Haploinsufficiency of phosphodiesterase 10A activates PI3K/AKT signaling independent of PTEN to induce an aggressive glioma phenotype

Glioblastoma is universally fatal and characterized by frequent chromosomal copy number alterations harboring oncogenes and tumor suppressors. In this study, we analyzed exome-wide human glioblastoma copy number data and found that cytoband 6q27 is an independent poor prognostic marker in multiple data sets. We then combined CRISPR-Cas9 data, human spatial transcriptomic data, and human and mouse RNA sequencing data to nominate PDE10A as a potential haploinsufficient tumor suppressor in the 6q27 region. Mouse glioblastoma modeling using the RCAS/tv-a system confirmed that Pde10a suppression induced an aggressive glioma phenotype in vivo and resistance to temozolomide and radiation therapy in vitro. Cell culture analysis showed that decreased Pde10a expression led to increased PI3K/AKT signaling in a Pten-independent manner, a response blocked by selective PI3K inhibitors. Single-nucleus RNA sequencing from our mouse gliomas in vivo, in combination with cell culture validation, further showed that Pde10a suppression was associated with a proneural-to-mesenchymal transition that exhibited increased cell adhesion and decreased cell migration. Our results indicate that glioblastoma patients harboring PDE10A loss have worse outcomes and potentially increased sensitivity to PI3K inhibition.

Causes of Death in Patients With Brain Metastases

BACKGROUND AND OBJECTIVES

Advances in targeted therapies and wider application of stereotactic radiosurgery (SRS) have redefined outcomes of patients with brain metastases. Under modern treatment paradigms, there remains limited characterization of which aspects of disease drive demise and in what frequencies. This study aims to characterize the primary causes of terminal decline and evaluate differences in underlying intracranial tumor dynamics in patients with metastatic brain cancer. These fundamental details may help guide management, patient counseling, and research priorities.

METHODS

Using NYUMets-Brain-the largest, longitudinal, real-world, open data set of patients with brain metastases-patients treated at New York University Langone Health between 2012 and 2021 with SRS were evaluated. A review of electronic health records allowed for the determination of a primary cause of death in patients who died during the study period. Causes were classified in mutually exclusive, but collectively exhaustive, categories. Multilevel models evaluated for differences in dynamics of intracranial tumors, including changes in volume and number.

RESULTS

Of 439 patients with end-of-life data, 73.1% died secondary to systemic disease, 10.3% died secondary to central nervous system (CNS) disease, and 16.6% died because of other causes. CNS deaths were driven by acute increases in intracranial pressure (11%), development of focal neurological deficits (18%), treatment-resistant seizures (11%), and global decline driven by increased intracranial tumor burden (60%). Rate of influx of new intracranial tumors was almost twice as high in patients who died compared with those who survived ( P < .001), but there was no difference in rates of volume change per intracranial tumor ( P = .95).

CONCLUSION

Most patients with brain metastases die secondary to systemic disease progression. For patients who die because of neurological disease, tumor dynamics and cause of death mechanisms indicate that the primary driver of decline for many may be unchecked systemic disease with unrelenting spread of new tumors to the CNS rather than failure of local growth control.

Comparison of pharmacological inhibitors of lysine-specific demethylase 1 in glioblastoma stem cells reveals inhibitor-specific efficacy profiles

Introduction

Improved therapies for glioblastoma (GBM) are desperately needed and require preclinical evaluation in models that capture tumor heterogeneity and intrinsic resistance seen in patients. Epigenetic alterations have been well documented in GBM and lysine-specific demethylase 1 (LSD1/KDM1A) is amongst the chromatin modifiers implicated in stem cell maintenance, growth and differentiation. Pharmacological inhibition of LSD1 is clinically relevant, with numerous compounds in various phases of preclinical and clinical development, but an evaluation and comparison of LSD1 inhibitors in patient-derived GBM models is lacking.

Methods

To assess concordance between knockdown of LSD1 and inhibition of LSD1 using a prototype inhibitor in GBM, we performed RNA-seq to identify genes and biological processes associated with inhibition. Efficacy of various LSD1 inhibitors was assessed in nine patient-derived glioblastoma stem cell (GSC) lines and an orthotopic xenograft mouse model.

Results

LSD1 inhibitors had cytotoxic and selective effects regardless of GSC radiosensitivity or molecular subtype. In vivo, LSD1 inhibition via GSK-LSD1 led to a delayed reduction in tumor burden; however, tumor regrowth occurred. Comparison of GBM lines by RNA-seq was used to identify genes that may predict resistance to LSD1 inhibitors. We identified five genes that correlate with resistance to LSD1 inhibition in treatment resistant GSCs, in GSK-LSD1 treated mice, and in GBM patients with low LSD1 expression.

Conclusion

Collectively, the growth inhibitory effects of LSD1 inhibition across a panel of GSC models and identification of genes that may predict resistance has potential to guide future combination therapies.

CTNI-42. GENOME-WIDE DNA METHYLATION PATTERNS IN VERTU: A RANDOMIZED PHASE II TRIAL OF VELIPARIB, RADIOTHERAPY AND TEMOZOLOMIDE IN PATIENTS WITH MGMT-UNMETHYLATED GLIOBLASTOMA

BACKGROUND

VERTU was a randomized phase II trial evaluating veliparib, a brain-penetrant PARP inhibitor, combined with radiotherapy and temozolomide, for patients with newly diagnosed MGMT-unmethylated glioblastoma. As part of planned correlative work after study completion, we assessed genome-wide DNA methylation patterns to predict methylation class, glioblastoma subtype and MGMT status.

METHODS

Patients were randomized 2:1 to experimental (60Gy/30 fractions with veliparib 200mg bid, then temozolomide 150-200mg/m2 D1-5 + veliparib 40mg bid D1-7 Q28D for 6 cycles) versus standard arm (60Gy/30 fractions with temozolomide 75mg/m2 daily, then temozolomide 150-200mg/m2 D1-5 Q28D for 6 cycles). The primary objective to improve 6-month progression-free survival (PFS-6m) was not met (doi: 10.1093/neuonc/noab111). Methylation data were generated using the Illumina Infinium Methylation EPIC bead chip array. Tumor tissues were categorized using the Heidelberg methylation-based classifier.

RESULTS

Methylation data were successfully generated for 98/125 patients (poor quality DNA [n = 12], no consent [n = 11], insufficient tissue [n = 4]). Those with classifier scores below 0.5 (n = 25), tumor microenvironment only (n = 6) and rediagnosis as pleomorphic xanthoastrocytoma (n = 1) were excluded, leaving n = 66. Methylation classes were GBM RTK II (n = 23, PFS-6m 43% [95%CI 23-62]), RTK I (n = 20, PFS-6m 50% [95%CI 27-69]), MES (n = 20, PFS-6m 40% [95%CI 19-60]), MID (n = 2) and G34 (n = 1). Glioblastoma subtypes were mesenchymal (n = 28, PFS-6m 50% [95%CI 30-66]), proneural (n = 24, PFS-6m 50% [95%CI 29-68]) and classical (n = 14, PFS-6m 36% [95%CI 13-59]). MGMT status were unmethylated (n = 58, PFS-6m 48% [95%CI 35-60]) and methylated (n = 8, PFS-6m 38% [95%CI 9-67]). There was no evidence of interaction between treatment arm and methylation class (excluding GBM MID and G34, P = 0.45), glioblastoma subtype (P = 0.68) or MGMT status (P = 0.52).

CONCLUSIONS

Genome-wide DNA methylation patterns in VERTU identified a spectrum of methylation-defined subgroups, reflecting tumoral heterogeneity. This may have utility for future clinical trials and practice. The effect of veliparib in VERTU appeared to be consistent across subgroups. ACTRN12615000407594.

EPCO-19. ADAPTIVE RESPONSES TO GENOME-WIDE DNA DAMAGE RESULT IN TOPOLOGIC GENOME REORGANIZATION IN GLIOBLASTOMA

In glioblastoma, treatment with radiation and chemotherapy leads to DNA-damage and most DNA breaks are faithfully repaired, but the impact on the epigenome is largely unknown. Using newly developed tools to enable these studies, we hypothesize that genome-wide DNA damage leads to local alterations in DNA-methylation, genome organization, and results in persistent gene-expression alterations near sites of repaired damage. We use patient-derived human glioblastoma stem-like cells (GSCs) as a model. DNA breaks are induced using (i) irradiation or (ii) a novel “multi-cut” CRISPR-Cas9 DNA break system followed by multi-omic profiling. With radiation, we find significant and wide-spread alterations in DNA-methylation after treating multiple glioblastoma cultures. However, it is challenging to study local alterations around sites of radiation induced damage because breaks are introduced at different sites in each cell, resulting in stochastic DNA methylation alterations. To circumvent this issue, we developed a multi-cut CRISPR-Cas9 DNA break system that targets 142 or 483 pre-defined loci. Induction of pre-mapped genome-wide cuts reproduces a similar level of toxicity as standard doses of radiation. To assess repair efficiency and confirm induction of breaks, we performed targeted sequencing of the 142 or 483 sites to allow for high coverage sequencing. To understand how DNA damage may lead to regional epigenetic and 3D chromatin organization changes, we performed HiC, Methylation-seq, ChIP-seq of the chromatin organizing factor CTCF and enhancer marker H3K27ac, as well as RNA-seq, before and after cut induction. Our findings show significant mega-base scale alterations in chromatin contacts centered around cut sites, enrichment of DNA methylation alterations at regulatory elements and altered gene-expression. The findings here provide a mechanistic view of the interplay between genome-wide DNA damage, DNA methylation and genome re-organization, and have wide ranging implications for the effect of DNA damage on the epigenome in glioblastoma.

