STAT3 signaling is activated preferentially in tumor-initiating cells in claudin-low models of human breast cancer

Hijacking 5-Fluorouracil Chemoresistance in Triple Negative Breast Cancer via microRNAs-Loaded Chitosan Nanoparticles

Chemotherapy is still the mainstay of treatment for triple-negative breast cancer (TNBC) patients. Yet only 20% of TNBC patients show a pathologic complete response (pCR) after neoadjuvant chemotherapy. 5-Fluorouracil (5-FU) is a stable cornerstone in all recommended chemotherapeutic protocols for TNBC patients. However, TNBC patients' innate or acquired chemoresistance rate for 5-FU is steeply escalating. This study aims to unravel the mechanism behind the chemoresistance of 5-FU in the aggressive TNBC cell line, MDA-MB-231 cells, to explore further the role of the tumor suppressor microRNAs (miRNAs), miR-1275, miR-615-5p, and Let-7i, in relieving the 5-FU chemoresistance in TNBC, and to finally provide a translational therapeutic approach to co-deliver 5-FU and the respective miRNA oligonucleotides using chitosan-based nanoparticles (CsNPs). In this regard, cellular viability and proliferation were investigated using MTT and BrdU assays, respectively. 5-FU was found to induce JAK/STAT and PI3K/Akt/mTOR pathways in MDA-MB-231 cells with contaminant repression of their upstream regulators miR-1275, miR-615-5p, and Let-7i. Moreover, CsNPs prepared using the ionic gelation method were chosen and studied as nanovectors of 5-FU and a combination of miRNA oligonucleotides targeting TNBC. The average particle sizes, surface charges, and morphologies of the different CsNPs were characterized using dynamic light scattering (DLS) and transmission electron microscopy (TEM), respectively. In addition, the encapsulation efficiency (EE%), drug loading capacity (DLC%), and release manner at two different pH values were assessed. In conclusion, the novel CsNPs co-loaded with 5-FU and the combination of the three miRNA oligonucleotides demonstrated synergistic activity and remarkable repression in cellular viability and proliferation of TNBC cells through alleviating the chemoresistance to 5-FU.

Interferon-Induced Bone Marrow Stromal Antigen 2 (BST2) Is A Functional Tumor-Initiating Cell Marker In Triple-Negative Breast Cancer

Tumor-initiating cells (TIC) are a tumor cell subpopulation thought to be responsible for therapeutic resistance and metastasis. Using a S ignal T ransducer and A ctivator of T ranscription (STAT) reporter, and a STAT-responsive lineage tracing system, we enriched for cells with enhanced mammosphere-forming potential in some, but not all, triple-negative breast cancer xenograft models (TNBC) indicating TIC-related and TIC-independent functions for STAT signaling. Single-cell RNA sequencing (scRNA-seq) of reporter-tagged xenografts identified a common interferon-associated transcriptional state, previously linked to inflammation and macrophage differentiation, in TIC. Similar transcriptional states exist in human breast cancer patient scRNA-seq datasets. Flow cytometric sorting using bone marrow stromal cell antigen 2 (BST2), a marker of this state, enriched for TIC, and BST2 knockdown reduced mammosphere-forming potential. These results suggest TIC may exploit the interferon response pathway to promote their activity in TNBC. Our results lay the groundwork to target interferon-associated pathways in TIC in a subset of TNBC.

Recent advances in targeted strategies for triple-negative breast cancer

Triple-negative breast cancer (TNBC), a highly aggressive subtype of breast cancer, negatively expresses estrogen receptor, progesterone receptor, and the human epidermal growth factor receptor 2 (HER2). Although chemotherapy is the main form of treatment for patients with TNBC, the effectiveness of chemotherapy for TNBC is still limited. The search for more effective therapies is urgent. Multiple targeted therapeutic strategies have emerged according to the specific molecules and signaling pathways expressed in TNBC. These include PI3K/AKT/mTOR inhibitors, epidermal growth factor receptor inhibitors, Notch inhibitors, poly ADP-ribose polymerase inhibitors, and antibody-drug conjugates. Moreover, immune checkpoint inhibitors, for example, pembrolizumab, atezolizumab, and durvalumab, are widely explored in the clinic. We summarize recent advances in targeted therapy and immunotherapy in TNBC, with the aim of serving as a reference for the development of individualized treatment of patients with TNBC in the future.

Deciphering Common Traits of Breast and Ovarian Cancer Stem Cells and Possible Therapeutic Approaches

Breast cancer (BC) and ovarian cancer (OC) are among the most common and deadly cancers affecting women worldwide. Both are complex diseases with marked heterogeneity. Despite the induction of screening programs that increase the frequency of earlier diagnosis of BC, at a stage when the cancer is more likely to respond to therapy, which does not exist for OC, more than 50% of both cancers are diagnosed at an advanced stage. Initial therapy can put the cancer into remission. However, recurrences occur frequently in both BC and OC, which are highly cancer-subtype dependent. Therapy resistance is mainly attributed to a rare subpopulation of cells, named cancer stem cells (CSC) or tumor-initiating cells, as they are capable of self-renewal, tumor initiation, and regrowth of tumor bulk. In this review, we will discuss the distinctive markers and signaling pathways that characterize CSC, their interactions with the tumor microenvironment, and the strategies they employ to evade immune surveillance. Our focus will be on identifying the common features of breast cancer stem cells (BCSC) and ovarian cancer stem cells (OCSC) and suggesting potential therapeutic approaches.

An Isoxazoloquinone Derivative Inhibits Tumor Growth by Targeting STAT3 and Triggering Its Ubiquitin-Dependent Degradation

BACKGROUND

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype, with shorter five-year survival than other breast cancer subtypes, and lacks targeted and hormonal treatment strategies. The signal transducer and activator of transcription 3 (STAT3) signaling is up-regulated in various tumors, including TNBC, and plays a vital role in regulating the expression of multiple proliferation- and apoptosis-related genes.

RESULTS

By combining the unique structures of the natural compounds STA-21 and Aulosirazole with antitumor activities, we synthesized a class of novel isoxazoloquinone derivatives and showed that one of these compounds, ZSW, binds to the SH2 domain of STAT3, leading to decreased STAT3 expression and activation in TNBC cells. Furthermore, ZSW promotes STAT3 ubiquitination, inhibits the proliferation of TNBC cells in vitro, and attenuates tumor growth with manageable toxicities in vivo. ZSW also decreases the mammosphere formation of breast cancer stem cells (BCSCs) by inhibiting STAT3.

CONCLUSIONS

We conclude that the novel isoxazoloquinone ZSW may be developed as a cancer therapeutic because it targets STAT3, thereby inhibiting the stemness of cancer cells.

Targeting the NF-κB pathway enhances responsiveness of mammary tumors to JAK inhibitors

Interactions between tumor cells and the tumor microenvironment are critical for tumor growth, progression, and response to therapy. Effective targeting of oncogenic signaling pathways in tumors requires an understanding of how these therapies impact both tumor cells and cells within the tumor microenvironment. One such pathway is the janus kinase (JAK)/signal transducer and activator or transcription (STAT) pathway, which is activated in both breast cancer cells and in tumor associated macrophages. This study demonstrates that exposure of macrophages to JAK inhibitors leads to activation of NF-κB signaling, which results in increased expression of genes known to be associated with therapeutic resistance. Furthermore, inhibition of the NF-κB pathway improves the ability of ruxolitinib to reduce mammary tumor growth in vivo. Thus, the impact of the tumor microenvironment is an important consideration in studying breast cancer and understanding such mechanisms of resistance is critical to development of effective targeted therapies.

