Depsipeptide (FR901228) induces histone acetylation and inhibition of histone deacetylase in chronic lymphocytic leukemia cells concurrent with activation of caspase 8-mediated apoptosis and down-regulation of c-FLIP protein

Depsipeptide is in clinical trials for chronic lymphocytic leukemia (CLL) on the basis of earlier observations demonstrating selective in vitro activity in CILL. We sought to determine the relationship of histone H3 and H4 acetylation, inhibition of histone deacetylase, and apoptosis observed in CLL cells to justify a pharmacodynamic end point in these clinical trials. We demonstrate that in vitro depsipeptide induces histone H3 and H4 acetylation and histone deacetylase enzyme inhibition at concentrations corresponding to the LC50 (concentration producing 50% cell death) for cultured CLL cells (0.038 muM depsipeptide). The changes histone acetylation are lysine involving H4 K5, H4 K12, and H3 K9, to a lesser extent H4 K8, but not H4 K16 H3 K14. Depsipeptide-induced is caspase dependent, selectively involving the tumor necrosis factor (TNF) (extrinsic pathway) initiating 8 and effector caspase 3. Activation 8 was accompanied by the regulation of cellular FLICE-inhibitory (c-FLIP, I-FLICE) without evidence Fas (CD95) up-regulation. Changes apoptotic proteins, including Bax, Mcl-1, and X-linked inhibitor of ptosis (XIAP), were not observed. Our results demonstrate a relationship between target enzyme inhibition of histone deacetylase, histone H3 and H4 acetylation, and apoptosis involving the TNF-receptor pathway of apoptosis that is not used by other therapeutic agents in CLL. These data suggest use of histone H3 and H4 acetylation, inhibition of histone deacetylase, and clown-regulation of FLIP as pharmacodynamic end points for further evaluation of this drug in patients. (C) 2003 by The American Society of Hematology.