Abstract 234: ITCC-P4: Genomic profiling and analyses of pediatric patient tumor and patient-derived xenograft (PDX) models for high throughput in vivo testing

Advancements in state-of-the-art molecular profiling techniques have resulted in better understanding of pediatric cancers and driver events. It has become apparent that pediatric cancers are significantly more heterogeneous than previously thought as evidenced by the number of novel entities and subtypes that have been identified with distinct molecular and clinical characteristics. For most of these newly recognized entities there are extremely limited treatment options available. The ITCC-P4 consortium is an international collaboration between several European academic centers and pharmaceutical companies, with the overall aim to establish a sustainable platform of >400 molecularly well-characterized PDX models of high-risk pediatric cancers, their tumors and matching controls and to use the PDX models for in vivo testing of novel mechanism-of-action based treatments. Currently, 251 models are fully characterized, including 182 brain and 69 non-brain PDX models, representing 112 primary models, 92 relapse, 42 metastasis and 4 progressions under treatment models. Using low coverage whole-genome and whole exome sequencing, somatic mutation calling, DNA copy number and methylation analysis we aim to define genetic features in our PDX models and estimate the molecular fidelity of PDX models compared to their patient tumor. Based on DNA methylation profiling we identified 43 different tumor subgroups within 18 cancer entities. Mutational landscape analysis identified key somatic and germline oncogenic drivers. Ependymoma PDX models displayed the C11orf95-RELA fusion event, YAP1, C11orf95 and RELA structural variants. Medulloblastoma models were driven by MYCN, TP53, GLI2, SUFU and PTEN. High-grade glioma samples showed TP53, ATRX, MYCN and PIK3CA somatic SNVs, along with focal deletions in CDKN2A in chromosome 9. Neuroblastoma models were enriched for ALK SNVs and/or MYCN focal amplification, ATRX SNVs and CDKN2A/B deletions. Tumor mutational burden across entities and copy number analysis was performed to identify allele-specific copy number detection in tumor-normal pairs. Large chromosomal aberrations (deletions, duplications) detected in the PDX models were concurrent with molecular alterations frequently observed in each tumor type -isochromosome 17 was detected in 5 medulloblastoma models, while deletion of chromosome arm 1p or gain of parts of 17q in neuroblastomas which correlate with tumor progression. We observe clonal evolution of somatic variants not only in certain PDX-tumor pairs but also between disease states. The multi-omics approach in this study provides insight into the mutational landscape and patterns of the PDX models thus providing an overview of molecular mechanisms facilitating the identification and prioritization of oncogenic drivers and potential biomarkers for optimal treatment therapies.

Citation Format: Apurva Gopisetty, Aniello Federico, Didier Surdez, Yasmine Iddir, Sakina Zaidi, Alexandra Saint-Charles, Joshua Waterfall, Elnaz Saberi-Ansari, Justyna Wierzbinska, Andreas Schlicker, Norman Mack, Benjamin Schwalm, Christopher Previti, Lena Weiser, Ivo Buchhalter, Anna-Lisa Böttcher, Martin Sill, Robert Autry, Frank Estermann, David Jones, Richard Volckmann, Danny Zwijnenburg, Angelika Eggert, Olaf Heidenreich, Fatima Iradier, Irmela Jeremias, Heinrich Kovar, Jan-Henning Klusmann, Klaus-Michael Debatin, Simon Bomken, Petra Hamerlik, Maureen Hattersley, Olaf Witt, Louis Chesler, Alan Mackay, Johannes Gojo, Stefano Cairo, Julia Schueler, Johannes Schulte, Birgit Geoerger, Jan J. Molenaar, David J. Shields, Hubert N. Caron, Gilles Vassal, Louis F. Stancato, Stefan M. Pfister, Natalie Jaeger, Jan Koster, Marcel Kool, Gudrun Schleiermacher. ITCC-P4: Genomic profiling and analyses of pediatric patient tumor and patient-derived xenograft (PDX) models for high throughput in vivo testing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 234.

Sphingosine-1-Phosphate Recruits Macrophages and Microglia and Induces a Pro-Tumorigenic Phenotype That Favors Glioma Progression

Glioblastoma is the most aggressive brain tumor in adults. Treatment failure is predominantly caused by its high invasiveness and its ability to induce a supportive microenvironment. As part of this, a major role for tumor-associated macrophages/microglia (TAMs) in glioblastoma development was recognized. Phospholipids are important players in various fundamental biological processes, including tumor-stroma crosstalk, and the bioactive lipid sphingosine-1-phosphate (S1P) has been linked to glioblastoma cell proliferation, invasion, and survival. Despite the urgent need for better therapeutic approaches, novel strategies targeting sphingolipids in glioblastoma are still poorly explored. Here, we showed that higher amounts of S1P secreted by glioma cells are responsible for an active recruitment of TAMs, mediated by S1P receptor (S1PR) signaling through the modulation of Rac1/RhoA. This resulted in increased infiltration of TAMs in the tumor, which, in turn, triggered their pro-tumorigenic phenotype through the inhibition of NFkB-mediated inflammation. Gene set enrichment analyses showed that such an anti-inflammatory microenvironment correlated with shorter survival of glioblastoma patients. Inhibition of S1P restored a pro-inflammatory phenotype in TAMs and resulted in increased survival of tumor-bearing mice. Taken together, our results establish a crucial role for S1P in fine-tuning the crosstalk between glioma and infiltrating TAMs, thus pointing to the S1P-S1PR axis as an attractive target for glioma treatment.

