Higher glioblastoma tumour burden reduces efficacy of chemotherapeutic agents: in vitro evidence

Lentivirus vector‑mediated genetic manipulation of oncogenic pathways induces tumor formation in rabbit brain

Translation of promising experimental therapies from rodent models to clinical success has been complicated as the novel therapies often fail in clinical trials. Existing rodent glioma models generally do not allow for preclinical evaluation of the efficiency of novel therapies in combination with surgical resection. Therefore, the aim of the present study was to develop a larger animal model utilizing lentivirus vector‑mediated oncogenic transformation in the rabbit brain. Lentiviruses carrying constitutively active AKT and H‑Ras oncogenes, and p53 small interfering (si)RNA were introduced into newborn rabbit neural stem cells (NSCs) and intracranially implanted into rabbits' brains to initiate tumor formation. In one of the ten rabbits a tumor was detected 48 days after the implantation of transduced NSCs. Histological features of the tumor mimic was similar to a benign Grade II ganglioglioma. Immunostaining demonstrated that the tissues were positive for AKT and H‑Ras. Strong expression of GFAP and Ki‑67 was also detected. Additionally, p53 expression was notably lower in the tumor area. The implantation of AKT, H‑Ras and p53 siRNA transduced NSCs for tumor induction resulted in ganglioglioma formation. Despite the low frequency of tumor formation, this preliminary data provided a proof of principle that lentivirus vectors carrying oncogenes can be used for the generation of brain tumors in rabbits. Moreover, these results offer noteworthy insights into the pathogenesis of a rare brain tumor, ganglioglioma.

Extent of resection affects prognosis for patients with glioblastoma in non-eloquent regions

Glioblastoma (GBM) is a malignant cerebral neoplasm carrying poor prognosis. The importance of extent of resection (EoR) in GBM patient outcomes has been argued in the literature. Previous studies included tumors in eloquent regions of the brain. This confounds the role of EoR by including patients with intrinsically worse outcomes but will be over-represented in the reduced EoR category. In a homogenous group of patients in whom GTR was considered achievable, we investigated the effect of increasing EoR on survival. A retrospective review of 51 patients was undertaken. Quantitative, volumetric analysis of pre-operative and post-operative magnetic resonance image was compared with corresponding clinical details. The primary outcome measured was post-operative overall survival. Median overall survival was 18.3 months for GTR patients compared to 11.6 months for non-GTR (p = 0.025). Median pre-operative contrast-enhancing tumor volume for GTR patients was 54.7 cm³ and 24.9 cm³ for non-GTR. Post-operative median residual tumor volume was 1.1 cm³ in the non-GTR cohort. In multivariate analyses, GTR (HR [95% CI] = 0.973 [0.954-0.994], p = 0.00559) and increasing EoR (HR [95% CI] = 0.964 [0.944-0.985], p = 0.000665) remained predictors of survival. Centile dichotomization of EoR revealed 74% (HR [95% CI] = 0.351 [0.128-0.958], p = 0.0409) as the lowest threshold conferring statistically significant survival benefit. Where technically feasible, both GTR and EoR remained as independent prognostic factors for survival. GTR remains the gold standard for surgical treatment of GBM in patients, 74% being the minimum EoR required to confer survival benefit.

LXRβ controls glioblastoma cell growth, lipid balance, and immune modulation independently of ABCA1

Cholesterol is a critical component of membranes and a precursor for hormones and other signaling molecules. Previously, we showed that unlike astrocytes, glioblastoma cells do not downregulate cholesterol synthesis when plated at high density. In this report, we show that high cell density induces ABCA1 expression in glioblastoma cells, enabling them to get rid of excess cholesterol generated by an activated cholesterol biosynthesis pathway. Because oxysterols are agonists for Liver X Receptors (LXRs), we investigated whether increased cholesterol activates LXRs to maintain cholesterol homeostasis in highly-dense glioblastoma cells. We observed that dense cells had increased oxysterols, which activated LXRβ to upregulate ABCA1. Cells with CRISPR-mediated knockdown of LXRβ, but not ABCA1, had decreased cell cycle progression and cell survival, and decreased feedback repression of the mevalonate pathway in densely-plated glioma cells. LXRβ gene expression poorly correlates with ABCA1 in glioblastoma patients, and expression of each gene correlates with poor patient prognosis in different prognostic subtypes. Finally, gene expression and lipidomics analyses cells revealed that LXRβ regulates the expression of immune response gene sets and lipids known to be involved in immune modulation. Thus, therapeutic targeting of LXRβ in glioblastoma might be effective through diverse mechanisms.

