Impact of Leukemia Microenvironment on Response to Targeted Therapies in AML

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The survival rate of acute myeloid leukemia (AML) patients is <20%, an outcome that has not changed in 30 years. This dismal outcome is largely due to development of drug resistance and relapsed disease. Thus, there is an urgent need for new strategies to target residual AML cells before they develop resistance. One strategy to reduce relapse is to target the secreted cytokines, growth factors, and immune cells within the bone marrow microenvironment that play a critical role in promoting leukemia cell survival, development of drug resistance, and immune evasion. Our long-term goal is to identify novel drug targets to selectively eradicate resistant leukemic clones and overcome drug resistance to improve the future treatment of AML patients. To do this, we have begun to identify the mechanisms by which the bone marrow microenvironment promotes survival of leukemia cells. In an ex vivo screen of 94 cytokines, we found that inflammatory cytokines, such as IL-1, HGF, MCPs, and FGF2, which are elevated in a diverse set of AML patients, profoundly affects the survival of AML cells. The increased survival and protection of these residual leukemia cells eventually leads to drug resistance, and targeting these survival pathways can overcome resistance. In addition to resistance to targeted therapy, we also have data to suggest the immune microenvironment is involved in immune evasion. Specifically, our data suggest that adaptive (T cell) immune responses are impaired in the context of the leukemia microenvironment. These results provided a proof-of-concept example in which targeting microenvironmental signals may significantly enhance effective targeting of residual leukemia cells. Since the AML microenvironment is extremely complex, we predict that various other inflammatory cytokines and cellular factors may modulate response to targeted therapy. Therefore, in the proposed study we will perform comprehensive profiling of the AML microenvironment pre and post drug treatment for secreted cytokines, marrow stromal gene expression signature, and immune cell characterization. We will leverage primary AML samples from ongoing clinical trials using Azacitidine, FLT3, BCL2, JAK2, PD-1 and MEK inhibitors. The data obtained will be integrated by using machine-learning approaches and prioritized pathways will be validated to identify their functional significance in drug resistance. We will test the hypothesis that in addition to intrinsic mechanisms, the secreted and cellular factors present in the microenvironment contribute to drug resistance and sensitivity in AML. Characterizing these extrinsic pathways will be critical in order to develop more effective combination therapies that enhance drug sensitivity and overcome resistance. Relevance: Elucidating how microenvironment-driven signaling influence drug response and survival of AML cells will help identify novel tractable targets for combination therapy. Our study will also be applicable to other cancers that are dependent on these inflammatory pathways.