Abstract 1259: Cetuximab induces autophagy that is mediated through downregulation of HIF1α/Bcl-2 and protects cancer cells escape from cetuximab-mediated therapeutic effects

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Cetuximab induces autophagy that is mediated through downregulation of HIF1α/Bcl-2 and protects cancer cells escape from cetuximab-mediated therapeutic effects Xinqun Li, Yang Lu, Ke Liang, and Zhen Fan Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas Targeting the epidermal growth factor receptor (EGFR) with receptor-blocking monoclonal antibodies such as cetuximab has clearly shown clinical benefits. However, the effect of this novel therapy is limited by both de novo and acquired resistance mechanisms. Increasing evidences indicate that pharmacological induction of autophagy can serve as a cytoprotective mechanism allowing cancer cells to escape from anticancer treatment-induced cell death. In this study, we found that autophagy was induced by cetuximab in several different types of human cancer cell lines, shown by increase in the levels of LC3 conversion, AVO formation, and the number of autophagosomes under electronic microscopy. The induction of autophagy correlated well with decrease in the activation-specific phosphorylation levels of Akt-S473 and mTOR-S2448, and decrease in the protein levels of HIF-1α and Bcl-2 after cetuximab treatment. Expression of myristoylated Akt or myristoylated PI3K, both of which are consititutively active, conferred complete resistance to cetuximab-induced LC3 conversion, so did transfection of the cells with a constitutively active HIF-1α mutant (HIF-1α/ΔODD) or Bcl-2. These data strongly indicate an involvement of the PI3K/Akt/HIF-1α/Bcl-2 pathway in cetuximab-induced autophagy. To understand the mechanisms by which cetuximab induces autophagy, we overexpressed Bcl2 in A431 cells and found it abolished cetuximab-induced association of Beclin-1/hVsp34, which in turn resulted in inhibition of autophagy. These results indicated a novel pathway leading to autophagy by cetuximab treatment. To determine the role of autophagy in cell death and survival after cetuximab treatment, we examined cell viability after the cetuximab-induced autophagy was suppressed by several means including expression knockdown of an autophagy gene, Atg7, treatment of cells with a lysosome inhibitor, chloroquine or with a class-III PI3K inhibitor, 3MA. We found the inhibition of autophagy clearly enhanced cetuximab-induced therapeutic effects, shown by increase in the levels of PARP cleavage and DNA fragmentation. Our data indicate that autophagy occurring after cetuximab treatment protects cells from cetuximab-induced therapeutic effects. Our results indicate that cetuximab induces autophagy through PI3K/Akt/HIF-1α/Bcl-2/Beclin-1/ hVsp34 pathway, which protects cancer cells from cetuximab treatment. Novel anti-autophagy strategies might prove to be useful for improving clinical outcomes of cetuximab treatment. 1 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 1259.