Landscape of toll-like receptors expression in tumor microenvironment of triple negative breast cancer (TNBC): Distinct roles of TLR4 and TLR8

Toll-like receptors in breast cancer immunity and immunotherapy

Toll-like receptors (TLRs) are a key family of pattern recognition receptors (PRRs) in the innate immune system. The activation of TLRs will not only prevent pathogen infection but also respond to damage-induced danger signaling. Increasing evidence suggests that TLRs play a critical role in breast cancer development and treatment. However, the activation of TLRs is a double-edged sword that can induce either pro-tumor activity or anti-tumor effect. The underlying mechanisms of these opposite effects of TLR signaling in cancer are not fully understood. Targeting TLRs is a promising strategy for improving breast cancer treatment, either as monotherapies or by improving other current therapies. Here we provide an update on the role of TLRs in breast cancer immunity and immunotherapy.

Mechanism of miR-7 mediating TLR4/TRAF6/NF-κB inflammatory pathway in colorectal cancer

This study is aimed at investigating the roles of Toll-like receptor 4 (TLR4) and microRNA-7 (miR-7) in colorectal cancer (CRC) development and progression. We assessed TLR4 and miR-7 expression in CRC cells and tissues using reverse transcription-quantitative polymerase chain reaction. The relationship between miR-7 and TLR4 was analyzed through dual luciferase reporter assays. MTT, wound healing, and cell invasion assays were conducted to examine the effects of TLR4 and miR-7 on CRC cell proliferation, migration, and invasion. Western blotting was used to explore the involvement of the TRAF6/NF-κB signaling pathway. miR-7 was underexpressed in CRC, while TLR4 levels were increased. miR-7 negatively regulated TLR4 expression and its knockdown enhanced CRC cell proliferation, migration, and invasion. TLR4 knockdown had the opposite effects. The TRAF6/NF-κB pathway was linked to TLR4's role in tumor progression. miR-7 might inhibit TRAF6/NF-κB target a signaling pathway of TLR4 and promote CRC occurrence. miR-7 may therefore be used as a sensitive biomarker in CRC patients.

Expression pattern, prognostic value and potential microRNA silencing of FZD8 in breast cancer

Breast cancer (BC) is one of the most widespread types of cancer affecting females, and therefore, early diagnosis is critical. BC is a complex heterogeneous disease affected by several key pathways. Among these, WNT proteins and their frizzled receptors (FZD) have been demonstrated to be crucial in regulating a number of cellular and molecular events in BC tumorigenesis. The role of the WNT receptor, FZD8, in BC has received minimal attention; for that reason, the present study examined the prognostic value of its protein expression pattern in a BC cohort. FZD8 cytoplasmic expression pattern analysis revealed that ~38% of the primary samples presented with a high expression profile, whereas ~63% of the samples had a low expression profile. Overall, ~46% of the malignant tissues in the lymph node-positive samples exhibited an increased FZD8 cytoplasmic expression, whereas 54% exhibited low expression levels. An increased expression of FZD8 was associated with several clinicopathological characteristics of the patients, including a low survival rate, tumor vascular invasion, tumor size and grade, and molecular subtypes. Affymetrix microarray triple-negative BC datasets were analyzed and compared with healthy breast tissues in order to predict the potential interfering microRNAs (miRNAs) in the WNT/FZD8 signaling pathway. A total of 29 miRNAs with the potential to interact with the WNT/FZD8 signaling pathway were identified, eight of which exhibited a significant prediction score. The target genes for each predicted miRNA were identified. On the whole, the findings of the present study suggest that FZD8 is a potential prognostic marker for BC, shedding some light onto the silencing mechanisms involved in the complex BC signaling.

