Vitamin D suppresses CD133+/CD44 + cancer stem cell stemness by inhibiting NF-κB signaling and reducing NLRP3 expression in triple-negative breast cancer

BACKGROUND AND OBJECTIVE

This study aims to investigate the role of Vitamin D (VD) in regulating the stemness and survival of CD133+/CD44 + breast cancer stem cells, and to explore the role of NLRP3 in this process.

METHODS

Breast cancer tissues were collected for RXRα and VDR expression analysis. A triple-negative breast cancer cell line was cultured and stem-like cells (CD133 + CD44+) isolated using flow cytometry. These cells were treated with VD, analyzing their stem-like properties, apoptosis and proliferation, as well as P65 nuclear expression and NLRP3 expression. After NLRP3 inflammasome activator treatment, the parameters were reassessed. RXRα and VDR interaction was confirmed using co-immunoprecipitation (CoIP). Finally, a subcutaneous xenograft model of triple-negative breast cancer was treated with VD and subsequently analyzed for stem-like properties, proliferation, apoptosis, and NLRP3 expression levels.

RESULTS

CD133+/CD44 + stem cells expressed high levels of SOX2 and OCT4. VD treatment resulted in a significant decrease in SOX2 and OCT4 expression, fewer sphere-forming colonies, lower proliferation ability, and more apoptosis. Additionally, VD treatment inhibited NF-κB signaling and reduced NLRP3 expression. The NLRP3 activator BMS-986,299 counteracted the effects of VD in vitro. In vivo, VD inhibited the growth of breast cancer stem cells, reducing both tumor volume and weight, and decreased NLRP3, SOX2, and OCT4 expression within tumor tissues.

CONCLUSION

Findings elucidate that VD mediates the modulation of stemness in CD133+/CD44 + breast cancer stem cells through the regulation of NLRP3 expression. The research represents novel insights on the implications for the application of VD in cancer therapies.

Identification of a Notch transcriptomic signature for breast cancer

BACKGROUND

Dysregulated Notch signalling contributes to breast cancer development and progression, but validated tools to measure the level of Notch signalling in breast cancer subtypes and in response to systemic therapy are largely lacking. A transcriptomic signature of Notch signalling would be warranted, for example to monitor the effects of future Notch-targeting therapies and to learn whether altered Notch signalling is an off-target effect of current breast cancer therapies. In this report, we have established such a classifier.

METHODS

To generate the signature, we first identified Notch-regulated genes from six basal-like breast cancer cell lines subjected to elevated or reduced Notch signalling by culturing on immobilized Notch ligand Jagged1 or blockade of Notch by γ-secretase inhibitors, respectively. From this cadre of Notch-regulated genes, we developed candidate transcriptomic signatures that were trained on a breast cancer patient dataset (the TCGA-BRCA cohort) and a broader breast cancer cell line cohort and sought to validate in independent datasets.

RESULTS

An optimal 20-gene transcriptomic signature was selected. We validated the signature on two independent patient datasets (METABRIC and Oslo2), and it showed an improved coherence score and tumour specificity compared with previously published signatures. Furthermore, the signature score was particularly high for basal-like breast cancer, indicating an enhanced level of Notch signalling in this subtype. The signature score was increased after neoadjuvant treatment in the PROMIX and BEAUTY patient cohorts, and a lower signature score generally correlated with better clinical outcome.

CONCLUSIONS

The 20-gene transcriptional signature will be a valuable tool to evaluate the response of future Notch-targeting therapies for breast cancer, to learn about potential effects on Notch signalling from conventional breast cancer therapies and to better stratify patients for therapy considerations.

A polymeric nanocarrier that eradicates breast cancer stem cells and delivers chemotherapeutic drugs

BACKGROUND

Drug nanocarriers can markedly reduce the toxicities and side effects of encapsulated chemotherapeutic drugs in the clinic. However, these drug nanocarriers have little effect on eradicating breast cancer stem cells (BCSCs). Although compounds that can inhibit BCSCs have been reported, these compounds are difficult to use as carriers for the widespread delivery of conventional chemotherapeutic drugs.

METHODS

Herein, we synthesize a polymeric nanocarrier, hyaluronic acid-block-poly (curcumin-dithiodipropionic acid) (HA-b-PCDA), and explore the use of HA-b-PCDA to simultaneously deliver chemotherapeutic drugs and eradicate BCSCs.

RESULTS

Based on molecular docking and molecular dynamics studies, HA-b-PCDA delivers 35 clinical chemotherapeutic drugs. To further verify the drug deliver ability of HA-b-PCDA, doxorubicin, paclitaxel, docetaxel, gemcitabine and camptothecin are employed as model drugs to prepare nanoparticles. These drug-loaded HA-b-PCDA nanoparticles significantly inhibit the proliferation and stemness of BCSC-enriched 4T1 mammospheres. Moreover, doxorubicin-loaded HA-b-PCDA nanoparticles efficiently inhibit tumor growth and eradicate approximately 95% of BCSCs fraction in vivo. Finally, HA-b-PCDA eradicates BCSCs by activating Hippo and inhibiting the JAK2/STAT3 pathway.

CONCLUSION

HA-b-PCDA is a polymeric nanocarrier that eradicates BCSCs and potentially delivers numerous clinical chemotherapeutic drugs.

BRD4/nuclear PD-L1/RelB circuit is involved in the stemness of breast cancer cells

BACKGROUND

Breast cancer (BC) is the most common cancer diagnosed in women worldwide. BC stem cells (BCSCs) have been known to be involved in the carcinogenesis of the breast and contribute to therapeutic resistance. The programmed death-ligand 1 (PD-L1) expression of BC correlated with a poor prognosis. Immunotherapies that target PD-L1 have great potential and have been successful when applied to cancer treatment. However, whether PD-L1 regulates BCSC formation is unknown.

METHODS

BCSCs were enriched by serum-free suspension culture. The properties of BCSCs were examined by mammosphere formation assay, CD44+/Cd24-, aldehyde dehydrogenase (ALDH) assay, CSC marker analysis, and mammosphere growth assay. To elucidate the functions of bromodomain-containing protein 4 (BRD4), nuclear PD-L1, and RelB proteins in the stemness of BCSCs, mammosphere formation was examined using BRD4 inhibitor and degrader, PD-L1 degrader, and RelB inhibitor. The antitumor function of 3',4',7,8-tetrahydroxyflavone (THF), a specific BRD4 inhibitor, was studied through in vivo tumor model and mouse studies, and the protein levels of c-Myc, PD-L1, and RelB were examined in tumor model under THF treatment.

