Pharmacological targets of breast cancer stem cells: a review

Targeting breast cancer stem cells through retinoids: A new hope for treatment

Breast cancer is a complex and diverse disease accounting for nearly 30% of all cancers diagnosed in females. But unfortunately, patients develop resistance to the existing chemotherapeutic regimen, resulting in approximately 90% treatment failure. With over half a million deaths annually, it is imperative to explore new therapeutic approaches to combat the disease. Within a breast tumor, a small sub-population of heterogeneous cells, with a unique ability of self-renew and differentiation and responsible for tumor formation, initiation, and recurrence are referred to as breast cancer stem cells (BCSCs). These BCSCs have been identified as one of the main contributors to chemoresistance in breast cancer, making them an attractive target for developing novel therapeutic strategies. These cells exhibit surface biomarkers such as CD44+, CD24-/LOW, ALDH, CD133, and CD49f phenotypes. Higher expression of CD44+ and ALDH activity has been associated with the formation of tumors in various cancers. Moreover, the abnormal regulation of signaling pathways, including Hedgehog, Notch, β-catenin, JAK/STAT, and P13K/AKT/mTOR, leads to the formation of cancer stem cells, resulting in the development of tumors. The growing drug resistance in BC is a significant challenge, highlighting the need for new therapeutic strategies to combat this dreadful disease. Retinoids, a large group of synthetic derivatives of vitamin A, have been studied as chemopreventive agents in clinical trials and have been shown to regulate various crucial biological functions including vision, development, inflammation, and metabolism. On a cellular level, the retinoid activity has been well characterized and translated and is known to induce differentiation and apoptosis, which play important roles in the outcome of the transformation of tissues into malignant. Retinoids have been investigated extensively for their use in the treatment and prevention of cancer due to their high receptor-binding affinity to directly modulate gene expression programs. Therefore, in this study, we aim to summarize the current understanding of BCSCs, their biomarkers, and the associated signaling pathways. Retinoids, such as Adapalene, a third-generation retinoid, have shown promising anti-cancer potential and may serve as therapeutic agents to target BCSCs.

Natural products derived from medicinal plants and microbes might act as a game-changer in breast cancer: a comprehensive review of preclinical and clinical studies

Breast cancer (BC) is the most prevalent neoplasm among women. Genetic and environmental factors lead to BC development and on this basis, several preventive - screening and therapeutic interventions have been developed. Hormones, both in the form of endogenous hormonal signaling or hormonal contraceptives, play an important role in BC pathogenesis and progression. On top of these, breast microbiota includes both species with an immunomodulatory activity enhancing the host's response against cancer cells and species producing proinflammatory cytokines associated with BC development. Identification of novel multitargeted therapeutic agents with poly-pharmacological potential is a dire need to combat advanced and metastatic BC. A growing body of research has emphasized the potential of natural compounds derived from medicinal plants and microbial species as complementary BC treatment regimens, including dietary supplements and probiotics. In particular, extracts from plants such as Artemisia monosperma Delile, Origanum dayi Post, Urtica membranacea Poir. ex Savigny, Krameria lappacea (Dombey) Burdet & B.B. Simpson and metabolites extracted from microbes such as Deinococcus radiodurans and Streptomycetes strains as well as probiotics like Bacillus coagulans and Lactobacillus brevis MK05 have exhibited antitumor effects in the form of antiproliferative and cytotoxic activity, increase in tumors' chemosensitivity, antioxidant activity and modulation of BC - associated molecular pathways. Further, bioactive compounds like 3,3'-diindolylmethane, epigallocatechin gallate, genistein, rutin, resveratrol, lycopene, sulforaphane, silibinin, rosmarinic acid, and shikonin are of special interest for the researchers and clinicians because these natural agents have multimodal action and act via multiple ways in managing the BC and most of these agents are regularly available in our food and fruit diets. Evidence from clinical trials suggests that such products had major potential in enhancing the effectiveness of conventional antitumor agents and decreasing their side effects. We here provide a comprehensive review of the therapeutic effects and mechanistic underpinnings of medicinal plants and microbial metabolites in BC management. The future perspectives on the translation of these findings to the personalized treatment of BC are provided and discussed.

