Mesenchymal cells regulate the response of acute lymphoblastic leukemia cells to asparaginase
Shotaro Iwamoto, … , Ching-Hon Pui, Dario Campana
Shotaro Iwamoto, … , Ching-Hon Pui, Dario Campana
Published April 2, 2007
Citation Information: J Clin Invest. 2007;117(4):1049-1057. https://doi.org/10.1172/JCI30235.
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Research Article Oncology

Mesenchymal cells regulate the response of acute lymphoblastic leukemia cells to asparaginase

Abstract

Because of their low asparagine synthetase (ASNS) expression and asparagine biosynthesis, acute lymphoblastic leukemia (ALL) cells are exquisitely sensitive to asparagine depletion. Consequently, asparaginase is a major component of ALL therapy, but the mechanisms regulating the susceptibility of leukemic cells to this agent are unclear. In 288 children with ALL, cellular ASNS expression was more likely to be high in T-lineage ALL and low in B-lineage ALL with TEL-AML1 or hyperdiploidy. However, ASNS expression levels in bone marrow–derived mesenchymal cells (MSCs), which form the microenvironment where leukemic cells grow, were on average 20 times higher than those in ALL cells. MSCs protected ALL cells from asparaginase cytotoxicity in coculture experiments. This protective effect correlated with levels of ASNS expression: downregulation by RNA interference decreased the capacity of MSCs to protect ALL cells from asparaginase, whereas enforced ASNS expression conferred enhanced protection. Asparagine secretion by MSCs was directly related to their ASNS expression levels, suggesting a mechanism — increased concentrations of asparagine in the leukemic cell microenvironment — for the protective effects we observed. These results provide what we believe to be a new basis for understanding asparaginase resistance in ALL and indicate that MSC niches in the bone marrow can form a safe haven for leukemic cells.

Authors

Shotaro Iwamoto, Keichiro Mihara, James R. Downing, Ching-Hon Pui, Dario Campana

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Figure 7

Expression of ASNS in MSCs determines the susceptibility of primary ALL cells to asparaginase.

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Expression of ASNS in MSCs determines the susceptibility of primary ALL ...
(A) Primary ALL cells, obtained from the diagnostic bone marrow of 35 children with ALL, were exposed for 48 hours to asparaginase (1.0 IU/ml) in the presence of MSCs with ASNS expression downregulated by siRNA or upregulated by ASNS transduction. Results were compared to those of parallel cultures using MSCs transduced with a scrambled siRNA construct or empty vector, respectively. Values are mean ± SD cell killing obtained in cultures with each MSC type relative to that of its corresponding control (indicated by the dashed line). Differences between the test and control cultures were significant (P < 0.05, Student’s t test) in all samples except 1–6 and 23 in cultures with MSCs underexpressing ASNS and 5 and 14–16 in cultures with MSCs overexpressing ASNS. (B) The mean cytotoxicity ratio obtained in cultures with MSCs overexpressing ASNS were subtracted from those with MSCs underexpressing ASNS to derive a protection index. Figure shows the relation between this protection index and genetic subtype in the 35 ALL samples. P = 0.068, hyperdiploid cases; *Cases lacking known genetic abnormalities, P = 0.023; Wilcoxon rank-sum test. (C) Relationship between protection index and ASNS transcript expression in ALL cells by real-time PCR. r2 by regression analysis is shown.