EPCO-47. ITCC-P4: GENOMIC PROFILING AND ANALYSES OF PEDIATRIC PATIENT TUMOR AND PATIENT-DERIVED XENOGRAFT (PDX) MODELS FOR HIGH THROUGHPUT IN VIVO TESTING

Advancements in state-of-the-art molecular profiling techniques has resulted in better understanding of pediatric cancers and their drivers. Conversely, it also became apparent that pediatric cancers are much more heterogeneous than previously thought. Many new types and subtypes of pediatric cancers have been identified with distinct molecular and clinical characteristics. However, for most newly recognized entities there is no specific treatment available yet. The ITCC-P4 consortium is a collaboration between many academic centers across Europe and several pharmaceutical companies involved in preclinical testing, with the overall aim to establish a sustainable platform of >400 molecularly well-characterized PDX models of high-risk pediatric cancers and to use them for in vivo testing of novel mechanism-of-action based treatments. Currently, 340 models are fully established, including 87 brain and 253 non-brain tumor models, together representing different tumor types both from primary (113) and relapsed (92)/metastatic disease (42). 252 of these models have been fully molecularly characterized, representing 18 pediatric cancer entities and 43 different subtypes. Using low coverage whole-genome and whole exome sequencing, somatic mutation calling, DNA copy number, transcriptome analysis and methylation profiling we have observed that the molecular profile of most PDX models closely mimics their original tumors. Clonal evolution of somatic variants was only observed in some PDX-tumor pairs or so between disease states. Somatic copy number variant analysis highlights specific alterations for instance MYB, MYC, MYCN, NTRK3, PTEN loss differently distributed between PDX-patient tumor pairs in high-grade gliomas. Overall, our results show that we have established >250 PDX models of solid pediatric cancers, that well represents the disease spectrum and that is currently being used for in vivo testing of standard of care drugs and targeted small molecules. Treatment responses will be directly linked to molecular data to identify potential biomarkers for prioritization or deprioritization of individual, patient-specific specific drugs.

IMMU-11. Evaluation of CAR-T cells targeting CD276 in medulloblastoma

Brain tumors are the most frequent category of solid tumors in children and have the highest mortality rate among all pediatric cancers. Although diagnosis and treatment have improved prognosis over the past decades for some childhood brain tumors, others remain lethal and current treatments are highly toxic to the developing brain, resulting in severe sequelae and considerably affecting the patient’s quality of life. Thus, new therapeutic options with reduced secondary effects are urgently needed. From this perspective, immunotherapies have gained a lot of attention due to their effectiveness in targeting tumor cells specifically. Chimeric-antigen receptor (CAR) T-cells recognize the target antigen on the surface of. CD276 is an immune checkpoint molecule that is expressed in a variety of solid tumor entities, including pediatric brain tumors. We analyzed the CD276 expression in our Patient-Derived-Xenograft (PDX) biobank of brain tumors and found that CD276 is ubiquitously expressed (ATRT, MB, EPN, GBM, ETMR, etc). Flow cytometry of MB PDX (n=4) confirmed CD276 expression of 97-99% of tumor cells, indicating that CD276 might be a good antigen target for CAR-T cell therapy of MBG3 and MBSHH. We found that second generation CAR-T cells targeting CD276 antigen significantly decreased tumor burden of the most aggressive MB subgroups (G3 and SHH-TP53mut PDX models) in NSG mice. We further treated NSG mice carrying a high tumor burden of the aggressive SHH-TP53mut PDX BT084 with second (CD28) and third generation (CD28-41BB) CD276-CAR-T cells. While both 2nd and 3rd generation improved the survival rates compared with CD19-CAR-T control cells, we found no difference in survival between the CD276 CAR-T generations, with no severe secondary effect during treatment. In conclusion, CD276 is a good antigen target for medulloblastoma, and warrants further evaluation for the treatment of medulloblastoma patients at relapse or as a maintenance therapy after standard treatment.

