Mathematical modeling of PDGF-driven glioblastoma reveals optimized radiation dosing schedules.

Glioblastomas (GBMs) are the most common and malignant primary brain tumors and are aggressively treated with surgery, chemotherapy, and radiotherapy. Despite this treatment, recurrence is inevitable and survival has improved minimally over the last 50 years. Recent studies have suggested that GBMs exhibit both heterogeneity and instability of differentiation states and varying sensitivities of these states to radiation. Here, we employed an iterative combined theoretical and experimental strategy that takes into account tumor cellular heterogeneity and dynamically acquired radioresistance to predict the effectiveness of different radiation schedules. Using this model, we identified two delivery schedules predicted to significantly improve efficacy by taking advantage of the dynamic instability of radioresistance. These schedules led to superior survival in mice. Our interdisciplinary approach may also be applicable to other human cancer types treated with radiotherapy and, hence, may lay the foundation for significantly increasing the effectiveness of a mainstay of oncologic therapy. PAPERCLIP:

Increased HOXA5 expression provides a selective advantage for gain of whole chromosome 7 in IDH wild-type glioblastoma.

Glioblastoma is the most frequently occurring and invariably fatal primary brain tumor in adults. The vast majority of glioblastomas is characterized by chromosomal copy number alterations, including gain of whole chromosome 7 and loss of whole chromosome 10. Gain of whole chromosome 7 is an early event in gliomagenesis that occurs in proneural-like precursor cells, which give rise to all isocitrate dehydrogenase (IDH) wild-type glioblastoma transcriptional subtypes. Platelet-derived growth factor A (PDGFA) is one gene on chromosome 7 known to drive gliomagenesis, but, given its location near the end of 7p, there are likely several other genes located along chromosome 7 that select for its increased whole-chromosome copy number within glioblastoma cells. To identify other potential genes that could select for gain of whole chromosome 7, we developed an unbiased bioinformatics approach that identified homeobox A5 (HOXA5) as a gene whose expression correlated with gain of chromosome 7 and a more aggressive phenotype of the resulting glioma. High expression of HOXA5 in glioblastoma was associated with a proneural gene expression pattern and decreased overall survival in both human proneural and PDGF-driven mouse glioblastoma. Furthermore, HOXA5 overexpression promoted cellular proliferation and potentiated radioresistance. We also found enrichment of HOXA5 expression in recurrent human and mouse glioblastoma at first recurrence after radiotherapy. Overall, this study implicates HOXA5 as a chromosome 7-associated gene-level locus that promotes selection for gain of whole chromosome 7 and an aggressive phenotype in glioblastoma.

Temporal Lobe Necrosis in Head and Neck Cancer Patients after Proton Therapy to the Skull Base.

PURPOSE: To demonstrate temporal lobe necrosis (TLN) rate and clinical/dose-volume factors associated with TLN in radiation-naïve patients with head and neck cancer treated with proton therapy where the field of radiation involved the skull base. MATERIALS AND METHODS: Medical records and dosimetric data for radiation-naïve patients with head and neck cancer receiving proton therapy to the skull base were retrospectively reviewed. Patients with <3 months of follow-up, receiving <45 GyRBE or nonconventional fractionation, and/or no follow-up magnetic resonance imaging (MRI) were excluded. TLN was determined using MRI and graded using Common Terminology Criteria for Adverse Events (CTCAE) v5.0. Clinical (gender, age, comorbidities, concurrent chemotherapy, smoking, radiation techniques) and dose-volume parameters were analyzed for TLN correlation. The receiver operating characteristic curve and area under the curve (AUC) were performed to determine the cutoff points of significant dose-volume parameters. RESULTS: Between 2013 and 2019, 234 patients were included. The median follow-up time was 22.5 months (range = 3.2-69.3). Overall TLN rates of any grade, ≥ grade 2, and ≥ grade 3 were 5.6% (N = 13), 2.1%, and 0.9%, respectively. The estimated 2-year TLN rate was 4.6%, and the 2-year rate of any brain necrosis was 6.8%. The median time to TLN was 20.9 months from proton completion. Absolute volume receiving 40, 50, 60, and 70 GyRBE (absolute volume [aV]); mean and maximum dose received by the temporal lobe; and dose to the 0.5, 1, and 2 cm3 volume receiving the maximum dose (D0.5cm3, D1cm3, and D2cm3, respectively) of the temporal lobe were associated with greater TLN risk while clinical parameters showed no correlation. Among volume parameters, aV50 gave maximum AUC (0.921), and D2cm3 gave the highest AUC (0.935) among dose parameters. The 11-cm3 cutoff value for aV50 and 62 GyRBE for D2cm3 showed maximum specificity and sensitivity. CONCLUSION: The estimated 2-year TLN rate was 4.6% with a low rate of toxicities ≥grade 3; aV50 ≤11 cm3, D2cm3 ≤62 GyRBE and other cutoff values are suggested as constraints in proton therapy planning to minimize the risk of any grade TLN. Patients whose temporal lobe(s) unavoidably receive higher doses than these thresholds should be carefully followed with MRI after proton therapy.

