Radiotherapy in Glioblastoma: the Past, the Present and the Future

Gelsolin knockdown confers radiosensitivity to glioblastoma cells

OBJECTIVE

Radiotherapy (RT) is a cornerstone of the glioblastoma (GBM) treatment. However, the resistance of tumour cells to radiation results in early recurrence. The mechanisms underlying GBM radioresistance remain unclear. Screening for differentially expressed genes (DEGs) related to radiation might be a potential solution to this problem.

METHOD

RT-associated DEGs were screened based on the RNA sequencing of 15 paired primary and recurrent GBMs. The mRNA and protein expression of candidate genes were validated in RNA sequencing of The Chinese Genome Atlas (CGGA) dataset and 18 cases of GBM samples. The relationship between the candidate gene and radiation was confirmed in irradiated GBM cells. The association of candidate gene with clinical characteristics and survival was investigated in the CGGA and TCGA dataset. Biological function and pathway analysis were explored by gene ontology analysis. The association of the candidate gene with radiosensitivity was verified using cell counting Kit-8, comet, and colony formation assays in vitro and subcutaneous tumour xenograft experiments in vivo.

RESULTS

Gelsolin (GSN) was selected for further study. GSN expression was significant elevated in recurrent GBM and up-regulated in irradiated GBM cell lines. High expression of GSN was enriched in malignant phenotype of glioma. Moreover, high expression of GSN was associated with poor prognosis. Further investigation demonstrated that GSN-knockdown (GSN-KD) combined with RT significantly inhibited cell proliferation and enhanced radiosensitivity in vivo and in vitro. Mechanistically, GSN-KD could lead to more serious DNA damage and promotes apoptosis after RT.

CONCLUSION

Radiation induced up-regulated of GSN. GSN-KD could enhance the radiosensitivity of GBM.

pH-Weighted amine chemical exchange saturation transfer echo planar imaging visualizes infiltrating glioblastoma cells

BACKGROUND

Given the invasive nature of glioblastoma, tumor cells exist beyond the contrast-enhancing (CE) region targeted during treatment. However, areas of non-enhancing (NE) tumors are difficult to visualize and delineate from edematous tissue. Amine chemical exchange saturation transfer echo planar imaging (CEST-EPI) is a pH-sensitive molecular magnetic resonance imaging technique that was evaluated in its ability to identify infiltrating NE tumors and prognosticate survival.

METHODS

In this prospective study, CEST-EPI was obtained in 30 patients and areas with elevated CEST contrast ("CEST+" based on the asymmetry in magnetization transfer ratio: MTRasym at 3 ppm) within NE regions were quantitated. Median MTRasym at 3 ppm and volume of CEST + NE regions were correlated with progression-free survival (PFS). In 20 samples from 14 patients, image-guided biopsies of these areas were obtained to correlate MTRasym at 3 ppm to tumor and non-tumor cell burden using immunohistochemistry.

RESULTS

In 15 newly diagnosed and 15 recurrent glioblastoma, higher median MTRasym at 3ppm within CEST + NE regions (P = .007; P = .0326) and higher volumes of CEST + NE tumor (P = .020; P < .001) were associated with decreased PFS. CE recurrence occurred in areas of preoperative CEST + NE regions in 95.4% of patients. MTRasym at 3 ppm was correlated with presence of tumor, cell density, %Ki-67 positivity, and %CD31 positivity (P = .001; P < .001; P < .001; P = .001).

CONCLUSIONS

pH-weighted amine CEST-EPI allows for visualization of NE tumor, likely through surrounding acidification of the tumor microenvironment. The magnitude and volume of CEST + NE tumor correlates with tumor cell density, degree of proliferating or "active" tumor, and PFS.

Combined BNCT-CIRT treatment planning for glioblastoma using the effect-based optimization

Objective. Boron neutron capture therapy (BNCT) and carbon ion radiotherapy (CIRT) are emerging treatment modalities for glioblastoma. In this study, we investigated the methodology and feasibility to combine BNCT and CIRT treatments. The combined treatment plan illustrated how the synergistic utilization of BNCT's biological targeting and CIRT's intensity modulation capabilities could lead to optimized treatment outcomes.Approach. The Monte Carlo toolkit, TOPAS, was employed to calculate the dose distribution for BNCT, while matRad was utilized for the optimization of CIRT. The biological effect-based approach, instead of the dose-based approach, was adopted to develop the combined BNCT-CIRT treatment plans for six patients diagnosed with glioblastoma, considering the different radiosensitivity and fraction. Five optional combined treatment plans with specific BNCT effect proportions for each patient were evaluated to identify the optimal treatment that minimizes damage on normal tissue.Main results. Individual BNCT exhibits a significant effect gradient along with the beam direction in the large tumor, while combined BNCT-CIRT treatments can achieve uniform effect delivery within the clinical target volume (CTV) through the effect filling with reversed gradient by the CIRT part. In addition, the increasing BNCT effect proportion in combined treatments can reduce damage in the normal brain tissue near the CTV. Besides, the combined treatments effectively minimize damage to the skin compared to individual BNCT treatments.Significance. The initial endeavor to combine BNCT and CIRT treatment plans is achieved by the effect-based optimization. The observed advantages of the combined treatment suggest its potential applicability for tumors characterized by pleomorphic, infiltrative, radioresistant and voluminous features.

The benefit of complete resection of contrast enhancing tumor in glioblastoma patients: A population-based study

Background

New treatment modalities have not been widely adopted for patients with glioblastoma (GBM) after the addition of temozolomide to radiotherapy. We hypothesize that increased extent of resection (EOR) has resulted in improved survival for surgically treated patients with glioblastoma at the population level.

Methods

Retrospective analysis of adult patients operated for glioblastoma in the population of South-Eastern Norway. Patients were stratified into Pre-temozolomide- (2003-2005), temozolomide- (2006-2012), and resection-focused period (2013-2019) and evaluated according to age and EOR.

Results

The study included 1657 adult patients operated on for supratentorial glioblastoma. The incidence of histologically confirmed glioblastoma increased from 3.7 in 2003 to 5.3 per 100 000 in 2019. The median survival was 11.4 months. Complete resection of contrast-enhancing tumor (CRCET) was achieved in 386 patients, and this fraction increased from 13% to 32% across the periods. Significant improvement in median survival was found between the first 2 periods and the last (10.5 and 10.6 vs. 12.3 months; P < .01), with a significant increase in 3- and 5-year survival probability to 12% and 6% (P < .01). Patients with CRCET survived longer than patients with non-CRCET (16.1 vs. 10.8 months; P < .001). The median survival doubled in patients ≥70 years and (12.1 months). Survival was similar between the time periods in patients where CRCET was achieved.

Conclusions

We demonstrate an improved survival of GBM patients at the population level associated with an increased fraction of patients with CRCET. The data support the importance of CRCET to improve glioblastoma patient outcomes.

The impact of short-course hypofractionated radiotherapy on multimodality treatment utilisation, compliance, and outcome in glioblastoma patients: a Danish patterns of care study

BACKGROUND

The aim of this retrospective registry-based Danish patterns of care study was (1) to evaluate the real-world utilisation of short-course hypofractionated radiotherapy (HFRT) in glioblastoma (GBM) patients over time, and (2) to evaluate the impact of short-course HFRT by assessing trends in multimodality treatment utilisation, compliance, and outcome.

