Asparagine synthetase expression is linked with L-asparaginase resistance in TEL-AML1-negative but not TEL-AML1-positive pediatric acute lymphoblastic leukemia

Resistance to L-asparaginase in leukemic cells may be caused by an elevated cellular expression of asparagine synthetase (AS). Previously, we reported that high AS expression did not correlate to L-asparaginase resistance in TEL-AML1-positive B-lineage acute lymphoblastic leukemia (ALL). In the present study we confirmed this finding in TEL-AML1-positive patients (n = 28) using microarrays. In contrast, 35 L-asparaginase-resistant TEL-AML1-negative B-lineage ALL patients had a significant 3.5-fold higher AS expression than 43 sensitive patients (P < .001). Using real-time quantitative polymerase chain reaction (RTQ-PCR), this finding was confirmed in an independent group of 39 TEL-AML1-negative B-lineage ALL patients (P = .03). High expression of AS was associated with poor prognosis (4-year probability of disease-free survival [pDFS] 58% +/- 11%) compared with low expression (4-year pDFS 83% +/- 7%; P = .009). We conclude that resistance to l-asparaginase and relapse risk are associated with high expression of AS in TEL-AML1-negative but not TEL-AML1-positive B-lineage ALL

Sensitivity to L-asparaginase is not associated with expression levels of asparagine synthetase in t(12;21)+ pediatric ALL

The (12;21) translocation resulting in TEL/AML1 gene fusion is present in about 25% of childhood precursor B-lineage acute lymphoblastic leukemia (ALL) and is associated with a good prognosis and a high cellular sensitivity to L-asparaginase (L-Asp). ALL cells are thought to be sensitive to L-Asp due to lower asparagine synthetase (AS) levels. Resistance to L-Asp may be caused by an elevated cellular level of AS or by the ability of resistant cells to rapidly induce the expression of the AS gene on L-Asp exposure. AS may be a target regulated by t(12;21). We studied the relationship between t(12;21) and the mRNA level of AS to investigate a possible mechanism underlying L-Asp sensitivity. Real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis surprisingly revealed that 30 patients positive for t(12;21) expressed 5-fold more AS mRNA compared with 17 patients negative for t(12;21) (P =.008) and 11 samples from healthy controls (P =.016). The mRNA levels of AS between t(12;21)(-) ALL and healthy controls did not differ. No difference was found between ALL patients positive or negative for t(12;21) in the capacity to up-regulate AS after in vitro L-Asp exposure, excluding a defective capacity for t(12;21) cells in up-regulating AS on L-Asp exposure. Moreover, no correlation was observed between AS mRNA expression and sensitivity to L-Asp. We conclude that the sensitivity of t(12;21)(+) childhood ALL to L-Asp is not associated with the expression level of the AS gene. Furthermore, we contradict the general thought that leukemic cells specifically lack AS compared with normal bone marrow and blood cells