The Therapeutic Potential of Targeting Tumor Microenvironment in Breast Cancer: Rational Strategies and Recent Progress

The tumor microenvironment (TME) is cellular environment in addition to harboring carcinoma cells, consists of different components (e.g., blood vessels, immune cells, fibroblasts, bone marrow‐derived inflammatory cells, lymphocytes, signaling molecules, and the extracellular matrix) that have an essential role on drug activity and efficacy. There is growing body of evidence showing its involvement in the progression and metastasis of different cancers, including breast cancer (BC). These observations provide a proof of concept of targeting TME compartments as a novel potential therapeutic approach in treatment of this malignancy, which is the main interested for current review. J. Cell. Biochem. 119: 111–122, 2018. © 2017 Wiley Periodicals, Inc.     

Modifying the tumour microenvironment and reverting tumour cells: New strategies for treating malignant tumours

The tumour microenvironment (TME) plays a pivotal role in tumour fate determination. The TME acts together with the genetic material of tumour cells to determine their initiation, metastasis and drug resistance. Stromal cells in the TME promote the growth and metastasis of tumour cells by secreting soluble molecules or exosomes. The abnormal microenvironment reduces immune surveillance and tumour killing. The TME causes low anti‐tumour drug penetration and reactivity and high drug resistance. Tumour angiogenesis and microenvironmental hypoxia limit the drug concentration within the TME and enhance the stemness of tumour cells. Therefore, modifying the TME to effectively attack tumour cells could represent a comprehensive and effective anti‐tumour strategy. Normal cells, such as stem cells and immune cells, can penetrate and disrupt the abnormal TME. Reconstruction of the TME with healthy cells is an exciting new direction for tumour treatment. We will elaborate on the mechanism of the TME to support tumours and the current cell therapies for targeting tumours and the TME—such as immune cell therapies, haematopoietic stem cell (HSC) transplantation therapies, mesenchymal stem cell (MSC) transfer and embryonic stem cell‐based microenvironment therapies—to provide novel ideas for producing breakthroughs in tumour therapy strategies.     

Thioridazine combined with carboplatin results in synergistic inhibition of triple negative breast cancer by targeting cancer stem cells

Cancer stem cells (CSCs) in triple-negative breast cancer (TNBC) are closely related to tumorigenesis and metastasis. Thioridazine (THZ) is a usual phenothiazine antipsychotic drug that can destroy CSCs. We aimed to explore whether THZ could sensitize metastatic TNBC cells, especially the CSCs, to carboplatin (CBP) treatment. Metastatic TNBC cells, 4T1 cells, and tumor-bearing mice were treated with THZ and CBP as monotherapy or combination therapy. MTT, flow cytometry, electron microscopy, immunohistochemistry and western blotting were applied to assess the cell viability, apoptosis, mitochondrial morphology and the relevant protein levels, respectively. Tumor size and lung metastasis under different treatments as well as tumorigenesis of residual tumor cells from each group were monitored. THZ combined with CBP inhibited 4T1 tumor cell proliferation and induced apoptosis by inhibiting the PI3K-AKT-mTOR pathway and activating estrogen receptor stress. THZ also showed strong activity against breast CSCs, THZ combined with CBP significantly destroyed cancer cells, inhibited lung metastasis and relieved the tumor burden; Our data demonstrated that THZ can sensitize TNBC cells to CBP treatment and this combination therapy may provide a bright strategy for TNBC treatment by targeting both cancer cells and CSCs.     

Natural products: Potential targets of TME related long non-coding RNAs in lung cancer