MEDB-50. Assessment of cellular radiosensitivity and DNA repair in medulloblastoma cell lines and patient-derivded xenograft slice cultures

Medulloblastoma (WHO grade 4) is the most common malignant brain tumor of childhood. Despite the high importance of radiotherapy for disease control, the mechanisms underlying response and resistance to radiotherapy are incompletely understood. Therefore, we assessed the radiosensitivity and DNA repair capacity of medulloblastoma cell lines in-vitro and of patient-derived xenograft (PDX) models ex-vivo. Cell survival after irradiation of seven medulloblastoma cell lines displaying different subgroups was assessed via colony formation assay (DAOY, UW228, UW473, SJMM4, ONS-76, HDMB-03, D283). The ONS-76 and the mouse SJMM4 cell line were the most radioresistant strains (surviving fraction after 6 Gy (SF6): 0.33 and 0.31, respectively), followed by UW473, UW 228 and DAOY cells (SF6 0.16-0.21). The non-WNT/non-SHH-activated cell lines HDMB-03 and D283 cells demonstrated profoundly higher cellular radiosensitivity (SF6 <0.05). Analysis of residual (24h after irradiation) DNA double-strand breaks (DSB) as assessed by co-localized γH2AX/53BP1-foci demonstrated a significant correlation between DSB repair capacity and cellular survival. To use a more reliable pre-clinical model for medulloblastoma, we further examined DNA repair foci in ex-vivo irradiated slice cultures of PDX models MED-113 (SHH) and NCH2194 & HT028 (Gr. 3). Immunofluorescence analyses of frozen sections demonstrated non-hypoxic (pimonidazole-negative) and proliferating (EdU-positive) cells at the outer rim of the tumor slices. Two hours after irradiation all three PDX models showed a strong increase in 53BP1-foci, clearly indicating DNA damage induction. Most radiation-induced DSB were repaired after 24h. In a first radiosensitization approach, we treated the HT028 model with the PARP inhibitor olaparib (1µM ± 2Gy irradiation). Twenty-four hours after treatment the sample displayed a strong increase in the amount and size of 53BP1-foci, indicating compromised DNA repair. Further in-vitro and ex-vivo investigations with the aim to predict individual radiosensitivity and effective radiosensitization strategies are ongoing.

MEDB-52. Organoids as preclinical models to improve and personalize disease outcome for sonic hedgehog medulloblastoma

Four main medulloblastoma (MB) molecular subgroups are known, including the sonic hedgehog (SHH) subgroup, which represents ~25% of MB cases. The 5-year overall survival of SHH-MB is ~80%. However, survival between patients is highly diverse and dependent on the driver mutation(s) of the tumor. Patients with TP53 mutated tumors (often accompanied with MYCN and/or GLI2 amplifications) don’t respond well to current therapies and have a 10-year overall survival below 20%. Therefore, there is a need for new and more tailored therapies for these patients. In this study we aim to screen patient-derived organoid models of TP53-mutated SHH MB with a library of ~200 different compounds. We have optimized the cultures of two PDX-derived and one patient-derived organoid line in vitro. The lines will be screened in a high-throughput manner and the best hits and combinations will be validated in corresponding in vivo PDX models. To further assess the role of specific mutations in therapy outcome of TP53-mutated SHH MB, cerebellar organoids generated from human iPSCs were genetically modified with overexpression of dominant-negative P53 (DNP53) alone or in combination with MYCN and/or GLI2. Introduction of DNP53 and MYCN overexpression in cerebellar organoids at day 28/35 leads to the outgrowth of a Ki67-positive proliferating mass after three weeks, indicating tumor growth. Further analyses are ongoing to see how they match SHH-MB patient tumors. These genetically engineered organoid models may elucidate the role of specific mutations in therapy response and/or resistance. In addition, as tumors in these genetically engineered cerebellar organoids arise in a microenvironment of normal cerebellar cell types, initial safety of drugs on cerebellar cells can be assessed. In conclusion, different organoid models of TP53-mutated SHH MB will enable us to find more effective treatments and to better understand how to treat patients with different mutation combinations.

MODL-04. Drug screening in Disorders with Abnormal DNA Damage Response/Repair (DADDR) andin vivo validation

INTRODUCTION: Disorders with Abnormal DNA Damage Response/Repair (DADDRs) are inherited conditions caused by constitutional mutations of DNA damage response and repair genes and are characterized by an increased cancer risk. Furthermore, affected individuals also show an elevated risk of secondary neoplasms as well as excessive toxicity, poor therapy response and increased mortality when treated with standard radiation and chemotherapy regimens. The main aim of this project is to screen for potential novel chemotherapeutic approaches for these cancer entities, and to employ faithful PDX models for in vivo validation. METHODS: In vitro drug screening was performed using a custom library composed of 345 compounds targeting 61 different proteins. For two specific DADDRs, Li-Fraumeni syndrome (LFS) and Constitutional Mismatch Repair Deficiency (CMMRD), two cancerous (glioblastoma and medulloblastoma) and one non-cancerous cell lines were selected to model each of these conditions. Performance of each drug was assessed based on its efficacy (sensitivity score) and genotoxicity (micronucleus assay). For DADDR PDX model establishment tumor material from DADDR patients is currently being injected orthotopically (brain tumors) or subcutaneously (non-brain tumors) into NSG mice. Following engraftment and expansion, the PDX models will be characterized molecularly and compared with original patient material. RESULTS AND OUTLOOK: In vitro screening revealed n=26 drugs that fulfilled the following criteria: a) favorable toxicity in cancerous cell lines compared to non-cancerous cell lines, b) little to no genotoxic effect in non-cancerous cell lines. These characteristics qualify them as potentially suitable candidates for novel therapeutic approaches specifically for DADDR patients. The hits included inhibitors of ATM/ATR, CHK1/CHK2, DHFR, mTOR and PI3K, as well as microtubule-associated compounds. Combination testing and further validation of these hits using disease-specific in vitro and in vivo PDX models is ongoing.