CTNI-57. RADIONUCLIDE THERAPY WITH 177LU-DOTATATE (LUTATHERA) IN ADULTS WITH ADVANCED INTRACRANIAL MENINGIOMA - INTERIM ANALYSIS RESULTS OF A SINGLE-ARM, OPEN-LABEL, MULTICENTER PHASE II STUDY

BACKGROUND

While most meningiomas are considered benign tumors, a subset of these tumors are characterized by a more aggressive clinical course and require multimodal treatment. Beyond surgical and radiotherapeutic options, there are no effective medical treatments available. Somatostatin receptor 2 (SSTR2) is expressed by the majority of meningiomas. 177Lu-DOTATATE is a SSTR2-targeting radionuclide that has been successful in neuroendocrine tumors. Here we report the results of the interim analysis of an ongoing clinical trial (NCT03971461) that is evaluating the effect of 177Lu-DOTATATE in treating progressive intracranial meningiomas.

METHODS

In this Simon two-stage design phase II study, adults with advanced intracranial meningiomas received 177Lu-DOTATATE 7.4 GBq (200 mCi) every eight weeks for four doses. 68Ga-DOTATATE PET-MRI was performed before and at the end of treatment. The primary endpoint was progression-free survival at 6 months (PFS-6). Correlative studies evaluated the association of PFS-6, objective response rate, progression-free survival, overall survival with radiographic tumor measurements, 68Ga-DOTATATE uptake on PET-MRI, SSTR2 expression in tumor, and meningioma methylation subclass.

RESULTS

Fourteen patients (F = 11, M = 3) with progressive meningiomas (WHO I = 3, II = 10, III = 1) have been enrolled. Median age was 63.1 (range 49-78) years. All patients previously underwent tumor resection and at least one course of radiation. Treatment with 177Lu-DOTATATE was well tolerated, no treatment-limiting toxicities were observed. Six of 14 patients (42%) achieved PFS-6. Radiographically, all six patients had achieved Stable Disease. A functional alteration of tumoral SSTR2 expression by 68Ga-DOTATATE PET-MR imaging was observed in three patients.

CONCLUSIONS

Treatment with SSTR2-targeting 177Lu-DOTATATE is well tolerated. In this interim analysis, six of 14 patients achieved PFS-6. This exceeds the predefined threshold to continue to stage two of this study. This clinical trial is now open to patient enrollment at two study sites in the US.

CTNI-38. UPDATE ON GBM AGILE: A GLOBAL, PHASE 2/3 ADAPTIVE PLATFORM TRIAL TO EVALUATE MULTIPLE REGIMENS IN NEWLY DIAGNOSED AND RECURRENT GLIOBLASTOMA

BACKGROUND

GBM AGILE (Glioblastoma Adaptive, Global, Innovative Learning Environment) is a biomarker based, multi-arm, international, seamless Phase 2/3 response adaptive randomization platform trial designed to rapidly identify experimental therapies that improve overall survival and confirm efficacious experimental therapies and associated biomarker signatures to support new drug approvals and registration. GBM AGILE is a collaboration between academic investigators, patient organizations and industry to support new drug applications for newly diagnosed and recurrent GBM.

METHODS

The primary objective of GBM AGILE is to identify therapies that effectively improve the overall survival in patients with ND or recurrent GBM. Bayesian response adaptive randomization is used within subtypes of the disease to assign participants to investigational arms based on their performance. Operating under a Master Protocol, GBM AGILE allows multiple drugs from different pharmaceutical/biotech companies to be evaluated simultaneously and/or over time against a common control. New experimental therapies are added as information about promising new drugs is identified while therapies are removed as they complete their evaluation. The master protocol/ trial infrastructure includes efficiencies through an adaptive trial design, shared control arm and operational processes to serve the goal of helping patients receive optimal care in a fast and efficient manner. GBM AGILE has screened over 1200 patients and enrollment rates are 3 to 4 times greater than traditional GBM trials, with active sites averaging 0.75 to 1 patients/sites/month. There are 41 active sites in the US, 4 active sites in Canada and 3 active sites in Europe with more sites anticipated to open across 5 countries in Europe. Expansion to China and Australia are under progress. Through the use of improved and flexible processes, GBM AGILE serves as a global trial that supports the efficient and rapid incorporation and evaluation of new experimental therapies for patients with GBM.Clinical trial information: NCT03970447.

P11.65.B GBM AGILE: A global, phase 2/3 adaptive platform trial to evaluate multiple treatment regimens in newly diagnosed and recurrent glioblastoma

Background

GBM AGILE (Glioblastoma Adaptive, Global, Innovative Learning Environment) is a biomarker based, multi-arm, international, seamless Phase 2/3 Response Adaptive Randomization platform trial designed to rapidly identify experimental therapies that improve overall survival and confirm efficacious experimental therapies and associated biomarker signatures to support new drug approvals and registration. It is a collaboration between academic investigators, patient organizations and industry, under the sponsorship of the non-profit organization, Global Coalition for Adaptive Research, to support new drug applications for newly diagnosed and recurrent GBM.

Material and Methods

The primary objective of GBM AGILE is to identify therapies that effectively improve overall survival in patients with newly diagnosed or recurrent GBM. Bayesian response adaptive randomization is used within subtypes of the disease to assign participants to investigational arms based on their performance. Operating under a master protocol, GBM AGILE allows multiple drugs from different pharmaceutical companies to be evaluated simultaneously and/or over time against a common control arm. Based on performance, a drug may graduate and move to a Stage 2 (Phase 3) within the trial, and the totality of the data can be used for a new drug application and registration process. New experimental therapies are added as information about promising new drugs is identified while other therapies are removed as they complete their evaluation. The master protocol/ trial infrastructure includes efficiencies through an adaptive trial design, shared control arm and operational processes such as risk-based monitoring and enhanced remote activities. With its adaptable structure, GBM AGILE has continued trial activation, inclusion of new investigational therapies, and enrollment globally through the challenges of a global pandemic.GBM AGILE provides an efficient mechanism to screen and develop robust information regarding the efficacy of proposed novel therapeutics and associated biomarkers for GBM and to quickly move therapies and biomarkers into clinic. GBM AGILE received initial approval from the United States FDA in April 2019, and in Europe through the Voluntary Harmonization Procedure (VHP) in April, 2021. As of 2022, AGILE has screened over 1000 patients studying multiple investigational treatments. Enrollment rates are 3 to 4 times greater than traditional GBM trials, with active sites averaging 0.75 to 1 patients/site/month.

Currently, there are 41 sites activated in the US, 4 in Canada and 2 in Switzerland and an estimated 24 sites yet to open in Germany, France, Switzerland, Italy and Austria. In addition to the continued expansion in Europe, effort is undergoing to extend the trial to China and Australia as well. Clinical trial information: NCT03970447

The incidence and predictors of new brain metastases in patients with non-small cell lung cancer following discontinuation of systemic therapy

OBJECTIVE

Patients with non-small cell lung cancer (NSCLC) metastatic to the brain are living longer. The risk of new brain metastases when these patients stop systemic therapy is unknown. The authors hypothesized that the risk of new brain metastases remains constant for as long as patients are off systemic therapy.

METHODS

A prospectively collected registry of patients undergoing radiosurgery for brain metastases was analyzed. Of 606 patients with NSCLC, 63 met the inclusion criteria of discontinuing systemic therapy for at least 90 days and undergoing active surveillance. The risk factors for the development of new tumors were determined using Cox proportional hazards and recurrent events models.

RESULTS

The median duration to new brain metastases off systemic therapy was 16.0 months. The probability of developing an additional new tumor at 6, 12, and 18 months was 26%, 40%, and 53%, respectively. There were no additional new tumors 22 months after stopping therapy. Patients who discontinued therapy due to intolerance or progression of the disease and those with mutations in RAS or receptor tyrosine kinase (RTK) pathways (e.g., KRAS, EGFR) were more likely to develop new tumors (hazard ratio [HR] 2.25, 95% confidence interval [CI] 1.33-3.81, p = 2.5 × 10-3; HR 2.51, 95% CI 1.45-4.34, p = 9.8 × 10-4, respectively).

CONCLUSIONS

The rate of new brain metastases from NSCLC in patients off systemic therapy decreases over time and is uncommon 2 years after cessation of cancer therapy. Patients who stop therapy due to toxicity or who have RAS or RTK pathway mutations have a higher rate of new metastases and should be followed more closely.

Treatment for Brain Metastases: ASCO-SNO-ASTRO Guideline

PURPOSE

To provide guidance to clinicians regarding therapy for patients with brain metastases from solid tumors.

METHODS

ASCO convened an Expert Panel and conducted a systematic review of the literature.

RESULTS

Thirty-two randomized trials published in 2008 or later met eligibility criteria and form the primary evidentiary base.

