Reciprocal Interactions of Leukemic Cells with Bone Marrow Stromal Cells Promote Enrichment of Leukemic Stell Cell Compartments in Response to Curcumin and Daunorubicin

A predominant challenge in developing curative leukemia therapy is interactions of leukemic cells with the bone marrow stromal microenvironment. We aimed to investigate the role of stromal cells, such as bone marrow mesenchymal stromal cells (BMSCs) and osteoblasts (OBs), in curcumin (CUR) and daunorubicin (DNR) induced apoptosis of acute myeloid leukemia (AML) cells. We used KG1 and U937 as leukemia cell line models and treated them with CUR and DNR. The cells were then co-cultured with BMSCs or a combination of BMSCs and OBs as feeders. After 24 hours of co-culture, BMSCs or OBs were sorted and separated from the leukemia cells and apoptosis levels were analyzed by annexin/propidium iodide (PI) staining on flow cytometry. Potentially involved molecular pathways were analyzed at gene and protein levels by Real time PCR and western blotting, respectively. The results showed AML cells cocultured with BMSCs plus OBs to be more resistant to drug induced-apoptosis compared to co-culture with BMSCs alone or without co-culture. Expression levels of OPN, CXCL-12, IL-6, STAT-3 and VCAM-1 were also significantly up-regulated in OBs and AML cells, at both mRNA and protein levels after co-culture, with concurrent enrichment of CD34+ AML cells. Our data showed, in a stromal cell niche-based model, that OBs revoke the influence of BMSCs on leukemic cells and promote enrichment of both CD34+ and CD34- leukemic stem cell (LSC) compartments in response to CUR and DNR. Up-regulation of OPN, CXCL-12, IL-6, STAT-3 and VCAM-1 in OBs and AML cells in co-culture might be part of molecular mechanisms that block CUR or CUR+DNR-induced apoptosis and promote enrichment of CD34+ and CD34- LSCs.