A novel enhancer regulates MGMT expression and promotes temozolomide resistance in glioblastoma

Temozolomide (TMZ) was used for the treatment of glioblastoma (GBM) for over a decade, but its treatment benefits are limited by acquired resistance, a process that remains incompletely understood. Here we report that an enhancer, located between the promoters of marker of proliferation Ki67 (MKI67) and O6-methylguanine-DNA-methyltransferase (MGMT) genes, is activated in TMZ-resistant patient-derived xenograft (PDX) lines and recurrent tumor samples. Activation of the enhancer correlates with increased MGMT expression, a major known mechanism for TMZ resistance. We show that forced activation of the enhancer in cell lines with low MGMT expression results in elevated MGMT expression. Deletion of this enhancer in cell lines with high MGMT expression leads to a dramatic reduction of MGMT and a lesser extent of Ki67 expression, increased TMZ sensitivity, and impaired proliferation. Together, these studies uncover a mechanism that regulates MGMT expression, confers TMZ resistance, and potentially regulates tumor proliferation

Genetically defined oligodendroglioma is characterized by indistinct tumor borders at MRI

BACKGROUND AND PURPOSE: In 2016, the World Health Organization revised the brain tumor classification, making IDH mutation and 1p/19q codeletion the defining features of oligodendroglioma. To determine whether imaging characteristics previously associated with oligodendroglial tumors are still applicable, we evaluated the MR imaging features of genetically defined oligodendrogliomas. MATERIALSANDMETHODS: One hundred forty-eight adult patients with untreated World Health Organization grade II and III infiltrating gliomas with histologic oligodendroglial morphology, known 1p/19q status, and at least 1 preoperative MR imaging were retrospectively identified. The association of 1p/19q codeletion with tumor imaging characteristics and ADC values was evaluated. RESULTS: Ninety of 148 (61%) patients had 1p/19q codeleted tumors, corresponding to genetically defined oligodendroglioma, and 58/148 (39%) did not show 1p/19q codeletion, corresponding to astrocytic tumors. Eighty-three of 90 (92%) genetically defined oligodendrogliomas had noncircumscribed borders, compared with 26/58 (45%) non-1p/19q codeleted tumors with at least partial histologic oligodendroglial morphology (P < .0001). Eighty-nine of 90 (99%) oligodendrogliomas were heterogeneous on T1- and/or T2-weighted imaging. In patients with available ADC values, a lower mean ADC value predicted 1p/19q codeletion (P = .0005). CONCLUSIONS: Imaging characteristics of World Health Organization 2016 genetically defined oligodendrogliomas differ from the previously considered characteristics of morphologically defined oligodendrogliomas. We found that genetically defined oligodendrogliomas were commonly poorly circumscribed and were almost always heterogeneous in signal intensity

Is the blood-brain barrier really disrupted in all glioblastomas? A critical assessment of existing clinical data

The blood-brain barrier (BBB) excludes the vast majority of cancer therapeutics from normal brain. However, the importance of the BBB in limiting drug delivery and efficacy is controversial in high-grade brain tumors, such as glioblastoma (GBM). The accumulation of normally brain impenetrant radiographic contrast material in essentially all GBM has popularized a belief that the BBB is uniformly disrupted in all GBM patients so that consideration of drug distribution across the BBB is not relevant in designing therapies for GBM. However, contrary to this view, overwhelming clinical evidence demonstrates that there is also a clinically significant tumor burden with an intact BBB in all GBM, and there is little doubt that drugs with poor BBB permeability do not provide therapeutically effective drug exposures to this fraction of tumor cells. This review provides an overview of the clinical literature to support a central hypothesis: that all GBM patients have tumor regions with an intact BBB, and cure for GBM will only be possible if these regions of tumor are adequately treated

Immunotherapy of intracranial G422 glioblastoma with dendritic cells pulsed with tumor extract or RNA

Objective: To investigate the anti-tumor efficacy of dendritic cell (DC)-based vaccines pulsed with tumor extracts or RNA in a mouse model of intracranial G422 glioblastoma. Methods: Bone marrow-derived DCs were pulsed exvivo with tumor extracts or RNA. Ninety female mice harboring 4-day-old intracranial G422 glioblastomas and 126 normal mice were treated with three spaced one week apart subcutaneous injections either with PBS, unpulsed DCs, G422 tumor extracts, RNA, DCs pulsed with G422 tumor extracts (DC/extract) or with RNA (DC/RNA). Seven days after the third immunization of normal mice, the spleens of 36 of them were harvested for cytotoxic T lyphocyte (CTL) assays and the others were challenged in the brain with G422 tumor cells. All the treated mice were followed for survival. Some mice brains were removed and examined pathologically when they died. Results: Immunization using DC/extract or DC/RNA significantly induced G422-specific CTL responses compared with control groups (P<0.01). Vaccination with DC/extract or DC/RNA, either prior to G422 tumor challenge or in tumor-harboring mice, significantly prolonged survival compared with other control groups (P<0.01). Conclusion: DCs pulsed with tumor extracts or RNA derived from autologous tumors has potential antitumor effects via activation of cell-mediated immunity. Our results suggest a useful therapeutic strategy against gliomas

