Abstract 4676: Cancer stem cell induces chemoresistance in breast cancer via macrophage migration inhibitory factor mediated activation of AKT pathway
Authors: Das Subhayan , Kundu Moumita , Parekh Aditya , Bharadwaj Deblina , Mandal Mahitosh 
Published: August 2019

Abstract
Chemoresistance is one of the significant problems of cancer management. Cellular crosstalk in tumor microenvironment plays a vital role in regulating the chemoresistance in cancer. Cancer stem cell (CSC) is one of the key players in the regulation of chemoresistance in cancer, and they modulate the tumor microenvironment to enhance the resistance to anti-cancer therapy. However, the exact mechanism by which CSC can influence the cellular crosstalk in the tumor microenvironment is mostly unknown. Macrophage migration inhibitory factor (MIF) is attributed to inducing therapeutic resistance in several cancers. We previously found a close relation of MIF secretion with a group of polyploid giant cells in chemoresistant breast cancer.
MIF secretion was increased in the media of the mammosphere of MDA MB 231 cell (231) as well as Doxorubicin (Dox) and 5-Fluorouracil (5FU) resistant 231 cells. MIF secretion also increased upon treating 231 with Dox and 5FU in a time-dependent manner. Addition of recombinant MIF in culture medium increased the resistance of 231 to chemotherapeutic agents, and a similar phenomenon was also observed upon treatment with conditioned medium from CSC. Chemoresistant breast cancer is enriched with the CSC population, and hence we hypothesized that the MIF was secreted from CSC populations and had a significant role in the regulation of chemoresistance in breast cancer. MIF expression was also increased in Chemoresistant breast cancer tissues compare to non-resistant ones. MIF also induced anti-apoptotic protein Bcl2 and Bcl-xl by downregulating Bax and Bad as well as contributed to the chemoresistant phenotype. Conditioned media from CSC and exogenous MIF were unable to induce chemoresistance in parental 231 cell line in the presence of 4-IPP, a MIF inhibitor. The anti-apoptotic effect of exogenous MIF was also reversed by the inhibitor. Thus we confirmed that MIF played a significant role in the regulation of resistant phenotype in breast cancer microenvironment. Upon further analysis of molecular pathways, we found phosphorylation of AKT corresponded with the MIF secretion in CSC as well as chemoresistant 231 cell lines. MIF was able to increase the level of phosphorylated AKT in 231 cell line in a dose-dependent manner. When chemoresistant 231 cells were treated with MIF inhibitor, the AKT phosphorylation was inhibited. Silencing the AKT pathway via siRNA reversed the sensitization of exogenous MIF and reduced the resistance of both parental 231 as well as resistant 231 cells.
So, overall we conclude that MIF plays a crucial role in inducing chemoresistance in breast cancer by upregulating anti-apoptotic protein Bcl2 and Bcl-xl & downregulating Bax and Bad through AKT phosphorylation. The MIF is mainly secreted by CSC population during self-renewal or stress caused by chemotherapy which activates anti-apoptotic pathways in tumor microenvironment.
Citation Format: Subhayan Das, Moumita Kundu, Aditya Parekh, Deblina Bharadwaj, Mahitosh Mandal. Cancer stem cell induces chemoresistance in breast cancer via macrophage migration inhibitory factor mediated activation of AKT pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4676.