Salinomycin Promotes Anoikis and Decreases the CD44+/CD24- Stem-Like Population via Inhibition of STAT3 Activation in MDA-MB-231 Cells

Beyond Death: Unmasking the Intricacies of Apoptosis Escape

Apoptosis, or programmed cell death, maintains tissue homeostasis by eliminating damaged or unnecessary cells. However, cells can evade this process, contributing to conditions such as cancer. Escape mechanisms include anoikis, mitochondrial DNA depletion, cellular FLICE inhibitory protein (c-FLIP), endosomal sorting complexes required for transport (ESCRT), mitotic slippage, anastasis, and blebbishield formation. Anoikis, triggered by cell detachment from the extracellular matrix, is pivotal in cancer research due to its role in cellular survival and metastasis. Mitochondrial DNA depletion, associated with cellular dysfunction and diseases such as breast and prostate cancer, links to apoptosis resistance. The c-FLIP protein family, notably CFLAR, regulates cell death processes as a truncated caspase-8 form. The ESCRT complex aids apoptosis evasion by repairing intracellular damage through increased Ca2+ levels. Antimitotic agents induce mitotic arrest in cancer treatment but can lead to mitotic slippage and tetraploid cell formation. Anastasis allows cells to resist apoptosis induced by various triggers. Blebbishield formation suppresses apoptosis indirectly in cancer stem cells by transforming apoptotic cells into blebbishields. In conclusion, the future of apoptosis research offers exciting possibilities for innovative therapeutic approaches, enhanced diagnostic tools, and a deeper understanding of the complex biological processes that govern cell fate. Collaborative efforts across disciplines, including molecular biology, genetics, immunology, and bioinformatics, will be essential to realize these prospects and improve patient outcomes in diverse disease contexts.

Small Molecule Therapeutics in the Pipeline Targeting for Triple-Negative Breast Cancer: Origin, Challenges, Opportunities, and Mechanisms of Action

Triple-negative breast cancer (TNBC) cells are devoid of estrogen receptors (ERs), progesterone receptor (PRs), and human epidermal growth factor receptor 2 (HER2), and it (TNBC) counts for about 10-15% of all breast cancers. TNBC is highly invasive, having a faster growth rate and a higher risk of metastasis and recurrence. Still, chemotherapy is one of the widely used options for treating TNBC. This study reviewed the histological and molecular characterization of TNBC subtypes, signaling pathways that are aberrantly expressed, and small molecules targeting these pathways, as either single agents or in combination with other therapeutic agents like chemotherapeutics, immunotherapeutics, and antibody-drug conjugates; their mechanisms of action, challenges, and future perspectives were also reviewed. A detailed analytical review was carried out using the literature collected from the SciFinder, PubMed, ScienceDirect, Google Scholar, ACS, Springer, and Wiley databases. Several small molecule inhibitors were found to be therapeutics for treating TNBC. The mechanism of action and the different signaling pathways through which the small molecules exert their effects were studied, including clinical trials, if reported. These small molecule inhibitors include buparlisib, everolimus, vandetanib, apatinib, olaparib, salidroside, etc. Some of the signaling pathways involved in TNBC, including the VEGF, PARP, STAT3, MAPK, EGFR, P13K, and SRC pathways, were discussed. Due to the absence of these biomarkers, drug development for treating TNBC is challenging, with chemotherapy being the main therapeutic agent. However, chemotherapy is associated with chemoresistance and a high toxicity to healthy cells as side effects. Hence, there is a continuous demand for small-molecule inhibitors that specifically target several signaling pathways that are abnormally expressed in TNBC. We attempted to include all the recent developments in this field. Any omission is truly unintentional.

Prognostic role of SOX2 and STAT3 expression on circulating T lymphocytes and CD44+/CD24neg cells in the locally advanced and metastatic breast cancer

BACKGROUND

Breast cancer (BC) is associated with a continuous increase in incidence, with high mortality rates in several countries. CD44, STAT3, and SOX2 are related to regulating of somatic cell division, tumorigenesis, and metastasis in BC.

METHODS

A cross-sectional study was carried out at the Hospital de Cancer de Pernambuco (HCP) between 2017 and 2018. Fifty-one women with locally advanced (LA) and 14 with metastatic BC were included in the study.

RESULTS

High CD44+/CD24neg and CD44+/CD24neg/SOX2+ levels in Luminal B (LB), HER2+, and triple-negative breast cancer (TNBC) compared with controls (p < 0.05). Low CD44+/CD24negSTAT3+ levels in LB, HER2+, and TNBC compared with controls (p < 0.05). High T lymphocytes, and low STAT3 + T, and SOX2 + T levels in BC patients (p < 0.05). High SOX2 + T levels in patients with axillary lymph node-negative (N0) compared with the axillary lymph node-positives (N1 and N2 groups; p < 0.05). High SOX2 + T levels in N1 compared to N2 (p < 0.05). High T lymphocytes and low SOX2 + T levels in the LA tumor compared to metastatic disease (p = 0.0007 and p = 0.02, respectively). High CD44 + /CD24negSTAT3+, and T lymphocyte levels in TNBC patients with LA tumor compared to metastatic (p < 0.05). Low STAT3 + T levels in TBNC patients with LA tumor compared to metastatic (p = 0.0266).

CONCLUSION

SOX2 and STAT3 expression on circulating T lymphocytes and CD44 + /CD24neg cells in peripheral blood have prognostic roles in breast cancer. SOX2 and STAT3 expression are potential predictive biomarkers of disease progression in breast cancer regardless of tumor subtype.

Effects of CD44 siRNA on inhibition, survival, and apoptosis of breast cancer cell lines (MDA-MB-231 and 4T1)

BACKGROUND

Breast cancer (BC) is one of the most common cancers in the world. Despite the many advances that have been made in treating patients, many patients are still resistant to treatment. CD44 is one of the surface glycoproteins of BC cells that plays an important role in the proliferation of these cells and inhibition of their apoptosis. Therefore, targeting it can be a treatment way for BC patients.