MATERIAL AND METHODS

Data of all adults with newly diagnosed pathology-confirmed GBM between 2011 and 2019 were extracted from the nationwide Danish Neuro-Oncology Registry. Short-course HFRT was defined as a fraction size of > 2 Gy to a planned dose of > 30 Gy. Patterns of care were assessed. To analyse trends in the assignment to short-course HFRT, and in radiotherapy (RT) compliance, multivariable logistic regression was applied. To analyse trends in survival, multivariable Cox regression was used.

RESULTS

In this cohort of 2416 GBM patients, the utilisation of short-course HFRT significantly increased from ca. 10% in 2011 to 33% in recent years. This coincided with the discontinued use of palliative regimens and a decreased use of conventional fractionation. The proportion of patients proceeding to RT remained stable at ca. 85%. The proportion of patients assigned to chemoradiotherapy (CRT) remained stable at ca. 60%; the use of short-course hypofractionated CRT increased with ca. 10%, while the use of conventionally fractionated CRT decreased with ca. 10%. Compliance with conventionally fractionated and short-course HFRT was respective 92% and 93%, and significantly increasing in recent years. In the complete cohort, the median overall survival remained stable at ca. 11 months. Assignment to short-course HFRT was independently associated with shorter survival.

CONCLUSION

In Denmark, the use of short-course HFRT significantly increased in recent years. Nonetheless, the overall utilisation of RT and chemotherapy did not increase on a population level. Nor did survival change. In contrast, compliance with both conventionally fractionated RT and short-course HFRT increased.

Short-course Palliative Hypofractionated Radiotherapy in Patients with Poor-prognosis High-grade Glioma: Survival and Quality of Life Outcomes from a Prospective Phase II Study

AIMS

To report longitudinal quality of life (QoL) outcomes and survival in patients with poor-prognosis high-grade glioma (HGG) treated with palliative hypofractionated radiotherapy.

MATERIALS AND METHODS

Patients with poor-prognosis HGG were accrued on a prospective study of short-course palliative hypofractionated radiotherapy (35 Gy/10 fractions/2 weeks). The European Organization for Research and Treatment of Cancer QoL core questionnaire (QLQ-C30) and brain cancer module (BN20) were used in English or validated Indian vernacular languages (Hindi and Marathi) for QoL assessment at baseline (before radiotherapy), the conclusion of radiotherapy, 1 month post-radiotherapy and subsequently at 3-monthly intervals until disease progression/death. Baseline QoL scores were compared with corresponding scores from a historical HGG cohort. Summary QoL scores were compared longitudinally over time by related samples Friedman's two-way test. Progression-free survival and overall survival were calculated using the Kaplan-Meier method and reported as 1-year estimates with 95% confidence intervals.

RESULTS

Forty-nine (89%) of 55 patients completed the planned course of hypofractionated radiotherapy. Longitudinal QoL data were available in 42 (86%) of 49 patients completing radiotherapy, comprising the present cohort. The median age of included patients, comprised mainly of glioblastoma patients (81%), was 57 years, with an interquartile range (IQR) of 50-66 years and a median baseline Karnofsky score of 60 (IQR = 50-60). Baseline QoL scores were significantly worse for several domains compared with a historical institutional cohort of HGG patients treated previously with conventionally fractionated radiotherapy, indicating negative selection bias. QoL scores remained stable for most domains after palliative hypofractionated radiotherapy, with statistically significant improvements in fatigue (P = 0.032), dyspnoea (P = 0.042) and motor dysfunction (P = 0.036) over time. At a median follow-up of 8 months, Kaplan-Meier estimates of 1-year progression-free survival and overall survival were 33.3% (95% confidence interval 21.7-51.1%) and 38.1% (95% confidence interval 25.9-56%), respectively.

CONCLUSION

Short-course palliative hypofractionated radiotherapy in patients with poor-prognosis HGG is associated with stable and/or improved QoL scores in several domains, making it a viable resource-sparing regimen.

Systematic Review of WHO Grade 4 Astrocytoma in the Cerebellopontine Angle: The Impact of Anatomic Corridor on Treatment Options and Outcomes

Background  Despite advances in multimodal oncologic therapies and molecular genetics, overall survival (OS) in patients with high-grade astrocytomas remains poor. We present an illustrative case and systematic review of rare, predominantly extra-axial World Health Organization (WHO) grade 4 astrocytomas located within the cerebellopontine angle (CPA) and explore the impact of anatomic location on diagnosis, management, and outcomes. Methods  A systematic review of adult patients with predominantly extra-axial WHO grade 4 CPA astrocytomas was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines through December 2022. Results  Eighteen articles were included comprising 21 astrocytomas: 13 exophytic tumors arising from the cerebellopontine parenchyma and 8 tumors originating from a cranial nerve root entry zone. The median OS was 15 months with one-third of cases demonstrating delayed diagnosis. Gross total resection, molecular genetic profiling, and use of ancillary treatment were low. We report the only patient with an integrated isocitrate dehydrogenase 1 (IDH-1) mutant diagnosis, who, after subtotal resection and chemoradiation, remains alive at 40 months without progression. Conclusion  The deep conical-shaped corridor and abundance of eloquent tissue of the CPA significantly limits both surgical resection and utility of device-based therapies in this region. Prompt diagnosis, molecular characterization, and systemic therapeutic advances serve as the predominant means to optimize survival for patients with rare skull base astrocytomas.

Treatment with quercetin increases Nrf2 expression and neuronal differentiation of sub ventricular zone derived neural progenitor stem cells in adult rats

BACKGROUND

The presence of neural precursor stem cells (NPSCs) in some parts of the adult brain and the potency of these types of cells with a therapeutic viewpoint, has opened up a new approach for the treatment and recovery of the defects of central nervous system (CNS). Quercetin, as an herbal flavonoid, has been extensively investigated and shown to have numerous restoratives, inhibitory, and protective effects on some cell-lines and disorders. The purpose of this study is to simultaneously investigate the effect of quercetin on the expression of the nuclear factor erythroid 2-related factor 2 (Nrf2) gene and the effect on the proliferation and differentiation of NPSCs derived from the subventricular zone (SVZ) of the brain of adult rats.

METHODS AND RESULTS

The cell obtained from SVZ cultured for one week and treated with quercetin at the concentrations of 1, 5, and 15 μM to evaluate the Nrf2 expression, proliferation and differentiation of NSCs after one week. Cellular and genetic results was performed by RT-PCR, MTT assay test, quantification of images with Image-J and counting. The results indicated that the quercetin increases expression of Nrf2 at concentration above 5 μM. Also differentiation and proliferation rate of NSCs is affected by various concentrations of quercetin in a dose-dependent manner.

CONCLUSION

These findings confirmed the dose-dependent effect of quercetin on proliferation and differentiation of cell. In addition, quercetin increased the expression of Nrf2 gene. By combining these two effects of quercetin, this substance can be considered an effective compound in the treatment of degenerative defects in CNS.

Personalized Treatment of Glioblastoma: Current State and Future Perspective

Glioblastoma (GBM) is the most aggressive glial tumor of the central nervous system. Despite intense scientific efforts, patients diagnosed with GBM and treated with the current standard of care have a median survival of only 15 months. Patients are initially treated by a neurosurgeon with the goal of maximal safe resection of the tumor. Obtaining tissue samples during surgery is indispensable for the diagnosis of GBM. Technological improvements, such as navigation systems and intraoperative monitoring, significantly advanced the possibility of safe gross tumor resection. Usually within six weeks after the surgery, concomitant radiotherapy and chemotherapy with temozolomide are initiated. However, current radiotherapy regimens are based on population-level studies and could also be improved. Implementing artificial intelligence in radiotherapy planning might be used to individualize treatment plans. Furthermore, detailed genetic and molecular markers of the tumor could provide patient-tailored immunochemotherapy. In this article, we review current standard of care and possibilities of personalizing these treatments. Additionally, we discuss novel individualized therapeutic options with encouraging results. Due to inherent heterogeneity of GBM, applying patient-tailored treatment could significantly prolong survival of these patients.

