The differentiating effect of retinoic acid and vincristine on acute myeloid leukemia.

We have shown previously that granulocytic maturation and differentiation occurred when HL-60 cells and leukemia cells from a patient with acute promyelocytic leukemia (APL) were exposed to all-trans retinoic acid (ATRA) after treatment with a noncytotoxic concentration of vincristine (VCR), suggesting that VCR might have synergistic action with ATRA in the treatment of APL. Leukemic cells obtained from 24 patients with AML were exposed to 20 nM VCR for 1 h, followed by 1 microM ATRA for 6 days. Changes in the expression of myeloid leukocyte antigens were observed using flow cytometry. Differentiation phenotype as determined by the decrease or increase in maturation cell marker was observed in three samples treated with VCR alone, four samples treated with RA alone, and two samples treated with the combination of VCR and RA. The results suggest that treatment using VCR and ATRA may be effective in the differentiation therapy of AML.