Radiation Therapy to Sites of Metastatic Disease as Part of Consolidation in High-Risk Neuroblastoma: Can Long-term Control Be Achieved?

PURPOSE: As part of consolidative therapy in high-risk neuroblastoma, modern protocols recommend radiation therapy (RT) both to the primary site and to sites of metastatic disease that persist after induction chemotherapy. Although there are abundant data showing excellent local control (LC) with 21 Gy directed at the primary site, there are few data describing the feasibility and efficacy of RT directed at metastatic sites of disease as part of consolidation. METHODS AND MATERIALS: All patients with neuroblastoma who received RT to metastatic sites of disease as a part of consolidative therapy at a single institution between 2000 and 2015 were reviewed. Among 159 patients, 244 metastases were irradiated. RESULTS: The median follow-up period among surviving patients was 7.4 years. Over 85% of the irradiated metastases were treated with 21 Gy (range, 10.5-36 Gy). Tumor recurrence occurred in 43 of 244 irradiated metastases (18%). The 5-year LC rate of treated metastatic sites was 81%. Metastatic sites that cleared with induction chemotherapy had improved LC compared with sites with persistent uptake on metaiodobenzylguanidine scans (LC rate, 92% vs 67%; P < .0001). LC at irradiated metastatic sites did not differ based on total number of sites irradiated or site of disease irradiated (bone vs soft tissue). Patients with bulky, resistant disease who were treated with 30 to 36 Gy had worse LC (P = .02). However, on multivariate analysis, only persistence after induction chemotherapy remained a significant prognostic factor for LC (hazard ratio, 3.7; P < .0001). Patients who had LC at irradiated metastatic sites had improved overall survival compared with those who did not (overall survival rate, 71% vs 50%; P < .0001). CONCLUSIONS: Response to chemotherapy is an important prognostic factor for LC at irradiated metastatic sites in neuroblastoma. Overall, consolidative RT appears to be an effective modality of LC. Long-term disease control can be achieved with such an approach.

Guiding brain tumor resection using surface-enhanced Raman scattering nanoparticles and a hand-held Raman scanner.

The current difficulty in visualizing the true extent of malignant brain tumors during surgical resection represents one of the major reasons for the poor prognosis of brain tumor patients. Here, we evaluated the ability of a hand-held Raman scanner, guided by surface-enhanced Raman scattering (SERS) nanoparticles, to identify the microscopic tumor extent in a genetically engineered RCAS/tv-a glioblastoma mouse model. In a simulated intraoperative scenario, we tested both a static Raman imaging device and a mobile, hand-held Raman scanner. We show that SERS image-guided resection is more accurate than resection using white light visualization alone. Both methods complemented each other, and correlation with histology showed that SERS nanoparticles accurately outlined the extent of the tumors. Importantly, the hand-held Raman probe not only allowed near real-time scanning, but also detected additional microscopic foci of cancer in the resection bed that were not seen on static SERS images and would otherwise have been missed. This technology has a strong potential for clinical translation because it uses inert gold-silica SERS nanoparticles and a hand-held Raman scanner that can guide brain tumor resection in the operating room.

Identification of global alteration of translational regulation in glioma in vivo.

