Tumors evade immune control by creating hostile microenvironments that perturb T cell metabolism and effector function 1 – 4 . However, it remains unclear how intratumoral T cells integrate and interpret metabolic stress signals. Here we report that ovarian cancer (OvCa), an aggressive malignancy refractory to standard treatments and current immunotherapies 5 – 8 , induces Endoplasmic Reticulum (ER) stress and activation of the IRE1α-XBP1 arm of the Unfolded Protein Response (UPR) 9 , 10 in T cells to control their mitochondrial respiration and anti-tumor function. XBP1 upregulation in T cells isolated from human OvCa specimens was associated with decreased intratumoral T cell infiltration and reduced IFNG mRNA expression. Malignant ascites fluid obtained from OvCa patients inhibited glucose uptake and caused N -linked protein glycosylation defects in T cells, leading to IRE1α/XBP1-driven suppression of mitochondrial activity and IFN-γ production. Mechanistically, XBP1 induction limited the influx of glutamine necessary to sustain T cell mitochondrial respiration under glucose-deprived conditions by regulating the abundance of glutamine carriers. Restoring N -linked protein glycosylation, abrogating IRE1α-XBP1 activation or enforcing expression of glutamine transporters enhanced mitochondrial respiration in human T cells exposed to OvCa ascites. XBP1-deficient T cells in the metastatic OvCa milieu exhibited global transcriptional reprogramming and improved effector capacity. Accordingly, OvCa-bearing mice lacking XBP1 selectively in T cells demonstrated superior anti-tumor immunity, delayed malignant progression and increased overall survival. Therefore, controlling ER stress or targeting IRE1α-XBP1 signaling may help restore T cell metabolic fitness and anti-tumor capacity in cancer hosts.

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Inositol-requiring enzyme 1[α] (IRE1[α])–X-box binding protein spliced (XBP1) signaling maintains endoplasmic reticulum (ER) homeostasis while controlling immunometabolic processes. Yet, the physiological consequences of IRE1α–XBP1 activation in leukocytes remain unexplored. We found that induction of prostaglandin-endoperoxide synthase 2 (Ptgs2/Cox-2) and prostaglandin E synthase (Ptges/mPGES-1) was compromised in IRE1α-deficient myeloid cells undergoing ER stress or stimulated through pattern recognition receptors. Inducible biosynthesis of prostaglandins, including the pro-algesic mediator prostaglandin E2 (PGE2), was decreased in myeloid cells that lack IRE1α or XBP1 but not other ER stress sensors. Functional XBP1 transactivated the human PTGS2 and PTGES genes to enable optimal PGE2 production. Mice that lack IRE1α–XBP1 in leukocytes, or that were treated with IRE1α inhibitors, demonstrated reduced pain behaviors in PGE2-dependent models of pain. Thus, IRE1α–XBP1 is a mediator of prostaglandin biosynthesis and a potential target to control pain.

Cancer stem cells (CSC) are the primary cell type responsible for metastasis and relapse. ABC-transporters are integral membrane proteins involved in the translocation of substrates across membranes protecting CSC from chemotherapeutic agents. A plant extract derived from C. spinosa (P2Et) previously investigated for its antitumor activity has been shown to reduce lung and spleen metastasis in mice that have been transplanted with breast cancer cells, suggesting that P2Et has a significant activity against cancer stem cells (CSC). P2Et extract was thoroughly characterized by HPLC/MS. The cytotoxicity of P2Et extract was evaluated using a MTT assay in human and murine cell lines with different profiles of resistance, by Pgp overexpression or by enrichment in cancer stem cells. The synergistic effect of P2Et with doxorubicin was evaluated in vitro in several cell lines and in vivo in mice transplanted with TS/A cells, a highly resistant cell line and enriched in CD44[Formula: see text]CD24[Formula: see text]CSC. The chromatographic fingerprint of P2Et extract revealed 13 gallotannins. We also found that P2Et extract was cytotoxic to cells regardless of their resistant phenotype. Similarly, complementary activities were observed as drug efflux reversion and antioxidant activity. Short-treatment with P2Et extract, revealed a synergistic effect with doxorubicin in resistant cell lines. In vivo the P2Et increases mice survival in a TS/A breast cancer model associated with augmentation of calreticulin expression. Our results suggest that P2Et treatment could be used as adjuvant along with conventional chemotherapy to treat tumors with a MDR phenotype or with high frequency of CSC.

Natural compounds are promising sources for anticancer therapies because of their multifunctional activity and low toxicity. Although the host immune response (IR) is clearly implicated in tumor control, the relationship between natural therapies and IR has not yet been elucidated. The present work evaluates IR induction after treatment with a gallotanninrich fraction from Caesalpinia spinosa (P2Et). Breast tumor 4T1 cells were used to evaluate antitumor properties and IR activation. Apoptosis and expression of immunogenic cell death (ICD) markers were assessed in vitro, whereas IR and postvaccination tumor evolution were assessed in vivo. P2Et fraction induced apoptotic cell death, displaying phosphatidylserine externalization and DNA fragmentation. ICD markers such as calreticulin, high-mobility group box 1 translocation from nuclei to cytoplasm, and ATP secretion were observed. Primary tumor control was improved by vaccination with P2Et-pretreated 4T1 cells (t-P2Et), yielding long-lasting ex vivo multifunctional CD4 + and CD8 + T lymphocytes (interleukin [IL]-2 + , tumor necrosis factor [TNF]-α + , interferon [IFN]-γ + ) that secrete IL-2, TNF-α, IL-4, IL-5, and IFN-γ after specific 4T1 cell stimulation. The present study constitutes the first demonstration of a long-lasting antitumor IR induction and primary tumor reduction induced by a complex natural fraction. These data reveal the potential use of this fraction as an adjuvant in breast cancer treatment.