Dual inhibition of BET and EP300 has antitumor activity in undifferentiated pleomorphic sarcomas and synergizes with ferroptosis induction [CRISPR?Cas9 knockout screen]
Purpose: Patients with UPS exhibit a poor prognosis and have few therapeutic options. Epigenetic modifiers has been extensively investigated in recent years leading to the development of novel therapeutic agents. Dual BET/EP300 inhibitors have shown synergistic antitumor activity and have recently entered clinical development. To date, no data related to potential of BET/EP300 inhibition as a treatment in UPS have been reported. Experimental design: To investigate the therapeutic potential of BET/EP300 inhibition, we first evaluated the prognostic value of BRD4 expression in 2 cohorts of sarcomas. wWe then investigated evaluated the antitumor activity of three compounds in vitro via MTT, apoptosis and cell cycle assays. The most potent inhibitor was evaluated in vivo in two animal models and the mechanisms of action were investigated by RNA sequencing, Western blotting and immunofluorescence staining. A CRISPR knockout screen was performed to identify resistance mechanisms. Results: High BRD4 expression were associated with worsened metastasis-free survival of sarcoma patients. Among the three compounds tested, the dual inhibitor NEO2734 was the most potent, decreased the viability of UPS cells in vitro through a regulation of E2F targets and cell cycle and decreased the tumor growth in vivo. Moreover, we identified GPX4 as a gene involved in resistance and showed synergy between BET inhibition and ferroptosis induction. Conclusion: The present study demonstrated that dual BET/EP300 inhibitors have a relevant anti-tumor activity in a subgroup of UPS characterized by expression of MYC-targets pathway and identified a potent combination therapeutic strategy that deserves further investigation in the clinical setting. Overall design: To decipher the mechanism of resistance to BET inhibition in UPS cell lines, We performed a genome-wide pooled lentiviral CRISPR?Cas9 knockout screen in KN473 cells stably infected with the cas9 nuclease. After GeCKO library infection and 72 h of NEO2734 treatment at 1 µM, a dose that normally does not kill KN473 cells, genomic DNA was extracted and sequenced by NGS to identify the genes whose knockout causes cell death and hypersensitivity to NEO2734