BackgroundLung cancer is a significant health concern worldwide due to high mortality and morbidity, despite the advances in diagnosis, treatment, and management. Recent experimental evidence from different models suggested long non-coding RNAs (lncRNAs) as major modulators of cancer stem cells (CSCs) in the tumor microenvironment (TME) to support metastasis and drug resistance in lung cancer. Evidence-based studies demonstrated that natural products interfere with TME functions.Purpose of studyTo establish lncRNAs of TME as novel targets of natural compounds for lung cancer management.Study designCurrent study used a combination of TME and lung CSCs, lncRNAs and enrichment and stemness maintenance, natural products and stem cell management, natural products and lncRNAs, natural products and targeted delivery as keywords to retrieve the literature from Scopus, Web of Science, PubMed, and Google Scholar. This study critically reviewed the current literature and presented cancer stem cells' ability in reprogramming lung TME.ResultsThis review found that TME related oncogenic and tumor suppressor lncRNAs and their signaling pathways control the maintenance of stemness in lung TME. This review explored natural phenolic compounds and found that curcumin, genistein, quercetin epigallocatechin gallate and ginsenoside Rh2 are efficient in managing lung CSCs. They modulate lncRNAs and their upstream mediators by targeting signaling and epigenetic pathways. This review also identified relevant nanotechnology-based phytochemical delivery approaches for targeting lung cancer.ConclusionBy critical literature analysis, TME related lncRNAs were identified as potential therapeutic targets, aiming to develop natural product-based therapeutics to treat metastatic and drug-resistant lung cancers.     

Cancer-associated fibroblasts: Mediators of head and neck tumor microenvironment remodeling

Cancer-associated fibroblasts (CAFs) are involved in critical aspects of head and neck squamous cell carcinoma (HNSCC) pathogenesis, such as the formation of a tumor-permissive extracellular matrix structure, angiogenesis, or immune and metabolic reprogramming of the tumor microenvironment (TME), with implications for metastasis and resistance to radiotherapy and chemotherapy. The pleiotropic effect of CAFs in TME is likely to reflect the heterogeneity and plasticity of their population, with context-dependent effects on carcinogenesis. The specific properties of CAFs provide many targetable molecules that could play an important role in the future therapy of HNSCC. In this review article, we will focus on the role of CAFs in the TME of HNSCC tumors. We will also discuss clinically relevant agents targeting CAFs, their signals, and signaling pathways, which are activated by CAFs in cancer cells, with the potential for repurposing for HNSCC therapy.     

Understanding the function of the tumor microenvironment,and compounds from marine organisms for breast cancer therapy

The pathology and physiology of breast cancer(BC),including metastasis,and drug resistance,is driven by multiple signaling pathways in the tumor microenvironment(TME),which hamper antitumor immunity.Recently,long non-coding RNAs have been reported to mediate pathophysiological developments such as metastasis as well as immune suppression within the TME.Given the complex biology of BC,novel personalized therapeutic strategies that address its diverse pathophysiologies are needed to improve clinical outcomes.In this review,we describe the advances in the biology of breast neoplasia,including cellular and molecular biology,heterogeneity,and TME.We review the role of novel molecules such as long non-coding RNAs in the pathophysiology of BC.Finally,we provide an up-to-date overview of anticancer compounds extracted from marine microorganisms,crustaceans,and fishes and their synergistic effects in combination with other anticancer drugs.Marine compounds are a new discipline of research in BC and offer a wide range of anti-cancer effects that could be harnessed to target the various pathways involved in BC development,thus assisting current therapeutic regimens.     

The metabolic flexibility of quiescent CSC: implications for chemotherapy resistance

Quiescence has been observed in stem cells (SCs), including adult SCs and cancer SCs (CSCs). Conventional chemotherapies mostly target proliferating cancer cells, while the quiescent state favors CSCs escape to chemotherapeutic drugs, leaving risks for tumor recurrence or metastasis. The tumor microenvironment (TME) provides various signals that maintain resident quiescent CSCs, protect them from immune surveillance, and facilitates their recurrence potential. Since the TME has the potential to support and initiate stem cell-like programs in cancer cells, targeting the TME components may prove to be a powerful modality for the treatment of chemotherapy resistance. In addition, an increasing number of studies have discovered that CSCs exhibit the potential of metabolic flexibility when metabolic substrates are limited, and display increased robustness in response to stress. Accompanied by chemotherapy that targets proliferative cancer cells, treatments that modulate CSC quiescence through the regulation of metabolic pathways also show promise. In this review, we focus on the roles of metabolic flexibility and the TME on CSCs quiescence and further discuss potential treatments of targeting CSCs and the TME to limit chemotherapy resistance.Subject terms: Cancer metabolism, Cancer microenvironment, Cancer stem cells     

Targeting tumor microenvironment in ovarian cancer: Premise and promise

Ovarian cancer is the leading cause of gynecological cancer-related mortality globally. The majority of ovarian cancer patients suffer from relapse after standard of care therapies and the clinical benefits from cancer therapies are not satisfactory owing to drug resistance. Certain novel drugs targeting the components of tumor microenvironment (TME) have been approved by US Food and Drug Administration in solid cancers. As such, the passion is rekindled to exploit the role of TME in ovarian cancer progression and metastasis for discovery of novel therapeutics for this deadly disease. In the current review, we revisit the recent mechanistic insights into the contributions of TME to the development, progression, prognosis prediction and therapeutic efficacy of ovarian cancer via modulating cancer hallmarks. We also explored potentially promising predictive and prognostic biomarkers for ovarian cancer patients.     

