Breast cancer stem-like cells: clinical implications and therapeutic strategies

Recent developments in targeting breast cancer stem cells (BCSCs): a descriptive review of therapeutic strategies and emerging therapies

Despite recent advancements in the diagnosis and treatment of breast cancer (BC), patient outcomes in terms of survival, recurrence, and disease progression remain suboptimal. A significant factor contributing to these challenges is the cellular heterogeneity within BC, particularly the presence of breast cancer stem cells (BCSCs). These cells are thought to serve as the clonogenic nexus for new tumor growth, owing to their hierarchical organization within the tumor. This descriptive review focuses on the evolving strategies to target BCSCs, which have become a pivotal aspect of therapeutic development. We explore a variety of approaches, including targeting specific tumor surface markers (CD133 and CD44), transporters, heat shock proteins, and critical signaling pathways like Notch, Akt, Hedgehog, KLF4, and Wnt/β-catenin. Additionally, we discuss the modulation of the tumor microenvironment through the CXCR-12/CXCR4 axis, manipulation of pH levels, and targeting hypoxia-inducible factors, vascular endothelial growth factor, and CXCR1/2 receptors. Further, this review focuses on the roles of microRNA expression, strategies to induce apoptosis and differentiation in BCSCs, dietary interventions, dendritic cell vaccination, oncolytic viruses, nanotechnology, immunotherapy, and gene therapy. We particularly focused on studies reporting identification of BCSCs, their unique properties and the efficacy of various therapeutic modalities in targeting these cells. By dissecting these approaches, we aim to provide insights into the complex landscape of BC treatment and the potential pathways for improving patient outcomes through targeted BCSC therapies.

KYNU Expression Promotes Cisplatin Resistance in Esophageal Cancer

Background: Chemotherapy resistance is a barrier to effective cancer prognoses. Cisplatin (CDDP) resistance is a major challenge for esophageal cancer (EC) therapy. A deeper understanding of the fundamental mechanisms of cisplatin resistance and improved targeting strategies are required in clinical settings. This study was performed to identify and characterize a marker of cisplatin resistance in EC cells. Method: KYSE140 and Eca-109 cells were subjected to escalating concentrations of cisplatin, resulting in the development of cisplatin-resistant KYSE140/CDDP and Eca-109/CDDP cell lines, respectively. RNA Sequencing (RNA-seq) was utilized to screen for the genes exhibiting differential expression between cisplatin-resistant and parental cells. Reverse transcription quantitative PCR was conducted to assess gene expression, and western blotting was employed to analyze protein levels. A sphere-formation assay was performed to validate tumor cell stemness. Cell counting kit-8 (CCK-8) experiments were conducted to confirm the sensitivity of cells to cisplatin. We examined the relationship between target genes and the clinicopathological features of patients with EC. Furthermore, the expression of target genes in EC tissues was evaluated via western blotting and fluorescence probe in situ hybridization (FISH). Results: KYNU was upregulated in cisplatin-resistant EC cells (KYSE140/CDDP and Eca-109/CDDP cells) and in EC tissues compared to that in the respective parental cell lines (KYSE140 and Eca-109 cells) and non-carcinoma tissues. Downregulation of KYNU increased cell sensitivity to cisplatin and suppressed tumor stemness, whereas abnormal KYNU expression had the opposite effect. KYNU expression was correlated with the expression of tumor stemness-associated factors (SOX2, Nanog, and OCT4) and the tumor size. Conclusions: KYNU may promote drug resistance in EC by regulating cancer stemness, and could serve as a biomarker and therapeutic target for EC.

