Defining alteration in bone marrow mesenchymal stem cells (MSC) from acute myeloid leukemia and exploring cultured MSC-conditioned media as a novel anti-leukemia therapy agent.

BACKGROUND: Bone marrow-resident mesenchymal stem cells (BM-MSC) often play a role in acute myeloid leukemia (AML) progression and drug resistance by exerting immunomodulatory effects on cellular as well as soluble milieu. The current study aimed to understand the dynamic interplay between AML-BM-MSC and their soluble factors in determining the fate of AML blasts within the microenvironment. METHODS: AML-BM-MSC were cultured and characterized for expression of phenotyping markers, multilineage differentiation potential, and gene expression analysis by microarray. To understand cross talk, AML-BM-MSC were co-cultured with the AML cell line OCI-AML2 and assessed for changes in cell cycle phases, mitochondrial activity, and cytarabine-induced cell death. Differential regulation of AML blast fate was evaluated by conducting co-culture experiments with cell-free-conditioned media (PD-MSC-CM) and in the presence of cell-cell contact of AML-BM-MSC. Further, PD-MSC-CM was assessed in vivo for tumor reduction potential using a leukemia xenograft model. RESULTS: Besides standard features, AML-BM-MSC exhibited increased vesicles, MSC bodies (exosomes), and mitochondria. Altered AML-BM-MSC demonstrated upregulation of inflammasome pathway markers in microarray, which was further validated by ELISA and quantitative real-time polymerase chain reaction. Co-culture experiments on AML-BM-MSC revealed protective effects on AML blasts in the presence of cytarabine. In contrast, PD-MSC-CM significantly inhibited AML cell growth alone and synergistically with cytarabine. Further, PD-MSC-CM significantly reduced tumor growth in the leukemia mouse model, and this effect was mediated by regulation of the NLRP3 inflammasome pathway. CONCLUSION: Summarizing, the leukemic blasts and AML-MSC in the BM microenvironment interact differentially in cell-cell contact compared to only soluble factors. Further, our study has provided innovative leads that PD-MSC-CM effectively abrogates leukemia tumor growth, enhances chemosensitivity and can be developed further as an immunomodulatory novel "off-the-shelf" therapeutic agent for leukemia.