IRE1α Disruption in Triple-Negative Breast Cancer Cooperates with Antiangiogenic Therapy by Reversing ER Stress Adaptation and Remodeling the Tumor Microenvironment

Abstract

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 prognosisimplicate 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. Statement of significance Pharmacologic IRE1α kinase inhibition reverses ultrastructural distension of the ER, normalizes the tumor vasculature, and remodels the cellular tumor microenvironment, attenuating TNBC growth in mice. Research.

Noncanonical mRNA decay by the endoplasmic-reticulum stress sensor IRE1α promotes cancer-cell survival

“…Moreover, only WT IRE1α-but not IRE1α-R887A-depleted RIDDLE-targeted mRNAs TNFAIP8L1, SIX2, and SNN ( The failure of IRE1α-R887A to oligomerize and to acquire the corresponding RIDDLE modality afforded a unique opportunity to test the functional significance of the latter. To this end, we leveraged earlier work demonstrating that certain breast cancer cell lines depend on IRE1α for viability during 3D growth 14 . In both cell lines, transgenic WT IRE1α indeed rescued the loss of viability conferred by Dox-inducible knockdown of endogenous IRE1α; by contrast, IRE1α-R887A failed comparably to restore cell survival ( Fig.…”

“…Accordingly, to examine mRNAs subject to IRE1-dependent decay, we applied two parallel RNA sequencing approaches: (1) classical RNAseq, which interrogates the steady-state transcriptome; and (2) global nuclear run-on sequencing (GROseq) 58 , which interrogates the nascent transcriptome. We determined dependency on IRE1α and ER stress by treating human MDA-MB-231 breast cancer cells, harboring homozygous wildtype (WT) or CRISPR/Cas9 knockout (KO) IRE1α alleles 14 , with the classical ER stressor thapsigargin (Tg).…”

“…UPR dysregulation contributes to several diseases [7][8][9][10][11] . Cancer cells often leverage the UPR, including IRE1α, to circumvent ER stress and maintain malignant growth 10,[12][13][14][15][16][17] . Better mechanistic understanding would help elucidate the UPR's role in disease, and advance its potential for medical translation.…”

Pharmacological Targeting of IRE1 in Cancer

“…IRE1 is emerging as a driver of migration, homing and invasion of cancer cells. Its activity modulates the adhesion of Glioblastoma multiform (GBM) cells [15], enhances metastasis of triple-negative breast cancer (TNBC) tumors to the lungs [14] and is related to chemoresistance in many types of cancers such as breast cancer, prostate cancer, multiple myeloma, leukemia and glioblastoma [3,7,10,14,34,46,49,50].…”

“…The impact of IRE1 modulation can be different in different types of cancers and studies on the precise roles of IRE1 in various cancers are essential for a relevant therapeutic intervention. For instance, studies showed that high levels of the major components of UPR, PERK, ATF6, IRE1 and both, unspliced and spliced XBP1, are observed in a variety of human tumors including brain, breast, gastric, kidney, liver, lung, and pancreatic cancers [13][14][15]27,36,49,60,61]. In addition, activation of IRE1 signaling led to a reduction in colorectal tumor growth and increased survival in mouse models [62], indicating that knowledge must drive the use of IRE1 targeting drugs.…”