Abstract 4706: Resveratrol potentiates the lethality of HDAC inhibitors in acute myelogenous leukemia cells

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Previous studies from our group and others have shown that interference with NF-κB RelA acetylation/activation significantly potentiates the activity of histone deacetylase inhibitors (HDACIs) in human leukemia and other transformed cells (Dai et al., Mol Cell Biol 25; 5429,2005; Dai et al., J Biol Chem 286:34036, 2011). The natural polyphenol resveratrol (RSV) is an activator of the class III HDAC SIRT1. Recently, preclinical evidence of RSV activity in leukemia has been described. In addition, clinical trials have established that RSV is very well tolerated in humans, with plasma concentrations > 250 μM achievable. Based upon these considerations, we hypothesized that a SIRT1 agonist, by deacetylating RelA, might enhance the antileukemic activity of clinically relevant HDACIs. To test this possibility, the impact of RSV on HDACI antileukemic activity was investigated. Co-administration (24 hr) of RSV (50 μM) with LBH589 (15 nM) or vorinostat (1.5 μM) synergistically induced mitochondrial injury (cytochrome c and AIF release), caspase activation, and apoptosis in AML cell lines (e.g., U937 cells). Of note, caspase 8 cleavage/activation was particularly pronounced after co-treatment, suggesting a potentially important functional role for the extrinsic apoptotic pathway in RSV/HDACI interactions. Similar interactions were also observed in AML cell lines bearing FLT3-ITD (e.g., MV4-11) and in primary AML blasts. These events were associated with deacetylation of RelA accompanied by inactivation of NF-κB, increased ROS formation, a marked increase in DNA damage (reflected by αH2A.X formation, an indicator of double strand DNA breaks), and abrogation of RSV-mediated S phase arrest. Genetic knockdown of SIRT1 by shRNA resulted in increased RelA acetylation and NF-κB activity, consistent with SIRT1 deacetylase actions. However, SIRT1 knockdown increased rather than decreased HDACI lethality, suggesting the contribution of NF-κB independent RSV actions to cell death. On the other hand, cells expressing dominant-negative caspase 8 were substantially protected from HDACI and HDACI/RSV lethality. Finally, co-administration of the antioxidant TBAP sharply reduced ROS generation, diminished caspase 8 activation and γH2AX formation, and prevented cell death in cells exposed to HDACI/RSV. Together, these findings indicate that clinically relevant concentrations of RSV significantly increase HDACI antileukemic activity through a process involving induction of oxidative injury (ROS), promotion of DNA damage, engagement of the extrinsic caspase cascade, potentiation of mitochondrial injury, and interruption of cell cycle regulation, culminating in apoptosis. They also imply that factors other than RelA deacetylation by RSV are primarily responsible for the enhanced antileukemic activity of this regimen. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4706. doi:1538-7445.AM2012-4706