RESULTS

BRD4 was upregulated in breast CSCs and regulates the stemness of BCs. The downregulation of BRD4 using BRD4 PROTAC, ARV-825, and BRD4 inhibitor, (+)-JQ1, inhibits mammosphere formation and reduces the levels of breast CSC markers (CD44+/CD24- and ALDH1), stem cell marker genes, and mammosphere growth. BRD4 inhibitor (JQ1) and degrader (ARV825) downregulate membrane and nuclear fractions of PD-L1 through the inhibition of PD-L1 transcript levels. The knockdown of PD-L1 inhibits mammosphere formation. Verteporfin, a PD-L1 degrader, inhibits the transcripts and protein levels of PD-L1 and downregulates the transcript and protein levels of RelB. Calcitriol, a RelB inhibitor, and the knockdown of RelB using si-RelB regulate mammosphere formation through interleukin-6 (IL-6) expression. THF is a natural product and a potent selective BRD4 inhibitor, inhibits mammosphere formation, and reduces the levels of CD44+/CD24- and mammosphere growth by downregulating c-Myc, PD-L1, and RelB. 3',4',7,8-THF shows tumoricidal activity and increased levels of CD3+CD4+ and CD3+CD8+ T-cells in the tumor and tumor-draining lymph nodes (TDLNs) in the murine tumor model using 4T1 and MC38 cells.

CONCLUSIONS

The results show the first evidence of the essential role of the BRD4/nuclear PD-L1/RelB axis in breast CSC formation. The nuclear PD-L1 regulates RelB, and the RelB/p65 complex induces IL6 and breast CSC formation. Targeting nuclear PD-L1 represents a potential and novel tool for immunotherapies of intractable BC. Video Abstract.

Effects of bromodomain and extra-terminal inhibitor JQ1 and interleukin-6 on breast cancer cells

BACKGROUND

Bromodomain and extra-terminal (BET) proteins are recognized acetylated lysine of histone 4 and act as scaffolds to recruit many other proteins to promoters and enhancers of active genes, especially at the super-enhancers of key genes, driving the transcription process and have been identified as potential therapeutic targets in breast cancer. However, the efficacy of BET inhibitors such as JQ1 in breast cancer therapy is impeded by interleukin-6 (IL-6) through an as-yet-defined mechanism.

METHODS AND RESULTS

We investigated the interplay between IL-6 and JQ1 in MCF-7 and MDA-MB-231 human breast cancer cells. The results demonstrate that the efficacy of JQ1 on the inhibition of cell growth and apoptosis was stronger in MDA-MB-231 cells than in MCF-7 cells. Further, MCF-7 cells, but not MDA-MB-231 cells, exhibited increased expression of CXCR4 following IL-6 treatment. JQ1 significantly reduced CXCR4 surface expression in both cell lines and diminished the effects of IL-6 pre-treatment on MCF-7 cells. While IL-6 suppressed the extension of breast cancer stem cells in MCF-7 cells, JQ1 impeded its inhibitory effect. In MCF-7 cells JQ1 increased the number of senescent cells in a time-dependent manner.

CONCLUSION

Analysis of gene expression indicated that JQ1 and IL-6 synergistically increase SNAIL expression and decrease c-MYC expression in MCF-7 cells. So, the BET proteins are promising, novel therapeutic targets in late-stage breast cancers. BET inhibitors similar to JQ1 show promise as therapeutic candidates for breast cancers, especially when triple-negative breast cancer cells are increased and/or tumor-promoting factors like IL-6 exist in the tumor microenvironment.

Impact of media compositions and culture systems on the immunophenotypes of patient-derived breast cancer cells

BACKGROUND

Heterogeneous tumor cells are thought to be a significant factor in the failure of endocrine therapy in estrogen receptor-positive (ER+) cancers. Culturing patient-derived breast cancer cells (PDBCCs) provides an invaluable tool in pre-clinical and translational research for the heterogeneity of cancer cells. This study aimed to investigate the effects of different media components and culture methods on the BCSC-associated immunophenotypes and gene expression in ER + PDBCCs.

METHODS

Ten patients with ER + breast cancer were employed in this study, six of whom had neoadjuvant chemotherapy and four of whom did not. PDBCCs were isolated by enzymatic methods using collagen I and hyaluronidase. PDBCCs were grown as monolayers in mediums with different compositions and as multicellular spheroid in a suspended condition. Collagen I-coated plate and ultralow attachment plate coated with polymer-X were used for monolayer and spheroid culture. Flow cytometry, immunofluorescent staining, RT-PCR, and RNA-sequencing were employed to examine the immunophenotype and genetic profile of PDBCCs.

RESULTS

More than 95% of PDBCCs sustain EpCAM high/+/fibroblast marker- phenotypes in monolayer conditions by subculturing 3-4 times. A83-01 removal induced senescent cells with high β-galactosidase activity. PDBCCs grown as monolayers were characterized by the majority of cells having an EpCAM+/CD49f + phenotype. Compared to full media in monolayer culture, EGF removal increased EpCAM+/CD49f - phenotype (13.8-fold, p = 0.028), whereas R-spondin removal reduced it (0.8-fold, p = 0.02). A83-01 removal increased EpCAM+/CD24 + phenotype (1.82-fold, p = 0.023) and decreased EpCAM low/-/CD44+/CD24- phenotype (0.45-fold, p = 0.026). Compared to monolayer, spheroid resulted in a significant increase in the population with EpCAM-/CD49+ (14.6-fold, p = 0.006) and EpCAM low/-/CD44+/CD24- phenotypes (4.16-fold, p = 0.022) and ALDH high activity (9.66-fold, p = 0.037). ALDH1A and EMT-related genes were upregulated. In RNA-sequencing analysis between spheroids and monolayers, a total of 561 differentially expressed genes (2-fold change, p < 0.05) were enriched in 27 KEGG pathways including signaling pathways regulating pluripotency of stem cells. In a recurrence-free survival analysis based on the Kaplan-Meier Plotter database of the up-and down-regulated genes identified in spheroids, 15 up-, and 14 down-regulated genes were associated with poor prognosis of breast cancer patients.

CONCLUSION

The media composition and spheroid culture method change in the BCSCs and EMT markers of PDBCCs, implying the importance of defining the media composition and culture method for studying PDBCCs in vitro.