NK Cells Lose Their Cytotoxicity Function against Cancer Stem Cell-Rich Radiotherapy-Resistant Breast Cancer Cell Populations

Cancer stem cells (CSCs) can be induced from differentiated cancer cells in the tumor microenvironment or in response to treatments and exhibit chemo- and radioresistance, leading to tumor recurrence and metastasis. We previously reported that triple negative breast cancer (TNBC) cells with acquired radioresistance exhibited more aggressive features due to an increased CSC population. Therefore, here, we isolated CSCs from radiotherapy-resistant (RT-R)-TNBC cells and investigated the effects of these CSCs on tumor progression and NK cell-mediated cytotoxicity. Compared to MDA-MB-231 and RT-R-MDA-MB-231 cells, CD24-/low/CD44+ cells isolated from RT-R-MDA-MB-231 cells showed increased proliferation, migration and invasion abilities, and induced expression of tumor progression-related molecules. Moreover, similar to MDA-MB-231 cells, CD24-/low/CD44+ cells recruited NK cells but suppressed NK cell cytotoxicity by regulating ligands for NK cell activation. In an in vivo model, CD24-/low/CD44+ cell-injected mice showed enhanced tumor progression and lung metastasis via upregulation of tumor progression-related molecules and altered host immune responses. Specifically, NK cells were recruited into the peritumoral area tumor but lost their cytotoxicity due to the altered expression of activating and inhibitory ligands on tumors. These results suggest that CSCs may cause tumor evasion of immune cells, resulting in tumor progression.

Apatinib Inhibits Stem Properties and Malignant Biological Behaviors of Breast Cancer Stem Cells by Blocking Wnt/β-catenin Signal Pathway Through Down-regulating LncRNA ROR

BACKGROUND

Cancer stem cells could influence tumor recurrence and metastasis.

OBJECTIVE

To develop a new effective treatment modality targeting breast cancer stem cells (BCSCs), and to explore the role of Apatinib in BCSCs.

METHODS

BCSCs were isolated from MDA-MB-231 cells by immune magnetic beads method. BCSCs were treated with Apatinib, lentiviral plasmids (lncRNA ROR) and iCRT-3 (Wnt pathway inhibitors). Viability, colony numbers, sphere numbers, apoptosis, migration, invasion of BCSCs were detected by MTT, colony formation, tumor sphere, flow cytometry, wound-healing, transwell assays, respectively. The expressions of markers (ABCG2, CD44, CD90, and CD24), epithelial-mesenchymal transition (EMT)-related molecules (E-cadherin, N-cadherin, Vimentin, MMP-2, MMP-9), and Wnt/β-catenin pathway-related proteins (Wnt3a, Wnt5a, β-catenin) in breast cancer stem cells were determined by performing Western blot and qRT-PCR analysis.

RESULTS

Apatinib decreased the viability and colony numbers of BCSCs in a concentration-dependent manner, and it also reduced sphere numbers, suppressed migration, invasion and lncRNA ROR expression, and induced apoptosis of BCSCs. However, these results were partially reversed by lncRNA ROR overexpression. Apatinib suppressed stem property, EMT process and Wnt/β-catenin pathway in BCSCs, which was partially reversed by lncRNA ROR overexpression. Moreover, lncRNA ROR overexpression increased the colony and sphere numbers, and promoted the cell viability, apoptosis inhibition, migration and invasion of BCSCs, but these effects were partially reversed by iCRT-3. LncRNA ROR overexpression increased the stem property, EMT process and Wnt/β-catenin pathway, which were partially counteracted by iCRT-3.

CONCLUSION

Apatinib inhibited stem property and malignant biological behaviors of BCSCs by blocking Wnt/β-catenin signal pathway through down-regulating lncRNA ROR.

