Interactions between histone deacetylase inhibitors (HDACIs) and the alkyl-lysophospholipid (ALP) perifosine were examined in human leukemia cells. Co-administration of sodium butyrate (SB), suberoylanilide hydroxamic acid (SAHA), or trichostatin with perifosine synergistically induced mitochondrial dysfunction (cytochrome c and AIF release), caspase-3 and -8 activation, apoptosis, and a marked decrease in cell growth in U937 as well as HL-60 and Jurkat leukemia cells. These events were associated with inactivation of ERK1/2 and Akt, p46 JNK activation, and a pronounced increase in generation of ceramide and reactive oxygen species (ROS). They were also associated with upregulation of Bak and a marked conformational change in Bax accompanied by membrane translocation. Ectopic expression of Bcl-2 delayed but was ultimately ineffective in preventing perifosine/HDACI-mediated apoptosis. Enforced expression of constitutively active MEK1 or myristoylated Akt blocked HDACI/perifosine-mediated ceramide production and cell death, suggesting that MEK/ERK and Akt inactivation play a primary role in these phenomena. However, inhibition of JNK activation (e.g., by the JNK inhibitor SP600125) did not attenuate SB/perifosine-induced apoptosis. In addition, the free radical scavenger N-acetyl-L-cysteine (NAC) attenuated ROS generation and apoptosis mediated by combined treatment. Finally, the acidic sphingomyelinase inhibitor desipramine attenuated HDACI/perifosine-mediated ceramide and ROS production as well as cell death. Together, these findings indicate that co-administration of HDACIs with perifosine in human leukemia cells leads to Akt and MEK/ERK disruption, a marked increase in ceramide and ROS production, and a striking increase in mitochondrial injury and apoptosis. They also raise the possibility that combining these agents may represent a novel antileukemic strategy.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]