Exploring the Application of Bifunctional Metal Chelators in Treating Triple-Negative Breast Cancer

Purpose: In this study, we independently synthesised and labelled a novel bidentate bifunctional chelating agent, ¹⁷⁷Lu-3,4-HOPO-Cetuximab, that achieved tight binding between targeting and radioactivity, and evaluated its targeted killing ability of cells in vitro and in vivo. Method: 3,4-HOPO was successfully synthesised through a series of chemical steps using malt phenol as the raw material, which was then coupled with Cetuximab labelled with ¹⁷⁷Lu. ¹⁷⁷Lu-3,4-HOPO-Cetuximab and ¹⁷⁷Lu-DOTA-Cetuximab was tested for its cell viability and cell-binding rate after different times and at different doses by CCK-8 and cell-binding experiments. ¹⁷⁷Lu-3,4-HOPO-Cetuximab (~500 μCi) and ¹⁷⁷Lu-DOTA-Cetuximab (~500 μCi) were injected into the tail vein of a subcutaneous metastasis mouse model of triple-negative breast cancer with a single injection, and tumour volume growth and body weight changes were regularly monitored for 20 days. The radioactivity distribution in nude mice was analysed after sacrifice, and the treated and untreated tumour tissues were analysed by HE staining. Result: The cell viability of ¹⁷⁷Lu-3,4-HOPO-Cetuximab declined exponentially after treatment for 48 h at 50 Bq/mL to 500 kBq/mL, respectively; the cell activity was slowed down from 8 to 96 h at a dose of 500 kBq; while the binding rate of 4T1 cells in ¹⁷⁷Lu-3,4-HOPO-Cetuximab from 1 to 24 h, respectively, increased logarithmically, which was similar with ¹⁷⁷Lu-DOTA-Cetuximab. After 20 days of treatment, the body weight of nude mice with ¹⁷⁷Lu-3,4-HOPO-Cetuximab and ¹⁷⁷Lu-DOTA-Cetuximab were hardly changed, while the body weight with physiological saline decreased significantly. The tumour inhibition rate of the ¹⁷⁷Lu-3,4-HOPO-Cetuximab and ¹⁷⁷Lu-DOTA-Cetuximab were (37.03 ± 11.16)% and (38.7 ± 5.1)%; HE staining showed that tumour cells were affected by the action of ¹⁷⁷Lu causing necrosis. Conclusion: The experiments showed that ¹⁷⁷Lu-3,4-HOPO-Cetuximab has a certain targeted therapeutic ability for triple-negative breast cancer, and it is expected to become a potential targeted nuclear medicine treatment for triple-negative breast cancer.

Targeted Drug Therapy to Overcome Chemoresistance in Triple-negative Breast Cancer

Triple-negative Breast Cancer (TNBC) is the most aggressive and prevailing breast cancer subtype. The chemotherapeutics used in the treatment of TNBC suffer from chemoresistance, dose-limiting toxicities and off-target side effects. As a result, conventional chemotherapeutics are unable to prevent tumor growth, metastasis and result in failure of therapy. Various new targets such as BCSCs surface markers (CD44, CD133, ALDH1), signaling pathways (IL-6/JAK/STAT3, notch), pro and anti-apoptotic proteins (Bcl-2, Bcl-xL, DR4, DR5), hypoxic factors (HIF-1α, HIF-2α) and drug efflux transporters (ABCC1, ABCG2 and ABCB1) have been exploited to treat TNBC. Further, to improve the efficacy and safety of conventional chemotherapeutics, researchers have tried to deliver anticancer agents specifically to the TNBCs using nanocarrier based drug delivery. In this review, an effort has been made to highlight the various factors responsible for the chemoresistance in TNBC, novel molecular targets of TNBC and nano-delivery systems employed to achieve sitespecific drug delivery to improve efficacy and reduce off-target side effects.

Signaling pathways governing breast cancer stem cells behavior

Breast cancer is the second common cancer and the leading cause of malignancy among females overall. Breast cancer stem cells (BCSCs) are a small population of breast cancer cells that play a critical role in the metastasis of breast cancer to other organs in the body. BCSCs have both self-renewal and differentiation capacities, which are thought to contribute to the aggressiveness of metastatic lesions. Therefore, targeting BCSCs can be a suitable approach for the treatment and metastasis of breast cancer. Growing evidence has indicated that the Wnt, NFκB, Notch, BMP2, STAT3, and hedgehog (Hh) signaling pathways govern epithelial-to-mesenchymal transition (EMT) activation, growth, and tumorigenesis of BCSCs in the primary regions. miRNAs as the central regulatory molecules also play critical roles in BCSC self-renewal, metastasis, and drug resistance. Hence, targeting these pathways might be a novel therapeutic approach for breast cancer diagnosis and therapy. This review discusses known signaling mechanisms involved in the stimulation or prevention of BCSC self-renewal, metastasis, and tumorigenesis.

