Abstract 5088: Blocking mesenchymal stem cell-induced CAIX hampers metastatic potential and chemoresistance in TNBC
Authors: Sarnella Annachiara , D'Avino Giuliana , Hill Billy , Alterio Vincenzo , Winum Jean Yves , De Simone Giuseppina , Cerchia Laura , Zannetti Antonella 
Published: September 2020

Abstract
Triple negative breast cancer (TNBC) is a heterogeneous disease, and even though it occurs in only 15-20% of all patients with breast cancer, it is characterized by an extremely high rate of mortality due to metastatic and drug-resistance recurrent disease. Chemotherapy is the primary established systemic treatment for TNBC patients in both the early and advanced-stages. The lack of targeted therapies and the poor prognosis of patients with TNBC have fostered a major effort to discover actionable molecular targets to treat patients with these tumors. Many evidences highlight the crucial role played by stromal cells in the hypoxic tumor microenvironment in promoting tumor growth, metastasis and chemoresistance. In this study, we aimed to investigate tumor-educated mesenchymal stem cells (TE-MSCs) function in supporting TNBC aggressive behavior through hypoxic-induced protein carbonic anhydrase IX (CAIX). First, we analyzed CAIX expression in a public data-set of 198 TNBC samples and in two TNBC cell lines (MDA-MB-231 and BT-549). All experiments were performed by growing the TNBC cells in normoxic (21% O2) and hypoxic conditions (1% O2) in presence of TE-MSCs or their conditioned medium (CM-MSC). CAIX expression was down-regulated using a specific siRNA. Cell migration and invasion assays were carried out using Boyden chamber uncoated and coated with matrigel, respectively. TNBC cell capability to form vascular-like tubular networks and mammospheres with stemness features were analyzed growing cells on Matrigel and Vitrogel-RGD, respectively. Furthermore, the ability of a novel molecule targeting CAIX (RC44) to hamper metastatic potential of TNBC cells as well as to sensitize them to cisplatin treatment was investigated. In addition, important signaling pathways underlying these mechanisms such as epithelial-mesenchymal-transition (EMT) markers (N-cadherin, β-catenin, slug) were analyzed by western blotting. TNBC cells grown in hypoxia in presence of TE-MSCs showed an increase of HIF-1α and CAIX levels as well as a strong enhancement of their ability to migrate, invade the extracellular matrix, form vascular channels and mammospheres. Furthermore, the effect of cisplatin on cell viability was reduced when TNBC cells were grown in these conditions thus demonstrating the protective effect of TE-MSCs against anti-cancer therapy. All these events were prevented when CAIX expression was inhibited by specific siRNA or its activity blocked by RC44. Furthermore, EMT program was hampered after CAIX inhibition. In conclusion, our findings suggest that targeting CAIX it is possible to hinder some malignant features of TNBC drastically modulated by mesenchymal stem cells in hypoxic microenvironment.
Citation Format: Annachiara Sarnella, Giuliana D'Avino, Billy Hill, Vincenzo Alterio, Jean Yves Winum, Giuseppina De Simone, Laura Cerchia, Antonella Zannetti. Blocking mesenchymal stem cell-induced CAIX hampers metastatic potential and chemoresistance in TNBC [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5088.