Implications of Toll-like receptors (TLRs) and their signaling mechanisms in human cancers

Most essential pattern-recognition receptors regulating innate immune functions are toll-like receptors (TLRs). TLRs are characterized by lack of concurrent epithelial markers and are typically identified by their gene expressions. One major mechanism by which TLRs generate their effector functions is by triggering inflammatory responses. Activation of TLRs can impact initiation, advancement, and control of cancers by regulating the inflammatory microenvironment. Several TLRs have been implicated in human cancers and some of them are identified as cancer biomarkers as well; for example, TLRs 2, 3, 5 are expressed more frequently in most cancers. Knowing the upregulation and downregulation of the TLR genes in human cancers will be useful for the development of newer therapeutic targets which can disrupt the pathways associated with such deregulation. We present here the various TLRs and their functions in human lung, gastric, breast, prostate, oral, ovarian, colorectal, cervical, esophageal, bladder and hepatic cancers.

Tumor heterogeneity: preclinical models, emerging technologies, and future applications

Heterogeneity describes the differences among cancer cells within and between tumors. It refers to cancer cells describing variations in morphology, transcriptional profiles, metabolism, and metastatic potential. More recently, the field has included the characterization of the tumor immune microenvironment and the depiction of the dynamics underlying the cellular interactions promoting the tumor ecosystem evolution. Heterogeneity has been found in most tumors representing one of the most challenging behaviors in cancer ecosystems. As one of the critical factors impairing the long-term efficacy of solid tumor therapy, heterogeneity leads to tumor resistance, more aggressive metastasizing, and recurrence. We review the role of the main models and the emerging single-cell and spatial genomic technologies in our understanding of tumor heterogeneity, its contribution to lethal cancer outcomes, and the physiological challenges to consider in designing cancer therapies. We highlight how tumor cells dynamically evolve because of the interactions within the tumor immune microenvironment and how to leverage this to unleash immune recognition through immunotherapy. A multidisciplinary approach grounded in novel bioinformatic and computational tools will allow reaching the integrated, multilayered knowledge of tumor heterogeneity required to implement personalized, more efficient therapies urgently required for cancer patients.

Immunogenic Cell Death-Relevant Damage-Associated Molecular Patterns and Sensing Receptors in Triple-Negative Breast Cancer Molecular Subtypes and Implications for Immunotherapy

Objectives

Triple-negative breast cancer (TNBC) is defined as a highly aggressive type of breast cancer which lacks specific biomarkers and drug targets. Damage-associated molecular pattern (DAMP)-induced immunogenic cell death (ICD) may influence the outcome of immunotherapy for TNBC patients. This study aims to develop a DAMPs gene signature to classify TNBC patients and to further predict their prognosis and immunotherapy outcome.

Methods

We identified the DAMPs-associated subtypes of 330 TNBCs using K-means analysis. Differences in immune status, genomic alterations, and predicted immunotherapy outcome were compared among each subtype.

Results

A total of 330 TNBCs were divided into three subtypes according to DAMPs gene expression: the nuclear DAMPs subtype, featuring the upregulation of nuclear DAMPs; the inflammatory DAMPs subtype, characterized by the gene set enrichment of the adaptive immune system and cytokine signaling in the immune system; and the DAMPs-suppressed subtype, having the lowest level of ICD-associated DAMPs. Among them, the inflammatory subtype patients had the most favorable survival, while the DAMPs-suppressed subtype was associated with the worst prognosis. The DAMPs subtyping system was successfully validated in the TCGA cohort. Furthermore, we systemically revealed the genomic alterations among the three DAMPs subtypes. The inflammatory DAMPs subtype was predicted to have the highest response rate to immunotherapy, suggesting that the constructed DAMPs clustering had potential for immunotherapy efficacy prediction.

Conclusion

We established a novel ICD-associated DAMPs subtyping system in TNBC, and DAMPs expression might be a valuable biomarker for immunotherapy strategies. Our work could be helpful to the development of new immunomodulators and may contribute to the development of precision immunotherapy for TNBC.

