Evaluation of cytotoxicity by flow cytometric drug sensitivity assay in childhood T-cell acute lymphoblastic leukemia

Risk-based treatment strategies have improved outcome in childhood B-precursor acute lymphoblastic leukemia, and in vitro drug sensitivity assessment using methyl-thiazol-tetrazolium (MTT) assay has been shown to be an independent prognostic marker. To date, such strategies in childhood T-cell acute lymphoblastic leukemia (T-ALL) have proved elusive, and in vitro drug sensitivity testing has had limited success in T-ALL due to poor T-cell lymphoblast survival in vitro. We have developed the flow cytometric drug sensitivity assay (FCDSA) to evaluate in vitro drug sensitivity. We studied 68 cases of childhood TALL for cytarabine (Ara-C) and daunorubicin sensitivity by FCDSA and compared the results with those obtained by MTT assay. Spontaneous apoptosis was correlated with cytotoxicity rates for both drugs by FCDSA, but not with the results obtained by MTT assay. Daunorubicin sensitivity had a positive correlation with Ara-C in individual cases by FCDSA; but not by MTT assay. Studies repeated on stored samples had comparable results for both drugs by FCDSA (P < 0.01), but not for Ara-C by MTT assay. Comparison of T-ALL sensitivity with acute myeloid leukemia (AML) cases revealed a unique pattern difference. Median cytotoxicity (expressed in arbitrary units) for Ara-C was 8 ( 0-47) and 27 (0-81), and daunorubicine cytotoxicity for T-ALL and AML samples was 79 (5-100) and 34 (0-98), respectively. Although age or white blood cell count at diagnosis was not associated with any particular drug response pattern, CD13 expression on T-lymphoblasts was associated with in vitro resistance. FCDSA is a reliable, practical and reproducible method that can be integrated into studies of drug-target cell interactions in T-ALL.