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Tumors of the central nervous system are the most common form of childhood malignancy, and remain the leading cause of cancer-related morbidity and mortality in children. Despite extensive efforts, the efficacy of the traditional treatments is limited and the overall prognosis is poor. In recent years it has become apparent that pediatric gliomas differ from their adult counterparts, explaining in part why the therapies extrapolated from adult gliomas have failed, and further supporting the need to understand the biology of the childhood disease. Deep sequencing studies on brain tumor specimens within various cancer genome consortia (e.g. ICGC PedBrain, TCGA) has yielded a wealth of information about molecular aberrations that had accumulated in tumors. This has unravelled a considerable degree of heterogeneity and thus resulted in the delineation of different molecular subgroups. Furthermore, it has provided comprehensive insights into tumor genomes deduction. Nevertheless, validation of oncogenically relevant genes and therapeutically actionable targets in an in vivo context still remains a major challenge in the process of developing novel treatment approaches. We have generated state-of-the-art in vivo methodologies based on somatic gene transfer for generating animal models faithfully recapitulating the molecular and clinical characteristics of the respective human counterpart. In this study, we focused on NTRK2 fusions and FGFR1 mutations and characterized the tumors obtained by either in utero electroporation or lentiviral injection into postnatal (P0-P1) mice. Tumor derived cell lines grown in stem cell media were tested for conventional therapies (e.g. TMZ) and screening of available small inhibitor compounds. In addition, we have characterized the tumor microenvironment of these lesions, mainly the infiltrating immune cell populations. This study thus represents an important contribution to the understanding of pediatric glioma biology as well as to translational efforts in developing new treatment approaches for these malignant tumors. Citation Format: Or Zohar, Itai Moshe, Ismer Britta, David T. Jones, Dinorah Friedmann-Morvinski. Generation, characterization and functional validation of novel preclinical models for human pediatric glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3042.

// Amos Toren 1 , Tatyana Pismenyuk 1 , Michal Yalon 1 , Shani Freedman 1 , Amos J. Simon 1 , Tamar Fisher 1 , Itai Moshe 1 , Juergen K.V. Reichardt 2 , Shlomi Constantini 3 , Yael Mardor 4 , David Last 4 , David Guez 4 , Dianne Daniels 4 , Moria Assoulin 4 , Ruty Mehrian-Shai 1 1 Pediatric Hemato-Oncology, Edmond and Lilly Safra Children's Hospital and Cancer Research Center, Sheba Medical Center, Tel Hashomer Affiliated to The Sackler School of Medicine, Tel-Aviv University, Tel Aviv, Israel 2 YachayTech University, Urcuqui, Ecuador 3 Department of Pediatric Neurosurgery, Dana Children’s Hospital, Tel-Aviv-Sourasky Medical Center, Israel 4 The Advanced Technology Center, Sheba Medical Center, Tel Hashomer Affiliated to The Sackler School of Medicine, Tel-Aviv University, Tel Aviv, Israel Correspondence to: Ruty Mehrian-Shai, email: Ruty.Shai@sheba.health.gov.il Keywords: glioblastoma multiforme, temozolomide, chemosensitivity, proliferation, zinc Abbreviations: GBM: Glioblastoma multiforme; TMZ: Temozolomide; ZnCl 2 : Zinc chloride Received: May 30, 2016 Accepted: July 19, 2016 Published: August 19, 2016 ABSTRACT Temozolomide (TMZ) is an alkylating agent that has become the mainstay treatment of the most malignant brain cancer, glioblastoma multiforme (GBM). Unfortunately only a limited number of patients positively respond to it. It has been shown that zinc metal reestablishes chemosensitivity but this effect has not been tested with TMZ. Using both in vitro and in vivo experimental approaches, we investigated whether addition of zinc to TMZ enhances its cytotoxicity against GBM. In vitro cell viability analysis showed that the cytotoxic activity of TMZ was substantially increased with addition of zinc and this response was accompanied by an elevation of p21, PUMA, BAX and Caspase-3 expression and a decrease in growth fraction as manifested by low ki67 and lower colony formation. Analysis of GBM as intracranial xenografts in athymic mice and administration of concurrent TMZ and zinc yielded results consistent with those of the in vitro analyses. The co-treatment resulted in significant reduction in tumor volume in TMZ/zinc treated mice relative to treatment with TMZ alone. Our results suggest that zinc may serve as a potentiator of TMZ therapy in GBM patients.