Aberrant function of pathogenic STAT3 mutant proteins is linked to altered stability of monomers and homodimers

STAT3 mutations, predominantly in the DNA-binding domain (DBD) and Src-homology 2 domain (SH2D), cause rare cases of immunodeficiency, malignancy, and autoimmunity. The exact mechanisms by which these mutations abrogate or enhance STAT3 function are not completely understood. Here, we examined how loss-of-function (LOF) and gain-of-function (GOF) STAT3 mutations within the DBD and SH2D affect monomer and homodimer protein stability as well as their effect on key STAT3 activation events, including recruitment to phosphotyrosine (pY) sites within peptide hormone receptors, tyrosine phosphorylation at Y705, dimerization, nuclear translocation, and DNA binding. The DBD LOF mutants showed reduced DNA binding when homodimerized, whereas the DBD GOF mutants showed increased DNA binding. DBD LOF and GOF mutants showed minimal changes in other STAT3 functions or in monomer or homodimer protein stability. However, SH2D LOF mutants demonstrated reduced conformational stability as either monomers or homodimers, leading to decreased pY-peptide recruitment, tyrosine phosphorylation, dimerization, nuclear localization, and DNA binding. In contrast, cancer-causing SH2D GOF mutants showed increased STAT3 homodimer stability, which increased their DNA binding. Of note, a small-molecule inhibitor of STAT3 that targets the tyrosine phosphopeptide-binding pocket within the STAT3 SH2D potently inhibited cell proliferation driven by STAT3 SH2D GOF mutants. These findings indicate that the stability of STAT3 protein monomer and homodimer is critical for the pathogenesis of diseases caused by SH2D LOF and GOF mutations and suggest that agents that modulate STAT3 monomer and/or homodimer protein stability may have therapeutic value in diseases caused by these mutations.

Ketoprofen suppresses triple negative breast cancer cell growth by inducing apoptosis and inhibiting autophagy

BACKGROUND

Triple-negative breast cancer (TNBC) is an invasive phenotype with undesirable clinical features, poor prognosis, and therapy resistance. Ketoprofen is a Non-steroidal anti-inflammatory drug (NSAID) with anti-tumor properties.

AIM

To investigate the effects of Ketoprofen on apoptosis and autophagy in TNBC cell line MDA-MB-231.

METHODS

The cytotoxic activity of Ketoprofen was assayed by the MTS method. Flowcytometry was utilized to measure the number of apoptotic MDA-MB-231 cells. The expression levels of apoptosis and autophagy markers, JAK2 and STAT3 were determined using quantitative real time-PCR (qRT-PCR) and western blotting methods.

RESULTS

Ketoprofen significantly decreased the proliferation of MDA-MB-231 cells compared to control cells. It also considerably induced apoptosis and apoptotic markers in these cells in comparison to controls. Treating the MADA-MB-231 cell line with Ketoprofen had an inhibitory effect on autophagy markers in this cell line. The use of FasL, as a death ligand, and ZB4, as an antibody that blocks the extrinsic pathway of apoptosis, revealed the involvement of the extrinsic pathway in the apoptosis-stimulating effect of Ketoprofen in the MADA-MB-231 cell line. Ketoprofen also hindered the phosphorylation and activation of JAK2 and STAT molecules leading to the inhibition of the JAK/STAT pathway in this TNBC cell line.

CONCLUSION

The outcomes of this study uncovered the anti-TNBC activity of Ketoprofen by inducing apoptosis and inhibiting viability and autophagy in MADA-MB-231 cells. Our data also suggested that Ketoprofen impedes apoptosis in TNBC cells by two different mechanisms including the induction of the extrinsic apoptotic pathway and inhibition of the JAK/STAT signaling.

Ginsenoside Rd ameliorates muscle wasting by suppressing the signal transducer and activator of transcription 3 pathway

BACKGROUND

The effects of some drugs, aging, cancers, and other diseases can cause muscle wasting. Currently, there are no effective drugs for treating muscle wasting. In this study, the effects of ginsenoside Rd (GRd) on muscle wasting were studied.

METHODS

Tumour necrosis factor-alpha (TNF-α)/interferon-gamma (IFN-γ)-induced myotube atrophy in mouse C2C12 and human skeletal myoblasts (HSkM) was evaluated based on cell thickness. Atrophy-related signalling, reactive oxygen species (ROS) level, mitochondrial membrane potential, and mitochondrial number were assessed. GRd (10 mg/kg body weight) was orally administered to aged mice (23-24 months old) and tumour-bearing (Lewis lung carcinoma [LLC1] or CT26) mice for 5 weeks and 16 days, respectively. Body weight, grip strength, inverted hanging time, and muscle weight were assessed. Histological analysis was also performed to assess the effects of GRd. The evolutionary chemical binding similarity (ECBS) approach, molecular docking, Biacore assay, and signal transducer and activator of transcription (STAT) 3 reporter assay were used to identify targets of GRd.

RESULTS

GRd significantly induced hypertrophy in the C2C12 and HSkM myotubes (average diameter 50.8 ± 2.6% and 49.9% ± 3.7% higher at 100 nM, vs. control, P ≤ 0.001). GRd treatment ameliorated aging- and cancer-induced (LLC1 or CT26) muscle atrophy in mice, which was evidenced by significant increases in grip strength, hanging time, muscle mass, and muscle tissue cross-sectional area (1.3-fold to 4.6-fold, vs. vehicle, P ≤ 0.05; P ≤ 0.01; P ≤ 0.001). STAT3 was found to be a possible target of GRd by the ECBS approach and molecular docking assay. Validation of direct interaction between GRd and STAT3 was confirmed through Biacore analysis. GRd also inhibited STAT3 phosphorylation and STAT3 reporter activity, which led to the inhibition of STAT3 nuclear translocation and the suppression of downstream targets of STAT3, such as atrogin-1, muscle-specific RING finger protein (MuRF-1), and myostatin (MSTN) (29.0 ± 11.2% to 84.3 ± 30.5%, vs. vehicle, P ≤ 0.05; P ≤ 0.01; P ≤ 0.001). Additionally, GRd scavenged ROS (91.7 ± 1.4% reduction at 1 nM, vs. vehicle, P ≤ 0.001), inhibited TNF-α-induced dysregulation of ROS level, and improved mitochondrial integrity (P ≤ 0.05; P ≤ 0.01; P ≤ 0.001).

CONCLUSIONS

GRd ameliorates aging- and cancer-induced muscle wasting. Our findings suggest that GRd may be a novel therapeutic agent or adjuvant for reversing muscle wasting.

Identification of potential microRNA diagnostic panels and uncovering regulatory mechanisms in breast cancer pathogenesis

Early diagnosis of breast cancer (BC), as the most common cancer among women, increases the survival rate and effectiveness of treatment. MicroRNAs (miRNAs) control various cell behaviors, and their dysregulation is widely involved in pathophysiological processes such as BC development and progress. In this study, we aimed to identify potential miRNA biomarkers for early diagnosis of BC. We also proposed a consensus-based strategy to analyze the miRNA expression data to gain a deeper insight into the regulatory roles of miRNAs in BC initiation. Two microarray datasets (GSE106817 and GSE113486) were analyzed to explore the differentially expressed miRNAs (DEMs) in serum of BC patients and healthy controls. Utilizing multiple bioinformatics tools, six serum-based miRNA biomarkers (miR-92a-3p, miR-23b-3p, miR-191-5p, miR-141-3p, miR-590-5p and miR-190a-5p) were identified for BC diagnosis. We applied our consensus and integration approach to construct a comprehensive BC-specific miRNA-TF co-regulatory network. Using different combination of these miRNA biomarkers, two novel diagnostic models, consisting of miR-92a-3p, miR-23b-3p, miR-191-5p (model 1) and miR-92a-3p, miR-23b-3p, miR-141-3p, and miR-590-5p (model 2), were obtained from bioinformatics analysis. Validation analysis was carried out for the considered models on two microarray datasets (GSE73002 and GSE41922). The model based on similar network topology features, comprising miR-92a-3p, miR-23b-3p and miR-191-5p was the most promising model in the diagnosis of BC patients from healthy controls with 0.89 sensitivity, 0.96 specificity and area under the curve (AUC) of 0.98. These findings elucidate the regulatory mechanisms underlying BC and represent novel biomarkers for early BC diagnosis.

Resistance to Trastuzumab

Simple Summary

Trastuzumab is a humanized antibody that has significantly improved the management and treatment outcomes of patients with cancers that overexpress HER2. Many research groups, both in academia and industry, have contributed towards understanding the various mechanisms engaged by trastuzumab to mediate its anti-tumor effects. Nevertheless, data from several clinical studies have indicated that a significant proportion of patients exhibit primary or acquired resistance to trastuzumab therapy. In this article, we discuss underlying mechanisms that contribute towards to resistance. Furthermore, we discuss the potential strategies to overcome some of the mechanisms of resistance to enhance the therapeutic efficacy of trastuzumab and other therapies based on it.