METHODS

In this study, the effect of anti-CD44 siRNA on the proliferation, apoptosis, and migration rate of MDA-MB-231 and 4T1 cells was investigated. The techniques used in this study were MTT assay, RT-PCR, and flow cytometry.

RESULTS

The apoptosis and proliferation rates in CD44 siRNA-treated cells were higher and lower, respectively, compared to untreated cells. Also, cell migration was less in treated cells compared to untreated cells. CD44 siRNA also decreased the expression of CXCR4, c-myc, Vimentin, ROCK, and MMP-9.

CONCLUSION

Finally, CD44 targeting can be a good treatment option to make BC cells more sensitive to apoptosis.

Potential therapeutic targets of the JAK2/STAT3 signaling pathway in triple-negative breast cancer

Triple-negative breast cancer (TNBC) poses a significant clinical challenge due to its propensity for metastasis and poor prognosis. TNBC evades the body's immune system recognition and attack through various mechanisms, including the Janus Kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway. This pathway, characterized by heightened activity in numerous solid tumors, exhibits pronounced activation in specific TNBC subtypes. Consequently, targeting the JAK2/STAT3 signaling pathway emerges as a promising and precise therapeutic strategy for TNBC. The signal transduction cascade of the JAK2/STAT3 pathway predominantly involves receptor tyrosine kinases, the tyrosine kinase JAK2, and the transcription factor STAT3. Ongoing preclinical studies and clinical research are actively investigating this pathway as a potential therapeutic target for TNBC treatment. This article comprehensively reviews preclinical and clinical investigations into TNBC treatment by targeting the JAK2/STAT3 signaling pathway using small molecule compounds. The review explores the role of the JAK2/STAT3 pathway in TNBC therapeutics, evaluating the benefits and limitations of active inhibitors and proteolysis-targeting chimeras in TNBC treatment. The aim is to facilitate the development of novel small-molecule compounds that target TNBC effectively. Ultimately, this work seeks to contribute to enhancing therapeutic efficacy for patients with TNBC.

Cancer stem cells: a target for overcoming therapeutic resistance and relapse

Cancer stem cells (CSCs) are a small subset of cells in cancers that are thought to initiate tumorous transformation and promote metastasis, recurrence, and resistance to treatment. Growing evidence has revealed the existence of CSCs in various types of cancers and suggested that CSCs differentiate into diverse lineage cells that contribute to tumor progression. We may be able to overcome the limitations of cancer treatment with a comprehensive understanding of the biological features and mechanisms underlying therapeutic resistance in CSCs. This review provides an overview of the properties, biomarkers, and mechanisms of resistance shown by CSCs. Recent findings on metabolic features, especially fatty acid metabolism and ferroptosis in CSCs, are highlighted, along with promising targeting strategies. Targeting CSCs is a potential treatment plan to conquer cancer and prevent resistance and relapse in cancer treatment.

Therapeutic vulnerabilities of cancer stem cells and effects of natural products

Covering: 1995 to 2022Tumors possess both genetic and phenotypic heterogeneity leading to the survival of subpopulations post-treatment. The term cancer stem cells (CSCs) describes a subpopulation that is resistant to many types of chemotherapy and which also possess enhanced migratory and anchorage-independent growth capabilities. These cells are enriched in residual tumor material post-treatment and can serve as the seed for future tumor re-growth, at both primary and metastatic sites. Elimination of CSCs is a key goal in enhancing cancer treatment and may be aided by application of natural products in conjunction with conventional treatments. In this review, we highlight molecular features of CSCs and discuss synthesis, structure-activity relationships, derivatization, and effects of six natural products with anti-CSC activity.

Anoikis resistance--protagonists of breast cancer cells survive and metastasize after ECM detachment

Breast cancer exhibits the highest global incidence among all tumor types. Regardless of the type of breast cancer, metastasis is a crucial cause of poor prognosis. Anoikis, a form of apoptosis initiated by cell detachment from the native environment, is an outside-in process commencing with the disruption of cytosolic connectors such as integrin-ECM and cadherin-cell. This disruption subsequently leads to intracellular cytoskeletal and signaling pathway alterations, ultimately activating caspases and initiating programmed cell death. Development of an anoikis-resistant phenotype is a critical initial step in tumor metastasis. Breast cancer employs a series of stromal alterations to suppress anoikis in cancer cells. Comprehensive investigation of anoikis resistance mechanisms can inform strategies for preventing and regressing metastatic breast cancer. The present review first outlines the physiological mechanisms of anoikis, elucidating the alterations in signaling pathways, cytoskeleton, and protein targets that transpire from the outside in upon adhesion loss in normal breast cells. The specific anoikis resistance mechanisms induced by pathological changes in various spatial structures during breast cancer development are also discussed. Additionally, the genetic loci of targets altered in the development of anoikis resistance in breast cancer, are summarized. Finally, the micro-RNAs and targeted drugs reported in the literature concerning anoikis are compiled, with keratocin being the most functionally comprehensive. Video Abstract.

Three-Dimensional Printing Enabled Droplet Microfluidic Device for Real-Time Monitoring of Single-Cell Viability and Blebbing Activity

Droplet-based microfluidics with the characteristics of high throughput, low sample consumption, increasing reaction speed, and homogeneous volume control have been demonstrated as a useful platform for biomedical research and applications. The traditional fabrication methods of droplet microfluidics largely rely on expensive instruments, sophisticated operations, and even the requirement of an ultraclean room. In this manuscript, we present a 3D printing-based droplet microfluidic system with a specifically designed microstructure for droplet generation aimed at developing a more accessible and cost-effective method. The performance of droplet generation and the encapsulation capacity of the setup were examined. The device was further applied to measure the variation in cell viability over time and monitor the cell's blebbing activity to investigate its potential ability and feasibility for single-cell analysis. The result demonstrated that the produced droplets remained stable enough to enable the long-time detection of cell viability. Additionally, cell membrane protrusions featuring the life cycle of bleb initiation, expansion, and retraction can be well-observed. Three-dimensional printing-based droplet microfluidics benefit from the ease of manufacture, which is expected to simplify the fabrication of microfluidics and expand the application of the droplet approach in biomedical fields.