Emerging role of RNA sensors in tumor microenvironment and immunotherapy

RNA sensors detect foreign and endogenous RNAs to protect the host by initiating innate and adaptive immune response. In tumor microenvironment (TME), activation of RNA sensors induces tumor-inhibitory cytotoxic T lymphocyte responses and inhibits the activity of immunosuppressive cells though stimulating type I IFN signaling pathway. These characteristics allow RNA sensors to be prospective targets in tumor immunotherapy. Therefore, a comprehensive understanding of the roles of RNA sensors in TME could provide new insight into the antitumor immunotherapy. Moreover, RNA sensors could be prominent triggering targets to synergize with immunotherapies. In this review, we highlight the diverse mechanisms of RNA sensors in cancer immunity and their emerging contributions in cancer immunotherapy, including monotherapy with RNA sensor agonists, as well as combination with chemotherapy, radiotherapy, immune checkpoint blockade or cancer vaccine.

TLR4 and pSTAT3 Expression on Circulating Tumor Cells (CTCs) and Immune Cells in the Peripheral Blood of Breast Cancer Patients: Prognostic Implications

TLR4 and pSTAT3 are key players in cancer inflammation and immune evasion; however, their role in the peripheral blood (PB) is largely unexplored. Herein we evaluated their expression in the circulating tumor cells (CTCs) and peripheral-blood mononuclear cells (PBMCs) of patients with early (n = 99) and metastatic (n = 100) breast cancer (BC). PB samples obtained prior to adjuvant and first-line therapy, were immunofluorescently stained for Cytokeratins/TLR4/pSTAT3/DAPI and analyzed via Ariol microscopy. TLR4+ CTCs were detected in 50% and 68% of early and metastatic CTC-positive patients, respectively, and pSTAT3+ CTCs in 83% and 68%, respectively. In metastatic patients, CTC detection was associated with a high risk of death (HR: 1.764, p = 0.038), while TLR4+ CTCs correlated with a high risk of disease progression (HR: 1.964, p = 0.030). Regarding PBMCs, TLR4 expression prevailed in metastatic disease (p = 0.029), while pSTAT3 expression was more frequent in early disease (p = 0.014). In early BC, TLR4 expression on PBMCs independently predicted for high risk of relapse (HR: 3.549; p = 0.009), whereas in metastatic BC, TLR4+/pSTAT3- PBMCs independently predicted for high risk of death (HR: 2.925; p = 0.012). These results suggest that TLR4/pSTAT3 signaling on tumor- and immune-cell compartments in the PB could play a role in BC progression, and may hold independent prognostic implications for BC patients.

Prognostic Value of NLRP3 Inflammasome and TLR4 Expression in Breast Cancer Patients

Inflammasome complexes play a pivotal role in different cancer types. NOD-like receptor protein 3 (NLRP3) inflammasome is one of the most well-studied inflammasomes. Activation of the NLRP3 inflammasome induces abnormal secretion of soluble cytokines, generating advantageous inflammatory surroundings that support tumor growth. The expression levels of the NLRP3, PYCARD and TLR4 were determined by immunohistochemistry in a cohort of primary invasive breast carcinomas (BCs). We observed different NLRP3 and PYCARD expressions in non-tumor vs tumor areas (p<0.0001). All the proteins were associated to more aggressive clinicopathological characteristics (tumor size, grade, tumor proliferative activity etc.). Univariate analyses were carried out and related Kaplan-Meier curves plotted for NLRP3, PYCARD and TLR4 expression. Patients with higher NLRP3 and TLR4 expression had worse 5-year disease-free survival (DFS) compared to patients with lower NLRP3 and TLR4 expression (p =0.021 and p = 0.009, respectively). In multivariate analysis, TLR4 was confirmed as independent prognostic factors for DFS (HR = 2.03, 95% CI 1.16–3.57, p = 0.014), and high NLRP3 expression showed a slight association with DFS (HR = 1.75, 95% CI 0.98–3.15, p = 0.06). In conclusion, we showed TLR4 expression as independent prognostic factors and we highlighted for the first time that high expression of NLRP3 is linked to a poor prognosis in BC patients. These results suggest that NLRP3 and TLR4 could be two new good prognostic factor for BC patients.