Abstract

One of the most impactful biologics for the treatment of breast cancer is the humanized monoclonal antibody, trastuzumab, which specifically recognizes the HER2/neu (HER2) protein encoded by the ERBB2 gene. Useful for both advanced and early breast cancers, trastuzumab has multiple mechanisms of action. Classical mechanisms attributed to trastuzumab action include cell cycle arrest, induction of apoptosis, and antibody-dependent cell-mediated cytotoxicity (ADCC). Recent studies have identified the role of the adaptive immune system in the clinical actions of trastuzumab. Despite the multiple mechanisms of action, many patients demonstrate resistance, primary or adaptive. Newly identified molecular and cellular mechanisms of trastuzumab resistance include induction of immune suppression, vascular mimicry, generation of breast cancer stem cells, deregulation of long non-coding RNAs, and metabolic escape. These newly identified mechanisms of resistance are discussed in detail in this review, particularly considering how they may lead to the development of well-rationalized, patient-tailored combinations that improve patient survival.

Targeting Breast Cancer Stem Cells Using Naturally Occurring Phytoestrogens

Breast cancer therapies have made significant strides in improving survival for patients over the past decades. However, recurrence and drug resistance continue to challenge long-term recurrence-free and overall survival rates. Mounting evidence supports the cancer stem cell model in which the existence of a small population of breast cancer stem cells (BCSCs) within the tumor enables these cells to evade conventional therapies and repopulate the tumor, giving rise to more aggressive, recurrent tumors. Thus, successful breast cancer therapy would need to target these BCSCs, as well the tumor bulk cells. Since the Women’s Health Initiative study reported an increased risk of breast cancer with the use of conventional hormone replacement therapy in postmenopausal women, many have turned their attention to phytoestrogens as a natural alternative. Phytoestrogens are plant compounds that share structural similarities with human estrogens and can bind to the estrogen receptors to alter the endocrine responses. Recent studies have found that phytoestrogens can also target BCSCs and have the potential to complement conventional therapy eradicating BCSCs. This review summarized the latest findings of different phytoestrogens and their effect on BCSCs, along with their mechanisms of action, including selective estrogen receptor binding and inhibition of molecular pathways used by BCSCs. The latest results of phytoestrogens in clinical trials are also discussed to further evaluate the use of phytoestrogen in the treatment and prevention of breast cancer.

In Vivo Modeling of Human Breast Cancer Using Cell Line and Patient-Derived Xenografts

Historically, human breast cancer has been modeled largely in vitro using long-established cell lines primarily in two-dimensional culture, but also in three-dimensional cultures of varying cellular and molecular complexities. A subset of cell line models has also been used in vivo as cell line-derived xenografts (CDX). While outstanding for conducting detailed molecular analysis of regulatory mechanisms that may function in vivo, results of drug response studies using long-established cell lines have largely failed to translate clinically. In an attempt to address this shortcoming, many laboratories have succeeded in developing clinically annotated patient-derived xenograft (PDX) models of human cancers, including breast, in a variety of host systems. While immunocompromised mice are the predominant host, the immunocompromised rat and pig, zebrafish, as well as the chicken egg chorioallantoic membrane (CAM) have also emerged as potential host platforms to help address perceived shortcomings of immunocompromised mice. With any modeling platform, the two main issues to be resolved are criteria for "credentialing" the models as valid models to represent human cancer, and utility with respect to the ability to generate clinically relevant translational research data. Such data are beginning to emerge, particularly with the activities of PDX consortia such as the NCI PDXNet Program, EuroPDX, and the International Breast Cancer Consortium, as well as a host of pharmaceutical companies and contract research organizations (CRO). This review focuses primarily on these important aspects of PDX-related research, with a focus on breast cancer.

Molecular Mechanisms, Biomarkers and Emerging Therapies for Chemotherapy Resistant TNBC

Triple-negative breast cancer (TNBC) is associated with high recurrence rates, high incidence of distant metastases, and poor overall survival (OS). Taxane and anthracycline-containing chemotherapy (CT) is currently the main systemic treatment option for TNBC, while platinum-based chemotherapy showed promising results in the neoadjuvant and metastatic settings. An early arising of intrinsic or acquired CT resistance is common and represents the main hurdle for successful TNBC treatment. Numerous mechanisms were uncovered that can lead to the development of chemoresistance. These include cancer stem cells (CSCs) induction after neoadjuvant chemotherapy (NACT), ATP-binding cassette (ABC) transporters, hypoxia and avoidance of apoptosis, single factors such as tyrosine kinase receptors (EGFR, IGFR1), a disintegrin and metalloproteinase 10 (ADAM10), and a few pathological molecular pathways. Some biomarkers capable of predicting resistance to specific chemotherapeutic agents were identified and are expected to be validated in future studies for a more accurate selection of drugs to be employed and for a more tailored approach, both in neoadjuvant and advanced settings. Recently, based on specific biomarkers, some therapies were tailored to TNBC subsets and became available in clinical practice: olaparib and talazoparib for BRCA1/2 germline mutation carriers larotrectinib and entrectinib for neurotrophic tropomyosin receptor kinase (NTRK) gene fusion carriers, and anti-trophoblast cell surface antigen 2 (Trop2) antibody drug conjugate therapy for heavily pretreated metastatic TNBC (mTNBC). Further therapies targeting some pathologic molecular pathways, apoptosis, miRNAS, epidermal growth factor receptor (EGFR), insulin growth factor 1 receptor (IGF-1R), and androgen receptor (AR) are under investigation. Among them, phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) and EGFR inhibitors as well as antiandrogens showed promising results and are under evaluation in Phase II/III clinical trials. Emerging therapies allow to select specific antiblastics that alone or by integrating the conventional therapeutic approach may overcome/hinder chemoresistance.

Current Advancements of Plant-Derived Agents for Triple-Negative Breast Cancer Therapy through Deregulating Cancer Cell Functions and Reprogramming Tumor Microenvironment

Triple-negative breast cancer (TNBC) is defined based on the absence of estrogen, progesterone, and human epidermal growth factor receptor 2 receptors. Currently, chemotherapy is the major therapeutic approach for TNBC patients; however, poor prognosis after a standard chemotherapy regimen is still commonplace due to drug resistance. Abnormal tumor metabolism and infiltrated immune or stromal cells in the tumor microenvironment (TME) may orchestrate mammary tumor growth and metastasis or give rise to new subsets of cancer cells resistant to drug treatment. The immunosuppressive mechanisms established in the TME make cancer cell clones invulnerable to immune recognition and killing, and turn immune cells into tumor-supporting cells, hence allowing cancer growth and dissemination. Phytochemicals with the potential to change the tumor metabolism or reprogram the TME may provide opportunities to suppress cancer metastasis and/or overcome chemoresistance. Furthermore, phytochemical intervention that reprograms the TME away from favoring immunoevasion and instead towards immunosurveillance may prevent TNBC metastasis and help improve the efficacy of combination therapies as phyto-adjuvants to combat drug-resistant TNBC. In this review, we summarize current findings on selected bioactive plant-derived natural products in preclinical mouse models and/or clinical trials with focus on their immunomodulatory mechanisms in the TME and their roles in regulating tumor metabolism for TNBC prevention or therapy.

Molecular targets and therapeutics in chemoresistance of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a specific subtype of breast cancer (BC), which shows immunohistochemically negative expression of hormone receptor i.e., Estrogen receptor and Progesterone receptor along with the absence of Human Epidermal Growth Factor Receptor-2 (HER2/neu). In Indian scenario the prevalence of BC is 26.3%, whereas, in West Bengal the cases are of 18.4%. But the rate of TNBC has increased up to 31% and shows 27% of total BC. Conventional chemotherapy is effective only in the initial stages but with progression of the disease the effectivity gets reduced and shown almost no effect in later or advanced stages of TNBC. Thus, TNBC patients frequently develop resistance and metastasis, due to its peculiar triple-negative nature most of the hormonal therapies also fails. Development of chemoresistance may involve various factors, such as, TNBC heterogeneity, cancer stem cells (CSCs), signaling pathway deregulation, DNA repair mechanism, hypoxia, and other molecular factors. To overcome the challenges to treat TNBC various targets and molecules have been exploited including CSCs modulator, drug efflux transporters, hypoxic factors, apoptotic proteins, and regulatory signaling pathways. Moreover, to improve the targets and efficacy of treatments researchers are emphasizing on targeted therapy for TNBC. In this review, an effort has been made to focus on phenotypic and molecular variations in TNBC along with the role of conventional as well as newly identified pathways and strategies to overcome challenge of chemoresistance.

