Elucidating cellular response to treatment with viral immunotherapies in pediatric high-grade glioma and medulloblastoma

HSV G207, a double-stranded, DNA virus, and the polio:rhinovirus chimera, PVSRIPO, a single positive-strand RNA virus, are viral immunotherapies being used to treat pediatric malignant brain tumors in clinical trials. The purpose of this work is to elucidate general response patterns and putative biomarkers of response. Multiple pediatric high-grade glioma and medulloblastoma cell lines were treated with various multiplicities of infection of G207 or PVSRIPO. There was a significant inverse correlation between expression of one HSV cellular receptor, CD111, and the lethal dose of 50% of cells (LD50) of cells treated with G207 (r = -0.985, P<0.001) but no correlation between PVSRIPO cellular receptor expression (CD155) and LD50. RNA sequencing of control cells and cells treated for 8 and 24 h revealed that there were few shared differentially expressed (DE) genes between cells treated with PVSRIPO and G207: GCLM, LANCL2, and RBM3 were enriched whilst ADAMTS1 and VEGFA were depleted. Likewise, there were few shared DE genes enriched between medulloblastoma and high-grade glioma cell lines treated with G207: GPSM2, CHECK2, SEPTIN2, EIF4G2, GCLM, GDAP1, LANCL2, and PWP1.  Treatment with G207 and PVSRIPO appear to cause disparate gene enrichment and depletion suggesting disparate molecular mechanisms in malignant pediatric brain tumors.

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.

STEM-21. REPURPOSING CLEMASTINE TO SUPPRESS GLIOBLASTOMA STEM CELLS

Glioblastoma stem cells (GSCs), also known as brain tumor initiating cells (BTICs), drive tumor progression, heterogeneity, and resistance to treatments, posing formidable challenges to advancing effective treatments against glioblastoma (GBM). We postulated that inducing BTIC differentiation can serve as a solution to diminishing their stem-like features. Here, we report that clemastine, an over-the-counter oral medication for allergy relief, attenuates stemness and proliferation of BTICs. These effects of clemastine were accompanied by altered transcriptional programs suggestive of a shift from maintaining stem cell identity to differentiation, resonating with the ability of clemastine to promote oligodendrocyte precursor cell (OPC) differentiation to mature oligodendrocytes. Genetic perturbation and small-molecule inhibition of putative pharmacological targets of clemastine revealed that Emopamil-binding protein (EBP), an enzyme in the sterol biosynthesis pathway, played a pivotal role in mediating the differentiating and anti-tumor effects of clemastine. Notably, loss-of-function assays showed that EBP expression was indispensable for BTIC propagation. In contrast, overexpression of EBP stimulated BTIC proliferation, thus uncovering a previously unknown role of sterol metabolism in BTIC maintenance. Finally, we demonstrated that a mouse neural stem cell-derived glioma model was similarly susceptible to clemastine treatment. Taken together, our study identifies pathways essential for the perpetuation of stemness in GBM, and implicates a non-oncology drug with a well-established safety profile that can be repurposed to mitigate the stem-like properties of GBM.

PATH-22. CLINICAL FEATURES AND MOLECULAR CHARACTERIZATION OF LEPTOMENINGEAL DISEASE IN PATIENTS WITH HIGH GRADE GLIOMA

INTRODUCTION

Leptomeningeal disease (LMD) is a challenging complication of high grade glioma (HGG) and critical questions remain unanswered regarding clinicopathologic risk factors, molecular associations, and optimal treatment.

METHODS

Patients with molecularly-profiled HGG (Caris Life Sciences; Phoenix, AZ) with LMD at two institutions were included. Medical records were reviewed for clinicopathological characteristics, treatment, and outcome. Kaplan-Meier estimates of patient survival were performed on censored data using Cox’s proportional hazard model.

RESULTS

43 patients (male: 33, female: 10; median age: 56 years) were identified, comprising 41 grade 4 (glioblastoma: 38; gliosarcoma: 2; H3K27M diffuse midline glioma: 1) and 2 grade 3 tumors (astrocytoma: 1; pleomorphic xanthoastrocytoma: 1). LMD diagnosed at HGG diagnosis (n=18) versus recurrence (n=22) was associated with longer post-LMD survival [pLMD-OS: 15.3m vs. 4.8m, HR: 0.07, 95% CI: 0.02-0.29, p=0.0004] but similar overall survival [mOS: 15.3m vs. 12.3m; HR: 0.82; 95% CI: 0.36-1.85; p=0.63]. Pathology-diagnosed LMD (n=15) versus MRI-diagnosed LMD (n=26) was associated with longer post-LMD survival [pLMD-OS: 15.4m vs. 5.2m, HR: 14.9, 95% CI: 0.01-0.30, p=0.0004] but similar overall survival [mOS: 17.1m vs. 12.3m; HR: 0.66; 95% CI: 0.3-1.58; p=0.38]. Post-LMD survival was significantly prolonged for supratentorial (n=28) versus infratentorial/spinal (n=4) locations regardless of the diagnostic modality [pLMD-OS: 2.6m vs. 11.3m, HR: 14.4, 95% CI: 2.73-75.7, p=0.0017], and did not significantly differ between symptomatic (n=20) and asymptomatic (n=23) patients [pLMD-OS: 4.8m vs. 11.2m, HR: 1.75, 95% CI: 0.82-3.77, p=0.15). pTERT mutation (81%), EGFR amplification (43%), and MGMT methylation (33%) were prevalent but IDH1 mutation was rare (2.8%). Comparison with a separate glioblastoma cohort (n=1400) suggested more frequent amplification of CHIC2, MDM4, and KDR, higher mutation rates of RUNX1, APC, and RAD51C, colder tumor microenvironment (TME), and lower expression of immune checkpoint-related genes.

CONCLUSIONS

Clinicopathological characteristics affect post-LMD survival, and cohort comparison suggests molecular and TME differences in LMD-HGG tumors.

TMIC-10. IDENTIFICATION, VALIDATION AND BIOLOGICAL CHARACTERIZATION OF NOVEL GLIOBLASTOMA TUMOUR MICROENVIRONMENT SUBTYPES: IMPLICATIONS FOR PRECISION IMMUNOTHERAPY

New precision medicine therapies are urgently required for glioblastoma (GBM). However, to date, efforts to subtype patients based on molecular profiles, have failed to direct treatment strategies. We hypothesized that interrogation of the GBM tumor microenvironment (TME) and identification of novel TME-specific subtypes could inform new precision treatment strategies. To this end, a refined and validated microenvironment cell population (MCP)-counter method was applied to &gt; 800 GBM patient tumours and validated by multiplex-immunohistochemistry. The MCP-counter deconvolution method interrogates the TME composition from transcriptomic data. Using this refined method, we classified the GLIOTRAIN(www.gliotrain.eu) IDHwt GBM cohort (n=123) into 3 novel clusters characterised by differences in TME composition and subsequently validated findings in the TCGA (n=69), CGGA (n=72) and DUKE (unpublished)(n=162) cohorts. TMEHigh tumours (30%) displayed elevated immune populations, functional orientation markers, immune checkpoint genes, and upregulated immunoregulatory pathways. Moreover, tertiary lymphoid structures were a feature of TMEHigh/mesenchymal+ patients. TMEMed (46%) tumours displayed heterogeneous immune populations and upregulated neuronal signalling pathways. TMELow (24%) tumours represented an ‘immune-desert’ group, high EGFR mutation frequency and upregulated EGFR signalling pathways. Longitudinal analysis of the GLASS cohort revealed TME-subtype transitions upon recurrence, influenced by TME composition changes. Finally, assessment of three GBM immunotherapy clinical trial cohorts revealed that TMEHigh patients treated with neo-adjuvant anti-PD1 have a significantly improved survival (P=0.04). Moreover, TMEHigh patients treated with anti-PD1 and an oncolytic virus (PVSRIPO) in the adjuvant setting, showed a trend towards improved survival (P=0.15 and P=0.056 respectively). Overall, we have established a novel TME-based classification system for application in intracranial malignancies. This system may be used to better inform a precision targeting approach in the brain tumour setting. For example, we hypothesise that patients bearing TMELow tumours may be amenable to neoadjuvant anti-TIM3 + EGFR inhibitor, TMEMed to anti-angiogenic immunotherapy, and TMEHigh patients to neoadjuvant anti-PD1 + anti-CTLA4.

CTIM-15. RESULTS OF A PHASE IB TRIAL OF RECOMBINANT POLIO:RHINOVIRUS IMMUNOTHERAPY FOR RECURRENT PEDIATRIC HIGH GRADE GLIOMA

BACKGROUND

Outcomes of recurrent pediatric high grade glioma (pHHG) are poor with a median overall survival (OS) of &lt; 6 months. Viral immunotherapy such as the polio:rhinovirus chimera, PVSRIPO, is a novel treatment approach for recurrent pHHG. PVSRIPO is genetically engineered to prevent neurovirulence. In adults with recurrent glioblastoma treated with PVSRIPO, 21% survived &gt; 36 months. The poliovirus receptor, CD155, is ubiquitously expressed in malignant pediatric brain tumors including pHHG.

METHODS

The primary objective of this Phase 1b clinical trial was to evaluate the safety and feasibility of PVSRIPO for recurrent pHGG. PVSRIPO was given at a single dose, 5x107 50% tissue-culture infectious dose (TCID50) administered by convection enhanced delivery (CED) to children with biopsy-confirmed recurrent pHHG between ≥ 1 and ≤ 5.5 in diameter. 3 mL of PVSRIPO was delivered at 0.5 mL/hr via a single catheter.

RESULTS

Eight patients were treated with PVSRIPO including 5 males and 3 females with a median age of 16.5 (range 9-19). Six patients had recurrent glioblastoma, 2 had recurrent anaplastic astrocytoma. The median number of previous recurrences prior to enrollment was 3.5 (range 1-5). Four patients received bevacizumab on-study for treatment-related peritumoral inflammation/edema. Six of 8 patients experienced 26 treatment related adverse events (AEs) possibly, probably, or definitely related to protocol treatment. There were no Grade 4 or 5 AEs. There were 3 Grade 3 AEs: 2 headaches and 1 seizure. There were no AEs related to biopsy or CED catheter insertion/removal. Median OS was 4.13 months (range 1.23-NA). One patient is currently alive at &gt; 21 months. Monocyte and T cell inflammatory phenotypes and total CD4+ T cells were increased in peripheral blood after treatment.

CONCLUSIONS

CED of PVSPRIO is both safe and feasible for the treatment of recurrent pHHG. Histologic correlative results will also be presented.

IMMU-43. CXCR3 SIGNALING ENGAGES GLIOMA INFILTRATING T CELLS AND IS REQUIRED FOR THE ANTITUMOR EFFICACY OF INNATE STIMULATING IMMUNOTHERAPY

BACKGROUND

T cell dysfunction is well documented in patients with gliomas, yet mechanisms explaining T cell dysfunction in gliomas are lacking. Recent evidence links CXCR3 signaling and functional immune surveillance in both preclinical models and human data sets.

METHODS

Bulk and single cell RNA-seq data sets were used to compare CXCR3 ligand expression in gliomas to that of other solid tumor types. The role of CXCR3 signaling in mediating the recruitment and phenotype of tumor infiltrating lymphocytes (TILs) was tested using CXCR3 blockade and genetic deletion of CXCR3 in murine tumor models. The capacity of relevant innate stimulating immunotherapies to induce CXCR3 ligands in human glioma tissue was assessed using an ex vivo glioma slice culture assay, and the contribution of CXCR3 signaling to polio virotherapy (PVSRIPO) and STING agonist therapy was tested in murine models.

