PROJECT SUMMARY This is a Supplement for my Mentored Clinical Scientist Development Award (K08-CA230190). K08-CA230190 was funded on 07/01/2020 and details a five-year plan to promote my career as an independent physician- scientist in the area of laboratory-based academic Hematology/Oncology. Under the guidance of my primary research mentor, Dr. Martin Carroll, at the University of Pennsylvania (UPENN), I have developed a structured training plan consisting of intensive laboratory research, didactics, and oversight by an experienced faculty advisory committee. The proposed research focuses on unanticipated responses to FLT3 targeted therapy in AML based on key insights from the clinical trials of these agents conducted at UPENN. Early generation FLT3 inhibitors (FLT3i) were met with lukewarm enthusiasm due to poor target specificity and limited bioavailability. Newer agents have recently been developed with improved activity against FLT3 and clinical efficacy as evidenced by clearance of leukemic blast cells. However, these agents are not curative and many patients respond with differentiation rather than eradication of the leukemic clone. This raises important questions about how FLT3 regulates the differentiation state of leukemia cells. In preliminary studies, I identified a novel pathway downstream of FLT3 inhibition that leads to rapid downregulation of the histone methyltransferase, EZH2. EZH2 is the catalytic component of the PRC2 transcriptional repressor. This research represents the first demonstration of FLT3 regulation of an epigenetic modifier. Loss of EZH2 activity has been linked to increased myeloid differentiation and decreased leukemogenicity, making it an attractive target to study as a potential mechanism for FLT3i-induced differentiation. This proposal aims to demonstrate that PRC2 is necessary for FLT3-ITD leukemogenesis (Aim 1), demonstrate that FLT3i functionally inhibit PRC2 activity (Aim 2), and determine the mechanism of EZH2 downregulation after FLT3 inhibition (Aim 3). These findings will provide insight into the biology of FLT3 signaling and identify improved approaches to induce terminal differentiation of FLT3-ITD leukemia cells. In undertaking the proposed studies and training plan, I will develop the skills and expertise necessary to establish an independent career in translational research. I am overjoyed with the birth of my first child on 11/22/2019; however, this critical life event has reduced my productivity prior to and during Year 1 of the K08 award period due to childcare demands. This administrative supplement will provide funding for a research technician to accelerate the pace of experiments and projects to help me continue to move forward in my path to independence.