Y705 and S727 are required for the mitochondrial import and transcriptional activities of STAT3, and for regulation of stem cell proliferation

The STAT3 transcription factor, acting both in the nucleus and mitochondria, maintains embryonic stem cell pluripotency and promotes their proliferation. In this work, using zebrafish, we determined in vivo that mitochondrial STAT3 regulates mtDNA transcription in embryonic and larval stem cell niches and that this activity affects their proliferation rates. As a result, we demonstrated that import of STAT3 inside mitochondria requires Y705 phosphorylation by Jak, whereas its mitochondrial transcriptional activity, as well as its effect on proliferation, depends on the MAPK target S727. These data were confirmed using mouse embryonic stem cells: although the Y705-mutated STAT3 cannot enter mitochondria, the S727 mutation does not affect import into the organelle and is responsible for STAT3-dependent mitochondrial transcription. Surprisingly, STAT3-dependent increase of mitochondrial transcription appears to be independent from STAT3 binding to STAT3-responsive elements. Finally, loss-of-function experiments, with chemical inhibition of the JAK/STAT3 pathway or genetic ablation of stat3 gene, demonstrated that STAT3 is also required for cell proliferation in the intestine of zebrafish.

Summary: Mitochondrial import of STAT3 requires Y705 phosphorylation by Jak, whereas STAT3 mitochondrial transcriptional activity and its effect on proliferation depend on the MAPK target S727.

The interaction of the severe acute respiratory syndrome coronavirus 2 spike protein with drug-inhibited angiotensin converting enzyme 2 studied by molecular dynamics simulation

BACKGROUND

Hypertension has been identified as the most common comorbidity in coronavirus disease 2019 (COVID-19) patients, and has been suggested as a risk factor for COVID-19 disease outcomes. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus enters host human cells via binding to host cell angiotensin-converting enzyme 2 (ACE2) receptors. Inhibition of ACE2 has been proposed as a potential therapeutic approach to block SARS-CoV-2 contagion. However, some experts suggest that ACE2 inhibition could worsen the infection. Here, we aimed to study the effect of ACE2 inhibition on the SARS-CoV-2 spike protein binding to ACE2.

METHOD

Crystallographic structures of the SARS-CoV-2 spike protein, the spike receptor-binding domain, native ACE2, and the ACE2 complexed with MLN-4760 were used as the study model structures. The spike proteins were docked to the ACE2 structures and the dynamics of the complexes, ligand-protein, and protein-protein interactions were studied by molecular dynamics simulation for 100 ns.

RESULTS

Our result showed that inhibition of ACE2 by MLN-4760 increased the affinity of the SARS-CoV-2 spike protein binding to ACE2. Results also revealed that spike protein binding to the ACE2 inhibited by MLN-4760 restored the enzymatic active conformation of the ACE2 from closed/inactive to open/active conformation by removing MLN-4760 binding from the ligand-binding pocket of ACE2.

CONCLUSION

We conclude that using ACE2 inhibitors can increase the risk of SARS-CoV-2 infection and worsen COVID-19 disease outcome. We also found that the SARS-CoV-2 can abrogate the function of ACE2 inhibitors and rescue the enzymatic activity of ACE2. Therefore, ACE2 inhibition is not a useful treatment against COVID-19 infection.

Immune profiling of pituitary tumors reveals variations in immune infiltration and checkpoint molecule expression

PURPOSE

Pituitary tumors are the second most common primary brain tumors. Functional tumors demonstrate increased PD-L1 expression, but expression of other checkpoint regulators has not been characterized. We sought to characterize the immune microenvironment of human pituitary tumors to identify new treatment opportunities.

METHODS

72 pituitary tumors were evaluated for expression of the immune regulatory markers programmed death ligand 1 (PD-L1), programmed death ligand 2 (PD-L2), V-domain Ig suppressor of T cell activation (VISTA), lymphocyte activation gene 3 (LAG3) and tumor necrosis factor receptor superfamily member 4 (OX40) by immunohistochemistry (IHC). Lymphocyte infiltration, macrophage infiltration, and angiogenesis were analyzed using IHC. Expression of pituitary tumor initiating cell marker CD15 and mismatch repair proteins MutS protein homolog 2 (MSH2) and MutS protein homolog 6 (MSH6) was also assessed.

RESULTS

Pituitary tumors were infiltrated by macrophages and T cells, and they expressed varying levels of PD-L1, PD-L2, VISTA, LAG3, and OX40. Functional tumors and tumors with high expression of tumor stem cell markers had higher immune cell infiltration and greater expression of immunosuppressive checkpoint regulators. Increased PD-L1 and LAG3 and reduced VISTA were observed in primary tumors compared to recurrent tumors.

CONCLUSION

Immune cell infiltration and checkpoint regulator expression vary depending on functional status and presence of pituitary tumor initiating cells. Functional tumors may have a particularly immunosuppressive microenvironment. Further studies of immune checkpoint blockade of pituitary tumors, particularly functional tumors, are warranted, though combination therapy may be required.

High dose acetaminophen inhibits STAT3 and has free radical independent anti-cancer stem cell activity

High-dose acetaminophen (AAP) with delayed rescue using n-acetylcysteine (NAC), the FDA-approved antidote to AAP overdose, has demonstrated promising antitumor efficacy in early phase clinical trials. However, the mechanism of action (MOA) of AAP's anticancer effects remains elusive. Using clinically relevant AAP concentrations, we evaluated cancer stem cell (CSC) phenotype in vitro and in vivo in lung cancer and melanoma cells with diverse driver mutations. Associated mechanisms were also studied. Our results demonstrated that AAP inhibited 3D spheroid formation, self-renewal, and expression of CSC markers when human cancer cells were grown in serum-free CSC media. Similarly, anti-CSC activity was demonstrated in vivo in xenograft models - tumor formation following in vitro treatment and ex-vivo spheroid formation following in vivo treatment. Intriguingly, NAC, used to mitigate AAP's liver toxicity, did not rescue cells from AAP's anti-CSC effects, and AAP failed to reduce glutathione levels in tumor xenograft in contrast to mice liver tissue suggesting nonglutathione-related MOA. In fact, AAP mediates its anti-CSC effect via inhibition of STAT3. AAP directly binds to STAT3 with an affinity in the low micromolar range and a high degree of specificity for STAT3 relative to STAT1. These findings have high immediate translational significance concerning advancing AAP with NAC rescue to selectively rescue hepatotoxicity while inhibiting CSCs. The novel mechanism of selective STAT3 inhibition has implications for developing rational anticancer combinations and better patient selection (predictive biomarkers) for clinical studies and developing novel selective STAT3 inhibitors using AAP's molecular scaffold.

The signaling pathways and targets of traditional Chinese medicine and natural medicine in triple-negative breast cancer

ETHNOPHARMACOLOGICAL RELEVANCE

Triple-negative breast cancer (TNBC) has a poorer prognosis than other subtypes due to its strong invasion and higher risk of distant metastasis. Traditional Chinese medicine (TCM) and natural medicine have the unique advantages of multitargets and small side-effects and may be used as long-term complementary and alternative therapies.

AIM OF THE REVIEW

The present article summarizes the classical signaling pathways and potential targets by the action of TCM and natural medicine (including extracts, active constituents and formulas) on TNBC and provides evidence for its clinical efficacy.

METHODS

The literature information was acquired from the scientific databases PubMed, Web of Science and CNKI from January 2010 to June 2020, and it was designed to elucidate the internal mechanism and role of TCM and natural medicine in the treatment of TNBC. The search key words included "Triple negative breast cancer" or "triple negative breast carcinoma", "TNBC" and "traditional Chinese medicine" or "Chinese herbal medicine", "medicinal plant", "natural plant", and "herb".