RESULTS

Relative to other solid tumors, gliomas express significantly lower levels of CXCR3 ligands (CXCL9, 10, and 11), which are largely expressed by tumor associated myeloid cells. Blocking CXCR3 signaling profoundly restricted TIL recruitment in murine gliomas, and resulted in decreased TIL stemness features coinciding with exacerbated exhaustion phenotypes. Polio virotherapy and STING agonism efficiently induced CXCR3 ligand production in fresh human glioma tissue in a manner dependent upon myeloid cells, and at levels similar to that induced by the same agents in melanoma and breast cancer tissue. CXCR3+ TILs expressed higher levels of memory and activation markers, proliferated more, and were required for the antitumor efficacy of both polio virotherapy and a STING agonist in mice.

CONCLUSION

This work indicates that CXCR3 signaling, a key contributor to cancer immune surveillance, is disrupted in human gliomas relative to other solid tumor types. Intratumor virotherapy and STING agonists hold potential to rectify diminished CXCR3 ligand expression in gliomas.

DNAR-08. THE ROLE OF SMARCAL1 AS A SYNTHETIC LETHAL VULNERABILITY IN ATRX-DEFICIENT GLIOMAS

Mechanisms to maintain telomere length over successive cell divisions are a requirement for cancer cell immortalization. Although many cancers maintain telomere length through the activation of telomerase, ~10-15% of human cancers use telomerase-independent mechanisms of telomere maintenance, termed Alternative Lengthening of Telomeres (ALT). In gliomas, the ALT phenotype is associated with loss-of-function mutations in the ATRX gene in IDH-mutant astrocytomas, adult and pediatric glioblastomas (GBM), high-grade astrocytomas with piloid features, and pleomorphic xanthoastrocytomas. In adult GBM, we previously identified a relatively rare subset of ALT-positive ATRX wildtype tumors that harbored loss-of-function mutations in the SMARCAL1 gene, and we found that loss of SMARCAL1 activity plays a causative role in the onset of ALT in these tumors. SMARCAL1 is an annealing helicase that localizes to sites of DNA damage and replication stress and catalyzes the reversal of stalled replication forks. To better understand the relationship between ATRX mutations, SMARCAL1 activity, and the ALT phenotype, we investigated the localization and function of SMARCAL1 in ALT-positive glioma cells and xenografts with native ATRX deficiency. We found that SMARCAL1 localizes to ALT-associated PML bodies in astrocytoma cell lines with concurrent ATRX and IDH1 mutations (derived from grade 3 and 4 tumors). Our data show that inducible suppression of SMARCAL1 via doxycycline-induced RNAi leads to increased DNA double-strand breaks, increased abundance of extrachromosomal telomeric repeats (c-circles), and increased sensitivity to irinotecan, a topoisomerase I inhibitor. In an orthotopic mouse model, SMARCAL1 depletion exhibited a chemosensitizing effect in combination with irinotecan against a patient-derived xenograft (astrocytoma, IDH-mutant Grade 4). Based on these data, we hypothesize that SMARCAL1 activity is critical for resolving ALT-associated replication stress in ATRX-deficient malignant gliomas. We therefore propose that SMARCAL1 functions as a synthetic lethal vulnerability in ATRX-deficient ALT-positive gliomas and that SMARCAL1 inhibition is a viable therapeutic strategy in these tumors.

BIOM-43. THE GENOMIC, TRANSCRIPTOMIC, AND EPIGENOMIC LANDSCAPE OF ISOCITRATE DEHYDROGENASE WILD TYPE GLIOBLASTOMA ACROSS THE AGE CONTINUUM

BACKGROUND

Older age is a poor prognostic factor for glioblastoma (GBM) patients. We tested whether the intrinsic molecular landscape of the tumor may contribute to this poor prognosis.

METHODS

In accordance with the 2021 WHO classification scheme, we included only isocitrate dehydrogenase (IDH) wild type GBM. Based on published literature, we defined older as age &gt; 65. RNA expression, gene amplification, tumor mutational burden (TMB) and mutational profiles were analyzed in three unique datasets: Tempus (n = 1,410), Caris (n = 1,432), and TCGA (n = 557). Comparison were made between &lt; 65 and ³ 65 year olds using Pearson’s Chi-squared tests, Fisher’s exact tests, or Wilcoxon rank-sum where appropriate.

RESULTS

From our evaluable gene sets, TERT promoter mutations were more prevalent in patients ³ 65 years old (Caris 82.64 vs 77.27%, p = 0.016; Tempus 58.0 vs 49.0%, p = 0.002). There were no significant differences in PDCD1, CD274, CD3E, TNFRSF18, CD40, CD8A, TNFRSF4, CTLA4, HAVCR2, TNFSF9, CD274, or CDKN2A; PDL-1 (by IHC); dMMR/MSI-H, TMB; CDK6 amplification, EGFR amplification, EGFR, EGFRvIII, EGFR fusions, MET fusions, PTEN, TP53, or NF-1. MGMT promoter methylation (Caris data) was more common in the older group (49.73 v 34.14%, p &lt; 0.001). TGCA data demonstrated that gene expression, TMB, and methylation did not change significantly with age. Additionally, PCOLCE2 and SLC10A4 were differentially methylated, and missense mutations, of any type, were more common in the older group (p=0.006).

CONCLUSION

Despite worse survival outcomes for older patients with IDHwt GBM as compared to younger counterparts, the molecular landscape is similar at the genomic, transcriptomic and epigenomic levels. The key exception is TERT promoter mutations that are more common in older GBM patients. Poorer survival is therefore not likely to be attributable solely to intratumoral factors.

CTIM-24. NUTMEG: A RANDOMIZED PHASE II STUDY OF NIVOLUMAB AND TEMOZOLOMIDE VERSUS TEMOZOLOMIDE ALONE IN NEWLY DIAGNOSED ELDERLY PATIENTS WITH GLIOBLASTOMA

BACKGROUND

Nivolumab is a PD-1 inhibitor with known safety profile. An increase in mutations as we age is well documented in glioblastoma and other cancers. Higher mutational load is associated with increased response to nivolumab in extracranial malignancies. NUTMEG examined the activity of nivolumab added to temozolomide in glioblastoma patients aged ≥ 65 years.

METHODS

NUTMEG was an international multicenter phase II trial for newly diagnosed glioblastoma patients aged ≥ 65 years, randomized 2:1 to experimental (40Gy/15 fractions with temozolomide 75mg/m2, then 6 cycles of temozolomide 150-200mg/m2 D1-5 Q28D + nivolumab 240mg D1,15 Q28D C1-4 and 480mg D1 Q28D C5-6) versus standard arm (40Gy/15 fractions with temozolomide 75mg/m2, then 6 cycles of temozolomide alone 150-200mg/m2 D1-5 Q28D), stratified by age, ECOG status, MGMT status and resection extent.

RESULTS

103 patients were enrolled (69 in experimental arm, 34 in standard arm). Median age was 73 years, 36% ECOG 0, 57% MGMT-unmethylated and 51% gross macroscopic resection. Median follow-up is 31 months to date, with 77 deaths (surviving patients to continue follow-up and final results will be presented). Median overall survival was 11.8 months in the experimental arm versus 12.0 months in the standard arm (HR 0.95 95%CI 0.59-1.53 for experimental relative to control). Six-month progression-free survival rate using mRANO was 64% in the experimental arm versus 49% in the standard arm (HR 0.81 95%CI 0.51-1.26). Grade 3/4 adverse events were reported in 46% of experimental arm (7% lung infection, 7% thromboembolic events, 6% fatigue, 6% muscle weakness) and in 29% of control arm (9% fatigue, 6% seizure, 6% thromboembolic events).

CONCLUSIONS

There was insufficient evidence of clinical benefit with nivolumab in this population. No new safety signals were identified. Central imaging review is underway and correlative studies will characterize the immune landscape, including mutational load, neoantigen and other immune markers. NCT04195139.

CTIM-23. DOSE ESCALATION TRIAL OF FC-ENGINEERED ANTI-CD40 MONOCLONAL ANTIBODY (2141-V11) ADMINISTERED INTRATUMORALLY WITH D2C7-IT VIA CONVECTION-ENHANCED DELIVERY (CED) FOR RECURRENT MALIGNANT GLIOMAS (RMGS)

BACKGROUND

D2C7-IT, a novel immunotoxin-based cytotoxic therapy, targets epidermal growth factor receptor (EGFR) and mutant EGFR variant III. In preclinical studies, D2C7-IT kills tumor cells and prolongs survival, but is unable to generate cures in all animals. We hypothesized that immunosuppression in glioblastoma limits D2C7-IT efficacy. Eliminating glioblastoma immunosuppression via CD40 co-stimulation is anticipated to enhance D2C7-IT-induced antitumor responses. In murine glioma models, CED of D2C7-IT+αCD40 generated cures and long-term tumor-specific adaptive immunity. Hence, we are conducting a phase 1 trial of D2C7-IT+2141-V11 (αhuman-CD40) administered via CED in rMG patients.

METHODS

Eligibility includes adult patients with solitary supratentorial rMG (WHO grade 3/4); ≥ 4 weeks after chemotherapy, bevacizumab, or study drug; adequate organ function; and KPS ≥ 70%. Cohorts of 3 patients are treated with increasing doses of 2141-V11 to determine the maximum tolerated dose when administered sequentially following D2C7-IT (166,075 ng) via CED at 0.5 mL/hr. Five dose levels (DLs) are evaluated (2141-V11 at: #1: 0.70 mg; #2: 2.0 mg; #2**: 3.0 mg #2*: 4.0 mg; #3: 7.0 mg).

RESULTS

As of May 29, 2022, 13 patients were treated (3 patients on DL1, DL2, and DL2**; 2 patients on DL3 and DL2*). No dose-limiting toxicities were observed; however, lower DLs were added due to higher frequency of adverse events (AEs) expected with D2C7-IT+2141-V11 with DL3 and DL2* (fever, neurologic symptoms). All patients remain alive 0.7-10.6 months after therapy. Grade ≥ 2 AEs due to D2C7-IT+2141-V11 include: headache (grade 3, n = 1; grade 2, n = 4); pyramidal tract disorder (grade 3, n = 1; grade 2, n = 2); paresthesia (grade 3, n = 1); dysphasia (grade 3, n = 1); seizures (grade 2; n = 2); fever (grade 2; n = 2); and one each of grade 2 depressed level of consciousness, fatigue, and concentration impairment. Enrollment is ongoing.

CONCLUSIONS

Intratumoral administration of D2C7-IT+2141-V11 via CED is safe, encouraging efficacy results are observed.

BSCI-20 STING EPIGENETIC SILENCING IN GLIOMAS CAN BE RESCUED BY METHYLTRANSFERASE INHIBITION: IMPLICATIONS FOR NOVEL THERAPEUTIC APPROACHES

The stimulator of interferon genes (STING) is a key component of the innate immune response to pathogenic cytosolic DNA, resulting in IRF3- and NFκB-dependent transcription of type I interferons (IFN) and pro-inflammatory cytokines. STING activation primes endogenous antitumor immunity and is disrupted in a variety of cancers. Here we investigate STING signalling in glioblastoma (GBM) patient samples. STING agonist treatment of ex vivo gliomas leads to inconsistent induction of type I IFN responses that are restricted to tumor associated myeloid cells. Indeed, single-cell transcriptome and multiplex immunofluorescence analyses demonstrate that STING expression is suppressed in neoplastic cells but not tumor-associated immune cells or stroma. Methylation analyses reveal a STING promoter region that is highly methylated in bulk tumor samples from glioma and other neuroectoderm-derived cancers, but not in most extracranial cancers. Methylation in this region strongly correlates inversely with STING RNA expression. STING epigenetic silencing is also present in normal fetal and adult brains. We demonstrate that STING expression in glioma cell lines may be rescued by decitabine, a DNA methyltransferase inhibitor (DNMTi) that is commonly used to treat hematologic malignancies. However, transduction of a STING-expressing vector into these glioma cell lines is insufficient to reconstitute STING signalling, suggesting that additional decitabine-stimulated mechanisms are necessary for STING pathway rescue. Collectively, our results suggest that epigenetic silencing of STING occurs early in brain development and may provide an immunosuppressive context for the genesis of brain tumors. Furthermore, our work raises the potential of epigenetic modulation to reconstitute STING signalling as a therapeutic strategy for glioblastoma and potentially other STING-silenced, immunologically-cold cancers.