Caloric restriction inhibits mammary tumorigenesis in MMTV-ErbB2 transgenic mice through the suppression of ER and ErbB2 pathways and inhibition of epithelial cell stemness in premalignant mammary tissues

Caloric intake influences the onset of many diseases, including cancer. In particular, caloric restriction (CR) has been reported to suppress mammary tumorigenesis in various models. However, the underlying cancer preventive mechanisms have not been fully explored. To this end, we aimed to characterize the anticancer mechanisms of CR using MMTV-ErbB2 transgenic mice, a well-established spontaneous ErbB2-overexpressing mammary tumor model, by focusing on cellular and molecular changes in premalignant tissues. In MMTV-ErbB2 mice with 30% CR beginning at 8 weeks of age, mammary tumor development was dramatically inhibited, as exhibited by reduced tumor incidence and increased tumor latency. Morphogenic mammary gland analyses in 15- and 20-week-old mice indicated that CR significantly decreased mammary epithelial cell (MEC) density and proliferative index. To understand the underlying mechanisms, we analyzed the effects of CR on mammary stem/progenitor cells. Results from fluorescence-activated cell sorting analyses showed that CR modified mammary tissue hierarchy dynamics, as evidenced by decreased luminal cells (CD24highCD49flow), putative mammary reconstituting unit subpopulation (CD24highCD49fhigh) and luminal progenitor cells (CD61highCD49fhigh). Mammosphere and colony-forming cell assays demonstrated that CR significantly inhibited mammary stem cell self-renewal and progenitor cell numbers. Molecular analyses indicated that CR concurrently inhibited estrogen receptor (ER) and ErbB2 signaling. These molecular changes were accompanied by decreased mRNA levels of ER-targeted genes and epidermal growth factor receptor/ErbB2 family members and ligands, suggesting ER-ErbB2 signaling cross-talk. Collectively, our data demonstrate that CR significantly impacts ER and ErbB2 signaling, which induces profound changes in MEC reprogramming, and mammary stem/progenitor cell inhibition is a critical mechanism of CR-mediated breast cancer prevention.

FGFR inhibitor, AZD4547, impedes the stemness of mammary epithelial cells in the premalignant tissues of MMTV-ErbB2 transgenic mice

The fibroblast growth factor receptor (FGFR) family of receptor tyrosine kinases (RTKs) regulates signaling pathways involved in cell proliferation and differentiation. Currently, the anti-tumor properties of FGFR inhibitors are being tested in preclinical and clinical studies. Nevertheless, reports on FGFR inhibitor-mediated breast cancer prevention are sparse. In this study, we investigated the anti-cancer benefits of AZD4547, an FGFR1-3 inhibitor, in ErbB2-overexpressing breast cancer models. AZD4547 (1-5 µM) demonstrated potent anti-proliferative effects, inhibition of stemness, and suppression of FGFR/RTK signaling in ErbB2-overexpressing human breast cancer cells. To study the in vivo effects of AZD4547 on mammary development, mammary epithelial cell (MEC) populations, and oncogenic signaling, MMTV-ErbB2 transgenic mice were administered AZD4547 (2-6 mg/kg/day) for 10 weeks during the 'risk window' for mammary tumor development. AZD4547 significantly inhibited ductal branching and MEC proliferation in vivo, which corroborated the in vitro anti-proliferative properties. AZD4547 also depleted CD24/CD49f-sorted MEC populations, as well as the CD61^highCD49f^high tumor-initiating cell-enriched population. Importantly, AZD4547 impaired stem cell-like characteristics in primary MECs and spontaneous tumor cells. Moreover, AZD4547 downregulated RTK, mTOR, and Wnt/β-catenin signaling pathways in premalignant mammary tissues. Collectively, our data provide critical preclinical evidence for AZD4547 as a potential breast cancer preventative and therapeutic agent.

Buformin inhibits the stemness of erbB-2-overexpressing breast cancer cells and premalignant mammary tissues of MMTV-erbB-2 transgenic mice

BACKGROUND

Metformin, an FDA-approved drug for the treatment of Type II diabetes, has emerged as a promising anti-cancer agent. Other biguanide analogs, including buformin and phenformin, are suggested to have similar properties. Although buformin was shown to reduce mammary tumor burden in carcinogen models, the anti-cancer effects of buformin on different breast cancer subtypes and the underlying mechanisms remain unclear. Therefore, we aimed to investigate the effects of buformin on erbB-2-overexpressing breast cancer with in vitro and in vivo models.