INSP-15. ITCC-P4: A sustainable platform of molecularly well-characterized PDX models of pediatric cancers for high throughputin vivo testing

Thanks to state-of-the-art molecular profiling techniques we by now have a much better understanding of pediatric cancers and what is driving them. On the other hand, we have also realized that pediatric cancers are much more heterogeneous than previously thought. Many new types and subtypes of pediatric cancers have been identified with distinct molecular and clinical characteristics. However, for many if not most of these new types and subtypes there is no specific treatment available, yet. In order to develop specific treatment protocols and to increase survival rates for pediatric cancer patients further, both at diagnosis and relapse/metastasis, we need a large collection of well-characterized preclinical models representing all the different types and subtypes. These models can be used for preclinical drug testing to prioritize the pediatric development of anticancer drugs that would be best targeting pediatric tumor biology. The ITCC-P4 consortium, which is a collaboration between many academic centers across Europe, several companies involved in in vivo preclinical testing, and ten pharmaceutical companies, started in 2017 with the overall aim to establish a sustainable platform of &gt;400 molecularly well-characterized PDX models of high-risk pediatric cancers and to use them for in vivo testing of novel mechanism-of-action based treatments. Currently, 340 models have been fully established, including 87 brain tumor models and 253 non-brain tumor models, together representing many different tumor types both from primary and relapsed/metastatic disease. Out of these 340 models, 252 have been fully molecularly characterized, most of them together with their matching original tumors, and almost of all these models are currently being subjected to in vivo testing using three standard of care drugs and six novel mechanism-of-action based drugs. In this presentation, an update on the current status of the ITCC-P4 platform and the data we collectively have generated thus far will be presented.

MODL-01. Targeting replication stress in pediatric brain tumors

Previously, we have found that Embryonal Tumors with Multilayered Rosettes (ETMR) tumor cells harboring high levels of R-loops, a potential marker for replication stress and genomic instability, are vulnerable to a combination of topoisomerase and PARP inhibitors. To follow up on this, we investigated whether other pediatric brain tumor types with high levels of R-loops, such as MYC-amplified Group 3 medulloblastoma (MB) and ZFTA-fusion positive ependymoma, are also sensitive to these inhibitors. First, we performed in vitro drug screens using HD-MB03, a Group 3 MB cell line, and the ETMR cell line BT183, and in both screens PARP inhibitors were identified as the most synergistic combination partners for the topoisomerase inhibitor Irinotecan, respectively the active metabolite SN-38. Normal Astrocytes were not sensitive to these combinations. Secondly, we performed in vivo studies using patient-derived xenograft (PDX) models injected subcutaneously or intracranially into NSG mice, and treated with the PARP inhibitor Pamiparib, Irinotecan or a combination of both. For a MYC-amplified Group 3 MB and a ZFTA-fusion positive Ependymoma model, both injected intracranially, treatment with Irinotecan or the combination led to a significant survival benefit and inhibition of tumor growth including transient tumor shrinkage, but addition of Pamiparib did not add any further benefit in vivo, even though intratumoral PARP was inhibited by at least 80%. In contrast, in the subcutaneously injected ETMR model, the combination treatment with Irinotecan and Pamiparib led to a synergistic effect and complete regression of the tumors. Further refinements of the treatment strategy as dose adaptations and the use of a pegylated version of SN-38 (PLX038A) did also not induce a synergistic effect of the drugs for the intracranial tumors. Additional in vivo studies to evaluate the differences in efficacy and whether these are tumor specific or due to incomplete brain penetrance of the drugs are ongoing.

Carbon ion radiotherapy eradicates medulloblastomas with chromothripsis in an orthotopic Li-Fraumeni patient-derived mouse model

Background

Medulloblastomas with chromothripsis developing in children with Li-Fraumeni Syndrome (germline TP53 mutations) are highly aggressive brain tumors with dismal prognosis. Conventional photon radiotherapy and DNA-damaging chemotherapy are not successful for these patients and raise the risk of secondary malignancies. We hypothesized that the pronounced homologous recombination deficiency in these tumors might offer vulnerabilities that can be therapeutically utilized in combination with high linear energy transfer carbon ion radiotherapy.

Methods

We tested high-precision particle therapy with carbon ions and protons as well as topotecan with or without PARP inhibitor in orthotopic primary and matched relapsed patient-derived xenograft models. Tumor and normal tissue underwent longitudinal morphological MRI, cellular (markers of neurogenesis and DNA damage-repair), and molecular characterization (whole-genome sequencing).

Results

In the primary medulloblastoma model, carbon ions led to complete response in 79% of animals irrespective of PARP inhibitor within a follow-up period of 300 days postirradiation, as detected by MRI and histology. No sign of neurologic symptoms, impairment of neurogenesis or in-field carcinogenesis was detected in repair-deficient host mice. PARP inhibitors further enhanced the effect of proton irradiation. In the postradiotherapy relapsed tumor model, median survival was significantly increased after carbon ions (96 days) versus control (43 days, P < .0001). No major change in the clonal composition was detected in the relapsed model.