SPCR-03 NEUROCOGNITIVE OUTCOMES FROM PHASE 1 TRIAL OF BMX-001 IN COMBINATION WITH CONCURRENT RADIATION THERAPY AND TEMOZOLOMIDE IN NEWLY DIAGNOSED HIGH-GRADE GLIOMA PATIENTS

INTRODUCTION

Neurocognitive dysfunction can result from radiation therapy which is the mainstay of treatment for high-grade glioma, particularly glioblastoma. Preclinical observations found that BMX-001, a novel metalloporphyrin, acts as a radioprotectant for normal CNS cells yet as a radiosensitizer to cancer cells in human GBM xenograft experiments. In a phase 1 study evaluating the safety of BMX-001 in combination with concurrent radiation therapy and temozolomide, we further studied neurocognitive function before and after concurrent radiation therapy and temozolomide in newly diagnosed high-grade glioma patients.

METHODS

We performed a phase 1 study of BMX-001 combined with radiation therapy (6-week total of 59.4-60 Gy) and temozolomide (75 mg/m2/day for 42 days). We administered BMX-001 as a subcutaneous injection at a loading dose before radiation therapy and temozolomide and then subsequent doses twice weekly for eight weeks. A key secondary endpoint was the evaluation of neurocognition. We performed neurocognitive testing with the computerized program CNS Vital Signsâ. This battery consists of seven tests: verbal memory, visual memory, finger tapping, symbol digit coding, the Stroop Test, a test of shifting attention, and a continuous performance test. We defined neurocognitive impairment at baseline as a z-score ≥ 1.5 SDs below the normative mean. We described improvements or declines in neurocognition at 2 and 6 months from baseline.

RESULTS

Fifteen patients (age 19-80 years) enrolled and underwent neurocognitive testing before and after RT. All patients had WHO grade 4 glioblastoma. Most subjects had neurocognitive impairment ranging from 46.7-to 80% on specific neurocognitive tests. At two months (N=15) and six months (N=9), most testing demonstrated improved neurocognitive performance.

CONCLUSIONS

Neurocognitive function is maintained and can improve after concurrent radiation therapy and temozolomide in this high-grade glioma cohort treated with BMX-001 during concurrent radiation therapy and temozolomide.

RARE-22 Characterizing the landscape of structural variants in adamantinomatous craniopharyngioma

INTRODUCTION: Adamantinomatous craniopharyngiomas (ACPs) are rare brain tumors that primarily occur in children and impact long-term morbidity and mortality. The canonical driver mutation for ACP growth occurs in CTNNB1 and leads to constitutive activation of the Wnt/β-catenin signaling pathway. In this study, we outline the genomic, transcriptomic, and structural variant (SV) landscape in a cohort of 41 ACP samples. METHODS: We performed whole-genome sequencing (WGS) and RNA-sequencing of 41 ACP samples. Matched normal samples were also characterized by WGS. Mutect2 was used to detect single nucleotide variants (SNVs) and indels, and copy number data was generated using the GATK pipeline. SvABA was used to perform SV analysis and to identify significantly recurrent breakpoints and juxtapositions. DESeq2 was used to perform differential gene expression analysis based on clinical and molecular annotation data. RESULTS: 29/41 (70%) of the ACP samples harbored missense mutations in exon 3 of CTNNB1, all of which have previously been reported in ACP tumors. SV analysis identified a median of 11.5 events per tumor. Overall, 9.7% of events were interchromosomal. Of the remainder, the majority (78.6%) were deletions. No SVs occurred within CTNNB1. A positive correlation (r = 0.533) was observed between the frequency of SVs and SNVs within samples. Analysis of significantly recurring breakpoints (SRBs) did not identify recurrent breakpoint events. Differential gene expression analysis comparing samples with and without CTNNB1 variants identified 2,143 differentially expressed genes with q-value < 0.05. CONCLUSION: This study identifies activating mutations in exon 3 of CTNNB1 in a large cohort of ACP samples. We also integrate SV and transcriptomic data to comprehensively investigate ACP tumor genomes and identify putative novel tumorigenic mechanisms that advance our understanding of ACP biology.

EPCT-05. Phase Ib study of unesbulin (PTC596) in children with newly diagnosed diffuse intrinsic pontine glioma (DIPG) and high-grade glioma (HGG): A report from the COllaborative Network for NEuro-Oncology Clinical Trials (CONNECT)

BACKGROUND: The B-cell-specific Moloney murine leukemia virus integration site-1 (BMI-1) protein, implicated in self-renewal and DNA-damage signaling, is highly expressed in DIPG and HGG. Preclinically, BMI-1 modulation by unesbulin (PTC596 [which mediates hyperphosphorylation and subsequent degradation of BMI-1]) leads to DIPG/HGG cell proliferation blockade, mitotic abnormalities, and tumor cell sensitization to radiation-induced DNA damage. METHODS: This phase Ib study sought to determine the maximally tolerated dose/ recommended phase 2 dose (RP2D) of unesbulin administered concurrently with radiotherapy and adjuvantly in children with newly diagnosed DIPG or HGG. Patients were enrolled according to a Rolling-6 design and received oral unesbulin twice weekly during radiotherapy and as maintenance therapy. RESULTS: Twenty-seven patients enrolled (median age: 8.5 years [range: 2-18]), including 18 patients with DIPG and nine patients with HGG. Unesbulin was administered in capsule formulation in the first nine patients, then tablet formulation for subsequent patients. Within the capsule formulation group, three dose-limiting toxicities (DLTs) were observed in two patients on dose level 2 (grade 4 neutropenia). Within the tablet formulation group, four DLTs were experienced by three patients on dose level 2 (grade 3 ALT elevation, grade 3 dehydration/vomiting, grade 3 decreased ejection fraction, grade 4 neutropenia). Dose level 1 was declared the RP2D, and six additional patients enrolled in the expansion cohort at this dose without DLTs. Most common drug-related grade 3/4 toxicities were neutropenia (48%), leucopenia (35%), and elevated ALT (26%). Similar pharmacokinetic profiles were observed for capsule and tablet formulations, consistent with adult data. Survival outcomes and genomics results will be shared at time of presentation. CONCLUSIONS: The RP2D of unesbulin in children newly diagnosed with DIPG or HGG is 200mg/m2 twice weekly, concurrent with and following radiotherapy. The recently opened surgical cohort will assess intratumoral pharmacokinetics and inhibition of tumor BMI-1 signaling, with results forthcoming.

ATRT-01. Reconstitution of cGAS/ STING pathway via epigenetic reprogramming leads to anti-viral inflammatory signaling in Atypical teratoid rhabdoid tumors (ATRTs)

BACKGROUND: Atypical teratoid rhabdoid tumors (ATRTs) are highly aggressive brain tumors that affect young children characterized by biallelic inactivation of the SMARCB1 gene. Though patients benefit from multimodal therapy, there is no improvement in overall survival which necessitates the exploration of alternative approaches. Innate-based immune and epigenetic therapies have shown benefits in several cancers. The role of innate immune signaling has not been investigated in ATRTs. Our previous data from several ATRT cell lines showed loss of expression of key innate signaling components, like cGAS and STING that are needed for sensing extracellular dsDNA. Additionally, ATRT cell lines do not respond to STING agonists, like cGAMP or ISD. RESULTS: Co-treatment of ATRT cell lines, BT-12 and BT-16 with two epigenetic modulators, panobinostat and decitabine, leads to re-expression of cGAS and STING in a time-dependent manner. Furthermore, treatment with decitabine alone leads to demethylation of several CpG sites on the STING promoter and increased expression of STING mRNA. Panobinostat and decitabine co-treatment reconstitute STING-mediated innate signaling, as measured by IRF-3 and STAT1 phosphorylation and production of ISG-15 and IFIT-1 after treatment with cGAMP, a STING agonist. Co-treatment with panobinostat and decitabine also induced expression of antiviral pro-inflammatory chemokines/cytokines in ATRT cell lines, including type III IFN, IL-6, IL-8, IL-28, and IL-29. CONCLUSION: Our data suggest that ATRT cell lines are unresponsive to innate agonists possibly due to the loss of expression of key innate immune components. However, the cGAS/STING pathway is reactivated by epigenetic drugs, specifically the combination of panobinostat and decitabine. This is further potentiated by treating with STING agonists like cGAMP. Combination treatment of ATRT cell lines with panobinostat and decitabine also induced antiviral inflammatory signaling. This response could be a potential treatment modality to inhibit tumor growth and/or mediate cancer immunotherapy in these aggressive tumors.

ATRT-17. A phase II study of continuous low dose panobinostat in paediatric patients with malignant rhabdoid tumours and atypical teratoid rhabdoid tumours

BACKGROUND: Panobinostat treatment has been shown to terminally differentiate malignant rhabdoid tumours (MRT) and atypical teratoid rhabdoid tumours (ATRT) in pre-clinical models. We report results of the open label, phase II study of oral panobinostat in patients with newly diagnosed or relapsed MRT/ATRT. AIMS: To assess the anti-tumour activity of low dose, continuous oral panobinostat as well as its associated toxicities. To assess the biological activity of low dose panobinostat by measuring histone H4 acetylation status in peripheral mononuclear cells (PMNC), and differentiation markers. METHODS: Following primary institutional standard of care induction and consolidation chemotherapy and/or radiation treatment, patients were enrolled and commenced on panobinostat as a continuous daily oral dose starting at 10mg/m²/day, with a three-week wash out period between therapies. Real-time acetylation status, measuring acetylated H4 on PMNC, was performed to determine the pharmacodynamics of panobinostat at different dosing levels. Patients were monitored for toxicity; dose reductions were in decrements of 2mg/m²/day. RESULTS: A total of 13 patients with newly diagnosed ATRT/MRT and one patient with relapsed MRT have been enrolled. The average age at enrollment was 3.6 years (range 0.8-6.8 years). The mean treatment duration was 206 days (13-344 days). Currently, six patients (42.9%) remain on study with a mean study duration of 531 days (range 13-895 days). 6/14 patients (42.9%) were removed due to disease progression at a mean study duration of 245 days (44-560 days). 2/14 patients (14.3%) withdrew due to toxicity. 12/14 patients (85.7%) required dose reductions. The main toxicities were thrombocytopaenia and leukopaenia (Grade III-IV). Real-time pharmacodynamic assessment of panobinostat, at a dose as low as 6mg/m²/day resulted in significant acetylation of histone H4 in PMNC. CONCLUSIONS: Treatment with low dose panobinostat is well tolerated in infants and children with MRT/ATRT, with significant acetylation of histone H4 in PMNC.

Chemotherapy strategies for young children newly diagnosed with desmoplastic/extensive nodular medulloblastoma up to the era of molecular profiling – a comparative outcomes analysis of prospective multi-center European and North American trials

Aims

Survival has been poor in several multi-center/national trials since the 1980s, either delaying, avoiding or minimizing brain irradiation in young children with medulloblastoma. The introduction of German regimens supplementing “standard” chemotherapy with both intravenous high-dose (HD-MTX) and intraventricular (IVENT-MTX) methotrexate, and North American regimens incorporating marrow-ablative chemotherapy with autologous hematopoietic cell rescue (HDCx+AuHCR), have reported encouraging outcomes. We performed a comparative outcomes analysis of these differing strategies for young children with desmoplastic/extensive nodular medulloblastoma.

Method

Data from 12 trials reported between 2005 and 2020 for children &lt;six-years-old with desmoplastic/extensive nodular medulloblastoma were reviewed; event-free (EFS) survival+/-standard errors were compared.

