Abstract 1588: Synergistic apoptosis by combination of natural compound EGCG and resveratrol in head and neck cancer: Potential role for AKT-dependent signaling

Abstract

Abstract Natural dietary agents have drawn great attention for cancer prevention because of their wide safety margin and ready availability. Green tea is one such agent that is widely used for chemoprevention (Amin et al. 2009, Kim et al., 2010). Recent clinical trials suggest that green tea alone might not be sufficient for chemoprevention of head and neck cancer (HNC) (Tsao et al., 2009). Therefore, identification of compounds which exhibit synergistic effects with green tea is warranted. In the current study, we investigated combination of green tea component EGCG and resveratrol (a major constituent of red wines and grapes), and found that their combination strongly induced apoptosis as measured by annexin-V staining and supported by cleavage of PARP and caspase 3. The combination of resveratrol (15 and 20 μM, which alone induce 10-15% apoptosis) with EGCG (30-80 μM, which also induce <10% apoptosis) strongly increased apoptosis (to 60-80%) in multiple HNC cell lines. Data analysis for the combination using CalcuSyn software suggests that the combination of EGCG and resveratrol has synergistic apoptotic effects with combination index between 0.4-0.7. Interestingly, a premalignant oral leukoplakia cell line was sensitive to relatively lower doses of the combination (5 and 10 μM resveratrol, 10 and 15 μM EGCG) than fully transformed cancer cell lines, suggesting that the combination of EGCG and resveratrol might be a suitable combination for prevention of HNC. To further elucidate the mechanism of synergistic apoptosis, we found that combination of EGCG and resveratrol strongly inhibited AKT and ERK phosphorylation along with its several downstream targets including p-mTOR, p-S6 and p-4EBP1. Retroviral transduction of constitutively active AKT significantly inhibited apoptosis induced by the combination (p=.003). We also found that the combination of EGCG and resveratrol strongly inhibited p-AMPK, a kinase that regulates autophagy, a protective mechanism during energy stress. The fact that inhibition of autophagy triggers apoptosis (Xu Y et al., 2011) suggests that inhibition of p-AMPK might also play a role in EGCG- and resveratrol-induced apoptosis. Furthermore, strong inhibition of anti-apoptotic Mcl-1 and survivin by the combination was observed as a consequence. Taken together, our studies identify a novel combination of two natural dietary agents, EGCG and resveratrol, which induces synergistic anti-tumor effects in both premalignant and fully transformed HNC cells by targeting multiple signal transduction pathways. The signaling pathways modulated by the combination of EGCG and resveratrol are critical for development of HNC, thus our study provides an important rationale for future preclinical and clinical development. (Supported by U01CA101244, R01CA112643, and P50CA128613 to DMS) 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 1588. doi:1538-7445.AM2012-1588