RECOMMENDATIONS

Surgery is a reasonable option for patients with brain metastases. Patients with large tumors with mass effect are more likely to benefit than those with multiple brain metastases and/or uncontrolled systemic disease. Patients with symptomatic brain metastases should receive local therapy regardless of the systemic therapy used. For patients with asymptomatic brain metastases, local therapy should not be deferred unless deferral is specifically recommended in this guideline. The decision to defer local therapy should be based on a multidisciplinary discussion of the potential benefits and harms that the patient may experience. Several regimens were recommended for non-small-cell lung cancer, breast cancer, and melanoma. For patients with asymptomatic brain metastases and no systemic therapy options, stereotactic radiosurgery (SRS) alone should be offered to patients with one to four unresected brain metastases, excluding small-cell lung carcinoma. SRS alone to the surgical cavity should be offered to patients with one to two resected brain metastases. SRS, whole brain radiation therapy, or their combination are reasonable options for other patients. Memantine and hippocampal avoidance should be offered to patients who receive whole brain radiation therapy and have no hippocampal lesions and 4 months or more expected survival. Patients with asymptomatic brain metastases with either Karnofsky Performance Status ≤ 50 or Karnofsky Performance Status < 70 with no systemic therapy options do not derive benefit from radiation therapy.Additional information is available at www.asco.org/neurooncology-guidelines.

EPCO-04. RADIOTHERAPY IS ASSOCIATED WITH GLOBAL METHYLATION ALTERATIONS IN PATIENT DERIVED GLIOBLASTOMA CELL LINES

PURPOSE/OBJECTIVE(S)

In glioblastoma, DNA methylation states are the most predictive marker of overall survival and response to therapy. Our understanding of how epigenetic states, such as DNA methylation, are “mis-repaired” after DNA damage repair is scant, hampering our ability to understand how treatment associated DNA methylation alterations may drive tumor resistance and growth.

MATERIALS AND METHODS

Three different patient derived IDH wild-type glioma stem cell (GSC) lines, in duplicates, were treated with radiation (20 Gray in 10 fractions vs. sham control) and allowed to recover prior to DNA methylation analysis with 850K methylation arrays. To analyze the methylation array data via bioinformatic methods we used RnBeads (version 2.4.0) and R (version 3.6.1) packages. We further focused our analysis to specific genomic regions, including CpG islands, promoters, gene bodies and CTCF motifs to understand how methylation alterations may differ between these and other genomic contexts following radiation.

RESULTS

There were widespread differential methylation (pre-treatment vs. radiation treatment) changes among the genomic regions examined. Interestingly, we found differential methylation changes at CTCF motifs, which play important DNA-methylation dependent roles in gene expression and chromatin architecture regulation. Hierarchical clustering, PCA and MDS analysis of DNA methylation status amongst CpG islands, promoters, gene bodies and CTCF domains revealed strong intra-sample differences, but not inter-sample differences (between GSC lines), suggesting radiation associated methylation alterations maybe loci and context dependent.

CONCLUSION

Radiation treatment is associated with wide-spread alterations of DNA methylation states in this patient derived glioblastoma model. Such alterations may drive gene expression changes or genomic architecture alterations that lead to treatment resistance, warranting further mechanistic investigation of the interplay between radiation induced DNA damage and local epigenetic state restoration following DNA damage repair.

NCOG-11. ASSOCIATION OF HYPERGLYCEMIA AND TUMOR SUBCLASS ON SURVIVAL IN IDH-WILDTYPE GLIOBLASTOMA

BACKGROUND

RNA expression and DNA methylation studies have identified different subclasses of isocitrate dehydrogenase (IDH)-wildtype (wt) glioblastoma (GBM). However, the prognostic significance of molecular subclasses is unclear. Although hyperglycemia has been previously associated with worse survival, attempts to lower glucose have yielded mixed responses. The role of hyperglycemia may be confounded by molecular heterogeneity and have different impact in molecularly distinct GBM subclasses.

METHODS

Clinical, laboratory, and molecular data on 89 IDH-wt GBMs profiled by clinical next-generation sequencing and treated with Stupp protocol were reviewed. IDH-wt GBMs were subclassified into RTKI (Proneural), RTKII (Classical) and Mesenchymal subtypes using DNA methylation. Average glucose was calculated by time-weighting plasma glucose measurements between diagnosis and last follow-up.

RESULTS

Patients were stratified into three groups using average glucose: tertile one (&lt; 100mg/dL), tertile two (100-115mg/dL), and tertile three ( &gt; 115mg/dL). Comparison across glucose tertiles revealed no significant differences in Karfnosky Performance Status (KPS), dexamethasone dose, MGMT methylation, or methylation subclass. Overall survival (OS) was not affected by methylation subclass (log-rank p=0.9) but decreased with higher glucose (log-rank p=0.015). Higher glucose tertiles were associated with poorer OS among RTK I (log-rank p=0.08) and mesenchymal tumors (log-rank p=0.05), but not RTK II (log-rank p=0.99). After controlling for age, KPS, dexamethasone dose, and MGMT status, glucose remained significantly associated with survival (adjusted hazard ratio=5.2, p=0.02). DNA methylation clustering did not identify a unique signature associated with high or low glucose levels. Metabolomic analysis of 23 tumors showed minimal variation across metabolites within the cohort with no differences across molecular subclasses.

CONCLUSION

Higher average glucose values were associated with poorer OS in RTKI and Mesenchymal IDH-wt GBM, but not RTKII. There were no discernible epigenetic or metabolomic differences between tumors in different glucose environments, suggesting a potential survival benefit with systemic glucose lowering in selected molecular subtype.

Update on Radiation Therapy for Central Nervous System Tumors

Radiation therapy has long been a critical modality of treatment of patients with central nervous system tumors, including primary brain tumors, brain metastases, and meningiomas. Advances in radiation technology and delivery have allowed for more precise treatment to optimize patient outcomes and minimize toxicities. Improved understanding of the molecular underpinnings of brain tumors and normal brain tissue response to radiation will allow for continued refinement of radiation treatment approaches to improve clinical outcomes for brain tumor patients. With continued advances in precision and delivery, radiation therapy will continue to be an important modality to achieve optimal outcomes of brain tumor patients.

RADI-19. The Incidence of New Brain Metastases in Patients with Non-Small Cell Lung Cancer Following Discontinuation of Systemic Therapy

Purpose

Patients with non-small cell lung cancer (NSCLC) metastatic to the brain increasingly are living longer due to improvements in systemic therapy and local modalities. The risk of new brain metastases when these patients stop systemic therapy is unknown. Recognizing patterns of new tumor occurrence is necessary to determine the frequency of follow-up and the need for further treatment.

Methods

We included patients in a prospective registry who had non-small cell lung cancer (NSCLC) brain metastases, discontinued systemic therapy for at least 90 days, and underwent active surveillance. 63 patients with 73 off-periods were studied. The risk factors for the development of new tumors were determined using Cox regression and multi-state Markov modeling.

Results

The median time to new brain metastases off systemic therapy was 16.0 months. The probability of developing an additional new tumor at 6, 12, and 18 months was 26%, 40%, and 53%, respectively. There were no additional new tumors 22 months after stopping therapy. Patients who discontinued therapy due to intolerance or progression of the disease and those with mutations in RAS or receptor tyrosine kinase pathways (e.g. KRAS, EGFR) were more likely to develop new tumors (HR: 2.21, 95% CI: 1.25–3.91, p=6.3 x 10^–3; HR: 2.03, 95% CI: 1.09–3.77, p=0.026, respectively).

Conclusion

The rate of new brain metastases from NSCLC in patients off systemic therapy decreases over time and is uncommon 2 years after cessation of cancer therapy. Patients who stop therapy due to toxicity or who have RAS or receptor tyrosine kinase pathway mutations have a higher rate of new metastases and should be followed more closely.

RTID-11. GBM AGILE: A GLOBAL, PHASE 2/3 ADAPTIVE PLATFORM TRIAL TO EVALUATE MULTIPLE REGIMENS IN NEWLY DIAGNOSED AND RECURRENT GLIOBLASTOMA

Developing new therapies for patients with glioblastoma (GBM) requires focused interaction between industry, academia, nonprofits, patient advocacy, and health authorities, and novel approaches to clinical trials. GBM Adaptive Global Innovative Learning Environment (GBM AGILE) Trial was designed by over 130 global key opinion leaders in consultation with health authorities to provide an optimal mechanism for phase 2/3 development in GBM. The Sponsor of GBM AGILE is the Global Coalition for Adaptive Research, whose mission is to accelerate the development of treatments rare and deadly diseases by serving as sponsor of innovative trials. GBM AGILE is an international platform trial designed to evaluate multiple therapies in newly diagnosed and recurrent GBM. Its goals are to identify effective therapies for GBM and match effective therapies with patient subtypes, with data generated to support regulatory filing for new drug applications. Bayesian response adaptive randomization is used within subtypes of the disease to assign participants to investigational arms based on their performance. The primary endpoint is overall survival. The trial is being conducted under a master Investigational New Drug Application/Clinical Trial Agreement and Master Protocol, allowing multiple drugs from different companies to be evaluated simultaneously and/or over time. The plan is to add experimental therapies as new information is identified and remove therapies as they complete their individual evaluation against a common control. GBM AGILE received IND approval from the FDA in April 2019, screening its first patient in June 2019. As of June 2020 over 200 patients have been screened. Expansion to Canada, Europe, China, and Australia is also underway. There is currently one investigational arm under evaluation in the trial, with two additional arms to be added in Q4 2020/ Q1 2021. Clinical trial information: NCT03970447.

