Project 3 Summary Chronic myeloid leukemia (CML), one of the most prevalent of human leukemias, is a natural model of dysregulated granulopoiesis driven by the BCR-ABL1 tyrosine kinase. Whereas tyrosine kinase inhibitors (TKIs) such as imatinib have dramatically improved the prognosis in CML, lifelong treatment is needed, with a corresponding large economic impact on the health care system. The two biggest unaddressed questions in the field of CML therapeutics are to understand the mechanism of primary resistance to TKI therapy, and to identify strategies to increase the rate that patients remain in molecular remission after discontinuation of TKI therapy, possibly representing permanent cure of the disease. The Scientific Premise of this Project is that new and clinically relevant insights into the biology of CML and its response to therapy can be gained by a more physiologically accurate mathematical model of the disease. The first Aim of this Project will leverage UCI's extensive expertise in mathematical modeling of complex biological phenomena to develop more sophisticated models of CML that incorporate physiologically relevant homeostatic feedback and feedforward regulatory interactions between normal and leukemic cells, and between stem cells and more differentiated cells. Optimal model structures will be vetted by a machine-based automated model selection process to arrive at a model that maintains appropriate stability and homeostasis, responds physiologically to stress and depletion of different cell compartments, and conforms to the limited existing qualitative data on CML hematopoiesis derived from mouse models and patient studies. In the second Aim, an innovative binary BCR-ABL1 transgenic mouse model will be used to determine for the first time the relevant parameters governing the production of the malignant blood cells in CML. Single-cell transcriptome analysis of normal and malignant hematopoietic stem/progenitor populations, including the heterogeneous multi-potential progenitor compartment, will generate important new knowledge about the heterogeneity of CML myelopoiesis and provide insight into the molecular mechanisms of feedback/feedforward regulation. Based on these preclinical studies, a novel clinical trial to gain insight into similar cell kinetic parameters in CML patients will be initiated. In the final Aim, certain predictions from the validated mathematical model will be tested in the transgenic mouse model. Among the hypotheses that can be tested straightaway are that the original burden of leukemic stem cells governs the initial response to TKI therapy and represents and important prognostic factor, and that treatments that stimulate leukemic stem cell cycle entry are optimally delivered intermittently rather than continuously. Additional hypotheses emerging from the modeling effort will be tested in years 3-5 of the grant. Together, the studies proposed in this Project will provide critical new knowledge about the pathogenesis of CML, inform new therapeutic strategies, and set the stage for future interventional clinical trials in CML.