Non-canonical BRAF mutations in AML development and therapeutic response

About This Grant

Project Summary/Abstract Acute myeloid leukemia (AML), the most common type of adult acute leukemia, originates from somatic mutation(s) which results in impaired differentiation and aberrant proliferation of hematopoietic stem/progenitor cells. We recently identified recurrent mutations in the gene BRAF, which encodes an integral kinase in the RAS/MAPK/ERK signaling pathway, in AML patients. Divergent from other cancer subtypes, the majority of the BRAF mutations we identified were outside of the well-characterized V600 codon hotspot and therefore, noncanonical mutations. Moreover, the presence of a BRAF mutation correlated with dismal survival outcomes for these AML patients, regardless of therapeutic regimen, suggesting that BRAF mutations may drive therapeutic resistance to front-line AML therapies. This is in contrast with other RAS/MAPK pathway mutant AMLs, which typically respond to the front-line chemotherapy regimens. Our preliminary data in novel BRAF-mutant mouse models indeed confirms these findings from our BRAF-mutant AML clinical cohort. Therefore, our understanding of how BRAF and more broadly, the RAS/MAPK pathway, can contribute to AML pathogenesis and drive therapeutic resistance remains incomplete. In this proposal, state-of-the-art approaches and models will be applied to interrogate innovative concepts in novel, genetically engineered mouse models (GEMM) and patient derived xenografts (PDX). Specifically, we will delineate the contributions of BRAF mutations to leukemogenesis, disease phenotype, and therapeutic response through a combination of single cell multiomic analysis of primary AML samples and functional dissection of BRAF-mutant GEMMs and BRAF-mutant AML PDXs. We expect to elucidate aberrant BRAF-driven signaling pathways and how these mechanisms alter hematopoietic output and cellular response to therapeutic agents. To achieve this, we will discover and examine abnormal hematopoietic output, dysregulated transcriptional programs, and rewired signaling pathway that are specific to leukemic clones harboring BRAF mutations (Aim 1). Next, we will interrogate mechanisms in BRAF-mutant cells that lead to resistance to front-line AML therapies and assess potential efficacious therapies for BRAF-mutant AML (Aim 2). The use of genetically engineered mouse models provides critical isogenic systems to dissect the contribution and impact of BRAF mutations in AML development without the vast heterogeneity and complexity observed in AML patient samples. Moreover, therapeutic studies in BRAF-mutant PDX models in vivo allow for insight into systemic effects of therapies in a native context and uncover important contributions of the bone marrow niche to therapeutic response. In sum, the proposed work will dissect critical contributions of BRAF mutations, and more broadly aberrant functions of RAS/MAPK pathway proteins, to AML pathogenesis and response to therapy to inform and develop novel therapeutic strategies that will improve AML patient outcomes.