Abstract 700: Targeting transcriptional co-activators YAP1/TAZ in fusion-positive rhabdomyosarcoma demonstrates a novel strategy in ablating fusion-driven sarcoma transcriptional programing

Abstract Background: Approximately one third of all sarcomas are characterized by recurrent chromosomal translocations, and these fusion-positive sarcomas remain among the most difficult to treat of all malignancies. Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood and a prototype fusion-oncogene-driven tumor. Fusion-positive rhabdomyosarcoma (FP-RMS) is driven by a chromosomal translocation encoding for the pathognomonic chimeric fusion product PAX3-FOXO1 (P3F). Because it is a large inherently disordered transcription factor lacking drug-binding sites, conventional efforts to directly target P3F have thus far proven futile, and 5-yr overall survival rates remain below 50%. Objective: We thus sought to identify therapeutically tractable co-activators or co-regulators that represent vulnerabilities to P3F transcriptional programing. Methods/Results: Interrogation of transcriptomic data and immunohistochemical (IHC) staining of human tissue microarrays demonstrated the transcriptional co-activators YAP1 and TAZ are highly abundant in FP-RMS tumors. We performed genetic gain- and loss-of-function experiments using RNAi and CRISPR/Cas9 to determine that YAP1/TAZ regulate many FP-RMS cancer phenotypes, including proliferation and xenograft tumor growth. Mechanistic studies using co-immunoprecipitation (co-IP) and co-IP-coupled mass spectrometry revealed a YAP1/TAZ-P3F physical interaction and that YAP1/TAZ and P3F share an enrichment for co-immunoprecipitated proteins involved in chromatin remodeling and DNA binding as well as transcriptional regulation. Functional studies using qRT-PCR, immunoblots, and reporter assays demonstrated YAP1/TAZ are positive regulators of P3F-mediated transcriptional activity. Unbiased approaches using RNA-Seq and quantitative tandem mass tag proteomics also demonstrated that YAP1/TAZ positively regulate the differential expression of P3F’s targets and gene signature. Pharmacologically targeting the YAP1/TAZ-P3F axis using novel NUAK1/2 kinase inhibitors that lead to YAP1/TAZ nuclear exclusion cause cell cycle arrest at the G2/M checkpoint as well as a decrease in FP-RMS cell viability through induction of apoptosis. Main Conclusions: Transcriptional co-activators YAP1/TAZ are highly abundant in FP-RMS tumors and are required for numerous FP-RMS cancer phenotypes. YAP1/TAZ physically associate with P3F to regulate P3F-mediated transcriptional activity. Therefore, while directly targeting P3F is not currently viable, we have identified YAP1/TAZ as therapeutically tractable dependencies to P3F transcriptional programing. Citation Format: Adam F. Pecoraro, Tooba Rashid, Breanne A. Burgess, Corinne M. Linardic, Michael D. Deel. Targeting transcriptional co-activators YAP1/TAZ in fusion-positive rhabdomyosarcoma demonstrates a novel strategy in ablating fusion-driven sarcoma transcriptional programing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 700.