Asparagine Synthetase in Pediatric Acute Leukemias: AML-M5 Subtype Shows Lowest Activity
The enzyme L-asparaginase is used to achieve maximum reduction of L-asparagine in blood and CSF. Lack of sufficient cellular activity of asparagine synthetase in blast cells compared to normal tissues is thought to be the basis of the antileukemic effect in ALL. While L-Asparaginase is routinely used in acute lymphoblastic leukemia its role and value in the treatment of acute myeloblastic leukemia is still being discussed. As the drug causes a number of relevant side effects, measuring the asparagine synthetase activity of individual patients’ blast cells might help to restrict the use to patients with low expression and to exclude others with high synthetase capacity from this treatment. We, therefore, established asparagine synthetase monitoring.
Peripheral or bone marrow blast cells were separated by Ficoll gradient centrifugation. Intracellular proteins (6000 g-supernatant) were incubated in excess of required substrates and the synthetased asparagine levels then measured after 0, 40, 80,100, and 140 min (HPLC). The interassay coefficient of variation was < 20% and showed good reproducibility (activity: nM asp aragine/mg protein/h).
As AML and ALL both showed comparable expression of asparagine synthetase, the possible value of L-asparaginase in the treatment of AML should be reconsidered. As a consequence we have initiated a multicenter trial to test the clinical activity in patients with relapsed AML-M5 and to determine the relationship between the response to L-asparaginase treatment and cellular asparagine synthetase activity, mRNA expression (d’Incalci, Milano) and in vitro asparaginase sensitivity (Pieters, Amsterdam).
KeywordsLymphoblastic Leukemia Blast Cell Acute Myeloblastic Leukemia Asparagine Synthetase Trypan Blue Solution
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