Targeting Breast Cancer Stem Cells

The potential roles of breast cancer stem cells (BCSCs) in tumor initiation and recurrence have been recognized for many decades. Due to their strong capacity for self-renewal and differentiation, BCSCs are the major reasons for poor clinical outcomes and low therapeutic response. Several hypotheses on the origin of cancer stem cells have been proposed, including critical gene mutations in stem cells, dedifferentiation of somatic cells, and cell plasticity remodeling by epithelial-mesenchymal transition (EMT) and the tumor microenvironment. Moreover, the tumor microenvironment, including cellular components and cytokines, modulates the self-renewal and therapeutic resistance of BCSCs. Small molecules, antibodies, and chimeric antigen receptor (CAR)-T cells targeting BCSCs have been developed, and their applications in combination with conventional therapies are undergoing clinical trials. In this review, we focus on the features of BCSCs, emphasize the major factors and tumor environment that regulate the stemness of BCSCs, and discuss potential BCSC-targeting therapies.

Phenazine derivatives attenuate the stemness of breast cancer cells through triggering ferroptosis

Breast cancer stem cells (BCSCs) are positively correlated with the metastasis, chemoresistance, and recurrence of breast cancer. However, there are still no drugs targeting BCSCs in clinical using for breast cancer treatment. Here, we tried to screen out small-molecule compounds targeting BCSCs from the phenazine library established by us before. We focused on the compounds without affecting cell viability and screened out three potential compounds (CPUL119, CPUL129, CPUL149) that can significantly attenuate the stemness of breast cancer cells, as evident by the decrease of stemness marker expression, CD44+/CD24- subpopulation, mammary spheroid-formation ability, and tumor-initiating capacity. Additionally, these compounds suppressed the metastatic ability of breast cancer cells in vitro and in vivo. Combined with the transcriptome sequencing analysis, ferroptosis was shown on the top of the most upregulated pathways by CPUL119, CPUL129, and CPUL149, respectively. Mechanistically, we found that these three compounds could trigger ferroptosis by accumulating and sequestering iron in lysosomes through interacting with iron, and by regulating the expression of proteins (IRP2, TfR1, ferritin) engaged in iron transport and storage. Furthermore, inhibition of ferroptosis rescued the suppression of these three compounds on breast cancer cell stemness. This study suggests that CPUL119, CPUL129, and CPUL149 can specifically inhibit the stemness of breast cancer cells through triggering ferroptosis and may be the potential compounds for breast cancer treatment.

Glycosphingolipids in human embryonic stem cells and breast cancer stem cells, and potential cancer therapy strategies based on their structures and functions

Expression profiles of glycosphingolipids (GSLs) in human embryonic stem cell (hESC) lines and their differentiated embryoid body (EB) outgrowth cells, consisting of three germ layers, were surveyed systematically. Several globo- and lacto-series GSLs were identified in undifferentiated hESCs and during differentiation of hESCs to EB outgrowth cells, and core structure switching of these GSLs to gangliosides was observed. Such switching was attributable to altered expression of key glycosyltransferases (GTs) in GSL biosynthetic pathways, reflecting the unique stage-specific transitions and mechanisms characteristic of the differentiation process. Lineage-specific differentiation of hESCs was associated with further GSL alterations. During differentiation of undifferentiated hESCs to neural progenitor cells, core structure switching from globo- and lacto-series to primarily gangliosides (particularly GD3) was again observed. During differentiation to endodermal cells, alterations of GSL profiles were distinct from those in differentiation to EB outgrowth or neural progenitor cells, with high expression of Gb₄Cer and low expression of stage-specific embryonic antigen (SSEA)-3, -4, or GD3 in endodermal cells. Again, such profile changes resulted from alterations of key GTs in GSL biosynthetic pathways. Novel glycan structures identified on hESCs and their differentiated counterparts presumably play functional roles in hESCs and related cancer or cancer stem cells, and will be useful as surface biomarkers. We also examined GSL expression profiles in breast cancer stem cells (CSCs), using a model of epithelial-mesenchymal transition (EMT)-induced human breast CSCs. We found that GD2 and GD3, together with their common upstream GTs, GD3 synthase (GD3S) and GD2/GM2 synthase, maintained stem cell phenotype in breast CSCs. Subsequent studies showed that GD3 was associated with epidermal growth factor receptor (EGFR), and activated EGFR signaling in breast CSCs and breast cancer cell lines. GD3S knockdown enhanced cytotoxicity of gefitinib (an EGFR kinase inhibitor) in resistant MDA-MB468 cells, both in vitro and in vivo. Our findings indicate that GD3S contributes to gefitinib resistance in EGFR-positive breast cancer cells, and is a potentially useful therapeutic target in drug-resistant breast cancers.

ER+ Breast Cancer Mammosphere Formation and Analysis

Mammosphere formation assays are a popular and convenient technique in the study of breast cancer by providing an in vitro mechanism by which to study breast cancer stem cell (BCSC) contribution to tumorigenesis, as well as more closely mimicking the three-dimensional tumor microenvironment. In these assays, BCSCs are stimulated to proliferate in low adherence tissue culture dishes and the resulting mammospheres exhibit activation of stem cell-related signaling pathways. Here we describe the process for generating and analyzing mammospheres under varying conditions.

Heterogeneity of BCSCs contributes to the metastatic organotropism of breast cancer

Breast cancer is one of the most-common female malignancies with a high risk of relapse and distant metastasis. The distant metastasis of breast cancer exhibits organotropism, including brain, lung, liver and bone. Breast cancer stem cells (BCSCs) are a small population of breast cancer cells with tumor-initiating ability, which participate in regulating distant metastasis in breast cancer. We investigated the heterogeneity of BCSCs according to biomarker status, epithelial or mesenchymal status and other factors. Based on the classical “seed and soil” theory, we explored the effect of BCSCs on the metastatic organotropism in breast cancer at both “seed” and “soil” levels, with BCSCs as the “seed” and BCSCs-related microenvironment as the “soil”. We also summarized current clinical trials, which assessed the safety and efficacy of BCSCs-related therapies. Understanding the role of BCSCs heterogeneity for regulating metastatic organotropism in breast cancer would provide a new insight for the diagnosis and treatment of advanced metastatic breast cancer.

Mineralized and GSH-responsive hyaluronic acid based nano-carriers for potentiating repressive effects of sulforaphane on breast cancer stem cells-like properties

Breast cancer stem cell (BCSC) properties are correlated with the malignancy of tumor cells. Sulforaphane (SFN), a natural isothiocyanate, has anti-cancer effects. However, SFN is an oil-like, hydrophobic and unstable substance. To enhance the inhibitory effect of SFN on BCSC-like properties, the mineralized hyaluronic acid-SS-tetradecyl nano-carriers (M-HA-SS-TA) were prepared. The nano-carriers possessed high SFN entrapment rate (92.36%) and drug-loading efficiency (33.64%). The carriers were responsive to the high reducing and mild acidic tumor micro-environment, leading to rapid SFN releasing from SFN-loaded nano-drug (SFN/M-HA-SS-TA). Through the specific recognition of breast cancer cells bearing CD44+ by HA, M-HA-SS-TA nano-carriers showed excellent tumor-targeting ability. Moreover, compared with free SFN, SFN/M-HA-SS-TA showed much stronger inhibition on the BCSC-like properties (invasiveness, self-renewal and tumor growth) both in vitro and in vivo. Together, these results suggested M-HA-SS-TA nano-carriers were promising platforms for tumor-targeted delivery of SFN, enhancing the therapeutic efficacy against BCSC-like properties by SFN.