Salinomycin mediated therapeutic targeting of circulating stem like cell population in oral cancer

CD44+ circulating tumor stem cells (CTSCs) have been significantly associated with aggressiveness, resistance and poor prognosis of oral cancer patients. Thus, targeted elimination of these CTSCs could be a new conceptual framework for enhancing the therapeutic outcome of patients. Docking of potential investigational molecules and simulation results identified Salinomycin as a potential lead compound that could effectively inhibit CD44 receptor. To assess the cytotoxic effect, immuno-magnetically sorted circulatory CD44+ cells were subjected to increasing concentrations of 5FU, Cisplatin and Salinomycin. Salinomycin demonstrated significant cytotoxic effect towards the CD44+ subpopulation in a dose and time dependent manner. Further the effect of these compounds was investigated on apoptosis, cell cycle, signaling pathways and gene expression profiles using Muse^TM flow cytometer and Real-Time PCR. It was observed that mRNA expression patterns of CD44v6, Nanog, AKT1, CDKN2A and β-catenin of Salinomycin treated CD44+ cells. Moreover, Salinomycin significantly induced programmed cell death by inducing G2/M cell cycle arrest and inhibiting MAPK/PI3K pathways in this chemo-resistant population. Thus, this study demonstrated the potential of Salinomycin to target the chemo-resistant circulating CD44 population by attenuating its proliferation and survival.Communicated by Ramaswamy H. Sarma.

Role of STAT3 in the initiation, progression, proliferation and metastasis of breast cancer and strategies to deliver JAK and STAT3 inhibitors

INTRODUCTION

Breast cancer (BC) accounts for the majority of cancers among the female population. Anomalous activation of various signaling pathways has become an issue of concern. The JAK-STAT signaling pathway is activated in numerous cancers, including BC. STAT3 is widely involved in BCs, as 40 % of BCs display phosphorylated STAT3. JAK-STAT signaling is crucial for proliferation, survival, metastasis and other cellular events associated with the tumor microenvironment. Hence, targeting this pathway has become an area of interest among researchers.

KEY FINDINGS

This review article focuses on the role of STAT3 in the initiation, proliferation, progression and metastasis of BC. The roles of various phytochemicals, synthetic molecules and biologicals against JAK-STAT and STAT3 in various cancers have been discussed, with special emphasis on BC.

SIGNIFICANCE

JAK and STAT3 are involved in various phases from initiation to metastasis, and targeting this pathway is a promising approach to inhibit the various stages of BC development and to prevent metastasis. A number of phytochemicals and synthetic and biological molecules have demonstrated potential inhibitory effects on JAK and STAT3, thereby paving the way for the development of better therapeutics against BC.

Understanding the cell survival mechanism of anoikis-resistant cancer cells during different steps of metastasis

Anchorage-independent survival of cancer cells is associated with metastasis as it enables cells to travel to secondary target sites. Tissue integrity is generally maintained by detachment-induced cell death called 'anoikis', but cancer cells undergoing the multistep metastatic process show resistance to anoikis. Anoikis resistance enables these cells to survive through the extracellular matrix (ECM) deprived phase, which starts when cancer cells detach and move into the circulation till cells reach to the secondary target site. Comprehensive analysis of the molecular and functional biology of anoikis resistance in cancer cells will provide crucial details about cancer metastasis, enabling us to identify novel therapeutic targets against cancer cell dissemination and ultimately secondary tumor formation. This review broadly summarizes recent advances in the understanding of cellular and molecular events leading to anoikis and anoikis resistance. It further elaborates more about the signaling cross-talk in anoikis resistance and its regulation during metastasis.

Targeting regulated cell death (RCD) with small-molecule compounds in triple-negative breast cancer: a revisited perspective from molecular mechanisms to targeted therapies

Triple-negative breast cancer (TNBC) is a subtype of human breast cancer with one of the worst prognoses, with no targeted therapeutic strategies currently available. Regulated cell death (RCD), also known as programmed cell death (PCD), has been widely reported to have numerous links to the progression and therapy of many types of human cancer. Of note, RCD can be divided into numerous different subroutines, including autophagy-dependent cell death, apoptosis, mitotic catastrophe, necroptosis, ferroptosis, pyroptosis and anoikis. More recently, targeting the subroutines of RCD with small-molecule compounds has been emerging as a promising therapeutic strategy, which has rapidly progressed in the treatment of TNBC. Therefore, in this review, we focus on summarizing the molecular mechanisms of the above-mentioned seven major RCD subroutines related to TNBC and the latest progress of small-molecule compounds targeting different RCD subroutines. Moreover, we further discuss the combined strategies of one drug (e.g., narciclasine) or more drugs (e.g., torin-1 combined with chloroquine) to achieve the therapeutic potential on TNBC by regulating RCD subroutines. More importantly, we demonstrate several small-molecule compounds (e.g., ONC201 and NCT03733119) by targeting the subroutines of RCD in TNBC clinical trials. Taken together, these findings will provide a clue on illuminating more actionable low-hanging-fruit druggable targets and candidate small-molecule drugs for potential RCD-related TNBC therapies.

Protective Effect of Liposomal Epigallocatechin-Gallate in Experimental Gentamicin-Induced Hepatotoxicity

Our study aimed to assess the effect of liposomal epigallocatechin-gallate (LEGCG) compared with epigallocatechin-gallate (EGCG) solution on hepatic toxicity induced by gentamicin (G) administration in rats. Five groups were evaluated, a control group (no G administration) and four groups that received G (1 mL, i.p, 80 mg/kg b.w. (body weight/day), for 7 days) to which we associated daily administration 30 min before G of EGCG (G-EGCG, 2.5 mg/0.1 kg b.w.), LEGCG (G-LEGCG, 2.5 mg/0.1 kg b.w.) or silymarin (100 mg/kg b.w./day). The nitro-oxidative stress (NOx), catalase (CAT), TNF-α, transaminases, creatinine, urea, metalloproteinase (MMP) 2 and 9, and liver histopathological changes were evaluated. LEGCG exhibited better efficacy than EGCG, improving the oxidant/antioxidant balance (p = 0.0125 for NOx and 0.0032 for CAT), TNF-α (p < 0.0001), MMP-2 (p < 0.0001), aminotransferases (p = 0.0001 for AST and 0.0136 for ALT), creatinine (p < 0.0001), urea (p = 0.0006) and histopathologic liver changes induced by gentamicin. Our study demonstrated the beneficial effect of EGCG with superior results of the liposomal formulation for hepatoprotection in experimental hepatic toxicity induced by gentamicin.