RESULTS

We described the antitumor activity of TCM and natural medicine in TNBC based on different signaling pathways. Plant medicine and herbal formulas regulated the related gene and protein expression via pathways such as PI3K/AKT/mTOR, MAPK and Wnt/β-catenin, which inhibit the growth, proliferation, migration, invasion and metastasis of TNBC cells.

CONCLUSION

The inhibitory effect of TCM and natural medicine on tumors was reflected in multiple levels and multiple pathways, providing reasonable evidence for new drug development. To make TCM and natural medicine widely and flexibly used in clinical practice, the efficacy, safety and mechanism of action need more in-depth experimental research.

Eucannabinolide, a novel sesquiterpene lactone, suppresses the growth, metastasis and BCSCS-like traits of TNBC via inactivation of STAT3

Signal transducer and activator of transcription 3 (STAT3) is an important therapeutic target to triple negative breast cancer (TNBC) treatment. In the present study, we aim to investigate the potential activity of Eucannabinolide (Euc), a novel sesquiterpene lactone separated from Eupatorium cannabinum Linn. against TNBC by targeting STAT3 and expect that Euc will be developed as an inhibitor of STAT3 in the treatment of TNBC. We found that Euc effectively suppressed STAT3 activation at tyrosine 705, inhibited its translocation to nucleus, and decreased its DNA binding capacity. Moreover, introduction of STAT3-short hairpin RNAs or STAT3 inhibitor S3I-201 attenuates the Euc-induced inhibition of cell viability. And, Euc inhibited cell viability, proliferation, metastasis and breast cancer stem cell-like traits but did not induce cytotoxicity in human mammary epithelial cells. The in vivo study similarly demonstrated that administration of Euc inhibited the growth of xenograft tumors and impaired tumor metastasis of a lung metastasis model. The above phenomena were associated with STAT3 dysfunction induced by Euc. In conclusion, Euc elicits the effects of anti-proliferation, anti-metastasis and anti-breast cancer stem cell-like traits in TNBC via targeting STAT3. These data highlight that development of Euc as a STAT3 inhibitor may offer a promising therapeutic strategy for TNBC.

STAT3 and p53: Dual Target for Cancer Therapy

The tumor suppressor p53 is considered the "guardian of the genome" that can protect cells against cancer by inducing cell cycle arrest followed by cell death. However, STAT3 is constitutively activated in several human cancers and plays crucial roles in promoting cancer cell proliferation and survival. Hence, STAT3 and p53 have opposing roles in cellular pathway regulation, as activation of STAT3 upregulates the survival pathway, whereas p53 triggers the apoptotic pathway. Constitutive activation of STAT3 and gain or loss of p53 function due to mutations are the most frequent events in numerous cancer types. Several studies have reported the association of STAT3 and/or p53 mutations with drug resistance in cancer treatment. This review discusses the relationship between STAT3 and p53 status in cancer, the molecular mechanism underlying the negative regulation of p53 by STAT3, and vice versa. Moreover, it underlines prospective therapies targeting both STAT3 and p53 to enhance chemotherapeutic outcomes.

Single-cell RNA-sequencing reveals distinct patterns of cell state heterogeneity in mouse models of breast cancer

Breast cancer stem cells (BCSCs) contribute to intra-tumoral heterogeneity and therapeutic resistance. However, the binary concept of universal BCSCs co-existing with bulk tumor cells is over-simplified. Through single-cell RNA-sequencing, we found that Neu, PyMT and BRCA1-null mammary tumors each corresponded to a spectrum of minimally overlapping cell differentiation states without a universal BCSC population. Instead, our analyses revealed that these tumors contained distinct lineage-specific tumor propagating cells (TPCs) and this is reflective of the self-sustaining capabilities of lineage-specific stem/progenitor cells in the mammary epithelial hierarchy. By understanding the respective tumor hierarchies, we were able to identify CD14 as a TPC marker in the Neu tumor. Additionally, single-cell breast cancer subtype stratification revealed the co-existence of multiple breast cancer subtypes within tumors. Collectively, our findings emphasize the need to account for lineage-specific TPCs and the hierarchical composition within breast tumors, as these heterogenous sub-populations can have differential therapeutic susceptibilities.

Mechanisms of cancer stem cell therapy

Cancer stem cells (CSCs) are responsible for carcinogenesis and tumorigenesis and are involved in drug and radiation resistance, metastasis, tumor relapse and initiation. Remarkably, they have other abilities such as inheritance of self-renewal and de-differentiation. Hence, targeting CSCs is considered a potential anti-cancer therapeutic strategy. Recent advances in the identification of biomarkers to recognize CSCs and the development of new techniques to evaluate tumorigenic and carcinogenic roles of CSCs are instrumental to this approach. Elucidation of signaling pathways that regulate CSCs colony progression and drug resistance are critical in establishing effective targeted therapies. CSCs play a central key role in immunomodulation, immune evasion and effector immunity, which alters immune system balancing. These include mTOR, SHH, NOTCH and Wnt/β-catering in cancer progression. In this review article, we discuss the importance of these CSCs pathways in cancer therapy.

Slug and E-Cadherin: Stealth Accomplices?

During physiological epithelial-mesenchymal transition (EMT), which is important for embryogenesis and wound healing, epithelial cells activate a program to remodel their structure and achieve a mesenchymal fate. In cancer cells, EMT confers increased invasiveness and tumor-initiating capacity, which contribute to metastasis and resistance to therapeutics. However, cellular plasticity that navigates between epithelial and mesenchymal states and maintenance of a hybrid or partial E/M phenotype appears to be even more important for cancer progression. Besides other core EMT transcription factors, the well-characterized Snail-family proteins Snail (SNAI1) and Slug (SNAI2) play important roles in both physiological and pathological EMT. Often mentioned in unison, they do, however, differ in their functions in many scenarios. Indeed, Slug expression does not always correlate with complete EMT or loss of E-cadherin (CDH1). For example, Slug plays important roles in mammary epithelial cell progenitor cell lineage commitment and differentiation, DNA damage responses, hematopoietic stem cell self-renewal, and in pathologies such as pulmonary fibrosis and atherosclerosis. In this Perspective, we highlight Slug functions in mammary epithelial cells and breast cancer as a “non-EMT factor” in basal epithelial cells and stem cells with focus reports that demonstrate co-expression of Slug and E-cadherin. We speculate that Slug and E-cadherin may cooperate in normal mammary gland and breast cancer/stem cells and advocate for functional assessment of such Slug⁺/E-cadherin^low/+ (SNAI2⁺/CDH1^low/+) “basal-like epithelial” cells. Thus, Slug may be regarded as less of an EMT factor than driver of the basal epithelial cell phenotype.

Two Sides of the Same Coin: The Role of Developmental pathways and pluripotency factors in normal mammary stem cells and breast cancer metastasis

Breast cancer initiation and progression are often observed as the result of dysregulation of normal developmental processes and pathways. Studies focused on normal mammary stem/progenitor cell activity have led to an understanding of how breast cancer cells acquire stemness-associated properties including tumor initiation, survival and multi-lineage differentiation into heterogeneous tumors that become difficult to target therapeutically. Importantly, more recent investigations have provided valuable insight into how key developmental regulators can impact multiple phases of metastasis, where they are repurposed to not only promote metastatic phenotypes such as migration, invasion and EMT at the primary site, but also to regulate the survival, initiation and maintenance of metastatic lesions at secondary organs. Herein, we discuss findings that have led to a better understanding of how embryonic and pluripotency factors contribute not only to normal mammary development, but also to metastatic progression. We further examine the therapeutic potential of targeting these developmental pathways, and discuss how a better understanding of compensatory mechanisms, crosstalk between pathways, and novel experimental models could provide critical insight into how we might exploit embryonic and pluripotency regulators to inhibit tumor progression and metastasis.