EPCO-11. IN VIVO FUNCTIONAL GENOMIC SCREEN IDENTIFIES WISP1 AS AN OVEREXPRESSED DRIVER OF GLIOBLASTOMA

There is a tremendous need to identify new genetic drivers of glioblastoma which can serve as potential therapeutic targets. In order to find new drivers, we leveraged genomic datasets to conduct a context specific in vivo functional genomic screen of overexpressed and/or amplified genes in GBM. We identified WISP1, a secreted extracellular matrix protein, to be an overexpressed driver in GBM. Overexpression of WISP1 was able to drive tumor growth in various in vivo models. Knockdown of WISP1 with shRNAs resulted in reduced colony formation in vitro and reduced tumor growth in vivo. Rescue experiments validated that the shRNAs were on target. Functional characterization of the protein revealed that the TSP module is necessary for the phenotype. Intriguingly, overexpression of WISP1 lacking the signal peptide module for secretion resulted in a strong phenotype. Co-culture and conditioned medium experiments further supported a secretion independent intracellular role of WISP1 in GBM. Though WISP1 is a secreted protein we have found some basal localization in the cytosol. Overall, we have revealed WISP1 to be a driver of GBM with possible therapeutic potential as a target. This study has expanded our understanding of WISP1 by supporting a new role as a driver in GBM which can function in a non-canonical manner in the cytosol. Overall, we have revealed WISP1 to be a driver of GBM with possible therapeutic potential as a target.

EPID-15. RACIAL AND SOCIOECONOMIC DISPARITIES DIFFERENTIALLY AFFECT OVERALL AND CAUSE-SPECIFIC SURVIVAL IN GLIOBLASTOMA

BACKGROUND

The prognostic role of racial and socioeconomic factors in patients with glioblastoma is controversially debated. We aimed to evaluate how these factors may affect survival outcomes in an overall and cause-specific manner using large, national cancer registry cohort data in the temozolomide chemoradiation era.

METHODS

The National Cancer Institute’s Surveillance, Epidemiology, and End Results database was queried for patients diagnosed with glioblastoma between 2005 and 2016. Overall survival was assessed using Cox proportional hazard models using disease intrinsic and extrinsic factors. Cause-specific mortality was assessed using cumulative incidence curves and modeled using multivariate cumulative risk regression.

RESULTS

A total of 28,954 patients met the prespecified inclusion criteria and were included in this analysis. The following factors were associated with all-cause mortality: age, calendar year of diagnosis, sex, treatment receipt, tumor size, tumor location, extent of resection, median household income, and race. Asian/Pacific Islanders and Hispanic Whites had lower mortality compared to Non-Hispanic Whites. Cause-specific mortality was associated with both racial and socioeconomic groups. After adjusting for treatment and tumor-related factors, Asian/Pacific and black patients had lower glioblastoma-specific mortality. However, lower median household income and black race were associated with significantly higher non-glioblastoma mortality.

CONCLUSION

Despite the aggressive nature of glioblastoma, racial and socioeconomic factors influence glioblastoma-specific and non-glioblastoma associated mortality. Our study shows that patient race has an impact on glioblastoma-associated mortality independently of tumor and treatment related factors. Importantly, socioeconomic and racial differences largely contribute to non-glioblastoma mortality, including death from other cancers, cardio- and cerebrovascular events.

CTNI-51. NEUROCOGNITIVE FUNCTION (NCF) OUTCOMES OF RTOG FOUNDATION 3508: A PHASE 3 TRIAL OF ABT-414 WITH CONCURRENT CHEMORADIATION AND ADJUVANT TEMOZOLOMIDE IN PATIENTS WITH EGFR-AMPLIFIED NEWLY DIAGNOSED GBM

RTOG 3508/AbbVie M13-813/INTELLANCE-1 was a phase 3 trial of depatuximab-mafodotin (depatux-m, formerly ABT-414) that accrued 639 patients with EGFR-amplified newly diagnosed GBM. At the pre-specified interim OS analysis, the futility criteria were met and there was no survival benefit from adding depatux-m to SOC. Pre-specified secondary NCF analyses included time to decline in verbal learning and memory as assessed by the HVLT-R Total Recall based on the reliable change index. Exploratory NCF analyses examined changes in other HVLT-R outcomes over time. As corneal epitheliopathy causing visual impairment is a known toxicity of depatux-m, NCF tests that did not depend on visual acuity were employed. NCF testing occurred at baseline, day 1 of the first cycle of adjuvant depatux-m, every other cycle (i.e., 8 weeks) thereafter, and at progression. Compliance with test completion was 95% at screening and 80%, 70%, 58%, 51%, 47% thereafter through cycle 9. The most common reasons for missing data was site error. Time to HVLT-R Total Recall decline trended worse in the depatux-m arm compared to placebo but the difference was not significant (12 month deterioration: 41.2%, 95% CI: 3.50–47.2 vs 32.4%, 95% CI: 26.6- 38.4, p=0.052). The depatux-m arm, in comparison to the placebo arm, showed greater decline from baseline on the HVLT-R at the following time points: cycle 3 (Total Recall: mean= -1.8, SD=5.7 vs mean= -0.5, SD=5.5, respectively, p=0.046; Delayed Recall: mean= -1.1, SD=3.0 vs. mean= -0.2, SD=2.7, respectively, p=0.01), cycle 7 (Total Recall: mean= -0.6, SD=5.1 vs mean= 1.4, SD=5.0, respectively, p=0.009; Delayed Recall: mean -0.6, SD=3.0 vs. mean= 0.5, SD=2.7, respectively, p=0.01), and cycle 9 (Delayed Recall: mean=-0.4, SD=2.7 vs. mean= 0.8, SD=2.4, respectively, p=0.003). Depatux-m added to concurrent chemoradiation and adjuvant temozolomide was associated with faster time to deterioration and worse episodic learning and memory over time than placebo.

EXTH-75. IN VITRO AND IN VIVO EFFICACY OF COMBINATORIAL INHIBITION OF LSD1 AND HDACS IN PATIENT DERIVED GLIOBLASTOMA STEM CELL MODELS

Inhibitors of histone deacetylases (HDACi) have been tested in glioblastoma (GBM), however, single agent clinical efficacy has not been proven, prompting study of combinatorial approaches. A rational HDACi combination strategy is with inhibition of LSD1, lysine specific demethylase 1, a histone demethylase known to exist in complex with HDAC1/2. We previously showed in vivo efficacy of combining a brain permeant LSD1 inhibitor, tranylcypromine (TCP) together with vorinostat. More selective inhibitors of LSD1 have been developed and were tested in the current study together with the HDACi, vorinostat or panobinostat in a panel of patient derived glioblastoma stem cell (GSC) lines that have been characterized as radio-resistant or radiosensitive. To test in vitro sensitivity, dose response experiments were conducted in nine GSC cell lines using three LSD1 inhibitors or two HDACi as single agents or in combination. Two non-tumor lines were also tested to assess selective cytotoxicity for brain tumor lines. Cell viability and clonogenicity assays were performed. Several radio-resistant GSC lines showed sensitivity to single agent LSD1 inhibitors, whereas some radio-sensitive GSCs did not, indicating distinct molecular mechanisms of response. Intracranial orthotopic xenograft models were used to test in vivo efficacy using the radioresistant GSC20 line. Interestingly, LSD1 inhibition alone promoted tumor burden reduction and better survival rates than combination treatment. RNA-Seq guided biomarkers of sensitivity to the LSD1/HDAC inhibitor combination were assessed in vitro and in vivo. Both in vivo and in vitro data show that GSC20 treated with GSK LSD1 inhibitor had higher levels of HKDC1 gene with in vivo data also showing elevated levels of FTH1. In vivo mouse data for vorinostat and combination treatment groups showed that only the FTH1 gene level was elevated, providing a potential explanation for low in vivo efficacy. Collectively, our data suggests that LSD1 inhibition represents a viable strategy in GBM.

ACTR-24. A RANDOMIZED PHASE II TRIAL OF VELIPARIB (V), RADIOTHERAPY (RT) AND TEMOZOLOMIDE (TMZ) IN PATIENTS (PTS) WITH UNMETHYLATED MGMT (uMGMT) GLIOBLASTOMA (GBM): THE VERTU STUDY

BACKGROUND

TMZ offers minimal benefit in pts with de novo uMGMT GBM. V is synergistic with RT and TMZ in uMGMT preclinical GBM models, safe when combined with either RT or TMZ clinically, but the triplet (V+RT+TMZ) is poorly tolerated. VERTU tested V in pts with uMGMT GBM.

METHODS

VERTU is a randomized Phase 2 trial comparing Standard Arm (Arm A), RT (60Gy/30 fractions) + TMZ (75mg/m2 daily) followed by TMZ (150–200mg/m2D 1–5) every 28 days for 6 cycles vs Experimental Arm (Arm B), RT (60Gy/30 fractions) + V (200mg PO BID) followed by TMZ (150–200mg/m2D 1–5) + V (40mg bid, D 1–7) every 28 days for 6 cycles in pts with de novo uMGMT GBM according to centralised testing.

RESULTS

125 pts were randomized 1:2 (41:84). The 2 groups were matched for age, sex, performance status and extent of resection. Median follow-up was 25.8 months and 91 pts had died. The 6-month Progression-Free Survival (6mPFS) for Arms A and B were 34% (95% CI 20–48) and 46% (95% CI 36–57) respectively. The median PFS for Arms A and B were 4.2m (95% CI 2.5–6.0) and 5.7m (95% CI 4.1–6.6) respectively (HR = 0.80, 95%CI 0.55–1.18). 55% of pts in both arms experienced Grade 3/4 adverse events (AEs) with no significant differences in frequency or severity between the arms. Most common Grade 3/4 AEs were thrombocytopenia, seizures, hyperglycaemia and diarrhoea.

