Blockade of MEK signaling potentiates 5‐Aza‐2′‐deoxycytidine‐induced apoptosis and upregulation of p21waf1 in acute myelogenous leukemia cells

We have recently reported that the mitogen‐activated protein kinase/ERK kinase (MEK) inhibitor AZD6244 (ARRY‐142886) strikingly potentiated the effects of histone deacetylase inhibitor to induce growth arrest and apoptosis of acute myelogeneous leukemia (AML) cells in association with enhanced upregulation of p21^waf1. This study examined the effects of the MEK inhibitor on the action of DNA methyltransferase inhibitor 5‐Aza‐2′‐deoxycytidine (5‐AzadC), another epigenetic agent in AML cells. AZD6244 significantly potentiated the ability of 5‐AzadC to induce growth arrest and apoptosis of NB4, and freshly isolated AML cells. In parallel, 5‐AzadC induced expression of p21^waf1 in AML cells, which was potently enhanced in the presence of AZD6244. Further studies explored the molecular mechanisms by which 5‐AzadC induced expression of p21^waf1 and found that a low dose of 5‐AzadC (1 μM) induced acetylation of histone H3 on the p21^waf1 gene promoter; however, higher dose of this compound (3 or 5 μM) potently induced DNA damage as assessed by expression of γH2AX, in NB4 cells. These effects were strikingly enhanced by concomitant blockade of MEK signaling. Furthermore, knock‐down of p21^waf1 by the siRNA rescued NB4 cells from 5‐AzadC‐mediated growth inhibition. Taken together, combination of 5‐AzadC and the MEK inhibitor may be useful for treatment of individuals with a subset of AML. © 2009 UICC