Treatment of malignant gliomas: radiotherapy, chemotherapy and integration of new targeted agents

Effects of glioblastoma-derived extracellular vesicles on the functions of immune cells

Glioblastoma is the most aggressive variant of glioma, the tumor of glial origin which accounts for 80% of brain tumors. Glioblastoma is characterized by astoundingly poor prognosis for patients; a combination of surgery, chemo- and radiotherapy used for clinical treatment of glioblastoma almost inevitably results in rapid relapse and development of more aggressive and therapy resistant tumor. Recently, it was demonstrated that extracellular vesicles produced by glioblastoma (GBM-EVs) during apoptotic cell death can bind to surrounding cells and change their phenotype to more aggressive. GBM-EVs participate also in establishment of immune suppressive microenvironment that protects glioblastoma from antigen-specific recognition and killing by T cells. In this review, we collected present data concerning characterization of GBM-EVs and study of their effects on different populations of the immune cells (T cells, macrophages, dendritic cells, myeloid-derived suppressor cells). We aimed at critical analysis of experimental evidence in order to conclude whether glioblastoma-derived extracellular vesicles are a major factor in immune evasion of this deadly tumor. We summarized data concerning potential use of GBM-EVs for non-invasive diagnostics of glioblastoma. Finally, the applicability of approaches aimed at blocking of GBM-EVs production or their fusion with target cells for treatment of glioblastoma was analyzed.

Correlation of the quantitative level of MGMT promoter methylation and overall survival in primary diagnosed glioblastomas using the quantitative MethyQESD method

AIMS

O(6)-methylguanine-DNA-methyltransferase (MGMT) promoter methylation is a high predictive factor for therapy results of temozolomide in patients with glioma. The objective of this work was to analyse the impact of MGMT promoter methylation in patients with primary diagnosed glioblastoma (GBM) relating to survival using a quantitative method (methylation quantification of endonuclease-resistant DNA, MethyQESD) by verifying a cut-off point for MGMT methylation provided by the literature (</≥10%) and calculating an optimal cut-off.

METHODS

67 patients aged 70 years or younger, operated between January 2013 and December 2015, with newly diagnosed IDH wild-type GBM and clinical follow-up were retrospectively investigated in this study. A known MGMT promoter methylation status was the inclusion criteria.

RESULTS

Median overall survival (OS) was 16.9 months. Patients who had a methylated MGMT promoter region of ≥10% had an improved OS compared with patients with a methylated promoter region of <10% (p=0.002). Optimal cut-off point for MGMT promoter methylation was 11.7% (p=0.012).

CONCLUSION

The results confirm that the quantitative level of MGMT promoter methylation is a positive prognostic factor in newly diagnosed patients with GBM. The cut-off provided by the literature (</≥10%) and the calculated optimal cut-off value of 11.7% give a statistically significant separation. Hence, MethyQESD is a reliable method to calculate MGMT promoter methylation in GBM.

Impact of 18F-FET PET on Target Volume Definition and Tumor Progression of Recurrent High Grade Glioma Treated with Carbon-Ion Radiotherapy

High-precision radiotherapy (HPR) of recurrent high grade glioma (HGG) requires accurate spatial allocation of these infiltrative tumors. We investigated the impact of ¹⁸F-FET PET on tumor delineation and progression of recurrent HGG after HPR with carbon ions. T₁ contrast enhanced MRI and ¹⁸F-FET-PET scans of 26 HGG patients were fused with radiotherapy planning volumes. PET-positive (PET+) tumor volumes using different isocontours (I%) were systematically investigated and compared with MRI-derived gross tumor volumes (GTV). Standardized uptake ratios (SUR) were further correlated with GTV and tumor progression patterns. In grade IV glioma, SUR > 2.92 significantly correlated with poor median overall survival (6.5 vs 13.1 months, p = 0.00016). We found no reliable SUR cut-off criteria for definition of PET+ volumes. Overall conformity between PET and MRI-based contours was low, with maximum conformities between 0.42–0.51 at I40%. The maximum sensitivity and specificity for PET+ volumes outside of GTV predicting tumor progression were 0.16 (I40%) and 0.52 (I50%), respectively. In 75% of cases, FLAIR hyperintense area covered over 80% of PET+ volumes. ¹⁸F-FET-PET derived SUR has a prognostic impact in grade IV glioma. The value of substantial mismatches between MRI-based GTV and PET+ volumes to improve tumor delineation in radiotherapy awaits further validation in randomized prospective trials.

