In Vitro Drug Testing in Patients with Acute Leukemia with Incubations Mimicking in Vivo Intracellular Drug Concentrations

The differential staining cytotoxicity (DiSC) assay was evaluated as a predictive test for response to therapy in patients with acute non-lymphoblastic leukemia. Incubations were designed in such a way that the intracellular concentrations of cytostatic drugs in vitro paralleled those in vivo. Leukemic cells were isolated from 53 patients with acute non-lymphocytic leukemia. 13 of these patients died early due to supportive care failure and were not evaluable for the predictive drug testing. Of the remaining 40 patients, 25 entered a complete remission (CR) and 15 had a resistant disease (RD). According to the patients randomization to therapy the cells were incubated with anthracyclines and Ara-C separately and in combination. After 4 days of culturing in liquid medium the in vitro cytotoxicity was determined by dye exclusion according to Weisenthal. The cytotoxic effect in vitro was significantly higher on cells from patients who achieved a CR compared to patients with RD after incubations with anthracyclines 0.2 mumol/l (p less than or equal to 0.005), Ara-C 0.5 mumol/l (p less than or equal to 0.05) and with the combination of anthracyclines with Ara-C (p less than or equal to 0.0005). The best predictive value was achieved when incubations with 0.2 mumol/l anthracyclines and 0.5 mumol/l Ara-C were analyzed together. With these incubations cells from 20 out of 21 patients who achieved CR showed either less than or equal to 60% surviving cells after the anthracycline incubation or less than or equal to 35% surviving cells after the Ara-C incubation. Cells from 11 out of 13 patients with RD did not fulfill either of these criteria. In vitro drug sensitivity was significantly correlated to a prolonged survival (p less than 0.01). We conclude that, when performed with incubations that mimic in vivo tumor cell exposure to cytostatic drugs, the DiSC assay shows a high correlation to clinical outcome for patients with acute non-lymphocytic leukemia.