Cell-cell contacts protect against t-BuOOH-induced cellular damage and ferroptosis in vitro

Ferroptosis is a recently discovered pathway of regulated necrosis dependent on iron and lipid peroxidation. It has gained broad attention since it is a promising approach to overcome resistance to apoptosis in cancer chemotherapy. We have recently identified tertiary-butyl hydroperoxide (t-BuOOH) as a novel inducer of ferroptosis. t-BuOOH is a widely used compound to induce oxidative stress in vitro. t-BuOOH induces lipid peroxidation and consequently ferroptosis in murine and human cell lines. t-BuOOH additionally results in a loss of mitochondrial membrane potential, formation of DNA double-strand breaks, and replication block. Here, we specifically address the question whether cell-cell contacts regulate t-BuOOH-induced ferroptosis and cellular damage. To this end, murine NIH3T3 or human HaCaT cells were seeded to confluence, but below their saturation density to allow the establishment of cell-cell contacts without inducing quiescence. Cells were then treated with t-BuOOH (50 or 200 µM, respectively). We revealed that cell-cell contacts reduce basal and t-BuOOH-triggered lipid peroxidation and consequently block ferroptosis. Similar results were obtained with the specific ferroptosis inducer erastin. Cell-cell contacts further protect against t-BuOOH-induced loss of mitochondrial membrane potential, and formation of DNA double-strand breaks. Interestingly, cell-cell contacts failed to prevent t-BuOOH-mediated replication block or formation of the oxidative base lesion 8-oxo-dG. Since evidence of protection against cell death was both (i) observed after treatment with hydrogen peroxide, methyl methanesulfonate or UV-C, and (ii) seen in several cell lines, we conclude that protection by cell-cell contacts is a widespread phenomenon. The impact of cell-cell contacts on toxicity might have important implications in cancer chemotherapy.

A Comparative Analysis of the Usefulness of Survival Prediction Models for Patients with Glioblastoma in the Temozolomide Era: The Importance of Methylguanine Methyltransferase Promoter Methylation, Extent of Resection, and Subventricular Zone Location

OBJECTIVE

Several survival prediction models for patients with glioblastoma have been proposed, but none is widely used. This study aims to identify the predictors of overall survival (OS) and to conduct an independent comparative analysis of 5 prediction models.

METHODS

Multi-institutional data from 159 patients with newly diagnosed glioblastoma who received adjuvant temozolomide concomitant chemoradiotherapy (CCRT) were collected. OS was assessed by Cox proportional hazards regression and adjusted for known prognostic factors. An independent CCRT patient cohort was used to externally validate the 1) RTOG (Radiation Therapy Oncology Group) recursive partitioning analysis (RPA) model, 2) Yang RPA model, and 3) Wee RPA model, Chaichana model, and the RTOG nomogram model. The predictive accuracy for each model at 12-month survival was determined by concordance indices. Calibration plots were performed to ascertain model prediction precision.

RESULTS

The median OS for patients who received CCRT was 19.0 months compared with 12.7 months for those who did not (P < 0.001). Independent predictors were: 1) subventricular zone II tumors (hazard ratio [HR], 1.6; 95% confidence interval [CI], 1.0-2.5); 2) methylguanine methyltransferase promoter methylation (HR, 0.36; 95% CI, 0.2-0.6); and 3) extent of resection of >85% (HR, 0.59; 95% CI, 0.4-0.9). For 12-month OS prediction, the RTOG nomogram model was superior to the RPA models with a c-index of 0.70. Calibration plots for 12-month survival showed that none of the models was precise, but the RTOG nomogram performed relatively better.

