Anti-Acute Myeloid Leukemia Activity of Chaetocin, a Novel Epigenetic Drug Inhibitor Inducing Oxidative Stress.

Recent studies have highlighted the importance of epigenetic modifications in the pathogenesis of Acute Myeloid Leukemia (AML). This results have been confirmed by the activity of new drug like DNA demethylating agents and histone deacetylase (HDAC) inhibitors in both in vivo and in vitro studies. Recently, Chaetocin, a natural fungal compound, has been identified as the first specific inhibitor of the histone methyltransferase SU(VAR)3–9 which plays a role in heterochromatin gene silencing. In this study, we decided to evaluate Chaetocin as a therapeutic agent in AML in vitro and to explore the related mechanisms. We show that Chaetocin induce dramatic cell death at nanomolar concentrations in U937 and HL60 (97.2% ± 0.4 and 91.6% ± 9 cell death at 100 nM chaetocin, respectively), and to a lesser extend in K562 (67.3% ± 1.6 cell death at 100 nM chaetocin), cell cultures. Cell death occurred at 24 h incubation time which correlated with induction of apoptosis as assessed by Annexin V/7-AAD staining and activation of downstream executioner caspase-3/7. Using transcription low-density array and quantitative RT- PCR, Chaetocin was showed to up-regulate gene transcription such as of the cell cycle inhibitor p21/WAF1 consistent with a role for the targeted SU(VAR)3–9 in heterochromatin gene silencing. In agreement with the recent report of Chaetocin being a promising new antimyeloma agent acting via imposition of oxidative stress, intracellular levels of oxidative species were increased in Chaetocin treated U937 cells in a time- and dose-dependent manner that correlated with induction of cell death. Furthermore, incubation of cells with N-acetyl cysteine, a cell-permeable precursor of intracellular glutathione reductant, prevented chaetocin-induced accumulation of oxidative species, transcription of selected genes (e.g. p21/WAF1), activation of caspase-3, and cell death. Finally, Chaetocin was found to increase the antileukemia activity of HDAC inhibitors and Aracytin, and thus appears as a promising agent for further study as a potential anti-AML therapeutic. Preliminary results obtained in vivo in xenograft models and ex vivo, using blasts of a panel of patients with AML, will be presented.