Targeting STAT3 signaling using stabilised sulforaphane (SFX-01) inhibits endocrine resistant stem-like cells in ER-positive breast cancer

Estrogen receptor (ER) positive breast cancer is frequently sensitive to endocrine therapy. Multiple mechanisms of endocrine therapy resistance have been identified, including cancer stem-like cell (CSC) activity. Here we investigate SFX-01, a stabilised formulation of sulforaphane (SFN), for its effects on breast CSC activity in ER+ preclinical models. SFX-01 reduced mammosphere formation efficiency (MFE) of ER+ primary and metastatic patient samples. Both tamoxifen and fulvestrant increased MFE and aldehyde dehydrogenase (ALDH) activity of patient-derived xenograft (PDX) tumors, which was reversed by combination with SFX-01. SFX-01 significantly reduced tumor-initiating cell frequency in secondary transplants and reduced the formation of spontaneous lung micrometastases by PDX tumors in mice. Mechanistically, we establish that both tamoxifen and fulvestrant induce STAT3 phosphorylation. SFX-01 suppressed phospho-STAT3 and SFN directly bound STAT3 in patient and PDX samples. Analysis of ALDH+ cells from endocrine-resistant patient samples revealed activation of STAT3 target genes MUC1 and OSMR, which were inhibited by SFX-01 in patient samples. Increased expression of these genes after 3 months' endocrine treatment of ER+ patients (n = 68) predicted poor prognosis. Our data establish the importance of STAT3 signaling in CSC-mediated resistance to endocrine therapy and the potential of SFX-01 for improving clinical outcomes in ER+ breast cancer.

Reciprocal expression of Annexin A6 and RasGRF2 discriminates rapidly growing from invasive triple negative breast cancer subsets

Actively growing tumors are often histologically associated with Ki67 positivity, while the detection of invasiveness relies on non-quantitative pathologic evaluation of mostly advanced tumors. We recently reported that reduced expression of the Ca2+-dependent membrane-binding annexin A6 (AnxA6) is associated with increased expression of the Ca2+ activated RasGRF2 (GRF2), and that the expression status of these proteins inversely influence the growth and motility of triple negative breast cancer (TNBC) cells. Here, we establish that the reciprocal expression of AnxA6 and GRF2 is at least in part, dependent on inhibition of non-selective Ca2+ channels in AnxA6-low but not AnxA6-high TNBC cells. Immunohistochemical staining of breast cancer tissues revealed that compared to non-TNBC tumors, TNBC tumors express lower levels of AnxA6 and higher Ki67 expression. GRF2 expression levels strongly correlated with high Ki67 in pretreatment biopsies from patients with residual disease and with residual tumor size following chemotherapy. Elevated AnxA6 expression more reliably identified patients who responded to chemotherapy, while low AnxA6 levels were significantly associated with shorter distant relapse-free survival. Finally, the reciprocal expression of AnxA6 and GRF2 can delineate GRF2-low/AnxA6-high invasive from GRF2-high/AnxA6-low rapidly growing TNBCs. These data suggest that AnxA6 may be a reliable biomarker for distant relapse-free survival and response of TNBC patients to chemotherapy, and that the reciprocal expression of AnxA6 and GRF2 can reliably delineate TNBCs into rapidly growing and invasive subsets which may be more relevant for subset-specific therapeutic interventions.

Antiparkinson Drug Benztropine Suppresses Tumor Growth, Circulating Tumor Cells, and Metastasis by Acting on SLC6A3/DAT and Reducing STAT3

Tumor growth, progression, and therapy resistance are crucial factors in the prognosis of cancer. The properties of three-dimensional (3D) tumor-like organoids (tumoroids) more closely resemble in vivo tumors compared to two-dimensionally cultured cells and are therefore effectively used for assays and drug screening. We here established a repurposed drug for novel anticancer research and therapeutics using a 3D tumoroid-based screening system. We screened six pharmacologically active compounds by using an original tumoroid-based multiplex phenotypic screening system with a matrix metalloproteinase 9 (MMP9) promoter-driven fluorescence reporter for the evaluation of both tumoroid formation and progression. The antiparkinson drug benztropine was the most effective compound uncovered by the screen. Benztropine significantly inhibited in vitro tumoroid formation, cancer cell survival, and MMP9 promoter activity. Benztropine also reduced the activity of oncogenic signaling transducers and trans-activators for MMP9, including STAT3, NF-κB, and β-catenin, and the properties of cancer stem cells/cancer-initiating cells. Benztropine and GBR-12935 directly targeted the dopamine transporter DAT/SLC6A3, whose genetic alterations such as amplification were correlated with poor prognosis for cancer patients. Benztropine also inhibited the tumor growth, circulating tumor cell (CTC) number, and rate of metastasis in a tumor allograft model in mice. In conclusion, we propose the repurposing of benztropine for anticancer research and therapeutics that can suppress tumor progression, CTC, and metastasis of aggressive cancers by reducing key pro-tumorigenic factors.

Tumor microenvironment: Challenges and opportunities in targeting metastasis of triple negative breast cancer

Triple negative breast cancer (TNBC) is most aggressive subtype of breast cancers with high probability of metastasis as well as lack of specific targets and targeted therapeutics. TNBC is characterized with unique tumor microenvironment (TME), which differs from other subtypes. TME is associated with induction of proliferation, angiogenesis, inhibition of apoptosis and immune system suppression, and drug resistance. Exosomes are promising nanovesicles, which orchestrate the TME by communicating with different cells within TME. The components of TME including transformed ECM, soluble factors, immune suppressive cells, epigenetic modifications and re-programmed fibroblasts together hamper antitumor response and helps progression and metastasis of TNBCs. Therefore, TME could be a therapeutic target of TNBC. The current review presents latest updates on the role of exosomes in modulation of TME, approaches for targeting TME and combination of immune checkpoint inhibitors and target chemotherapeutics. Finally, we also discussed various phytochemicals that alter genetic, transcriptomic and proteomic profiles of TME along with current challenges and future implications. Thus, as TME is associated with the hallmarks of TNBC, the understanding of the impact of different components can improve the clinical benefits of TNBC patients.

Highlighted STAT3 as a potential drug target for cancer therapy

Signal transducer and activator of transcription 3 (STAT3) is a cytoplasmic transcription factor that regulates cell proliferation, differentiation, apoptosis, angiogenesis, inflammation and immune responses. Aberrant STAT3 activation triggers tumor progression through oncogenic gene expression in numerous human cancers, leading to promote tumor malignancy. On the contrary, STAT3 activation in immune cells cause elevation of immunosuppressive factors. Accumulating evidence suggests that the tumor microenvironment closely interacts with the STAT3 signaling pathway. So, targeting STAT3 may improve tumor progression, and anti-cancer immune response. In this review, we summarized the role of STAT3 in cancer and the tumor microenvironment, and present inhibitors of STAT3 signaling cascades.

Radiation induces an inflammatory response that results in STAT3-dependent changes in cellular plasticity and radioresistance of breast cancer stem-like cells

Purpose: Pro-inflammatory cytokines within the tumor microenvironment, such as IL-6, contribute to the maintenance of stem cells and promote their survival following treatment. The IL-6/STAT3 pathway is a key regulator of genes involved in cancer progression. Activation of STAT3 promotes expansion of cancer stem cells in triple negative breast cancer. Radiation has also been shown to expand cancer stem cell populations and can induce stemness in nonstem cells. However, the role of IL-6/STAT3 in radiation-induced changes in cellular plasticity is unclear.Materials and methods: Expression and secretion of IL-6 from triple-negative breast cancer cell lines SUM159PT and MDA-MB-231 were determined after radiation treatment by real-time PCR and ELISA. Activation of STAT3 after radiation was determined by western blotting. Changes in cellular plasticity induced by radiation were determined by examining ALDEFLUOR activity, gene expression analysis of aldehyde dehydrogenase isoforms and mammosphere forming assays with and without the addition of STAT3 inhibitors. To determine the effect of radiation on nonstem cell populations, experiments were also carried out in ALDEFLUOR sorted cells.Results: Radiation induced an inflammatory response in both cell lines that resulted in activation of STAT3. Additionally, radiation induced a stem-like state as evidenced by an increased activity and expression of the ALDH isoforms ALDH1A1 and ALDH1A3, and increased self-renewal capabilities. Radiation increased ALDH activity and self-renewal in non-stem cell (ALDH-) populations, suggesting radiation-induced cellular reprograming. However, inhibition of STAT3 blocked the radiation-induced stem-like state in both ALDEFLUOR positive and negative populations, and enhanced radiosensitivity.Conclusions: Radiation-induced changes in cellular plasticity are STAT3 dependent and may be a potential target to reduce radioresistance in TNBC and improve treatment outcome.

