Ferroptosis of tumour neutrophils causes immune suppression in cancer.

Ferroptosis is a non-apoptotic form of regulated cell death that is triggered by the discoordination of regulatory redox mechanisms culminating in massive peroxidation of polyunsaturated phospholipids. Ferroptosis inducers have shown considerable effectiveness in killing tumour cells in vitro, yet there has been no obvious success in experimental animal models, with the notable exception of immunodeficient mice1,2. This suggests that the effect of ferroptosis on immune cells remains poorly understood. Pathologically activated neutrophils (PMNs), termed myeloid-derived suppressor cells (PMN-MDSCs), are major negative regulators of anti-tumour immunity3-5. Here we found that PMN-MDSCs in the tumour microenvironment spontaneously die by ferroptosis. Although decreasing the presence of PMN-MDSCs, ferroptosis induces the release of oxygenated lipids and limits the activity of human and mouse T cells. In immunocompetent mice, genetic and pharmacological inhibition of ferroptosis abrogates suppressive activity of PMN-MDSCs, reduces tumour progression and synergizes with immune checkpoint blockade to suppress the tumour growth. By contrast, induction of ferroptosis in immunocompetent mice promotes tumour growth. Thus, ferroptosis is a unique and targetable immunosuppressive mechanism of PMN-MDSCs in the tumour microenvironment that can be pharmacologically modulated to limit tumour progression.

Estrogen promotes luteolysis by redistributing prostaglandin F2α receptors within primate luteal cells.

Prostaglandin F2α (PGF2α) has been proposed as a functional luteolysin in primates. However, administration of PGF2α or prostaglandin synthesis inhibitors in vivo both initiate luteolysis. These contradictory findings may reflect changes in PGF2α receptors (PTGFRs) or responsiveness to PGF2α at a critical point during the life span of the corpus luteum. The current study addressed this question using ovarian cells and tissues from female cynomolgus monkeys and luteinizing granulosa cells from healthy women undergoing follicle aspiration. PTGFRs were present in the cytoplasm of monkey granulosa cells, while PTGFRs were localized in the perinuclear region of large, granulosa-derived monkey luteal cells by mid-late luteal phase. A PTGFR agonist decreased progesterone production in luteal cells obtained at mid-late and late luteal phases, but did not decrease progesterone production by granulosa cells or luteal cells from younger corpora lutea. These findings are consistent with a role for perinuclear PTGFRs in functional luteolysis. This concept was explored using human luteinizing granulosa cells maintained in vitro as a model for luteal cell differentiation. In these cells, PTGFRs relocated from the cytoplasm to the perinuclear area in an estrogen- and estrogen receptor-dependent manner. Similar to our findings with monkey luteal cells, human luteinizing granulosa cells with perinuclear PTGFRs responded to a PTGFR agonist with decreased progesterone production. These data support the concept that PTGFR stimulation promotes functional luteolysis only when PTGFRs are located in the perinuclear region. Estrogen receptor-mediated relocation of PTGFRs within luteal cells may be a necessary step in the initiation of luteolysis in primates.

Myeloid Cell COX-2 deletion reduces mammary tumor growth through enhanced cytotoxic T-lymphocyte function.

