Suggestions for Escaping The Dark Ages for Pediatric Diffuse Intrinsic Pontine Glioma Treated with Radiotherapy: Analysis of Prognostic Factors From The National Multicenter Study

Purpose This multicenter retrospective study aimed to investigate prognostic factors for survival, encompassing clinical and radiologic features and treatments, in newly diagnosed diffuse intrinsic pontine glioma (DIPG) patients treated with radiotherapy. Methods Patients <30 years of age who underwent radiotherapy as an initial treatment for DIPG between 2000 and 2018 were included; patients who did not undergo an MRI at diagnosis and those with pathologically diagnosed grade I glioma were excluded. We examined medical records of 162 patients collected from 10 participating centers in Korea. The patients’ clinical and radiological variables, molecular and histopathologic data, and treatment response were evaluated to identify the prognosticators for DIPG and estimate survival outcomes. Results The median follow-up period was 10.8 months (interquartile range, 7.5–18.1). The 1- and 2-year overall survival (OS) rates were 53.5% and 19.0%, respectively, with a median OS of 13.1 months. Long term survival rate (≥2 years) was 16.7%, and median OS was 43.6 months. Age (<10 years), poor performance status, treatment before 2010, and post-radiotherapy necrosis were independent prognostic factors related to poor OS in the multivariate analysis. In patients with increased post-radiotherapy necrosis, the median OS was 13.3 months for bevacizumab group and 11.4 months for no-bevacizumab group (P = 0.138). Conclusion Therapeutic strategy for DIPG has remained unchanged over time, and its prognosis remains poor. Our findings suggest that appropriate efforts are needed to reduce the occurrence of post-radiotherapy necrosis. Further well-designed clinical trials are recommended to improve the poor prognosis observed in DIPG patients.

In diffuse intrinsic pontine gliomas, non-coding RNA expression is significantly varied dependent on overall survival

Diffuse intrinsic pontine glioma is a kind of pediatric brain cancer that kills 99 percent of patients within five years and for which there are no conventional chemotherapies. It is crucial for new treatments to comprehend the cancer's transcriptional activity. Using a published dataset, we compared the transcriptomes of tumors from patients who lived longer or less than six months. Among the genes whose expression changed most, we observed that numerous microRNAs and snoRNAs were present. The publication's findings are the first evidence of variable levels of non-coding RNA expression in diffuse intrinsic pontine glioma.

CTNI-56. EVALUATING DRUG DISTRIBUTION IN CHILDREN WITH DIFFUSE INTRINSIC PONTINE GLIOMA (DIPG) TREATED WITH CONVECTION ENHANCED DRUG DELIVERY

BACKGROUND There is currently no method for evaluating drug distribution and tumour coverage using the convection-enhanced drug delivery (CED) technique in Diffuse Intrinsic Pontine Glioma (DIPG). AIMS To determine an imaging protocol that can be used to assess the distribution of infusate in children with DIPG treated with CED of carboplatin and sodium valproate. METHODS 12 children with DIPG received between 4–18ml of infusate, through 2 pairs of catheters to encompass tumour volume on 2 days. Volumetric T2W and Diffusion Weighted Imaging (DWI) MRI sequences were performed before and after the first cycle of CED therapy and Apparent Diffusion Coefficient (ADC) maps were calculated. The tumour volume pre and post CED was automatically segmented (ITKSnap) on T2W and ADC on the basis of signal intensity. The ADC maps pre and post infusion were registered and subtracted (FSL) to visualize the infusate distribution. RESULTS ADC and T2W demonstrated a significant (&lt; 0.001) change in mean tumour volume post-infusion (mean ADC volume pre: 19.8ml, post 24.4ml; mean T2W volume pre 19.4ml, post 23.4ml). A significant correlation (p&lt; 0.001) was observed for the difference in tumour volume and the actual infused volume (ADC, r=0.76, T2W, r=0.70). There was a significant increase (p&lt; 0.001) in mean ADC and mean T2W signal intensity ratio post-infusion, no significant correlation with infusion volume. Finally, pixel-by-pixel subtraction of the ADC maps pre and post infusion visually demonstrated high signal intensity, presumed infusate coverage of the tumour. CONCLUSIONS ADC and T2W MR sequences could potentially be used to evaluate the volume of distribution of infusate delivered by CED, paramount to ensure tumour coverage and leading to more effective therapy evaluation. This will facilitate the use of CED in future clinical trials.