Protective Effect of Liposomal Epigallocatechin-Gallate in Experimental Gentamicin-Induced Hepatotoxicity

Our study aimed to assess the effect of liposomal epigallocatechin-gallate (LEGCG) compared with epigallocatechin-gallate (EGCG) solution on hepatic toxicity induced by gentamicin (G) administration in rats. Five groups were evaluated, a control group (no G administration) and four groups that received G (1 mL, i.p, 80 mg/kg b.w. (body weight/day), for 7 days) to which we associated daily administration 30 min before G of EGCG (G-EGCG, 2.5 mg/0.1 kg b.w.), LEGCG (G-LEGCG, 2.5 mg/0.1 kg b.w.) or silymarin (100 mg/kg b.w./day). The nitro-oxidative stress (NOx), catalase (CAT), TNF-α, transaminases, creatinine, urea, metalloproteinase (MMP) 2 and 9, and liver histopathological changes were evaluated. LEGCG exhibited better efficacy than EGCG, improving the oxidant/antioxidant balance (p = 0.0125 for NOx and 0.0032 for CAT), TNF-α (p < 0.0001), MMP-2 (p < 0.0001), aminotransferases (p = 0.0001 for AST and 0.0136 for ALT), creatinine (p < 0.0001), urea (p = 0.0006) and histopathologic liver changes induced by gentamicin. Our study demonstrated the beneficial effect of EGCG with superior results of the liposomal formulation for hepatoprotection in experimental hepatic toxicity induced by gentamicin.

Protective Effect of Liposomal Epigallocatechin-Gallate in Experimental Gentamicin-Induced Hepatotoxicity

Our study aimed to assess the effect of liposomal epigallocatechin-gallate (LEGCG) compared with epigallocatechin-gallate (EGCG) solution on hepatic toxicity induced by gentamicin (G) administration in rats. Five groups were evaluated, a control group (no G administration) and four groups that received G (1 mL, i.p, 80 mg/kg b.w. (body weight/day), for 7 days) to which we associated daily administration 30 min before G of EGCG (G-EGCG, 2.5 mg/0.1 kg b.w.), LEGCG (G-LEGCG, 2.5 mg/0.1 kg b.w.) or silymarin (100 mg/kg b.w./day). The nitro-oxidative stress (NOx), catalase (CAT), TNF-α, transaminases, creatinine, urea, metalloproteinase (MMP) 2 and 9, and liver histopathological changes were evaluated. LEGCG exhibited better efficacy than EGCG, improving the oxidant/antioxidant balance (p = 0.0125 for NOx and 0.0032 for CAT), TNF-α (p < 0.0001), MMP-2 (p < 0.0001), aminotransferases (p = 0.0001 for AST and 0.0136 for ALT), creatinine (p < 0.0001), urea (p = 0.0006) and histopathologic liver changes induced by gentamicin. Our study demonstrated the beneficial effect of EGCG with superior results of the liposomal formulation for hepatoprotection in experimental hepatic toxicity induced by gentamicin.

Salinomycin as a potent anticancer stem cell agent: State of the art and future directions

Cancer stem cells (CSCs) are a small subpopulation of cells within a tumor that can both self‐renew and differentiate into other cell types forming the heterogeneous tumor bulk. Since CSCs are involved in all aspects of cancer development, including tumor initiation, cell proliferation, metastatic dissemination, therapy resistance, and recurrence, they have emerged as attractive targets for cancer treatment and management. Salinomycin, a widely used antibiotic in poultry farming, was identified by the Weinberg group as a potent anti‐CSC agent in 2009. As a polyether ionophore, salinomycin exerts broad‐spectrum activities, including the important anti‐CSC function. Studies on the mechanism of action of salinomycin against cancer have been continuously and rapidly published since then. Thus, it is imperative for us to update its literature of recent research findings in this area. We here summarize the notable work reported on salinomycin's anticancer activities, intracellular binding target(s), effects on tumor microenvironment, safety, derivatives, and tumor‐specific drug delivery; after that we also discuss the translational potential of salinomycin toward clinical application based on current multifaceted understandings.

The C-terminal HSP90 inhibitor NCT-58 kills trastuzumab-resistant breast cancer stem-like cells

N-terminal HSP90 inhibitors in development have had issues arising from heat shock response (HSR) induction and off-target effects. We sought to investigate the capacity of NCT-58, a rationally-synthesized C-terminal HSP90 inhibitor, to kill trastuzumab-resistant HER2-positive breast cancer stem-like cells. NCT-58 does not induce the HSR due to its targeting of the C-terminal region and elicits anti-tumor activity via the simultaneous downregulation of HER family members as well as inhibition of Akt phosphorylation. NCT-58 kills the rapidly proliferating bulk tumor cells as well as the breast cancer stem-like population, coinciding with significant reductions in stem/progenitor markers and pluripotent transcription factors. NCT-58 treatment suppressed growth and angiogenesis in a trastuzumab-resistant xenograft model, concomitant with downregulation of ICD-HER2 and HSF-1/HSP70/HSP90. These findings warrant further investigation of NCT-58 to address trastuzumab resistance in heterogeneous HER2-positive cancers.