Post-transcriptional regulation of gene expression contributes to the protein output of a cell, however, methods for measuring translational regulation in complex in vivo systems are lacking. Here, we describe a sensitive method for measuring translational regulation in defined cell populations from heterogeneous tissue in vivo. We adapted the translating ribosome affinity purification (TRAP) methodology to measure the relative occupancy of individual mRNA transcripts in translating ribosomes in the Olig2-positive tumor cell population in a genetically engineered mouse model (GEM) of glioma. Global measurement of paired ribosome-bound and total cellular mRNA populations from tumor cells in vivo identified a broad distribution of relative ribosome occupancies amongst mRNA species that was highly reproducible across biological samples. Comparison of the translation state of glioma cells to non-transformed oligodendrocyte progenitor cells in normal brain identified global alteration of translation in tumor, and specifically of genes involved in cell division and synthetic metabolism. Furthermore, investigation of alteration in steady state translational efficiencies upon loss of PTEN, one of the most frequently mutated and deleted tumor suppressors in glioma, identified differential translation of proteins involved in cellular respiration, canonically regulated by PI3K/Akt signaling, and cellular glycosylation profiles, deregulation of which is known to be associated with tumor progression. Application of the translation efficiency profiling method described here to other biological contexts and conditions would extend our knowledge of the scope and impact of this important mode of gene regulation in complex in vivo systems.

Astrocyte-specific expression patterns associated with the PDGF-induced glioma microenvironment.

BACKGROUND: The tumor microenvironment contains normal, non-neoplastic cells that may contribute to tumor growth and maintenance. Within PDGF-driven murine gliomas, tumor-associated astrocytes (TAAs) are a large component of the tumor microenvironment. The function of non-neoplastic astrocytes in the glioma microenvironment has not been fully elucidated; moreover, the differences between these astrocytes and normal astrocytes are unknown. We therefore sought to identify genes and pathways that are increased in TAAs relative to normal astrocytes and also to determine whether expression of these genes correlates with glioma behavior. METHODOLOGY/PRINCIPAL FINDINGS: We compared the gene expression profiles of TAAs to normal astrocytes and found the Antigen Presentation Pathway to be significantly increased in TAAs. We then identified a gene signature for glioblastoma (GBM) TAAs and validated the expression of some of those genes within the tumor. We also show that TAAs are derived from the non-tumor, stromal environment, in contrast to the Olig2+ tumor cells that constitute the neoplastic elements in our model. Finally, we validate this GBM TAA signature in patients and show that a TAA-derived gene signature predicts survival specifically in the human proneural subtype of glioma. CONCLUSIONS/SIGNIFICANCE: Our data identifies unique gene expression patterns between populations of TAAs and suggests potential roles for stromal astrocytes within the glioma microenvironment. We show that certain stromal astrocytes in the tumor microenvironment express a GBM-specific gene signature and that the majority of these stromal astrocyte genes can predict survival in the human disease.

A brain tumor molecular imaging strategy using a new triple-modality MRI-photoacoustic-Raman nanoparticle.

The difficulty in delineating brain tumor margins is a major obstacle in the path toward better outcomes for patients with brain tumors. Current imaging methods are often limited by inadequate sensitivity, specificity and spatial resolution. Here we show that a unique triple-modality magnetic resonance imaging-photoacoustic imaging-Raman imaging nanoparticle (termed here MPR nanoparticle) can accurately help delineate the margins of brain tumors in living mice both preoperatively and intraoperatively. The MPRs were detected by all three modalities with at least a picomolar sensitivity both in vitro and in living mice. Intravenous injection of MPRs into glioblastoma-bearing mice led to MPR accumulation and retention by the tumors, with no MPR accumulation in the surrounding healthy tissue, allowing for a noninvasive tumor delineation using all three modalities through the intact skull. Raman imaging allowed for guidance of intraoperative tumor resection, and a histological correlation validated that Raman imaging was accurately delineating the brain tumor margins. This new triple-modality-nanoparticle approach has promise for enabling more accurate brain tumor imaging and resection.

The EphA2 receptor drives self-renewal and tumorigenicity in stem-like tumor-propagating cells from human glioblastomas.

In human glioblastomas (hGBMs), tumor-propagating cells with stem-like characteristics (TPCs) represent a key therapeutic target. We found that the EphA2 receptor tyrosine kinase is overexpressed in hGBM TPCs. Cytofluorimetric sorting into EphA2(High) and EphA2(Low) populations demonstrated that EphA2 expression correlates with the size and tumor-propagating ability of the TPC pool in hGBMs. Both ephrinA1-Fc, which caused EphA2 downregulation in TPCs, and siRNA-mediated knockdown of EPHA2 expression suppressed TPCs self-renewal ex vivo and intracranial tumorigenicity, pointing to EphA2 downregulation as a causal event in the loss of TPCs tumorigenicity. Infusion of ephrinA1-Fc into intracranial xenografts elicited strong tumor-suppressing effects, suggestive of therapeutic applications.