Relevance of in vitro leukaemia cell survival to short- and long term clinical outcome in AML

In ninety-three cases of newly diagnosed acute myeloid leukaemia (AML) we i nvestigated the importance to short- and long term clinical outcome of the in vitro short term leukaemia cell survival as measured by a 4-day MTT (3-[ 4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide)-assay. In 67 pa tients treated by intravenous remission induction therapy we found that pat ients who after the first induction cycle or after induction therapy overal l achieved a complete remission (CR) had leukaemia cells with significantly lower in vitro cell survival ability than calls of non-responders (p=0.02 and 0.06, respectively). These relations remained statistically significant in subsequent multivariate analyses. Likewise, a favourable effect of low in vitro leukaemia cell survival on overall survival of the patients was de tected in the (largest) subgroup of adult patients treated uniformly by the same remission induction regimen as well as in all patients. However, in t he 44 patients, who achieved CR, the in vitro leukaemia cell survival did n ot show significance to remission duration or time to first relapse. Furthe rmore, the leukaemia cell survival (MTT-assay) did not to correlate with th e Bcl-2 expression level (quantitative flow cytometry) of the leukaemia cel ls (r=0.18, n=34, p=0.32). In addition, in a cell line model employing the growth factor dependent MO7 human AML cell line, growth factor withdrawal w as associated with rapid onset of cellular apoptosis as evaluated by morpho logy, occurrence of a subG1 peak in DNA histograms, and loss of cellular ac tivity in the MTT-assay. In contrast, a more moderate decline in Bcl-2 expr ession and gradual loss of ability to exclude the trypan blue dye was seen in the leukaemia cells in response to growth factor withdrawal. We conclude , that the MTT-assay provides a simple and sensitive method for measuring i n vitro cell survival. The differences in leukaemia cell survival seen in A ML may well be clinically relevant and may help to provide a better underst anding of clinical drug resistance.