Single and double modified salinomycin analogs target stem-like cells in 2D and 3D breast cancer models

Breast cancer remains one of the leading cancers among women. Cancer stem cells (CSCs) are tumor-initiating cells which drive progression, metastasis, and reoccurrence of the disease. CSCs are resistant to conventional chemo- and radio-therapies and their ability to survive such treatment enables tumor reestablishment. Metastasis is the main cause of mortality in women with breast cancer, thus advances in treatment will depend on therapeutic strategies targeting CSCs. Salinomycin (SAL) is a naturally occurring polyether ionophore antibiotic known for its anticancer activity towards several types of tumor cells. In the present work, a library of 17 C1-single and C1/C20-double modified SAL analogs was screened to identify compounds with improved activity against breast CSCs. Six single- and two double-modified analogs were more potent (IC50 range of 1.1 ± 0.1-1.4 ± 0.2 µM) toward the breast cancer cell line MDA-MB-231 compared to SAL (IC50 of 4.9 ± 1.6 µM). Double-modified compound 17 was found to be more efficacious than SAL against the majority of cancer cell lines in the NCI-60 Human Tumor Cell Line Panel. Compound 17 was more potent than SAL in inhibiting cell migration and cell renewal properties of MDA-MB-231 cells, as well as inducing selective loss of the CD44+/CD24/low stem-cell-like subpopulation in both monolayer (2D) and organoid (3D) culture. The present findings highlight the therapeutic potential of SAL analogs towards breast CSCs and identify select compounds that merit further study and clinical development.

Anticancer Mechanisms of Salinomycin in Breast Cancer and Its Clinical Applications

Breast cancer (BC) is the most frequent cancer among women worldwide and is the leading cause of cancer-related deaths in women. Cancer cells with stem cell-like features and tumor-initiating potential contribute to drug resistance, tumor recurrence, and metastasis. To achieve better clinical outcomes, it is crucial to eradicate both bulk BC cells and breast cancer stem cells (BCSCs). Salinomycin, a monocarboxylic polyether antibiotic isolated from Streptomyces albus, can precisely kill cancer stem cells (CSCs), particularly BCSCs, by various mechanisms, including apoptosis, autophagy, and necrosis. There is increasing evidence that salinomycin can inhibit cell proliferation, invasion, and migration in BC and reverse the immune-inhibitory microenvironment to prevent tumor growth and metastasis. Therefore, salinomycin is a promising therapeutic drug for BC. In this review, we summarize established mechanisms by which salinomycin protects against BC and discuss its future clinical applications.

Upregulation of V-ATPase by STAT3 Activation Promotes Anoikis Resistance and Tumor Metastasis

Most cancer mortality results from metastatic tumor cells and not the localized tumor. Overcoming anoikis is one of the most important steps for detached tumor cells to migrate and metastasize. However, the molecular mechanisms remain to be fully deciphered. Herein, our study revealed upregulation of vacuolar ATPase (V-ATPase) in cancer cells during ECM detachment plays a key role in anoikis evasion. V-ATPase is an enzyme complex that utilizes energy from ATP hydrolysis to maintain cellular homeostasis and had been reported to enhance cancer progression. In this study, V-ATPase inhibition sensitized human cervical cancer, breast cancer, and murine melanoma cells to anoikis via increased ROS production, accumulation of misfolded protein, and impaired pulmonary metastasis in vivo. Scavenging ROS restored anoikis resistance and clearance of misfolded protein accumulation in the tumor cells. Mechanistically, STAT3 upregulates V-ATPase expression while blockade of STAT3 activity repressed V-ATPase expression in these tumor cells as well as sensitized cells to anoikis, increased ROS production, and misfolded protein accumulation. Altogether, our data demonstrate an unreported role of STAT3 in mediating the upregulation of V-ATPase to promote anoikis resistance, thus provides an alternative option to target cancer metastasis.

Plasticity of Cancer Stem Cell: Origin and Role in Disease Progression and Therapy Resistance

In embryonic development and throughout life, there are some cells can exhibit phenotypic plasticity. Phenotypic plasticity is the ability of cells to differentiate into multiple lineages. In normal development, plasticity is highly regulated whereas cancer cells re-activate this dynamic ability for their own progression. The re-activation of these mechanisms enables cancer cells to acquire a cancer stem cell (CSC) phenotype- a subpopulation of cells with increased ability to survive in a hostile environment and resist therapeutic insults. There are several contributors fuel CSC plasticity in different stages of disease progression such as a complex network of tumour stroma, epidermal microenvironment and different sub-compartments within tumour. These factors play a key role in the transformation of tumour cells from a stable condition to a progressive state. In addition, flexibility in the metabolic state of CSCs helps in disease progression. Moreover, epigenetic changes such as chromatin, DNA methylation could stimulate the phenotypic change of CSCs. Development of resistance to therapy due to highly plastic behaviour of CSCs is a major cause of treatment failure in cancers. However, recent studies explored that plasticity can also expose the weaknesses in CSCs, thereby could be utilized for future therapeutic development. Therefore, in this review, we discuss how cancer cells acquire the plasticity, especially the role of the normal developmental process, tumour microenvironment, and epigenetic changes in the development of plasticity. We further highlight the therapeutic resistance property of CSCs attributed by plasticity. Also, outline some potential therapeutic options against plasticity of CSCs. Graphical Abstract .

Epithelial-mesenchymal transition sensitizes breast cancer cells to cell death via the fungus-derived sesterterpenoid ophiobolin A

The epithelial-mesenchymal transition (EMT) imparts properties of cancer stem-like cells, including resistance to frequently used chemotherapies, necessitating the identification of molecules that induce cell death specifically in stem-like cells with EMT properties. Herein, we demonstrate that breast cancer cells enriched for EMT features are more sensitive to cytotoxicity induced by ophiobolin A (OpA), a sesterterpenoid natural product. Using a model of experimentally induced EMT in human mammary epithelial (HMLE) cells, we show that EMT is both necessary and sufficient for OpA sensitivity. Moreover prolonged, sub-cytotoxic exposure to OpA is sufficient to suppress EMT-imparted CSC features including sphere formation and resistance to doxorubicin. In vivo growth of CSC-rich mammary cell tumors, is suppressed by OpA treatment. These data identify a driver of EMT-driven cytotoxicity with significant potential for use either in combination with standard chemotherapy or for tumors enriched for EMT features.

