The current study was undertaken to determine the relevance of leukemic blast cell proliferative activity, cellular parameters of Ara-C metabolism and the in vitro sensitivity to GM-CSF in association with the clinical response to TAD-9 induction therapy in 66 patients with de novo acute myeloid leukemia (AML). Proliferative activity was assessed by 3H-thymidine (3H-TdR) incorporation and thymidine kinase (TK) activity, parameters of Ara-C metabolism comprised the activities of deoxycytidine kinase (DCK) and DNA polymerase alpha (poly alpha) as well as Ara-CTP concentrations and 3H-Ara-C uptake into DNA. GM-CSF sensitivity was determined by in vitro incubation of blasts for 48 h with or without GM-CSF (100 U/ml) followed by an additional 4 h concurrent exposure to GM-CSF and 3H-TdR (0.5 microCi/ml). The following results were obtained as expressed by median values and ranges: 3H-TdR incorporation: 1.07 pmol/10(5) cells (0.0-10.1), TK: 7.3 pmol/min/mg protein (1.3-56.0), DCK: 9.3 pmol/min/mg protein (0.77-47.1), poly alpha: 1.7 pmol/min/mg protein (0.00-28.9), Ara-CTP: 53.3 ng/10(7) cells (13.3-211.0), 3H-Ara-C uptake: 0.06 pmol/10(5) cells (0.0-0.57). 3H-Ara-C uptake was correlated with 3H-TdR incorporation (r = 0.74) and with the (S-phase dependent) activities of TK (r = 0.73) and poly alpha (r = 0.71, but not with DCK activity or intracellular Ara-CTP content. Blast cells of 37 from 55 analyzed patients were found to be sensitive to GM-CSF stimulation as defined by an increase in 3H-TdR incorporation > or = 1.5-fold over control values after the 48 h GM-CSF exposure. In vitro data were related with clinical response to TAD-9 induction therapy in 43 patients with newly diagnosed AML, taking the blast cell reduction at day 10 or 16 to < 5% or > or = 5% residual blasts as early parameter for adequate or inadequate response, respectively. While neither 3H-Ara-C uptake, nor intracellular Ara-CTP concentration, TK nor DCK activity were predictive for response, a high 3H-TdR incorporation and a high poly alpha activity were associated with adequate blast cell reduction. Median values of 3H-TdR incorporation were 2.26 pmol/10(5) cells for patients with adequate blast cell clearance and 0.80 pmol/10(5) cells for patients with inadequate blast cell clearance (P = 0.11), the respective values for poly alpha were 3.22 pmol/min/mg protein for responders and 1.1 pmol/min/mg protein for non-responders (P = 0.0085).(ABSTRACT TRUNCATED AT 400 WORDS)