Therapeutic efficacy of 166Holmium siloxane in microbrachytherapy of induced glioblastoma in minipig tumor model

Glioblastoma is considered the most common malignant primary tumor of central nervous system. In spite of the current standard and multimodal treatment, the prognosis of glioblastoma is poor. For this reason, new therapeutic approaches need to be developed to improve the survival time of the glioblastoma patient. In this study, we performed a preclinical experiment to evaluate therapeutic efficacy of 166Ho microparticle suspension administered by microbrachytherapy on a minipig glioblastoma model. Twelve minipigs were divided in 3 groups. Minipigs had injections into the tumor, containing microparticle suspensions of either 166Ho (group 1; n = 6) or 165Ho (group 2; n = 3) and control group (group 3; n = 3). The survival time from treatment to euthanasia was 66 days with a good state of health of all minipigs in group 1. The median survival time from treatment to tumor related death were 8.6 and 7.3 days in groups 2 and control, respectively. Statistically, the prolonged life of group 1 was significantly different from the two other groups (p < 0.01), and no significant difference was observed between group 2 and control (p=0.09). Our trial on the therapeutic effect of the 166Ho microparticle demonstrated an excellent efficacy in tumor control. The histological and immunohistochemical analysis showed that the efficacy was related to a severe 166Ho induced necrosis combined with an immune response due to the presence of the radioactive microparticles inside the tumors. The absence of reflux following the injections confirms the safety of the injection device.

Treatment planning with a 2.5 MV photon beam for radiation therapy

PURPOSE

The shallow depth of maximum dose and higher dose fall-off gradient of a 2.5 MV beam along the central axis that is available for imaging on linear accelerators is investigated for treatment of shallow tumors and sparing the organs at risk (OARs) beyond it. In addition, the 2.5 MV beam has an energy bridging the gap between kilo-voltage (kV) and mega-voltage (MV) beams for applications of dose enhancement with high atomic number (Z) nanoparticles.

METHODS

We have commissioned and utilized a MATLAB-based, open-source treatment planning software (TPS), matRad, for intensity-modulated radiation therapy (IMRT) dose calculations. Treatment plans for prostate, liver, and head and neck (H&N), nasal cavity, two orbit cases, and glioblastoma multiforme (GBM) were performed and compared to a conventional 6 MV beam. Additional Monte Carlo calculations were also used for benchmarking the central axis dose.

RESULTS

Both beams had similar planning target volume (PTV) dose coverage for all cases. However, the 2.5 MV beam deposited 6%-19% less integral doses to the nasal cavity, orbit, and GBM cases than 6 MV photons. The mean dose to the heart in the liver plan was 10.5% lower for 2.5 MV beam. The difference between the doses to OARs of H&N for two beams was under 3%. Brain mean dose, brainstem, and optic chiasm max doses were, respectively, 7.5%-14.9%, 2.2%-8.1%, and 2.5%-19.0% lower for the 2.5 MV beam in the nasal cavity, orbit, and GBM plans.

CONCLUSIONS

This study demonstrates that the 2.5 MV beam can produce clinically relevant treatment plans, motivating future efforts for design of single-energy LINACs. Such a machine will be capable of producing beams at this energy beneficial for low- and middle-income countries, and investigations on dose enhancement from high-Z nanoparticles.

Profiling of gene expression in the brain associated with anxiety-related behaviors in the chronic phase following cranial irradiation

Although the brain is exposed to cranial irradiation in many clinical contexts, including malignant brain tumor therapy, such exposure can cause delayed neuropsychiatric disorders in the chronic phase. However, how specific molecular mechanisms are associated with irradiation-induced behavioral dysfunction, especially anxiety-like behaviors, is unclear. In the present study, we evaluated anxiety-like behaviors in adult C57BL/6 mice using the open-field (OF) and elevated plus maze (EPM) tests 3 months following single cranial irradiation (10 Gy). Additionally, by using RNA sequencing (RNA-seq), we analyzed gene expression profiles in the cortex and hippocampus of the adult brain to demonstrate the molecular mechanisms of radiation-induced brain dysfunction. In the OF and EPM tests, mice treated with radiation exhibited increased anxiety-like behaviors in the chronic phase. Gene expression analysis by RNA-seq revealed 89 and 106 differentially expressed genes in the cortex and hippocampus, respectively, following cranial irradiation. Subsequently, ClueGO and STRING analyses clustered these genes in pathways related to protein kinase activity, circadian behavior, and cell differentiation. Based on our expression analysis, we suggest that behavioral dysfunction following cranial irradiation is associated with altered expression of Cdkn1a, Ciart, Fos, Hspa5, Hspb1 and Klf10. These novel findings may provide potential genetic targets to investigate for the development of radioprotective agents.

Development of In Vitro Assays for Advancing Radioimmunotherapy against Brain Tumors

Glioblastoma (GBM) is the most common primary brain tumor. Due to high resistance to treatment, local invasion, and a high risk of recurrence, GBM patient prognoses are often dismal, with median survival around 15 months. The current standard of care is threefold: surgery, radiation therapy, and chemotherapy with temozolomide (TMZ). However, patient survival has only marginally improved. Radioimmunotherapy (RIT) is a fourth modality under clinical trials and aims at combining immunotherapeutic agents with radiotherapy. Here, we develop in vitro assays for the rapid evaluation of RIT strategies. Using a standard cell irradiator and an Electric Cell Impedance Sensor, we quantify cell migration following the combination of radiotherapy and chemotherapy with TMZ and RIT with durvalumab, a PD-L1 immune checkpoint inhibitor. We measure cell survival using a cloud-based clonogenic assay. Irradiated T98G and U87 GBM cells migrate significantly (p < 0.05) more than untreated cells in the first 20−40 h post-treatment. Addition of TMZ increases migration rates for T98G at 20 Gy (p < 0.01). Neither TMZ nor durvalumab significantly change cell survival in 21 days post-treatment. Interestingly, durvalumab abolishes the enhanced migration effect, indicating possible potency against local invasion. These results provide parameters for the rapid supplementary evaluation of RIT against brain tumors.

Temporal Trends in Glioblastoma Survival: Progress then Plateau

BACKGROUND

Survival of patients with glioblastoma (GBM) increased in the 2000s, most prominently after the addition of temozolomide to the standard-of-care treatment protocol. The reason for subsequent improvements in survival in the late 2000s and early 2010s was less clear, with explanations including the introduction of bevacizumab, better surgical methods, and advances in supportive care. It is uncertain whether the trend of improving population-level survival has continued.

MATERIALS AND METHODS

Data from the Surveillance, Epidemiology, and End Results (SEER) Program was analyzed comparing survival of adult GBM patients diagnosed in consecutive 3-year periods from 2000 to 2017. Kaplan-Meier survival analysis and Cox proportional hazards models were used.