In the last few years, the extent of heterogeneity between tumors of a given class has become increasingly evident. Thus, tumors should optimally be treated differently according to their individual genetic alterations. Within the ICGC PedBrain Tumor Project, we have analyzed >150 low-grade and high-grade pediatric gliomas with whole-genome DNA and RNA sequencing, and have identified a wide variety of genetic alterations responsible for tumor growth. This includes novel point mutations, fusions and duplications in oncogenes such as NTRK2, FGFR1 and ALK. In some cases these alterations also define distinct molecular subgroups of glioma as judged by DNA methylation profiling. In order to identify new targeted therapy options for pediatric gliomas, mouse models recapitulating the human disease are required for testing of more specific inhibitors. We have therefore generated a series of novel models which are now being characterized and pre-clinically treated. Initial results with ALK or NTRK fusions show that our somatic gene transfer methods (RCAS- or in utero electroporation-based) can be used to rapidly generate new orthotopic brain tumor models, and that specific inhibitors against chosen oncogenes have a greater effect on tumor growth compared to standard therapy. The murine tumor cells can also be cultivated as neurospheres for functional testing and e.g. high-throughput screens. In addition to the basic biological understanding of tumorigenic mechanisms that can now be elucidated in more detail, we aim to rapidly translate our pre-clinical results in a manner that we hope will directly benefit patients in the clinic.

Background Gliomas are the most common CNS tumors in pediatric patients. Despite extensive efforts, the efficacy of the traditional treatments is limited and the overall prognosis is poor. Data from various studies have indicated a genetic diversity between Pediatric and adult gliomas that may imply for the need of dedicated therapeutic approaches for pediatric gliomas. Using whole-genome sequencing, we have identified a wide variety of genetic alterations in low-grade and high-grade pediatric glioma patients that were found to be of interest in terms of their pattern of occurrence and the availability of targeted inhibitors. These genetic aberrations include novel point mutations, gene fusions and duplications in oncogenic factors such as NTRK2 and FGFR1. In order to study the role of this mutated genes in pediatric glioma and to identify and pre-clinically test new therapeutic targets, in vivo models recapitulating the human disease are required. Methods In order to validate the role of the selected mutated genes in pediatric tumorigenesis we cloned these genetic aberrations into Cre-inducible lentiviral vectors and injected them directly into the brain of Cre transgenic post-natal 1 (PN1) pups. In vitro, we used the same lentiviral vectors to transduce embryonic neural stem cells to assess their transformation capacity. Results We generated a series of novel pediatric glioma models with different combinations of oncogenes and tumor suppressor genes that leads to high mortality rate. Characterization of these tumors by immunofluorescence staining was consistent with common glioma markers. We also established primary cell lines from the generated tumors that are now being used for functional testing of specific inhibitors. In addition, we performed RNAseq analysis in order to assess the human relevance of these generated mouse models and to elucidate the mechanism of action of these mutations. Conclusions We were able to generate novel pediatric glioma mouse models that can be used to examine selected mutations found in human pediatric gliomas and serve as a pre-clinical tool for testing novel therapeutic targets. Legal entity responsible for the study The authors. Funding DKFZ-MOST grant. Disclosure All authors have declared no conflicts of interest.

In muscular dystrophies (MD) the loss of muscle and its ability to function are associated with fibrosis. We evaluated the efficacy of halofuginone in reducing fibrosis in the dy2J/dy2J mouse model of congenital MD. Mice were injected intraperitoneally with 5 μg of halofuginone 3 times a week for 5 or 15 weeks, starting at the age of 3 weeks. Halofuginone caused a reduction in collagen synthesis in hindlimb muscles. This was associated with reductions in the degenerated area, in cell proliferation, in the number of myofibers with central nuclei, with increased myofiber diameter, and with enhanced motor coordination and balance. Halofuginone caused a reduction in infiltrating fibroblasts that were located close to centrally nucleated myofibers. Our results suggest that halofuginone reduced the deleterious effects of fibrosis, thus improving muscle integrity. Halofuginone meets the criteria for a novel antifibrotic therapy for MD patients. Muscle Nerve, 2010

Inhibitors of poly[ADP-ribose] polymerase 1 (PARPis) show promise for treatment of cancers which lack capacity for homologous recombination repair (HRR). However, new therapeutic strategies are required in order to overcome innate and acquired resistance to these drugs and thus expand the array of cancers that could benefit from them. We show that human cancer cell lines which respond poorly to ABT-888 (a PARPi), become sensitive to it when co-treated with vorinostat (a histone deacetylase inhibitor (HDACi)). Vorinostat also sensitized PARPis insensitive cancer cell lines to 6-thioguanine (6-TG)-a drug that targets PARPis sensitive cells. The sensitizing effect of vorinostat was associated with increased phosphorylation of eukaryotic initiation factor (eIF) 2α which in and of itself increases the sensitivity of cancer cells to ABT-888. Importantly, these drug combinations did not affect survival of normal fibroblasts and breast cells, and significantly increased the inhibition of xenograft tumor growth relative to each drug alone, without affecting the mice weight or their liver and kidney function. Our results show that combination of vorinostat and ABT-888 could potentially prove useful for treatment of cancer with innate resistance to PARPis due to active HRR machinery, while the combination of vorinostat and 6-TG could potentially overcome innate or acquired resistance to PARPis due to secondary or reversal BRCA mutations, to decreased PARP-1 level or to increased expression of multiple drug resistant proteins. Importantly, drugs which increase phosphorylation of eIF2α may mimic the sensitizing effect of vorinostat on cellular response to PARPis or to 6-TG, without activating all of its downstream effectors.