Chemosensitivity testing of fresh leukaemia cells using the MTT colorimetric assay.

We have determined the feasibility of using the MTT colorimetric assay for measuring the sensitivity of fresh leukaemia cells to cytotoxic agents. A linear relationship was seen between the number of leukaemic cells plated and the resulting absorbance in the MTT assay at day 4. For 2 X 10(5) cells/well from CLL peripheral lymphocytes, the mean absorbance (measured at 540 nm) was 0.41. Similar curves were obtained with the assay carried out between days 3 and 7. ID50 values for CLL lymphocytes exposed to adriamycin (ADM) were in the range of 0.02-0.29 micrograms/ml, a similar range to that given by the DiSC dye exclusion assay. Sensitization of leukaemia cells to ADM by verapamil or cyclosporin A could be demonstrated in some patients but not in others. The lymphocytes from one patient with prolymphocytic leukaemia were abnormally resistant to ionizing radiation. These cells also showed resistance to melphalan and adriamycin but not to vincristine. The MTT assay appears to offer an attractive option for in vitro chemosensitivity testing in leukaemia, determination of cross-resistance profiles and studies of resistance modifiers.