INVITRO AND INVIVO KILLING OF ACUTE LYMPHOBLASTIC-LEUKEMIA CELLS BY L-ASPARAGINASE

  • 1 August 1989
    • journal article
    • research article
    • Vol. 49  (15) , 4363-4368
Abstract
L-Asparaginase (ASNase) is a potent antileukemic enzyme routinely used in the treatment of children with acute lymphoblastic leukemia. As part of investigations of the biological activity of ASNase, we have developed techniques which measure the in vitro and in vivo cell killing ability of ASNase. To study the effect of ASNase on in vitro survival of primary lymphoblasts, bone marrow mononuclear cells obtained from untreated patients with acute lymphoblastic leukemia were cultured with and without ASNase. After 5 days, viable cells cell counted using trypan blue exclusion to calculate total cell kill due to ASNase. Propidium iodide exclusion, leukemia cell surface antigens, and flwo cytometry were used to determine leukemia cell kill due to ASNase. Comparison of leukemia cell kill and total cell kill showed a direct linear relationship (n = 24, r = 0.7), preferential killing of leukemia cells by ASNase (slope = 0.66), and that use of leukemia cell surface markers yielded a more accurate measurement of leukemia cell killing. ASNase at concentrations from 0.0001 to 0.1 IU/ml had equal effects on extent of leukemia cell killing (P = 0.3 to 0.7), suggestign the absence of a dose response at the ASNase concentrations tested. As a measure of the in vivo response to ASNase treatment, the number of viable bone marrow leukemia cells in the patient prior to and 5 days after treatment with ASN ase was measured as the product of (% of rhodamine 123 fluorescent [Viable] cells) .times. (absolute leukemic infiltrate). The change which occurred in the viable leukemic infiltrate was the same for patients whether they received 15,00 or 2,500 IU/m2 of ASNase as a single drug. There was a linear correlation (n = 8, r = 0.9) between in vivo and in vitro leukemia cell killing by ASNase. Thus, the in vitro assay described here can be used to predict in vivo sensitivity to ASNasee in acute lymphoblastic leukemia.