IRE1α disruption in triple-negative breast cancer cooperates with anti-angiogenic therapy by reversing ER stress adaptation and remodeling the tumor microenvironment

• Published in: Cancer research (Chicago, Ill.) Ill.), 2020-04, Vol.80 (11), p.2368-2379
• Main Authors: Harnoss, Jonathan M, Le Thomas, Adrien, Reichelt, Mike, Guttman, Ofer, Wu, Thomas D, Marsters, Scot A, Shemorry, Anna, Lawrence, David A, Kan, David, Segal, Ehud, Merchant, Mark, Totpal, Klara, Crocker, Lisa M, Mesh, Kathryn, Dohse, Monika, Solon, Margaret, Modrusan, Zora, Rudolph, Joachim, Koeppen, Hartmut, Walter, Peter, Ashkenazi, Avi
• Format: Article
• Language: English
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.CAN-19-3108

Cancer cells exploit the unfolded protein response (UPR) to mitigate endoplasmic reticulum (ER) stress caused by cellular oncogene activation and a hostile tumor microenvironment (TME). The key UPR sensor IRE1α resides in the ER and deploys a cytoplasmic kinase-endoribonuclease module to activate the transcription factor XBP1s, which facilitates ER-mediated protein folding. Studies of triple-negative breast cancer (TNBC)—a highly aggressive malignancy with a dismal post-treatment prognosis—implicate XBP1s in promoting tumor vascularization and progression. However, it remains unknown whether IRE1α adapts the ER in TNBC cells and modulates their TME, and whether IRE1α inhibition can enhance anti-angiogenic therapy—previously found to be ineffective in TNBC patients. To gauge IRE1α function, we defined an XBP1s-dependent gene signature, which revealed significant IRE1α pathway activation in multiple solid cancers, including TNBC. IRE1α knockout in TNBC cells markedly reversed substantial ultrastructural expansion of the ER within these cells upon growth in vivo . IRE1α disruption also led to significant remodeling of the cellular TME, increasing pericyte numbers while decreasing cancer-associated fibroblasts and myeloid-derived suppressor cells. Pharmacological IRE1α kinase inhibition strongly attenuated growth of cell-line-based and patient-derived TNBC xenografts in mice and synergized with anti-VEGF-A treatment to cause tumor stasis or regression. Thus, TNBC cells critically rely on IRE1α to adapt their ER to in vivo stress and to adjust the TME to facilitate malignant growth. TNBC reliance on IRE1α is an important vulnerability that can be uniquely exploited in combination with anti-angiogenic therapy as a promising new biologic approach to combat this lethal disease.