5-aza-2'-deoxycytidine therapy in patients with acute leukemia inhibits DNA methylation.

The effect of 5-aza-2'-deoxycytidine (5-AZA-dCyd) on methylation of DNA in blood leukemic cells from patients with lymphoid and myeloid leukemia was investigated. After treatment with continuous infusion of 5-AZA-dCyd (1.0 mg/kg/h) the blood leukemic cells were isolated and incubated in vitro with [6-3H]deoxycytidine and the incorporation of radioactivity into 5-methylcytosine and cytosine of DNA determined. 5-AZA-dCyd produced greater than 70% inhibition of DNA methylation in the leukemic cells. The antileukemic action of 5-AZA-dCyd may be related to the inhibition of DNA methylation.