EXTH-58. THERAPEUTIC HDAC INHIBITION IN HYPERMUTANT DIFFUSE INTRINSIC PONTINE GLIOMA

Diffuse intrinsic pontine glioma (DIPG) continues to carry a dismal prognosis despite a growing understanding of its epigenetic regulation. While generally reclassified as diffuse midline glioma, H3 K27M-mutant (DMG), a subgroup of DIPGs do not harbor the classic histone mutation, with a further subset exhibiting a hypermutant phenotype. To evaluate whether hypermutant DIPG shares transcriptional vulnerabilities with H3K27M-mutant DMG, we screened a biopsy-derived treatment-naive PMS2 mutant DIPG model (PBT-24FH) for sensitivity to a panel of HDAC inhibitors (HDACi). In vitro evaluation of cell viability revealed the low nanomolar IC50 of quisinostat (50nM) and romidepsin (2nM). Dose-dependent increases in H3 acetylation and c-PARP were confirmed by western blot. Despite romidepsin’s superior potency in vitro, quisinostat demonstrated greater efficacy in an in vivo PBT-24FH flank study. 42 days following drug initiation, quisinostat-treated mice displayed dramatic tumor regression (mean volume= 33mm3, n= 7) compared to mice treated with romidepsin (mean volume= 669mm3, n= 7)(p= 0.005), or vehicle (mean volume= 990mm3, n= 6)(p&lt; 0.001). Immunohistochemistry of quisinostat-treated tumors revealed few residual tumor cells displaying a low proliferative index. To evaluate cross-resistance, romidepsin-treated mice (mean volume= 1158mm3, n= 2) were switched to quisinostat treatment and displayed swift tumor regression (mean volume after 25 days of quisinostat= 419mm3), emphasizing quisinostat’s in vivo cytotoxic effect against both large tumors and tumors previously treated by another HDACi. To evaluate quisinostat’s effect on other hypermutant tumors, we tested HCT-116, a colon cancer cell line bearing a biallelic MLH1 deletion and observed similar cytotoxicity. We also aim to repeat these studies utilizing additional pediatric hypermutant high grade glioma models. Transcriptomic and proteomic investigations are underway to identify the mechanism of action underlying quisinostat-induced cytotoxicity. Ultimately, we are the first to demonstrate in vivo efficacy of the HDACi quisinostat against hypermutant DIPG, supporting further investigation and clinical advancement.

TAMI-80. CELLULAR METABOLISM IN DIFFUSE INTRINSIC PONTINE GLIOMA

Diffuse intrinsic pontine glioma (DIPG) is an aggressive form of brain tumor in children, comprising &gt;10% of all pediatric brain tumors. The median survival after diagnosis is &lt; 1 year. Since DIPG tumors infiltrate brainstem and pons, they are inoperable. Currently radiotherapy is the mainstay of treatment, and there is a great need for novel therapies for the treatment of DIPG. Cellular metabolism plays a key role in carcinogenesis, unravelling active metabolic pathways in DIPG would help in developing targeted therapies. Glucose and glutamine are the two major nutrients necessary for the growth and proliferation of cancer cells. In this study, we have investigated the glucose and glutamine metabolism in SF8628 DIPG cells using 1H/13C NMR and GC-MS based metabolic flux analysis. SF8628 cells were grown in DMEM containing 11.0 mM glucose, supplemented with 10% FBS, and 2.0 mM glutamine at 37 °C under humidified air and 5% CO2. When cells reached confluency (replicates = 4), treated with 11.0 mM [U-13C]glucose or 4.0 mM glutamine in DMEM (supplemented with 10% FBS). After 24 h, cells were harvested for NMR/GC-MS analysis. The 13C-isotopomer analysis revealed that SF8628 cells produced 25.26 ± 10.63% acetyl-CoA from [U-13C]glucose which is ~3.7 times higher than that produced from GBM cells (6.83 ± 0.76%; our previous work), suggesting that DIPGs are metabolically very active. [U-13C]glutamine metabolism showed that DIPG cells also have an active TCA cycle metabolism (citrate M+4; 40.07 ± 1.06%) and moderately active reductive carboxylation pathway (citrate M+5; 10.59 ± 1.13%). Inhibition of both glycolytic and glutaminolysis pathways will be valuable in developing treatment strategies for DIPGs and these studies are in progress.

DDRE-07. TARGETING TUMOR HYPOXIA AND MITOCHONDRIAL METABOLISM WITH ANTI-PARASITIC DRUGS AS AN APPROACH TO IMPROVE THE RADIOSENSITIVITY OF DIFFUSE INTRINSIC PONTINE GLIOMA

Diffuse intrinsic pontine glioma (DIPG) is an incurable pediatric brain tumor with a median survival of 12 months. Current management is limited to radiotherapy; however, the tumor recurs secondary to radioresistance. Tumor hypoxia appears to be one of the major contributors to radioresistance of DIPG, as oxygenation is critical to successful radiotherapy treatment. Therefore, strategies to alleviate hypoxia could enhance the effectiveness of radiotherapy and result in improved survival outcomes of patients with DIPG. Recent approaches to target tumor hypoxia are predicated on inhibiting mitochondrial respiration of the tumors to decrease oxygen consumption rate (OCR) and increase oxygenation. Here, we aimed to identify a safe but potent mitochondrial inhibitor that could decrease OCR and hypoxia, and improve the radiosensitivity of DIPG. A subset of anti-parasitic drugs (atovaquone, ivermectin, quinacrine, mefloquine and proguanil) which are known mitochondrial inhibitors were studied against a panel of patient-derived DIPG cell lines. We assessed their antiproliferative effects, OCR inhibition and radiosensitising efficacy using cell proliferation, extracellular flux and colony formation assays. Among the five tested drug candidates, atovaquone was found to be the most potent OCR inhibitor with minimal antiproliferative effects on DIPG cultures. It also decreased hypoxia in 3-dimensional DIPG neurospheres, reduced the expression of hypoxia-inducible factor-1α and improved the radiosensitivity of neurospheres of DIPG. Its anti-mitochondrial role was further confirmed by inhibition of various mitochondrial parameters and increase in reactive oxygen species. Overall, these results provide promising in vitro evidence of atovaquone as a hypoxia modifier and radiosensitiser in DIPG and pave a way for rapid translation to in vivo studies.

