Understanding the crosstalk between AML cells and bone marrow stromal cells to overcome treatment resistance

Although tremendous progress has been made in developing and applying in clinics molecular targeted therapies for acute myeloid leukemia (AML), drug resistance and relapses, mostly due to clonal selection and the protective effect of the leukemic bone marrow microenvironment, are still major issues. We developed a strategy based on a combination of drugs inducing proteotoxic and oxidative stress. We demonstrated that it efficiently leads to the death of AML cell lines and primary leukemic stem cells (LSCs) bearing the mutation FLT3-ITD, without affecting normal HSCs, in vitro and in vivo. However, bone marrow stromal cells (BMSCs) protect AML cells by reducing the amount of oxidative stress generated by the treatment in a co-culture system. Our focus is to investigate the mechanisms contributing to the protective abilities of the BMSCs. Furthermore, aiming to optimize the combination of drugs to increase their translational potential, we evaluated the efficacy of combining proteotoxic stress with different drugs at the cutting edge in clinical trials for AML, among which is the BCL-2 inhibitor Venetoclax. We tested the sensitivity of FLT3-ITD+ AML cell lines and primary LSCs to different treatments in monoculture or in coculture with BMSCs, in 2D or 3D models. In parallel, we evaluated the efficacy of the combination RBA plus Venetoclax in an in vivo orthotopic murine model of AML. We demonstrate that the combination of proteotoxic stress and Venetoclax is effective against FLT3-ITD+ AML cells in vitro, overcoming the protection provided by BMSCs in a coculture system without affecting their viability, and in vivo significantly prolonging the life span of a murine model of FLT3-ITD+ AML. Importantly, our investigations into the crosstalk between AML cells and BMSCs upon different treatments reveal the involvement of mechanotransduction signaling in the BMSCs for the first time. Thus, our finding opens new paths for research and potential therapeutic strategies.