In vivo effects of a histone deacetylase inhibitor, FK228, on human acute promyelocytic leukemia in NOD/Shi-scid/scid mice

Histone acetylation and deacetylation are closely linked to transcriptional activation and repression, respectively. Iii acute promyelocytic leukemia (APL), histone deacetylase inhibitors (HDACIs) have a synergistic effect with all-trans retinoic acid (ATRA) in vitro to induce differentiation. Here we report ira vitro and in vivo effects of a HDACI, FK228 (formerly FR901228 or depsipeptide), on the human APII cell line NB4. FK228 had a strong and irreversible cytotoxicity compared with another HDACI, trichostatin A. In vivo administration of ATRA or FK228 alone partly inhibited the growth of established tumors of NB4 subcutaneously transplanted in NOD/Shi-scid/scid mice, and the combination was synergistically effective. Histopathological examination revealed that the combination induced apoptosis and differentiation as well as histone acetylation, Intravenous injection of NB4 in NOD/Shi-scid/scid mice followed by combination treatment significantly prevented leukemia death, whereas single administration did not. These findings suggest that FK228 is a promising agent to enhance ATRA-sensitivity in the treatment of APL.