Development of a transplantable glioma tumour model from genetically engineered mice: MRI/MRS/MRSI characterisation

The initial aim of this study was to generate a transplantable glial tumour model of low-intermediate grade by disaggregation of a spontaneous tumour mass from genetically engineered models (GEM). This should result in an increased tumour incidence in comparison to GEM animals. An anaplastic oligoastrocytoma (OA) tumour of World Health Organization (WHO) grade III was obtained from a female GEM mouse with the S100β-v-erbB/inK4a-Arf (+/-) genotype maintained in the C57BL/6 background. The tumour tissue was disaggregated; tumour cells from it were grown in aggregates and stereotactically injected into C57BL/6 mice. Tumour development was followed using Magnetic Resonance Imaging (MRI), while changes in the metabolomics pattern of the masses were evaluated by Magnetic Resonance Spectroscopy/Spectroscopic Imaging (MRS/MRSI). Final tumour grade was evaluated by histopathological analysis. The total number of tumours generated from GEM cells from disaggregated tumour (CDT) was 67 with up to 100 % penetrance, as compared to 16 % in the local GEM model, with an average survival time of 66 ± 55 days, up to 4.3-fold significantly higher than the standard GL261 glioblastoma (GBM) tumour model. Tumours produced by transplantation of cells freshly obtained from disaggregated GEM tumour were diagnosed as WHO grade III anaplastic oligodendroglioma (ODG) and OA, while tumours produced from a previously frozen sample were diagnosed as WHO grade IV GBM. We successfully grew CDT and generated tumours from a grade III GEM glial tumour. Freezing and cell culture protocols produced progression to grade IV GBM, which makes the developed transplantable model qualify as potential secondary GBM model in mice.

Current status of local therapy in malignant gliomas--a clinical review of three selected approaches

Malignant gliomas are the most frequently occurring, devastating primary brain tumors, and are coupled with a poor survival rate. Despite the fact that complete neurosurgical resection of these tumors is impossible in consideration of their infiltrating nature, surgical resection followed by adjuvant therapeutics, including radiation therapy and chemotherapy, is still the current standard therapy. Systemic chemotherapy is restricted by the blood-brain barrier, while methods of local delivery, such as with drug-impregnated wafers, convection-enhanced drug delivery, or direct perilesional injections, present attractive ways to circumvent these barriers. These methods are promising ways for direct delivery of either standard chemotherapeutic or new anti-cancer agents. Several clinical trials showed controversial results relating to the influence of a local delivery of chemotherapy on the survival of patients with both recurrent and newly diagnosed malignant gliomas. Our article will review the development of the drug-impregnated release, as well as convection-enhanced delivery and the direct injection into brain tissue, which has been used predominantly in gene-therapy trials. Further, it will focus on the use of convection-enhanced delivery in the treatment of patients with malignant gliomas, placing special emphasis on potential shortcomings in past clinical trials. Although there is a strong need for new or additional therapeutic strategies in the treatment of malignant gliomas, and although local delivery of chemotherapy in those tumors might be a powerful tool, local therapy is used only sporadically nowadays. Thus, we have to learn from our mistakes in the past and we strongly encourage future developments in this field.

Contribution of case reports to glioblastoma research: systematic review and analysis of pattern of citation

INTRODUCTION

Research activity related to different aspects of diagnosis, epidemiology and treatment of glioblastoma has increased during recent years. Authors of scientific publications are able to choose between different formats including case reports. Little is known about their influence on advancement of the field or scientific merits. Do glioblastoma case reports attract attention or do they go largely unrecognized?

METHODS

Different measures of impact, visibility and quality of published research are available, each with its own pros and cons. For the present evaluation (to the best of our knowledge the first one on this subject), article citation rate was chosen. The databases PubMed and Scopus were searched for articles that were published during the 5-year time period between 2006 and 2010.

