LAUSR

Introduction: Emergence of chemoresistance is one of the major concerns in cancer management. Development of chemoresistance is associated with several genotypical and phenotypical changes in cancer cells, making them less vulnerable to chemotherapeutic assaults. Integrins are the class of adhesion molecules which help to bind cells with extracellular matrix (ECM) and regulate key signaling pathways. Chemoresistant cells have altered interaction with ECM along with changes in their survival pathways which might have resulted from these altered interactions. Here we hypothesize that the state of chemoresistance is associated with the change in expression of integrin which triggers the intracellular signaling augmenting the chemoresistance in breast cancer. Methodology: To model the chemoresistance, we developed chemoresistant clones from MDA MB 231 (231) breast cancer cell line by treating it with sub-lethal doses of the Doxorubicin over several cycles. To examine the immediate effect of Doxorubicin, the cell line was treated in a time-dependent manner. Xenograft model of breast cancer was developed and treated with Doxorubicin at 5mg/kg/week dose for two weeks. The residual tumor was considered as the in vivo model of chemoresistance. The initial screening of expression of all integrins was carried out by qPCR and confirmed by western blot and Immunohistochemistry (IHC). Downstream pathway analysis was carried out by western blot and IHC. Integrin β1 (ITGB1) was transiently overexpressed and down-regulated by appropriate plasmids containing either ITGB1 gene or shRNA. Results: The initial screening showed that ITGB1 was significantly up-regulated in Doxorubicin resistant clones of 231 (DOX-R) which was confirmed by western blot. Similarly, the expression of ITGB1 was found to be increased in Doxorubicin treated 231 cells and xenograft model. The expression of ITGB1 was also increased in human breast cancer tissue subjected to neo-adjuvant therapy. Upon evaluating the mitogenic pathways in DOX-R, we found that elevated p-ERK1 expression correlated with ITGB1 expression. Further, we found that an interaction between ITGB1 and focal adhesion kinase (FAK) leading to Ras-Raf activation was crucial for regulating ERK1 phosphorylation. These findings were also confirmed in the xenograft model. Next, upon overexpressing ITGB1, we found a significant increase in phosphorylation of ERK1 as well as FAK-Ras-Raf pathway. These proteins seemed to be down-regulated on transient attenuation of ITGB1. The inhibition of ITGB1 also decreased the sensitivity of 231 and DOX-R cells to Doxorubicin. Conclusion: Our study established that ITGB1 influence ERK1 pathway to augment Doxorubicin resistance in breast cancer and inhibition of ITGB1 causes a significant reversal of chemoresistance. These findings indicate that ITGB1 can be a valuable theranostic marker for breast cancer management. Citation Format: Subhayan Das, Bikash Ch Jena, Swati Mundre, Aditya Parekh, Y Rajesh, Pralay Mitra, Mahitosh Mandal. Integrin β1 regulates doxorubicin resistance in breast cancer via FAK-mediated activation of ERK1 pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4022.