Results

The German HIT-SKK’92 and HIT-SKK’00 trials incorporating HD-MTX and IVENT-MTX reported 85+/-8% and 95+/-5% 5-10-year EFS respectively; a third trial (ACNS1221) incorporating HIT-SKK therapy but without IVENT-MTX reported only 49+/-10% EFS. Three trials (Head Start I and II combined and CCG-99703) employing induction chemotherapy without HD-MTX, followed by one or three HDCx+AuHCR cycles, reported 3-5-year EFS of 67+/-16% and 79+/-11%. Two trials employing HD-MTX-containing induction chemotherapy (Head Start III and ACNS0334), followed by one or three HDCx+AuHCR cycles, reported 3-5-year EFS of 89+/-6% and 100%, respectively. Finally, four trials utilizing neither IVENT-MTX nor HDCx+AuHCR (UK-CNS-9204, CCG-9921, COG-P9934 and SJYC07) reported 2-5 year EFS of 35+/-11%, 77+/-9%, 58+/-8% and 53+/-9% respectively.

Conclusion

A trend towards better EFS for young children with desmoplastic/extensive nodular medulloblastoma is observed in trials including eitherHD-MTX and IVENT-MTX or including HD-MTX-containing induction chemotherapy and HDCx+AuHCR. Trials excluding HD-MTX, IVENT-MTX and HDCx+AuHCR have poorer outcomes.

IMMU-04. VACCINATING AGAINST NOVEL CYTOMEGALOVIRUS ANTIGENS IN GLIOBLASTOMA USING A PEPTIDE VACCINE IN COMBINATION WITH TEMOZOLOMIDE

INTRODUCTION

Cytomegalovirus (CMV) antigens are excellent anti-tumor immunotherapeutic targets in glioblastoma (GBM). The PERFORMANCE trial (IRB-pro34208, IND-15846) assessed the feasibility, safety and optimal adjuvant temozolomide (TMZ) regimen to be used with PEP-CMV vaccination in adults with newly-diagnosed GBM.

METHODS

Seropositive CMV patients (n=16) were randomized into two arms and treated with standard of care RT-TMZ (SOC) (150-200 mg/m2/day on days 1-5 per 28-day cycle) or dose-intensive TMZ (DI) (75-100 mg/m2/day on days 1-21 per 28-day cycle). Patients received intradermal PEP-CMV vaccines (500μg of CMVpp65 synthetic long peptide (SLP) mixed with Montanide ISA-51) on days 23, 37 and 51 following TMZ. All patients received tetanus/diphtheria toxoid (Td) preconditioning at the vaccination site on day 22. Serum cytokine levels were measured pre-vaccination, 1-hour and 2-hours post vaccination. PEP-CMV specific circulating PBMCs were quantified at baseline and after each vaccine.

RESULTS

Of the 16 trial patients, 7 experienced site-reactions, 4 had grade-II Immune Related Adverse Events (IRAEs), and 4 experienced flu-like grade-III IRAEs. Inflammatory cytokines (IL-2, IFNγ, MIP-1a, IL-8, TNFα, and IL-10) were elevated in patients with grade-III responses 2-hours post vaccine 1. Td p2/p30 specific PBMC levels were similar between IRAEs. However, pp65 responsive PBMCs were elevated at baseline in patients with grade-III reactions compared to site-reaction suggesting pre-existing peptide specific responses may lead to increased vaccine immunogenicity. PBMCs specific for pp65 increased with number of consecutive vaccines. No difference in progression free survival (PFS) or overall survival (OS) was observed between TMZ regimens.

CONCLUSION

PEP-CMV vaccination with Td preconditioning is feasible and generates immune responses specific to pp65 in patients with newly diagnosed GBM. Importantly, IRAEs were associated with antitumor efficacy. The mild IRAEs in PERFORMANCE are likely indicative of vaccine potency and can be managed through standard premedication as has been used in other trials with similar IRAEs.

IMMU-07. A PHASE I STUDY OF MULTIPLE PEPTIDE TUMOR-ASSOCIATED ANTIGEN VACCINES IN NEWLY DIAGNOSED GLIOBLASTOMA

INTRODUCTION

Targeting tumor-associated antigens (TAAs) via peptide vaccination has been tested against malignant glioma with minimal success. Poor responses are attributed to relatively low antigen level expression of the TAA and insufficient CD8+ T cell responses. Including a universal class II epitope that provides CD4+ T cell help towards CD8+ responses has been tested with the immunogenic tetanus toxoid epitope P30, but P30 has been employed as a separate peptide in this regard. The current study will employ targeting of three major glioma TAAs: EphA2, pp65 from Cytomegalovirus, and survivin. The ability to induce more potent TAA-specific immune responses will be tested using two novel strategies: P30-linked TAA peptides and a combinatorial vaccination of the linked peptides (P30-EPS).

HYPOTHESES

In Evaluation of Tumor Associated P30-Peptide Antigen I (ETAPA-I), P30-EPS is anticipated to have an acceptable toxicity profile. Multi-peptide vaccination is thought to bypass tumor heterogeneity and selection of antigen-negative clones, known as antigen escape. Moreover, the administration of EPS covalently linked to P30 is anticipated to increase the magnitude of antigen-specific immune responses and elicit both CD4- and CD8-mediated immune recognition.

TRIAL DESIGN/OBJECTIVES

A maximum of 24 patients with newly diagnosed, unmethylated WHO grade IV glioma will be treated. Following resection and standard of care chemoradiation, patients will be vaccinated serially during the priming phase (Day 1-22) and booster phase (Day 84 and 140). All P30-EPS vaccines during priming and boosting phases are co-administered with the adjuvant Hiltonol (Oncovir, poly-ICLC), and patients self-administer Hiltonol throughout the booster phase. The primary endpoint will evaluate the safety profile of P30-EPS. Secondary objectives include polyfunctional T-cell responses specific to EphA2, pp65 and survivin, TCR diversity, and survival.

CONCLUSION

We describe a study that employs known TAA targets of malignant glioma with the novel strategy of combinatorial class II-linked peptide vaccination.

IMMU-06. TARGETING IDH1 MUTANT GRADE II RECURRENT GLIOMAS USING A PEPTIDE VACCINATION STRATEGY

INTRODUCTION

While primary GBM is largely heterogeneous and devoid of homogeneously expressed neoantigens, mutant IDH1 (R132H) is a uniformly expressed hallmark in &gt;70% of low grade gliomas. As such, IDH1 mutations represent a potentially valuable vaccination target.

METHODS

Here, we report an update on the immunogenicity results of the mutant IDH1 peptide vaccine alone and in combination with temozolomide (TMZ). In the phase I RESIST clinical trial (NCT02193347), patients with recurrent and resectable IDH1 R132H mutant grade 2 glioma received peptide vaccinations composed of 500 µg of mutant IDH1 peptide and 150 µg of GM-CSF mixed 1:1 with Montanide adjuvant prior to surgical resection. Vaccines 1, 2, and 3 were given 15 (+/-) 3 days apart. 7-12 days after vaccine 3, patients underwent standard of care tumor (SOC) resection. After resection, patients with grade 2 gliomas were given up to 15 doses of peptide vaccine in combination with TMZ regimens while patients with transformed grade 3 gliomas were given up to 15 doses of peptide vaccine in combination with SOC radiation therapy + TMZ regimens. T cell responses against the mutant peptide were measured after vaccine 3 using IFN-γ ELISPOT and intracellular flow cytometry for IL-2, TNFα,and IFNγ.

RESULTS

3/20 patients were taken off the study before completion of study related activities. 1/20 patients progressed before completion of all vaccines. Out of 134 total doses of vaccine delivered, only one dose generated a grade 2 or higher injection site reaction according to the CTCAE guidelines. Vaccination with the mutant peptide led to an overall increase in IFN-γ+ spot-forming splenocytes specific to the mutant peptide (p=0.0408).

CONCLUSION

Administering the mutant IDH1 peptide vaccine in patients with recurrent IDH-mutant gliomas was able to induce anti-IDH1 R132H immune responses in this initial phase I study.

Photosynthetic quantum efficiency in south-eastern Amazonian trees may be already affected by climate change

Tropical forests are experiencing unprecedented high-temperature conditions due to climate change that could limit their photosynthetic functions. We studied the high-temperature sensitivity of photosynthesis in a rainforest site in southern Amazonia, where some of the highest temperatures and most rapid warming in the Tropics have been recorded. The quantum yield (F_v /F_m ) of photosystem II was measured in seven dominant tree species using leaf discs exposed to varying levels of heat stress. T₅₀ was calculated as the temperature at which F_v /F_m was half the maximum value. T₅ is defined as the breakpoint temperature, at which F_v /F_m decline was initiated. Leaf thermotolerance in the rapidly warming southern Amazonia was the highest recorded for forest tree species globally. T₅₀ and T₅ varied between species, with one mid-storey species, Amaioua guianensis, exhibiting particularly high T₅₀ and T₅ values. While the T₅₀ values of the species sampled were several degrees above the maximum air temperatures experienced in southern Amazonia, the T₅ values of several species are now exceeded under present-day maximum air temperatures.

BIOL-10. DISTRIBUTION AND VULNERABILITY OF TRANSCRIPTIONAL OUTPUTS ACROSS THE GENOME IN MYC-AMPLIFIED MEDULLOBLASTOMA CELLS

Myc plays a central role in tumorigenesis by orchestrating the expression of genes essential to numerous cellular processes. While it is well established that Myc functions by binding to its target genes to regulate their transcription, the distribution of the transcriptional output across human genome in Myc-amplified cancer cells, and the susceptibility of such transcriptional outputs to therapeutic interferences remain to be fully elucidated. Here, we analyze the distribution of transcriptional outputs in Myc-amplified medulloblastoma (MB) cells by profiling nascent total RNAs within a temporal context. This profiling reveals a major portion of transcriptional action in these cells was directed at the genes fundamental to cellular infrastructures, including rRNAs and particularly those in the mitochondrial genome (mtDNA). Notably, even when Myc protein was depleted by as much as 80%, the impact on transcriptional outputs across the genome was limited, with notable reduction mostly in genes of involved in ribosomal biosynthesis, genes residing in mtDNA or encoding mitochondria-localized proteins, and those encoding histones. In contrast to the limited direct impact of Myc depletion, we found that the global transcriptional outputs were highly dependent on the activity of Inosine Monophosphate Dehydrogenases (IMPDHs), rate limiting enzymes for de novo guanine nucleotide synthesis and whose expression in tumor cells was positively correlated with Myc’s expression. Blockage of IMPDHs attenuated the global transcriptional outputs with a particularly strong inhibitory effect on the aforementioned infrastructure genes, which was accompanied by the abrogation of MB cell’s proliferation in vitro and in vivo. Together, our findings reveal a real time action of Myc as a transcriptional factor in tumor cells, gain new insight into the pathogenic mechanism underlying Myc-driven tumorigenesis, and support IMPDHs as a therapeutic vulnerability in MB cells empowered by a high level of Myc oncoprotein.

