The histone deacetylase inhibitor sodium butyrate induces DNA topoisomerase II expression and confers hypersensitivity to etoposide in human leukemic cell lines
The differentiating agent and histone deacetylase inhibitor, sodium butyrate (NaB), was shown previously to cause a transient, 3–17-fold induction of human DNA topoisomerase II (topo II) gene promoter activity and a 2-fold increase in topo II protein early in monocytic differentiation of HL-60 cells. This observation has now been extended to other short chain fatty acids and aromatic butyrate analogues, and evidence is presented that human topo II promoter induction correlates closely with histone H4 acetylation status. Because increased topo II expression is associated with enhanced efficacy of topo II-poisoning antitumor drugs such as etoposide, the hypothesis tested in this report was whether NaB pretreatment could sensitize HL-60 myeloid leukemia and K562 erythroleukemia cells to etoposide-triggered DNA damage and cell death. A 24–72 h NaB treatment (0.4–0.5 mM) induced topo II 2–2.5-fold in both HL-60 and K562 cells and caused a dose-dependent enhancement of etoposide-stimulated, protein-linked DNA complexes in both cell lines. At concentrations with minimal effects on cell cycle kinetics (0.4 mM in HL-60; 0.5 mM in K562), NaB pretreatment also modestly enhanced etoposide-triggered apoptosis in HL-60 cells, as determined morphologically after acridine orange/ethidium bromide staining, and substantially increased K562 growth inhibition and poly(ADP-ribose)polymerase cleavage after etoposide exposure. Therefore, a temporal window may exist whereby a differentiating agent may sensitize experimental leukemias to a cytotoxic antitumor agent. These results indicate that histone deacetylase inhibitors should be investigated for etoposide sensitization of other butyrate-responsive hematopoietic and nonhematopoietic tumor lines in vitro and in vivo.