Abstract 227: Manipulation of hypoxia-NFκB pathway to target breast cancer stem cells.

Abstract

Abstract Background Although the existence of cancer stem cells (CSCs) is still debatable, it is widely accepted that the cancer cells expressing CSC markers are highly resistant to chemo-radiation therapy. Up to 60% of locally advanced solid tumours exhibit hypoxia. Accumulated evidence demonstrates that hypoxia induces epithelial-to-mesenchymal transition and CSCs phenotypes in cancer cells. The pathways between hypoxia and CSCs are still largely in the dark. NFκB is a transcription factor being involved in chemo-radiation resistance. Activation of NFκB by hypoxia in a wide range of cells in inflammatory conditions has been identified for more than a decade. Recently, emerging evidence demonstrates that NFκB is also a key factor maintaining the stemness in breast CSCs. Therefore NFκB may mediate and be involved in hypoxia-induced CSCs phenotypes. Our previous studies show that disulfiram (DS), an anti-alcoholism drug, reverses chemoresistance of a variety of anticancer drugs in several types of cancer. In this study, we used an in vitro model to investigate the relationship between hypoxia-NFκB pathway and CSC phenotypes in two breast cancer cell lines (T47D and MCF7). The effect of DS on hypoxia-NFκB pathway and the cytotoxicity of conventional anticancer drugs (paclitaxel, gemcitabine and doxorubicin) in CSCs were also observed. RESULTS A huge proportion of hypoxic cells were detected in mammospheres. NFκB activation (AKT phosphorylation, IκBα degradation, p65 nuclear translocation, phosphorylation and NFκB transactivation) was detected in the CSCs. The percentage of breast cancer cells with CSC markers (ALDH+, CD24low/CD44high) is significantly increased in the NFκB p65 transfected cell lines. The transfected cell lines are highly resistant to doxorubicin, paclitaxel and gemcitabine. In contrast, breast CSCs do not show any resistance to DS. The cytotoxicity of DS is copper-dependent and cancer specific with no cytotoxicity in normal cell lines. CI-isobologram analysis demonstrates that DS significantly enhances cytotoxicity of conventional anticancer drugs (doxorubicin: 8 - 11-fold; gemcitabine: 1.2 - 23.5-fold; paclitaxel: 4 - 10-fold). DS simultaneously activates ROS-JNK pathway and blocks p65 nuclear translocation. The effect of DS on stemness of breast cancer cell lines is confirmed by its elimination of ALDH+VE CD24Low/CD44High population in mammospheres. To prolong the half-life of DS in bloodstream, we recently developed a liposome encapsulated DS. The liposomal DS shows very strong anticancer activity in an animal cancer model. CONCLUSIONS Our results demonstrate that hypoxia-NFκB pathway is involved in maintaining the stemness and chemoresistance in breast CSCs. DS is highly cytotoxic to breast CSCs and enhances cytotoxicity of conventional anticancer drugs. This may be caused by simultaneous induction of ROS and inhibition of NFkB pathway. Citation Format: Peng Liu, Sarah Brown, Vinodh Kannappan, Angel L. Armesilla, John L. Darling, Weiguang Wang. Manipulation of hypoxia-NFκB pathway to target breast cancer stem cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 227. doi:10.1158/1538-7445.AM2013-227 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.