The effect of dexamethasone on functional properties of HL60 cells during all-trans retinoic acid induced differentiation. Are there implications for the retinoic acid syndrome?

Differentiation therapy for acute promyelocytic leukemia (APL) using all-trans-retinoic acid (ATRA) has improved the prognosis of the disease. ATRA therapy also causes a newly recognized clinical syndrome, the "retinoic acid syndrome" (RAS), which can be successfully managed with dexamethasone. Because aberrant function of maturing leukemic granulocytes may cause this syndrome, and because dexamethasone is useful clinically, we studied functional properties of maturing HL60 cells cultured in the presence and absence of dexamethasone. HL60 cells were cultured for 4 days with ATRA and studied daily to determine acquisition of mature neutrophil-like properties including phagocytosis, NBT reduction, actin polymerization, chemotaxis and adhesion molecule expression. Undifferentiated HL60 cells could not polymerize actin or reduce NBT, and exhibited only a minimal ability to undergo chemotaxis or ingest latex beads. Following 4 days of maturation with ATRA, the cells would increase F-actin content in response to interleukin-8, ingest latex beads, migrate in a chemotaxis chamber, reduce NBT, and express CD11b. When dexamethasone was added to the cells in culture, there was no major enhancement or suppression of these properties. We also studied the effect of dexamethasone on functional properties of normal neutrophils and found minimal if any effect on their function. Overall, these studies suggest that in vitro, dexamethasone has little effect on the function of leukemic and normal granulocytes. To further investigate the pathophysiology of the retinoic acid syndrome, future studies may need to use endothelial cells, cytokines, or granulocytes obtained from APL patients.