CONCLUSIONS

The RTOG nomogram best predicted 12-month OS. Methylguanine methyltransferase promoter methylation status, subventricular zone tumor location, and volumetric extent of resection should be considered when constructing prediction models.

Disabled cell density sensing leads to dysregulated cholesterol synthesis in glioblastoma

A hallmark of cellular transformation is the evasion of contact-dependent inhibition of growth. To find new therapeutic targets for glioblastoma, we looked for pathways that are inhibited by high cell density in astrocytes but not in glioma cells. Here we report that glioma cells have disabled the normal controls on cholesterol synthesis. At high cell density, astrocytes turn off cholesterol synthesis genes and have low cholesterol levels, but glioma cells keep this pathway on and maintain high cholesterol. Correspondingly, cholesterol pathway upregulation is associated with poor prognosis in glioblastoma patients. Densely-plated glioma cells increase oxygen consumption, aerobic glycolysis, and the pentose phosphate pathway to synthesize cholesterol, resulting in a decrease in reactive oxygen species, TCA cycle intermediates, and ATP. This constitutive cholesterol synthesis is controlled by the cell cycle, as it can be turned off by cyclin-dependent kinase inhibitors and it correlates with disabled cell cycle control though loss of p53 and RB. Finally, glioma cells, but not astrocytes, are sensitive to cholesterol synthesis inhibition downstream of the mevalonate pathway, suggesting that specifically targeting cholesterol synthesis might be an effective treatment for glioblastoma.

Extent of resection of peritumoral diffusion tensor imaging–detected abnormality as a predictor of survival in adult glioblastoma patients

OBJECTIVE

Diffusion tensor imaging (DTI) has been shown to detect tumor invasion in glioblastoma patients and has been applied in surgical planning. However, the clinical value of the extent of resection based on DTI is unclear. Therefore, the correlation between the extent of resection of DTI abnormalities and patients' outcome was retrospectively reviewed.

METHODS

A review was conducted of 31 patients with newly diagnosed supratentorial glioblastoma who underwent standard 5-aminolevulinic acid–aided surgery with the aim of maximal resection of the enhancing tumor component. All patients underwent presurgical MRI, including volumetric postcontrast T1-weighted imaging, DTI, and FLAIR. Postsurgical anatomical MR images were obtained within 72 hours of resection. The diffusion tensor was split into an isotropic (p) and anisotropic (q) component. The extent of resection was measured for the abnormal area on the p, q, FLAIR, and postcontrast T1-weighted images. Data were analyzed in relation to patients' outcome using univariate and multivariate Cox regression models controlling for possible confounding factors including age, O6-methylguanine-DNA-methyltrans-ferase methylation status, and isocitrate dehydrogenase–1 mutation.

RESULTS

Complete resection of the enhanced tumor shown on the postcontrast T1-weighted images was achieved in 24 of 31 patients (77%). The mean extent of resection of the abnormal p, q, and FLAIR areas was 57%, 83%, and 59%, respectively. Increased resection of the abnormal p and q areas correlated positively with progression-free survival (p = 0.009 and p = 0.006, respectively). Additionally, a larger, residual, abnormal q volume predicted significantly shorter time to progression (p = 0.008). More extensive resection of the abnormal q and contrast-enhanced area improved overall survival (p = 0.041 and 0.050, respectively).

CONCLUSIONS

Longer progression-free survival and overall survival were seen in glioblastoma patients in whom more DTI-documented abnormality was resected, which was previously shown to represent infiltrative tumor. This highlights the potential usefulness and the importance of an extended resection based on DTI-derived maps.

Has the survival of patients with glioblastoma changed over the years?