Revisiting ovarian cancer microenvironment: a friend or a foe?

Development of ovarian cancer involves the co-evolution of neoplastic cells together with the adjacent microenvironment. Steps of malignant progression including primary tumor outgrowth, therapeutic resistance, and distant metastasis are not determined solely by genetic alterations in ovarian cancer cells, but considerably shaped by the fitness advantage conferred by benign components in the ovarian stroma. As the dynamic cancer topography varies drastically during disease progression, heterologous cell types within the tumor microenvironment (TME) can actively determine the pathological track of ovarian cancer. Resembling many other solid tumor types, ovarian malignancy is nurtured by a TME whose dark side may have been overlooked, rather than overestimated. Further, harnessing breakthrough and targeting cures in human ovarian cancer requires insightful understanding of the merits and drawbacks of current treatment modalities, which mainly target transformed cells. Thus, designing novel and precise strategies that both eliminate cancer cells and manipulate the TME is increasingly recognized as a rational avenue to improve therapeutic outcome and prevent disease deterioration of ovarian cancer patients.     

High-density lipoproteins: A promising tool against cancer

High-density lipoproteins (HDL) are well known for their protective role against the development and progression of atherosclerosis. Atheroprotection is mainly due to the key role of HDL within the reverse cholesterol transport, and to their ability to exert a series of antioxidant and anti-inflammatory activities. Through the same mechanisms HDL could also affect cancer cell proliferation and tumor progression. Many types of cancers share common alterations of cellular metabolism, including lipid metabolism. In this context, not only fatty acids but also cholesterol and its metabolites play a key role. HDL were shown to reduce cancer cell content of cholesterol, overall rewiring cholesterol homeostasis. In addition, HDL reduce oxidative stress and the levels of pro-inflammatory molecules in cancer cells and in the tumor microenvironment (TME). Here, HDL can also help in reverting tumor immune escape and in inhibiting angiogenesis. Interestingly, HDL are good candidates for drug delivery, targeting antineoplastic agents to the tumor mass mainly through their binding to the scavenger receptor BI. Since they could affect cancer development and progression per se, HDL-based drug delivery systems may render cancer cells more sensitive to antitumor agents and reduce the development of drug resistance.     

LIN9 confers paclitaxel resistance in triple negative breast cancer cells by upregulating CCSAP

LIN9 functions to regulate cell mitotic process.Dysregulation of LIN9 expression is associated with development of human cancers.In this study we assessed the association of LIN9 expression with paclitaxel resistance and clarified the underlying mechanisms for the first time.LIN9 expression in breast cancer tissues was retrieved from publicly available online databases and statistically analyzed.Human TNBC cell lines MDA-MB-231 and MDA-MB-468 and their corresponding paclitaxelresistant sublines 231PTX and 468PTX were used to assess the expression of LIN9 by qRT-PCR and Western blot,cell growth by cell counting,cell viability by MTS assay,and cell apoptosis by flow cytometry.The data showed that high LIN9 expression in breast cancer patients receiving chemotherapy was related to poor overall survival (OS).LIN9 expression was upregulated in paclitaxel-resistant TNBC cells compared to their parental cells.Knockdown of LIN9 or treatment of paclitaxel-resistant TNBC cells with a bromo-and extra-terminal domain inhibitor (BETi) JQ1 which also decreased LIN9 expression enhanced the sensitivity of paclitaxel-resistant TNBC cells to paclitaxel.Mechanistically,decreased LIN9 in resistant cell lines reduced tumor cell viability,promoted multinucleated cells formation and induced tumor cell apoptosis,potentially by directly regulating microtubule-binding protein CCSAP.In conclusion,high LIN9 expression contributed to poor clinical outcomes and paclitaxel resistance in TNBC and BETi,targeting LIN9 expression,could be a reversible drug for PTX-resistant TNBC patients.     

