ATRT-22. HIGH-THROUGHPUT DRUG SCREENING OF FDA-APPROVED CANCER DRUGS REVEALS POTENTIAL THERAPEUTIC APPROACHES FOR ATYPICAL TERATOID RHABDOID TUMOUR

Atypical teratoid/rhabdoid tumors (ATRT), are the most common brain tumor in children under the age of 1 year with an overall survival of ~17%. Like extracranial rhabdoid tumors, ATRT is exclusively characterized by bi-allelic loss of SMARCB1, a critical subunit of the SWI/SNF chromatin remodeling complex, implicating epigenetic deregulation in the pathogenesis of disease. We have previously shown the ability of the histone deacetylase inhibitor, panobinostat, to mimic SMARCB1-mediated SWI/SNF functions in extracranial rhabdoid tumors to inhibit tumor growth by driving multi-lineage differentiation in vitro and in vivo. Whether this also applies to ATRT is unknown. Using a panel of human-derived ATRT cell lines, representing defined molecular subgroups, we have shown that prolonged treatment with panobinostat at nanomolar concentrations results in markedly reduced clonogenicity, and increased senescence, preceded by increased H3K27 acetylation, decreased H3K27 trimethylation and EZH2 expression. To determine potentially synergistic therapies, we performed high-throughput drug screening of 622 compounds already in advanced clinical trials or FDA-approved for other indications, across our panel of ATRT models and identified 30 common compounds, which decrease cell viability by >50%, with no effect on neural stem cell controls and 12 compounds which demonstrated subgroup specificity, highlighting the necessity to consider therapies in the molecular context. In addition to HDACi, consistent with our panobinostat in vitro findings, inhibitors of CDK, survivin and PI3K were the top hits. In vitro and in vivo validation of these compounds alone, and in combination with panobinostat is ongoing.