Enhancer reprogramming underlies therapeutic utility of a SMARCA2 degrader in SMARCA4 mutant cancer [ATAC-Seq]

Lung cancer is the top cause of cancer mortality. Despite recent advances, the majority of patients with lung cancer still lack effective therapeutic options, underscoring the dire need for additional treatment approaches. Genomic studies have identified frequent mutations in subunits of the SWI/SNF chromatin remodeling complex including SMARCA4 and ARID1A in non-small cell lung cancer with a frequency of up to 33% in advanced stage disease, making it the most frequently mutated complex in lung cancer. Recent reports have identified the paralogue SMARCA2 to be synthetic lethal to SMARCA4 suggesting SMARCA2 is a valuable therapeutic target. However, the discovery of selective inhibitors of SMARCA2 has been challenging. To overcome this hurdle, we have utilized iterative structure-activity relationship (SAR) studies to develop novel, potent and selective SMARCA2 degrading small molecules based on proteolysis targeting chimera (PROTAC) technology. We demonstrated that YD23, our lead SMARCA2 PROTAC, potently and selectively induces degradation of SMARCA2. Mechanistically, we show that SMARCA2 degradation in SMARCA4-mutant cells induces a profound reprograming of the enhancer landscape with marked loss of chromatin accessibility at enhancers of genes involved in cell proliferation. Furthermore, we identified nuclear effectors of the Hippo pathway, YAP/TEAD, as key co-conspirators of SMARCA2 in driving the growth of SMARCA4-mutant cancer cells that can be disrupted by our degrader. Finally, we show that YD23 has a potent tumor growth inhibitory activity in SMARCA4-mutant xenograft tumors. These findings provide the mechanistic basis for development of SMARCA2 degraders as synthetic lethal therapeutics against SMARCA4 mutant tumors.