Triple-negative breast cancer cells rely on kinase-independent functions of CDK8 to evade NK-cell-mediated tumor surveillance

Triple-negative breast cancer (TNBC) is an aggressive malignant disease that is responsible for approximately 15% of breast cancers. The standard of care relies on surgery and chemotherapy but the prognosis is poor and there is an urgent need for new therapeutic strategies. Recent in silico studies have revealed an inverse correlation between recurrence-free survival and the level of cyclin-dependent kinase 8 (CDK8) in breast cancer patients. CDK8 is known to have a role in natural killer (NK) cell cytotoxicity, but its function in TNBC progression and immune cell recognition or escape has not been investigated. We have used a murine model of orthotopic breast cancer to study the tumor-intrinsic role of CDK8 in TNBC. Knockdown of CDK8 in TNBC cells impairs tumor regrowth upon surgical removal and prevents metastasis. In the absence of CDK8, the epithelial-to-mesenchymal transition (EMT) is impaired and immune-mediated tumor-cell clearance is facilitated. CDK8 drives EMT in TNBC cells in a kinase-independent manner. In vivo experiments have confirmed that CDK8 is a crucial regulator of NK-cell-mediated immune evasion in TNBC. The studies also show that CDK8 is involved in regulating the checkpoint inhibitor programmed death-ligand 1 (PD-L1). The CDK8–PD-L1 axis is found in mouse and human TNBC cells, underlining the importance of CDK8-driven immune cell evasion in these highly aggressive breast cancer cells. Our data link CDK8 to PD-L1 expression and provide a rationale for investigating the possibility of CDK8-directed therapy for TNBC.Subject terms: Breast cancer, Immune evasion     

Histone deacetylase 2 knockout suppresses immune escape of triple-negative breast cancer cells via downregulating PD-L1 expression

The PD-L1 overexpression is an important event of immune escape and metastasis in triple-negative breast cancer (TNBC), but the molecular mechanism remains to be determined. Interferon gamma (IFNγ) represents a major driving force behind PD-L1 expression in tumor microenvironment, and histone deacetylase 2 (HDAC2) is required for IFN signaling. Here, we investigated the regulation of HDAC2 on the IFNγ-induced PD-L1 expression in TNBC cells. We found the HDAC2 and PD-L1 expression in TNBC was significantly higher than that in non-TNBC, and HDAC2 was positively correlated with PD-L1 expression. HDAC2 promoted PD-L1 induction by upregulating the phosphorylation of JAK1, JAK2, and STAT1, as well as the translocation of STAT1 to the nucleus and the recruitment of STAT1 to the PD-L1 promoter. Meanwhile, HDAC2 was recruited to the PD-L1 promoter by STAT1, and HDAC2 knockout compromised IFNγ-induced upregulation of H3K27, H3K9 acetylation, and the BRD4 recruitment in PD-L1 promoter. In addition, significant inhibition of proliferation, colony formation, migration, and cell cycle of TNBC cells were observed following knockout of HDAC2 in vitro. Furthermore, HDAC2 knockout reduced IFNγ-induced PD-L1 expression, lymphocyte infiltration, and retarded tumor growth and metastasis in the breast cancer mouse models. This study may provide evidence that HDAC2 promotes IFNγ-induced PD-L1 expression, suggesting a way for enhanced antitumor immunity when targeting the HDAC2 in TNBC.Subject terms: Breast cancer, Immune evasion     

G Protein Coupled Receptor Kinase 3 Regulates Breast Cancer Migration,Invasion, and Metastasis

Triple negative breast cancer (TNBC) is a heterogeneous disease that has a poor prognosis and limited treatment options. Chemokine receptor interactions are important modulators of breast cancer metastasis; however, it is now recognized that quantitative surface expression of one important chemokine receptor, CXCR4, may not directly correlate with metastasis and that its functional activity in breast cancer may better inform tumor pathogenicity. G protein coupled receptor kinase 3 (GRK3) is a negative regulator of CXCR4 activity, and we show that GRK expression correlates with tumorigenicity, molecular subtype, and metastatic potential in human tumor microarray analysis. Using established human breast cancer cell lines and an immunocompetent in vivo mouse model, we further demonstrate that alterations in GRK3 expression levels in tumor cells directly affect migration and invasion in vitro and the establishment of distant metastasis in vivo. The effects of GRK3 modulation appear to be specific to chemokine-mediated migration behaviors without influencing tumor cell proliferation or survival. These data demonstrate that GRK3 dysregulation may play an important part in TNBC metastasis.     