RESULTS

A total of 38,352 patients diagnosed with GBM between 2000 and 2017 met inclusion criteria. Median survival and percent survival to 12 and 24 months all progressively increased between 2000 and 2011. There were no significant differences in survival comparing 2009-2011 with 2012-2014 or 2015-2017. During the 2015-2017 period, median survival was 11 months, with 12 and 24-month survival proportions of 45.7% (95% confidence interval, 44.5-47.0) and 19.0% (95% confidence interval, 18.6-21.2), respectively.

CONCLUSIONS

After a period of progressive improvement in GBM survival between 2000 and 2011, survival plateaued. Subsequent advances since 2011 have not yet been translated to improved survival on the population-level as of 2017.

Changes of healthy brain tissue after salvage radiotherapy of glioblastoma

Background

Salvage radiotherapy (SRT) with photons is a valid treatment option for patients suffering from recurrent glioblastoma (GBM). However, the tolerance of healthy brain to ionizing radiation (IR) is limited. The aim of this study was to determine to what extent brain structures in the radiographically tumor-free hemisphere change after repeated radiotherapy.

Methods

Five of 26 patients treated with SRT for local recurrence of GBM were found to have magnetic resonance imaging (MRI) studies available for complete volumetric analysis before and after primary chemo-radiation and after SRT. Manual segmentation and joint segmentation (JS) based on a convolutional neural network were used for the segmentation of the gray matter, the white matter and the ventricles in T1 MRIs.

Results

Qualitative results of manual segmentation and JS were comparable. After primary chemo-radiation and SRT, the volume of the contralateral ventricles increased steadily by 1.3–4.75% (SD ± 2.8 %, R² = 0.82; P = <.01) with a manual segmentation and by 1.4–7.4% (SD 2.1%, R² = 0.48; P = .025) with JS. The volume of the cortex decreased by 3.4–7.3% except in one patient, the cortex volume increased by 2.5% (SD ± 2.9%, R² = 0.18; P = .19) when measured manually. When measured with JS GM decreased by 1.0–7.4%, in one case it increased by 3.0% (SD = 3.2%, P = .22, R² = 0.18). The white matter remained stable when assessed with manual segmentation (P = .84, R² = 0.004) or JS (P = .44, R² = 0.07).

Conclusion

SRT of relapsed GBM leads to continuous changes of the tumor-free contralateral brain by means of manual segmentation or JS. The cortex seems more susceptible to repeated RT compared to the white matter. Larger cohort studies and complementary functional analysis are encouraged.

K-RAS Acts as a Critical Regulator of CD44 to Promote the Invasiveness and Stemness of GBM in Response to Ionizing Radiation

Radiation therapy is a current standard-of-care treatment and is used widely for GBM patients. However, radiation therapy still remains a significant barrier to getting a successful outcome due to the therapeutic resistance and tumor recurrence. Understanding the underlying mechanisms of this resistance and recurrence would provide an efficient approach for improving the therapy for GBM treatment. Here, we identified a regulatory mechanism of CD44 which induces infiltration and mesenchymal shift of GBM. Ionizing radiation (IR)-induced K-RAS/ERK signaling activation elevates CD44 expression through downregulation of miR-202 and miR-185 expression. High expression of CD44 promotes SRC activation to induce cancer stemness and EMT features of GBM cells. In this study, we demonstrate that the K-RAS/ERK/CD44 axis is a key mechanism in regulating mesenchymal shift of GBM cells after irradiation. These findings suggest that blocking the K-RAS activation or CD44 expression could provide an efficient way for GBM treatment.

Radiotherapy of High-Grade Gliomas: First Half of 2021 Update with Special Reference to Radiosensitization Studies

Albeit the effort to develop targeted therapies for patients with high-grade gliomas (WHO grades III and IV) is evidenced by hundreds of current clinical trials, radiation remains one of the few effective therapeutic options for them. This review article analyzes the updates on the topic "radiotherapy of high-grade gliomas" during the period 1 January 2021-30 June 2021. The high number of articles retrieved in PubMed using the search terms ("gliom* and radio*") and manually selected for relevance indicates the feverish research currently ongoing on the subject. During the last semester, significant advances were provided in both the preclinical and clinical settings concerning the diagnosis and prognosis of high-grade gliomas, their radioresistance, and the inevitable side effects of their treatment with radiation. The novel information concerning tumor radiosensitization was of special interest in terms of therapeutic perspective and was discussed in detail.

Local delivery to malignant brain tumors: potential biomaterial-based therapeutic/adjuvant strategies

Glioblastoma (GBM) is the most aggressive malignant brain tumor and is associated with a very poor prognosis. The standard treatment for newly diagnosed patients involves total tumor surgical resection (if possible), plus irradiation and adjuvant chemotherapy. Despite treatment, the prognosis is still poor, and the tumor often recurs within two centimeters of the original tumor. A promising approach to improving the efficacy of GBM therapeutics is to utilize biomaterials to deliver them locally at the tumor site. Local delivery to GBM offers several advantages over systemic administration, such as bypassing the blood-brain barrier and increasing the bioavailability of the therapeutic at the tumor site without causing systemic toxicity. Local delivery may also combat tumor recurrence by maintaining sufficient drug concentrations at and surrounding the original tumor area. Herein, we critically appraised the literature on local delivery systems based within the following categories: polymer-based implantable devices, polymeric injectable systems, and hydrogel drug delivery systems. We also discussed the negative effect of hypoxia on treatment strategies and how one might utilize local implantation of oxygen-generating biomaterials as an adjuvant to enhance current therapeutic strategies.

Glioma-Specific Diffusion Signature in Diffusion Kurtosis Imaging

Purpose: This study aimed to assess the relationship between mean kurtosis (MK) and mean diffusivity (MD) values from whole-brain diffusion kurtosis imaging (DKI) parametric maps in preoperative magnetic resonance (MR) images from 2016 World Health Organization Classification of Tumors of the Central Nervous System integrated glioma groups. Methods: Seventy-seven patients with histopathologically confirmed treatment-naïve glioma were retrospectively assessed between 1 August 2013 and 30 October 2017. The area on scatter plots with a specific combination of MK and MD values, not occurring in the healthy brain, was labeled, and the corresponding voxels were visualized on the fluid-attenuated inversion recovery (FLAIR) images. Reversely, the labeled voxels were compared to those of the manually segmented tumor volume, and the Dice similarity coefficient was used to investigate their spatial overlap. Results: A specific combination of MK and MD values in whole-brain DKI maps, visualized on a two-dimensional scatter plot, exclusively occurs in glioma tissue including the perifocal infiltrative zone and is absent in tissue of the normal brain or from other intracranial compartments. Conclusions: A unique diffusion signature with a specific combination of MK and MD values from whole-brain DKI can identify diffuse glioma without any previous segmentation. This feature might influence artificial intelligence algorithms for automatic tumor segmentation and provide new aspects of tumor heterogeneity.

Survival impact of incidental subventricular zone irradiation in IDH-wildtype glioblastoma

BACKGROUND AND PURPOSE

The subventricular zone (SVZ) is an important niche for neural stem cells but probably also for brain tumor propagating cells, including the glioblastoma stem cell. The SVZ may become a target for radiation therapy in glioblastoma patients. However, reports studying the effect of irradiation of the SVZ on glioblastoma patient survival show conflicting results. We studied the correlation between incidental SVZ radiation dose and survival in a cohort of isocitrate dehydrogenase-wildtype (IDHwt) glioblastoma patients with inclusion of important survival prognosticators.