LGG-08. TREATMENT OUTCOMES AND TOLERABILITY OF TRAMETINIB IN PROGRESSIVE CIRCUMSCRIBED LOW-GRADE GLIOMAS

Circumscribed low-grade gliomas comprise roughly one-third of pediatric CNS tumors. Most of these tumors are caused by activating mutations in the mitogen-activated protein kinase (MAPK) pathway. Drugs targeting the MAPK pathway are effective in other cancers and are being utilized in low-grade gliomas. We describe treatment outcomes and toxicities in a series of thirteen low-grade glioma patients treated with trametinib. We performed a retrospective chart review to evaluate response on T2/FLAIR MRI images per updated RANO criteria, visual outcomes, tolerability, and durability of response in progressive low-grade glioma patients treated with trametinib. Thirteen patients age 22 months to 34 years were included. Best radiographic response on therapy included 2/13 partial response, 3/13 minimal response, 5/13 stable disease, and 3/13 progressive disease. Diagnoses included pilocytic astrocytoma (n=6), desmoplastic infantile ganglioglioma (DIG; n=1), and low-grade glial neoplasms (n=2). Molecular drivers included BRAF:KIAA1549 fusion (n=3), V600E mutation (n=1), and somatic NF1 mutation (n=1). Three patients had germline NF1. In patients with partial or minimal response, best response was seen after longer durations of therapy; 4 of 5 best responses occurred after at least 12 months on therapy. Five patients completed prescribed therapy. Three patients remain stable off therapy at 6, 12, and 21 months; two patients recurred at 1 and 10 months off therapy. Skin manifestations were the predominant form of toxicity. This was more severe in older males, and symptoms improved with intermittent dosing. All patients with optic pathway tumors showed at least stable vision throughout treatment, with some patients having dramatic improvement. Trametinib is effective and well-tolerated in patients with low-grade glioma. Dermatologic toxicity can be mitigated by intermittent dosing. Best responses tended to occur later in therapy, sometimes after relatively stable MRIs. Patients with optic pathway lesions showed stable to improved vision even in the absence of significant radiographic response.

EPCT-01. A NOVEL PEPTIDE VACCINE DIRECTED TO CMV PP65 FOR TREATMENT OF RECURRENT MALIGNANT GLIOMA AND MEDULLOBLASTOMA IN CHILDREN AND YOUNG ADULTS: PRELIMINARY RESULTS OF A PHASE I TRIAL

Introduction

The cytomegalovirus (CMV) antigen, pp65, is ubiquitously expressed in malignant glioma and medulloblastoma but not in healthy brain. The objective of this Phase I trial (NCT03299309) was to assess the safety and feasibility of a novel pp65 peptide vaccine (PEP-CMV) in children and young adults with recurrent medulloblastoma and malignant glioma.

Methods

Vaccines contain a synthetic long peptide (SLP) of 26 amino acids encoding multiple potential class I, class II, and antibody epitopes of CMV pp65 across several haplotypes. This SLP is administered as an emulsion in Montanide ISA 51. Patients receive a single course of temozolomide to induce lymphopenia, tetanus/diphtheria toxoid site preconditioning, then vaccines administered intradermally every two weeks for 3 doses, then monthly.

Results

To date, 22 patients have been enrolled. Diagnoses include medulloblastoma (n=2), glioblastoma (n=12), anaplastic oligodendroglioma (n=2), anaplastic astrocytoma (n=3), and malignant glioma NOS (n=3). Mean number of prior treatment regimens is 4.9 (range 1–12). Mean age is 22yo (range 6–35) and 45% of patients are male. The median KPS is 80. The median number of vaccines given at time of analysis is 3.3 (range 1–12). There have been no ≥ 3 Grade toxicities related to the vaccine. One patient developed nausea, vomiting, palpitations, and tachycardia after vaccination and had elevated inflammatory cytokines consistent with cytokine release syndrome. Median PFS is 2.5 months (95% CI: 1.7,4.5) and median OS is 6.5 months (95% CI 3.3, 7.9). Immune response to pp65 as determined by ELISpot was found in 75% of patients. On MRI 6 of the 11 evaluable patients have had at least stable disease with three of those having a partial response.

Conclusions

Preliminary results demonstrate that PEP-CMV is well-tolerated and elicits an immune response in heavily pretreated, multiply recurrent patients. A multi-institutional Phase II trial is scheduled to open fall 2021.

ATRT-08. A PHASE II STUDY OF CONTINUOUS LOW DOSE PANOBINOSTAT IN PAEDIATRIC PATIENTS WITH MALIGNANT RHABDOID TUMORS/ATYPICAL TERATOID RHABDOID TUMORS

BACKGROUND

Panobinostat treatment has been shown to terminally differentiate malignant rhabdoid tumor (MRT)/atypical teratoid rhabdoid tumors (ATRT) in pre-clinical models. This is an open label, phase II study of panobinostat in patients with newly diagnosed or relapsed MRT/ATRT. AIMS: To assess the anti-tumor activity of low dose, continuous panobinostat, its associated toxicities, the biological activity of low dose panobinostat by measuring histone acetylation status in peripheral mononuclear cells (PMNC), and markers of differentiation in fresh tumor tissue specimens.

METHODS

Following cycles of induction and consolidation chemotherapy and/or radiation treatment, patients were enrolled and commenced on panobinostat as a continuous daily oral dose starting at 10mg/m² following a three-week wash out period between therapies. Real-time acetylation status, measuring acetylated H4 on PMNC, was performed to determine the pharmacodynamics of panobinostat. Patients were monitored for drug toxicities with the possibility of dose reductions in decrements of 2mg/m².

RESULTS

Six patients with newly diagnosed ATRT/MRT and one patient with relapsed MRT have been enrolled to date. The average age at enrollment was 2.5 years. Currently, six patients (85.7%) remain on study with a mean treatment duration of 170 days (range 44–327 days). One patient was removed from study at day 44 due to disease progression. The main dose-limiting toxicity observed to date has been myelosuppression. Panobinostat, at a dose of 10mg/m², caused significant acetylation of H4 in PMNC.

CONCLUSIONS

Treatment with panobinostat appears to be well tolerated in infants with MRT/ATRT, with successful real-time pharmacodynamic assessment of H4 acetylation.

MBCL-19. CHEMOTHERAPY STRATEGIES FOR YOUNG CHILDREN NEWLY DIAGNOSED WITH DESMOPLASTIC/EXTENSIVE NODULAR MEDULLOBLASTOMA UP TO THE ERA OF MOLECULAR PROFILING – A COMPARATIVE OUTCOMES ANALYSIS OF PROSPECTIVE MULTI-CENTER EUROPEAN AND NORTH AMERICAN TRIALS

BACKGROUND/OBJECTIVE

Survival has been poor in several multi-center/national trials since the 1980s, either delaying, avoiding or minimizing brain irradiation in young children with medulloblastoma. The introduction of German regimens incorporating both intravenous high-dose (HD-MTX) and intraventricular (IVENT-MTX) methotrexate, and North American regimens utilizing marrow-ablative chemotherapy with autologous hematopoietic cell rescue (HDCx+AuHCR), have reported encouraging outcomes. We performed a comparative outcomes analysis of these strategies for young children with desmoplastic/extensive nodular medulloblastoma (D/ENMB).

DESIGN/METHODS

Data from 12 trials reported between 2005 and 2019 for children &lt;six-years-old with D/ENMB were reviewed; event-free (EFS) with standard errors were compared.

RESULTS

The German HIT-SKK’92 and HIT-SKK’00 trials incorporating HD-MTX and IVENT-MTX reported 85+/-8% and 95+/-5% 5-10-year EFS respectively; a third trial (ACNS1221) incorporating HIT-SKK therapy but without IVENT-MTX reported 49+/-10% EFS. Three trials (Head Start I/II combined and CCG-99703) employing induction chemotherapy without HD-MTX, followed by 1/3 HDCx+AuHCR cycles, reported 3-5-year EFS of 67+/-16% and 79+/-11%. Two trials employing HD-MTX-containing induction chemotherapy (Head Start III and ACNS0334), followed by 1/3 HDCx+AuHCR cycles, reported 3-5-year EFS of 89+/-6% and 100%, respectively. Finally, four trials utilizing neither IVENT-MTX nor HDCx+AuHCR (UK-CNS-9204, CCG-9921, COG-P9934 and SJYC07) reported 2-5-year EFS of 35+/-11%, 77+/-9%, 58+/-8% and 53+/-9%.

CONCLUSIONS

A trend towards better EFS for young children with D/ENMB is observed in trials including either HD-MTX as well as IVENT-MTX or including HD-MTX-containing induction chemotherapy and HDCx+AuHCR. Trials excluding HD-MTX, IVENT-MTX and HDCx+AuHCR have poorer outcomes.

MBCL-25. PILOT STUDY OF A SURGERY AND CHEMOTHERAPY-ONLY APPROACH IN THE UPFRONT THERAPY OF CHILDREN WITH WNT-POSITIVE STANDARD RISK MEDULLOBLASTOMA: UPDATED OUTCOMES

BACKGROUND

Wnt+ medulloblastoma (WPM) is a favorable subtype with EFS > 90% when treating postoperatively with craniospinal irradiation and posterior fossa boost (CSI/XRT) followed by adjuvant chemotherapy. This pilot study explored the safety of omitting radiation in standard-risk WPM.

METHODS

Subjects had to meet standard-risk criteria (< 1.5 cm2 residual tumor, no metastatic spread, no anaplasia) and have a WPM. Subjects received chemotherapy following the COGACNS0331 AAB-AAB-AAB (A=cisplatin/CCNU/VCR; B=cyclophosphamide/vincristine) backbone.

RESULTS

Six children were enrolled on study treatment prior to early study closure. Subject #1 completed planned protocol therapy but relapsed 3 months following the completion of therapy. Subject #2 completed planned protocol therapy but relapsed 6 months following the completion of therapy. In both cases, relapse was local and disseminated. Further accrual was halted. Both subjects were salvaged with CSI/XRT followed by adjuvant chemotherapy. Of the remaining 4 subjects, two had recently completed planned protocol therapy at the time of study closure and received CSI/XRT while in remission and remain in remission approximately one year from the completion of treatment. One subject aborted protocol therapy and transitioned to a Head Start regimen and remains in remission 10 months from completion of therapy. The final subject had just completed protocol therapy and had new areas of restricted diffusion concerning for early relapse. Went on to receive CSI/XRT but subsequently relapsed and is now receiving salvage chemotherapy.

CONCLUSIONS

Chemotherapy following ACNS0331, omitting CSI/XRT, appears to be insufficient for the treatment of non-metastatic WPM.

MBCL-37. CHEMOTHERAPY STRATEGIES FOR YOUNG CHILDREN NEWLY DIAGNOSED WITH CLASSIC (CLMB) OR ANAPLASTIC/LARGE CELL (A/LCMB) MEDULLOBLASTOMA UP TO THE ERA OF MOLECULAR PROFILING – A COMPARATIVE OUTCOMES ANALYSIS

BACKGROUND/OBJECTIVE

The introduction of German regimens, supplementing “standard” chemotherapy with both intravenous high-dose (HD-MTX) and intraventricular (IVENT-MTX) methotrexate, and North American regimens incorporating marrow-ablative chemotherapy with autologous hematopoietic cell rescue (HDCx+AuHCR), report encouraging outcomes for young children with medulloblastoma. We performed a comparative outcomes analysis of treatment strategies for young children with ClMB or A/LCMB. DESIGN/

METHODS

Data from 12 prospective multi-center trials published between 2005 and 2019 for children <six-years-old with ClMB or A/LCMB were reviewed; survivals were compared.

RESULTS

COG-9921, UKCCSG-CNS9204, COG-P9934 and SJYCO7 employing standard chemotherapy with either no or risk-based irradiation, reported 3-5-year event-free survival (EFS) of 17+/-5%, 33+/-28% (ClMB), 14+/-7% and 13.8+/-9% (ClMB) respectively, with reported EFS of 0% for A/LCMB in UKCCSG-CNS9204 and SJYCO7. HIT-SKK’87, HIT-SKK’92 and HIT-SKK’00 incorporating HD-MTX and IVENT-MTX reported 2-10-year EFS of 30–34+/-10–11% for ClMB and 33+/-27% (HIT-SSK’00) for A/LCMB. Head Start HS-I-II combined, CCG-99703 and HS-III employing induction chemotherapy, with or without HD-MTX, followed by single or tandem HDCx+AuHCR reported 3-5-year EFS of 42+/-14%, 50+/-11% and 27+/-6% for ClMB, with EFS for A/LCMB of 38+/-13% (HS-III). Finally, 5-year overall survivals for ACNS0334, without or with induction HD-MTX, are 39% and 69% respectively for ClMB and A/LCMB combined.

