Bone marrow stromal cells modulate mouse ENT1 activity and protect leukemia cells from cytarabine induced apoptosis.
BACKGROUND
Despite 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.


METHODS
Using 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 (3)H-adenosine.


RESULTS
Leukemia 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.


CONCLUSIONS
The 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.
Departamento de Hematología y Oncología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
Patricia
P
Macanas-Pirard
Andrea
A
Leisewitz
Richard
R
Broekhuizen
Kelly
K
Cautivo
Francisco M
FM
Barriga
Francisco
F
Leisewitz
Victoria
V
Gidi
Erick
E
Riquelme
Viviana P
VP
Montecinos
Pilar
P
Swett
Pelayo
P
Besa
Pablo
P
Ramirez
Mauricio
M
Ocqueteau
Alexis M
AM
Kalergis
Matthew
M
Holt
Michael
M
Rettig
John F
JF
DiPersio
Bruno
B
Nervi
D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001854:Bone Marrow Cells / Q000187:drug effects / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003561:Cytarabine / Q000494:pharmacology* / Q000627:therapeutic use; D033721:Equilibrative Nucleoside Transporter 1 / Q000378:metabolism*; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D017154:Stromal Cells / Q000187:drug effects / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000964:Antimetabolites, Antineoplastic; D033721:Equilibrative Nucleoside Transporter 1; C498476:SLC29A1 protein, mouse; D003561:Cytarabine