Camalexin, an indole phytoalexin, inhibits cell proliferation, migration, and mammosphere formation in breast cancer cells via the aryl hydrocarbon receptor

Breast cancer is the most commonly diagnosed cancer among women worldwide. Despite a variety of drugs available for the treatment of patients with breast cancer, drug resistance remains a significant clinical problem. Therefore, there is an urgent need to develop drugs with new mechanisms of action. Camalexin is the main indole phytoalexin in Arabidopsis thaliana and other crucifers. Camalexin inhibits the proliferation of various cancer cells. However, the mechanism by which camalexin inhibits cell proliferation remains unclear. In this study, we found that camalexin inhibited cell proliferation and migration of breast cancer cell lines. Furthermore, camalexin also suppressed breast cancer stem cell-derived mammosphere formation. We previously reported that the ligand-activated transcription factor aryl hydrocarbon receptor (AhR) agonist suppresses mammosphere formation. Several compounds with indole structures are known to act as AhR agonists. Therefore, we hypothesized that the inhibition of mammosphere formation by camalexin may involve AhR activation. We found that camalexin increased the nuclear translocation of AhR, AhR-mediated transcriptional activation, and expression of AhR target genes. In addition, camalexin suppressed mammosphere formation in AhR-expressing breast cancer cells more than in the breast cancer cells that lacked AhR expression. Taken together, the data demonstrate that camalexin is a novel AhR agonist and that the inhibition of cell proliferation, migration, and mammosphere formation by camalexin involves the activation of AhR. Our findings suggest that camalexin, an AhR agonist, may be a novel therapeutic agent for breast cancer.

Hopea odorata Extract Can Efficiently Kill Breast Cancer Cells and Cancer Stem-Like Cells in Three-Dimensional Culture More Than in Monolayer Cell Culture

INTRODUCTION

The breast cancer cells with CD44⁺CD24^- phenotype are known to play an important role in tumorigenesis, drug resistance, and cancer recurrence. Breast cancer cells with CD44⁺CD24^- phenotype are cultured in three-dimensional (3D) stereotype showing the recapitulation of tumors in vivo such as cell differentiation, heterogeneity, and microenvironment. Using this 3D model in anti-cancer compound research results in a more accurate reflection than conventional monolayer cell culture. This study aimed to identify the antitumor activity of Hopea odorata methanol extract (HO-MeOH-E) on breast cancer cells and cancer stem-like cells in both models of three-dimensional culture (3D) and monolayer cell culture (2D).

METHODS

HO-MeOH-E was produced from Hopea odorata plant. The VN9 breast cancer cells (VN9) were collected and expanded from the previous study. The breast cancer stem-like cells (VN9CSC) were sorted from the VN9 based on phenotype CD44⁺CD24^-. Both VN9 and VN9CSC were used to culture in monolayer culture (2D) and organoids (3D) before they were used to treat with HO-MeOH-E. Two other anticancer drugs, doxorubicin and tirapazamine, were used as references. The antitumor activities of extracts and drugs were determined via two assays: antiproliferation using the Alamar blue assay and cell cycle assay.

RESULTS

The results showed that HO-MeOH-E was sensitive to both VN9 and VN9CSC in 3D more than 2D culture (IC₅₀ on 3D organoids 144.8 ± 2.172 μg/mL and on 2D 340.2 ± 17.01 μg/mL for VN9CSC (p < 0.001); IC₅₀ on 3D organoids 2055 ± 82.2 μg/mL and on 2D 430.6 ± 8.612 μg/mL for VN9 (p < 0.0001), respectively). HO-MeOH-E inhibits VN9CSC proliferation by blocking S phase and increasing the populations of apoptotic cells; this is consensus to the effect of tirapazamine (TPZ) which is used in hypoxia-activated chemotherapy.

CONCLUSION

Taken these results, HO-MeOH-E has the potential effect in hypoxia-activated chemotherapy specifically on breast cancer stem-like cells with CD44⁺CD24^- phenotype.

Breast cancer stem cells, heterogeneity, targeting therapies and therapeutic implications

Both hereditary and sporadic breast cancer are suggested to develop from a stem cell subcomponent retaining most key stem cell properties but with dysregulation of self-renewal pathways, which drives tumorigenic differentiation and cellular heterogeneity. Cancer stem cells (CSCs), characterized by their self-renewal and differentiation potential, have been reported to contribute to chemo-/radio-resistance and tumor initiation and to be the main reason for the failure of current therapies in breast cancer and other CSC-bearing cancers. Thus, CSC-targeted therapies, such as those inducing CSC apoptosis and differentiation, inhibiting CSC self-renewal and division, and targeting the CSC niche to combat CSC activity, are needed and may become an important component of multimodal treatment. To date, the understanding of breast cancer has been extended by advances in CSC biology, providing more accurate prognostic and predictive information upon diagnosis. Recent improvements have enhanced the prospect of targeting breast cancer stem cells (BCSCs), which has shown promise for increasing the breast cancer remission rate. However, targeted therapy for breast cancer remains challenging due to tumor heterogeneity. One major challenge is determining the CSC properties that can be exploited as therapeutic targets. Another challenge is identifying suitable BCSC biomarkers to assess the efficacy of novel BCSC-targeted therapies. This review focuses mainly on the characteristics of BCSCs and the roles of BCSCs in the formation, maintenance and recurrence of breast cancer; self-renewal signaling pathways in BCSCs; the BCSC microenvironment; potential therapeutic targets related to BCSCs; and current therapies and clinical trials targeting BCSCs.

SETDB2 promoted breast cancer stem cell maintenance by interaction with and stabilization of ΔNp63α protein

The histone H3K9 methyltransferase SETDB2 is involved in cell cycle dysregulation in acute leukemia and has oncogenic roles in gastric cancer. In our study, we found that SETDB2 plays essential roles in breast cancer stem cell maintenance. Depleted SETDB2 significantly decreased the breast cancer stem cell population and mammosphere formation in vitro and also inhibited breast tumor initiation and growth in vivo. Restoring SETDB2 expression rescued the defect in breast cancer stem cell maintenance. A mechanistic analysis showed that SETDB2 upregulated the transcription of the ΔNp63α downstream Hedgehog pathway gene. SETDB2 also interacted with and methylated ΔNp63α, and stabilized ΔNp63α protein. Restoring ΔNp63α expression rescued the breast cancer stem cell maintenance defect which mediated by SETDB2 knockdown. In conclusion, our study reveals a novel function of SETDB2 in cancer stem cell maintenance in breast cancer.