RUNX2 as a promising therapeutic target for malignant tumors

The transcription factor runt-related protein 2 (RUNX2) has an important impact on the transformation of bone marrow mesenchymal stem cells to osteoblasts. Further studies have shown that RUNX2 plays a key role in the invasion and metastasis of cancers. RUNX2 is a “key” molecule in the regulatory network comprised of multiple signaling pathways upstream and its target downstream molecules. Due to the complex regulatory mechanisms of RUNX2, the specific mechanism underlying the occurrence, development and prognosis of malignant tumors has not been fully understood. Currently, RUNX2 as a promising therapeutic target for cancers has become a research hotspot. Herein, we reviewed the current literature on the modulatory functions and mechanisms of RUNX2 in the development of malignant tumors, aiming to explore its potential clinical application in the diagnosis, prognosis and treatment of tumors.

13R,20-Dihydroxydocosahexaenoic Acid, a Novel Dihydroxy- DHA Derivative, Inhibits Breast Cancer Stemness through Regulation of the Stat3/IL-6 Signaling Pathway by Inducing ROS Production

Breast cancer is a major health problem worldwide. Cancer stem cells (CSCs) are known to mediate breast cancer metastasis and recurrence and are therefore a promising therapeutic target. In this study, we investigated the anti-inflammatory effect of 13R,20-dihydroxydocosahexaenoic acid (13R,20-diHDHA), a novel dihydroxy-DHA derivative, which was synthesized through an enzymatic reaction using cyanobacterial lipoxygenase. We found that 13R,20-diHDHA reduced the macrophage secretion of the inflammatory cytokines, IL-6 and TNF-α, and thus appeared to have anti-inflammatory effects. As the inflammatory tumor microenvironment is largely devoted to supporting the cancer stemness of breast cancer cells, we investigated the effect of 13R,20-diHDHA on breast cancer stemness. Indeed, 13R,20-diHDHA effectively inhibited breast cancer stemness, as evidenced by its ability to dose-dependently inhibit the mammospheres formation, colony formation, migration, and invasion of breast CSCs. 13R,20-diHDHA reduced the populations of CD44^high/CD24^low and aldehyde dehydrogenase (ALDH)-positive cells and the expression levels of the cancer stemness-related self-renewal genes, Nanog, Sox2, Oct4, c-Myc, and CD44. 13R,20-diHDHA increased reactive oxygen species (ROS) production, and the generated ROS reduced the phosphorylation of nuclear signal transducer and activator of transcription 3 (Stat3) and the secretion of IL-6 by mammospheres. These data collectively suggest that 13R,20-diHDHA inhibits breast cancer stemness through ROS production and downstream regulation of Stat3/IL-6 signaling, and thus might be developed as an anti-cancer agent acting against CSCs.

DR5 antibody conjugated lipid-based nanocarriers of gamma-secretase inhibitor for the treatment of triple negative breast cancer

In the present study, Death receptor-5 (DR5) antibody conjugated solid lipid nanoparticles (DR5-DAPT-SLNs) has been formulated for effective intracellular of γ-secretase inhibitor, N-[N-(3,5-Difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester (DAPT) to cancer cells. Emulsification-solvent evaporation, followed by EDC cross-linking methods, was employed to prepare DR5 targeted DAPT-SLNs (DR5-DAPT-SLNs). The formulation was characterized by its particle size, shape, and surface charge. The in vitro & in vivo anticancer efficacy was studied in MDA-MB231 triple negative breast cancer (TNBC) cells and DMBA induced breast cancer model in mice, respectively. The results show that thatDR5-DAPT-SLNs is found to be a spherical shape with an average particle size of 187 ± 0.98 nm and having an average surface charge of 23 ± 2.3 mV. DR5-DAPT-SLNs have higher cytotoxicity in MDA-MB231 cells compared to DAPT-SLNs (non-targeted) and the bulk drug. However, in DR5 negative HEK 293 noncancer cells, the formulation shows minimal cytotoxic effects. The above results, therefore, demonstrate DR5 mediated uptake is responsible for improved cytotoxicity of DAPT. In the in vivo anticancer study, DR5-DAPT-SLNs show greater tumor regression when compared to DAPT-SLNs and the bulk drug. In conclusion, the results of the present study demonstrate that the DR5-DAPT-SLNs selectively target cancer cells and potentiate the anticancer efficacy of DAPT against TNBC cells.