PATIENTS AND METHODS

In this retrospective analysis, only adult patients with supratentorial IDHwt glioblastoma were included who were treated with temozolomide-based chemoradiotherapy after surgery. The SVZ was contoured on the radiotherapy planning imaging. Cox proportional regression overall survival (OS) analysis was used to study the correlation between SVZ dose and survival. Age, Karnofsky Performance Score, extent of resection and O⁶-methylguanine-methyl-DNA-transferase gene promoter (MGMTp) methylation were used as covariates in multivariate analysis.

RESULTS

In total, 137 patients were included. Median OS was 13.3 months. The MGMTp methylation was present in 40% of cases. Ipsilateral SVZ (iSVZ) mean dose was 44.4 Gy and 27.2 Gy for the contralateral SVZ (cSVZ). Univariate survival analysis showed an inverse relationship between cSVZ mean dose and OS (HR 1.029 (1.003-1.057); p= .032). However, there was no correlation between cSVZ mean dose and OS in multivariate analysis. iSVZ dose did not correlate with survival.

CONCLUSION

In this cohort of 137 IDHwt glioblastoma patients, iSVZ did not correlate with OS. Higher cSVZ dose was inversely correlated with OS in univariate survival analysis but lost its significance in multivariate analysis, including MGMTp-methylation. Hence, the correlation between SVZ radiation and glioblastoma patient survival remains unclear. Carefully designed prospective studies are needed to provide unequivocal results on this controversial topic.

CyberKnife for Recurrent Malignant Gliomas: A Systematic Review and Meta-Analysis

BACKGROUND AND OBJECTIVE

Possible treatment strategies for recurrent malignant gliomas include surgery, chemotherapy, radiotherapy, and combined treatments. Among different reirradiation modalities, the CyberKnife System has shown promising results. We conducted a systematic review of the literature and a meta-analysis to establish the efficacy and safety of CyberKnife treatment for recurrent malignant gliomas.

METHODS

We searched PubMed, MEDLINE, and EMBASE from 2000 to 2021 for studies evaluating the safety and efficacy of CyberKnife treatment for recurrent WHO grade III and grade IV gliomas of the brain. Two independent reviewers selected studies and abstracted data. Missing information was requested from the authors via email correspondence. The primary outcomes were median Overall Survival, median Time To Progression, and median Progression-Free Survival. We performed subgroup analyses regarding WHO grade and chemotherapy. Besides, we analyzed the relationship between median Time To Recurrence and median Overall Survival from CyberKnife treatment. The secondary outcomes were complications, local response, and recurrence. Data were analyzed using random-effects meta-analysis.

RESULTS

Thirteen studies reporting on 398 patients were included. Median Overall Survival from initial diagnosis and CyberKnife treatment was 22.6 months and 8.6 months. Median Time To Progression and median Progression-Free Survival from CyberKnife treatment were 6.7 months and 7.1 months. Median Overall Survival from CyberKnife treatment was 8.4 months for WHO grade IV gliomas, compared to 11 months for WHO grade III gliomas. Median Overall Survival from CyberKnife treatment was 4.4 months for patients who underwent CyberKnife treatment alone, compared to 9.5 months for patients who underwent CyberKnife treatment plus chemotherapy. We did not observe a correlation between median Time To Recurrence and median Overall Survival from CyberKnife. Rates of acute neurological and acute non-neurological side effects were 3.6% and 13%. Rates of corticosteroid dependency and radiation necrosis were 18.8% and 4.3%.

CONCLUSIONS

Reirradiation of recurrent malignant gliomas with the CyberKnife System provides encouraging survival rates. There is a better survival trend for WHO grade III gliomas and for patients who undergo combined treatment with CyberKnife plus chemotherapy. Rates of complications are low. Larger prospective studies are warranted to provide more accurate results.

Randomized Controlled Immunotherapy Clinical Trials for GBM Challenged

Simple Summary

Although multiple meta-analyses on active specific immunotherapy treatment for glioblastoma multiforme (GBM) have demonstrated a significant prolongation of overall survival, no single research group has succeeded in demonstrating the efficacy of this type of treatment in a prospective, double-blind, placebo-controlled, randomized clinical trial. In this paper, we explain how the complexity of the tumor biology and tumor–host interactions make proper stratification of a control group impossible. The individualized characteristics of advanced therapy medicinal products for immunotherapy contribute to heterogeneity within an experimental group. The dynamics of each tumor and in each patient aggravate comparative stable patient groups. Finally, combinations of immunotherapy strategies should be integrated with first-line treatment. We illustrate the complexity of a combined first-line treatment with individualized multimodal immunotherapy in a group of 70 adults with GBM and demonstrate that the integration of immunogenic cell death treatment within maintenance chemotherapy followed by dendritic cell vaccines and maintenance immunotherapy might provide a step towards improving the overall survival rate of GBM patients.

Abstract

Immunotherapies represent a promising strategy for glioblastoma multiforme (GBM) treatment. Different immunotherapies include the use of checkpoint inhibitors, adoptive cell therapies such as chimeric antigen receptor (CAR) T cells, and vaccines such as dendritic cell vaccines. Antibodies have also been used as toxin or radioactive particle delivery vehicles to eliminate target cells in the treatment of GBM. Oncolytic viral therapy and other immunogenic cell death-inducing treatments bridge the antitumor strategy with immunization and installation of immune control over the disease. These strategies should be included in the standard treatment protocol for GBM. Some immunotherapies are individualized in terms of the medicinal product, the immune target, and the immune tumor–host contact. Current individualized immunotherapy strategies focus on combinations of approaches. Standardization appears to be impossible in the face of complex controlled trial designs. To define appropriate control groups, stratification according to the Recursive Partitioning Analysis classification, MGMT promotor methylation, epigenetic GBM sub-typing, tumor microenvironment, systemic immune functioning before and after radiochemotherapy, and the need for/type of symptom-relieving drugs is required. Moreover, maintenance of a fixed treatment protocol for a dynamic, deadly cancer disease in a permanently changing tumor–host immune context might be inappropriate. This complexity is illustrated using our own data on individualized multimodal immunotherapies for GBM. Individualized medicines, including multimodal immunotherapies, are a rational and optimal yet also flexible approach to induce long-term tumor control. However, innovative methods are needed to assess the efficacy of complex individualized treatments and implement them more quickly into the general health system.

Immune Escape in Glioblastoma Multiforme and the Adaptation of Immunotherapies for Treatment

Glioblastoma multiforme (GBM) is the most frequently occurring primary brain tumor and has a very poor prognosis, with only around 5% of patients surviving for a period of 5 years or more after diagnosis. Despite aggressive multimodal therapy, consisting mostly of a combination of surgery, radiotherapy, and temozolomide chemotherapy, tumors nearly always recur close to the site of resection. For the past 15 years, very little progress has been made with regards to improving patient survival. Although immunotherapy represents an attractive therapy modality due to the promising pre-clinical results observed, many of these potential immunotherapeutic approaches fail during clinical trials, and to date no immunotherapeutic treatments for GBM have been approved. As for many other difficult to treat cancers, GBM combines a lack of immunogenicity with few mutations and a highly immunosuppressive tumor microenvironment (TME). Unfortunately, both tumor and immune cells have been shown to contribute towards this immunosuppressive phenotype. In addition, current therapeutics also exacerbate this immunosuppression which might explain the failure of immunotherapy-based clinical trials in the GBM setting. Understanding how these mechanisms interact with one another, as well as how one can increase the anti-tumor immune response by addressing local immunosuppression will lead to better clinical results for immune-based therapeutics. Improving therapeutic delivery across the blood brain barrier also presents a challenge for immunotherapy and future therapies will need to consider this. This review highlights the immunosuppressive mechanisms employed by GBM cancers and examines potential immunotherapeutic treatments that can overcome these significant immunosuppressive hurdles.