Background:

Over the last decade, the approach to the management of brain tumours and the understanding of glioblastoma tumour biology has advanced and a number of therapeutic interventions have evolved, some of which have shown statistically significant effects on overall survival (OS) and progression-free survival in glioblastoma. The aim of this study is to compare survival in glioblastoma patients over a 10-year period (1999–2000 and 2009–2010).

Methods:

A retrospective cohort study was performed. Identification of all histologically confirmed glioblastoma in a single centre in years 1999, 2000, 2009 and 2010, and production of survival analysis comparing 1999–2000 and 2009–2010 were achieved.

Results:

A total of 317 patients were included in the analysis (133 in year 1999–2000, and 184 in year 2009–2010). Cox regression analysis showed that the survival was significantly longer in patients in years 2009–2010 than those in 1999–2000 at P<0.001 with HR=0.56, confidence interval (CI) (0.45–0.71). The 1- and 3-year survival rates were 20.7% and 4.4%, respectively, for patients in 1999–2000, improving to 40.0% and 10.3%, respectively, for patients in 2009–2010. The comparisons between the two groups in survival at 1, 2 and 3 years are all statistically significant at P<0.001, respectively. The median OS was 0.36 and 0.74 in 1999–2000 and 2009–2010 groups, respectively.

Conclusions:

Over this period, OS from glioblastoma has increased significantly in our unit. We believe this is due to the institution of evidence-based surgical and oncological strategies practised in a multidisciplinary setting.

Validation of an imageable surgical resection animal model of Glioblastoma (GBM)

BACKGROUND

Glioblastoma (GBM) is the most common and malignant primary brain tumour having a median survival of just 12-18 months following standard therapy protocols. Local recurrence, post-resection and adjuvant therapy occurs in most cases.

NEW METHOD

U87MG-luc2-bearing GBM xenografts underwent 4.5mm craniectomy and tumour resection using microsurgical techniques. The cranial defect was repaired using a novel modified cranial window technique consisting of a circular microscope coverslip held in place with glue.

RESULTS

Immediate post-operative bioluminescence imaging (BLI) revealed a gross total resection rate of 75%. At censor point 4 weeks post-resection, Kaplan-Meier survival analysis revealed 100% survival in the surgical group compared to 0% in the non-surgical cohort (p=0.01). No neurological defects or infections in the surgical group were observed. GBM recurrence was reliably imaged using facile non-invasive optical bioluminescence (BLI) imaging with recurrence observed at week 4.

COMPARISON WITH EXISTING METHOD(S)

For the first time, we have used a novel cranial defect repair method to extend and improve intracranial surgical resection methods for application in translational GBM rodent disease models. Combining BLI and the cranial window technique described herein facilitates non-invasive serial imaging follow-up.

CONCLUSION

Within the current context we have developed a robust methodology for establishing a clinically relevant imageable GBM surgical resection model that appropriately mimics GBM recurrence post resection in patients.

When gross total resection of a glioblastoma is possible, how much resection should be achieved?

OBJECTIVE

The efficacy of extensive resection on prolonging survival for patients with glioblastoma (GBM) is controversial because prior studies have included tumors with dissimilar resection capabilities. The true isolated effect of increasing resection on survival for GBM therefore remains unclear.

METHODS

Adult patients who underwent surgery of an intracranial newly diagnosed GBM at an academic tertiary-care institution from 2007 to 2011 were reviewed. Preoperative images were reviewed by 3 neurosurgeons independently. Tumors considered amenable to gross total resection based on preoperative imaging by all neurosurgeons were included. Multivariate proportional hazards regression analysis was used to identify if an association existed between residual volume (RV) and extent of resection (EOR) with survival.

RESULTS

Of the 292 patients with newly diagnosed GBM, 84 (29%) were amenable to gross total resection. The median (interquartile range) pre and postoperative tumor volumes were 27 (13.8-54.4) and 0.9 (0-2.7) cm(3), respectively. The mean percent resection was 91.7% ± 1.3%. In multivariate analysis, after controlling for age, functional status, and adjuvant therapies, RV (hazards ratio [HR] [95% confidence interval (CI)] = 1.114 [1.033-1.193], P = 0.006) and EOR (HR [95% CI] = 0.959 [0.934-0.985], P = 0.003) were each independently associated with survival. The RV and EOR with the greatest reduction in the risk of death was <2 cm(3) and >95%, respectively. Likewise, RV (HR [95% CI] = 1.085 [1.010-1.178], P = 0.01) and EOR (HR [95% CI] = 0.962 [0.930-0.998], P = 0.04) each remained independently associated with recurrence.