Autophagy and Tumour Chemotherapy

Chemotherapy is an important means of treating malignant tumours. The main role of chemotherapy drugs is to induce cell death. However, the apoptotic pathways of many tumour cells are often severely impaired, leading to failure of chemotherapy-induced apoptosis. With the in-depth study of autophagy in recent years, this process has been found to play an important role in the chemoresistance of tumours. Autophagy may have different effects on tumour cells depending on the specific environment. In addition, tumour stem cells and the tumour microenvironment are closely related to tumour recurrence and metastasis. It is also important to study the role of autophagy in tumour stem cells and the microenvironment to investigate chemotherapy resistance.

Phenyl boronic acid-modified lipid nanocarriers of niclosamide for targeting triple-negative breast cancer

Aim: To study the active targeting efficacy of phenylboronic acid-modified niclosamide solid lipid nanoparticles (PBA-Niclo-SLN) in triple-negative breast cancer (TNBC). Materials & methods: PBA-Niclo-SLNs were formulated by an emulsification-solvent evaporation method using PBA-associated stearylamine (PBSA) as lipid. The drug uptake and the anticancer propensity of PBA-Niclo-SLN were studied in TNBC (MDA-MB231) cells and tumor-bearing mice. Results: PBA-Niclo-SLN formulation resulted in greater antitumor efficacy by inducing G0/G1 cell cycle arrest and apoptosis. Besides, PBA-Niclo-SLN effectively inhibited STAT3, CD44+/CD24- TNBC stem cell subpopulation, epithelial–mesenchymal transition markers. Besides, PBA-Niclo-SLN selectively accumulated at the tumor site with more significant tumor regression and improved the survivability in TNBC tumor-bearing mice. Conclusion: PBA-Niclo-SLN formulation would be an effective strategy to eradicate TNBC cells (breast cancer stem cells and nonbreast cancer stem cells) efficiently.

HIF-2α regulates CD44 to promote cancer stem cell activation in triple-negative breast cancer via PI3K/AKT/mTOR signaling

BACKGROUND

Breast cancer is a common malignant tumor that seriously threatens women’s health. Breast cancer stem cell (CSC)-like cell population may be the main factor for breast cancer metastasis. Therefore, targeted therapy for CSCs has great potential significance. Hypoxia-inducible factor is a transcription factor widely expressed in tumors. Studies have shown that down-regulation of the hypoxia signaling pathway inhibits tumor stem cell self-renewal and increases the sensitivity of stem cells to radiotherapy and chemotherapy mediated by hypoxia-inducible factor-2α (HIF-2α). However, the specific mechanism remains unclear and further research is necessary.

AIM

To investigate the effect of HIF-2α down-regulation on stem cell markers, microsphere formation, and apoptosis in breast cancer cell line MDA-MB-231 under hypoxia and its possible mechanism.

METHODS

Immunohistochemistry was used to detect the expression of HIF-2α and CD44 in triple-negative breast cancer (TNBC) and non-TNBC tissues. Double-labeling immunofluorescence was applied to detect the co-expression of HIF-2α and CD44 in MDA-MB-231 cells and MCF-7 cells. HIF-2α was silenced by RNA interference, and the expression of CD44 and transfection efficiency were detected by real-time fluorescent quantitative PCR. Further, flow cytometry, TdT-mediated X-dUTP nick end labeling, and mammosphere formation assays were used to evaluate the effect of HIF-2α on CSCs and apoptosis. The possible mechanisms were analyzed by Western blot.

RESULTS

The results of immunohistochemistry showed that HIF-2α was highly expressed in both TNBC and non-TNBC, while the expression of CD44 in different molecular types of breast cancer cells was different. In in vitro experiments, it was found that HIF-2α and CD44 were expressed almost in the same cell. Compared with hypoxia + negative-sequence control, HIF-2α small interfering ribonucleic acid transfection can lower the expression of HIF-2α and CD44 mRNA(P < 0.05), increase the percentage of apoptotic cells (P < 0.05), and resulted in a reduction of CD44⁺/CD24⁻ population (P < 0.05) and mammosphere formation (P < 0.05) in hypoxic MDA-MB-231 cells. Western blot analysis revealed that phosphorylated protein-serine-threonine kinase (p-AKT) and phosphorylated mammalian target of rapamycin (p-mTOR) levels in MDA-MB-231 decreased significantly after HIF-2α silencing (P < 0.05).