CONCLUSION

VERTU demonstrated that a novel treatment strategy for patients with de novo uMGMT GBM was feasible and tolerable. The observed 6mPFS and PFS were similar in both arms. Overall survival and other endpoints will be presented. Central MRI review, biomarker analyses, including DNA repair and methylation signature analyses are ongoing.

(ANZCTR#ACTRN12615000407594).

ACTR-21. A RANDOMIZED, DOUBLE-BLIND, PLACEBO-CONTROLLED PHASE 3 TRIAL OF DEPATUXIZUMAB MAFODOTIN (ABT-414) IN EPIDERMAL GROWTH FACTOR RECEPTOR (EGFR) AMPLIFIED (AMP) NEWLY DIAGNOSED GLIOBLASTOMA (nGBM)

BACKGROUND

Approximately 50% of nGBMs harbor EGFR-amp. Depatuxizumab mafodotin (depatux-m) is an antibody drug conjugate: a monoclonal antibody that binds activated EGFR (wild-type and EGFRvIII mutant) linked to a microtubule-inhibitor toxin. Pre-clinical and earlier clinical trials suggested efficacy.

METHODS

RTOGF 3508/AbbVie M13-813 (INTELLANCE-1, NCT02573324) was a phase 3 academic-industry collaboration (RTOG-Foundation, AbbVie). Eligible adults (KPS ≥ 70, EGFR-amp nGBM, centrally confirmed histology and biomarkers) were randomized 1:1 to radiotherapy (RT) and temozolomide and either depatux-m (2.0 mg/kg during RT, 1.25 mg/kg thereafter, q 14 days) or placebo, stratified by region of world, RPA class, MGMT methylation, and EGFRvIII mutation. Primary endpoint was overall survival (OS), with 640 patients planned for randomization; 441 events yielded 85% power to detect 25% reduction in hazard of death (HR 0.75), one-sided 2.5% level of significance by stratified weighted log-rank.

RESULTS

2229 patients were screened and 639 (median age 60, range 22–84; 394 men, 62%) randomized. Pre-specified interim analysis after 346 events (≥ 75% required) found no OS improvement for depatux-m over placebo (median 18.9 vs. 18.7 months, HR 1.01, 95% CI 0.82–1.25, one-sided p= 0.63). Progression-free survival (PFS) trended toward depatux-m (median 8.0 vs. 6.3 months; HR 0.84, 95% CI 0.70–1.02), particularly among the ~50% with EGFRvIII mutation (median 8.3 vs. 5.9 months, HR 0.72, 95% CI 0.56–0.93) but without an OS improvement (median 19.8 vs. 18.2, HR=0.95, 95% CI 0.71–1.27). Ocular side effects (grade ≥ 1) occurred in 95% of depatux-m treated patients, 61% grade 3–4, causing 12% to discontinue, and were the most common treatment related adverse events.

CONCLUSION

Interim analysis demonstrated no OS benefit for treating EGFR-amp nGBM with depatux-m. PFS trended toward favoring depatux-m, particularly in the EGFRvIII harboring subgroup. No new important safety risks were identified. The trial was stopped for futility. Active patients are permitted to continue treatment.

RTHP-23. PROSPECTIVE TRIAL OF CONVENTIONALLY FRACTIONATED DOSE CONSTRAINTS FOR RE-IRRADIATION OF PRIMARY BRAIN TUMORS

PURPOSE/OBJECTIVE

Dose constraints for re-irradiation of recurrent primary brain tumors are not well-established, especially for treatment volumes too large for stereotactic radiotherapy. This prospective trial was performed to test dose constraints for conventionally-fractionated re-irradiation of recurrent primary brain tumors

MATERIALS/METHODS

A single-institution, prospective trial of 21 adults with recurrent brain tumors was performed. Electronic dosimetry records from the first course of radiation (RT1) were obtained and deformed onto the simulation CT for the second course of radiation (RT2). Treatment plans for RT2 were developed that met protocol-assigned dose constraints for RT2 alone and the composite dose of RT1+RT2. Dose constraints were also based on histology and interval since RT1. The primary endpoint was the rate of symptomatic brain necrosis after RT2.

RESULTS

Twenty one adults enrolled from March 2017 to May 2018. Twelve had glioblastoma, four had oligodendroglioma, two had anaplastic astrocytoma, and one each had choroid plexus papilloma, hemangiopericytoma, and pleomorphic xanthroastrocytoma (PXA). Twenty patients were treated with VMAT and one was treated with proton CSI. Median RT1-RT2 interval was 45 months (range, 9–141 months). Median RT2 dose was 42.8 Gy (range, 17.5–60 Gy). Median PTV volume was 208 cc (range, 7–1537 cc). Median imaging followup was 9 months (range, 1–20 months). Two months after RT2, the patient with PXA developed a trapped temporal horn adjacent to the RT2 treatment volume; pathology from emergent resection revealed necrotic brain tissue. The patient recovered fully and lived another 18 months until dying of disease progression. No other patient developed symptomatic radionecrosis. Median overall survival from RT2 for all patients was 11 months (range, 3–20 months).

CONCLUSION

Re-irradiation can be performed with conventionally fractionated schemes. Given the low rate of symptomatic radionecrosis, the dose constraints described here are a starting point for future studies of conventionally fractionated re-irradiation.

NIMG-03. PROSPECTIVE PHASE II RANDOMIZED TRIAL COMPARING PROTON THERAPY VS. PHOTON IMRT FOR GBM: SECONDARY ANALYSIS COMPARISON OF PROGRESSION FREE SURVIVAL BETWEEN RANO VS. CLINICAL AND RADIOLOGICAL ASSESSMENT

PURPOSE

To compare tumor progression based on clinical radiological assessment and on Response Assessment in Neuro-Oncology (RANO) criteria between GBM patients treated with proton radiotherapy (PT) vs. photon intensity modulated radiotherapy (IMRT).

METHODS

Eligible patients were enrolled on the described prospective phase II trial and had MR imaging at baseline and follow-up beyond 12 weeks from treatment completion. ‘Clinical’ progression was based on a radiology report of progression in combination with changes in treatment due to suspected disease progression. A single blinded observer applied RANO criteria to determine the RANO-based tumor progression.

RESULTS

Of 90 enrolled patients, 66 were evaluable, with median follow-up of 19.8 (Range: 3.2–65.1) months; median of 22.6 months for PT (n=25) vs. 18.9 months for IMRT (n=41). Median time to progression (TTP) was 7.9 months based on clinical progression criteria (8.1 months IMRT, 6.3 months PT) and 7.2 months (7.3 months IMRT, 5.7 months PT) by RANO criteria (p=ns for all). Median ‘clinical’ progression-free survival (PFS) was 8.7 (Range: 6.4–11.1) months; 8.9 months IMRT vs. 8.7 months PT (p=0.065). Median RANO PFS was 8.3 (range, 5.8–11.6) months: 8.3 months IMRT vs. 6.9 months PT (p=0.226). There were 14 discrepant cases: 3 had progression based on ‘clinical’ but not RANO criteria, and 11 had progression based on RANO but not ‘clinical’ criteria.

CONCLUSION

Based on this secondary analysis of a randomized trial of PT vs. IMRT for GBM, there was no difference in tumor progression relative to treatment technique used. There was no statistical difference in PFS noted between clinical and RANO-based assessments, but RANO criteria identified progression more often than clinical assessment, and TTP was shortened with the use of RANO criteria alone. Further development of tumor assessment tools that improve consistency and accuracy of determining tumor progression are needed to guide therapeutic trials in GBM.

RTHP-18. PROSPECTIVE PHASE II RANDOMIZED TRIAL COMPARING PROTON THERAPY VS. PHOTON IMRT FOR NEWLY DIAGNOSED GBM: SECONDARY ANALYSIS COMPARISON OF GENDER AND NEUTROPHIL-LYMPHOCYTE RATIO (NLR) IN GBM OUTCOMES

BACKGROUND

While glioblastoma (GBM) is more prevalent in males, studies show that females with GBM tend to have longer overall survival (OS) than males. Pretreatment neutrophil to lymphocyte ratio (NLR) has also proven to be prognostic in GBM, with lower NLR having favorable outcomes. This secondary analysis of a prospective randomized trial of proton vs. photon intensity modulated radiotherapy aims to explore the interaction of gender and NLR on GBM outcomes.

METHODS

Analysis was performed on the full patient population. Kaplan-Meier methods estimated OS with censoring at last follow-up for those who were alive. Univariate (UVA) and multivariate (MVA)Cox proportional hazards models assessed predictors of OS.

RESULTS

Of 90 patients, 77 were included (43 males; 34 females) with median age of 52 years (range: 26–82 years). Median OS was longer for females than males (30.7 vs 18.2 months, p=0.004). On UVA, patients with NLR below median value (NLR= 3.1) tended to have longer OS than those above median, though not meeting statistical significance (23.1 vs. 17.9 months, p=0.051). Difference in OS was statistically significant in females (OS 36.4 months NLR >median vs. 16.7 months NLR< median, p=0.002), but not in males (OS 17.8 months NLR >median vs. 19.1 NLR< median, p=0.95). MVA analysis was consistent, with female gender predicting reduced hazard ratio (HR) (0.28, p=0.034) and females with below median NLR showing a reduced HR over those with above median (0.28, p=0.005). Again, males did not benefit (HR 0.90, p=0.77).

