Combination of all-trans retinoic acid with butyric acid and its prodrugs markedly enhancing differentiation of human acute promyelocytic leukemia NB4 cells

Abstract

Objective: To use NB4, an authentic human acute promyelocytic leukemia cell line, as well as the marrow cells from patients with acute promyelocytic leukemia (APL), containing the PML/RAR alpha fusion gene and fused protein to examine the growth inhibition and cytodifferentiation induced by all-trans retinoic acid (ATRA), butyric acid (BA) and its prodrug tributyrin (TB) either as a single agent or in combinations.

Methods: NB4 and APL cells were cultured in presence of ATRA, BA and TB respectively either as a single agent or in combinations at various concentration ratio. Cell growth was measured and myeloid differentiation was determined by morphology and the percentage of positive nitroblue tetrazolium reduction (NBT) on consecutive days over the whole process of culture.

Results: NB4 cells can be induced by ATRA alone and synergistically induced by the combinations of BA or TB with ATRA to differentiate. The synergy was reflected by a remarkable decrease in the effective concentration of ATRA required in the combinations in comparison with it as a sole agent. The combinations also shortened the time for the cells to reach the same level of maturation as that needed for ATRA alone. The potentiation on ATRA-induced differentiation of NB4 cells seemed depending on an appropriate concentration ratio of each inducer in the combinations and the time of action. A preliminary result of in vitro induction of primarily cultured leukemic cells from APL patients by the combined inducers was promising.

Conclusion: The combinations of ATRA with BA or TB at an appropriate ratio may improve the clinical outcome of differentiation therapy for APL patients.