Project Description/Abstract The targeting of chromatin modifiers is an increasingly attractive novel strategy to therapeutically inhibit transcription factors. MYC, one of the most frequently amplified oncogenes in cancer, is one such transcription factor that has proved difficult to target directly. Pediatric MYC-amplified medulloblastoma is a devastating disease. 25% of all medulloblastoma harbor amplification of MYC-isoforms that result in activation of MYC pathways. These tumors exhibit resistance to standard therapies used to treat medulloblastoma and are characterized by rapid and rampant tumor progression. Strategies to inhibit MYC activation pathways are desperately needed in the clinic for children diagnosed with this disease. Recently, inhibition of the epigenetic readers, BET-bromodomain proteins, has been found to be effective in suppressing the growth of preclinical models of MYC driven tumors, including medulloblastoma. Indeed, early phase clinical trials involving BET-bromodomain inhibitors are planned for children with recurrent MYC-driven tumors including medulloblastoma. However, the precise mechanism of action of these inhibitors remains unclear. In addition, clinical experience with other novel small molecule inhibitors has revealed that cancers evolve to acquire resistance to targeted therapeutics. Characterizing resistance mechanisms allows for novel therapeutic strategies to be designed to overcome these mechanisms and increase clinical efficacy of targeted therapeutics. The goal of this proposal is to systematically characterize cancer cell evolution in response to BET-bromodomain inhibition. This project will shed insight on the mechanism of action of BET-bromodomain inhibitors and guide the development of combination therapies to optimize efficacy. Cancers have been shown to acquire genetic alterations to develop resistance to targeted therapeutics. However, the mechanisms by which cancers evolve to acquire resistance to inhibition of chromatin modifiers have not been determined. BET-bromodomain proteins regulate the transcription of genes key to determination of cell-identity and cell-state. BET-bromodomain inhibitors have been shown to alter cell-state and cell-identity. It is thus possible that changes in cell-state can influence sensitivity to BET-bromodomain inhibition and contribute to the development of resistance. This proposal will systematically characterize the resistance mechanisms to BET-bromodomain inhibition in MYC-amplified medulloblastoma. To achieve this, a number of novel methodologies will be applied to characterize the genomic and epigenomic alterations that contribute to the acquisition of resistance to BET-bromodomain inhibition. This proposal will determine whether the acquisition of resistance is predetermined, will identify specific alterations in genes that contribute to resistance and will explore how resistance to BET-bromodomain inhibition is influenced by This work will guide the devel...