Comparative cytotoxicity of dexamethasone and prednisolone in childhood acute lymphoblastic leukemia

Purpose: The relative cytotoxicity of prednisolone and dexamethasone in acute lymphoblastic leukemia (ALL) is controversial. We therefore compared the direct antileukemic activities of these compounds in stroma-supported cultures of leukemic lymphoblasts. Materials and Methods: Bone marrow samples from children with B-lineage ALL were cultured on allogeneic: bone marrow-derived stromal layers and exposed to various concentrations of glucocorticoids. After 4 days of culture, the number of viable leukemic cells was counted by flow cytometry and compared with that in parallel cultures without drugs. Results: In 28 B-lineage ALL samples tested, the concentration producing 50% cytotoxicity (LC(50)) of prednisolone ranged from 2.0 to 7,978 nmol/L (median, 43.5 nmol/L), and that of dexamethasone from 0.6 to 327 nmol/L (median, 7.5 nmol/L). Despite the wide variability of responses among samples, there was an excellent correlation between LC(50) values obtained with the two drugs (linear r=.99, P<.0001; Spearman rank-order r=.77, P<.0001). The median ratio of dexamethasone to prednisolone LC(50) and LC(90) values was 1:5.5 (range, 1:1.0 to 1:24.4 for LC(50); 1:1.1 to 1:25.5 for LC(90)). Studies with ALL cell lines demonstrated that both drugs were cytotoxic through induction of apoptosis. Stromal layers did not absorb or inactivate measurable amounts of corticosteroids, which indicates that the assay system did not bios results toward increased drug resistance. Conclusion: In a bone marrow-derived microenvironment, dexamethasone is five to six times more cytotoxic (on a molar basis) than prednisolone, in agreement with the antiinflammatory activities of these drugs. This finding may serve to guide the selection of dexamethasone dosage in the treatment of ALL. (C) 1996 by American Society of Clinical Oncology.