Susceptibility of AML cells to in vitro apoptosis correlates with heat shock protein 70 (hsp 70) expression.

Acute myeloid leukaemia (AML) cells from some individuals rapidly undergo apoptosis during in vitro culture. We have analysed this mode of cell death in AML cells harvested from patients at initial presentation and during subsequent treatment/relapse. Using flow cytometric analysis of propidium iodide-stained cells and quantitation of the subdiploid apoptotic peak, we observed that leukaemic cells from patients with AML displayed a heterogenous susceptibility to apoptosis in terms of the rate of accumulation of apoptotic cells. After 48 h incubation in the absence of added serum or exogenous growth factors the percentage of apoptotic cells ranged from 3% to 99%. This susceptibility to apoptosis correlated significantly with intracellular expression of hsp70 (P = 0.009), but not hsp90, and was also associated with the presence of p53 and low levels of expression of bcl-2.