Mentor Name: David Langenau

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and shares similarities with skeletal muscle. RMS is characterized by three subtypes: alveolar RMS (ARMS), linked to PAX3-FOXO1 or PAX7-FOXO1 translocations, and embryonal RMS (ERMS), linked to upregulation of the RAS pathway, and spindle cell/sclerosing rhabdomyosarcoma (SS-RMS) contain NCOA2::VGLL2 translocations or the MYOD1L122R mutation and RAS pathway activation. Frontline treatment for RMS consists of a combination of chemotherapies known as VAC (vincristine, actinomycin D and cyclophosphamide). However, around 30% of patients experience relapse due to the development of VAC chemoresistance. Tumor relapse and progression are largely driven by cancer stem cells (CSCs), which have self-renewal and proliferative capabilities. These cells share characteristics with stem cells and can recreate the entire heterogeneity of the tumor. The Langenau lab has recently generated VAC RMS cell and identified that many models develop long-term resistance to VAC by upregulation of CSCs. However, the mechanism by which these CSCs are upregulated is unknown. This work will have two major objectives. Aim 1 will use a CRISPR screen to identify genes and pathways that are required to maintain resistance to VAC. These cell-intrinsic vulnerabilities will pinpoint pathways that mediate chemotherapy resistance and likely lead to the elevation of the overall fraction of cancer stem cells. Aim 2 will test new drugs targeting the encoded proteins identified in Aim1 to effectively eliminate VAC-resistant tumors in vitro. Self-renewal pathways in RMS progenitor cells likely play a crucial role in chemoresistance, and targeting these novel pathways identified through the CRISPR screen may help re-sensitize the cells to VAC therapy.