Overview
Hematologic malignancies are an ideal disease model to study classical questions in cancer biology, given the ease of sample access and extensive description of the normal hematopoietic differentiation cascade. Genetic studies in acute myeloid leukemia (AML) have revealed a hierarchical arrangement of mutations such that certain mutations are postulated to be acquired either early or late in disease progression. This stepwise acquisition of mutations results in a genetically heterogeneous collection of clones. The receptor tyrosine kinase, FLT3, is the most commonly mutated gene in AML and typically presents as a subclonal, late event. Mutations typically manifest as internal tandem duplications (ITDs) in the juxtamembrane domain leading to constitutive kinase activation. Despite being mutated in only a subset of leukemic cells, FLT3 mutations are associated with poor prognosis. Tyrosine kinase inhibitors (TKIs e.g. gilteritinib) demonstrate substantive clinical efficacy, but invariably lead to relapse, in a subset of cases due to second-site FLT3 mutations and/or mutations in other signaling pathways. It remains unclear when a given leukemia is dependent upon FLT3 mutations, and how a subclonal oncogene portends such poor prognosis yet has therapeutic utility. In a broader context, understanding the functional roles of clonal and subclonal mutations in AML initiation and maintenance has fundamental mechanistic and therapeutic implications.
Current Projects
1: Oncogenic dependency in leukemic stem cells
The receptor tyrosine kinase, FLT3, is the most commonly mutated gene in acute myeloid leukemia. While two tyrosine kinase inhibitors (TKIs) have been FDA approved for therapeutic intervention, relapse is common with resistance mutations found in alternative signaling pathways as well as in FLT3 itself. It remains unclear what effect TKIs have on quiescent leukemic stem cells and whether they are capable of eradicating this cell population. We will seek to understand how quiescent leukemic stem cells respond to therapy by juxtaposing chemical vs genetic inhibition. In the long term seek to understand how cooperating mutations influence the quantity and characteristics of this stem cell pool.
Graduate student rotation project: Researcher will explore oncogene-dependency using small molecule inhibitors and novel mouse models capable of turning on/off FLT3. Experimental approaches will include ex vivo culture, flow cytometry, viral infection, and RNA-sequencing.
2: Evaluating cell of origin in FLT3-driven acute myeloid leukemia.
Despite being the most commonly mutated gene in AML, FLT3 is often present as a late event in clonal evolution with preceding mutations frequently occurring in DNMT3A, IDH2, and NPM1. Preclinical mouse models studies suggest that each of these mutations are sufficient to license FLT3-mediated leukemic transformation, yet with distinct latencies and immunophenotypic outputs. We hypothesize that these differences are a result of synergistic mutation combinations in distinct cell of origin. Our lab will approach this question using inducible mouse models and synthetic biology approaches for cell type specific control. In the long term, we seek to progress towards complete in vivo modeling through the development of novel cell type specific recombinase mouse lines.
Graduate student rotation project: Researcher will determine which hematopoietic stem/progenitor cell types are competent to be transformed into leukemia by mutant FLT3. Experimental approaches will include ex vivo culture, flow cytometry, and genetic engineering approaches.
3 : Investigate interclonal interactions in leukemic progression
Genomic profiling in mouse and human have demonstrated that leukemias contain both single mutant clones indicative of underlying clonal hematopoiesis and genetically dense multi-mutant clones. We hypothesize that this stepwise acquisition of mutations results in a genetically diverse ecosystem where clones interact either in supporting or suppressing other genetically distinct clones. Our group will investigate inter-clonal interactions and competition through the lens of FLT3 mutant AML, investigating several key questions including: Does the presence of a FLT3-mutant clone affect the fitness of antecedent clones? To investigate clonal heterogeneity and paracrine interactions we will integrate single cell genomic profiling in clinical isolates and mouse models of subclonal FLT3-mutations, mechanistically evaluate candidate paracrine factors ex vivo, and evaluate their role in disease progression in vivo.
Graduate student rotation: Researcher will integrate existing genomic data with mouse models of disease to identify paracrine factors that influence clonal outgrowth. Experiments will involve computational identification of putative paracrine factors, ex vivo drug and ligand treatments, flow cytometry, and RNA-sequencing.
