Bone Marrow Stromal Cells Modulate Mouse ENT1 Activity and Protect Leukemia Cells from Cytarabine Induced Apoptosis

Abstract

BackgroundDespite a high response rate to chemotherapy, the majority of patients with acute myeloid leukemia (AML) are destined to relapse due to residual disease in the bone marrow (BM). The tumor microenvironment is increasingly being recognized as a critical factor in mediating cancer cell survival and drug resistance. In this study, we propose to identify mechanisms involved in the chemoprotection conferred by the BM stroma to leukemia cells.MethodsUsing a leukemia mouse model and a human leukemia cell line, we studied the interaction of leukemia cells with the BM microenvironment. We evaluated in vivo and in vitro leukemia cell chemoprotection to different cytotoxic agents mediated by the BM stroma. Leukemia cell apoptosis was assessed by flow cytometry and western blotting. The activity of the equilibrative nucleoside transporter 1 (ENT1), responsible for cytarabine cell incorporation, was investigated by measuring transport and intracellular accumulation of 3H-adenosine.ResultsLeukemia cell mobilization from the bone marrow into peripheral blood in vivo using a CXCR4 inhibitor induced chemo-sensitization of leukemia cells to cytarabine, which translated into a prolonged survival advantage in our mouse leukemia model. In vitro, the BM stromal cells secreted a soluble factor that mediated significant chemoprotection to leukemia cells from cytarabine induced apoptosis. Furthermore, the BM stromal cell supernatant induced a 50% reduction of the ENT1 activity in leukemia cells, reducing the incorporation of cytarabine. No protection was observed when radiation or other cytotoxic agents such as etoposide, cisplatin and 5-fluorouracil were used.ConclusionThe BM stroma secretes a soluble factor that significantly protects leukemia cells from cytarabine-induced apoptosis and blocks ENT1 activity. Strategies that modify the chemo-protective effects mediated by the BM microenvironment may enhance the benefit of conventional chemotherapy for patients with AML.

The CCL2/CCR2 Axis Affects Transmigration and Proliferation but Not Resistance to Chemotherapy of Acute Myeloid Leukemia Cells

“…We previously published that the BM stromal cells secrete soluble factors that protect human AML cells from Ara-C induced apoptosis [20]. We explored whether cytokine CCL2, normally secreted by BM stromal cells, could chemoprotect THP-1 cells from Ara-C induced apoptosis.…”

“…We previously demonstrated in vivo that the BM stroma supports and protects AML cells as a mechanism from chemotherapy resistance [20]. It is well known that the SDF-1/CXCR4 axis plays a crucial role in homing AML and HSCs to the BM.…”

“…It is well known that the SDF-1/CXCR4 axis plays a crucial role in homing AML and HSCs to the BM. Furthermore, we have shown that the CXCR4 inhibitor, AMD3100, mobilizes AML cells from the BM to the PB [3, 20]. We showed that AMD3100 treatment of leukemic mice significantly enhanced the efficacy of chemotherapy (Ara-C) treatment due to AML mobilization from the BM to the PB.…”

Randomized phase II trial of cytosine arabinoside with and without the CHK1 inhibitor MK-8776 in relapsed and refractory acute myeloid leukemia

“…In a mouse model of AML, BM stromal cells have been shown to secrete a soluble factor that mediates chemoprotection. (46) Alternatively, marrow stroma-derived SDF-1 has also been implicated in protecting AML marrow blasts from chemotherapy. (47, 48)…”

The role of adhesion molecules in acute myeloid leukemia and (hemato)oncology: A systematic review

“…[112][113][114] ). Mechanisms including CXCR4/SDF-1α axis and VLA-4/VCAM-1 pathway mediate interactions with bone marrow stromal cells protect malignant cells from chemo-and radiotherapy 92,115,116 . The role of CXCR4 in AML was illustrated by experiments showing reduction in engraftment of primary human AML cells into NOD/ SCID mice recipients treated with antibody to CXCR4 (ref.…”