Conclusion

The high efficacy and favorable toxicity profile of carbon ions warrants further investigation in primary medulloblastomas with chromothripsis. Postradiotherapy relapsed medulloblastomas exhibit relative resistance compared to treatment-naïve tumors, calling for exploration of multimodal strategies.

H3.3-K27M drives neural stem cell-specific gliomagenesis in a human iPSC-derived model

Diffuse intrinsic pontine glioma (DIPG) is an aggressive childhood tumor of the brainstem with currently no curative treatment available. The vast majority of DIPGs carry a histone H3 mutation leading to a lysine 27-to-methionine exchange (H3K27M). We engineered human induced pluripotent stem cells (iPSCs) to carry an inducible H3.3-K27M allele in the endogenous locus and studied the effects of the mutation in different disease-relevant neural cell types. H3.3-K27M upregulated bivalent promoter-associated developmental genes, producing diverse outcomes in different cell types. While being fatal for iPSCs, H3.3-K27M increased proliferation in neural stem cells (NSCs) and to a lesser extent in oligodendrocyte progenitor cells (OPCs). Only NSCs gave rise to tumors upon induction of H3.3-K27M and TP53 inactivation in an orthotopic xenograft model recapitulating human DIPGs. In NSCs, H3.3-K27M leads to maintained expression of stemness and proliferative genes and a premature activation of OPC programs that together may cause tumor initiation.

ETMR-03. THE ROLE OF FOXR2 IN PEDIATRIC BRAIN CANCER

Forkhead Box R2 (FOXR2) is a transcription factor of the Forkhead Box family that has been correlated with tumorigenesis, aberrant cell growth or tumor progression. Expression of FOXR2 in pediatric brain tumors is, besides in subsets of medullo-, pineo- and glioblastoma, primarily present in CNS neuroblastoma with FOXR2 activation (CNS NB-FOXR2), a novel entity that we in 2016 identified from the former class of primitive neuroectodermal tumors of the central nervous system (CNS-PNET). Analyzing CNS-NB-FOXR2 tumors we found that FOXR2 mRNA is expressed in an anti-correlative manner compared to the proto-oncogenes MYC and MYCN. With immunoprecipitation analyses we show that FOXR2 binds to MYC and MYCN and is thereby stabilizing these proteins. These observations on the interaction and the anti-correlative manner suggest that FOXR2 and MYC(N) may drive tumor formation in a molecularly similar fashion. To investigate this further we stably expressed FOXR2, MYCN and MYC and a combination of FOXR2 with MYC(N) in human neural stem cells (hNSC) and injected these in the striatum of NSG mice. We could show that hNSC itself do not from a tumor, whereas the expression of FOXR2 and/or MYC(N) in hNSC results in tumorigenesis. Tumors expressing both, FOXR2 and MYC(N) were growing faster than tumors with FOXR2 alone. In addition, tumors are currently being analyzed by ChIP-sequencing for FOXR2, MYC, and MYCN, to better understand the mechanisms how FOXR2 drives tumor formation compared to its interaction partners MYC and MYCN.

MODL-02. TARGETING REPLICATION STRESS IN PEDIATRIC BRAIN TUMORS

Pediatric brain tumors harboring amplifications or high overexpression of MYC-/MYCN are often associated with poor outcome. High MYC(N) expression in these tumors leads to increased transcription, which can be in conflict with DNA replication and subsequently can cause replication stress, R-loops and DNA damage. We hypothesize that high MYC(N) expression makes them vulnerable to DNA damage response inhibitors (DDRi) and even more vulnerable to combinations of DDRi and chemotherapeutics. To test this hypothesis we performed in vitro drug experiments using Group 3 medulloblastoma (MB) and ETMR cell lines. IC50-values were evaluated of topoisomerase inhibitor Irinotecan (SN-38) and Pamiparib (BGB-290), a brain-penetrant PARP-inhibitor, in monotherapy. All cell lines were sensitive for SN-38 and showed IC50-values in the low nM-range but PARP-inhibitors were ineffective. However, a significant decrease in IC50 can be observed when SN-38 and Pamiparib are used in combination. For in vivo treatments, we injected NSG mice with luciferase labelled patient-derived xenograft- (PDX-) cells of various models (MB Group 3, MB SHH, ETMR, RELA EPN), monitored tumor growth via IVIS and randomized the mice into four groups (vehicle, BGB-290, Irinotecan and Irinotecan+Pamiparib) when a predefined threshold of tumor growth was reached. Mice were treated with Irinotecan (or vehicle) once per day i.p. and Pamiparib (or vehicle) twice per day per oral gavage. Treatment with Pamiparib did not show any survival benefit, but mice treated with Irinotecan or the combination showed a clear survival benefit. Treatments are ongoing and more results will be presented at the conference.