CONCLUSIONS

A trend towards better outcomes for young children with ClMB and A/LCMB is observed in trials including either HD-MTX and IVENT-MTX or including HD-MTX-containing induction chemotherapy and HDCx+AuHCR. Trials excluding HD-MTX, IVENT-MTX and HDCx+AuHCR have poorer outcomes.

ATRT-19. EPIGENETIC REPROGRAMMING LEADS TO INNATE IMMUNE PATHWAY ACTIVATION IN AT/RT

BACKGROUND

Atypical teratoid/rhabdoid tumors (AT/RT) are highly aggressive brain tumors affecting early childhood and are characterized by bi-allelic inactivation of the SMARCB1 gene. Though patients benefit from multimodal therapy, there is no improvement in overall survival necessitating exploration of alternative approaches including innate-based immune therapy and epigenetic therapy, which have shown promise in treating adult brain tumors and other cancers. Though reconstitution of SMARCB1 in SMARCB1-deficient cells leads to activation of interferon-stimulated genes, the role of innate immune signaling has not been investigated in AT/RTs.

METHODS

Our data from a panel of AT/RT cell lines indicates loss of expression of key innate signaling components, like RIG-I, MDA-5, cGAS and STING that are required for sensing extracellular dsRNA and dsDNA. These cell lines also do not respond to dsDNA-based or dsRNA-based innate agonists. However, co-treatment of the BT-16 cell line with two epigenetic drugs, panobinostat and 5-azacytidine leads to re-expression of STING and RIG-I. Panobinostat/5-azacytidine co-treatment followed by either genomic DNA (dsDNA agonist) or poly(I:C) (dsRNA agonist) treatment results in induction of innate responses, measured by STAT1 phosphorylation and production of ISG-15 and IFIT-1.

CONCLUSION

Our data suggests that AT/RT cell lines are unresponsive to innate agonists possibly due to the loss of expression of key innate immune components. However, these pathways can be reactivated by epigenetic drugs and further potentiated by dsDNA/dsRNA-based innate agonists. Combined epigenetic reprogramming and innate pathway stimulation may serve as a potential therapy option for treating AT/RT.

THER-05. GENETICALLY STABLE POLIOVIRUS VECTOR CARRYING H3.3K27M ANTIGEN FOR TREATMENT OF DIFFUSE MIDLINE GLIOMA BY INTRAMUSCULAR INJECTION

BACKGROUND

H3 K27M-mutant diffuse midline glioma (DMG) is invariably lethal. Viruses naturally engage innate immunity, induce antigen presentation, and mediate CD8 T cell priming against foreign antigens. Polioviruses, in particular, are uniquely tropic for dendritic cells (DC) and potently activate DC, inducing Th1-dominant cytokine profiles, CD8 T cell immunity, and enhanced epitope presentation. Thus, poliovirus is ideally suited for vectored delivery of signature tumor neoantigens, e.g. the H3 K27M feature of DMG. However, poliovirus vector design is inherently limited by genetic instability and the underlying neuropathogenicity of poliovirus.

METHODS

We created a genetically stable, polio:rhinovirus chimera vector devoid of neuropathogenicity and modified for stable expression of the HLA-A2 restricted H3.3 K27M antigen (RIPO (H3.3)).

RESULTS

RIPO(H3.3) infects, activates, and induces H3.3K27M antigen presentation in DCs in vitro. Given intramuscularly in vivo, RIPO(H3.3) recruits and activates DCs with Th1-dominant cytokine profiles, efficiently primes H3.3K27M-specific CD8 T cells, induces antigen-specific CD8 T cell migration to the tumor site, delays tumor growth, and enhances survival in murine tumor models.

CONCLUSION

This novel approach leverages the unique ability of polioviruses to activate DCs while simultaneously introducing the H3.3 K27M antigen. In this way, DCs are activated optimally in situ, while being simultaneously infected to express/present tumor antigen. RIPO(H3.3), given by intramuscular injection, will be evaluated in a clinical trial for children with H3 K27M-mutant diffuse midline glioma.

EPCT-13. CMV PP65 RNA-PULSED DENDRITIC CELL VACCINES FOR PEDIATRIC GLIOBLASTOMA AND MEDULLOBLASTOMA: PHASE I TRIAL RESULTS

BACKGROUND

Recurrent medulloblastoma and malignant glioma are lethal tumors that are virtually incurable. The cytomegalovirus (CMV) antigen pp65 is ubiquitously expressed on medulloblastoma and malignant glioma but not on healthy brain. We evaluated autologous CMV pp65 RNA-pulsed dendritic cell (DC) vaccines in children and young adults in a phase I trial.

METHODS

Circulating monocytes were harvested using leukapheresis, differentiated into DCs, matured, and pulsed with pp65 RNA using electroporation. DCs were packaged into vaccines (2x10⁷DC/vaccine) and administered intradermally following tetanus-diphtheria toxoid site preconditioning every 2 weeks x3, then monthly. The primary objectives of the study were to establish the feasibility of generating at least 3 vaccines and safety. An exploratory objective was to evaluate the ability of vaccination to create and enhance patient pp65-specific T cell responses.

RESULTS

Eleven patients were enrolled with medulloblastoma (n=3) or glioblastoma (n=8). Ages ranged from 9–30 years old (mean 15.5y). Ten of 11 patients (91%) generated at least 3 vaccines (mean 6.2). Eight patients received at least 3 vaccines. To date, 4 patients have received all generated vaccines without progression, 4 patients have progressed, and 2 patients are still receiving vaccines. There have not been any severe adverse events probably or definitely related to vaccines. More mature data will be presented at ISPNO.

CONCLUSIONS

Leukapheresis and monocyte differentiation is a feasible strategy for generating adequate DCs for active immunization in children with malignant brain tumors. CMV pp65 RNA-pulsed DCs are well-tolerated and immunogenic. Efficacy endpoints will be evaluated in a subsequent phase II trial.

COVD-25. THE PARADOXICAL EFFECTS OF COVID-19 ON CANCER CARE IN THE NEURO-ONCOLOGY SETTING

COVID-19 has caused ongoing interruptions to healthcare systems worldwide, shifting care to virtual platforms, and placing significant economic and logistical burdens on clinical practice. The pandemic has created uncertainty in delivering the standard of care, both in areas of cancer diagnosis and treatment, especially within neuro-oncology. Due to the pandemic, care and operational planning goals have shifted to infection prevention, modifying recommendations to decrease viral transmission and increasing telemedicine use, potentially creating a burden on implementing evidence-based medicine. These dynamics have since begun to redefine traditional practice and research regimens, impacting the comprehensive care that cancer patients can and should receive; and the enduring consequences for the delivery of healthcare. The impact of COVID-19 on oncology practice and trials might endure well beyond the short- to mid-term of the active pandemic. Therefore, these shifts must be accompanied by improved training and awareness, enhanced infrastructure, and evidence-based support to harness the positives and offset the potential negative consequences of the impacts of COVID-19 on cancer care. To address these paradoxical effects, we will conduct iterative, qualitative (face-to-face/video conference) interviews with neuro-oncology clinical and research professionals and adult brain tumor patients receiving care during the pandemic. We will capture unique aspects of oncology care: the lived, subjective, situated, and contingent accounts of patients and medical professionals, especially during a pandemic. We will also specifically compare the impact of telehealth during the pandemic on delivery of care to complex neuro-oncology patients. A summary of this in-depth, qualitative approach will result in a sophisticated understanding of neuro-oncology care on the frontline at a time of crisis, as experienced during a pandemic, to articulate best practices for future implementation.

IMMU-18. INTERPLAY BETWEEN IDH1 AND ATRX MUTATIONS GOVERN INNATE IMMUNE RESPONSES IN GLIOMAS

Innate-based immunotherapies are becoming increasingly important for treating brain tumor patients. About 50% of WHO grade II and III gliomas carry mutations in IDH1 and ATRX genes. Mutant IDH1 results in the production of 2-hydroxyglutarate, an oncometabolite that promotes global metabolic and epigenetic alterations. ATRX is a SWI-SNF chromatin remodeling protein that is involved in cell cycle regulation and maintenance of genomic stability. Both IDH1 and ATRX mutations have been implicated in dysfunctional immune signaling in cancer cells. However, the interplay between these mutations in mediating innate immune responses has not been investigated in gliomas. We have derived human and mouse glioma cell lines carrying mutations in IDH1 (IDH1R132H) and/or ATRX, which we then used to generate both immune competent and nude mice models. Treating the ATRX knockout (KO) cell lines with dsRNA-based innate stimuli led to an early induction in phospho-IRF3, and late induction in phospho-STAT1 and ISG15, suggesting that ATRX deletion may enable a potent activation of type I interferon production and sensitize glioma cells to dsRNA-based innate stimuli. Our syngeneic murine glioma models confirm a survival advantage for mice carrying ATRX-KO tumors. These tumors also exhibit enhanced infiltration of T-cells and expression of activated macrophage markers. On the other hand, presence of IDH1R132H led to a suppression in baseline expression of key innate immune players, which could be rescued by the mutant IDH1 inhibitor, BAY-1436032. Cells harboring IDH1R132H and ATRX-KO retained sensitivity to dsRNA indicating that IDH1R132H does not dampen the ATRX KO-mediated sensitivity to dsRNA. Our models are under evaluation with a combination of BAY-1436032 and clinically relevant dsRNA-based innate therapies. Our data indicates the presence of an interplay between IDH1 and ATRX mutations that may regulate innate signaling in gliomas. Understanding the mechanisms governing this interplay may aid in designing therapies that exploit this interplay.

CTIM-21. PEPTIDE VACCINE DIRECTED TO CMV pp65 FOR TREATMENT OF RECURRENT MALIGNANT GLIOMA AND MEDULLOBLASTOMA IN CHILDREN AND YOUNG ADULTS: PRELIMINARY RESULTS OF A PHASE I TRIAL

INTRODUCTION

The cytomegalovirus (CMV) antigen, pp65, is ubiquitously expressed in malignant glioma and medulloblastoma but not in healthy brain. The objective of this Phase I trial (NCT03299309) was to assess the safety and feasibility of a novel pp65 peptide vaccine (PEP-CMV) in children and young adults with recurrent medulloblastoma and malignant glioma.

METHODS

Vaccines contain a synthetic long peptide (SLP) of 26 amino acids encoding multiple potential class I, class II, and antibody epitopes of CMV pp65 across several haplotypes. This SLP is administered as an emulsion in Montanide ISA 51. Patients receive a single course of temozolomide to induce lymphopenia, tetanus/diphtheria toxoid site preconditioning, then vaccines administered intradermally every two weeks for 3 doses, then monthly.

RESULTS

To date, 17 patients have been enrolled. Diagnoses include medulloblastoma (n=1), glioblastoma (n=9), anaplastic oligodendroglioma (n=2), anaplastic astrocytoma (n=2), and malignant glioma NOS (n=3). Mean number of prior treatment regimens is 4.9 (range 1–12). Mean age is 22yo (range 6–35) and 41% of patients are male. The median KPS is 80. The median number of vaccines given at time of analysis is 3.3 (range 1–12). There have been no ≥ 3 Grade toxicities related to the vaccine. One patient developed nausea, vomiting, palpitations, and tachycardia after vaccination and had elevated inflammatory cytokines consistent with cytokine release syndrome. Median PFS is 2.5 months (95% CI: 0.8, not estimable) and median OS is 6.5 months (95% CI 1.8, not estimable). Interim analysis of immune monitoring bloodwork and perfusion MRI to quantify responses to PEP-CMV has been delayed due to COVID-19. However, adults with GBM who received PEP-CMV (NCT02864368) had significant (p≤0.05) increases in GCSF, GM-CSF, IFN-γ, IL-10, IL-2, IL-8, MIP1-α, and TNF-α levels.