CONCLUSION

Consistent with prior publications, females and all patients with lower pre-treatment NLR with newly diagnosed GBM had longer OS. However, combining these two factors revealed that the benefits from lower pre-treatment NLR were conferred only in females with no impact on males. This different impact of NLR between genders may suggest innate immune differences in gender during response to malignancy.

ACTR-34. SINGLE AGENT ONC201 IN PREVIOUSLY-TREATED, PROGRESSIVE ADULT H3 K27M-MUTANT GLIOMA

H3 K27M-mutant gliomas often manifest as midline gliomas, have a dismal prognosis, and have no established or effective treatments at recurrence. ONC201 is the first clinical bitopic DRD2 antagonist/ClpP agonist and is under evaluation in Phase II trials for gliomas and other cancers. We previously reported in vitro studies suggesting dysregulated dopamine receptor expression and enhanced ONC201 sensitivity among H3 K27M-mutant gliomas. Following these observations, adults with midline H3 K27M-mutant glioma patients were enrolled to a dedicated Phase II clinical trial (NCT03295396), a multi-arm Phase II trial (NCT0252569), and expanded access protocols under the Sponsor’s IND. An integrated radiographic analysis with an objective response rate primary endpoint in patients who received ONC201 monotherapy with confirmed H3 K27M-mutant glioma (not primarily in the pons or spinal cord and without leptomeningeal spread) that was progressive and measurable disease by RANO criteria, >90 days from completion of prior radiation, and had KPS >60. As of December 15, 2018, 15 patients have received single agent ONC201 who meet these criteria (n=9 NCT03295396; n=5 NCT0252569; n=1 expanded access). ONC201 was orally administered at 625 mg weekly, except for one patient dosed once every 3 weeks. As midline gliomas can exhibit a mixture of contrast-enhancing and non-contrast-enhancing disease, objective response was assessed by blinded independent central review using RANO-HGG and RANO-LGG criteria for each patient. Best response to date by RANO-HGG criteria is at least 27%: 1 CR, 3 PR, 7 SD, and 4 PD; by RANO-LGG is at least 36%: 1 CR, 1 PR, 3 minor response (MR), 4 SD, 5 PD, 1 unevaluable. By RANO-HGG, median onset of response is 2.6 months (range 1.3–3.4); median duration of response has not been reached with a median follow-up of 7.7 months (range 1.8–29.8). Updated radiographic response, pharmacodynamics, safety, and other clinical outcomes will be reported.

DDIS-32. MEK INHIBITORS INDUCES NEURONAL DIFFERENTIATION IN EGFR AMPLIFIED GLIOMA STEM LIKE CELLS

The median survival for patients with glioblastoma (GBM) is 12–15 months highlighting the need for better therapeutic strategies for this deadly disease. Genomic and epigenomic sequencing analysis at the single cell level have identified multiple genomic aberrations as potential targets for therapeutic intervention in GBM. EGFR and PDGFR amplification are evident in nearly 40% and 12% of human GBM, respectively. Although the first and second-generation EGFR tyrosine kinase small molecule inhibitors failed to show long term therapeutic benefit in GBM patients, multiple factors such as incorrect patient selection, acquired resistance, and drug-target heterogeneity may all lead to clinical failure of targeted therapies. Although the multilevel genomic characterization of gliomas are increasing, the clinical translation of these findings is beginning to unravel. In this study, we attempted to correlate the genomic variations using an unbiased high throughput drug screen using primary glioma stem-like cell (GSCs) as our model system. An unbiased high-throughput screen utilizing our GSC models identified that glioblastoma cells harboring focal EGFR amplification are sensitive to mitogen-activated protein kinase (MEK) inhibitors. MEK inhibition induced apoptosis in EGFR amplified cells at low concentration. RNA sequence analysis of cells treated with MEK inhibitors revealed upregulation of genes related to neuronal differentiation and down regulation of MEK target genes in MEK sensitive glioma stem cells. Additionally, RNA sequencing of GSCs with acquired MEK inhibitor resistance demonstrated an upregulation of oncogenic transcription factor ETS Variant Gene 1 (ETV1) as a mediator of resistance. Overall our data suggest that the MEK inhibition in combination with ETV inhibitors could be a potential therapeutic target for a subset of GBM patients.

BSCI-12. COMPREHENSIVE GENOMIC ANALYSIS OF BRAIN METASTASES FROM MULTIPLE CANCER TYPES

PURPOSE: Brain metastases occur in approximately 8–10% of patients with cancer, and the incidence has increased over the past decades. The most common primary tumors responsible for brain metastases are lung cancer, melanoma, renal cell carcinoma (RCC), breast cancer and colorectal cancer. The precise mechanisms by which genomic and transcriptional abnormalities drive the formation of brain metastases remain unclear. Here, we conducted comprehensive genomic and transcriptional analysis with paired primary tumor tissue (or extracranial metastasis tissue) and brain metastasis tissue using whole-exome sequencing (WES), mRNA-Seq and global methylation profiling. METHODS: Frozen, paired brain metastasis tissue and primary tumor tissue (or extracranial metastasis tissue) and white blood cells were acquired from RCC (n=12), breast cancer (n=17), lung cancer (n=15) and melanoma (n=14) patients, followed by extraction of DNA and RNA. WES and mRNA-Seq were performed on the Illumina HiSeq4000 platform. For methylation profiling, DNA was analyzed using Illumina Infinium MethylationEPIC Beadchip arrays. RESULTS: Somatic mutations or methylation of VHL gene were identified in 81.8% of RCC patients. Gene Set Enrichment Analysis revealed significant enrichment for hypoxia pathway transcripts in RCC brain metastases relative to primary tumors. The most common alterations in breast and lung cancer patients were TP53 mutations with frequencies of 50.0% and 73.3%, followed by ERBB2 alterations (43.8%) in breast cancer patients and mutually exclusive alterations of EGFR (33.3%) and KRAS (26.7%) in lung cancer patients. Mutually exclusive alterations of NRAS (42.9%) and BRAF (42.9%) were also observed in melanoma patients. Gene expression and epigenetic analysis revealed characteristics of brain metastases depending on primary cancer types. CONCLUSIONS: Comprehensive genomic analysis of brain metastases from four different cancer types revealed that brain metastasis tissues have unique genomic, transcriptional and epigenetic profiles according to histopathology groups. Therefore, the therapeutic strategies should be designed based at least in part on tumor histiogenesis.

MLTI-01. IMMUNOLOGICAL REPROGRAMMING IN THE CNS TUMOR MICROENVIRONMENT AND THERAPEUTIC EFFICACY OF RADIOTHERAPY WITH STAT3 BLOCKADE

BACKGROUND: Patients with central nervous system (CNS) tumors are typically treated with radiation therapy, but this is not curative and results in the upregulation of p-STAT3 that drives invasion, angiogenesis, and immune suppression. Therefore, we investigated the combined effect of an inhibitor of the STAT3 pathway that is currently in clinical trials (WP1066) and whole-brain radiation therapy (WBRT) in murine models of CNS malignancy. METHODS: C57BL/6 mice underwent intracerebral implantation of either B16 melanoma or GL261 glioma cells, WBRT, and treatment with WP1066 a blood-brain barrier penetrant inhibitor of the STAT3 pathway or the two in combination. The role of the immune system was evaluated using tumor rechallenge strategies, immune incompetent backgrounds, immune monitoring, and nanostring gene expression analysis of 770 immune-related genes from immune cells, including those directly isolated from the CNS tumor microenvironment. RESULTS: The combination of WP1066 and WBRT resulted in long-term survivors and enhanced median survival time relative to monotherapy. Immunological memory appeared to be induced, because mice were protected during subsequent tumor rechallenge. Therapeutic efficacy was completely lost in immune incompetent mice. Extensive functional immune monitoring and nanostring profiling followed by bioinformatic processing revealed that the most robust immunological responses were located in the CNS tumor microenvironment rather than the periphery. An unbiased analysis of the immune-cell heat maps of the combination therapy relative to monotherapy were notable for upregulation of T-cell functional genes, dendritic cell function, MHC expression, and antigen presentation in the CNS tumor. These data highly suggest that antigen presentation and T-cell effector function are requirements within the tumor microenvironment of the CNS for full antitumor immune-mediated activities. CONCLUSION: This study indicates that the combination of STAT3 inhibition and WBRT enhances the therapeutic effect against established tumors in the CNS by inducing dendritic cell maturation and activation in the CNS tumor.

RADI-27. ROLE OF STEREOTACTIC RADIOSURGERY IN THE CARE OF PATIENTS WITH &gt;/= 25 CUMULATIVE BRAIN METASTASES

INTRODUCTION: Stereotactic radiosurgery (SRS) is an accepted treatment for multiple brain metastases. However, the upper limit of the number of brain metastases over the course of care suitable for this approach is controversial. METHODS: From a review of our prospective registry, 48 patients treated with SRS for ≥ 25 brain metastases in either single or multiple sessions between 2013 and 2019 were identified. Patient, tumor, and treatments characteristics were evaluated. Clinical outcomes and overall survival (OS) were analyzed. RESULTS: Thirty-one females (64.6%) and 17 males (35.4%) with a median age of 56 years (25–91) were included. Primary diagnoses included lung (n=23, 47.9%), breast (n=13, 27.1%), melanoma (n=8, 16.7%), and other (n=4, 8.33%). Initial median GPA index was 2 (0.5–3). Nine patients (18.8%) had received whole brain radiation therapy (WBRT) prior to first SRS treatment, with a median dose of 35Gy (30–40.5Gy). Ten patients (20.8%) received WBRT after initial SRS, with a median dose of 30Gy (20-30Gy). Thus, only 19 patients (40%) ever received WBRT. Median number of radiosurgeries per patient was 3 (1–12). Median number of cumulative tumors irradiated was 31 (25–110). Median number of tumors irradiated at first SRS was 10 (1–35). Median marginal dose for the largest tumor per session was 16Gy (10-21Gy). Median SRS total tumor volume was 6.8cc (0.8–23.4). Median follow-up since initial SRS was 16 months (1–71). At present, 21 (43.7%) are alive. Median OS from the diagnosis of brain metastases was 31 months (2–97), and OS from the time of first SRS, 22 months (1–70). Median KPS at first SRS and last follow-up was the same (90). Sixty-three percent did not require a corticosteroid course. CONCLUSION: In selected patients with a large number of cumulative brain metastases (≥ 25), SRS is effective and safe. Therefore, WBRT may not be required in this population.