RTID-06. TRENDS IN INTERNATIONAL INVESTMENT IN CHILDHOOD, ADOLESCENT AND YOUNG ADULT (CYA) BRAIN TUMOR RESEARCH 2006-2018, WITH A FOCUS ON DIFFUSE INTRINSIC PONTINE GLIOMA (DIPG)

Organizations funding brain tumor research want to identify gap areas for funding individually or in collaboration and want to better understand existing project focus to maximize new project investments. The International Cancer Research Partnership and the US Coalition Against Childhood Cancer used international research portfolio data to assess the landscape of CYA brain tumor research. From 2006-2018, investment for brain tumor research increased from $13m to $73m, and as a percentage of the CYA portfolio, brain tumor research received the highest percent investment (30%) in 2018. Research into treatment had risen (from $6m to $38m) as had research into biology (from $3m to $19m) - an essential foundation for more future personalized treatments. Given the lifelong impact on survivors it was encouraging that survivorship research investment had also started to increase. While 5-year survival for CYA cancers is now over 80%, survival for Diffuse Intrinsic Pontine Glioma (DIPG) remains very low. To assess capacity for future progress, several indicators were considered. The number of new DIPG projects per year increased from an average of 3 per year (2006-2012) to 11 (2013-2018) and funding increased from $0.5m (2006) to $10m (2018). Also, by 2018, 9 projects included a training component to build future research capacity. The number of laboratories researching DIPG increased from 2 in the US (2006) to 53 institutions in 6 countries (2018). Recent years had seen increased funding for pre-clinical models essential for identifying new targets. Collaborative initiatives such as DIPG-Open and DIPG-All had been funded to collect biological samples and accelerate translation of therapeutics to the clinic. Despite evidence that 5-year survival had improved from 1% to 2%, clearly major advances need to be made in new treatments, and monitoring the funding landscape carefully to make strategic investments will be essential.

CTIM-08. SAFETY, EFFICACY, AND SURVIVAL RESULTS FROM A PHASE 1 STUDY OF THE ONCOLYTIC ADENOVIRUS DNX-2401 FOLLOWED BY STANDARD OF CARE RADIOTHERAPY FOR NEWLY DIAGNOSED DIFFUSE INTRINSIC PONTINE GLIOMA (DIPG)

BACKGROUND Diffuse intrinsic pontine glioma (DIPG) is the most lethal pediatric brain tumor. Median overall survival (OS) with standard of care radiation therapy (RT) is approximately 8-10 months and 2-year survival is &lt; 10%. A Phase 1 single-center study was conducted to evaluate the oncolytic adenovirus, DNX-2401 (tasadenoturev), followed by RT for DIPG. METHODS Newly-diagnosed DIPG patients 1-18 years old received a tumor biopsy through the cerebellar peduncle followed by intratumoral injection of 1e10 – 5e10 vp DNX-2401 and conventional RT 1-3 weeks later. RESULTS Subjects were enrolled (n=12) from December 2017 to January 2020 and had a median age of 9 years (range 3-18) and Lansky/Karnofsky performance scores of 90-100 (n=4; 33%) or 70-80 (n=8; 67%). Genetic assessment was completed for 11 subjects (92%) and histone 3 K27M mutations were identified in 10 subjects, including H3F3A (n=8), HIST2H3C (n=1), and HIST1H3B (n=1); 1 subject was H3 wildtype (n=1). TP53 mutations were identified in 5 subjects (42%). DNX-2401 was administered followed by RT (n=11; 92%). No dose-limiting toxicities were observed and the treatment regimen was well-tolerated. The most commonly reported adverse events (≥ 5 subjects), regardless of study drug relationship, include asthenia, headache, vomiting, pyrexia, and neurological deterioration. Three serious adverse events were reported including grade 3 abdominal pain, grade 3 lymphopenia, and grade 3 clinical deterioration. Tumor reductions were reported for 9 subjects (75%), including 2 confirmed (17%) and 2 unconfirmed (17%) responses per RAPNO criteria. As of the data cutoff, median OS is 19.7 months and OS-24 is 32% with follow-up ongoing for 3 subjects (26.9, 25.6, 13.7 months). CONCLUSIONS DNX-2401 followed by RT can be safely administered to DIPG. Survival outcomes are encouraging, thus warranting further evaluation in a Phase 2 study.