TWIST1-mediated transcriptional activation of PDGFRβ in breast cancer stem cells promotes tumorigenesis and metastasis

Epidermal growth factor receptor inhibition potentiates chemotherapeutics-mediated sensitization of metastatic breast cancer stem cells

BACKGROUND

Metastasis has been a cause of the poor prognosis and cancer relapse of triple-negative breast cancer (TNBC) patients. The metastatic nature of TNBC is contributed by the breast cancer stem cells (CSCs) which have been implicated in tumorigenesis. Higher expression of epidermal growth factor receptor (EGFR) in breast CSCs has been used as a molecular target for breast cancer therapeutics. Thus, it necessitates the design and generation of efficacious EGFR inhibitors to target the downstream signaling associated with the cellular proliferation and tumorigenesis of breast cancer.

AIM

To generate efficacious EGFR inhibitors that can potentiate the chemotherapeutic-mediated mitigation of breast cancer tumorigenesis.

METHODS AND RESULTS

We identified small molecule EGFR inhibitors using molecular docking studies. In-vitro screening of the compounds was undertaken to identify the cytotoxicity profile of the small-molecule EGFR inhibitors followed by evaluation of the non-cytotoxic compounds in modulating the doxorubicin-induced migration, in-vitro tumorigenesis potential, and their effect on the pro-apoptotic genes' and protein markers' expression in TNBC cells. Compound 1e potentiated the doxorubicin-mediated inhibitory effect on proliferation, migration, in-vitro tumorigenesis capacity, and induction of apoptosis in MDA-MB-231 cells, and in the sorted CD24+-breast cancer cells and CD24-/CD44+-breast CSC populations. Orthotopic xenotransplantation of the breast CSCs-induced tumors in C57BL/6J mice was significantly inhibited by the low dose of Doxorubicin in the presence of compound 1e as depicted by molecular and immunohistochemical analysis.

CONCLUSION

Thus, the study suggests that EGFR inhibition-mediated sensitization of the aggressive and metastatic breast CSCs in TNBCs toward chemotherapeutics may reduce the relapse of the disease.

ZEB1 potentiates chemoresistance in breast cancer stem cells by evading apoptosis

Chemoresistance renders a challenge to the clinics to treat breast cancer patients. Current treatment strategies are effective in mitigating tumor growth but remain largely ineffective against cancer-initiating cells or breast Cancer Stem Cells (CSCs). Epithelial-to-mesenchymal-transition (EMT) regulates breast CSC physiology. Zinc finger E-box binding homeobox 1 (ZEB1) is a key EMT-transcription factor that regulates breast CSC - differentiation and metastasis. However, its potential role in modulating tumor chemoresistance has not yet been fully understood. In-silico analysis revealed a higher ZEB1 expression in breast cancer patients that leads to decreased overall and relapse-free survival. We generated sorted breast CSC with stable ZEB1 overexpression (CD24-/CD44+GFP-ZEB1) and/or silencing (CD24-/CD44+ZEB1 shRNA) as well as breast cancer cells with stable ZEB1 overexpression (CD24+GFP-ZEB1) and/or silencing (CD24+ZEB1 shRNA). An increased colony-forming efficiency and doxorubicin accumulation correlated with decreased promoter activity and expression profile of ABCC1 drug-efflux ABC transporter in CD24-/CD44+GFP-ZEB1. Additionally, CD24-/CD44+GFP-ZEB1 demonstrated doxorubicin-induced higher anti-apoptotic and lower pro-apoptotic protein expressions in the mitochondrial and cytosolic fractions. Chemoresistant CD24-/CD44+GFP-ZEB1 cells depicted 1000-fold higher IC-50 values of doxorubicin and decreased activation of JNK-p38 stress kinase molecular signaling-dependent mammosphere forming efficiency to evade apoptosis. Thus, ZEB1 and its downstream effectors are plausible therapeutic targets for the mitigation of breast cancer chemoresistance in patients.

