APOPTOTIC DEATH IN ADENOCARCINOMA CELL-LINES INDUCED BY BUTYRATE AND OTHER HISTONE DEACETYLASE INHIBITORS

n-Butyrate inhibits the growth of colon cancer cell lines. In the HCT 116 eel line, butyrate-induced growth inhibition is almost fully rever sible, whereas in the VACO 5 cell line, a subpopulation undergoes apop tosis within 30 hr of treatment with butyrate. Concurrent treatment of VACO 5 cells with butyrate and the phorbol ester 12-O-tetradecanoylph orbol 13-acetate (TPA) accelerates and increases the incidence of cell death to nearly 100% of the population, whereas HCT 116 cells largely remain alive during treatment with this combination. The action of bu tyrate as an inhibitor of histone deacetylase was assessed in these ce ll lines by examining extracted core histones for their electrophoreti c mobility in Triton/acid/urea gels. The concentrations of butyrate th at were effective for inducing apoptosis were similar to the concentra tions that caused hyperacetylation of core histones in the VACO 5 cell line. Furthermore, an examination of other carboxylic acids for induc tion of apoptosis revealed a rank order that corresponded to the order of potency in causing hyperacetylation of core histones. Specifically , the active acids were 3-5 carbons in length and lacked substitution at the 2-position. Isovaleric and propionic acids, in particular, prov ed to be effective inducers of both hyperacetylation and apoptosis at 5 mM concentrations, a finding of potential relevance to the unusual p ancytopenia occurring after acidotic episodes in isovaleric and propio nic acidemias. The duration of butyrate treatment required for chromat in fragmentation (10-20 hr) corresponded to the time required for hist one H4 to become predominantly tetraacetylated. Furthermore, trichosta tin A, a structurally dissimilar inhibitor of histone deacetylase, mim icked butyrate-induced apoptosis of VACO 5 cells and growth inhibition of HCT 116 cells. The dramatic enhancement of VACO 5 cell death by TP A, and the high level resistance of HCT 116 cells to butyrate were not evident from histone acetylation determinations. Thus, applications o f butyrate for cytoreduction therapy will benefit from pharmacodynamic assessment of histone acetylation, but will require additional work t o predict susceptibility to butyrate-induced death. (C) 1997 Elsevier Science Inc.