MDSCs in breast cancer: an important enabler of tumor progression and an emerging therapeutic target

Deciphering the landscape of triple negative breast cancer from microenvironment dynamics and molecular insights to biomarker analysis and therapeutic modalities

Triple negative breast cancer (TNBC) displays a notable challenge in clinical oncology due to its invasive nature which is attributed to the absence of progesterone receptor (PR), estrogen receptor (ER), and human epidermal growth factor receptor (HER-2). The heterogenous tumor microenvironment (TME) of TNBC is composed of diverse constituents that intricately interact to evade immune response and facilitate cancer progression and metastasis. Based on molecular gene expression, TNBC is classified into four molecular subtypes: basal-like (BL1 and BL2), luminal androgen receptor (LAR), immunomodulatory (IM), and mesenchymal. TNBC is an aggressive histological variant with adverse prognosis and poor therapeutic response. The lack of response in most of the TNBC patients could be attributed to the heterogeneity of the disease, highlighting the need for more effective treatments and reliable prognostic biomarkers. Targeting certain signaling pathways and their components has emerged as a promising therapeutic strategy for improving patient outcomes. In this review, we have summarized the interactions among various components of the dynamic TME in TNBC and discussed the classification of its molecular subtypes. Moreover, the purpose of this review is to compile and provide an overview of the most recent data about recently discovered novel TNBC biomarkers and targeted therapeutics that have proven successful in treating metastatic TNBC. The emergence of novel therapeutic strategies such as chemoimmunotherapy, chimeric antigen receptor (CAR)-T cells-based immunotherapy, phytometabolites-mediated natural therapy, photodynamic and photothermal approaches have made a significant positive impact and have paved the way for more effective interventions.

Biological mechanisms and immunotherapy of brain metastases in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a leading cause of cancer-related mortality worldwide, with Brain Metastases serving as a significant adverse prognostic factor. The blood-brain barrier poses a substantial challenge in the treatment of brain metastases, as it restricts the penetration of many anticancer agents. Novel immunotherapy, such as immune checkpoint inhibitors (ICIs) have emerged as promising treatment for NSCLC and its associated brain metastases. This review summarizes the biological mechanism underlying NSCLC brain metastases and provides an overview of the current landscape of immunotherapy, exploring the mechanism of action and clinical applications of these advanced treatments.

Histone acetylation modulators in breast cancer

Breast cancer is the most prevalent cancer in women worldwide. Aberrant epigenetic reprogramming such as dysregulation of histone acetylation has been associated with the development of breast cancer. Histone acetylation modulators have been targeted as potential treatments for breast cancer. This review comprehensively discusses the roles of these modulators and the effects of their inhibitors on breast cancer. In addition, epigenetic reprogramming not only affects breast cancer cells but also the immunosuppressive myeloid cells, which can facilitate breast cancer progression. Therefore, the review also highlights the roles of these immunosuppressive myeloid cells and summarizes how histone acetylation modulators affect their functions and phenotypes. This review provides insights into histone acetylation modulators as potential therapeutic targets for breast cancer.

Inhibiting CXCR4 reduces immunosuppressive effects of myeloid cells in breast cancer immunotherapy

Patients with triple negative breast cancer (TNBC) show only modest response rates to immune checkpoint inhibitor immunotherapy, motivating ongoing efforts to identify approaches to boost efficacy. Using an immunocompetent mouse model of TNBC, we investigated combination therapy with an anti-PD-1 immunotherapy antibody plus balixafortide, a cyclic peptide inhibitor of CXCR4. Cell-based assays demonstrated that balixafortide functions as an inverse agonist, establishing a mode of action distinct from most compounds targeting CXCR4. Combination anti-PD-1 plus balixafortide significantly reduced growth of orthotopic tumors and extended overall survival relative to single agent therapy or vehicle. Adding balixafortide to anti-PD-1 increased numbers of tertiary lymphoid structures, a marker of local tumor immune responses associated with favorable response to immunotherapy in TNBC. Single cell RNA sequencing revealed that combination anti-PD-1 plus balixafortide reduced T cell exhaustion and increased markers of effector T cell activity. Combination therapy also reduced signatures of immunosuppressive myeloid derived suppressor cells (MDSCs) in tumors. MDSCs isolated from mice treated with anti-PD-1 plus balixafortide showed reduced inhibition of T cell proliferation following ex vivo stimulation. These studies demonstrate that combining inhibition of CXCR4 with anti-PD-1 to enhances responses to checkpoint inhibitor immunotherapy in TNBC, supporting future clinical trials.