Suppressing Dazl modulates tumorigenicity and stemness in human glioblastoma cells

Background

Glioblastoma is devastating cancer with a high frequency of occurrence and poor survival rate and it is urgent to discover novel glioblastoma-specific antigens for the therapy. Cancer-germline genes are known to be related to the formation and progression of several cancer types by promoting tumor transformation. Dazl is one such germline gene and is up-regulated in a few germ cell cancers. In this study, we analyzed the expression of Dazl in human glioblastoma tissues and cells, and investigated its significance in proliferation, migration, invasion and chemoresistance of the glioblastoma cell lines.

Methods

We evaluated the expression of Dazl in different pathologic grades of glioblastoma tissues by immunohistochemistry. We assessed the expression of Dazl in glioblastoma cells and normal human astrocytes (NHA) cells by western blotting and RT-qPCR. Then we generated Dazl knockout glioblastoma cell lines using the CRISPR/Cas9 gene-editing technology to explore the cellular function of Dazl. We detected the proliferation and germline traits via CCK-8 assays and alkaline phosphatase staining, respectively. Boyden chamber assays were performed to measure glioblastoma cell migration and invasion. Crystal violet staining was used to determine the number of viable cells after the treatment of Doxorubicin and Temozolomide. Finally, we used subcutaneous xenograft studies to measure the growth of tumors in vivo.

Results

We found that Dazl was upregulated in glioblastoma tissues and glioblastoma cell lines. Dazl knockdown glioblastoma cells showed decreased cellular proliferation, migration, invasion, and resistance in vitro, and inhibited the initiation of glioblastoma in vivo. The glioblastoma cell lines A172, U251, and LN229 were found to express stem cell markers CD133, Oct4, Nanog, and Sox2. The expression of these markers was downregulated in Dazl-deficient cells.

Conclusions

Our results indicated that Dazl contributes to the tumorigenicity of glioblastoma via reducing cell stemness. Therefore, cancer-germline genes might represent a new paradigm of glioblastoma-initiating cells in the treatment of malignant tumors.

Feasibility of intratumoral 165Holmium siloxane delivery to induced U87 glioblastoma in a large animal model, the Yucatan minipig

Glioblastoma is the most aggressive primary brain tumor leading to death in most of patients. It comprises almost 50-55% of all gliomas with an incidence rate of 2-3 per 100,000. Despite its rarity, overall mortality of glioblastoma is comparable to the most frequent tumors. The current standard treatment combines surgical resection, radiotherapy and chemotherapy with temozolomide. In spite of this aggressive multimodality protocol, prognosis of glioblastoma is poor and the median survival remains about 12-14.5 months. In this regard, new therapeutic approaches should be developed to improve the life quality and survival time of the patient after the initial diagnosis. Before switching to clinical trials in humans, all innovative therapeutic methods must be studied first on a relevant animal model in preclinical settings. In this regard, we validated the feasibility of intratumoral delivery of a holmium (Ho) microparticle suspension to an induced U87 glioblastoma model. Among the different radioactive beta emitters, 166Ho emits high-energy β(-) radiation and low-energy γ radiation. β(-) radiation is an effective means for tumor destruction and γ rays are well suited for imaging (SPECT) and consequent dosimetry. In addition, the paramagnetic Ho nucleus is a good asset to perform MRI imaging. In this study, five minipigs, implanted with our glioblastoma model were used to test the injectability of 165Ho (stable) using a bespoke injector and needle. The suspension was produced in the form of Ho microparticles and injected inside the tumor by a technique known as microbrachytherapy using a stereotactic system. At the end of this trial, it was found that the 165Ho suspension can be injected successfully inside the tumor with absence or minimal traces of Ho reflux after the injections. This injection technique and the use of the 165Ho suspension needs to be further assessed with radioactive 166Ho in future studies.

Using data extracted from a radiotherapy record & verify system to infer outcomes of patients treated for radical brain cancer

Aim:

The aims of this study were to explore the outcome measures that can be recorded in a radiotherapy IT system and the extract mortality results for a group of patients receiving radical radiotherapy treatment for primary brain cancer.

Method:

Treatment mortality outcomes were extracted from a radiotherapy database and were compared to treatment technique used between 1 January 2011 and 31 December 2017. The patients selected received 1 course of radiotherapy of 60 Gray in 30 treatments (n = 270). These patients received either Conformal Radiotherapy (CRT) (n = 127) or Volumetric Modulated Arc Therapy (VMAT) (n = 143). Kaplan–Meier plots were generated for these two groups to assess the survival. The median survival was 20·1 months (95%CI = 16·8−23·4) and 14·0 months (95%CI = 11·1−16·5) for CRT and VMAT, respectively.

Discussion:

Surprisingly, the results of this data extraction demonstrated that CRT gave better survival for this group of patients, than VMAT. The reason for the difference in survival is unclear and more data are needed to explain the result.

Conclusion:

This demonstrates that not only that a radiotherapy database can be used to extract outcome measures but that it must be done to explore where a change in treatment delivery has been of benefit to the patients or not.

Hypofractionated stereotactic radiotherapy combined with chemotherapy or not in the management of recurrent malignant gliomas: A systematic review and meta-analysis

Hypofractionated stereotactic radiotherapy (HFSRT) is a common salvage treatment for recurrent malignant glioma (MG). However, it remains controversial whether the combination of HFSRT and chemotherapy could improve survival for patients with recurrent MG compared to HFSRT alone. The present systematic review and meta-analysis aims to investigate this question, and tries to determine to what extent the addition of chemotherapy to HFSRT affects survival. A systematic review was performed to analyse the survival for patients treated with HFSRT combined with chemotherapy or not. Hazard ratios (HRs) with 95% confidence intervals (CIs) for overall survival (OS) were pooled with random effects; and standard mean difference (MD) with 95% CIs for OS were pooled using the same strategy. A total of 7 studies including 388 patients with recurrent MG were eligible for our study. The OS survival of patients receiving combination therapy ranged from 8.7 to 23 months, and the median OS of patients underwent HFSRT ranged from 3.9 to 12 months. The meta-analyses resulted in the pooled HR of 0.44 (95% CI 0.30-0.65, p < 0.0001) (Cochran Q statistic 4.70, P = 0.320, I² = 14.8%) and pooled standard MD of 0.80 months (95% CI 0.41-1.18, p < 0.001) (Cochran Q statistic 10.16, p = 0.71, I² = 50.8%). The present study suggests that HFSRT + chemotherapy confers a slight survival improvement for patients with recurrent MG as compared with sole HFSRT management. To draw a more solid conclusion, greater investigation is warranted.