RESULTS

We identified 5831 articles dealing with glioblastoma. Of these, 286 (4.9%) reported on single patient cases and 15 (0.26%) were reports of two cases. The median number of citations was 1 (range 0-37). Stratified by year of publication, the median number ranged from 0 for those published in 2010 to 3 for those published in 2006. Citations appeared to gradually increase during the first 2-3 years after publication. As compared to other articles, case reports were significantly less likely to receive a large number of citations.

CONCLUSION

Compared to other formats, the proportion of case reports was limited and few of them were highly cited. It cannot be excluded that case reports without citation provide interesting information to some readers. However, their educational value is difficult to quantify.

Glioblastoma research 2006-2010: pattern of citation and systematic review of highly cited articles

High and continuously increasing research activity related to different aspects of pathogenesis, epidemiology, diagnosis and treatment of glioblastoma has been performed between 2006 and 2010. Different measures of impact, visibility and quality of published research are available, each with its own pros and cons. For this review, article citation rate was chosen. Articles were identified through systematic search of the abstract database PubMed followed by analyses of total number of citations and proportion of highly cited articles, arbitrarily defined as those with ≥100, 50-99, and 25-49 citations, respectively (citation database Scopus). Overall 5831 scientific articles on the subject were published during this time period. 1.5% of all articles accumulated at least 100 citations, 3.2% were cited between 50 and 99 times, and 7.5% were cited between 25 and 49 times. Among the 10 most cited articles, 7 reported on genomic analyses, molecular subclasses of glioblastoma and/or stem cells. Overall, 18 randomized clinical trials were published between 2006 and 2010, including those with phase II design. Thirty-nine percent of them accumulated at least 50 citations and 72% were cited at least 25 times. In general, annual citation rate appeared to gradually increase during the first 2-3 years after publication before reaching high levels. A large variety of preclinical and clinical topics achieved at least 25 citations. However, areas such as quality of life, side effects, and end-of-life care were underrepresented. Efforts to increase their visibility might be warranted.

Upregulation of PTEN in glioma cells by cord blood mesenchymal stem cells inhibits migration via downregulation of the PI3K/Akt pathway

Background

PTEN (phosphatase and tensin homologue deleted on chromosome ten) is a tumor suppressor gene implicated in a wide variety of human cancers, including glioblastoma. PTEN is a major negative regulator of the PI3K/Akt signaling pathway. Most human gliomas show high levels of activated Akt, whereas less than half of these tumors carry PTEN mutations or homozygous deletions. The unique ability of mesenchymal stem cells to track down tumor cells makes them as potential therapeutic agents. Based on this capability, new therapeutic approaches have been developed using mesenchymal stem cells to cure glioblastoma. However, molecular mechanisms of interactions between glioma cells and stem cells are still unknown.

Methodology/Principal Findings

In order to study the mechanisms by which migration of glioma cells can be inhibited by the upregulation of the PTEN gene, we studied two glioma cell lines (SNB19 and U251) and two glioma xenograft cell lines (4910 and 5310) alone and in co-culture with human umbilical cord blood-derived mesenchymal stem cells (hUCBSC). Co-cultures of glioma cells showed increased expression of PTEN as evaluated by immunofluorescence and immunoblotting assays. Upregulation of PTEN gene is correlated with the downregulation of many genes including Akt, JUN, MAPK14, PDK2, PI3K, PTK2, RAS and RAF1 as revealed by cDNA microarray analysis. These results have been confirmed by reverse-transcription based PCR analysis of PTEN and Akt genes. Upregulation of PTEN resulted in the inhibition of migration capability of glioma cells under in vitro conditions. Also, wound healing capability of glioma cells was significantly inhibited in co-culture with hUCBSC. Under in vivo conditions, intracranial tumor growth was inhibited by hUCBSC in nude mice. Further, hUCBSC upregulated PTEN and decreased the levels of XIAP and Akt, which are responsible for the inhibition of tumor growth in the mouse brain.

Conclusions/Significance

Our studies indicated that upregulation of PTEN by hUCBSC in glioma cells and in the nude mice tumors downregulated Akt and PI3K signaling pathway molecules. This resulted in the inhibition of migration as well as wound healing property of the glioma cells. Taken together, our results suggest hUCBSC as a therapeutic agent in treating malignant gliomas.

