TMOD-06. LOSS OF DICER COOPERATES WITH TUMOR SUPPRESSORS TO INITIATE METASTATIC MEDULLOBLASTOMA

摘要: Medulloblastoma (MB) represents the most common embryonal tumour of the Central Nervous System in childhood. MB occurs in the cerebellum and molecular features dictate the classification into four subgroups. Although Group3 (Gr3) MB tumours are dominated by primitive progenitorlike cells, the cells of origin remain unidentified. Gr3 MB is associated with relatively common MYC family member amplification and overexpression, often combined with p53 pathway defects at relapse. Molecularly stratified treatment is not yet available, causing Gr3 MB and its subsequent relapse to often represent an unstoppable progressive disease. The limited understanding of Gr3 tumorigenesis and targeted therapy development is also due to the lack of faithful in vivo models and consequently, their use in preclinical studies. We have now developed a new germline genetically engineered mouse model (GEMM), harbouring MYCN amplification in a p53 inactive background (tamoxifen-inducible p53 activation, Trp53ERTAM). The purpose of the GEMM is to investigate the developmental significance of MYC aberration in putative Gr3 MB cells of origin and exploit it in preclinical studies. A LSL-MYCN-Luciferase strain was crossed with mice expressing Cre recombinase under the Blbp promoter and subsequently to Trp53ERTAM inducible mice. As result, the MYCN overexpression alone did not generate tumours, conversely to the combination of MYCN with p53 deregulation. Tumours arise exclusively in the hindbrain of homozygote mice, with a penetrance of 100% and a latency of~ 135 days. Pathology report suggests tumours are Gr3 MB with large cell …