SUN-122 Nuclear PDCD4 Expression Predicts Good Clinical Outcome in Luminal A-Like and Luminal B-Like Breast Cancer Subtypes

Hormone receptor-positive (HR+, estrogen and/or progesterone receptor-positive) and HER2-negative breast cancer (BC) subtype is a biologically heterogeneous entity that comprises 70% of BCs. This subtype includes both luminal (Lum) A- and B-like subtypes, which have differences in prognosis and sensitivity to endocrine therapies. The development of biomarkers guiding treatment decisions in these settings is required. Tumor suppressor PDCD4 (programmed cell death 4), which can be found both in the nucleus (NPDCD4) or the cytoplasm (CPDCD4), inhibits tumor growth and metastasis, and its loss is associated with poor prognosis in solid tumors. To explore the clinical relevance of PDCD4 in BC, we analyzed its expression by immunohistochemistry in a cohort of 619 patients with primary invasive BC. We found that 34.7% of patients showed NPDCD4 and 21.3% showed CPDCD4. NPDCD4 positivity, but not CPDCD4, was associated with lower clinical stage (P = 0.0003), with presence of more differentiated tumors (P = 6.4x10-6), and with estrogen and progesterone receptor (PR) expression (P = 9.2x10-9 and P = 2.8x10-9, respectively). Kaplan-Meier analysis revealed that NPDCD4 expression was associated with a longer overall survival (OS) and disease-free survival (DFS) in LumA-like (P = 0.008 and P = 0.028, respectively) and LumB-like (P = 0.004 and P = 0.012, respectively) subtypes. Interestingly, patients with LumB-like tumors displaying NPDCD4 presented estimated OS and DFS rates similar to the ones observed in patients with LumA-like tumors also expressing NPDCD4, indicating that its presence improves the clinical outcome of LumB-like patients. Multivariate Cox regression analysis identified NPDCD4 as an independent predictor of good clinical outcome in both LumA-like (HR: 0.45, 95% CI 0.22-0.96, P = 0.038) and LumB-like (HR: 0.28, 95% CI 0.10-0.80, P = 0.018) subtypes. We validated our results by in silico analysis using expression data from the METABRIC cohort. Bioinformatics analysis of BC cells from the Cancer Cell Line Encyclopedia revealed a positive correlation between PDCD4 and PR expression (P = 0.015). Since LumB-like tumors present a higher risk of resistance to endocrine therapy and both PR and PDCD4 levels in this subtype are lower than in the LumA-like one, we postulated that the presence of PR may modulate PDCD4 expression. Silencing of PR expression in HR+ cells decreased PDCD4 protein levels while reconstitution of PR in a PR-null cell line increased them, confirming PR requirement for PDCD4 modulation. In line with PDCD4 physiological function, its knockdown increased cell migration capability of HR+ BC cells, whereas its restoration led to a decrease in cell migration of HR-negative BC models. Our findings identified NPDCD4 positivity as a novel biomarker of clinical outcome in LumA- and B-like subtypes and revealed PDCD4 reconstitution as a novel therapeutic strategy in BC.

Abstract B25: Blockade of Stat3 oncogene addiction induces cellular senescence and reveals a cell-nonautonomous activity suitable for cancer immunotherapy

Stat3 is constitutively activated in diverse cancers and acts as a critical mediator of tumor immune evasion. Previously, we described in murine breast cancer (BC) models that blockade of Stat3 activation induces cellular senescence. Although senescent cells are growth arrested, they remain metabolically active and develop a senescence-associated secretory phenotype (SASP) that can have pro- as well as antitumorigenic effects. Our objectives were to characterize the composition and activity of the SASP induced by Stat3 blockade (SASP-Stat3) and to develop an immunotherapy (IT) based on this SASP. Here we report that Stat3 knockdown induced senescence and growth arrest only in tumor cells that exhibit constitutive activation of this oncogene (oncogene addiction), such as 4T1 BC and B16-OVA (herein “B16”) melanoma cells. Moreover, we observed that the SASP-Stat3 from 4T1 and B16 cells had several layers of antitumor effects. One of the effects relied on inhibition of tumor cell proliferation, migration and angiogenic activity. The other enhanced T-cell proliferation and activation in vitro. Furthermore, these effects were not observed with the conditioned medium (CM) from Stat3-blocked MCA cells, which are not Stat3 addicted. In order to translate these findings to a potential clinical application, we designed an immunization protocol based on the administration of irradiated wild-type cancer cells together with a depot of the SASP-Stat3. Therapeutic IT with SASP-Stat3 in mice bearing 4T1 or B16 tumors decreased tumor growth compared with control CM (CM-Control). In 4T1 tumors, we also observed a decrease in pulmonary metastasis vs. CM-Control. In addition, combination of the SASP-Stat3-based IT with an anti PD-1 antibody enhanced the antitumor activity against B16 tumor growth. We observed that this synergistic antitumor effect was the result of the involvement of different subsets of immune cells: SASP-Stat3-based IT activates CD4+ T cells and NK cells, while anti PD-1 therapy targets CD8+ T cells. Next, we studied the composition of the SASP-Stat3 through cytokine array and proteomic studies and disclosed several T cells and NK cells-attracting chemokines, IFNγ-induced cytokines and IFN-associated proteins (IP-10, RANTES, IL-15, MCP-1, ISG15 and IFI35). Taken together, these results demonstrate that Stat3 blockade in tumor cells that are addicted to this oncogene results in the induction of cellular senescence with the production of a SASP that has antitumoral and immune-stimulating activities. Cytokines and proteins from the SASP can be used to formulate an effective adjuvant to enhance the antitumor effect of anti-PD-1 antibodies.