METHODS

MTT, cell cycle, clonogenic/CFC, ALDEFLUOR, tumorsphere, and Western blot analyses were used to determine the effects of buformin on cell growth, stem cell populations, stem cell-like properties, and signaling pathways in SKBR3 and BT474 erbB-2-overexpressing breast cancer cell lines. A syngeneic tumor cell transplantation model inoculating MMTV-erbB-2 mice with 78617 mouse mammary tumor cells was used to study the effects of buformin (1.2 g buformin/kg chow) on tumor growth in vivo. MMTV-erbB-2 mice were also fed buformin for 10 weeks, followed by analysis of premalignant mammary tissues for changes in morphological development, mammary epithelial cell (MEC) populations, and signaling pathways.

RESULTS

Buformin significantly inhibited SKBR3 and BT474 cell growth, and in vivo activity was demonstrated by considerable growth inhibition of syngeneic tumors derived from MMTV-erbB-2 mice. In particular, buformin suppressed stem cell populations and self-renewal in vitro, which was associated with inhibited receptor tyrosine kinase (RTK) and mTOR signaling. Consistent with in vitro data, buformin suppressed mammary morphogenesis and reduced cell proliferation in MMTV-erbB-2 mice. Importantly, buformin decreased MEC populations enriched with mammary reconstitution units (MRUs) and tumor-initiating cells (TICs) from MMTV-erbB-2 mice, as supported by impaired clonogenic and mammosphere formation in primary MECs. We further demonstrated that buformin-mediated in vivo inhibition of MEC stemness is associated with suppressed activation of mTOR, RTK, ER, and β-catenin signaling pathways.

CONCLUSIONS

Overall, our results provide evidence for buformin as an effective anti-cancer drug that selectively targets TICs, and present a novel prevention and/or treatment strategy for patients who are genetically predisposed to erbB-2-overexpressing breast cancer.

Microfluidic co-culture system for cancer migratory analysis and anti-metastatic drugs screening

Tumour metastasis is an important reason for cancer death, and cancer cell migration is an important step in the process of tumour metastasis. Studying cancer cell migration is of great significance. Here, we present a novel microfluidic co-culture system and establish mild, moderate and severe cancer models by using HMEpiC and MDA-MB-231 cells to study cancer cell migration and anti-cancer drug screening. Using this device, we achieved high cell viability (over 90%) and a stable analysis of the migration ability of cancer cells. We observed that the density of the cancer cells determined the probability of the occurrence of metastatic cells and that the induction of normal cells affected the metastatic velocity of each cancer cell. We verified that the increase in the migration ability of MDA-MB-231 cells co-cultured with HMEpiC cells was relative to the increased secretion of IL-6 and that this was verified by an IL-6 inhibitor assay. This co-culture also led to decreased CK-14 secretion and morphological changes in HMEpiC cells. Finally, significant inhibition of paclitaxel and tamoxifen on cancer migration was observed. Taken together, our microfluidic device could be a useful tool for the quantitation of the migratory capability and anti-metastatic drug screening.

Management and Outcomes in Metaplastic Breast Cancer

Metaplastic breast cancer (MBC) constitutes a rare clinical entity with special clinicopathologic, immunohistochemical, and molecular features. Resistance to systemic therapies, whether chemotherapy or hormonal therapy, is among its main characteristics, which in turn explains the poor prognosis and renders its management a challenge. Thus, the scope of the present review is to discuss the current therapeutic strategies for MBC in clinical practice and the corresponding outcomes and to suggest possible directions for future research. Potential novel targeted therapies could provide a hope for better outcomes but limited data are available owing to the rarity of MBC. As knowledge accumulates on the pathogenesis and genetic characteristics of MBC, emphasis should be given to the implementation of more targeted treatments, which will allow more efficient and individualized management of the disease.