The combined differentiating effect of retinoic acid and vincristine on acute promyelocytic leukemia

We have previously shown that HL-60 cells exposed to all-trans retinoic acid (ATRA) after treatment with a non-cytotoxic concentration of vincristine (VCR) result in granulocytic maturation and differentiation, suggesting that VCR might exhibit a synergistic action with ATRA in the treatment of acute promyelocytic leukemia. In this report, leukemic cells obtained from a patient with acute promyelocytic leukemia were exposed to 20 nM VCR for 1 h followed by 1 mu M ATRA for 6 days. An increase in the expression of mature myelocyte antigens, CD11b and CD15, was observed as determined by flow cytometric analysis. Treatment of VCR or ATRA alone, however, did not have any effect on the expression of these mature myelocyte antigens of the leukemic cells. These results suggest that combined VCR and ATRA may be more efficient in the differentiation therapy of acute promyelocytic leukemia, particularly in those cases showing a slow response to ATRA therapy. (C) 1997 Elsevier Science Ltd.