Isogenic Models of Pediatric AML for Interrogating Different RAS Pathway Mutations
Mentor: Kevin Shannon
Progress has been made in the treatment of pediatric acute myeloid leukemia (AML) over the past 3 decades. However, the backbone of front-line therapeutic protocols has not changed, and cure rates remain around 60%. New therapies and approaches are clearly needed to improve outcomes. Compared to adult AML, the genetic landscape of pediatric AML includes a lower overall mutation rate with distinct molecular patterns in which RAS pathway mutations are overrepresented with a recent comprehensive sequencing study uncovering somatic RAS-activating mutations in ~50% of pediatric AMLs. RAS mutations are common in many other human cancers, and extensive data indicate that aberrant signaling through the Raf/MEK/ERK and PI3K/AKT pathways drive the proliferation and survival of AML and other RAS-mutant tumors. Additional evidence of the importance of RAS pathway signaling in AML comes from therapies targeting FLT3 mutations, which are present in 20-30% of cases and serve as a poor prognostic marker. Selective FLT3 inhibitors have yielded promising results in adult AML patients, but resistance is common with NRAS mutations particularly prominent at relapse. As trials of FLT3 inhibitors for pediatric AML move forward, there is a high likelihood that RAS pathway mutations will also be a major driver of resistance. Previous studies published by the Shannon Lab revealed unexpected biologic and phenotypic differences upon inactivation of the Nf1 tumor suppressor gene or endogenous NRAS/KRAS oncogene expression in the blood and bone marrow of mice. These data suggest that AML cells with these distinct RAS pathway mutations might have unique dependencies and also respond differently to some targeted therapies. The central aim of this project is to develop isogenic AML cell line models of pediatric AML characterized by NF1, KRAS, and NRAS mutations to interrogate these RAS pathway mutations in a controlled system. Importantly, these models will enable us to assay and compare the functional and biochemical properties of NF1 inactivation and of mutant NRAS and KRAS proteins expressed at endogenous levels. Moreover, this isogenic system will be a useful tool for testing small molecule inhibitors of various effectors in the hyperactive RAS pathway and will allow us to test specific mechanism-based hypotheses such as that NF1, but not NRAS and KRAS, mutant AML cells will be sensitive to SHP-2 inhibitors. Insights into the functional significance of these mutations could lead to new avenues for targeted therapies and inform of their potential as a predictive biomarker for treatment selection in pediatric AML.