Citation Format: Mara De Martino, Mercedes Tkach, María F. Mercogliano, Mauro E. Cenciarini, María F. Chervo, Cecilia J. Proietti, Patricia V. Elizalde, Eliane Piaggio, Roxana Schillaci. Blockade of Stat3 oncogene addiction induces cellular senescence and reveals a cell-nonautonomous activity suitable for cancer immunotherapy [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B25.

Blockade of Stat3 oncogene addiction induces cellular senescence and reveals a cell-nonautonomous activity suitable for cancer immunotherapy

Stat3 is constitutively activated in several tumor types and plays an essential role in maintaining their malignant phenotype and immunosupression. To take advantage of the promising antitumor activity of Stat3 targeting, it is vital to understand the mechanism by which Stat3 regulates both cell autonomous and non-autonomous processes. Here, we demonstrated that turning off Stat3 constitutive activation in different cancer cell types induces senescence, thus revealing their Stat3 addiction. Taking advantage of the senescence-associated secretory phenotype (SASP) induced by Stat3 silencing (SASP-siStat3), we designed an immunotherapy. The administration of SASP-siStat3 immunotherapy induced a strong inhibition of triple-negative breast cancer and melanoma growth associated with activation of CD4 + T and NK cells. Combining this immunotherapy with anti-PD-1 antibody resulted in survival improvement in mice bearing melanoma. The characterization of the SASP components revealed that type I IFN-related mediators, triggered by the activation of the cyclic GMP-AMP synthase DNA sensing pathway, are important for its immunosurveillance activity. Overall, our findings provided evidence that administration of SASP-siStat3 or low dose of Stat3-blocking agents would benefit patients with Stat3-addicted tumors to unleash an antitumor immune response and to improve the effectiveness of immune checkpoint inhibitors.

Molecular mechanisms underlying progesterone receptor action in breast cancer: Insights into cell proliferation and stem cell regulation

The ovarian steroid hormone progesterone and its nuclear receptor, the Progesterone Receptor (PR), play an essential role in the regulation of cell proliferation and differentiation in the mammary gland. In addition, experimental and clinical evidence demonstrate their critical role in controlling mammary gland tumorigenesis and breast cancer development. When bound to its ligand, the main action of PR is as a transcription factor, which regulates the expression of target genes networks. PR also activates signal transduction pathways through a rapid or non-genomic mechanism in breast cancer cells, an event that is fully integrated with its genomic effects. This review summarizes the molecular mechanisms of the ligand-activated PR actions that drive epithelial cell proliferation and the regulation of the stem cell population in the normal breast and in breast cancer.

Revisiting progesterone receptor (PR) actions in breast cancer: Insights into PR repressive functions

Progesterone receptor (PR) is a master regulator in female reproductive tissues that controls developmental processes and proliferation and differentiation during the reproductive cycle and pregnancy. PR also plays a role in progression of endocrine-dependent breast cancer. As a member of the nuclear receptor family of ligand-dependent transcription factors, the main action of PR is to regulate networks of target gene expression in response to binding its cognate steroid hormone, progesterone. Liganded-PR transcriptional activation has been thoroughly studied and associated mechanisms have been described while progesterone-mediated repression has remained less explored. The present work summarizes recent advances in the understanding of how PR-mediated repression is accomplished in breast cancer cells and highlights the significance of fully understanding the determinants of context-dependent PR action.

Tamoxifen Resistance in Breast Cancer Is Regulated by the EZH2-ERα-GREB1 Transcriptional Axis

Resistance to cancer treatment can be driven by epigenetic reprogramming of specific transcriptomes in favor of the refractory phenotypes. Here we discover that tamoxifen resistance in breast cancer is driven by a regulatory axis consisting of a master transcription factor, its cofactor, and an epigenetic regulator. The oncogenic histone methyltransferase EZH2 conferred tamoxifen resistance by silencing the expression of the estrogen receptor α (ERα) cofactor GREB1. In clinical specimens, induction of DNA methylation of a particular CpG-enriched region at the GREB1 promoter negatively correlated with GREB1 levels and cell sensitivity to endocrine agents. GREB1 also ensured proper cellular reactions to different ligands by recruiting distinct sets of ERα cofactors to cis-regulatory elements, which explains the contradictory biological effects of GREB1 on breast cancer cell growth in response to estrogen or antiestrogen. In refractory cells, EZH2-dependent repression of GREB1 triggered chromatin reallocation of ERα coregulators, converting the antiestrogen into an agonist. In clinical specimens from patients receiving adjuvant tamoxifen treatment, expression levels of EZH2 and GREB1 were correlated negatively, and taken together better predicted patient responses to endocrine therapy. Overall, our work suggests a new strategy to overcome endocrine resistance in metastatic breast cancer by targeting a particular epigenetic program.Significance: This study suggests a new strategy to overcome endocrine resistance in metastatic breast cancer by targeting a particular epigenetic program defined within. Cancer Res; 78(3); 671-84. ©2017 AACR.