Functional loss of a noncanonical BCOR-PRC1.1 complex accelerates SHH-driven medulloblastoma formation

In this study, Kutscher et al. investigated the transcriptional corepressor BCOR as a putative tumor suppressor and used a genetically engineered mouse model to delete exons 9/10 of Bcor in GNPs during development. Their data suggest that BCOR–PRC1.1 disruption leads to Igf2 overexpression, which transforms preneoplastic cells to malignant tumors.

Medulloblastoma is a malignant childhood brain tumor arising from the developing cerebellum. In Sonic Hedgehog (SHH) subgroup medulloblastoma, aberrant activation of SHH signaling causes increased proliferation of granule neuron progenitors (GNPs), and predisposes these cells to tumorigenesis. A second, cooperating genetic hit is often required to push these hyperplastic cells to malignancy and confer mutation-specific characteristics associated with oncogenic signaling. Somatic loss-of-function mutations of the transcriptional corepressor BCOR are recurrent and enriched in SHH medulloblastoma. To investigate BCOR as a putative tumor suppressor, we used a genetically engineered mouse model to delete exons 9/10 of Bcor (Bcor^ΔE9–10) in GNPs during development. This mutation leads to reduced expression of C-terminally truncated BCOR (BCOR^ΔE9–10). While Bcor^ΔE9–10 alone did not promote tumorigenesis or affect GNP differentiation, Bcor^ΔE9–10 combined with loss of the SHH receptor gene Ptch1 resulted in fully penetrant medulloblastomas. In Ptch1^+/−;Bcor^ΔE9–10 tumors, the growth factor gene Igf2 was aberrantly up-regulated, and ectopic Igf2 overexpression was sufficient to drive tumorigenesis in Ptch1^+/− GNPs. BCOR directly regulates Igf2, likely through the PRC1.1 complex; the repressive histone mark H2AK119Ub is decreased at the Igf2 promoter in Ptch1^+/−;Bcor^ΔE9–10 tumors. Overall, our data suggests that BCOR–PRC1.1 disruption leads to Igf2 overexpression, which transforms preneoplastic cells to malignant tumors.

Abstract A25: Evaluation of Drug Disposition in Supratentorial Ependymoma

Introduction: The majority of pediatric supratentorial (ST) ependymomas (EPN) is driven by distinct gene fusions between C11orf95 and RELA. The resultant molecular group of ST-EPN-RELA tumors is characterized by constitutive activation of NF-κB signaling and deregulation of the p53 pathway. In contrast to surgery and radiotherapy, chemotherapy has failed to demonstrate significant benefit in the management of affected children. Alternative strategies including enhanced drug delivery, combination treatments, or application of new selective compounds are needed to tackle this disease.

Material and Methods: RNAi and drug screening methods were applied to identify potential therapeutic approaches using ST-EPN-RELA cell lines. In order to identify optimal dosing strategies of selected drugs and to assess effects of combinatorial treatment approaches on blood-brain barrier (BBB) penetration, cerebral microdialysis combined with ultraperformance liquid chromatography and tandem mass spectrometry (UPLC-MS/MS) was applied. This approach allowed for exact, continuous, and time-dependent drug quantification in tumors or healthy tissue in freely moving experimental mice. Patient-derived xenograft models of ST-EPN-RELA were treated to investigate toxicity and outcome parameters.

Results: Regulation of p53 signaling and nuclear protein shuttling were identified as promising therapeutic approaches. While low-dose dactinomycin could successfully reestablish p53 function in ST-EPN-RELA cells in vitro, penetration of the drug across the BBB was found to be very poor and did not result in a survival benefit of tumor-bearing mice. Preliminary results of alternative strategies such as combination with efflux pump inhibitors, liposomal packaging, and inhibition of XPO1 being the sole nuclear exporter of p53 hold promise to overcome these constraints.

Conclusion: Oncogenic dependencies of ST-EPN-RELA are currently difficult to target. Preclinical evaluation of effective drug disposition combined with long-term treatment studies may help to better select promising compounds and thereby increase success rates of early clinical trials in patients with ST-EPN-RELA in the future.

Citation Format: Julia Benzel, Max Sauter, Norman Mack, Abigail Davis, Johanna Weiss, Philipp Uhl, Jürgen Burhenne, Kendra K. Maass, Jens-Martin Hübner, Hendrik Witt, Anang Shelat, Amar Gajjar, Santhosh A. Upadhyaya, Aylin Camgoz, Frank Buchholz, Sina Oppermann, Marcel Kool, Daisuke Kawauchi, Olaf Witt, Walter E. Haefeli, Stefan M. Pfister, Clinton Stewart, Kristian W. Pajtler. Evaluation of Drug Disposition in Supratentorial Ependymoma [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A25.

