combining the percentage of stained cells with EI were determined for both markers. Overall, there was a positive correlation between EGFR and HSP90 expression (EI; r=0.275, P<0.001; ES, r=0.333, P<0.001). The expression of EGFR and HSP90 was significantly higher in the tumour centre, compared to the infiltration front (EI, P=0.002; ES, P<0.001). Survival data were available in 96 IDH-wildtype cases, and high expression of EGFR (ES only) was in trend associated with better outcome, but failed to meet statyistical significance (P=0.061). A combination of EGFR and HSP90, however, discriminated between different prognostic groups, with EGFRlow/HSP90low tumours showing the worst prognosis in univariate analysis (P=0.001), and in multivariate analysis including the other relevant prognostic factors age, MGMT status and postoperative treatment [n=76; hazard ratio (HR)=0.571; 95% confidence interval (CI) 0.328-0.996; P=0.048]. EGFR expression stratified most pronounced among HSP90low tumours, where the EGFRhigh phenotype was associated with longer survival. Our results reveal a variable reliance on the signalling pathway by EGFR in GBM, IDH-wildtype. Low co-expression was associated with worse prognosis.

Re-irradiation after gross total resection of recurrent glioblastoma : Spatial pattern of recurrence and a review of the literature as a basis for target volume definition

BACKGROUND

Currently, patients with gross total resection (GTR) of recurrent glioblastoma (rGBM) undergo adjuvant chemotherapy or are followed up until progression. Re-irradiation, as one of the most effective treatments in macroscopic rGBM, is withheld in this situation, as uncertainties about the pattern of re-recurrence, the target volume, and also the efficacy of early re-irradiation after GTR exist.

METHODS

Imaging and clinical data from 26 consecutive patients with GTR of rGBM were analyzed. The spatial pattern of recurrences was analyzed according to the RANO-HGG criteria ("response assessment in neuro-oncology criteria for high-grade gliomas"). Progression-free (PFS) and overall survival (OS) were analyzed by the Kaplan-Meier method. Furthermore, a systematic review was performed in PubMed.

RESULTS

All but 4 patients underwent adjuvant chemotherapy after GTR. Progression was diagnosed in 20 of 26 patients and 70% of recurrent tumors occurred adjacent to the resection cavity. The median extension beyond the edge of the resection cavity was 20 mm. Median PFS was 6 months; OS was 12.8 months. We propose a target volume containing the resection cavity and every contrast enhancing lesion as the gross tumor volume (GTV), a spherical margin of 5-10 mm to generate the clinical target volume (CTV), and a margin of 1-3 mm to generate the planning target volume (PTV). Re-irradiation of this volume is deemed to be safe and likely to prolong PFS.

CONCLUSION

Re-irradiation is worth considering also after GTR, as the volumes that need to be treated are limited and re-irradiation has already proven to be a safe treatment option in general. The strategy of early re-irradiation is currently being tested within the GlioCave/NOA 17/Aro 2016/03 trial.

Tweety-Homolog 1 Drives Brain Colonization of Gliomas

Early and progressive colonization of the healthy brain is one hallmark of diffuse gliomas, including glioblastomas. We recently discovered ultralong (>10 to hundreds of microns) membrane protrusions [tumor microtubes (TMs)] extended by glioma cells. TMs have been associated with the capacity of glioma cells to effectively invade the brain and proliferate. Moreover, TMs are also used by some tumor cells to interconnect to one large, resistant multicellular network. Here, we performed a correlative gene-expression microarray and in vivo imaging analysis, and identified novel molecular candidates for TM formation and function. Interestingly, these genes were previously linked to normal CNS development. One of the genes scoring highest in tests related to the outgrowth of TMs was tweety-homolog 1 (TTYH1), which was highly expressed in a fraction of TMs in mice and patients. Ttyh1 was confirmed to be a potent regulator of normal TM morphology and of TM-mediated tumor-cell invasion and proliferation. Glioma cells with one or two TMs were mainly responsible for effective brain colonization, and Ttyh1 downregulation particularly affected this cellular subtype, resulting in reduced tumor progression and prolonged survival of mice. The remaining Ttyh1-deficient tumor cells, however, had more interconnecting TMs, which were associated with increased radioresistance in those small tumors. These findings imply a cellular and molecular heterogeneity in gliomas regarding formation and function of distinct TM subtypes, with multiple parallels to neuronal development, and suggest that Ttyh1 might be a promising target to specifically reduce TM-associated brain colonization by glioma cells in patients.SIGNIFICANCE STATEMENT In this report, we identify tweety-homolog 1 (Ttyh1), a membrane protein linked to neuronal development, as a potent driver of tumor microtube (TM)-mediated brain colonization by glioma cells. Targeting of Ttyh1 effectively inhibited the formation of invasive TMs and glioma growth, but increased network formation by intercellular TMs, suggesting a functional and molecular heterogeneity of the recently discovered TMs with potential implications for future TM-targeting strategies.

Comparative analysis of the effects of a sphingosine kinase inhibitor to temozolomide and radiation treatment on glioblastoma cell lines

Glioblastoma multiforme (GBM) exhibits high resistance to the standard treatment of temozolomide (TMZ) combined with radiotherapy, due to its remarkable cell heterogeneity. Accordingly, there is a need to target alternative molecules enhancing specific GBM autocrine or paracrine mechanisms and amplifying the effect of standard treatment. Sphingosine 1-phosphate (S1P) is such a lipid target molecule with an important role in cell invasion and proliferation. Sphingosine kinase inhibitors (SKI) prevent S1P formation and induce increased production of reactive oxygen species (ROS), which may potentiate radiation cytotoxicity. We analyzed the effect of SKI singular versus combined treatments with TMZ and radiation on 2 human GBM cell lines characterized by a lack of MGMT expression and low or high expression of the anti-oxidant enzyme, glutathione peroxidase 1 (GPx1). Effects were drug concentration-, cell line-dependent and partly ROS-mediated. Clonogenic survival assay demonstrates that SKI was more effective than TMZ in increasing the sensitivity of U87 cells, which express low GPx1 amount, to a 2 Gy X-ray dose. Addition of both SKI and TMZ drastically decreased U87 cells survival compared with the combination temozolomide/radiation. SKI less effectively than TMZ sensitized LN229 cells to the 2 Gy X-ray dose. Its combination to TMZ in absence of irradiation was as efficient as TMZ combination with X-ray. We provide first evidence for SKI as an alternative or complementary treatment to TMZ, and for efficient combinations of low doses of drugs and X-ray. These may help as novel bi-modal and tri-modal therapies to contend with GBM heterogeneity.

Nutritional and Nanotechnological Modulators of Microglia

Microglia are the essential responders to alimentary, pharmacological, and nanotechnological immunomodulators. These neural cells play multiple roles as surveyors, sculptors, and guardians of essential parts of complex neural circuitries. Microglia can play dual roles in the central nervous system; they can be deleterious and/or protective. The immunomodulatory effects of alimentary components, gut microbiota, and nanotechnological products have been investigated in microglia at the single-cell level and in vivo using intravital imaging approaches, and different biochemical assays. This review highlights some of the emerging questions and topics from studies involving alimentation, microbiota, nanotechnological products, and associated problems in this area of research. Some of the advantages and limitations of in vitro and in vivo models used to study the neuromodulatory effects of these factors, as well as the merits and pitfalls of intravital imaging modalities employed are presented.