CONCLUSION

This is the first study to evaluate RV and EOR in a more uniform population of patients with tumors of similar surgical capabilities. This study shows that achieving a decreased RV and/or an increased EOR is independently associated with survival and recurrence in those patients with tumors with similar resection capacities.

In vitro drug response and efflux transporters associated with drug resistance in pediatric high grade glioma and diffuse intrinsic pontine glioma

Pediatric high-grade gliomas (pHGG), including diffuse intrinsic pontine gliomas (DIPG), are the leading cause of cancer-related death in children. While it is clear that surgery (if possible), and radiotherapy are beneficial for treatment, the role of chemotherapy for these tumors is still unclear. Therefore, we performed an in vitro drug screen on primary glioma cells, including three DIPG cultures, to determine drug sensitivity of these tumours, without the possible confounding effect of insufficient drug delivery. This screen revealed a high in vitro cytotoxicity for melphalan, doxorubicine, mitoxantrone, and BCNU, and for the novel, targeted agents vandetanib and bortezomib in pHGG and DIPG cells. We subsequently determined the expression of the drug efflux transporters P-gp, BCRP1, and MRP1 in glioma cultures and their corresponding tumor tissues. Results indicate the presence of P-gp, MRP1 and BCRP1 in the tumor vasculature, and expression of MRP1 in the glioma cells themselves. Our results show that pediatric glioma and DIPG tumors per se are not resistant to chemotherapy. Treatment failure observed in clinical trials, may rather be contributed to the presence of drug efflux transporters that constitute a first line of drug resistance located at the blood-brain barrier or other resistance mechanism. As such, we suggest that alternative ways of drug delivery may offer new possibilities for the treatment of pediatric high-grade glioma patients, and DIPG in particular.

Factors associated with survival for patients with glioblastoma with poor pre-operative functional status

Patients with glioblastoma (GB) are known to have poor prognoses, and among these patients, those with poor neurological function have an even poorer prognosis. Consequently, aggressive surgeries and adjuvant therapies are often withheld because of this dismal outlook. The effects of aggressive therapies in this small subset of patients remain unknown. The goal of this study was to evaluate outcomes and factors associated with survival for poor functioning patients who underwent aggressive resection of their GB. Adult patients who underwent surgical resection of an intracranial primary GB at an academic tertiary-care institution between 1997 and 2007 were retrospectively reviewed. Patients with a Karnofsky Performance Scale (KPS) score of ≤60 were included. A total of 100 patients with primary GB met the inclusion criteria. The average age (± standard deviation) and KPS score of this cohort were 54 ± 15 years and 53 ± 12, respectively. No patient (0%) experienced perioperative mortality, and 0 (0%), 10 (10%), and 3 (3%) of patients incurred a new or increasing language, motor, and visual deficit, respectively. At last follow-up, 88 (88%) patients died with a median survival of 6.6 months. The factors associated with improved survival were age <65 year (p = 0.005), tumor size >2 cm (p = 0.01), radical tumor resection (p=0.01), and temozolomide (p = 0.001). This study identifies a subset of patients with poor functional status who may benefit from aggressive surgical resection.

Independent association of extent of resection with survival in patients with malignant brain astrocytoma

OBJECT

With recent advances in the adjuvant treatment of malignant brain astrocytomas, it is increasingly debated whether extent of resection affects survival. In this study, the authors investigate this issue after primary and revision resection of these lesions.