Fzd2 Contributes to Breast Cancer Cell Mesenchymal-Like Stemness and Drug Resistance

Cancer cell stemness is responsible for cancer relapse, distal metastasis, and drug resistance. Here we identified that Frizzled 2 (Fzd2), one member of Wnt receptor Frizzled family, induced human breast cancer (BC) cell stemness via noncanonical Wnt pathways. Fzd2 was overexpressed in human BC tissues, and Fzd2 overexpression was associated with an unfavorable outcome. Fzd2 knockdown (KD) disturbed the mesenchymal-like phenotype, migration, and invasion of BC cells. Moreover, Fzd2 KD impaired BC cell mammosphere formation, reduced Lgr5⁺ BC cell subpopulation, and enhanced sensitivity of BC cells to chemical agents. Mechanistically, Fzd2 modulated and bound with Wnt5a/b and Wnt3 to activate several oncogenic pathways such as interleukin-6 (IL-6)/Stat3, Yes-associated protein 1 (Yap1), and transforming growth factor-β1 (TGF-β1)/Smad3. These data indicate that Fzd2 contributes to BC cell mesenchymal-like stemness; targeting Fzd2 may inhibit BC recurrence, metastasis, and chemoresistance.

Targeting Breast Cancer Stem Cells: A Methodological Perspective

Cancer Stem Cells (CSCs) constitute a subpopulation at the top of the tumor cell hierarchy that contributes to tumor heterogeneity and is uniquely capable of seeding new tumors. Because of their biological properties, CSCs have been pointed out as therapeutic targets for the development of new therapies against breast cancer. The identification of drugs that selectively target breast CSCs requires a clear understanding of their biological functions and the experimental methods to evaluate such hallmarks. Herein, we review the methods to study breast CSCs properties and discuss their value in the preclinical evaluation of CSC-targeting drugs.

Mechanisms of Chemotherapy Resistance in Triple-Negative Breast Cancer-How We Can Rise to the Challenge

Triple-negative (TNBC) is the most lethal subtype of breast cancer owing to high heterogeneity, aggressive nature, and lack of treatment options. Chemotherapy remains the standard of care for TNBC treatment, but unfortunately, patients frequently develop resistance. Accordingly, in recent years, tremendous effort has been made into elucidating the mechanisms of TNBC chemoresistance with the goal of identifying new molecular targets. It has become evident that the development of TNBC chemoresistance is multifaceted and based on the elaborate interplay of the tumor microenvironment, drug efflux, cancer stem cells, and bulk tumor cells. Alterations of multiple signaling pathways govern these interactions. Moreover, TNBC's high heterogeneity, highlighted in the existence of several molecular signatures, presents a significant obstacle to successful treatment. In the present, in-depth review, we explore the contribution of key mechanisms to TNBC chemoresistance as well as emerging strategies to overcome them. We discuss novel anti-tumor agents that target the components of these mechanisms and pay special attention to their current clinical development while emphasizing the challenges still ahead of successful TNBC management. The evidence presented in this review outlines the role of crucial pathways in TNBC survival following chemotherapy treatment and highlights the importance of using combinatorial drug strategies and incorporating biomarkers in clinical studies.

Alterations in Wnt- and/or STAT3 signaling pathways and the immune microenvironment during metastatic progression

Metastatic breast cancer is an extremely complex disease with limited treatment options due to the lack of information about the major characteristics of metastatic disease. There is an urgent need, therefore, to understand the changes in cellular complexity and dynamics that occur during metastatic progression. In the current study, we analyzed the cellular and molecular differences between primary tumors and paired lung metastases using a syngeneic p53-null mammary tumor model of basal-like breast cancer. Distinct subpopulations driven by the Wnt- and/or STAT3 signaling pathways were detected in vivo using a lentiviral Wnt- and STAT3 signaling reporter system. A significant increase in the overlapping populations driven by both the Wnt- and STAT3 signaling pathways was observed in the lung metastases as compared to the primary tumors. Furthermore, the overlapping populations showed a higher metastatic potential relative to the other populations and pharmacological inhibition of both signaling pathways was shown to markedly reduce the metastatic lesions in established lung metastases. An analysis of the unique molecular features of the lung metastases revealed a significant association with immune response signatures. Specifically, Foxp3 gene expression was markedly increased and elevated levels of Foxp3 + Treg cells were detected in close proximity to lung metastases. Collectively, these studies illustrate the importance of analyzing intratumoral heterogeneity, changes in population dynamics, and the immune microenvironment during metastatic progression.

C/EBPδ links IL-6 and HIF-1 signaling to promote breast cancer stem cell-associated phenotypes

To improve cancer patient outcome significantly, we must understand the mechanisms regulating stem-like cancer cells, which have been implicated as a cause of metastasis and treatment resistance. The transcription factor C/EBPδ can exhibit pro- and anti-tumorigenic activities, but the mechanisms underlying the complexity of its functions are poorly understood. Here we identify a role for breast cancer cell intrinsic C/EBPδ in promoting phenotypes that have been associated with cancer stem cells (CSCs). While C/EBPδ expression is not abundant in most metastatic breast cancers, our data support a pro-tumorigenic role of C/EBPδ when expressed in subsets of tumor cells and/or through transient activation by the tumor microenvironment or loss of substrate adhesion. Using genetic mouse models and human breast cancer cell lines, we show that deletion or depletion of C/EBPδ reduced expression of stem cell factors and stemnness markers, sphere formation and self-renewal, along with growth of tumors and established experimental metastases in vivo. C/EBPδ is also known as a mediator of the innate immune response, which is enhanced by hypoxia and interleukin-6 (IL-6) signaling, two conditions that also play important roles in cancer progression. Our mechanistic data reveal C/EBPδ as a link that engages two positive feedback loops, in part by directly targeting the IL-6 receptor (IL6RA) gene, and, thus, amplifying IL-6 and HIF-1 signaling. This study provides a molecular mechanism for the synergism of tumor microenvironmental conditions in cancer progression with potential implications for the targeting of CSCs.

Metformin selectively targets 4T1 tumorspheres and enhances the antitumor effects of doxorubicin by downregulating the AKT and STAT3 signaling pathways

Recent studies have reported that metformin (Met), the first-line medication for the treatment of type 2 diabetes, exhibited anticancer and chemoprotective effects in diverse cancer cells. In this study, we investigated the effects of Met on the drug-resistance of 4T1 murine breast cancer tumorspheres (TS) and the mechanism responsible for its drug-resistance. 4T1 TS exhibited accumulations of cells at the G₀/G₁ phase compared with cells in monolayer culture, which suggested the majority of cells in TS were quiescent. Furthermore, it was identified that activations of the signal transducer and activator of transcription 3 (STAT3) and protein kinase B (AKT) signaling pathways in 4T1 TS conferred drug-resistance to doxorubicin (Dox) and lapatinib (Lapa). However, Met selectively targeted TS rather than cells in monolayer culture and increased the cytotoxic effect of Dox on TS by inhibiting activations of the STAT3 and AKT signaling pathways. These observations suggested that inhibitions of STAT3 and AKT underlie the selective cytotoxic effects of Met on TS. In addition, Met exhibited synergistic antitumor effects with Dox on 4T1 tumor-bearing BALB/c mice. Our findings suggest that combinations of Met and cytotoxic anticancer drugs may offer an advantage for treating drug-resistant breast cancer.

Ganoderma lucidum extract (GLE) impairs breast cancer stem cells by targeting the STAT3 pathway

The aggressive nature of triple negative breast cancer (TNBC) may be explained in part by the presence of breast cancer stem cells (BCSCs), a subpopulation of cells, which are involved in tumor initiation, progression, metastasis, recurrence, and therapy resistance. The signal transducer and activator of transcription 3 (STAT3) pathway participates in the development and progression of BCSCs, but its role in TNBC remains unclear. Here, we report that Ganoderma lucidum extract (GLE), a medicinal mushroom with anticancer activity, acts on BCSCs in vitro and in TNBC pre-clinical animal tumor models by downregulating the STAT3 pathway. We show that GLE significantly reduces TNBC cell viability, and down-regulates total and phosphorylated STAT3 expression. This is consistent with the reduction of OCT4, NANOG and SOX2 expression, reduction in the BCSC population by loss of the ALDH1 and CD44⁺/CD24^– population, the deformation of mammospheres, and the strong reduction in animal tumor volume and tumor weight. Analysis of the BCSC compartment in tumors revealed that GLE decreases the STAT3 pathway and the expression of OCT4, NANOG, and SOX2 in BCSCs. These findings demonstrate that the anti-cancer activity of GLE targets BCSCs of TNBC through the downregulation of the STAT3 pathway.