β1,4-Galactosyltransferase V Modulates Breast Cancer Stem Cells through Wnt/β-catenin Signaling Pathway

PURPOSE

Breast cancer stem cells (BCSCs) contribute to the initiation, development, and recurrence of breast carcinomas. β1,4-Galactosyltransferase V (B4GalT5), which catalyzes the addition of galactose to GlcNAcβ1-4Man of N-glycans, is involved in embryogenesis. However, its role in the modulation of BCSCs remains unknown.

Materials and Methods

The relationship between B4GalT5 and breast cancer stemness was investigated by online clinical databases and immunohistochemistry analysis. Mammosphere formation, fluorescence-activated cell sorting (FACS), and in-vivo assays were used to evaluate B4GalT5 expression in BCSCs and its effect on BCSCs. B4GalT5 regulation of Wnt/β-catenin signaling was examined by immunofluorescence and Ricinus communis agglutinin I pull-down assays. Cell surface biotinylation and FACS assays were performed to assess the association of cell surface B4GalT5 and BCSCs.

RESULTS

B4GalT5, but not other B4GalTs, was highly correlated with BCSC markers and poor prognosis. B4GalT5 significantly increased the stem cell marker aldehyde dehydrogenase 1A1 (ALDH1A1) and promoted the production of CD44+CD24-/low cells and the formation of mammospheres. Furthermore, B4GalT5 overexpression resulted in dramatic tumor growth in vivo. Mechanistically, B4GalT5 modified and protected Frizzled-1 from degradation via the lysosomal pathway, promoting Wnt/β-catenin signaling which was hyperactivated in BCSCs. B4GalT5, located on the surface of a small subset of breast carcinoma cells, was not responsible for the stemness of BCSCs.

CONCLUSION

B4GalT5 modulates the stemness of breast cancer through glycosylation modification to stabilize Frizzled-1 and activate Wnt/β-catenin signaling independent of its cell surface location. Our studies highlight a previously unknown role of B4GalT5 in regulating the stemness of breast cancer and provide a potential drug target for anticancer drug development.

Valproic acid, a histone deacetylase inhibitor, induces apoptosis in breast cancer stem cells

Cancer stem-like cells (CSCs) are a cell subpopulation that can reinitiate tumors, resist chemotherapy, give rise to metastases and lead to disease relapse because of an acquired resistance to apoptosis. Especially, epigenetic alterations play a crucial role in the regulation of stemness and also have been implicated in the development of drug resistance. Hence, in the present study, we examined the cytotoxic and apoptotic activity of valproic acid (VPA) as an inhibitor of histone deacetylases (HDACs) against breast CSCs (BCSCs). Increased expression of stemness markers were determined by western blotting in mammospheres (MCF-7s, a cancer stem cell-enriched population) propagated from parental MCF-7 cells. Anti-growth activity of VPA was determined via ATP viability assay. The sphere formation assay (SFA) was performed to assess the inhibitory effect of VPA on the self-renewal capacity of MCF-7s cells. Acetylation of histon H3 was detected with ELISA assay. Cell death mode was performed by Hoechst dye 33342 and propidium iodide-based flouresent stainings (for pyknosis and membrane integrity), by M30 and M65 ELISA assays (for apoptosis and primary or secondary necrosis) as well as cytofluorimetric analysis (caspase 3/7 activity and annexin-V-FITC staining for early and late stage apoptosis). VPA exhibited anti-growth effect against both MCF-7 and MCF-7s cells in a dose (0.6-20 mM) and time (24, 48, 72 h) dependent manner. As expected, MCF-7s cells were found more resistant to VPA than MCF-7 cells. It was observed that VPA prevented mammosphere formation at relatively lower doses (2.5 and 5 mM) while the acetylation of histon H3 was increased. At the same doses, VPA increased the M30 levels, annexin-V-FITC positivity and caspase 3/7 activation, implying the induction of apoptosis. The secondary necrosis (late stage of apoptosis) was also evidenced by nuclear pyknosis with propidium iodide staining positivity. Taken together, inhibition of HDACs is cytotoxic to BCSCs by apoptosis. Our results suggested that targeting the epigenetic regulation of histones may be a novel approach and hold significant promise for successful treatment of breast cancer.

Perspectives of Reprogramming Breast Cancer Metabolism

Reprogramming of cellular metabolism is one of the hallmarks of breast cancer. Breast cancer cells remodel metabolic network to maintain their transformed state and survive in a harsh tumor microenvironment. Dysregulated metabolism further interacts with cellular signaling and epigenetics to promote breast cancer development. Meanwhile, breast cancer stem cells exhibit unique metabolic features, which are critical for therapeutic resistance and tumor recurrence. Besides, aberrant metabolism of breast cancer cells reshapes tumor microenvironment, such as promoting cancer vascularization and sabotaging tumor immunity, to accelerate tumor progression. These special metabolic traits not only open vulnerabilities of breast cancer by targeting essential metabolic pathways but also provide promising diagnostic and prognostic biomarkers to facilitate clinical investigations. Studies in the last few decades have significantly advanced our understanding of mechanisms underlying the reprogramming of breast cancer metabolism and metabolic regulation of breast cancer biology. Targeting tumor metabolism serves as a potentially effective therapeutic approach to suppress breast cancer.

Anti-invasion Effects of Cannabinoids Agonist and Antagonist on Human Breast Cancer Stem Cells

Studies show that cancer cell invasion or metastasis is the primary cause of death in malignancies including breast cancer. The existence of cancer stem cells (CSCs) in breast cancer may account for tumor initiation, progression, and metastasis. Recent studies have reported different effects of cannabinoids on cancer cells via CB1 and CB2 cannabinoid receptors. In the present study, the effects of ACEA (a selective CB1 receptor agonist) and AM251 (a selective CB1 antagonist) on CSCs and their parental cells were investigated. Breast CSCs derived from MDA-MB-231 cell line were sorted and characterized with CD44⁺/CD24^-/low/ESA⁺ phenotype. It was observed that ACEA decreased CD44⁺/CD24^-/low/ESA⁺ cancer stem cell invasiveness. Conversely, AM251 increased the invasion by more than 20% (at the highest concentrations) in both MDA-MB-231 and CSCs. Our results did not show any correlation between reduced invasion and cytotoxic effects of the drug. Since one of the main cancer recurrence factors is anti-cancer drugs fail to inhibit CSC population, this observation would be useful for cancer treatment.