The molecular landscape of ETMR at diagnosis and relapse

Embryonal tumours with multilayered rosettes (ETMRs) are aggressive paediatric embryonal brain tumours with a universally poor prognosis1. Here we collected 193 primary ETMRs and 23 matched relapse samples to investigate the genomic landscape of this distinct tumour type. We found that patients with tumours in which the proposed driver C19MC2-4 was not amplified frequently had germline mutations in DICER1 or other microRNA-related aberrations such as somatic amplification of miR-17-92 (also known as MIR17HG). Whole-genome sequencing revealed that tumours had an overall low recurrence of single-nucleotide variants (SNVs), but showed prevalent genomic instability caused by widespread occurrence of R-loop structures. We show that R-loop-associated chromosomal instability can be induced by the loss of DICER1 function. Comparison of primary tumours and matched relapse samples showed a strong conservation of structural variants, but low conservation of SNVs. Moreover, many newly acquired SNVs are associated with a mutational signature related to cisplatin treatment. Finally, we show that targeting R-loops with topoisomerase and PARP inhibitors might be an effective treatment strategy for this deadly disease.

YAP1 subgroup supratentorial ependymoma requires TEAD and nuclear factor I-mediated transcriptional programmes for tumorigenesis

YAP1 fusion-positive supratentorial ependymomas predominantly occur in infants, but the molecular mechanisms of oncogenesis are unknown. Here we show YAP1-MAMLD1 fusions are sufficient to drive malignant transformation in mice, and the resulting tumors share histo-molecular characteristics of human ependymomas. Nuclear localization of YAP1-MAMLD1 protein is mediated by MAMLD1 and independent of YAP1-Ser127 phosphorylation. Chromatin immunoprecipitation-sequencing analyses of human YAP1-MAMLD1-positive ependymoma reveal enrichment of NFI and TEAD transcription factor binding site motifs in YAP1-bound regulatory elements, suggesting a role for these transcription factors in YAP1-MAMLD1-driven tumorigenesis. Mutation of the TEAD binding site in the YAP1 fusion or repression of NFI targets prevents tumor induction in mice. Together, these results demonstrate that the YAP1-MAMLD1 fusion functions as an oncogenic driver of ependymoma through recruitment of TEADs and NFIs, indicating a rationale for preclinical studies to block the interaction between YAP1 fusions and NFI and TEAD transcription factors.

The molecular mechanisms driving proliferation in the pediatric brain cancer epdendymoma are poorly understood. Here the authors show that a YAP1- MAMLD1 fusion drives tumor formation in mice and show that the fusion protein can collaborate with the TEAD and NFI transcription factors.

Preclinical drug screen reveals topotecan, actinomycin D, and volasertib as potential new therapeutic candidates for ETMR brain tumor patients

Background

Embryonal tumor with multilayered rosettes (ETMR) is a rare and aggressive embryonal brain tumor that solely occurs in infants and young children and has only recently been recognized as a separate brain tumor entity in the World Health Organization classification for CNS tumors. Patients have a very dismal prognosis with a median survival of 12 months upon diagnosis despite aggressive treatment. The aim of this study was to develop novel treatment regimens in a preclinical drug screen in order to inform potentially more active clinical trial protocols.

Methods

We have carried out an in vitro and in vivo drug screen using the ETMR cell line BT183 and its xenograft model. Furthermore, we have generated the first patient-derived xenograft (PDX) model for ETMR and evaluated our top drug candidates in an in vitro drug screen using this model.

Results

BT183 cells are very sensitive to the topoisomerase inhibitors topotecan and doxorubicin, to the epigenetic agents decitabine and panobinostat, to actinomycin D, and to targeted drugs such as the polo-like kinase 1 (PLK1) inhibitor volasertib, the aurora kinase A inhibitor alisertib, and the mammalian target of rapamycin (mTOR) inhibitor MLN0128. In xenograft mice, monotherapy with topotecan, volasertib, and actinomycin D led to a temporary response in tumor growth and a significant increase in survival. Finally, using multi-agent treatment regimens of topotecan or doxorubicin combined with methotrexate and vincristine, the response in tumor growth and survival was further increased compared with mice receiving single treatments.

Conclusions

We have identified several promising candidates for combination therapies in future clinical trials for ETMR patients.

High throughput screening of natural products for anti-mitotic effects in MDA-MB-231 human breast carcinoma cells

Some of the most effective anti-mitotic microtubule-binding agents, such as paclitaxel (Taxus brevifolia) were originally discovered through robust National Cancer Institute botanical screenings. In this study, a high-through put microarray format was utilized to screen 897 aqueous extracts of commonly used natural products (0.00015-0.5 mg/mL) relative to paclitaxel for anti-mitotic effects (independent of toxicity) on proliferation of MDA-MB-231 cells. The data obtained showed that less than 1.34 % of the extracts tested showed inhibitory growth (IG50 ) properties <0.0183 mg/mL. The most potent anti-mitotics (independent of toxicity) were Mandrake root (Podophyllum peltatum), Truja twigs (Thuja occidentalis), Colorado desert mistletoe (Phoradendron flavescens), Tou Gu Cao [symbol: see text] Speranskia herb (Speranskia tuberculata), Bentonite clay, Bunge root (Pulsatilla chinensis), Brucea fruit (Brucea javanica), Madder root (Rubia tinctorum), Gallnut of Chinese Sumac (Melaphis chinensis), Elecampane root (Inula Helenium), Yuan Zhi [symbol: see text] root (Polygala tenuifolia), Pagoda Tree fruit (Melia Toosendan), Stone root (Collinsonia Canadensis), and others such as American Witchhazel, Arjun, and Bladderwrack. The strongest tumoricidal herbs identified from amongst the subset evaluated for anti-mitotic properties were wild yam (Dioscorea villosa), beth root (Trillium Pendulum), and alkanet root (Lithospermum canescens). Additional data was obtained on a lesser-recognized herb: (S. tuberculata), which showed growth inhibition on BT-474 (human ductal breast carcinoma) and Ishikawa (human endometrial adenocarcinoma) cells with ability to block replicative DNA synthesis, leading to G2 arrest in MDA-MB-231 cells. In conclusion, these findings present relative potency of anti-mitotic natural plants that are effective against human breast carcinoma MDA-MB-231 cell division.