Cyclooxygenase-2 (COX-2) expression is associated with poor prognosis across a range of human cancers, including breast cancer. The contribution of tumor cell-derived COX-2 to tumorigenesis has been examined in numerous studies; however, the role of stromal-derived COX-2 is ill-defined. Here, we examined how COX-2 in myeloid cells, an immune cell subset that includes macrophages, influences mammary tumor progression. In mice engineered to selectively lack myeloid cell COX-2 [myeloid-COX-2 knockout (KO) mice], spontaneous neu oncogene-induced tumor onset was delayed, tumor burden reduced, and tumor growth slowed compared with wild-type (WT). Similarly, growth of neu-transformed mammary tumor cells as orthotopic tumors in immune competent syngeneic myeloid-COX-2 KO host mice was reduced compared with WT. By flow cytometric analysis, orthotopic myeloid-COX-2 KO tumors had lower tumor-associated macrophage (TAM) infiltration consistent with impaired colony stimulating factor-1-dependent chemotaxis by COX-2 deficient macrophages in vitro. Further, in both spontaneous and orthotopic tumors, COX-2-deficient TAM displayed lower immunosuppressive M2 markers and this was coincident with less suppression of CD8(+) cytotoxic T lymphocytes (CTLs) in myeloid-COX-2 KO tumors. These studies suggest that reduced tumor growth in myeloid-COX-2 KO mice resulted from disruption of M2-like TAM function, thereby enhancing T-cell survival and immune surveillance. Antibody-mediated depletion of CD8(+), but not CD4(+) cells, restored tumor growth in myeloid-COX-2 KO to WT levels, indicating that CD8(+) CTLs are dominant antitumor effectors in myeloid-COX-2 KO mice. Our studies suggest that inhibition of myeloid cell COX-2 can potentiate CTL-mediated tumor cytotoxicity and may provide a novel therapeutic approach in breast cancer therapy.

Heterodimerization with the prostacyclin receptor triggers thromboxane receptor relocation to lipid rafts.

OBJECTIVE: Prostacyclin and thromboxane mediate opposing cardiovascular actions through receptors termed IP and TP, respectively. When dimerized with IP, the TP shifts to IP-like function. IP localizes to cholesterol-enriched membrane rafts, but TP and IPTP heterodimer localization is not defined. We examined these receptors' membrane localization and the role of rafts in receptor function. METHODS AND RESULTS: Microdomain distribution of IP, TP, and IPTP heterodimers was examined in COS-7 cells by measuring energy transfer from renilla luciferase-fused receptors to fluorescently labeled rafts. IP raft association was confirmed. TP was raft excluded, but redistributed to rafts upon dimerization with IP. Signaling of the IP and IPTP heterodimer, but not TP alone, was suppressed after raft disruption by cholesterol depletion. Cholesterol enrichment also selectively suppressed IP and IPTP function. Native IP and IPTP signaling in smooth muscle cells and macrophages were similarly sensitive to cholesterol manipulation, whereas macrophages from hypercholesterolemic mice displayed suppressed IP and IPTP function. CONCLUSIONS: IP and TP function within distinct microdomains. Raft incorporation of TP in the IPTP heterodimer likely facilitates its signaling shift. We speculate that changes in IP and IPTP signaling after perturbation of membrane cholesterol may contribute to cardiovascular disease associated with hypercholesterolemia.

Mammary carcinoma cell derived cyclooxygenase 2 suppresses tumor immune surveillance by enhancing intratumoral immune checkpoint activity.