High-content cell death imaging using quantum dot-based TIRF microscopy for the determination of anticancer activity against breast cancer stem cell

We report a two color monitoring of drug-induced cell deaths using total internal reflection fluorescence (TIRF) as a novel method to determine anticancer activity. Instead of cancer cells, breast cancer stem cells (CSCs) were directly tested in the present assay to determine the effective concentration (EC₅₀ ) values of camptothecin and cisplatin. Phosphatidylserine and HMGB1 protein were concurrently detected to observe apoptotic and necrotic cell death induced by anticancer drugs using quantum dot (Qdot)-antibody conjugates. Only 50-to-100 breast CSCs were consumed at each cell chamber due to the high sensitivity of Qdot-based TIRF. The high sensitivity of Qdot-based TIRF, that enables the consumption of a small number of cells, is advantageous for cost-effective large-scale drug screening. In addition, unlike MTT assay, this approach can provide a more uniform range of EC₅₀ values because the average values of single breast CSCs fluorescence intensities are observed to acquire EC₅₀ values as a function of dose. This research successfully demonstrated the possibility that Qdot-based TIRF can be widely used as an improved alternative to MTT assay for the determination of anticancer drug efficacies.

Transcriptome sequencing of HER2-positive breast cancer stem cells identifies potential prognostic marker

In cancer stem cell theory, breast cancer stem cells (BCSCs) are postulated to be the root cause of recurrence and metastasis in breast cancer. Discovery of new biomarkers and development of BCSC-targeted therapy are practical issues that urgently need to be addressed in the clinic. However, few breast cancer stem cell targets are known. Given that there are few BCSCs, performing transcriptome sequencing on them thus far has not been possible. With the emergence of single-cell sequencing technology, we have now undertaken such a study. We prepared single-cell suspensions, which were sorted using flow cytometry from breast tumor tissue and adjacent normal breast tissue from two HER2-positive patients. We obtained BCSCs, breast cancer cells, mammary cells, and CD44⁺ mammary cells. Transcriptome sequencing was then performed on these four cell types. Using bioinformatics, we identified 404 differentially expressed BCSC genes from the HER2-positive tumors and preliminary explored transcriptome characteristics of BCSCs. Finally, by querying a public database, we found that CA12 was a novel prognostic biomarker in HER2-positive breast cancer, which also had prognostic value in all breast cancer types. In conclusion, our results suggest that CA12 may be associated with BCSCs, especially HER2-positive BCSCs, and is a potential novel therapeutic target and biomarker.

Prognostic Value of a BCSC-associated MicroRNA Signature in Hormone Receptor-Positive HER2-Negative Breast Cancer

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Biology-driven strategy can be used in development of prognostic model.

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The BCSC-associated miRNA classifier can predict prognosis for HR + HER2 − breast cancer.

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The BCSC-associated miRNA classifier outperforms IHC4 scoring and 21-gene RS.

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Chemotherapy can improve DRFS in patients predicted as high-risk.

Breast cancer patients with high proportion of cancer stem cells (BCSCs) have poor clinical outcomes. MiRNAs regulate key features of BCSCs as oncogenes or tumor suppressors. Although hormone receptor (HR)-positive, HER2-negative breast cancers are the most common subtype, current methods are inadequate to predict its clinical outcome. In this multicenter study, we identified and validated a 10 BCSC-associated-miRNA classifier that can predict survival for HR + HER2 − patients. Retrospective analysis showed that this classifier outperformed IHC4 scoring and 21-gene Recurrence Score (RS), and chemotherapy could improve survival in high-risk patients determined by this classifier. This model may facilitate personalized clinical decision for HR + HER2 − individuals.

Purpose

Breast cancer patients with high proportion of cancer stem cells (BCSCs) have unfavorable clinical outcomes. MicroRNAs (miRNAs) regulate key features of BCSCs. We hypothesized that a biology-driven model based on BCSC-associated miRNAs could predict prognosis for the most common subtype, hormone receptor (HR)-positive, HER2-negative breast cancer patients.

Patients and Methods

After screening candidate miRNAs based on literature review and a pilot study, we built a miRNA-based classifier using LASSO Cox regression method in the training group (n = 202) and validated its prognostic accuracy in an internal (n = 101) and two external validation groups (n = 308).

Results

In this multicenter study, a 10-miRNA classifier incorporating miR-21, miR-30c, miR-181a, miR-181c, miR-125b, miR-7, miR-200a, miR-135b, miR-22 and miR-200c was developed to predict distant relapse free survival (DRFS). With this classifier, HR + HER2 − patients were scored and classified into high-risk and low-risk disease recurrence, which was significantly associated with 5-year DRFS of the patients. Moreover, this classifier outperformed traditional clinicopathological risk factors, IHC4 scoring and 21-gene Recurrence Score (RS). The patients with high-risk recurrence determined by this classifier benefit more from chemotherapy.

Conclusions

Our 10-miRNA-based classifier provides a reliable prognostic model for disease recurrence in HR + HER2 − breast cancer patients. This model may facilitate personalized therapy-decision making for HR + HER2 − individuals.

Downregulation of CXCR7 inhibits proliferative capacity and stem cell-like properties in breast cancer stem cells

Breast cancer stem cells (bCSCs) are considered an obstacle in breast cancer therapy because they exhibit long-term proliferative potential, phenotypic plasticity and high resistance to the current therapeutics. CXC chemokine receptor type 7 (CXCR7), which provides a growth advantage to breast cancer cells, has recently been demonstrated to play an important role in the maintenance of stem cell-like properties in the CSCs of glioblastoma and lung cancer, yet its role in bCSCs remains elusive. In this study, CD44⁺/CD24^low bCSC-enriched cells (bCSCs for short) were isolated from MCF-7 cells, and CXCR7 was stably knocked down in bCSCs via lentivirus-mediated transduction with CXCR7 short hairpin RNA (shRNA). Knockdown of CXCR7 in bCSCs decreased the proportion of CD44⁺/CD24^low cells, and markedly reduced the clonogenicity of the cells. Moreover, silencing of CXCR7 downregulated the expression of stem cell markers, such as aldehyde dehydrogenase 1 (ALDH1), Oct4, and Nanog. In addition, CXCR7 silencing in bCSCs suppressed cell proliferation and G1/S transition in vitro, and delayed tumor growth in vivo in a xenograft mouse model. In situ immunohistochemical analysis revealed a reduction in Ki-67 expression and enhanced apoptosis in the xenograft tumors as a result of CXCR7 silencing. Furthermore, combined treatment with CXCR7 silencing and epirubicin displayed an outstanding anti-tumor effect compared with either single treatment. Our study demonstrates that CXCR7 plays a critical role in the maintenance of stem cell-like properties and promotion of growth in bCSCs, and suggests that CXCR7 may be a candidate target for bCSCs in breast cancer therapy.