LIPH promotes metastasis by enriching stem‐like cells in triple‐negative breast cancer

Lipase member H (LIPH), a novel member of the triglyceride lipase family. The clinical implications of its expression in breast cancer are still unclear. Therefore, in this study, we investigated the associations between LIPH and the tumorigenic behaviours of 144 triple‐negative breast cancer (TNBC) patients. The ratio and mammosphere‐forming ability of CD44+/CD24? stem‐like cells were tested. The role of LIPH in breast cancer cell migration and invasion was also evaluated. In addition, the effect of LIPH silencing on mitochondrial respiration was determined using the Seahorse assay. Finally, the effect of LIPH silencing on protein expression was determined via tandem mass tag‐based spectrometry and Western blotting. We found that LIPH expression was associated with metastasis in lymph nodes and distant organs (P = 0.025), resulting in poor survival among breast cancer patients (P = 0.027). LIPH knockdown significantly decreased both the ratio of CD44⁺/CD24^? stem‐like cells and their mammosphere‐forming ability. LIPH silencing promoted apoptosis, arrested cell cycle in the G2/M phase, mitigated the oxidation‐related oxygen consumption rate in the mitochondria, and reduced metabolism. LIPH inhibited adhesion between tumour cells and enhanced the epithelial‐mesenchymal transition. Tandem mass spectrometric analysis presented 68 proteins were differentially expressed in LIPH‐silenced cells and LIPH‐mediated modulation of tumour cell adhesion depended on integrin‐related CAPN2 and paxillin signalling. Overall, our findings provided strong evidence that LIPH up‐regulation promoted metastasis and the stemness of TNBC cells. Therefore, targeting LIPH is a potentially viable strategy for preventing metastasis in TNBC.     

Lamin B2 promotes the progression of triple negative breast cancer via mediating cell proliferation and apoptosis

Triple negative breast cancer (TNBC) is a more common type of breast cancer with high distant metastasis and poor prognosis. The potential role of lamins in cancer progression has been widely revealed. However, the function of lamin B2 (LMNB2) in TNBC progression is still unclear. The present study aimed to investigate the role of LMNB2 in TNBC. The cancer genome atlas (TCGA) database analysis and immunohistochemistry (IHC) were performed to examine LMNB2 expression levels. LMNB2 short hairpin RNA plasmid or lentivirus was used to deplete the expression of LMNB2 in human TNBC cell lines including MDA-MB-468 and MDA-MB-231. Alterations in cell proliferation and apoptosis in vitro and the nude mouse tumorigenicity assay in vivo were subsequently analyzed. The human TNBC tissues shown high expression of LMNB2 according to the bioinformation analysis and IHC assays. LMNB2 expression was correlated with the clinical pathological features of TNBC patients, including pTNM stage and lymph node metastasis. Through in vitro and in vivo assays, we confirmed LMNB2 depletion suppressed the proliferation and induced the apoptosis of TNBC cells, and inhibited tumor growth of TNBC cells in mice, with the decrease in Ki67 expression or the increase in caspase-3 expression. In conclusion, LMNB2 may promote TNBC progression and could serve as a potential therapeutic target for TNBC treatment.     