Targeting breast tumor extracellular matrix and stroma utilizing nanoparticles

Breast cancer is a complicated malignancy and is known as the most common cancer in women. Considerable experiments have been devoted to explore the basic impacts of the tumor stroma, particularly the extracellular matrix (ECM) and stromal components, on tumor growth and resistance to treatment. ECM is made up of an intricate system of proteins, glycosaminoglycans, and proteoglycans, and maintains structural support and controls key signaling pathways involved in breast tumors. ECM can block different drugs such as chemotherapy and immunotherapy drugs from entering the tumor stroma. Furthermore, the stromal elements, such as cancer-associated fibroblasts (CAFs), immune cells, and blood vessels, have crucial impacts on tumor development and therapeutic resistance. Recently, promising outcomes have been achieved in using nanotechnology for delivering drugs to tumor stroma and crossing ECM in breast malignancies. Nanoparticles have various benefits for targeting the breast tumor stroma, such as improved permeability and retention, extended circulation time, and the ability to actively target the area. This review covers the latest developments in nanoparticle therapies that focus on breast tumor ECM and stroma. We will explore different approaches using nanoparticles to target the delivery of anticancer drugs like chemotherapy, small molecule drugs, various antitumor products, and other specific synthetic therapeutic agents to the breast tumor stroma. Furthermore, we will investigate the utilization of nanoparticles in altering the stromal elements, such as reprogramming CAFs and immune cells, and also remodeling ECM.

Delineating the nexus between gut-intratumoral microbiome and osteo-immune system in bone metastases

Emerging insights in osteoimmunology have enabled researchers to explore in depth the role of immune modulation in regulating bone health. Bone is one of the common sites of metastasis notably in case of breast cancer, prostate cancer and several other cancer types. High calcium ion concentration and presence of several factors within the mineralized bone matrix including TGF-β, BMP etc., aid in tumor growth and proliferation. Accumulating evidence has substantiated the role of the gut-microbiota (GM) in tumorigenesis, further providing a strong impetus for the growing "immune-cancer-gut microbiota" relationship. Recent advancements in research further highlight the importance of the intra-tumor microbiota in conjunction with GM in cancer metastasis. Intratumoral microbiota owing to their ability to cause genetic instability, mutations, and epigenetic modifications within the tumor microenvironment, has been recognized to affect cancer cell physiology. The host microbiota and immune system crosstalk shapes the innate and adaptive arms of the immune system, which is the key player in cancer progression. In this review, we aim to decipher the role of microorganisms mediating bone metastasis by shedding light on the immuno-onco-microbiome (IOM) axis. We discussed the feasible cancer therapeutic interventions based on the modulation of the microbiome-immune cell axis which includes prebiotics, probiotics, and postbiotics. Here, we leverage the conceptual framework based on the published articles on microbiota-based therapies to target bone metastases. Understanding this complicated nexus will provide insights into fundamental factors governing bone metastases which will subsequently help in managing this malignancy with better efficacy.

Sirtinol, a SIRT1 inhibitor, inhibits the EMT and metastasis of 4T1 breast cancer cells and impacts the tumor microenvironment

INTRODUCTION

The impact of epigenetic drugs on metastasis and the immunological microenvironment is poorly understood. In this study, we looked at how sirtinol, a SIRT1 inhibitor, affected epithelial-mesenchymal transition (EMT), metastasis, and the immune cells.

MATERIALS AND METHODS

In vitro experiments were carried out using tumor conditioned medium (TCM). For in vivo experiments, sirtinol was administered i.p. in tumor bearing BALB/c mice at a dose of 2 mg/kg body weight either alone or in combination with cisplatin. Estimation of cytokines was carried out using ELISA or ELIspot. Estimation of different markers was done using flow cytometry or western blot.

RESULTS

Sirtinol, a SIRT1 inhibitor, was found to be cytotoxic to 4T1 breast cancer cells with no synergistic effects with cisplatin, both under in vitro and in vivo conditions (p < 0.05). Sirtinol significantly reduced cancer cell metastasis to the spleen which was supported by in vitro findings such as decreased vimentin expression and cell mobility in migration and wound healing assays (p < 0.01). Studies on the effects of 4T1 tumor-conditioned medium on spleen cells indicated changes in T cell proliferation as well as differentiation (p < 0.01). In tumor bearing mice, spleen cells showed elevated IFN-γ secretion, increased CD11b+ cells, and decreased T cells (p < 0.01). This was reversed by sirtinol as well as the combination treatment, which may also have contributed to metastasis inhibition (p < 0.01).

CONCLUSION

Sirtinol, a SIRT1 inhibitor inhibits EMT and metastasis of 4T1 breast cancer cells and also has an impact on the immune microenvironment.

