Evaluation of Environment Mediated Innate Drug Resistance in Leukemia

Abstract

Bone marrow micro-environment is a reservoir and sanctuary for the maintenance, survival and the behavior of the hematopoietic stem cells. Malignant myeloblasts rearchitects the bone marrow micro-environment for a deleterious symbiotic relationship via contact dependent and independent manner. Henceforth, we undertook an unbiased approach to understand the interactions between the major components of the bone marrow micro-environment mesenchymal stromal cells and the leukemic cells. Our gene expression profiling results strongly corroborated with the existing literature of bone marrow micro-environment mediated drug resistance. Prominent signaling pathways which were up regulated was NF-kB and PI3KAKT genes which prompted us to evaluate these signaling pathways in the protective effect provided by the stromal cells to leukemic cells against daunorubicin and cytosine arabinoside. We employed, small molecules and drug screening approach targeting these pathways with specific inhibitors significantly overcome the bone marrow microenvironment mediated drug resistance both in a contact dependent and independent system. To further evaluate the paracrine mediated protective effect offered by the stromal cells we focused on the mechanisms of cell-cell contact and observed the importance of the extracellular vesicles (EVs) in both the physiological and pathological conditions. EVs carry signaling molecules such as miRNA, proteins, and subcellular organelles and regulates the signaling cascades in the receiving cells. Inhibiting the extracellular vesicles secretion abrogated protective effect offered by the stromal cells both in a contact dependent and independent manner and down regulated the NF-kB and PI3K-AKT signaling. The study highlights the complexity of the bone marrow micro-environment in the promoting drug resistance and identified multiple players and targets to overcome the protective effect using pharmacological and genetic knockdown and over expression approaches. newline