A novel effect of DNA methyltransferase and histone deacetylase inhibitors: NFκB inhibition in malignant myeloblasts

Malignant myeloblasts arising in high-risk myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) are characterized by the constitutive activation of the anti-apoptotic transcription factor NFκB. We found that DNA methyltransferase (DNMT) inhibitors (such as azacytidine and 5-aza-′-deoxycytidine) and histone deacetylase (HDAC) inhibitors (such as trichostatin and valproic acid) efficiently induced apoptosis in the P39 MDS/ AML cell line, correlating with an inhibition of NFκB (which translocated from the nucleus to the cytoplasm). This effect was obtained rapidly, within a few hours, suggesting that it was not due to epigenetic reprogramming. Indeed, DNMT and HDAC inhibitors reduced the phosphorylation of the NFκB- activating kinase IKKα/β, and this effect was also observed in enucleated cells. Finally, circulating myeloblasts from AML patients treated with the DNMT inhibitor 5-aza-2′-deoxycytidine manifested a rapid (2 hours post-treatment) inhibition of NFκB and IKKα/β. Altogether, these results indicate that DNMT and HDAC inhibitors can inhibit the constitutive activation of NFκB in malignant myeloblasts in vitro and in vivo through a novel mechanism.