Herpes Simplex Virus 1 encephalitis with normal cerebrospinal fluid after brain radiotherapy in a patient with glioblastoma. A case report and review of literature

Herpes simplex virus encephalitis (HSE) is the most common cause of letal encephalitis and its prevalence appears higher among oncologic patients who undergo brain radiotherapy (RT). We describe a case of 76-year-old woman with glioblastoma multiforme (GBM) who developed HSE shortly after brain RT. Cerebrospinal fluid analysis (CSF) was normal and the diagnosis was driven by brain MRI and EEG. Prompt introduction of antiviral therapy improved the clinical picture. We highlight the importance of EEG and brain MRI for the diagnosis and suggest the possibility of antiviral profilaxys in oncologic patients who undergo brain RT. (www.actabiomedica.it)

What Neuroradiologists Need to Know About Radiation Treatment for Neural Tumors

Radiation oncologists and radiologists have a unique and mutually dependent relationship. Radiation oncologists rely on diagnostic imaging to locate the tumor and define the treatment target volume, evaluation of response to therapy, and follow-up. Accurate interpretation of post-treatment imaging requires diagnostic radiologists to have a basic understanding of radiation treatment planning and delivery. There are various radiation treatment modalities such as 3D conformal radiation therapy, intensity modulated radiation therapy and stereotactic radiosurgery as well as different radiation modalities such as photons and protons that can be used for treatment. All of these have subtle differences in how the treatment is planned and how the imaging findings might be affected. This paper provides an overview of the basic principles of radiation oncology, different radiation treatment modalities, how radiation therapy is planned and delivered, how knowledge of this process can help interpretation of images, and how the radiologist can contribute to this process.

Immunotherapy in CNS cancers: the role of immune cell trafficking

Glioblastoma (GBM) is a highly malignant CNS tumor with very poor survival despite intervention with conventional therapeutic strategies. Although the CNS is separated from the immune system by the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier, emerging evidence of immune surveillance and the selective infiltration of GBMs by immune suppressive cells indicates that there is breakdown or compromise of these physical barriers. This in turn offers hope that immunotherapy can be applied to specifically target and reduce tumor burden. One of the major setbacks in translating immunotherapy strategies is the hostile microenvironment of the tumor that inhibits trafficking of effector immune cells such as cytotoxic T lymphocytes into the CNS. Incorporating important findings from autoimmune disorders such as multiple sclerosis to understand and thereby enhance cytotoxic lymphocyte infiltration into GBM could augment immunotherapy strategies to treat this disease. However, although these therapies are designed to evoke a potent immune response, limited space in the brain and cranial vault reduces tolerance for immune therapy-induced inflammation and resultant brain edema. Therefore, successful immunotherapy requires that a delicate balance be maintained between activating and retaining lasting antitumor immunity.

NK Cell-Based Glioblastoma Immunotherapy

Glioblastoma (GB) is the most aggressive and most common malignant primary brain tumor diagnosed in adults. GB shows a poor prognosis and, unfortunately, current therapies are unable to improve its clinical outcome, imposing the need for innovative therapeutic approaches. The main reason for the poor prognosis is the great cell heterogeneity of the tumor mass and its high capacity for invading healthy tissues. Moreover, the glioblastoma microenvironment is capable of suppressing the action of the immune system through several mechanisms such as recruitment of cell modulators. Development of new therapies that avoid this immune evasion could improve the response to the current treatments for this pathology. Natural Killer (NK) cells are cellular components of the immune system more difficult to deceive by tumor cells and with greater cytotoxic activity. Their use in immunotherapy gains strength because they are a less toxic alternative to existing therapy, but the current research focuses on mimicking the NK attack strategy. Here, we summarize the most recent studies regarding molecular mechanisms involved in the GB and immune cells interaction and highlight the relevance of NK cells in the new therapeutic challenges.

Repolarization of myeloid derived suppressor cells via magnetic nanoparticles to promote radiotherapy for glioma treatment

Although radiotherapy has been established as a major therapeutic modality for glioma, radical new avenues are critically needed to prevent inevitable tumor recurrence. Herein, we utilized a magnetic nanoparticle-based platform with cationic polymer modification to promote radiotherapy for glioma treatment. We found that the nanoplatform induced cytotoxicity to glioma cells under radiation as well as promoting significant survival benefits in both immunocompetent and aythmic mice with glioma. Utilizing the magnetic properties of the nanoparticles, we were able to ascertain that myeloid derived suppressor cells (MDSC) were taking up nanoparticles in the brain tumor. The observed efficacy was attributed to destruction of glioma cells as well as MDSCs repolarization from immunosuppressive phenotype to a pro-inflammatory phenotype, which promoted antitumor effects and synergistically promoted radio-therapeutic effects. Our nanoparticles provide a robust dual-targeting platform for glioma radiotherapy by simultaneous eradication of tumor cells and manipulation of myeloid phenotypes in the central nervous system.

Radiotherapy of Glioblastoma 15 Years after the Landmark Stupp's Trial: More Controversies than Standards?

Background

The current standard of care of glioblastoma, the most common primary brain tumor in adults, has remained unchanged for over a decade. Nevertheless, some improvements in patient outcomes have occurred as a consequence of modern surgery, improved radiotherapy and up-to-date management of toxicity. Patients from control arms (receiving standard concurrent chemoradiotherapy and adjuvant chemotherapy with temozolomide) of recent clinical trials achieve better outcomes compared to the median survival of 14.6 months reported in Stupp’s landmark clinical trial in 2005. The approach to radiotherapy that emerged from Stupp’s trial, which continues to be a basis for the current standard of care, is no longer applicable and there is a need to develop updated guidelines for radiotherapy within the daily clinical practice that address or at least acknowledge existing controversies in the planning of radiotherapy.

The goal of this review is to provoke critical thinking about potentially controversial aspects in the radiotherapy of glioblastoma, including among others the issue of target definitions, simultaneously integrated boost technique, and hippocampal sparing.

Conclusions

In conjunction with new treatment approaches such as tumor-treating fields (TTF) and immunotherapy, the role of adjuvant radiotherapy will be further defined. The personalized approach in daily radiotherapy practice is enabled with modern radiotherapy systems.

Direct-Current Electric Field Distribution in the Brain for Tumor Treating Field Applications: A Simulation Study

Tumor Treating Fields (TTFields) in combination with chemotherapy and/or radiotherapy have been clinically reported to provide prolonged overall survival in glioblastoma patients. Alternating electric fields with frequencies of 100~300 kHz and magnitudes of 1~3 V/cm are shown to suppress the growth of cancer cells via interactions with polar molecules within dividing cells. Since it is difficult to directly measure the electric fields inside the brain, simulation models of the human head provide a useful tool for predicting the electric field distribution. In the present study, a three-dimensional finite element head model consisting of the scalp, the skull, the dura, the cerebrospinal fluid, and the brain was built to study the electric field distribution under various applied potentials and electrode configurations. For simplicity, a direct-current electric field was used in the simulation. The total power dissipation and temperature elevation due to Joule heating in different head tissues were also evaluated. Based on the results, some guidelines are obtained in designing the electrode configuration for personalized glioblastoma electrotherapy.

Utilizing 18F-fluoroethyltyrosine (FET) positron emission tomography (PET) to define suspected nonenhancing tumor for radiation therapy planning of glioblastoma

AIM

The authors sought to evaluate the impact of 18F-fluoroethyltyrosine (FET) positron emission tomography (PET) on radiation therapy planning for patients diagnosed with glioblastoma (GBM) and the presence of suspected nonenhancing tumors compared with standard magnetic resonance imaging (MRI).