Lipid nanocapsules co-encapsulating paclitaxel and salinomycin for eradicating breast cancer and cancer stem cells

Cancer stem cells (CSCs) comprise a diminutive population of the tumor but pose major obstacles in cancer treatment, often their presence being correlated with poor prognosis, therapeutic resistance and relapse. Nanocarriers of combined drugs regimes demonstrate improved pharmacokinetics and decreased systemic toxicity by targeting the bulk tumor cells along with CSCs, holding the key to future successful chemotherapy. Herein, we developed lipid nanocapsules (LNCs) with co-encapsulated paclitaxel (PTX) and salinomycin (SAL) to eliminate breast cancer cells (MCF-7; non-bCSCs) and cancer stem cells (bCSCs) respectively. LNCs loaded with either PTX or SAL alone or in combination were fabricated by the phase inversion temperature (PIT) method. Physicochemical properties such as nano-size (90 ± 5 nm) and spherical morphology of LNCs were confirmed by dynamic light scattering (DLS) and scanning electron microscopy (SEM) respectively. More than 98 % encapsulation efficiency of drug, alone or in combination, and their controlled drug release was obtained. Drug loaded LNCs were efficiently internalized and exhibited cytotoxicity in non-bCSCs and bCSCs, with dual drug loaded LNCs offering superior cytotoxicity and anti-bCSCs property. Drug loaded nanocapsules induced apoptosis in bCSCs, potentiated with the co-delivery of paclitaxel and salinomycin. Synergistic cytotoxic effect on both cells, non-bCSCs and bCSCs and effective reduction of the tumor mammospheres growth by co-encapsulated paclitaxel and salinomycin suggest LNCs to be promising for treatment of breast cancer.

Mechanisms for Modulating Anoikis Resistance in Cancer and the Relevance of Metabolic Reprogramming

The attachment of cells to the extracellular matrix (ECM) is the hallmark of structure–function stability and well-being. ECM detachment in localized tumors precedes abnormal dissemination of tumor cells culminating in metastasis. Programmed cell death (PCD) is activated during tumorigenesis to clear off ECM-detached cells through “anoikis.” However, cancer cells develop several mechanisms for abrogating anoikis, thus promoting their invasiveness and metastasis. Specific factors, such as growth proteins, pH, transcriptional signaling pathways, and oxidative stress, have been reported as drivers of anoikis resistance, thus enhancing cancer proliferation and metastasis. Recent studies highlighted the key contributions of metabolic pathways, enabling the cells to bypass anoikis. Therefore, understanding the mechanisms driving anoikis resistance could help to counteract tumor progression and prevent metastasis. This review elucidates the dynamics employed by cancer cells to impede anoikis, thus promoting proliferation, invasion, and metastasis. In addition, the authors have discussed other metabolic intermediates (especially amino acids and nucleotides) that are less explored, which could be crucial for anoikis resistance and metastasis.

Small-Molecule Drug Discovery in Triple Negative Breast Cancer: Current Situation and Future Directions

Triple negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, but an effective targeted therapy has not been well-established so far. Considering the lack of effective targets, where do we go next in the current TNBC drug development? A promising intervention for TNBC might lie in de novo small-molecule drugs that precisely target different molecular characteristics of TNBC. However, an ideal single-target drug discovery still faces a huge challenge. Alternatively, other new emerging strategies, such as dual-target drug, drug repurposing, and combination strategies, may provide new insight into the improvement of TNBC therapeutics. In this review, we focus on summarizing the current situation of a series of candidate small-molecule drugs in TNBC therapy, including single-target drugs, dual-target drugs, as well as drug repurposing and combination strategies that will together shed new light on the future directions targeting TNBC vulnerabilities with small-molecule drugs for future therapeutic purposes.

Trailblazing perspectives on targeting breast cancer stem cells

Breast cancer (BCa) is one of the most prevalent malignant tumors affecting women's health worldwide. The recurrence and metastasis of BCa have made it a long-standing challenge to achieve remission-persistent or disease-undetectable clinical outcomes. Cancer stem cells (CSCs) possess the ability to self-renew and generate heterogeneous tumor bulk. The existence of CSCs has been found to be vital in the initiation, metastasis, therapy resistance, and recurrence of tumors across cancer types. Because CSCs grow slowly in their dormant state, they are insensitive to conventional chemotherapies; however, when CSCs emerge from their dormant state and become clinically evident, they usually acquire genetic traits that make them resistant to existing therapies. Moreover, CSCs also show evidence of acquired drug resistance in synchrony with tumor relapses. The concept of CSCs provides a new treatment strategy for BCa. In this review, we highlight the recent advances in research on breast CSCs and their association with epithelial-mesenchymal transition (EMT), circulating tumor cells (CTCs), plasticity of tumor cells, tumor microenvironment (TME), T-cell modulatory protein PD-L1, and non-coding RNAs. On the basis that CSCs are associated with multiple dysregulated biological processes, we envisage that increased understanding of disease sub-classification, selected combination of conventional treatment, molecular aberration directed therapy, immunotherapy, and CSC targeting/sensitizing strategy might improve the treatment outcome of patients with advanced BCa. We also discuss novel perspectives on new drugs and therapeutics purposing the potent and selective expunging of CSCs.

Coriolic Acid (13-(S)-Hydroxy-9Z, 11E-octadecadienoic Acid) from Glasswort (Salicornia herbacea L.) Suppresses Breast Cancer Stem Cell through the Regulation of c-Myc

Cancer stem cells have certain characteristics, such as self-renewal, differentiation, and drug resistance, which are related to tumor progression, maintenance, recurrence, and metastasis. In our study, we targeted breast cancer stem cells (BCSCs) using a natural compound, coriolic acid, from Salicornia herbacea L. This compound was isolated by mammosphere formation inhibition bioassay-guided fractionation and identified by using NMR spectroscopy and electrospray ionization mass spectrometry. Coriolic acid inhibited the formation of mammospheres and induced BCSC apoptosis. It also decreased the subpopulation of CD44^high/CD24^low cells, a cancer stem cell (CSC) phenotype, and specific genes related to CSCs, such as Nanog,Oct4, and CD44. Coriolic acid decreased the transcriptional and translational levels of the c-Myc gene, which is a CSC survival factor. These results indicated that coriolic acid could be a novel compound to target BCSCs via regulation of c-Myc.