Distinguishing glioma recurrence from treatment effect after radiochemotherapy and immunotherapy

Recent advancements have made radiation and chemotherapy the standard of care for newly diagnosed glioblastomas. The use of these therapies has resulted in an increased diagnosis of pseudoprogression and radiation-induced necrosis. Standard MRI techniques are inadequate in differentiating tumor recurrence from posttreatment effects. Diagnosis of a posttreatment lesion as glioma recurrence rather than radiochemotherapy or immunotherapy treatment effect is critical. This increase in accuracy plays a role as newer immunotherapies incurring posttreatment effects on MRI emerge. Advancements with magnetic resonance spectroscopy, diffusion-weighted imaging, and functional positron emission tomography scans have shown promising capabilities. Further investigations are necessary to assess the imaging algorithms and accuracy of these modalities to differentiate true glioma recurrence from radiotherapy or immunotherapy treatment effect.

3D conformal radiotherapy and cisplatin for recurrent malignant glioma

PURPOSE

To determine the maximum tolerated dose of 3D conformal radiotherapy in combination with Cisplatin for patients with recurrent malignant gliomas.

METHODS

From 1999-2003, nine patients with recurrent malignant glioma received fractionated radiotherapy and Cisplatin (20 mg/m2/d IV on days 1-5) in a Phase I radiation dose escalation trial. Three sequential dose levels were evaluated: 25 Gy, 30 Gy, and 35 Gy, using 5 Gy fractions. All patients received prior external beam radiation (median dose 59.4 (20-60) Gy) and five patients received prior chemotherapy.

RESULTS

Six male and three female patients were enrolled with a median age of 52 years, and a median Karnofsky performance status score of 70. The median re-irradiated tumor volume was 18.9 (0.1-78.5) cm3 and the median follow-up was 8.8 (3.2-31.2) months. One patient (30 Gy/ 6 fractions) experienced medically reversible acute grade 3 toxicity. A second patient (35 Gy/ 7 fractions) experienced acute grade 2 toxicity and histology showed tumor and radiation effect. A third patient (25 Gy/ 5 fractions) experienced late grade 3 toxicity from radiation necrosis. The radiological responses consisted of complete response (1 patient), partial response (1 patient), and stable disease (2 patients). The median overall survival was 8.8 months (95% CI 8.0-9.9), and the median disease free interval was 2.0 months (95% CI 1.4-4.4). Seven patients received chemotherapy following re-irradiation and Cisplatin.

CONCLUSION

The maximum tolerated dose of 3D conformal fractionated radiotherapy was 30 Gy in 6 fractions with low dose Cisplatin, which was well tolerated in terms of acute toxicity for our patient population. This regimen demonstrated only modest efficacy in the treatment of recurrent malignant glioma. Combinations of conformal re-irradiation and other systemic agents may merit investigation. Currently our recommended dose is 30 Gy in 6 fractions for selected patients.

Therapeutic options for recurrent high-grade glioma in adult patients: Recent advances

Despite of postoperative radiotherapy plus temozolomide for newly diagnosed glioblastoma multiforme (GBM) and improvements in the molecular characterization of high-grade glioma, these tumors continue to relapse. We reviewed all clinical studies of re-treatment published between May 2000 and September 2005. In groups of highly selected patients with re-treatment for GBM, median survival reaches 26-27 months. Re-treatment was stereotactic radiotherapy (mostly with additional chemotherapy) or re-resection plus either photodynamic treatment, radioimmunotherapy and temozolomide, or systemic and local chemotherapy. Thus, intense local treatment was always a component of more successful strategies. Additional data suggest that chemotherapy is more efficacious when minimal residual disease is present, although the recent trials have not uncovered a clear regimen of choice. Early trials of immunotherapy and toxin-delivery demonstrate the feasibility of these approaches and encouraging median survival times. Response to erlotinib was more common if tumors had epidermal growth factor receptor gene amplification, protein overexpression and low levels of phosphorylated PKB/Akt. Individual tailoring of such strategies based on molecular profiling is hoped to improve the outcome.