METHODS AND MATERIALS

Patients with GBM and contrast-enhanced MRI scans showing regions suspicious of nonenhancing tumor underwent postoperative FET-PET before commencing radiation therapy. Two clinical target volumes (CTVs) were created using pre- and postoperative MRI: MRI fluid-attenuated inversion recovery (FLAIR) sequences (CTV_FLAIR) and MRI contrast sequences with an expansion on the surgical cavity (CTV_Sx). FET-PET was used to create biological tumor volumes (BTVs) by encompassing FET-avid regions, forming BTV_FLAIR and BTV_Sx. Volumetric analyses were conducted between CTVs and respective BTVs using Wilcoxon signed-rank tests. The volume increase with addition of FET was analyzed with respect to BTV_FLAIR and BTV_Sx. Presence of focal gadolinium contrast enhancement within previously nonenhancing tumor or within the FET-avid region was noted on MRI scans at 1 and 3 months after radiation therapy.

RESULTS

Twenty-six patients were identified retrospectively from our database, of whom 24 had demonstrable FET uptake. The median CTV_FLAIR, CTV_Sx, BTV_FLAIR, and BTV_Sx were 57.1 mL (range, 1.1-217.4), 83.6 mL (range, 27.2-275.8), 62.8 mL (range, 1.1-307.3), and 94.7 mL (range, 27.2-285.5), respectively. When FET-PET was used, there was a mean increase in volume of 26.8% from CTV_FLAIR to BTV_FLAIR and 20.6% from CTV_Sx to BTV_Sx. A statistically significant difference was noted on Wilcoxon signed-rank test when assessing volumetric change between CTV_FLAIR and BTV_FLAIR (P < .0001) and CTV_Sx and BTV_Sx (P < .0001). Six of 24 patients (25%) with FET avidity before radiation therapy showed focal gadolinium enhancement within the radiation therapy portal.

CONCLUSIONS

FET-PET may help improve delineation of GBM in cases with a suspected nonenhancing component. This may result in improved radiation therapy target delineation and reduce the risk of potential geographical miss.

SUMMARY

We investigated the impact of 18F-fluoroethyltyrosine (FET) positron emission tomography (PET) on radiation therapy planning for patients diagnosed with glioblastoma (GBM) and a suspected nonenhancing tumor compared with standard magnetic resonance imaging. We performed volumetric analyses between clinical target volumes and respective biological target volumes using Wilcoxon signed-rank tests. FET-PET may help improve delineation of GBM in cases with a suspected nonenhancing component and reduce the risk of potential geographical miss.

Advances in Radiotherapy for Glioblastoma

External beam radiotherapy (RT) has long played a crucial role in the treatment of glioblastoma. Over the past several decades, significant advances in RT treatment and image-guidance technology have led to enormous improvements in the ability to optimize definitive and salvage treatments. This review highlights several of the latest developments and controversies related to RT, including the treatment of elderly patients, who continue to be a fragile and vulnerable population; potential salvage options for recurrent disease including reirradiation with chemotherapy; the latest imaging techniques allowing for more accurate and precise delineation of treatment volumes to maximize the therapeutic ratio of conformal RT; the ongoing preclinical and clinical data regarding the combination of immunotherapy with RT; and the increasing evidence of cancer stem-cell niches in the subventricular zone which may provide a potential target for local therapies. Finally, continued development on many fronts have allowed for modestly improved outcomes while at the same time limiting toxicity.

Autophagic flux response and glioblastoma sensitivity to radiation

Objective:

Glioblastoma is the most common primary brain tumor in adults and one of the most lethal human tumors. It constitutes a unique non-metastasizing human tumor model with high resistance to radiotherapy and chemotherapy. The current study investigates the association between autophagic flux and glioblastoma cell resistance.

Methods:

The expression kinetics of autophagy- and lysosome-related proteins following exposure of two glioblastoma cell lines (T98 and U87) to clinically relevant radiation doses was examined. Then, the response of cells resistant to radiotherapy and chemotherapy was investigated after silencing of LC3A, LC3B, and TFEB genes in vitro and in vivo.

Results:

Following irradiation with 4 Gy, the relatively radioresistant T98 cells exhibited enhanced autophagic flux. The more radiosensitive U87 cell line suffered a blockage of autophagic flux. Silencing of LC3A, LC3B, and TFEB genes in vitro, significantly sensitized cells to radiotherapy and temozolomide (U87: P < 0.01 and < 0.05, respectively; T98: P < 0.01 and < 0.01, respectively). Silencing of the LC3A gene sensitized mouse xenografts to radiation.

Conclusions:

Autophagy in cancer cells may be a key factor of radio-resistance and chemo-resistance in glioblastoma cells. Blocking autophagy may improve the efficacy of radiochemotherapy for glioblastoma patients.

Sodium butyrate induces senescence and inhibits the invasiveness of glioblastoma cells

Sodium butyrate (SB), a short chain (C-4) saturated fatty acid, is present in the human bowel at increased concentrations (~2 mM) as a food metabolite. It has been demonstrated that SB exerts an anti-tumor effect as a histone deacetylase inhibitor; however, its precise mechanism of action remains to be elucidated. The present study focused on the mechanisms underlying the effects of SB on glioblastoma (GB) cell proliferation, motility and invasion. In human GB A172 cells, flow cytometry and a Boyden chamber assay demonstrated that physiological concentrations of SB (0.25–4.00 mM) dose-dependently inhibited cell proliferation and invasion. SB also affected cellular morphology, with increases in cell area and the number of focal adhesions observed. However, the phosphorylation (Y397 site) of focal adhesion kinase (FAK) was increased, while that of myosin light chain (S19 site) was unaltered. All of these SB-induced effects were reversible and attenuated following SB withdrawal. In addition, A172 cells treated with SB exhibited positivity for senescence-associated (SA) β-galactosidase (gal) staining and elevated protein expression of p53 and p21 in a time- and dose-dependent manner, whereas the expression of p21 mRNA decreased. Knockdown of p21 expression using small interfering RNA reversed the inhibition of cell growth inhibition and positivity for SA β-gal staining, but did not reverse the inhibition of cell motility and enhanced phosphorylation of FAK. This suggests that cells require p21 to induce senescence but not for SB-mediated decreased motility. Therefore, the current study demonstrated that SB inhibits GB cell proliferation, induces cells to senesce and inhibits tumor cell invasion, indicating that it may be developed as a novel therapeutic strategy to treat GB.

NAMPT overexpression induces cancer stemness and defines a novel tumor signature for glioma prognosis

Gliomas are the most prevalent primary malignant brain tumors associated with poor prognosis. NAMPT, a rate-limiting enzyme that boosts the nicotinamide adenine dinucleotide (NAD) regeneration in the salvage pathway, is commonly expressed in these tumors. NAD metabolism is required to maintain tissue homeostasis. To maintain metabolism, cancer cells require a stable NAD regeneration circuit. However, high levels of NAD confer resistance to therapy to these tumors, usually treated with Temozolomide (TMZ). We report that NAMPT overexpression in glioma cell lines increases tumorigenic properties controlling stem cell pathways and enriching the cancer-initiating cell (CIC) population. Furthermore, NAMPT expression correlated with high levels of Nanog, CD133 and CIC-like cells in glioblastoma directly extracted from patients. Meta-analysis reveals that NAMPT is also a key factor inducing cancer stem pathways in glioma cells. Furthermore, we report a novel NAMPT-driven signature which stratify prognosis within tumor staging. NAMPT signature also correlates directly with EGFR positive and IDH negative tumors. Finally, NAMPT inhibition increases sensitivity to apoptosis in both NAMPT-expressing cells and tumorspheres. Therefore, NAMPT represents a novel therapeutic target in Glioma progression and relapse.