Epigenetic and molecular mechanisms underlying the antileukemic activity of the histone deacetylase inhibitor belinostat in human acute promyelocytic leukemia cells.

Therapeutic strategies targeting histone deacetylase (HDAC) inhibition have become promising in many human malignancies. Belinostat (PXD101) is a hydroxamate-type HDAC inhibitor tested in phase I and II clinical trials in solid tumors and hematological cancers. However, little is known about the use of belinostat for differentiation therapy against acute myelogenous leukemia. Here, we characterize the antileukemia activity of belinostat as a single drug and in combination with all-trans-retinoic acid (RA) in promyelocytic leukemia HL-60 and NB4 cells. Belinostat exerted dose-dependent growth-inhibitory or proapoptotic effects, promoting cell cycle arrest at the G0/G1 or the S transition. Apoptosis was accompanied by activation of caspase 3, degradation of PARP-1, and cell cycle-dependent changes in the expression of survivin, cyclin E1, and cyclin A2. Belinostat induced a dose-dependent reduction in the expression of EZH2 and SUZ12, HDAC-1, HDAC-2, and histone acetyltransferase PCAF (p300/CBP-associated factor). Belinostat increased acetylation of histone H4, H3 at K9 and H3 at K16 residues in a dose-dependent manner, but did not reduce trimethylation of H3 at K27 at proapoptotic doses. Combined treatment with belinostat and RA dose dependently accelerated and reinforced granulocytic differentiation, accompanied by changes in the expression of CD11b, C/EBPα (CCAAT/enhancer binding protein-α), and C/EBPε. Our results concluded the usefulness of belinostat, as an epigenetic drug, for antileukemia and differentiation therapy.