Abstract 4238: DNA-methylation based epigenetic signatures predict and deconvolute somatic genomic alterations in gliomas

PURPOSE: Genomic alterations classify cancers into subtypes with distinct clinical management and prognoses. Molecular classification of gliomas, the most common and lethal primary brain tumor, define tumors into distinct biologic and clinical entities. Mutation of isocitrate dehydrogenese (IDH) is associated with hypermethylation of CpG sites in gene promotors. Other alterations, including telomerase (TERTp) mutation, ATRX mutation, chromosome 1p/19q co-deletion (1p19q codel), and gene expression subtype (Classical/CL, Mesenchymal/MES, Proneural/PN), have yet to be associated with an epigenetic signature. We hypothesized that DNA methylation signatures would classify gliomas based on genetic alterations and give insight into the development of each subtype. The resulting platform functions as a unified diagnostic (UniD) with high processivity applicable to clinical diagnosis and generalizable across molecular oncology.

METHODS: Machine learning algorithms were applied to whole methylome data to build classifiers for IDH, TERTp, and ATRX mutations; 1p19q codel and gene expression subtype. Models were validated with data from a phase III trial of anaplastic gliomas.

RESULTS: Individual models were generated and prediction accuracies for IDH, TERTp, and ATRX mutations, and 1p19q codel were 100%, 98.3%, 90.48%, and 99.21% in test set and 89.9%, 82.8%, 92.47%, and 89.99% in the validation clinical trial data. The prediction model for gene expression subtype, a previously reported classifier enriched for characteristic somatic alterations, achieved 72% accuracy. Analysis of the misclassified cases revealed that the characteristic alterations associated with the expression subtypes were more correctly classified by methylation than by gene expression. Methylation-determined CL subtype showed high EGFR (p-value = 0.04) and amplification (p-value = 0.00019) compared to transcriptional MES samples, and low expression (p-value = 0.08) and amplification (p-value = 0.056) in methylation-determined MES but transcriptional CL samples.

CONCLUSION: Distinct DNA methylation signatures were associated with key somatic genomic alterations in gliomas. It improved the existing classifiers based on gene expression and provided a unique clinical diagnostic platform for rapid determination of glioma subtype at the time of patient diagnosis. The extensive and significant relationship between cancer epigenetic signatures indicates that this approach would have broad applicability to other tumor types and lead to similar unified diagnostic platforms. A R package (UniD) is provided for implantation of this diagnostic platform.

Citation Format: Jie Yang, Qianghu Wang, Ravesanker Ezhilarasan, Lihong Long, Benedikt Wiestler, Wolfgang Wick, Yinsen Miao, Erik Sulman. DNA-methylation based epigenetic signatures predict and deconvolute somatic genomic alterations in gliomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4238.

Abstract 2741: Comprehensive molecular profiling of primary tumors and paired distant metastases in non-small cell lung cancer

Despite complete resection, many non-small cell lung cancer (NSCLC) patients still develop and succumb to distant metastases, which is a major cause of cancer-related death worldwide. However, our understanding of the molecular mechanisms driving metastasis is rudimentary. We performed whole exome sequencing, RNA sequencing (RNA-seq), methylation microarray, and immunohistochemistry using multiple immune markers on 8 pairs of NSCLC primary tumors and matched distant metastases including 7 metachronous brain and 1 synchronous liver metastases. On average, 60% of all somatic mutations (22% to 90%) and 86% of canonical cancer gene mutations were shared between primary tumors and paired distant metastases. Metastases also resembled paired primary tumors closely in regard to their mutational spectrum, copy number aberrations, allelic imbalance, and methylation profiles. Genomic aberrations unique to metastases were rather patient-specific than commonly observed across multiple patients. Of particular interest, subclonal architecture analysis suggested that monoclonal metastatic seeding is a prevalent mode of metastasis in NSCLC. We validated these findings in a large published dataset consisting of 38 pairs of primary lung tumors and matched distant metastases. RNA-seq showed gene expression profiles in metastases were similar to those of paired primary tumors. Metastases commonly up-regulated metabolism-associated pathways and down-regulated immune-related pathways, consistent with the immunohistochemical staining data for CD3, CD4, CD8, CD20, CD68, PD1, and PD-L1. Our data suggest that distant metastasis is a late event during carcinogenesis and that a majority of genomic and epigenetic aberrations occur before metastatic outgrowth. While molecular mechanisms underlying postsurgical distant metastasis seem to be variable among NSCLC patients, immune suppression may be a common characteristic of cancer cells with metastatic plasticity.

Citation Format: Won-Chul Lee, Daniel Gomez, Jianhua Zhang, Alexandre Reuben, Ali Jalali, Whijae Roh, Chia Chin Wu, Wei Lu, Chi-Wan Chow, Junya Fujimoto, Mara Antonoff, Cesar Moran, Erik Sulman, Ganesh Rao, Stephen Swisher, John Heymach, Ignacio I. Wistuba, Andrew Futreal, Jianjun Zhang. Comprehensive molecular profiling of primary tumors and paired distant metastases in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2741.

Differences in patterns of care and outcomes between grade II and grade III molecularly defined 1p19q co-deleted gliomas

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It is the largest series to report on 1618 1p19q co-deleted gliomas.

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51% of grade II get resection alone whereas 86% of grade III get adjuvant therapy.

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In a propensity score matched cohort, grade was significant for survival.

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Hazard for death for grade III 1p19q co-deleted gliomas was about 3.6 times higher.

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Oligodendroglioma histology was associated with a lower likelihood of death</span>.

Molecular markers are redefining classification of lower grade gliomas and ushering in a paradigm shift in their management. Our objective was to evaluate the differences in pattern of care and outcome by comparing grade II and grade III molecularly defined 1p19q co-deleted gliomas. We evaluated 1618 patients in the National Cancer Database diagnosed with 1p19q co-deleted gliomas from 2010 through 2014 and treated with surgery followed by radiation therapy (RT), chemotherapy (CT), or combined-modality therapy. Differences in patterns of care included that fifty-one percent of grade II tumors received surgery alone, whereas most patients with grade III tumors (86%) received surgery or biopsy followed by a form of post-operative therapy (p < 0.001). In a propensity score matched cohort, the Cox multivariable proportional hazards model with frailty testing identified significant covariates were age, comorbidity, histology and grade. Outcomes were different in overall survival even after adjusting for treatment received. The hazard for death for grade III 1p19q co-deleted gliomas was about 3.6 times higher ([HR] 3.69, 95% confidence interval [CI] 2.03–6.68, p < 0.001) than grade II 1p19q gliomas. Oligodendroglioma histology was associated with a lower likelihood of death (HR 0.40, 95% CI 0.23–0.70, p < 0.001). Our study is among the largest series to report on 1p19q co-deleted gliomas, which would otherwise require decades to acquire outside of large databases.

Abstract 4858: Efficacy of the protein arginine methyltransferase PRMT5 inhibitor GSK591 in glioma stem-like cells

Protein arginine methyltransferase (PRMTs) function as epigenetic regulators of transcription and play a major role in gene regulation. PRMTs are upregulated in gastric, colorectal and lung cancer, and lymphoma and leukemia. PRMT5 is capable of forming symmetric dimethylarginine (SDMA) residues, and has been reported as a therapeutic target in glioblastoma, as its expression has been correlated with tumor grade and progression. In this study, the in vitro therapeutic efficacy of PRMT5 inhibitor GSK591 was investigated in a panel of gliomas stem-like cell (GSC) lines with specific molecular subtypes. Genomic, proteiomic (reverse protein lysate array, RPPA), methylation status and GSC subtype were correlated with drug IC50 to find predictors of drug sensitivity. The efficacy of inhibiting PRMT5 activity was retained at low dose of GSK591 in a small number of GSCs. Western blotting data showed high expression of PRMT5 and multiple bands of SDMAs in most GSCs tested (n=31), indicating PRMT5 enzymatic activity in GSC cell lines. Evidence of PRMT5 inhibition was demonstrated at low doses (&lt; 1.5 uM) in 4 GSC lines (13%) as shown by the total inhibition of SDMA expression in a dose- and time-dependent fashion after GSK591 treatment. The sensitivity of GSK591 correlated with low methylation of multiple genes pretreatment, including MAGI2, EGR2, and DUSP16. In addition, upregulated genes in sensitive GSCs correlated with proliferation signatures using gene set enrichment analyses (GSEA). Together, our study demonstrated that inhibition of PRMT5 activity and its substrate product SDMA correlated with inhibition of tumor growth. These promising in vitro results have led to ongoing experiments to evaluate the efficacy of GSK591 in intracranial xenograft models and the underlying mechanism of sensitivity and resistance to PRMT5 inhibition.