Resting natural killer cells promote the progress of colon cancer liver metastasis by elevating tumor-derived stem cell factor

The abundance and biological contribution of natural killer (NK) cells in cancer are controversial. Here, we aim to uncover clinical relevance and cellular roles of NK cells in colon cancer liver metastasis (CCLM). Here, we integrated single-cell RNA-sequencing, spatial transcriptomics (ST), and bulk RNA-sequencing datasets to investigate NK cells' biological properties and functions in the microenvironment of primary and liver metastatic tumors. Results were validated through an in vitro co-culture experiment based on bioinformatics analysis. Useing single-cell RNA-sequencing and ST, we mapped the immune cellular landscape of colon cancer and well-matched liver metastatic cancer. We discovered that GZMK+ resting NK cells increased significantly in tumor tissues and were enriched in the tumor regions of both diseases. After combining bulk RNA and clinical data, we observed that these NK cell subsets contributed to a worse prognosis. Meanwhile, KIR2DL4+ activated NK cells exhibited the opposite position and relevance. Pseudotime cell trajectory analysis revealed the evolution of activated to resting NK cells. In vitro experiments further confirmed that tumor-cell-co-cultured NK cells exhibited a decidual-like status, as evidenced by remarkable increasing CD9 expression. Functional experiments finally revealed that NK cells exhibited tumor-activating characteristics by promoting the dissociation of SCF (stem cell factor) on the tumor cells membrane depending on cell-to-cell interaction, as the supernatant of the co-culture system enhanced tumor progression. In summary, our findings revealed resting NK cells exhibited a clinical relevance with CCLM, which may be exploited for novel strategies to improve therapeutic outcomes for patients with CCLM.

Myeloid‑derived suppressor cells as targets of emerging therapies and nanotherapies (Review)

Breast cancer (BC) is the leading cause of cancer-related mortality among women worldwide. Immunotherapies are a promising approach in cancer treatment, particularly for aggressive forms of BC with high mortality rates. However, the current eligibility for immunotherapy remains limited to a limited fraction of patients with BC. Myeloid-derived suppressor cells (MDSCs), originating from myeloid cells, are known for their dual role in immunosuppression and tumor promotion, significantly affecting patient outcomes by fostering the formation of premetastatic niches. Consequently, targeting MDSCs has emerged as a promising avenue for further exploration in therapeutic interventions. Leveraging nanotechnology-based drug delivery systems, which excel in accumulating drugs within tumors via passive or active targeting mechanisms, are a promising strategy for the use of MDSCs in the treatment of BC. The present review discusses the immunosuppressive functions of MDSCs, their role in BC, and the diverse strategies for targeting them in cancer therapy. Additionally, the present review discusses future advancements in BC treatments focusing on MDSCs. Furthermore, it elucidates the mechanisms underlying MDSC activation, recruitment and differentiation in BC progression, highlighting the clinical characteristics that render MDSCs suitable candidates for the therapy and targeted nanotherapy of BC.

Enhancing cancer immunotherapy: Nanotechnology-mediated immunotherapy overcoming immunosuppression

Immunotherapy is an important cancer treatment method that offers hope for curing cancer patients. While immunotherapy has achieved initial success, a major obstacle to its widespread adoption is the inability to benefit the majority of patients. The success or failure of immunotherapy is closely linked to the tumor's immune microenvironment. Recently, there has been significant attention on strategies to regulate the tumor immune microenvironment in order to stimulate anti-tumor immune responses in cancer immunotherapy. The distinctive physical properties and design flexibility of nanomedicines have been extensively utilized to target immune cells (including tumor-associated macrophages (TAMs), T cells, myeloid-derived suppressor cells (MDSCs), and tumor-associated fibroblasts (TAFs)), offering promising advancements in cancer immunotherapy. In this article, we have reviewed treatment strategies aimed at targeting various immune cells to regulate the tumor immune microenvironment. The focus is on cancer immunotherapy models that are based on nanomedicines, with the goal of inducing or enhancing anti-tumor immune responses to improve immunotherapy. It is worth noting that combining cancer immunotherapy with other treatments, such as chemotherapy, radiotherapy, and photodynamic therapy, can maximize the therapeutic effects. Finally, we have identified the challenges that nanotechnology-mediated immunotherapy needs to overcome in order to design more effective nanosystems.

Extracellular vesicles derived from immune cells: Role in tumor therapy

Extracellular vesicles (EVs), which have a lipid nano-sized structure, are known to contain the active components of parental cells and play a crucial role in intercellular communication. The progression and metastasis of tumors are influenced by EVs derived from immune cells, which can simultaneously stimulate and suppress immune responses. In the past few decades, there has been a considerable focus on EVs due to their potential in various areas such as the development of vaccines, delivering drugs, making engineered modifications, and serving as biomarkers for diagnosis and prognosis. This review focuses on the substance information present in EVs derived from innate and adaptive immune cells, their effects on the immune system, and their applications in cancer treatment. While there are still challenges to overcome, it is important to explore the composition of immune cells released vesicles and their potential therapeutic role in tumor therapy. The review also highlights the current limitations and future prospects in utilizing EVs for treatment purposes.