CONCLUSIONS

Preliminary results demonstrate that PEP-CMV is feasible and well-tolerated in heavily pretreated, multiply recurrent patients.

NCOG-23. PATTERNS OF DISTRESS IN OLDER PATIENTS WITH GLIOBLASTOMA: A FOLLOW-UP TO A SINGLE INSTITUTION CROSS-SECTIONAL STUDY OF DISTRESS IN PRIMARY BRAIN TUMOR PATIENTS

INTRODUCTION

We previously reported to SNO, high levels of psychosocial distress in adult patients with primary brain tumors (PBTs), particularly during the first 6 months following diagnosis. The purpose of this follow-up study was to identify patterns of distress among older (≥ 65 years) patients with glioblastoma (GBM) compared to their younger (ages 18-64) counterparts.

METHODS

In our initial cross-sectional study, we collected the National Comprehensive Cancer Network’s Distress Thermometer (NCCN-DT) and problem list from adult patients with PBTs (WHO grades I-IV) seen at our institution between December 2013 and February 2016. We performed subsequent analyses on a subset of patients with GBM.

RESULTS

We identified 343 patients with GBM from the original dataset, of which 23.0% (n= 78) were ≥ 65 years old. The proportion of patients ≥ 65 years old with elevated distress (i.e. DT ≥ 4) was greater than the proportion of younger patients reporting elevated distress (47.4% vs 30.6%; p= 0.0068). Elevated distress was significantly greater during the first 6 months post diagnosis for all ages (p= 0.008). In subgroup analyses, a decrease in distress beyond 6 months was seen in younger patients (45.7% vs 27.4%; p= 0.021), but not in older patients. In older patients, a greater number of problems were selected on the NCCN DT and problem list tool: emotional and physical concerns were reported more frequently compared to their younger counterparts. Older patients were more likely to report difficulty with “bathing” and “getting around” (p= 0.009, p&lt; 0.001, respectively). There were no differences in older versus younger GBM patients with regard to housing, transportation, treatment decisions, depression, fatigue, or memory.

CONCLUSIONS

In contrast to their younger counterparts, older patients with GBM experienced elevated levels of distress and a greater absolute number of specific psychosocial problems, mostly related to emotional and physical concerns.

BIOM-17. BRAF MUTATION IS AN EARLY EVENT IN THE EVOLUTION OF A SUBSET OF GLIOBLASTOMAS AND IS ASSOCIATED WITH INCREASED PD-L1 EXPRESSION

INTRODUCTION

BRAF is a RAF-family kinase that regulates MAPK/ERK signaling. Activating BRAF mutations, including V600E, are common in circumscribed low-grade gliomas of childhood and young adulthood, but are uncommon in infiltrative astrocytomas, including glioblastoma. Their role in glioblastoma initiation and progression requires analysis of large datasets given the low frequency (1.0%) in TCGA IDH-wild-type glioblastomas.

METHODS

Molecular profiling was done on 4679 FFPE gliomas by next-generation sequencing at Caris Life Sciences, of which 3170 underwent RNA-sequencing for gene fusion and 4603 DNA-sequencing for mutations. MGMT promoter methylation was tested by pyrosequencing and PD-L1 IHC was performed using the SP142 clone.

RESULTS

Excluding variants of uncertain significance, BRAF mutations/fusions were most common in pleomorphic xanthoastrocytoma (PXA; N=12/24, 50%), glioneuronal tumors (N=6/13, 46%), pilocytic astrocytoma (PA; N=15/48, 31%), and ganglioglioma (n=5/18, 28%). BRAF fusions were uncommon (N=17), most frequent in PA (N=8/31, 26%) where they were associated with older age at daignosis (P=0.043), and typically involved KIAA1549 as fusion partner (70%). BRAF-mutated/fused glioblastoma patients (N=59/3126, 2%) were younger than BRAF-wild-type glioblastoma patients (54 versus 59 years, P=3.5x10-3); more likely to be MGMT-unmethylated (75% versus 56%, P=5.0x10-3); and 3x more likely to express PD-L1 (55% versus 17%, P=2.1x10-10). In tumors harboring a V600E mutation, the variant allele frequency (VAF) was similar in glioblastoma as in PXA, PA, ganglioglioma, and glioneuronal tumors (median VAF=35%).

CONCLUSIONS

BRAF-mutated glioblastoma were 3x more likely to express PD-L1 than BRAF-wild-type glioblastoma. We observed no differences in BRAF V600E clonality in BRAF-mutated glioblastoma compared to BRAF-mutated PXA, PA, ganglioglioma, and glioneuronal tumors, suggesting BRAF mutation is an initiating event in the clonal evolution of a subset of glioblastoma. There is rationale to evaluate combined BRAF inhibition with checkpoint inhibition in BRAF-mutated glioblastoma, potentially synergizing the complete response profile of the former with the durable response profile of the latter.

EPCO-21. STING PROMOTER EPIGENETIC SILENCING IN GLIOBLASTOMA

The Stimulator of interferon genes (STING) protein is a critical component of the innate immune response to pathogenic and cytosolic self DNA. The importance of STING signalling has recently been demonstrated in a number of tumor types, including glioblastoma (GBM), and its activation through STING agonism is a promising antitumor therapeutic avenue. Recent studies have shown a loss of STING expression in cancer and an overall dysregulation of the CGAS/STING pathway. A potential mechanism of STING silencing is the methylation of its promoter. Using bulk methylation array data from patient samples, we explore epigenetic control of the TMEM173 gene that encodes STING. We find that the STING promoter is highly methylated in glioblastoma and that STING RNA expression is correspondingly low. Methylation data from normal brain and non-cancer cerebral diseases reveal a consistent pattern of STING promoter hypermethylation in these diverse states. The degree of bulk STING methylation in GBM samples inversely correlates with tumor purity and markers of immune infiltration. Single-cell transcriptome sequencing reveals that STING is expressed specifically in immune cells and endothelial cells, but not glioma cells. Collectively these results suggest that STING signalling is disrupted in GBM, that STING is epigenetically silenced by DNA methylation in the tumor, and that STING expression in bulk GBM tumor samples arises from infiltrating immune cells in the tumor microenvironment. Therapeutic approaches stimulating the innate STING signalling pathway are therefore likely to be effective on infiltrating immune cells rather than tumor cells themselves. This work motivates further study into mechanisms of STING activation in the broader GBM tumor microenvironment.

CTIM-23. A PHASE 1 TRIAL OF D2C7-IT IN COMBINATION WITH ATEZOLIZUMAB IN RECURRENT WHO GRADE IV MALIGNANT GLIOMA (MG)

BACKGROUND

D2C7 immunotoxin (D2C7-IT) is a dual-specific recombinant immunotoxin comprising an EGFR-wt and mutant-specific (EGFRvIII) monoclonal antibody fragment and a genetically engineered form of the pseudomonas exotoxin. When injected directly into the tumor mass by convection enhanced delivery (CED), in addition to direct tumor cell killing, immunotoxins induce secondary immune responses by the activation of CD4+ and CD8+ T-cells. We completed a phase 1 dose escalation study of D2C7-IT injected by CED into recurrent WHO grade III-IV MG and identified the phase 2 dose (6,920 ng/mL). Three patients remain in partial response more than 58, 38, and 32 months after a single D2C7-IT intratumoral infusion. As optimal induction of anti-tumor immune responses by immunotoxins is impeded by potent MG-mediated immunosuppression, we are assessing the toxicity of the combination of D2C7-IT with atezolizumab in patients with recurrent WHO grade IV MG.

METHODS

Eligibility includes adult patients with recurrence of a solitary supratentorial WHO grade IV MG; ≥4 weeks after chemotherapy, bevacizumab or study drug; adequate organ function; and KPS &gt;70%. Patient receives an intratumoral infusion of D2C7-IT and initiates two weeks later atezolizumab at 1200mg, followed by atezolizumab every 3 weeks for up to 2 years. Two cohorts of 3 patients are initially accrued to assess the toxicity of the combination. Assuming accrual continues after the initial two cohorts of 3 patients, an additional 12 patients will be accrued to the study.

RESULT

The first enrolled patient experienced a grade 3 DLT (grade III ALT elevation) after the first infusion of atezolizumab, but showed a more extensive immunotherapeutic effect by imaging than observed with patients on the D2C7-IT monotherapy trial. Enrollment is ongoing.

CONCLUSION

D2C7-IT monotherapy has shown prolonged survival and disease control in some patients. We are now evaluating the combination of D2C7-IT with checkpoint inhibition.

NCOG-38. CLINICAL CHARACTERISTICS OF LOW GRADE GLIOMA PATIENTS WITH NON-CANONICAL IDH1 AND IDH2 MUTATIONS

BACKGROUND

Low grade gliomas (LGGs) develop in young adults and represent 10-15% of all glial tumors. While LGG patients can have longer survival than higher grade tumors, progression, transformation, and ultimately mortality occurs. Mutations in Isocitrate dehydrogenase 1/2 (IDH1/IDH2) are prevalent in LGG and are responsible for gliomagenesis. The classic IDH1 mutation is located at 132 codon and represented as p.Arg132His, but there are non-canonical IDH1 and IDH2 mutations. We sought to compare clinical characteristics of LGG patients with classic IDH1 p.Arg132His mutation to LGG patients with non-canonical IDH1 and IDH2 mutations.

METHODS

We queried an IRB-approved registry retrospectively from 12/2004- 9/2019. We included IDH1/IDH2 mutant LGG (WHO grade II) and known IDH1 and IDH2 targeted mutation analysis using standard PCR followed by DNA sequencing to detect point mutations in IDH1/IDH2 genes. We obtained available clinical and histopathological data. We estimated progression-free survival (PFS), time to transformation (TT), and overall survival (OS) using Kaplan-Meier methods.

RESULTS

We identified 267 LGG patients with median follow-up of 9.1 yrs (95%CI 8.4-9.9 yrs). Classic IDH1 p.Arg132His mutation occurred in 223 (83.9%) patients. IDH2 mutations occurred in 14 (5.2%) patients. Non-canonical IDH1 mutations were in 30 (11.2%) patients and included the following mutations: p.Arg132Cys (13), p.Arg132Gly (10), p.Arg132Ser (4), p.Arg132Leu (1), p.Arg119Gln (1), and p.Arg172Met (1). Initial presentation, OS, and TT did not differ between IDH1/IDH2 groups. PFS differed significantly between groups with improved median PFS in IDH2 mutant LGG (5.4 yrs; 95%CI 3.5-25.2) versus classic IDH1 mutant LGG (4.1 yrs; 95%CI 3.7-4.9 yrs) and non-canonical IDH1 mutant LGG (2.6 yrs; 95%CI 2.1-4.8) (log-rank p=0.019). Notably, non-canonical mutations were more common in astrocytoma (22/30; 73.3%) than other LGG histologies (p=0.018).

CONCLUSIONS

In this cohort, LGG patients with non-canonical mutations have a shorter time to progression than patients with classic p.Arg132His mutation and IDH2 mutations.

EPID-06. QUANTIFYING THE POTENTIAL PUBLIC HEALTH IMPACT OF VARICELLA ZOSTER VIRUS (VZV) VACCINATION ON GLIOMA INCIDENCE

BACKGROUND

Varicella zoster virus (VZV) is a neurotropic a-herpesvirus that causes chickenpox and establishes latency in the dorsal root ganglion. Live attenuated VZV vaccine was approved for use in 1995, with the CDC estimating 95% of teens had been vaccinated in 2014. Prior epidemiological literature suggests an association between VZV infection and glioma risk.

METHODS

We conducted a systematic review and meta-analysis of prior studies on the association between VZV infection and glioma risk. We also identified genetic instruments for VZV infection from prior GWAS and tested these for association with glioma risk in TCGA and GliomaScan (2244 cases, 4914 controls).