INTRODUCTION: Systemic inhibition of the inflammatory enzyme cyclooxygenase (COX) 2 decreases the risk of breast cancer and its recurrence. However, the biology of COX-2 in the multicellular tumor microenvironment is poorly defined. METHODS: Mammary tumor onset and multiplicity were examined in ErbB2 transgenic mice that were deficient in mammary epithelial cell COX-2 (COX-2(MEC)KO) compared to wild type (WT) mice. Tumors were analyzed, by real time PCR, immune-staining and flow cytometry, for proliferation, apoptosis, angiogenesis and immune microenvironment. Lentiviral shRNA delivery was used to knock down (KD) COX-2 in ErbB2-transformed mouse breast cancer cells (COX-2KD), and growth as orthotopic tumors was examined in syngenic recipient mice, with or without depletion of CD8+ immune cells. RESULTS: Mammary tumor onset was delayed, and multiplicity halved, in COX-2(MEC)KO mice compared to WT. COX-2(MEC)KO tumors showed decreased expression of Ki67, a proliferation marker, as well as reduced VEGFA, its receptor VEGFR2, endothelial NOS and the vascular endothelial marker CD31, indicating reduced tumor vascularization. COX-2(MEC)KO tumors contained more CD4+ T helper (Th) cells and CD8+ cytotoxic immune cells (CTL) consistent with increased immune surveillance. The ratio of Th markers Tbet (Th1) to GATA3 (Th2) was higher, and levels of Retnla, a M2 macrophage marker, lower, in COX-2(MEC)KO tumor infiltrating leukocytes compared to WT, suggesting a prevalence of pro-immune Th1 over immune suppressive Th2 lymphocytes, and reduced macrophage polarization to the immune suppressive M2 phenotype. Enhanced immune surveillance in COX-2(MEC)KO tumors was coincident with increased intratumoral CXCL9, a T cell chemoattractant, and decreased expression of T lymphocyte co-inhibitory receptors CTLA4 and PD-1, as well as PD-L1, the ligand for PD-1. PD-L1 was also decreased in IFNγ-treated COX-2KD mouse mammary cancer cells in vitro and, compared to control cells, growth of COX-2KD cells as orthotopic tumors in immune competent mice was markedly suppressed. However, robust growth of COX-2KD tumor cells was evident when recipients were depleted of CD8+ cells. CONCLUSIONS: The data strongly support that, in addition to its angiogenic function, tumor cell COX-2 suppresses intratumoral cytotoxic CD8+ immune cell function, possibly through upregulation of immune checkpoints, thereby contributing to tumor immune escape. COX-2 inhibition may be clinically useful to augment breast cancer immunotherapy.

Efficacy of a Small-Molecule Inhibitor of KrasG12D in Immunocompetent Models of Pancreatic Cancer.

Mutations in the KRAS oncogene are found in more than 90% of patients with pancreatic ductal adenocarcinoma (PDAC), with Gly-to-Asp mutations (KRASG12D) being the most common. Here, we tested the efficacy of a small-molecule KRASG12D inhibitor, MRTX1133, in implantable and autochthonous PDAC models with an intact immune system. In vitro studies validated the specificity and potency of MRTX1133. In vivo, MRTX1133 prompted deep tumor regressions in all models tested, including complete or near-complete remissions after 14 days. Concomitant with tumor cell apoptosis and proliferative arrest, drug treatment led to marked shifts in the tumor microenvironment (TME), including changes in fibroblasts, matrix, and macrophages. T cells were necessary for MRTX1133's full antitumor effect, and T-cell depletion accelerated tumor regrowth after therapy. These results validate the specificity, potency, and efficacy of MRTX1133 in immunocompetent KRASG12D-mutant PDAC models, providing a rationale for clinical testing and a platform for further investigation of combination therapies. SIGNIFICANCE: Pharmacologic inhibition of KRASG12D in pancreatic cancer models with an intact immune system stimulates specific, potent, and durable tumor regressions. In the absence of overt toxicity, these results suggest that this and similar inhibitors should be tested as potential, high-impact novel therapies for patients with PDAC. See related commentary by Redding and Grabocka, p. 260. This article is highlighted in the In This Issue feature, p. 247.

Deletion of cyclooxygenase 2 in mouse mammary epithelial cells delays breast cancer onset through augmentation of type 1 immune responses in tumors.

Inhibition of cyclooxygenase (COX) 2, which is associated with >40% of breast cancers, decreases the risk of tumorigenesis and breast cancer recurrence. To study the role of COX-2 in breast cancer, we engineered mice that lack selectively mammary epithelial cell (MEC) COX-2 (COX-2 KO(MEC)). Compared with wild type (WT), MEC from COX-2 KO(MEC) mice expressed >90% less COX-2 messenger RNA (mRNA) and protein and produced 90% less of the dominant pro-oncogenic COX-2 product, prostaglandin (PG) E(2). We confirmed COX-2 as the principle source of PGE(2) in MEC treated with selective COX-2 and COX-1 inhibitors. Tumors were induced in mice using medroxyprogesterone acetate and 7,12-dimethylbenz[a]anthracene. Breast cancer onset was significantly delayed in COX-2 KO(MEC) compared with WT (P = 0.03), equivalent to the delay following systemic COX-2 inhibition with rofecoxib. Compared with WT, COX-2 KO(MEC) tumors showed increased mRNA for Caspase-3, Ki-67 and common markers for leukocytes (CD45) and macrophages (F4/80). Analysis of multiple markers/cytokines, namely CD86, inducible nitric oxide synthase (iNOS), interleukin-6, tumor necrosis factor α (TNFα) and Tim-3 indicated a shift toward antitumorigenic type 1 immune responses in COX-2 KO(MEC) tumors. Immunohistochemical analysis confirmed elevated expression of CD45, F4/80 and CD86 in COX-2 KO(MEC) tumors. Concordant with a role for COX-2 in restraining M1 macrophage polarization, CD86 and TNFα expression were offset by exogenous PGE(2) in bone marrow-derived macrophages polarized in vitro to the M1 phenotype. Our data reveal the importance of epithelial COX-2 in tumor promotion and indicate that deletion of epithelial COX-2 may skew tumor immunity toward type 1 responses, coincident with delayed tumor development.