Salinomycin promotes T-cell proliferation by inhibiting the expression and enzymatic activity of immunosuppressive indoleamine-2,3-dioxygenase in human breast cancer cells

Indoleamine 2,3 dioxygenase (IDO) is upregulated in many tumor types, including breast cancer, and plays a reputable role in promoting tumor immune tolerance. The importance of the immunosuppressive mechanism of IDO by suppressing T-cell function has garnered profound interest in the development of clinical IDO inhibitors. Herein, we established a screening method with cervical HeLa cells to induce IDO expression using interferon-γ (IFN-γ). After screening our chemical library, we found that salinomycin potently inhibited IFN-γ-stimulated kynurenine synthesis with IC₅₀ values of 3.36-4.66 μM in both human cervical and breast cancer cells. Salinomycin lowered the IDO1 and IDO2 expression with no impact on the expression of tryptophan-2,3-dioxygenase. Interestingly, salinomycin potently repressed the IDO1 enzymatic activity by directly targeting the proteins in cells. Molecular docking revealed an alignment that favors nucleophilic attack of salinomycin in the catalytic domain of IDO1. Activation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway by IFN-γ was significantly suppressed by salinomycin, via inhibiting the Jak1, Jak2, and STAT1/3 phosphorylation. Moreover, it inhibited IFN-γ-induced activation of the nuclear factor (NF)-κB pathway by inhibiting IκB degradation and NF-κB phosphorylation without affecting BIN1 expression. Furthermore, salinomycin significantly restored the proliferation of T cells co-cultured with IFN-γ-treated breast cancer cells and potentiated antitumor activity of cisplatin in vivo. These findings suggest that salinomycin suppresses kynurenine synthesis by inhibiting the catalytic activity of IDO1 and its expression by inhibiting the JAK/STAT and NF-κB pathways. Salinomycin warrants further investigation as a novel dual-functional IDO inhibitor for cancer immunotherapy.

Integrin-EGFR interaction regulates anoikis resistance in colon cancer cells

Anoikis resistance is an essential property of cancer cells that allow the extra-cellular matrix-detached cells to survive in a suspended state in body fluid in order to metastasize and invade to distant organs. It is known that integrins play an important role in anoikis resistance, but detailed mechanisms are not well understood. Here we report that highly metastatic colon cancer cells showed a higher degree of anoikis resistance than the normal intestinal epithelial cells. These anoikis-resistant cancer cells express high-levels of integrin-α2, β1, and activated EGFR in the anchorage-independent state than the anchorage-dependent state. In contrast, normal intestinal epithelial cells failed to elevate these proteins. Interestingly, a higher co-association of EGFR with integrin-α2β1/-α5β1 was observed on the surface of anoikis-resistant cells. Thus, in the absence of extra-cellular matrix, integrins in association with EGFR activates downstream effectors ERK and AKT and suppress Caspase-3 activation to induce anoikis resistance as was confirmed from the gene-ablation and pharmacological inhibitor studies. Interestingly, these anoikis-resistant cancer cells express high-level of cancer stem cell signatures (CD24, CD44, CD133, EpCAM) and pluripotent stem cell markers (OCT-4, SOX-2, Nanog) as well as drug-resistant pumps (ABCG2, MDR1, MRP1). Altogether, our findings unravel the interplay between integrin-α2β1/-α5β1 and EGFR in anoikis resistance and suggest that the resistant cells are cancer initiating or cancer stem cells, which may serve as a promising target to combat metastasis of cancer.

Transcriptomic insight into salinomycin mechanisms in breast cancer cell lines: synergistic effects with dasatinib and induction of estrogen receptor β

BACKGROUND

Tumors are heterogeneous in nature, composed of different cell populations with various mutations and/or phenotypes. Using a single drug to encounter cancer progression is generally ineffective. To improve the treatment outcome, multiple drugs of distinctive mechanisms but complementary anticancer activities (combination therapy) are often used to enhance antitumor efficacy and minimize the risk of acquiring drug resistance. We report here the synergistic effects of salinomycin (a polyether antibiotic) and dasatinib (a Src kinase inhibitor).

METHODS

Functionally, both drugs induce cell cycle arrest, intracellular reactive oxygen species (iROS) production, and apoptosis. We rationalized that an overlapping of the drug activities should offer an enhanced anticancer effect, either through vertical inhibition of the Src-STAT3 axis or horizontal suppression of multiple pathways. We determined the toxicity induced by the drug combination and studied the kinetics of iROS production by fluorescence imaging and flow cytometry. Using genomic and proteomic techniques, including RNA-sequencing (RNA-seq), reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and Western Blot, we subsequently identified the responsible pathways that contributed to the synergistic effects of the drug combination.

RESULTS

Compared to either drug alone, the drug combination showed enhanced potency against MDA-MB-468, MDA-MB-231, and MCF-7 human breast cancer (BC) cell lines and tumor spheroids. The drug combination induces both iROS generation and apoptosis in a time-dependent manner, following a 2-step kinetic profile. RNA-seq data revealed that the drug combination exhibited synergism through horizontal suppression of multiple pathways, possibly through a promotion of cell cycle arrest at the G1/S phase via the estrogen-mediated S-phase entry pathway, and partially via the BRCA1 and DNA damage response pathway.

CONCLUSION

Transcriptomic analyses revealed for the first time, that the estrogen-mediated S-phase entry pathway partially contributed to the synergistic effect of the drug combination. More importantly, our studies led to the discoveries of new potential therapeutic targets, such as E2F2, as well as a novel drug-induced targeting of estrogen receptor β (ESR2) approach for triple-negative breast cancer treatment, currently lacking of targeted therapies.