METHODS

The authors retrospectively reviewed the cases of 1215 patients who underwent surgery for malignant brain astrocytomas (World Health Organization [WHO] Grade III or IV) at a single institution from 1996 to 2006. Patients with deep-seated or unresectable lesions were excluded. Based on MR imaging results obtained < 48 hours after surgery, gross-total resection (GTR) was defined as no residual enhancement, near-total resection (NTR) as having thin rim enhancement of the resection cavity only, and subtotal resection (STR) as having residual nodular enhancement. The independent association of extent of resection and subsequent survival was assessed via a multivariate proportional hazards regression analysis.

RESULTS

Magnetic resonance imaging studies were available for review in 949 cases. The mean age and mean Karnofsky Performance Scale (KPS) score at time of surgery were 51 +/- 16 years and 80 +/- 10, respectively. Surgery consisted of primary resection in 549 patients (58%) and revision resection for tumor recurrence in 400 patients (42%). The lesion was WHO Grade IV in 700 patients (74%) and Grade III in 249 (26%); there were 167 astrocytomas and 82 mixed oligoastrocytoma. Among patients who underwent resection, GTR, NTR, and STR were achieved in 330 (35%), 388 (41%), and 231 cases (24%), respectively. Adjusting for factors associated with survival (for example, age, KPS score, Gliadel and/or temozolomide use, and subsequent resection), GTR versus NTR (p < 0.05) and NTR versus STR (p < 0.05) were independently associated with improved survival after both primary and revision resection of glioblastoma multiforme (GBM). For primary GBM resection, the median survival after GTR, NTR, and STR was 13, 11, and 8 months, respectively. After revision resection, the median survival after GTR, NTR, and STR was 11, 9, and 5 months, respectively. Adjusting for factors associated with survival for WHO Grade III astrocytoma (age, KPS score, and revision resection), GTR versus STR (p < 0.05) was associated with improved survival. Gross-total resection versus NTR was not associated with an independent survival benefit in patients with WHO Grade III astrocytomas. The median survival after primary resection of WHO Grade III (mixed oligoastrocytomas excluded) for GTR, NTR, and STR was 58, 46, and 34 months, respectively.

CONCLUSIONS

In the authors' experience with both primary and secondary resection of malignant brain astrocytomas, increasing extent of resection was associated with improved survival independent of age, degree of disability, WHO grade, or subsequent treatment modalities used. The maximum extent of resection should be safely attempted while minimizing the risk of surgically induced neurological injury.

Pharmacotherapy for adults with tumors of the central nervous system

Tumors of the adult central nervous system are among the most common and most chemoresistant neoplasms. Malignant tumors of the brain and spinal cord collectively account for approximately 1.3% of all cancers and 2.2% of all cancer-related deaths. Novel pharmacological approaches to nervous system tumors are urgently needed. This review presents the current approaches and challenges to successful pharmacotherapy of adults with malignant tumors of the central nervous system and discusses novel approaches aimed at overcoming these challenges.

The Role of Surgery in High-grade Glioma – Is Surgical Resection Justified? A Review of the Current Knowledge

Introduction: The aims of this article were to review the role of surgical resection in the management of high-grade gliomas and to determine whether there is any survival benefit from surgical resection. Methods: A literature review of the influence of surgical resection on outcome was carried out. Relevant original and review papers were obtained through a PubMed search using the following keywords: glioma, resection, prognosis and outcome. Results: Presently, there is a lack of evidence to support a survival benefit with aggressive glioma resection, but this should not detract patients from undergoing surgery as there are many other clinical benefits of glioma excision. In addition, limiting surgical morbidity through the use of adjuvant techniques such as intraoperative magnetic resonance imaging (MRI), functional MRI and awake craniotomy is becoming increasingly important. Conclusions: Ideally, a randomised controlled trial would be the best way to resolve the issue of whether (and to what extent) surgical resection leads to improvements in patient outcome and survival, but this would not be ethical. The second best option would be well-controlled retrospective studies with a multivariate analysis of all potential confounding factors. Key words: Astrocytoma, Brain tumour, Glioma, Outcome, Resection, Surgery, Survival