Prostaglandin E2 acts via multiple receptors to regulate plasminogen-dependent proteolysis in the primate periovulatory follicle.

The ovulatory gonadotropin surge regulates expression of plasminogen activator (PA) family members within the ovarian follicle, which are implicated in follicle wall degradation at ovulation. Gonadotropin also stimulates follicular prostaglandin E2 (PGE2) production, which is required for follicle rupture. To determine whether the ovulatory gonadotropin surge regulates PA-mediated proteolysis via PGE2 in the primate follicle, monkeys received gonadotropins to stimulate follicle development. Follicular aspirates or whole ovaries were obtained before (0 h) and after human chorionic gonadotropin (hCG) administration to span the periovulatory interval. Granulosa cell levels of tissue-type PA (tPA) and PA inhibitor type 1 (PAI-1) proteins were low at 0 h hCG and higher after hCG administration. In situ zymography showed no ovarian tPA activity 0 h after hCG; tPA activity was present in granulosa cells obtained after hCG treatment. Importantly, tPA and PAI-1 proteins and tPA activity were low/nondetectable in granulosa cells obtained after treatment with hCG and the PG synthesis inhibitor celecoxib. To determine whether hCG stimulation of tPA and PAI-1 requires PGE2, granulosa cells obtained at 0 h were cultured with hCG plus indomethacin to inhibit PG production; some cells also received PGE2 or an agonist selective for one PGE2 receptor (EP). PGE2, an EP2 agonist, and an EP3 agonist increased tPA protein, whereas PGE2, an EP1 agonist, and an EP3 agonist increased PAI-1 protein. Therefore, gonadotropin increases granulosa cell tPA and PAI-1 protein levels and tPA-dependent proteolytic activity. PGE2 also increases tPA and PAI-1 protein levels in granulosa cells, suggesting that elevated PGE2 late in the periovulatory interval acts to stimulate proteolysis and follicle rupture.

Tumor cell-intrinsic EPHA2 suppresses anti-tumor immunity by regulating PTGS2 (COX-2).

Resistance to immunotherapy is one of the biggest problems of current oncotherapeutics. WhileT cell abundance is essential for tumor responsiveness to immunotherapy, factors that define the T cell inflamed tumor microenvironment are not fully understood. We conducted an unbiased approach to identify tumor-intrinsic mechanisms shaping the immune tumor microenvironment(TME), focusing on pancreatic adenocarcinoma because it is refractory to immunotherapy and excludes T cells from the TME. From human tumors, we identified EPHA2 as a candidate tumor intrinsic driver of immunosuppression. Epha2 deletion reversed T cell exclusion and sensitized tumors to immunotherapy. We found that PTGS2, the gene encoding cyclooxygenase-2, lies downstream of EPHA2 signaling through TGFß and is associated with poor patient survival. Ptgs2 deletion reversed T cell exclusion and sensitized tumors to immunotherapy; pharmacological inhibition of PTGS2 was similarly effective. Thus, EPHA2-PTGS2 signaling in tumor cells regulates tumor immune phenotypes; blockade may represent a novel therapeutic avenue for immunotherapy-refractory cancers. Our findings warrant clinical trials testing the effectiveness of therapies combining EPHA2-TGFß-PTGS2 pathway inhibitors with anti-tumor immunotherapy, and may change the treatment of notoriously therapy-resistant pancreatic adenocarcinoma.