High-Throughput Screening to Identify Plant Derived Human LDH-A Inhibitors

Aims

Lactate dehydrogenase (LDH)-A is highly expressed in diverse human malignant tumors, parallel to aggressive metastatic disease, resistance to radiation/chemotherapy and clinically poor outcome. Although this enzyme constitutes a plausible target in treatment of advanced cancer, there are few known LDH-A inhibitors.

Study Design

In this work, we utilized a high-throughput enzyme micro-array format to screen and evaluate > 900 commonly used medicinal plant extracts (0.00001-.5 mg/ml) for capacity to inhibit activity of recombinant full length human LDHA; EC .1.1.1.27.

Methodology

The protein sequence of purified enzyme was confirmed using 1D gel electrophoresis- MALDI-TOF-MS/MS, enzyme activity was validated by oxidation of NADH (500μM) and kinetic inhibition established in the presence of a known inhibitor (Oxalic Acid).

Results

Of the natural extracts tested, the lowest IC₅₀s [<0.001 mg/ml] were obtained by: Chinese Gallnut (Melaphis chinensis gallnut), Bladderwrack (Fucus vesiculosus), Kelp (Laminaria Japonica) and Babul (Acacia Arabica). Forty-six additional herbs contained significant LDH-A inhibitory properties with IC₅₀s [<0.07 mg/ml], some of which have common names of Arjun, Pipsissewa, Cinnamon, Pink Rose Buds/Petals, Wintergreen, Cat’s Claw, Witch Hazel Root and Rhodiola Root.

Conclusion

These findings reflect relative potency by rank of commonly used herbs and plants that contain human LDH-A inhibitory properties. Future research will be required to isolate chemical constituents within these plants responsible for LDH-A inhibition and investigate potential therapeutic application.

Predictors of compliance with recommended cervical cancer screening schedule: a population-based study

BACKGROUND

The prevalence of routine cervical cancer screening and compliance with screening schedules are low compared to the Year 2000 objectives. Identifying predictors of routine screening and screening schedule compliance will help achieve these objectives.

METHODS

We analyzed data from probability samples of 1,609 Missouri women responding to both the 1994 Behavioral Risk Factor Surveillance System (BRFSS) and the Missouri Enhanced Survey (ES). We generated prevalence odds ratios to identify predictors of non-compliance to cervical cancer screening guidelines. Also, among a sample of women reporting a reason for last Pap test, we estimated the relative odds of a screening v. diagnostic exam.

RESULTS

In the combined probability sample, compliance with screening schedule was likely among women younger than 50 years of age and women who had either a recent mammography or a clinical breast exam. Being African-American, not experiencing a cost barrier when seeking medical care, having at least a high-school education and health coverage were each associated with an increased compliance with a screening schedule in the combined probability sample. Among women in the combined probability sample, whites, those who experienced no cost barrier to seeking medical care, the non-obese, and those who had a recent mammography were each more likely to have had a screening as opposed to a diagnostic exam.

DISCUSSION

Cancer control and cardiovascular (CVD) prevention programs should consider jointly targeting those at high risk for cervical cancer and CVD because of aging and associated high-risk behavior such as non-compliance with cervical cancer screening, smoking, and obesity. Also, further research is needed to examine whether the increased compliance with cervical cancer screening guidelines among African American women may be in part due to higher occurrence of diagnostic Pap smears.

Patterns of sedentary lifestyle in Missouri

Sedentary lifestyle is a major modifiable risk factor for chronic disease in Missouri. Survey data was examined for the prevalence of sedentary lifestyle in Missouri. Sedentary lifestyle was higher among blacks, older adults, persons with lower levels of education or income, and obese persons. Based on the current trend, Missouri is unlikely to achieve the year 2000 objective of < or = 50% prevalence of sedentary lifestyle.

A kinetic model of membrane repair

Two microelectrodes are inserted into a Xenopus laevis egg. Rectangular current pulses are injected through one microelectrode and the voltage induced across the cell membrane is measured via the second electrode. The transmembrane resistance, as deduced from the injected current and the measured voltage, is taken as a measure of membrane integrity. The cell membrane is punctured with a glass fiber. The fall and subsequent recovery of transmembrane resistance are recorded. It is confirmed that cell membranes do exhibit repair and that repair is enhanced by the presence of calcium ion. A kinetic model of membrane repair is proposed.