Abstract LT015: Overcoming chemotherapy resistance in triple negative breast cancer via targeting lysyl oxidase (LOX)
Authors: Saatci Ozge , Akbulut Ozge , Rezaeain Abdol-Hossein , Banister Carolyn , Sikirzhytski Vitali , Aksoy Sercan , Akyol Aytekin , Uner Aysegul , Buckhaults Phillip , Chernov Mikhail , McInnes Campbell , Riazalhosseini Yasser , Sahin Ozgur 
Published: March 2021

Abstract
Chemoresistance is a major obstacle in the treatment of triple negative breast cancer (TNBC), the most aggressive breast cancer subtype. To overcome chemoresistance, we have selected TNBC tumors for chemotherapy resistance in vivo, characterized their transcriptomes by RNA-sequencing and identified hypoxia-induced ECM re-modeler, lysyl oxidase (LOX) as a key inducer of chemoresistance. LOX overexpression has two distinct effects in hypoxic tumors treated with chemotherapy. As an ECM remodeler, LOX enhances collagen cross-linking and fibronectin assembly, thereby decreasing drug penetration. In addition, LOX exerts a surprising novel effect on transcription, increasing the expression of Integrin Subunit Alpha 5 (ITGA5), the major receptor for fibronectin (FN1), leading to activation of Focal Adhesion Kinase (FAK)/Src signaling and chemoresistance. Inhibition of LOX or ITGA5 with shRNA-mediated knockdown or inhibition of FAK or Src kinases with small molecule inhibitors in combination with doxorubicin greatly enhanced tumor growth inhibition in vivo relative to individual treatments. The role of LOX in chemoresistance has further been demonstrated using chemoresistant TNBC patient-derived xenografts (PDXs) and organoids, treated with doxorubicin alone or in combination with the LOX family inhibitor, BAPN. Notably, higher LOX, ITGA5, or FN1 levels are associated with shorter survival in chemotherapy treated TNBC patients. Currently available LOX inhibitors suffer from lack of specificity and high toxicity. To identify a more potent and selective LOX inhibitor, we performed a high-throughput screen (HTS) of a diversified small-molecule library. HTS resulted in identification of several hits that inhibit LOX enzymatic activity without any cytotoxicity. A lead compound was identified after the screening of hits based on their inhibitory effects on LOX enzymatic activity and the degree of chemosensitization in collagen-embedded cells. We are currently performing structure-activity relationship (SAR) analysis to optimize the lead compound for more potent activity and better drug-like properties. In addition, we are analyzing the mechanisms through which LOX enhances ITGA5 transcription and how the enzymatic activity of LOX contributes to transcriptional regulation. Our study provides a pre-clinical rationale for the development and testing of LOX inhibitors to overcome chemotherapy resistance in TNBC patients.
Citation Format: Ozge Saatci, Ozge Akbulut, Abdol-Hossein Rezaeain, Carolyn Banister, Vitali Sikirzhytski, Sercan Aksoy, Aytekin Akyol, Aysegul Uner, Phillip Buckhaults, Mikhail Chernov, Campbell McInnes, Yasser Riazalhosseini, Ozgur Sahin. Overcoming chemotherapy resistance in triple negative breast cancer via targeting lysyl oxidase (LOX) [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr LT015.