Lack of immunoediting in murine pancreatic cancer reversed with neoantigen.

In carcinogen-driven cancers, a high mutational burden results in neoepitopes that can be recognized immunologically. Such carcinogen-induced tumors may evade this immune response through "immunoediting," whereby tumors adapt to immune pressure and escape T cell-mediated killing. Many tumors lack a high neoepitope burden, and it remains unclear whether immunoediting occurs in such cases. Here, we evaluated T cell immunity in an autochthonous mouse model of pancreatic cancer and found a low mutational burden, absence of predicted neoepitopes derived from tumor mutations, and resistance to checkpoint immunotherapy. Spontaneous tumor progression was identical in the presence or absence of T cells. Moreover, tumors arising in T cell-depleted mice grew unchecked in immune-competent hosts. However, introduction of the neoantigen ovalbumin (OVA) led to tumor rejection and T cell memory, but this did not occur in OVA immune-tolerant mice. Thus, immunoediting does not occur in this mouse model - a likely consequence, not a cause, of absent neoepitopes. Because many human tumors also have a low missense mutational load and minimal neoepitope burden, our findings have clinical implications for the design of immunotherapy for patients with such tumors.

Targeting COX-2 abrogates mammary tumorigenesis: Breaking cancer-associated suppression of immunosurveillance.

Three studies addressed the role of cyclooxygenase-2 (COX-2) in mammary tumorigenesis using epithelial and macrophage COX-2 knockout mice. Deletion of COX-2 in either cell restored, at least partially, tumor immunosurveillance either by changing macrophage function to offset pro-tumor effects, or by attracting more cytotoxic T lymphocytes and natural killer cells to the tumor. These studies suggest benefits from targeted COX-2 selective inhibition in combination with immunotherapies.

Primate granulosa cell response via prostaglandin E2 receptors increases late in the periovulatory interval.

Successful ovulation requires elevated follicular prostaglandin E2 (PGE2) levels. To determine which PGE2 receptors are available to mediate periovulatory events in follicles, granulosa cells and whole ovaries were collected from monkeys before (0 h) and after administration of an ovulatory dose of hCG to span the 40-h periovulatory interval. All PGE2 receptor mRNAs were present in monkey granulosa cells. As assessed by immunofluorescence, PTGER1 (EP1) protein was low/nondetectable in granulosa cells 0, 12, and 24 h after hCG but was abundant 36 h after hCG administration. PTGER2 (EP2) and PTGER3 (EP3) proteins were detected by immunofluorescence in granulosa cells throughout the periovulatory interval, and Western blotting showed an increase in PTGER2 and PTGER3 levels between 0 h and 36 h after hCG. In contrast, PTGER4 (EP4) protein was not detected in monkey granulosa cells. Granulosa cell response to PGE2 receptor agonists was examined 24 h and 36 h after hCG administration, when elevated PGE2 levels present in periovulatory follicles initiate ovulatory events. PGE2 acts via PTGER1 to increase intracellular calcium. PGE2 increased intracellular calcium in granulosa cells obtained 36 h, but not 24 h, after hCG; this effect of PGE2 was blocked by a PTGER1 antagonist. A PTGER2-specific agonist and a PTGER3-specific agonist each elevated cAMP in granulosa cells obtained 36 h, but not 24 h, after hCG. Therefore, the granulosa cells of primate periovulatory follicles express multiple receptors for PGE2. Granulosa cells respond to agonist stimulation of each of these receptors 36 h, but not 24 h, after hCG, supporting the hypothesis that granulosa cells are most sensitive to PGE2 as follicular PGE2 levels peak, leading to maximal PGE2-mediated periovulatory effects just before ovulation.