RESULTS

In six previous studies, individuals with positive chickenpox history or anti-VZV IgG seropositivity had 1.8-fold lower odds of glioma (ORmeta=0.55, 95%Cl=0.39–0.77), with similar effects by grade. GWAS hits for personal history of chickenpox (HLA-A Gly107 and rs9266089) and shingles (HLA-AArg97, HLA-DRB1 PheSerHis13, rs2523591, rs41316748 and rs7047299) were not associated with glioma risk, nor were polygenic scores (P &gt;0.05).

DISCUSSION

Prior VZV infection is associated with reduced glioma risk and, based on analysis of genetic instruments, this appears to be an acquired protection caused by VZV infection rather than innate immunologic differences. VZV infection in known to elicit a broader antibody response than vaccination, but it is unknown whether VZV vaccination provides comparable protection against glioma. Because 89% of U.S. adults have had chickenpox, the “prevented fraction” of glioma due to chickenpox is ~29% of annual incidence. If VZV vaccination confers an equivalent 1.8-fold reduction in glioma risk, this prevented fraction could increase to 32%. However, if VZV vaccination is less protective, it could decrease to just 2%. This potentially drastic increase in glioma incidence in coming decades merits mechanistic studies comparing the neuro-immunologic consequences of VZV vaccination versus chickenpox infection and warrants early public health attention.

TMOD-27. EFFICACY OF SOLUBLE PANOBINOSTAT (MTX110) IN PRECLINICAL MODELS OF ADULT GLIOBLASTOMA

INTRODUCTION

Panobinostat is a histone deacetylase (HDAC) inhibitor with antineoplastic and anti-angiogenic effects in glioma. HDAC inhibitors have demonstrated therapeutic efficacy preclinically via multiple mechanisms, including the induction of cell-cycle arrest, differentiation, senescence, apoptosis, mitotic cell death, autophagy, generation of reactive oxygen species, inhibition of angiogenesis and metastasis, and improvement in tumor immunity. One of the biggest challenges in treating glioblastoma is achieving effective local drug concentrations, and trials using systemic administration of therapeutics have failed in GBM despite compelling pre clinical evidence. MTX110 (Midatech Pharma plc) is a water-soluble form of panobinostat currently in clinical development for DIPG and medulloblastoma using direct tumour delivery. We explored the therapeutic potential of MTX110 in GBM in our preclinical in vivo adult brain tumor models.

METHODS

Tumor-bearing mice were stratified to either the vehicle control or treatment group based on median tumor volume and were treated with Panobinostat/MTX110 at a dose of 15mg/kg IP, twice weekly for 5 consecutive weeks. The response to treatment was assessed by delay in tumor growth in days, expressed as a T (Treated) - C (Control) value. Statistical analysis was performed using SAS (a statistical analysis program) and the Wilcoxon rank order test.

RESULTS

MTX110 produced non-significant growth delays of 10.76 and 2.01 days (p Value ≥ 0.072 NS) in IDH wild type xenograft lines. However, in an IDH1 mutated line, MTX110 produced a significant growth delay of 23.35 days (p Value ≤ 0.018). Further work is ongoing to look at the therapeutic potential of MTX110 in combination with radiation in both IDH wild type and IDH mutated xenograft lines.

Cluster analysis of urinary tobacco biomarkers among U.S. adults: Population Assessment of Tobacco and Health (PATH) biomarker study (2013-2014)

Tobacco use delivers nicotine, tobacco-specific nitrosamines (TSNAs), volatile organic compounds (VOCs), and polycyclic aromatic hydrocarbons (PAHs), which are metabolized and excreted in urine offering useful biomarkers of exposure. Previous studies compared individual toxicants across tobacco users. Based on a group of biomarkers, cluster analysis was used to define tobacco toxicant exposure profiles. Clusters with distinct exposure profiles, were determined and described, based on levels of urinary biomarkers of exposure to nicotine, TSNAs, VOCs, and PAHs among a national sample of current, established, adult tobacco users, and examine the association of use behavior and cluster membership. The PATH Biomarker Wave 1 data were analyzed. Current established tobacco users with complete urinary biomarker data were included (N = 6724). User groups included cigarette smokers, users of electronic cigarette (ECIG), smokeless tobacco (SLT), and dual and poly tobacco users. Cluster analysis, pairwise comparisons, and multinomial logistic regression were conducted. Cigarette smokers were primarily in clusters with high biomarker concentrations across all groups, but actual concentrations were associated with smoking quantity. A cluster with high TSNAs but low levels of PAHs and VOCs was heavily populated by SLT users. Exclusive ECIG users, depending on use frequency, were predominantly in clusters with low biomarker concentrations, except for one cluster that had relatively high TSNAs. Clusters heavily populated by dual and poly tobacco users were the same as those heavily populated by cigarette smokers. Ten exposure profiles (clusters) were determined and linked to tobacco use behavior. Findings could inform future research and policy initiatives.

Cyclic Peptide [R4W4] in Improving the Ability of First-Line Antibiotics to Inhibit Mycobacterium tuberculosis Inside in vitro Human Granulomas

Tuberculosis (TB) is currently one of the leading causes of global mortality. Medical non-compliance due to the length of the treatment and antibiotic side effects has led to the emergence of multidrug-resistant (MDR) strains of Mycobacterium tuberculosis (M. tb) that are difficult to treat. A current therapeutic strategy attempting to circumvent this issue aims to enhance drug delivery to reduce the duration of the antibiotic regimen or dosage of first-line antibiotics. One such agent that may help is cyclic peptide [R₄W₄], as it has been shown to have antibacterial properties (in combination with tetracycline) against methicillin-resistant Staphylococcus aureus (MRSA) in the past. The objective of this study is to test cyclic peptide [R₄W₄] both alone and in combination with current first-line antibiotics (either isoniazid or pyrazinamide) to study the effects of inhibition of M. tb inside in vitro human granulomas. Results from our studies indicate that [R₄W₄] is efficacious in controlling M. tb infection in the granulomas and has enhanced inhibitory effects in the presence of first-line antibiotics.

Current medulloblastoma subgroup specific clinical trials

Medulloblastoma is a heterogeneous disease with at least four distinct molecular subgroups: wingless (WNT), sonic hedgehog (SHH), Group 3, and Group 4. Recently there has been considerable progress defining the molecular drivers and prognostic factors of each subgroup. However, this information has only rarely been used to stratify risk or impact treatment. The purpose of this work is to provide an update on current clinical trials that provide molecularly stratified treatment paradigms. A search was conducted on ClinicalTrials.gov using the following search terms: "medulloblastoma and subgroup", "medulloblastoma and SHH", "medulloblastoma and WNT", and "medulloblastoma and Non-WNT/Non-SHH". This search resulted in nine distinct clinical trials, five for newly diagnosed medulloblastoma and four for recurrent medulloblastoma. Four trials for newly diagnosed medulloblastoma had a component of craniospinal irradiation reduction for patients with WNT medulloblastoma. Molecularly stratified trials for recurrent medulloblastoma largely focus on SHH. As these trials are ongoing, there are limited data available. A trial in which newly-diagnosed WNT patients received modest chemotherapy without radiation has been closed to accrual due to several early failures. Phase II trials evaluating vismodegib for SHH medulloblastoma in children and adults have been disappointing. In conclusion, although there is an expanding array of clinical trials which incorporate molecular data in prescribing treatment for newly-diagnosed and recurrent medulloblastoma, treatments for these diseases are fairly uniform, with craniospinal radiation dose being the main variable. As the drivers of the distinct subgroups and their associated prognoses are better elucidated, future clinical trials and novel targeted agents are needed to improve outcomes and reduce toxicity where feasible.

Outcomes of a randomized controlled trial assessing a smartphone Application to reduce unmet needs among people diagnosed with CancEr (ACE)

BACKGROUND

Smartphone technology represents an opportunity to deliver practical solutions for people affected by cancer at a scale that was previously unimaginable, such as information, appointment monitoring, and improved access to cancer support services. This study aimed to determine whether a smartphone application (app) reduced the unmet needs among people newly diagnosed with cancer.

METHODS

A single blind, multisite randomized controlled trial to determine the impact of an app-based, 4-month intervention. Newly diagnosed cancer patients were approached at three health service treatment clinics.

RESULTS

Eighty-two people were randomized (intervention; n = 43 and control; n = 39), average age was 59.5 years (SD: 12.9); 71% female; 67% married or in a de facto relationship. At baseline, there were no differences in participants' characteristics between the groups. No significant effects, in reducing unmet needs, were demonstrated at the end of intervention (4-month) or 12-month follow-up. Overall, 94% used the app in weeks 1-4, which decreased to 41% in weeks 13-16. Mean app use time per participant: Cancer Information, 6.9 (SD: 18.9) minutes; Appointment Schedule, 5.1 (SD: 9.6) minutes; Cancer Services 1.5 minutes (SD: 6.8); Hospital Navigation, 1.4 (SD: 2.8) minutes.

CONCLUSIONS

Despite consumer involvement in the design of this smartphone technology, the app did not reduce unmet needs. This may have been due to the study being underpowered. To contribute to a meaningful understanding and improved implementation of smartphone technology to support people affected by cancer, practical considerations, such as recruitment issues and access to, and confidence with, apps, need to be considered. Australian New Zealand Clinical Trials Registration (ACTRN) Trial Registration: 12616001251415; WEF 7/9/2016.

PDCT-03. CHEMOTHERAPY STRATEGIES FOR YOUNG CHILDREN NEWLY DIAGNOSED WITH MEDULLOBLASTOMA UP TO THE ERA OF MOLECULAR PROFILING – A COMPARATIVE OUTCOMES ANALYSIS

BACKGROUND/OBJECTIVE

Survival had been poor in several multi-center/national studies since the 1980s attempting to delay, avoid or minimize brain irradiation in young children with medulloblastoma. The introduction of regimens in Germany incorporating both intravenous high-dose (HD-MTX) and intraventricular (IVENT-MTX) methotrexate, as well as regimens in North America incorporating marrow-ablative chemotherapy with autologous hematopoietic cell rescue (HDCx+AuHCR), have reported encouraging outcomes. The objective of this report is to perform a comparative outcomes analysis of these differing strategies.

METHODS

Data from 17 prospective multi-center trials published between 1990 and 2018 for children under six years old with medulloblastoma were reviewed; event-free (EFS) and overall survivals (OS) were compared.

RESULTS

Two trials using full-dose cranio-spinal irradiation with or without chemotherapy reported 5-year survivals of 32–38%. Three trials using standard chemotherapy with delayed irradiation reported 2-4-year EFS and OS of 23–34% and 31–46%. Two trials employing standard chemotherapy without irradiation reported 3-5-year EFS and OS of 22–33% and 34–43%. Four trials incorporating HD-MTX with or without IVENT-MTX reported 5-10-year EFS and OS of 56–59% and 67–80%, and 31% and 59% respectively; one trial with HD-MTX without IVENT-MTX for localized desmoplastic/nodular medulloblastoma (DN-MB) reported 2-year EFS and OS of 52% and 92%. Finally, five trials employing induction chemotherapy, with or without HD-MTX, followed by single or tandem HDCx+AuHCR have reported 3-5-year EFS and OS of 45–60% and 60–70%.

CONCLUSIONS

The best survivals are observed in trials including HD-MTX and IVENT-MTX or including HD-MTX during induction followed by HDCx+AuHCR. Because histology/biology (classic and large cell/anaplastic versus DN-MB; SHH versus non-SHH subtypes) have crucial prognostic roles, EFS and irradiation-free survival advantages require analysis in these settings. The benefit of these trials appears true for all young children with medulloblastoma. Risk-adapted treatment stratification for young children may be improved by molecular profiling of SHH- and non-SHH medulloblastoma.