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Background & Objectives: Although the outcome of children with acute lymphoblastic leukaemia (ALL) has improved dramatically over the last decade, some children still fare poorly and relapses are seen. The sensitivity of leukaemic cells to corticosteroids has emerged as an important prognostic factor in ALL. The t(9,22) translocation, resulting in the bcr-abl fusion gene, is a non-random translocation found in B-lineage acute lymphoblastic leukaemia. It is also known to be an independent poor prognostic factor for long-term disease free survival. We studied the association between the presence of bcr-abl fusion gene and in vitro prednisolone resistance in children with B-lineage acute lymphoblastic leukaemia at diagnosis., Methods: A total of 23 children (aged 1-16 yr, median age: 12 yr) with B-lineage acute lymphoblastic leukaemia at diagnosis were included in the study. The presence of bcr-abl fusion gene was determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and the in-vitro resistance to prednisolone was measured by short term colorimetric methyl thiazol tetrazolium (MTT) assay., Results: A median LD50 (lethal dose for 50% cells) for prednisolone in bcr-abl positive children (n=7) was 1.6 mg/ml (range: 0.25-5.0 mg/ml) and that of bcr-abl negative children (n=16) was 0.35 mg/ml (range 0.62-1.0 mg/ml). The median LD50 for prednisolone differed significantly between the bcr-abl positive and negative groups of children with acute lymphoblastic leukaemia (P<0.005)., Interpretation & Conclusion: This is probably the first report to show that leukaemic blasts of bcr-abl positive children with ALL are about four-fold resistant to prednisolone as compared to blasts from bcr-abl negative children. This suggests that one of the reasons for the poor prognosis of bcr-abl positive ALL could be a lower steroid sensitivity.

Background & Objectives: Drug sensitivity assays are useful in oncology practice for evaluating the sensitivity of malignant cells to anti-cancer drugs. The usefulness of such assays for the prediction of clinical response to therapy has also been demonstrated. The existing methods used for this purpose are time consuming and labour intensive. Here we report a simplified flow cytometry based assay for evaluating the in vitro drug sensitivity of leukaemic cells., Methods: The chemo-sensitivity of three human leukaemic cell lines (a lymphoblastoid cell line, Jurkat; an erythroleukaemic cell line, K 562 and a myelomonocytic cell line HL-60) was investigated by flow cytometry. Flow cytometry was used to determine LD50 (50% inhibitory concentration) for prednisolone on Jurkat and daunorubicin on HL 60 and K 562 cell lines respectively. Per cent cell death could directly be assessed on a flow cytometer by measuring the fluorescence after staining with propidium iodide (PI). For comparison MTT assay was also performed using prednisolone on Jurkat and daunorubicin on HL-60., Results: Cytotoxic effect of drugs was found to be dose dependent. Mean LD50 of prednisolone for Jurkat cells by flow cytometry was 0.805 +/- 0.058 mg/ml and by MTT assay 0.866 +/- 0.115 mg/ml. Mean LD50 of daunorubicin for HL-60 was 1.96 +/- 0.05 micrograms/ml by flow cytometry and 1.90 +/- 0.282 micrograms/ml by MTT assay. The mean LD50 of daunorubicin to K 562 was 0.49 +/- 0.049 mg/ml by the flow cytometry method. The inter-assay variation for the LD50 by flow cytometry based assay was found to be 6, 14 and 10 per cent for Jurkat, HL-60 and K 562 respectively., Interpretation & Conclusion: We report a flow cytometry based drug-sensitivity assay for leukaemic cells, which uses a single dye staining and is rapid, technically simple and reproducible. The results compare well with the more commonly used MTT assay, which is labour intensive and time consuming. The limitation of our method is that it can only be used for studying cells in suspension and is therefore not suitable for adherent cell lines.