Preparation and biological evaluation of 10B-enriched 3-[5-{2-(2,3-dihydroxyprop-1-yl)-o-carboran-1-yl}pentan-1-yl]thymidine (N5-2OH), a new boron delivery agent for boron neutron capture therapy of brain tumors

3-[5-{2-(2,3-Dihydroxyprop-1-yl)-o-carboran-1-yl}pentan-1-yl]thymidine (compound 1, N5-2OH) belongs to a novel class of boron delivery agents for neutron capture therapy, which was designated 3-carboranylthymidine analogue (3CTAs). Two shorter and more convenient synthetic routes were developed for the synthesis of 1 in the 10B-enriched form, which is necessary for its preclinical and clinical evaluation in neutron irradiation studies. For more insight on structure-activity relationships, various stereochemical and geometrical isomers of 1 were synthesized and their specificities as substrate for human thymidine kinase 1 (hTK1) were evaluated. A computational model for the binding of various isomers of 1 to the active site of hTK1 was developed. Preliminary studies carried out in F98 glioma bearing rats that had received a 10B-enriched form of 1 followed by neutron irradiation demonstrated a significant prolongation in survival times compared to control animals, suggesting that further studies are warranted to evaluate the therapeutic potential of 1.

Reirradiation of recurrent high-grade gliomas using amino acid PET (SPECT)/CT/MRI image fusion to determine gross tumor volume for stereotactic fractionated radiotherapy

PURPOSE

To develop a valid treatment strategy for recurrent high-grade gliomas using stereotactic hypofractionated reirradiation based on biologic imaging and temozolomide.

PATIENTS AND METHODS

The trial included a total of 44 patients with recurrent high-grade gliomas (1 patient with anaplastic oligodendroglioma, 8 with anaplastic astrocytoma, 33 with glioblastoma multiforme, and 2 with gliosarcoma) after previous surgery and postoperative conventional radiotherapy +/- chemotherapy. For fractionated stereotactic radiotherapy (SFRT) treatment planning, the gross tumor volume was defined by (11)C-methionine positron emission tomography (MET-PET) or (123)I-alpha-methyl-tyrosine (IMT) single-photon computed emission tomography (SPECT)/computed tomography (CT)/magnetic resonance imaging (MRI) fusion in 82% of the patients and by CT/T1+gadolinium-MRI image fusion in 18% of the patients. Six fractions of 5 Gy were administered in 6 days. In 29 of 44 patients (66%), chemotherapy with temozolomide (200 mg/m(2) body surface/day) was given in one to two cycles before and four to five cycles after SFRT. The patients were evaluated in follow-up by clinical investigators and MRI or CT every 3 months after SFRT until death. In cases suspicious for radiation necrosis, a MET-PET or IMT-SPECT investigation was performed.

RESULTS

The median survival time in the whole group was 8 months. Treatment planning based on PET(SPECT)/CT/MRI imaging was associated with improved survival in comparison to treatment planning using CT/MRI alone: median survival time 9 months vs. 5 months (p = 0.03, log-rank). Median survival time were 11 months for patients who received SFRT based on biologic imaging plus temozolomide and significantly lower, 6 months for patients treated with SFRT without biologic imaging, without temozolomide or without both (p = 0.008, log rank). The most important prognostic factor in univariate analysis was a long interval between initial diagnosis and recurrence (p = 0.0002, log-rank). In the multivariate model, time interval to retreatment (p = 0.006) and temozolomide (p = 0.04) remained statistically significant. No acute neurologic toxicity Grade 3 or higher and no Grade 4 hematologic toxicity was observed.

CONCLUSION

This is the first study of biologic imaging optimized SFRT plus temozolomide in recurrent high-grade gliomas. It demonstrates the feasibility and safety of this approach. The most striking result of the trial is the statistically significant longer survival time in the univariate analysis for patients reirradiated using MET-PET or IMT-SPECT/CT/MRI image fusion in the treatment planning, in comparison to patients treated based on MRI/CT alone. Multivariate analysis confirmed a significant survival benefit from multimodal treatment (i.e., addition of temozolomide), despite the limited number of patients. Whether treatment planning with SPECT/PET independently influences survival has to be studied in a larger series of patients.