Circulating Adipose Fatty Acid Binding Protein Is a New Link Underlying Obesity-Associated Breast/Mammary Tumor Development

It is clear that obesity increases the risk of many types of cancer, including breast cancer. However, the underlying molecular mechanisms by which obesity is linked to cancer risk remain to be defined. Herein, we report that circulating adipose fatty acid binding protein (A-FABP) promotes obesity-associated breast cancer development. Using clinical samples, we demonstrated that circulating A-FABP levels were significantly increased in obese patients with breast cancer in comparison with those without breast cancer. Circulating A-FABP released by adipose tissue directly targeted mammary tumor cells, enhancing tumor stemness and aggressiveness through activation of the IL-6/STAT3/ALDH1 pathway. Importantly, genetic deletion of A-FABP successfully reduced tumor ALHD1 activation and obesity-associated mammary tumor growth and development in different mouse models. Collectively, these data suggest circulating A-FABP as a new link between obesity and breast cancer risk, thereby revealing A-FABP as a potential new therapeutic target for treatment of obesity-associated cancers.

Thioridazine inhibits self-renewal in breast cancer cells via DRD2-dependent STAT3 inhibition, but induces a G1 arrest independent of DRD2

Thioridazine is an antipsychotic that has been shown to induce cell death and inhibit self-renewal in a broad spectrum of cancer cells. The mechanisms by which these effects are mediated are currently unknown but are presumed to result from the inhibition of dopamine receptor 2 (DRD2). Here we show that the self-renewal of several, but not all, triple-negative breast cancer cell lines is inhibited by thioridazine. The inhibition of self-renewal by thioridazine in these cells is mediated by DRD2 inhibition. Further, we demonstrate that DRD2 promotes self-renewal in these cells via a STAT3- and IL-6-dependent mechanism. We also show that thioridazine induces a G1 arrest and a loss in cell viability in all tested cell lines. However, the reduction in proliferation and cell viability is independent of DRD2 and STAT3. Our results indicate that although there are cell types in which DRD2 inhibition results in inhibition of STAT3 and self-renewal, the dramatic block in cancer cell proliferation across many cell lines caused by thioridazine treatment is independent of DRD2 inhibition.

Breast cancer stem cell markers CD44 and ALDH1A1 in serum: distribution and prognostic value in patients with primary breast cancer

Background: CD44 and ALDH1 have been recognized as the most widely used markers to identify breast cancer stem cells (BCSCs). However, limited to tissue sample and rare population, BCSCs have always been not easily detected. We aimed to measure CD44 and ALDH1A1 (major contributor to ALDH1 activity) levels in serum and explore the prognostic value in primary breast cancer patients.

Methods: This study included 140 primary breast cancer patients with stage I-III. Serum samples were collected before surgery and stored at -80 degrees. CD44 and ALDH1A1 were measured by chemiluminescent assay.

Results: High serum CD44 levels (≥ 417.4 ng/mL) were correlated with postmenopausal status (P = 0.006), estrogen receptor negativity (P = 0.025), progesterone receptor negativity (P = 0.002) and adjuvant chemotherapy (P = 0.003). The mean serum CD44 levels of luminal group (406.4 ± 68.3 ng/mL) were significantly lower than triple negative group (506.8 ± 175.5 ng/mL) (P < 0.001). There was no correlation between serum ALDH1A1 levels and molecular subtypes. Multivariate analysis revealed that high serum CD44 level (≥ 417.4 ng/mL), was an independent factor for PFS (P = 0.019) and OS (P = 0.008). However, serum ALDH1A1 has no impact on either PFS (P = 0.613) or OS (P = 0.441).

Conclusion: Serum CD44 was an independent prognostic indicator in primary breast cancer. However, serum ALDH1A1 has no impact on survivals and might not be an appropriate candidate to predict prognosis for breast cancer.

Breast cancer stem cells: Features, key drivers and treatment options

The current view is that breast cancer is a stem cell disease characterized by the existence of cancer cells with stem-like features and tumor-initiating potential. These cells are made responsible for tumor dissemination and metastasis. Common therapies by chemotherapeutic drugs fail to eradicate these cells and rather increase the pool of cancer stem cells in tumors, an effect that may increase the likelyhood of recurrence. Fifteen years after the first evidence for a small stem-like subpopulation playing a major role in breast cancer initiation has been published a large body of knowledge has been accumulated regarding the signaling cascades and proteins involved in maintaining stemness in breast cancer. Differences in the stem cell pool size and in mechanisms regulating stemness in the different breast cancer subtypes have emerged. Overall, this knowledge offers new approaches to intervene with breast cancer stem cell activity. New options are particularly needed for the treatment of triple-negative breast cancer subtype, which is particularly rich in cancer stem cells and is also the subtype for which specific therapies are still not available.

Biological processes and signal transduction pathways regulated by the protein methyltransferase SETD7 and their significance in cancer

Protein methyltransferases have been shown to methylate histone and non-histone proteins, leading to regulation of several biological processes that control cell homeostasis. Over the past few years, the histone-lysine N-methyltransferase SETD7 (SETD7; also known as SET7/9, KIAA1717, KMT7, SET7, SET9) has emerged as an important regulator of at least 30 non-histone proteins and a potential target for the treatment of several human diseases. This review discusses current knowledge of the structure and subcellular localization of SETD7, as well as its function as a histone and non-histone methyltransferase. This work also underlines the putative contribution of SETD7 to the regulation of gene expression, control of cell proliferation, differentiation and endoplasmic reticulum stress, which indicate that SETD7 is a candidate for novel targeted therapies with the aim of either stimulating or inhibiting its activity, depending on the cell signaling context.

Highly Tumorigenic Diffuse Large B Cell Lymphoma Cells Are Produced by Coculture with Stromal Cells

BACKGROUND/AIMS

Diffuse large B cell lymphoma (DLBCL) is heterogeneous. We aimed to explore how tumor microenvironment promotes lymphoma cell aggressiveness and heterogeneity.

METHODS

We created a coculture system using human DLBCL cells and mouse bone marrow stromal cells. Proliferative capacity, drug resistance, clonogenicity, and tumorigenicity were compared in lymphoma cells from the coculture system and lymphoma cells cultured alone. Expression of Notch signaling associated genes was evaluated using real-time reverse transcriptase PCR and Western blot.

RESULTS

Lymphoma cells in the coculture system differentiated into a suspended cell group and an adherent cell group. They acquired a stronger proliferative capacity and drug resistance than lymphoma cells cultured alone, and differences existed between the adherent cell and suspended cell groups. The suspended cell group acquired the most powerful clonogenic and tumorigenic potential. However, Notch3 was exclusively expressed in the adherent lymphoma cell group and the use of N-[N-(3, 5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester, an inhibitor of Notch pathway, could abolish the emergence of highly aggressive lymphoma cells.

CONCLUSION

Highly tumorigenic lymphoma cells could be generated by coculture with stromal cells, and it was dependent on Notch3 expression in the adjacent lymphoma cells through interaction with stromal cells.

Mammary Stem Cells and Breast Cancer Stem Cells: Molecular Connections and Clinical Implications

Cancer arises from subpopulations of transformed cells with high tumor initiation and repopulation ability, known as cancer stem cells (CSCs), which share many similarities with their normal counterparts. In the mammary gland, several studies have shown common molecular regulators between adult mammary stem cells (MaSCs) and breast cancer stem cells (bCSCs). Cell plasticity and self-renewal are essential abilities for MaSCs to maintain tissue homeostasis and regenerate the gland after pregnancy. Intriguingly, these properties are similarly executed in breast cancer stem cells to drive tumor initiation, tumor heterogeneity and recurrence after chemotherapy. In addition, both stem cell phenotypes are strongly influenced by external signals from the microenvironment, immune cells and supportive specific niches. This review focuses on the intrinsic and extrinsic connections of MaSC and bCSCs with clinical implications for breast cancer progression and their possible therapeutic applications.