MicroR-760 suppresses cancer stem cell subpopulation and breast cancer cell proliferation and metastasis: By down-regulating NANOG

BACKGROUND AND OBJECTIVE

Emerging evidences suggest that cancer stem cells are responsible for tumor aggressive, metastasis and therapeutic resistance. To data, the mechanism underlying breast cancer stem cell (BCSC) population within tumor metastasis remains to be fully elucidated. The current study was to investigate the potential role of microRNA-760 (miR-760) and its associated target gene in population and metastasis of BCSC.

METHODS

Characteristic BCSCs surface markers (CD44(+)/CD24(-/low)) were determined by flow cytometry in breast cancer MCF-7 and BT-549 cells. Quantitative RT-PCR was used to evaluate miR-760 and NANOG mRNA expression. Expression of NANOG protein was determined using western blot. Cell proliferation was determined by MTT assay. The model of breast cancer cell xenograft was used to evaluate the effect of miR-760 on tumor growth.

RESULTS

BT-549 cell has substantially more CD44(+)/CD24(-/low) subpopulation than MCF-7 cell. Moreover, BT-549 cell expressed lower level of miR-760 and higher level of NANOG than MCF-7cell. By result from cellular miR-760 modulation, we found that miR-760 overexpression suppressed CD44(+)/CD24(-/low) population as well as inhibited cell proliferation and migration of BT-549. On the contrary, knockdown of miR-760 promoted CD44(+)/CD24(-/low) population and migration of MCF-7 cells. By luciferase reporter assay, miR-760 was proved to be functional associated with NANOG via regulating its expression. This functional interaction was showed to be involved in controlling proliferation and migration of MCF-7 and BT-549 cell.

CONCLUSION

These data suggest that the target of miR-760/NANOG axis may represent a new therapeutic approach to suppress breast cancer stem cell subpopulation thereby prevent cancer metastasis.

Kazinol-E is a specific inhibitor of ERK that suppresses the enrichment of a breast cancer stem-like cell population

Growing evidence shows that cancer stem-like cells (CSLCs) contribute to breast cancer recurrence and to its resistance to conventional therapies. The extracellular signal-regulated kinase (ERK) signaling pathway is a major determinant in the control of diverse cellular processes, including the maintenance of CSLCs. In this study, we found that Kazinol-E, an antioxidant flavan from Broussonetia kazinoki, decreased the CSLC population of a breast cancer cell line, MCF7. The CSLC population, characterized by CD44 high/CD24 low expression or by high Aldehyde dehydrogenase 1 activity, was decreased by a concentration of Kazinol-E that did not affect the growth of bulk-cultured MCF7 cells. Kazinol-E did not decrease EGF-induced ERK phosphorylation in CSLCs, but did block the phosphorylation of an ERK substrate, p90RSK2, at Thr359/Ser363. We further demonstrated that EGF-induced ERK activity was blocked by Kazinol-E in a wild-type K-Ras-expressing non-small cell lung cancer cell line H226B. An in vitro kinase assay with purified ERK1 and p90RSK2 as its substrate demonstrated a direct inhibition of ERK activity by Kazinol E. Additionally, a the molecular docking study provided putative binding modes of Kazinol-E into the ATP binding pocket of ERK1 Collectively, these results suggest that Kazinol-E is a direct inhibitor of ERK1, and more studies are warranted to develop this reagent for therapeutic breast CSLC targeting.

ALDH(+)/CD44(+) cells in breast cancer are associated with worse prognosis and poor clinical outcome

BACKGROUND

Breast cancer stem cells (BCSCs) play essential roles in tumor metastasis and contribute to remarkably negative clinical outcomes. Recently, aldehyde dehydrogenase (ALDH) and CD44 positivity (ALDH(+)/CD44(+)) was identified as a marker of BCSCs in vitro/in vivo studies. The aim of this study was to evaluate the prevalence of ALDH(+)/CD44(+) cells in breast cancer and the association of these two markers with clinicopathological features and clinical outcomes.

MATERIALS AND METHODS

We investigated the prevalence of ALDH1A3(+)/CD44(+) cells in a cohort of 144 formalin-fixed, paraffin-embedded (FFPE) breast cancer tissues. The tissues were stained for ALDH1A3 and CD44 by single and dual immunohistochemistry (dIHC). The associations among the prevalence of ALDH1A3(+)/CD44(+) cells, the clinicopathological features and the clinical outcomes of the patients were also analyzed.

RESULTS

ALDH1A3(+)/CD44(+) cells were present in 39 patients (27.1%). By the Mann-Whitney U test, the Pearson Chi-square test or Fisher's exact test, it was demonstrated that the prevalence of ALDH1A3(+)/CD44(+) cells was closely correlated with larger tumor size (p=0.001), nodal metastasis status (p=0.043), more advanced clinical stage (p=0.021) and distant metastasis after initial surgery (p=0.001). In a univariate survival analysis, the presence of ALDH1A3(+)/CD44(+) tumor cells had a significant negative association with both disease-free survival (DFS) and overall survival (OS) (pDFS<0.001; pOS<0.001). The negative clinical outcomes in ALDH1A3(+)/CD44(+) tumors were further confirmed by a multivariate analysis using Cox proportional hazard models (pDFS<0.001, HR=3.155; pOS=0.001, HR=3.193). This was also true with respect to the clinical treatment regimens of chemotherapy (pDFS<0.001; pOS=0.001), radiotherapy (pDFS=0.004; pOS=0.004), and endocrine therapy (pDFS<0.001; pOS<0.001).

CONCLUSION

In summary, our results indicate that the prevalence of ALDH1A3(+)/CD44(+) tumor cells in breast cancer is significantly associated with worse prognostic factors and favors a poor prognosis.

