Mentor Name: John Prensner

Atypical teratoid/rhabdoid tumor (ATRT) is a rare and highly aggressive pediatric brain tumor that predominantly affects infants and young children. Despite intensive multimodal therapy– including surgery, chemotherapy, and radiation– clinical outcomes remain poor, and treatment resistance is a major contributor to disease recurrence and mortality. Identifying mechanisms that drive resistance to current and emerging therapies is therefore critical to improving outcomes for children with ATRT. Recent work in our lab has identified translation inhibition as a promising therapeutic strategy in ATRT. Omacetaxine (homoharringtonine, HHT), a ribosomal translation inhibitor, has demonstrated anti-tumor activity; however, preliminary data indicate that increased STAT3 expression in MYC-subtype correlates to HHT resistance in ATRT, suggesting that JAK/STAT signaling may play a central role in resistance to translation-targeting therapies. Herein, we will develop a research project focused on understanding resistance to translation inhibition in ATRT and defining a dual-targeting strategy to overcome resistance. In this project, we will use the patient derived cell models of ATRT including their molecular subtypes (e.g. MYC- and SHH-type) to develop and characterize acquired HHT resistance by chronically treating cells with clinically relevant concentrations of HHT. Alternatively, we will use the cDNA plasmids of STAT3 and generate null mutants using the Gibson method to generate the resistance model in ATRT. We will test these constructs for STAT3 stability and induction of IL6 in HEK293T cells. With these models, we will test synergistic dosing of STAT3 inhibitors and PROTACS with HHT. Primary read-outs will be cell viability and apoptosis using CellTiter Glo, Caspase 3/7 activation, Western blot and annexin V binding assay. We will further employ flank xenografts in NSG mice to test in vivo dosing of the STAT3 PROTACs and HHT. In addition, we will probe the molecular basis for drug resistance by investigating the STAT3 signaling pathway. For this we will develop the observation that IL6, an upstream effector of STAT3 signaling, is highly upregulated in MYC-type ATRT. We will also delineate epigenetic mechanisms underlying STAT3 in HHT-resistant ATRT using chromatin profiling approaches (CUT&RUN) to identify regulatory networks associated with resistance. Together, these studies aim to uncover actionable vulnerabilities in resistant ATRT and inform rational combination therapies. This project will provide us with rigorous training in translational cancer biology and deepen our commitment to a career bridging biomedical research and pediatric oncolog