Triple combination of retinoic acid, low concentration of cytarabine and dimethylformamide induces differentiation of human acute myeloid leukaemic blasts.

Differentiation induction therapy provides an alternative for treatment of patients with acute myeloid leukaemia (AML) who are either unsuitable for or unresponsive to conventional cytotoxic chemotherapy. The effect of a triple combination of retinoic acid (RA) + low concentration of cytarabine (Ara-C) + dimethylformamide (DMF) on the differentiation of blasts from 24 AML patients was studied. Nonadherent mononuclear cells were cultured at a concentration of 5 x 10(5) cells/ml in 24-well tissue culture plates containing RPMI 1640 culture medium with 20% fetal calf serum, 10% autologous serum and 10% 5637-conditioned medium and incubated with 10(-6) M RA, 10(-6) M Ara-C and/or 100 mM DMF alone and in combination with each other for 6 days in primary culture at 37 degrees C in a humidified incubator under 5% CO2. The triple combination of 10(-6) M RA + 10(-6) M Ara-C + 100 mM DMF induced 90% of blasts from 22 out of 24 AML patients to differentiate. These highly effective results justify a clinical trial of this triple combination for AML patients who are either unsuitable for or unresponsive to conventional cytotoxic chemotherapy.