Background In breast cancer, complex interactions between tumor cells and cells within the surrounding stroma, such as macrophages, are critical for tumor growth, progression, and therapeutic response. Recent studies have highlighted the complex nature and heterogeneous populations of macrophages associated with both tumor-promoting and tumor-inhibiting phenotypes. Defining the pathways that drive macrophage function is important for understanding their complex phenotypes within the tumor microenvironment. Signal transducer and activator of transcription (STAT) transcription factors, such as STAT5, are key regulators of immune cell function. The studies described here investigate the functional contributions of STAT5 to tumor-associated macrophage function in breast cancer. Methods Initial studies were performed using a panel of human breast cancer and mouse mammary tumor cell lines to determine the ability of tumor cell-derived factors to induce STAT5 activation in macrophages. Further studies used these models to identify soluble factors that activate STAT5 in macrophages. To delineate STAT5-specific contributions to macrophage function, a conditional model of myeloid STAT5 deletion was used for in vitro, RNA-sequencing, and in vivo studies. The effects of STAT5 deletion in macrophages on tumor cell migration and metastasis were evaluated using in vitro co-culture migration assays and an in vivo tumor cell-macrophage co-injection model. Results We demonstrate here that STAT5 is robustly activated in macrophages by tumor cell-derived factors and that GM-CSF is a key cytokine stimulating this pathway. The analysis of RNA-seq studies reveals that STAT5 promotes expression of immune stimulatory genes in macrophages and that loss of STAT5 in macrophages results in increased expression of tissue remodeling factors. Finally, we demonstrate that loss of STAT5 in macrophages promotes tumor cell migration in vitro and mammary tumor metastasis in vivo. Conclusions Breast cancer cells produce soluble factors, such as GM-CSF, that activate the STAT5 pathway in macrophages and drive expression of inflammatory factors. STAT5 deletion in myeloid cells enhances metastasis, suggesting that STAT5 activation in tumor-associated macrophages protects against tumor progression. Understanding mechanisms that drive macrophage function in the tumor microenvironment will ultimately lead to new approaches that suppress tumor-promoting functions while enhancing their anti-tumor functions.

Background We quantified and characterized the outcomes of ablation in persistent atrial fibrillation (PersAF) subjects, and the utility of electroanatomical mapping with a market-released high-density (HD) mapping catheter. Methods PersAF subjects received electroanatomical mapping with the Advisor™ HD Grid mapping catheter, Sensor Enabled™ (HD Grid) and radiofrequency (RF) ablation to gather data regarding ablation strategies, mapping efficiency, quality, and outcomes. Subjects were enrolled from January 2019 to April 2020 across 25 international sites and followed for 12 months after the procedure. Results Three hundred thirty-four PersAF subjects (average age 64.2 years; 76% male; 25.4% previous AF ablation) were enrolled. Multiple map types were generated in a variety of rhythms using HD Grid. Significant differences in low voltage areas were identified in maps generated with the HD Wave Solution™ electrode configuration when compared to the standard configuration, which in some cases, influenced physicians’ ablation strategies. PV-only ablation strategy was used in 59.0% of subjects and 34.1% of subjects received PV ablation and additional lesions. Of the subjects, 82.0% were free from recurrent atrial arrhythmias at 12 months and new or increased dose of class I/III antiarrhythmic drugs. About 6.0% of subjects experienced a serious adverse event or serious adverse device effect through 12 months including 1 event deemed related to HD Grid and the index procedure by the investigator and 1 death unrelated to study devices. Conclusions The results of this study (NCT03733392) support the safety and utility of electroanatomical mapping with HD Grid in subjects with complex arrhythmias, such as PersAF in the real-world setting. Supplementary Information The online version contains supplementary material available at 10.1007/s10840-022-01442-3.

Breast cancer is the second leading cause of cancer-related mortalities in women. Triple-negative is the most lethal type of breast cancer with poorest survival rates. Triple-negative breast cancers do not respond to conventional hormone receptor targeted therapies and thus inhibitors for other overactivated signaling pathways are being investigated. The Janus Kinase (JAK)/Signal Transducer and Activator of Transcription (STAT) is an oncogenic transcription factor pathway expressed in tumor and stromal cell populations. Inhibitors of this pathway such as ruxolitinib are being studied for treatment of triple-negative breast cancer but their efficacy in patients is limited. A significant barrier to the success of these inhibitors in the clinic is the lack of information about mechanisms of resistance. Tumor-associated macrophages (TAMs) are important components of the immune-suppressive environment within the tumor and are associated with poor outcome. We found that JAK inhibition in TAMs leads to induction of tumor-promoting genes that mediate therapeutic resistance of the tumor to JAK inhibition. A subset of the activated tumor promoting genes are known transcriptional targets of the NF-κB transcription factor pathway. We hypothesize that JAK inhibition activates tumor-promoting pathways in TAMs through activation of the NF-κB pathway and targeting these tumor-promoting pathways in combination with JAK inhibition will be beneficial over single therapy. We aim to elucidate activation of NF-κB in TAMs, to identify the mechanism of the observed pro-tumor response. In addition, we aim to target epiregulin, an EGFR ligand which was observed to be one of the most significantly upregulated genes in TAMs treated with JAK inhibitor. We hypothesize that targeting effects of macrophage-derived epiregulin in combination with JAK inhibition will overcome macrophage-mediated therapeutic resistance. This work will provide useful information about novel pathways that can be targeted to combat the compensatory negative effects of TAMs on tumor-targeted therapies. The results will also pave the way for development of novel inhibitor combinations targeting the tumor microenvironment in addition to targeting the tumor, and ultimately benefit patients who do not respond to single therapies. Citation Format: Aditi S. Bapat, Emily Jesser, Chelsea Lassiter, Kaylee Schwertfeger. Role of NF-κB and epiregulin in tumor-associated macrophages promoting therapeutic resistance to JAK inhibition [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr PO017.

Despite advances in treating breast cancer, limited targeted therapeutics exist for the triple negative breast cancer (TNBC) subtype, therefore it remains the most fatal relative to other breast cancer subtypes. Since TNBC tumor cells utilize the Janus Kinase (JAK)/Signal Transducer and Activator of Transcription (STAT) pathway for growth and proliferation signals, new therapeutics are being developed to target components of this pathway like STAT5. However, this pathway is also important for infiltrating inflammatory cells such as, macrophages, and their function in the tumor microenvironment. My data indicates that STAT5 is critical for tissue remodeling phenotypes and cell survival in macrophages, which can have a significant impact on tumor progression. I have observed increases in macrophage production of extracellular matrix components when STAT5 signaling is impaired, as well as a localization of STAT5-active macrophages at the tumor border suggesting a role in metastatic restraint. I have also shown that loss of STAT5 in tumor-associated macrophages correlates to an increase in tumor metastases in vivo. The goal of my research is to define the specific functional contributions of STAT5 to macrophage polarization and macrophage-mediated resistance of tumors to JAK/STAT inhibition. To address these questions, my research employs the use of mouse mammary tumor models, clinically-relevant JAK/STAT inhibition and conditional knockout strategies to understand how macrophages can shift from tumor-hostile to tumor-friendly, as well as, provide rationale for potential therapeutic interventions to maintain an anti-tumor response against TNBC. Citation Format: Emily A. Jesser, Kathryn L. Schwertfeger. Loss of STAT5 in macrophages potentiates tissue remodeling and tumor-promoting phenotype in breast cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr PO026.

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