Twist1‑mediated transcriptional activation of Claudin‑4 promotes cervical cancer cell migration and invasion

Claudin-4, a member of the claudin multigene family, participates in events associated with mesenchymal-like activity of cancerous cells. Claudin-4 expression is upregulated in cervical cancer tissue compared with that in adjoining non-neoplastic tissue. However, the mechanisms that regulate Claudin-4 expression in cervical cancer are poorly understood. Moreover, whether Claudin-4 contributes to the migration and invasion of cervical cancer cells remains unclear. By western blotting, reverse transcription-qPCR, bioinformatics analysis, dual-luciferase reporter assay, chromatin immunoprecipitation assay, wound healing assay and Transwell migration/invasion assay, the present study confirmed that Claudin-4 was a downstream target of Twist1, a helix-loop-helix transcriptional factor, the activity of which has a positive correlation with Claudin-4 expression. Mechanistically, Twist1 directly binds to Claudin-4 promoter, resulting in the transactivation of expression. The depletion of the Twist1-binding E-Box1 domain on Claudin-4 promoter via CRISPR-Cas9 knockout system downregulates Claudin-4 expression and suppresses the ability of cervical cancer cells to migrate and invade by elevating E-cadherin levels and lowering N-cadherin levels. Following activation by transforming growth factor-β, Twist1 induces Claudin-4 expression, thus enhancing migration and invasion of cervical cancer cells. In summary, the present data suggested that Claudin-4 was a direct downstream target of Twist1 and served a critical role in promoting Twist1-mediated cervical cancer cell migration and invasion.

Pericytes in the tumor microenvironment

Pericytes are a type of mural cell located between the endothelial cells of capillaries and the basement membrane, which function to regulate the capillary vasomotor and maintain normal microcirculation of local tissues and organs and have been identified as a significant component in the tumor microenvironment (TME). Pericytes have various interactions with different components of the TME, such as constituting the pre-metastatic niche, promoting the growth of cancer cells and drug resistance through paracrine activity, and inducing M2 macrophage polarization. While changes in the TME can affect the number, phenotype, and molecular markers of pericytes. For example, pericyte detachment from endothelial cells in the TME facilitates tumor cells in situ to invade the circulating blood and is beneficial to local capillary basement membrane enzymatic hydrolysis and endothelial cell proliferation and budding, which contribute to tumor angiogenesis and metastasis. In this review, we discuss the emerging role of pericytes in the TME, and tumor treatment related to pericytes. This review aimed to provide a more comprehensive understanding of the function of pericytes and the relationship between pericytes and tumors and to provide ideas for the treatment and prevention of malignant tumors.

Cell density modulates chemoresistance in breast cancer cells through differential expression of ABC transporters

BACKGROUND

Breast cancer patients undergoing chemotherapy encounter a significant challenge of chemoresistance because of drug efflux by ATP-binding cassette (ABC) transporters. Breast cancer cell density alters considerably throughout the early stages of primary and secondary tumor development. Although cell density in culture influences kinetics, the effects of varying cell densities on the chemoresistance of breast cancer cells remains largely unexplored.

METHODS AND RESULTS

We observed chemotherapeutics-induced differential gene and protein expression of ABC transporters in luminal and basal breast cancer cells cultured at low and high seeding densities. Low-density cultures depicted a significant increase in the mRNA expression of ABC transporters-ABCG2, ABCG1, ABCC4, ABCA2, ABCA3, ABCC2, ABCC3, ABCC6, ABCC7, and ABCC9 as compared with high-density cultures. Next, cells at both low and high seeding densities when pre-treated with cyclosporine A (CsA), a pan-inhibitor of ABC transporters, resulted in increased sensitization to chemotherapeutics-doxorubicin and tamoxifen at markedly low IC50 concentrations suggesting the role of ABC transporters. Finally, markedly high doxorubicin-drug accumulation, significantly increased expression of N-cadherin, and a significant decrease in chemotherapeutics-induced in vitro tumorigenesis was observed in low-density seeded breast cancer cells when pre-treated with CsA suggesting ABC transporters inhibition-mediated increased efficacy of chemotherapeutics.

CONCLUSION

These findings suggest that breast cancer cells grown at low seeding density imparts chemoresistance towards doxorubicin or tamoxifen by a differential increase in the expression of ABC transporters. Thus, a combinatorial treatment strategy including ABC transporter inhibitors and chemotherapeutics can be a way forward for overcoming the breast cancer chemoresistance.

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.