Abstract 3595: Abrogation of Akt signaling by Isobavachalcone contributes to its antiproliferative effect towards human cancer cells

Abstract The Akt (Protein kinase B, PKB) kinase is a key intermediate of many cellular processes and plays a critical role in cancer promotion and progression. Akt signaling pathway has attached much attention as a promising target for the development of cancer therapeutics. It was showed previously that Isobavachalcone (IBC), a natural chalcone, inhibits the proliferation of human neuroblastoma cells by causing cell apoptosis. However, the precise mechanisms of growth suppressive effects of IBC were not clear. The purpose of this study was to investigate the inhibitory activity of IBC on Akt signaling, which is probably involved in the proliferation inhibition induced by IBC. Here, the anti-proliferative activity of IBC was further verified in six human cancer cell lines, including ovarian carcinoma cell OVCAR-8, prostate carcinoma cell PC3, colorectal carcinoma cell colo205, breast carcinoma cell MCF-7, lung carcinoma cell A549 and hepatocellular carcinoma cell HepG2. Modeling results from the Sybyl/FlexiDock program suggested that IBC potentially bond to the ATP-binding pocket of Akt, which indicated that IBC might be a potential Akt inhibitor. Studies performed using the in vitro Akt kinase assay kit confirmed that IBC could directly target and inhibit Akt kinase in an ATP-competitive manner. Results from cell-based assays also revealed that IBC significantly abated Akt phosphorylation at Ser-473 and cellular Akt kinase activity, but did not interfere with Thr-308 phosphorylation of Akt. Consistent with Akt inhibition, IBC abrogated EGF-stimulated nuclear translocation of Akt as evaluated by fluorescence confocal microscopy. Cellular phosphorylation of Akt downstream substrates, including GSK3β, mTOR, p70S6K, 4E-BP1, XIAP and Bad, was also diminished by IBC. Consequently, significant levels of apoptosis were detected in IBC-treated cancer cells. Typical morphologic features of apoptosis, including chromatin condensation, nuclear fragmentation and formation of apoptotic bodies, were observed in IBC-treated cells by DAPI staining. Meanwhile, IBC also evoked cleavage of pro-caspase-9 and pro-caspase-3, poly (ADP-ribose) polymerase (PARP) degradation, up-regulation of reactive oxygen species (ROS) production and down-regulation of the ratio between Bcl-2 and Bax. Thus, IBC-induced apoptosis was associated with caspase- and ROS-involved mitochondria pathway. Taken together, we first reported IBC inhibited cancer proliferation by abrogation of Akt signaling, providing evidence for the further application of IBC as a novel therapeutic agent for human cancer therapy. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3595.