The mechanism of action of L-asparaginase in childhood acute lymfoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most frequent type of childhood cancer. The key component in the therapy, L-asparaginase (ASNase), hydrolyzes plasma asparagine and glutamine. Leukemic cells are sensitive to the depletion due to low activity of asparagine synthetase. Although the treatment is very effective, resistance and side effects remain a serious problem in some cases and its mechanism of action is not well understood. In this study, we wanted to elucidate the effect of ASNS expression level on the sensitivity of ALL cells to ASNase treatment. Our aim was also to clarify the intracellular consequences of the amino acid depletion to define the reason of different patients' response. We used four ALL cell lines (NALM-6, RS4;11, REH, and UOCB-6) and 30 diagnostic bone marrow samples of ALL patients to study the relationship between ASNS expression and sensitivity to ASNase using MTS proliferation assay. RNA interference was used to study the effect of a range of ASNS levels on the response to ASNase treatment. Using a cell line model with a gradually knocked-down ASNS gene, we defined a cutoff level below which ASNS gene expression does not correlate with sensitivity to ASNase. Importantly, ASNS gene expression in patients' ALL blasts is below this level. We confirmed that there was no..