Abstract 3545: Autophagy inhibition as a therapeutic strategy in cancer

Abstract

Abstract Autophagy is an evolutionarily conserved process involving degradation of cellular components in lysosomes to maintain protein and organelle quality control, and temporarily sustain cell viability in response to stressful stimuli. Several studies have demonstrated the dual role of autophagy in tumorigenesis as both a tumor suppressor and a protector of cancer cell survival under stress. It is well recognized that anticancer therapies, such as chemotherapy and irradiation (RT), induce autophagy as a pro-survival response, likely resulting in therapeutic resistance. Therefore, concurrent autophagy inhibition as a chemo- and RT-sensitizer has generated great interest in cancer therapy. We generated Beclin1+/+ and Beclin1+/- immortalized mouse mammary epithelial cells (iMMECs) stably expressing the apoptosis inhibitor BCL-2 and the autophagy marker EGFP-LC3 to investigate how acute autophagy inhibition and chronic autophagy deregulation impact tumor sensitivity to anticancer drugs commonly used against breast cancer. We also used human cancer cell lines, including MCF-7, PANC-1, MIA PaCa-2 and HCT-116 cells, to explore whether pharmacologic autophagy inhibition or genetic knockdown of autophagy regulators exhibits a synergistic anticancer effect with newer antineoplastic drugs, such as mTOR inhibitors (CCI-779 and RAD001) and novel antimicrotubule agents (ixabepilone). Treatment efficacy was evaluated by clonogenic survival and cytotoxicity assays in 2D- and 3D-epithelial cell culture in vitro and by tumor responsiveness assays in mice in vivo. Autophagy inhibition sensitized Beclin1+/+ apoptosis-defective iMMECs to doxorubicin, but not to paclitaxel, and had an even greater impact on autophagy-deficient cells. Moreover, autophagy inhibition via choloroquine or Beclin1 knockdown enhanced the treatment efficacy of mTOR inhibitors on MCF-7, PANC-1, MIA PaCa-2 and HCT116 cells in vitro and in xenograft tumors in nude mice in vivo. These studies provide insight into how autophagy functional status in tumors impacts treatment responsiveness and into how to best incorporate pharmacologic autophagy modulation in the decision tree for cancer treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3545. doi:10.1158/1538-7445.AM2011-3545