Citation Format: Vikram Shaw, Yuji Piao, Soon Young Park, Jianwen Dong, Emmanuel Martinez-Ledesma, Caroline Carrillo, Verlene Henry, Ravesanker Ezhilarasan, Erik Sulman, Veerakumar Balasubramaniyan, John F. de Groot. Efficacy of the protein arginine methyltransferase PRMT5 inhibitor GSK591 in glioma stem-like cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4858.

Abstract 4819: High-throughput screening of glioma stem-like cells (GSCs) identifies synergistic therapeutic combination of FGFR inhibitor and CDK4/6 inhibitor

High-grade gliomas are challenging tumors to treat. The lack of efficacy of single-agent therapy emphasizes the importance of developing combination strategies to overcome acquired resistance. Quantitative high-throughput screening (HTS) of 2 and 3 drug combinations at 5 concentrations (maximal concentration of 1 uM) of each agent were evaluated in a panel of GSCs to identify potentially novel combination therapy. Genomic, proteiomic (reverse protein lysate array, RPPA) and GSC subtype were correlated with drug IC50 to find biomarkers of drug sensitivity. GSCs were classified as sensitive (IC50 ≤ 1µM) or resistant (IC50 &gt;1µM) for single-agent screening. The Bliss independence model and combination index (CI) criteria were used to quantify the synergy of compound combinations. Evaluation of drug combination data for synergistic combination identified FGFR inhibitor LY2874455 and CDK4/6 inhibitor LY2835219 as the most effective combinations for multiple drug sets. Abnormal activation of FGFR and alterations in the CDKN2A-CDK4/6-Retinoblastoma 1 (RB1) pathway have been implicated in glioblastoma pathogenesis. We further investigated the in vitro combination efficacy of FGFR inhibitor and CDK4/6 inhibitor. Compared to single agent, combination of FGFR inhibitor and CDK4/6 inhibitor induced prominent cleaved poly ADP ribose polymerase (c-PARP), an index of apoptosis, which was further confirmed by Annexin V staining. Combination therapy significantly inhibited p-RB, p-STAT3, p-Akt, p-Erk and p-c-Jun expression compared to single agent. Genomic data demonstrated that high PDGFRα expression and low methylation correlated to sensitivity to the FGFR and CDK4/6 inhibitor combination. These findings were validated by demonstrating that this synergistic sensitivity was decreased by knocking out PDGFRα by CRISP/Cas9 system with the combination index (CI) at IC50 increased from 0.964 to 2.247. In addition, Western blotting showed that expression of PDGFRα and Notch1 was significantly inhibited by combination treatment. However, this combination failed to show any survival and tumor inhibition benefits in intracranial xenograft mouse models.

Citation Format: Jianwen Dong, Emmanuel Martinez-Ledesma, Nghi Nguyen, Shaofang Wu, Yuji Piao, Ningyi Tiao, Soon Young Park, David Brunell, Clifford Stephan, Roel Verhaak, Erik Sulman, Veerakumar Balasubramaniyan, John F. de Groot. High-throughput screening of glioma stem-like cells (GSCs) identifies synergistic therapeutic combination of FGFR inhibitor and CDK4/6 inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4819.

Abstract 2945: Arsenic trioxide sensitizes glioma stem cells to brain penetrant PI3K and mTOR inhibitor GDC-0084

Glioblastoma is the most aggressive primary malignant brain tumor with few effective therapies. The current study evaluated arsenic trioxide (As2O3, ATO), a small-molecular agent that inhibits tumor growth via promoting promyelocytic leukemia protein (PML) degradation, in combination with multiple PI3K/mTOR inhibitors using high-throughput screening (HTS) to validate if ATO reverses glioblastoma resistance to PI3K/mTOR-targeted therapy. Quantitative single-agent and 2-drug combinations (5 drug doses, maximal concentration of 1 uM of each agent) were evaluated in 20 patient-derived glioma stem-like cells (GSCs). ATO was applied as an “anchor” drug and several mTOR and EGFR inhibitors as “probe” drugs to explore potential combination efficacy. Data from single-agent screening demonstrated that brain penetrant PI3K/mTOR inhibitor GDC-0084 potently inhibited cell viability with an IC50 ranging from 0.12μM to 5.78μM under normoxic conditions. Under hypoxic conditions, 10 of the 16 GSC cell lines remained sensitive, indicating less efficacy of GDC-0084 in the setting of a hypoxic microenvironment. Evaluation of drug combinations identified ATO and GDC-0084 as the most effective combination in vitro. ATO was synergistic with GDC-0084 in several GSCs resistant to GDC-0084 monotherapy. GSC sensitivity to GDC-0084 as single agent and in combination correlated with apoptosis, angiogenesis and PI3K/Akt pathways using gene set enrichment analyses (GSEA). In vitro combination treatment significantly inhibited PML, p-S6, p-AKT and p-mTOR expressions compared to single agent. In an orthotopic mouse model of glioma, targeting PI3K/mTOR with GDC-0084 prolonged the median survival to 81 days compared to 69 days in the control group. The efficacy of combining ATO and GDC-0084 in an orthotopic GSC mouse model is ongoing. Our studies confirm prior work demonstrating the efficacy of combining GDC-0084 with ATO, which now requires clinical validation.

Citation Format: Jianwen Dong, Emmanuel Martinez-Ledesma, Nghi Nguyen, Caroline Carrillo, Yuji Piao, Verlene Henry, Soon Young Park, Ningyi Tiao, Clifford Stephan, Roel Verhaak, Erik Sulman, Veerakumar Balasubramaniyan, John F. de Groot. Arsenic trioxide sensitizes glioma stem cells to brain penetrant PI3K and mTOR inhibitor GDC-0084 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2945.

Abstract 1122: MST4 phosphorylation of ATG4B regulates autophagic activity, tumorigenicity, and radio resistance in glioblastoma

Autophagy-mediated intracellular catabolism sustains the rapid growth of established tumors and tumors in response to multiple stresses including genotoxic/cytotoxic therapies. Here we identify and validate ATG4B, a key regulator that stimulates autophagic process by promoting autophagosome through reversible modification of ATG8 as a novel substrate of mammalian sterile20-like kinase (STK) 26/MST4 that is less known for its function in cellular process (none in autophagy) and unknown authentic substrates in cancer. We show that MST4 phosphorylates ATG4B at serine residue 383, which stimulates ATG4B activity and increases autophagic flux. Inhibition of MST4 or ATG4B activities suppresses autophagic process and the tumorigenicity of glioblastoma (GBM) cells. Furthermore, radiation induces MST4 expression, ATG4B phosphorylation and autophagy. Inhibiting ATG4B in combination with radiotherapy in treating mice with intracranial GBM tumor xenografts markedly slows tumor growth and provides significant survival benefit to animal subjects. This study not only describes a novel regulatory mechanism by which the MST4-ATG4B axis accelerates autophagic process, regulates GBM tumorigenicity, and responses to radiotherapy (RT), but also explores imminent clinical utility of combination of ATG4B inhibition with RT to suppress orthotopic GBM tumor xenografts. This study should prove generalizable to other types of cancer and have positive impacts in advancing our knowledge of cancer biology and designing new cancer treatments.

Citation Format: Tianzhi Huang, Chung Kwon Kim, Angel A. Alvarez, Rajendra P Pangeni, Xuechao Wan, xiao song, Taiping shi, Yongyong Yongyong, Namratha Sastry, Craig Horbinski, Songjian Lu, Roger Stupp, John Kessler, Ryo Nishikawa, Ichiro Nakano, Erik Sulman, Xinghua Lu, Charles David James, Xiao-Ming Yin, Bo Hu, Shi-Yuan Cheng. MST4 phosphorylation of ATG4B regulates autophagic activity, tumorigenicity, and radio resistance in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1122.

The polo-like kinase 1 inhibitor volasertib synergistically increases radiation efficacy in glioma stem cells

Background

Despite the availability of hundreds of cancer drugs, there is insufficient data on the efficacy of these drugs on the extremely heterogeneous tumor cell populations of glioblastoma (GBM).

Results

The PKIS of 357 compounds was initially evaluated in 15 different GSC lines which then led to a more focused screening of the 21 most highly active compounds in 11 unique GSC lines using HTS screening for cell viability. We further validated the HTS result with the second-generation PLK1 inhibitor volasertib as a single agent and in combination with ionizing radiation (IR). In vitro studies showed that volasertib inhibited cell viability, and high levels of the anti-apoptotic protein Bcl-xL expression were highly correlated with volasertib resistance. Volasertib sensitized GSCs to radiation therapy by enhancing G2/M arrest and by inducing apoptosis. Colony-formation assay demonstrated that volasertib plus IR synergistically inhibited colony formation. In intracranial xenograft mouse models, the combination of volasertib and radiation significantly inhibited GSC tumor growth and prolonged median survival compared with radiation treatment alone due to inhibition of cell proliferation, enhancement of DNA damage, and induction of apoptosis.

Conclusions

Our results reinforce the potential therapeutic efficacy of volasertib in combination with radiation for the treatment of GBM.

Methods

We used high-throughput screening (HTS) to identify drugs, out of 357 compounds in the published Protein Kinase Inhibitor Set, with the greatest efficacy against a panel of glioma stem cells (GSCs), which are representative of the classic cancer genome atlas (TCGA) molecular subtypes.