Optimizing Whole Brain Radiation Therapy Dose and Fractionation: Results From a Prospective Phase 3 Trial (NCCTG N107C [Alliance]/CEC.3)

Purpose: Whole brain radiation therapy (WBRT) remains a commonly used cancer treatment, although controversy exists regarding the optimal dose/fractionation to optimize intracranial tumor control and minimize resultant cognitive deficits. Methods and Materials: NCCTG N107C [Alliance]/CEC.3 randomized 194 patients with brain metastases to either stereotactic radiosurgery alone or WBRT after surgical resection. Among the 92 patients receiving WBRT, sites predetermined the dose/fractionation that would be used for all patients treated at that site (either 30 Gy in 10 fractions or 37.5 Gy in 15 fractions). Analyses were performed using Kaplan-Meier estimates, log rank tests, and Fisher's exact tests. Results: Among 92 patients treated with surgical resection and adjuvant WBRT, 49 were treated with 30 Gy in 10 fractions (53%), and 43 were treated with 37.5 Gy in 15 fractions (47%). Baseline characteristics, including cognitive testing, were well balanced between groups with the exception of primary tumor type (lung cancer histology was more frequent with protracted WBRT: 72% vs 45%, P =.01), and 93% of patients completed the full course of WBRT. A more protracted WBRT dose regimen (37.5 Gy in 15 fractions) did not significantly affect time to cognitive failure (hazard ratio [HR], 0.9; 95% confidence interval [CI], 0.6-1.39; P =.66), surgical bed control (HR, 0.52 [95% CI, 0.22-1.25], P =.14), intracranial tumor control (HR, 0.56 [95% CI, 0.28-1.12], P =.09), or overall survival (HR, 0.72 [95% CI, 0.45-1.16], P =.18). Although there was no reported radionecrosis, there is a statistically significant increase in the risk of at least 1 grade 653 adverse event with 37.5 Gy in 15 fractions versus 30 Gy in 10 fractions (54% vs 31%, respectively, P =.03). Conclusions: This post hoc analysis does not demonstrate that protracted WBRT courses reduce the risk of cognitive deficit, improve tumor control in the hypoxic surgical cavity, or otherwise improve the therapeutic ratio. Adverse events were significantly higher with the lengthened course of WBRT. For patients with brain metastases where WBRT is recommended, shorter course hypofractionated regimens remain the current standard of care

Genomic and phenotypic characterization of a broad panel of patient-derived xenografts reflects the diversity of glioblastoma

Purpose: Glioblastoma is the most frequent and lethal primary brain tumor. Development of novel therapies relies on the availability of relevant preclinical models. We have established a panel of 96 glioblastoma patient-derived xenografts (PDX) and undertaken its genomic and phenotypic characterization. Experimental Design: PDXs were established from glioblastoma, IDH-wildtype (n \ubc 93), glioblastoma, IDH-mutant (n \ubc 2), diffuse midline glioma, H3 K27M-mutant (n \ubc 1), and both primary (n \ubc 60) and recurrent (n \ubc 34) tumors. Tumor growth rates, histopathology, and treatment response were characterized. Integrated molecular profiling was performed by whole-exome sequencing (WES, n \ubc 83), RNA-sequencing (n \ubc 68), and genome-wide methylation profiling (n \ubc 76). WES data from 24 patient tumors was compared with derivative models. Results: PDXs recapitulate many key phenotypic and molecular features of patient tumors. Orthotopic PDXs show characteristic tumor morphology and invasion patterns, but largely lack microvascular proliferation and necrosis. PDXs capture common and rare molecular drivers, including alterations of TERT, EGFR, PTEN, TP53, BRAF, and IDH1, most at frequencies comparable with human glioblastoma. However, PDGFRA amplification was absent. RNA-sequencing and genome-wide methylation profiling demonstrated broad representation of glioblastoma molecular subtypes. MGMT promoter methylation correlated with increased survival in response to temozolomide. WES of 24 matched patient tumors showed preservation of most genetic driver alterations, including EGFR amplification. However, in four patient-PDX pairs, driver alterations were gained or lost on engraftment, consistent with clonal selection. Conclusions: Our PDX panel captures the molecular heterogeneity of glioblastoma and recapitulates many salient genetic and phenotypic features. All models and genomic data are openly available to investigators