SLUG and SOX9 Cooperatively Regulate Tumor Initiating Niche Factors in Breast Cancer

Presence of tumor initiating cells and a proper niche is essential for metastatic colonization. SLUG and SOX9 transcription factors play essential roles in induction and maintenance of tumor initiating capacity in breast cancer cells. On the other hand, Tenascin-C and Periostin are crucial factors in metastatic niche that support tumor initiating capability in breast cancer. In this study, regulatory effect of SLUG and SOX9 transcription factors on the expression of Tenascin-C and Periostin was examined. SLUG and SOX9 were overexpressed and knocked-down in MCF7 and MDA-MB-231 cells, respectively. The cells as little and highly invasive breast cancer-derived cells were infected by inducing and shRNA lentivirus constructs. Then, Tenascin-C and Periostin as well as SLUG and SOX9 expression levels were measured in the cells via Real-Time PCR. Simultaneous overexpression of SLUG and SOX9 significantly induced Tenascin-C and Periostin expression. SLUG and SOX9 knock-down also significantly reduced the expression of Tenascin-C and Periostin. In this analysis Periostin showed the most deviation in both up- and down-regulation levels. This regulatory effect might shed light to a crosstalk between factors involved in the tumor initiating capacity and metastatic niche of the breast cancer.

MicroRNA-34a suppresses the breast cancer stem cell-like characteristics by downregulating Notch1 pathway

MicroRNAs play pivotal roles in cancer stem cell regulation. Previous studies have shown that microRNA-34a (miR-34a) is downregulated in human breast cancer. However, it is unknown whether and how miR-34a regulates breast cancer stem cells. Notch signaling is one of the most important pathways in stem cell maintenance and function. In this study, we verified that miR-34a directly and functionally targeted Notch1 in MCF-7 cells. We reported that miR-34a negatively regulated cell proliferation, migration, and invasion and breast cancer stem cell propagation by downregulating Notch1. The expression of miR-34a was negatively correlated with tumor stages, metastasis, and Notch1 expression in breast cancer tissues. Furthermore, overexpression of miR-34a increased chemosensitivity of breast cancer cells to paclitaxel (PTX) by downregulating the Notch1 pathway. Mammosphere formation and expression of the stemness factor ALDH1 were also reduced in the cells treated with miR-34a and PTX compared to those treated with PTX alone. Taken together, our results indicate that miR-34a inhibited breast cancer stemness and increased the chemosensitivity to PTX partially by downregulating the Notch1 pathway, suggesting that miR-34a/Notch1 play an important role in regulating breast cancer stem cells. Thus miR-34a is a potential target for prevention and therapy of breast cancer.

A novel peptide-based recognition probe for the sensitive detection of CD44 on breast cancer stem cells

Metastasis and recurrence of breast cancer remain significant clinical problems. The expression level of CD44 protein is higher in breast cancer-initiating cancer stem cells; therefore, the early detection of CD44 using a sensitive diagnostic probe is important for breast cancer diagnosis and therapeutic purposes. In this study, we fabricated a polyvalent directed peptide polymer (PDPP) that specifically recognized the CD44 biomarker, as confirmed by immunocytochemistry tests and fluorescence-activated cell sorting assessment. Our results indicate that PDPP is useful as a novel tool for the sensitive detection of breast cancer stem cells.

Sunitinib significantly suppresses the proliferation, migration, apoptosis resistance, tumor angiogenesis and growth of triple-negative breast cancers but increases breast cancer stem cells

The majority of triple-negative breast cancers (TNBCs) are basal-like breast cancers. However there is no reported study on anti-tumor effects of sunitinib in xenografts of basal-like TNBC (MDA-MB-468) cells. In the present study, MDA-MB-231, MDA-MB-468, MCF-7 cells were cultured using RPMI 1640 media with 10% FBS. Vascular endothelia growth factor (VEGF) protein levels were detected using ELISA (R & D Systams). MDA-MB-468 cells were exposed to sunitinib for 18 hours for measuring proliferation (3H-thymidine incorporation), migration (BD Invasion Chamber), and apoptosis (ApopTag and ApoScreen Anuexin V Kit). The effect of sunitinib on Notch-1 expression was determined by Western blot in cultured MDA-MB-468 cells. 10⁶ MDA-MB-468 cells were inoculated into the left fourth mammary gland fat pad in athymic nude-foxn1 mice. When the tumor volume reached 100 mm³, sunitinib was given by gavage at 80 mg/kg/2 days for 4 weeks. Tumor angiogenesis was determined by CD31 immunohistochemistry. Breast cancer stem cells (CSCs) isolated from the tumors were determined by flow cytometry analysis using CD44⁺/CD24^- or low. ELISA indicated that VEGF was much more highly expressed in MDA-MB-468 cells than MDA-MB-231 and MCF-7 cells. Sunitinib significantly inhibited the proliferation, invasion, and apoptosis resistance in cultured basal like breast cancer cells. Sunitinib significantly increased the expression of Notch-1 protein in cultured MDA-MB-468 or MDA-MB-231 cells. The xenograft models showed that oral sunitinib significantly reduced the tumor volume of TNBCs in association with the inhibition of tumor angiogeneisis, but increased breast CSCs. These findings support the hypothesis that the possibility should be considered of sunitinib increasing breast CSCs though it inhibits TNBC tumor angiogenesis and growth/progression, and that effects of sunitinib on Notch expression and hypoxia may increase breast cancer stem cells. This work provides the groundwork for an innovative therapeutic strategy in TNBC therapy by using sunitinib plus γ-secretase inhibitor to simultaneously target angiogenesis and CSC.

Engineering anti-GD2 monoclonal antibodies for cancer immunotherapy

Ganglioside GD2 is highly expressed on neuroectoderm-derived tumors and sarcomas, including neuroblastoma, retinoblastoma, melanoma, small cell lung cancer, brain tumors, osteosarcoma, rhabdomyosarcoma, Ewing's sarcoma in children and adolescents, as well as liposarcoma, fibrosarcoma, leiomyosarcoma and other soft tissue sarcomas in adults. Since GD2 expression in normal tissues is restricted to the brain, which is inaccessible to circulating antibodies, and in selected peripheral nerves and melanocytes, it was deemed a suitable target for systemic tumor immunotherapy. Anti-GD2 antibodies have been actively tested in clinical trials for neuroblastoma for over the past two decades, with proven safety and efficacy. The main limitations have been acute pain toxicity associated with GD2 expression on peripheral nerve fibers and the inability of antibodies to treat bulky tumor. Several strategies have been developed to reduce pain toxicity, including bypassing complement activation, using blocking antibodies, or targeting of O-acetyl-GD2 derivative that is not expressed on peripheral nerves. To enhance anti-tumor efficacy, anti-GD2 monoclonal antibodies and fragments have been engineered into immunocytokines, immunotoxins, antibody drug conjugates, radiolabeled antibodies, targeted nanoparticles, T-cell engaging bispecific antibodies, and chimeric antigen receptors. The challenges of these approaches will be reviewed to build a perspective for next generation anti-GD2 therapeutics in cancer therapy.