Etmr-10. Development and Characterization of a Novel Immunocompetent Orthotopic Mouse Model for the Study of Embryonal Tumors With Multilayered Rosettes (Etmrs)

Abstract BACKGROUND ETMRs are highly aggressive CNS embryonal tumors with a median survival of 12 months. They are characterized by the presence of multilayered rosettes, amplification of the C19MC microRNA cluster, and high expression of LIN28A; all which are used as diagnostic markers of ETMR. To understand more deeply the mechanisms involved in ETMR pathogenesis, as well as to test immune therapies, it is necessary to develop appropriate immunocompetent murine models that resemble human ETMRs, which are currently scarce. Thus, the aim of our study is the generation and characterization of a novel preclinical ETMR mouse model. METHODS The murine PNET cell line DF1-MYC, produced using a MYC overexpressing RCAS model on a C57BL/6J background, and corresponding allografts were implanted into the supratentorial region of 4-week-old NSG and immunocompetent NTV-a p53floxed mice. Mice were monitored and sacrificed. For efficacy studies, the survival curves were plotted according to the Kaplan-Meier method. For tumor histological analysis and immunohistochemistry, FFPE brain sections were stained with H&E or antibodies against Ki67, c-Myc and Lin28a. Transcriptional profile was characterized by RNA-seq. RESULTS DF1-MYC-bearing NP53 mice did not develop tumors except one mouse that showed a small tumor with multilayered rosettes. With the goal of achieving complete penetrance, we injected DF1-MYC cells orthotopically in NSG mice and allografts subsequently in NP53 mice. Specifically, our MYC384 allograft ETMR mouse model show a penetrance of 70% with a median survival of 36 days. Importantly, the MYC384 allograft model recapitulates histopathologic features of human ETMR, including the presence of highly proliferative undifferentiated cells with multilayered rosettes. Moreover, we are working on overexpressing Lin28a and c-Myc in MYC384 to create a more realistic molecular model of ETMR while allowing us to achieve 100% penetrance. CONCLUSION We describe MYC384 as a potential relevant immunocompetent mouse model of ETMR with almost complete penetrance.