An in vitro study of blast cell metabolism in acute myeloid leukaemia using the MTT assay

We have utilized the MTT assay to measure the metabolic activity of cells from the bone marrow of 55 patients with acute myeloid leukaemia (AML), myelodysplastic syndrome (MDS) and non-clonal disease. Doubling dilutions of cells were exposed to MTT for 3-4 h. The mean optical density of the formazan produced by each cell dilution was plotted and the gradient of the line produced was calculated, higher gradients indicating more metabolically active cells. Results showed that the median activity of mononuclear cells from seven patients with non-clonal disease was 0.202 (range 0.175-0.253); blast cells from 27 patients with de novo AML had a median activity of 0.187 (range 0.079-0.345) and 13 patients with MDS a median of 0.155 (range 0.062-0.311). Seven assays on mononuclear cells from five patients in remission had a median activity of 0.203 (range 0.190-0.248), indicating no significant difference between these and normal patients. There was no correlation between the metabolic activity of cells when compared with their proliferative capacity, cell size and expression of P-glycoprotein. Following exposure of the AML patients' blast cells to the anthracyclines, cytosine arabinoside, 6-thioguanine and etoposide, cell survival was measured using the MTT assay. While there was no correlation between the in vitro sensitivity of these cells to the anthracyclines or etoposide, less metabolically active cells showed significantly greater sensitivity to 6-thioguanine. Conversely, the more active cells appeared to be more sensitive to cytosine arabinoside. Patients whose blasts cells showed higher metabolic activity appeared to achieve remission and had a longer mean survival time. Therefore, by using a simple technique we were able to establish that some patients were more likely to respond to certain cytotoxic regimes. Our preliminary study reflected the multifactorial nature of clinical response in AML and MDS, so providing further information on the relationship between cellular metabolic activity and treatment failure.