Inhibition of heat shock protein (Hsp) 27 potentiates the suppressive effect of Hsp90 inhibitors in targeting breast cancer stem-like cells

Heat shock protein (Hsp) 90 is an ATP-dependent chaperone and its expression has been reported to be associated with poor prognosis of breast cancer. Cancer stem cells (CSCs) are particular subtypes of cells in cancer which have been demonstrated to be important to tumor initiation, drug resistance and metastasis. In breast cancer, breast CSCs (BCSCs) are identified as CD24-CD44 + cells or cells with high intracellular aldehyde dehydrogenase activity (ALDH+). Although the clinical trials of Hsp90 inhibitors in breast cancer therapy are ongoing, the BCSC targeting effect of them remains unclear. In the present study, we discovered that the expression of Hsp90α was increased in ALDH + human breast cancer cells. Geldanamycin (GA), a Hsp90 inhibitor, could suppress ALDH + breast cancer cells in a dose dependent manner. We are interesting in the insufficiently inhibitory effect of low dose GA treatment. It was correlated with the upregulation of Hsp27 and Hsp70. By co-treatment with HSP inhibitors, quercetin or KNK437 potentiated BCSCs, which determined with ALDH+ population or mammosphere cells, toward GA inhibition, as well as anti-proliferation and anti-migration effects of GA. With siRNA mediated gene silencing, we found that knockdown of Hsp27 could mimic the effect of HSP inhibitors to potentiate the BCSC targeting effect of GA. In conclusion, combination of HSP inhibitors with Hsp90 inhibitors could serve as a potential solution to prevent the drug resistance and avoid the toxicity of high dose of Hsp90 inhibitors in clinical application. Furthermore, Hsp27 may play a role in chemoresistant character of BCSCs.     

The lysosomal TRPML1 channel regulates triple negative breast cancer development by promoting mTORC1 and purinergic signaling pathways

The triple-negative breast cancer (TNBC) that comprises approximately 10%–20% of breast cancers is an aggressive subtype lacking effective therapeutics. Among various signaling pathways, mTORC1 and purinergic signals have emerged as potentially fruitful targets for clinical therapy of TNBC. Unfortunately, drugs targeting these signaling pathways do not successfully inhibit the progression of TNBC, partially due to the fact that these signaling pathways are essential for the function of all types of cells. In this study, we report that TRPML1 is specifically upregulated in TNBCs and that its genetic downregulation and pharmacological inhibition suppress the growth of TNBC. Mechanistically, we demonstrate that TRPML1 regulates TNBC development, at least partially, through controlling mTORC1 activity and the release of lysosomal ATP. Because TRPML1 is specifically activated by cellular stresses found in tumor microenvironments, antagonists of TRPML1 could represent anticancer drugs with enhanced specificity and potency. Our findings are expected to have a major impact on drug targeting of TNBCs.     

Targeting amphiregulin (AREG) derived from senescent stromal cells diminishes cancer resistance and averts programmed cell death 1 ligand (PD‐L1)‐mediated immunosuppression

Aging is characterized by a progressive loss of physiological integrity, while cancer represents one of the primary pathological factors that severely threaten human lifespan and healthspan. In clinical oncology, drug resistance limits the efficacy of most anticancer treatments, and identification of major mechanisms remains a key to solve this challenging issue. Here, we highlight the multifaceted senescence‐associated secretory phenotype (SASP), which comprises numerous soluble factors including amphiregulin (AREG). Production of AREG is triggered by DNA damage to stromal cells, which passively enter senescence in the tumor microenvironment (TME), a process that remarkably enhances cancer malignancy including acquired resistance mediated by EGFR. Furthermore, paracrine AREG induces programmed cell death 1 ligand (PD‐L1) expression in recipient cancer cells and creates an immunosuppressive TME via immune checkpoint activation against cytotoxic lymphocytes. Targeting AREG not only minimized chemoresistance of cancer cells, but also restored immunocompetency when combined with classical chemotherapy in humanized animals. Our study underscores the potential of in vivo SASP in driving the TME‐mediated drug resistance and shaping an immunosuppressive niche, and provides the proof of principle of targeting major SASP factors to improve therapeutic outcome in cancer medicine, the success of which can substantially reduce aging‐related morbidity and mortality.     

三阴型乳腺癌的化学治疗和靶向治疗进展

三阴型乳腺癌(Triple negative Breast cancer,TNBC)占乳腺癌总数的15%,是一种免疫组织化学亚型。通常发生于青年女性,有很高的复发率,内脏和中枢神经系统转移早,病程短、死亡率高。对大多数TNBC患者,常规化疗是主要的治疗方式。20%患者有很好的化疗敏感性,对化疗耐药的TNBC患者靶向治疗为当前研究的热点,寻找乳腺癌新的治疗靶点,提出TNBC新的治疗策略,有望去改善TNBC患者的预后。