CONCLUSION

Down-regulation of HIF-2α expression can inhibit the stemness of human breast cancer MDA-MB-231 cells and promote apoptosis, and its mechanism may be related to the CD44/phosphoinosmde-3-kinase/AKT/mTOR signaling pathway.

Nanoparticles Targeting STATs in Cancer Therapy

Over the past decades, an increase in the incidence rate of cancer has been witnessed. Although many efforts have been made to manage and treat this life threatening condition, it is still one of the leading causes of death worldwide. Therefore, scientists have attempted to target molecular signaling pathways involved in cancer initiation and metastasis. It has been shown that signal transducers and activator of transcription (STAT) contributes to the progression of cancer cells. This important signaling pathway is associated with a number of biological processes including cell cycle, differentiation, proliferation and apoptosis. It appears that dysregulation of the STAT signaling pathway promotes the migration, viability and malignancy of various tumor cells. Hence, there have been many attempts to target the STAT signaling pathway. However, it seems that currently applied therapeutics may not be able to effectively modulate the STAT signaling pathway and suffer from a variety of drawbacks such as low bioavailability and lack of specific tumor targeting. In the present review, we demonstrate how nanocarriers can be successfully applied for encapsulation of STAT modulators in cancer therapy.

The regulatory roles of lncRNAs in the process of breast cancer invasion and metastasis

Breast cancer (BC) is the most common cancer and principal cause of death among females worldwide. Invasion and metastasis are major causes which influence the survival and prognosis of BC. Therefore, to understand the molecule mechanism underlying invasion and metastasis is paramount for developing strategies to improve survival and prognosis in BC patients. Recent studies have reported that long non-coding RNAs (lncRNAs) play critical roles in the regulation of BC invasion and metastasis through a variety of molecule mechanisms that endow cells with an aggressive phenotype. In this article, we focused on the function of lncRNAs on BC invasion and metastasis through participating in epithelial-to-mesenchymal transition, strengthening cancer stem cells generation, serving as competing endogenous lncRNAs, influencing multiple signaling pathways as well as regulating expressions of invasion-metastasis related factors, including cells adhesion molecules, extracellular matrix, and matrix metallo-proteinases. The published work described has provided a better understanding of the mechanisms underpinning the contribution of lncRNAs to BC invasion and metastasis, which may lay the foundation for the development of new strategies to prevent BC invasion and metastasis.

Friend leukemia virus integration 1 is a predictor of poor prognosis of breast cancer and promotes metastasis and cancer stem cell properties of breast cancer cells

Breast cancer is the most common cancer in women worldwide; despite the developments in diagnosis and therapy, recurrence and metastasis remain the main causes of death among patients with breast cancer. This study aimed to identify a promising biomarker for this disease. The study clarified (1) the association between Friend leukemia virus integration 1 (FLI-1) and various molecular subtypes and (2) the prognostic value of FLI-1 in breast cancer. To the best of our knowledge, this study is the first to report that FLI-1 is a predictor of poor prognosis in patients with breast cancer and overexpressed in the triple negative breast cancer (TNBC) subtype. To further verify the effect of FLI-1 in promoting the metastasis of TNBC, we performed a series of functional experiments in vitro and orthotopic xenograft experiments in the mammary fat pad of nude mice. FLI-1, as a transcription factor, bound to the promoters of key EMT-related genes (CDH1 and VIM), and regulated their expressions at the transcriptional level, thus induced epithelial-mesenchymal transition (EMT). The overexpression of FLI-1 significantly upregulated the expression of mesenchymal markers. After the modulation of FLI-1, the changes in mammary stem cell markers (ALDH1A1 and CD133) and the capacity to form mammospheres were consistent with those of the EMT-related markers. The orthotopic xenograft models further confirmed that the attenuation of stem cell traits after silencing FLI-1 decreased the ability of tumorigenesis. These results indicate that FLI-1 is a useful predictor of poor prognosis in patients with breast cancer. Furthermore, the preliminary exploration of metastatic mechanism in the patients with TNBC will provide a potential target to treat breast cancer in the near future.