Mechanisms of myeloid-derived suppressor cell-mediated immunosuppression in colorectal cancer and related therapies

Severe immunosuppression is a hallmark of colorectal cancer (CRC). Myeloid-derived suppressor cells (MDSCs), one of the most abundant components of the tumor stroma, play an important role in the invasion, metastasis, and immune escape of CRC. MDSCs create an immunosuppressive microenvironment by inhibiting the proliferation and activation of immunoreactive cells, including T and natural killer cells, as well as by inducing the proliferation of immunosuppressive cells, such as regulatory T cells and tumor-associated macrophages, which, in turn, promote the growth of cancer cells. Thus, MDSCs are key contributors to the emergence of an immunosuppressive microenvironment in CRC and play an important role in the breakdown of antitumor immunity. In this narrative review, we explore the mechanisms through which MDSCs contribute to the immunosuppressive microenvironment, the current therapeutic approaches and technologies targeting MDSCs, and the therapeutic potential of modulating MDSCs in CRC treatment. This study provides ideas and methods to enhance survival rates in patients with CRC.

Protein Signature Differentiating Neutrophils and Myeloid-Derived Suppressor Cells Determined Using a Human Isogenic Cell Line Model and Protein Profiling

Myeloid-derived suppressor cells (MDSCs) play an essential role in suppressing the antitumor activity of T lymphocytes in solid tumors, thus representing an attractive therapeutic target to enhance the efficacy of immunotherapy. However, the differences in protein expression between MDSCs and their physiological counterparts, particularly polymorphonuclear neutrophils (PMNs), remain inadequately characterized, making the specific identification and targeting of MDSCs difficult. PMNs and PMN-MDSCs share markers such as CD11b+CD14-CD15+/CD66b+, and some MDSC-enriched markers are emerging, such as LOX-1 and CD84. More proteomics studies are needed to identify the signature and markers for MDSCs. Recently, we reported the induced differentiation of isogenic PMNs or MDSCs (referred to as iPMNs and iMDSCs, respectively) from the human promyelocytic cell line HL60. Here, we profiled the global proteomics and membrane proteomics of these cells with quantitative mass spectrometry, which identified a 41-protein signature ("cluster 6") that was upregulated in iMDSCs compared with HL60 and iPMN. We further integrated our cell line-based proteomics data with a published proteomics dataset of normal human primary monocytes and monocyte-derived MDSCs induced by cancer-associated fibroblasts. The analysis identified a 38-protein signature that exhibits an upregulated expression pattern in MDSCs compared with normal monocytes or PMNs. These signatures may provide a hypothesis-generating platform to identify protein biomarkers that phenotypically distinguish MDSCs from their healthy counterparts, as well as potential therapeutic targets that impair MDSCs without harming normal myeloid cells.

Breaking Barriers: The Promise and Challenges of Immune Checkpoint Inhibitors in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a highly aggressive malignancy with pronounced immunogenicity, exhibiting rapid proliferation and immune cell infiltration into the tumor microenvironment. TNBC's heterogeneity poses challenges to immunological treatments, inducing resistance mechanisms in the tumor microenvironment. Therapeutic modalities, including immune checkpoint inhibitors (ICIs) targeting PD-1, PD-L1, and CTLA-4, are explored in preclinical and clinical trials. Promising results emerge from combining ICIs with anti-TGF-β and VISTA, hindering TNBC tumor growth. TNBC cells employ complex evasion strategies involving interactions with stromal and immune cells, suppressing immune recognition through various cytokines, chemokines, and metabolites. The recent focus on unraveling humoral and cellular components aims to disrupt cancer crosstalk within the tumor microenvironment. This review identifies TNBC's latest resistance mechanisms, exploring potential targets for clinical trials to overcome immune checkpoint resistance and enhance patient survival rates.

TME-Related Biomimetic Strategies Against Cancer

The tumor microenvironment (TME) plays an important role in various stages of tumor generation, metastasis, and evasion of immune monitoring and treatment. TME targeted therapy is based on TME components, related pathways or active molecules as therapeutic targets. Therefore, TME targeted therapy based on environmental differences between TME and normal cells has been widely studied. Biomimetic nanocarriers with low clearance, low immunogenicity, and high targeting have enormous potential in tumor treatment. This review introduces the composition and characteristics of TME, including cancer‑associated fibroblasts (CAFs), extracellular matrix (ECM), tumor blood vessels, non-tumor cells, and the latest research progress of biomimetic nanoparticles (NPs) based on TME. It also discusses the opportunities and challenges of clinical transformation of biomimetic nanoparticles.