Salinomycin Treatment Specifically Inhibits Cell Proliferation of Cancer Stem Cells Revealed by Longitudinal Single Cell Tracking in Combination with Fluorescence Microscopy

A cell line derived from a tumor is a heterogeneous mixture of phenotypically different cells. Such cancer cell lines are used extensively in the search for new anticancer drugs and for investigating their mechanisms of action. Most studies today are population-based, implying that small subpopulations of cells, reacting differently to the potential drug go undetected. This is a problem specifically related to the most aggressive single cancer cells in a tumor as they appear to be insensitive to the drugs used today. These cells are not detected in population-based studies when developing new anticancer drugs. Thus, to get a deeper understanding of how all individual cancer cells react to chemotherapeutic drugs, longitudinal tracking of individual cells is needed. Here we have used digital holography for long time imaging and longitudinal tracking of individual JIMT-1 breast cancer cells. To gain further knowledge about the tracked cells, we combined digital holography with fluorescence microscopy. We grouped the JIMT-1 cells into different subpopulations based on expression of CD24 and E-cadherin and analyzed cell proliferation and cell migration for 72 h. We investigated how the cancer stem cell (CSC) targeting drug salinomycin affected the different subpopulations. By uniquely combining digital holography with fluorescence microscopy we show that salinomycin specifically targeted the CD24− subpopulation, i.e., the CSCs, by inhibiting cell proliferation, which was evident already after 24 h of drug treatment. We further found that after salinomycin treatment, the surviving cells were more epithelial-like due to the selection of the CD24+ cells.

The stem cell inhibitor salinomycin decreases colony formation potential and tumor-initiating population in docetaxel-sensitive and docetaxel-resistant prostate cancer cells

BACKGROUND

Prostate cancer (PCa) is one of the most frequently diagnosed tumors in men. In general, therapies for localized PCa are curative. However, treatment of advanced PCa is considered palliative since development of therapy resistance occurs rapidly. It has been shown that tumor-initiating cells are likely involved in therapy resistance. They are not eliminated by conventional therapies and thereby lead to tumor progression and relapse. The aim of this study was to evaluate the effects of the known stem cell inhibitor salinomycin on this critical subpopulation of cells.

METHODS

Expression of the cell surface markers CD24 and CD44 was assessed by immunofluorescence and fluorescence-activated cell sorting. Colony formation efficiency and classification of colony types with varying tumor-initiating potential (holoclones, meroclones, and paraclones) were analyzed in an automated way by the newly developed CATCH-colonies software in the absence or presence of salinomycin.

RESULTS

Automated high-resolution colony formation analysis consistently identified the various colony types in a broad range of PCa cell lines. Serial clonogenic assays confirmed that holoclones show the highest colony formation potential and maintain their tumor-initiating capacity over multiple rounds. Furthermore, holoclones showed high expression of CD44, while CD24 was not expressed in these clones, thus representing the well-described tumor-initiating CD24^- /CD44^high population. Salinomycin decreased the CD24^- /CD44^high population in both docetaxel-sensitive PC3 and docetaxel-resistant (DR) PC3-DR. Moreover, treatment of PC3, DU145, PC3-DR, and DU145-DR with salinomycin led to a significant reduction in the colony formation potential by targeting the colonies with high tumor-initiating potential.

CONCLUSIONS

Taken together, we demonstrated that salinomycin specifically targets the tumor-initiating cell population in docetaxel-sensitive and docetaxel-resistant PCa cells and may represent a potential therapeutic approach for the treatment of advanced PCa.

Cancer stem cells and their unique role in metastatic spread

Cancer stem cells (CSC) possess abilities generally associated with embryonic or adult stem cells, especially self-renewal and differentiation, but also dormancy and cellular plasticity that allow adaption to new environmental circumstances. These abilities are ideal prerequisites for the successful establishment of metastasis. This review highlights the role of CSCs in every step of the metastatic cascade from cancer cell invasion into blood vessels, survival in the blood stream, attachment and extravasation as well as colonization of the host organ and subsequent establishment of distant macrometastasis.

Cancer stem-like cells with hybrid epithelial/mesenchymal phenotype leading the collective invasion

Collective invasion of cancer cells is the key process of circulating tumor cell (CTC) cluster formation, and greatly contributes to metastasis. Cancer stem-like cells (CSC) have a distinct advantage of motility for metastatic dissemination. To verify the role of CSC in the collective invasion, we performed 3D assays to investigate the collective invasion from cancer cell spheroids. The results demonstrated that CSC can significantly promote both collective and single-cell invasion. Further study showed that CSC prefer to move outside and lead the collective invasion. More interestingly, approximately 60% of the leader CSC in collective invasion co-expressed both epithelial and mesenchymal genes, while only 4% co-expressed in single invasive CSC, indicating that CSC with hybrid epithelial/mesenchymal phenotype play a key role in cancer cell collective invasion.

Insights into new mechanisms and models of cancer stem cell multidrug resistance

The acquisition of genetic alterations, clonal evolution, and the tumor microenvironment promote cancer progression, metastasis and therapy resistance. These events correspond to the establishment of the great phenotypic heterogeneity and plasticity of cancer cells that contribute to tumor progression and resistant disease. Targeting resistant cancers is a major challenge in oncology; however, the underlying processes are not yet fully understood. Even though current treatments can reduce tumor size and increase life expectancy, relapse and multidrug resistance (MDR) ultimately remain the second cause of death in developed countries. Recent evidence points toward stem-like phenotypes in cancer cells, promoted by cancer stem cells (CSCs), as the main culprit of cancer relapse, resistance (radiotherapy, hormone therapy, and/or chemotherapy) and metastasis. Many mechanisms have been proposed for CSC resistance, such as drug efflux through ABC transporters, overactivation of the DNA damage response (DDR), apoptosis evasion, prosurvival pathways activation, cell cycle promotion and/or cell metabolic alterations. Nonetheless, targeted therapy toward these specific CSC mechanisms is only partially effective to prevent or abolish resistance, suggesting underlying additional causes for CSC resilience. This article aims to provide an integrated picture of the MDR mechanisms that operate in CSCs' behavior and to propose a novel model of tumor evolution during chemotherapy. Targeting the pathways mentioned here might hold promise and reveal new strategies for future clinical therapeutic approaches.

Lovastatin-mediated MCF-7 cancer cell death involves LKB1-AMPK-p38MAPK-p53-survivin signalling cascade

There is increasing evidence that statins, which are widely used in lowering serum cholesterol and the incidence of cardiovascular diseases, also exhibits anti‐tumour properties. The underlying mechanisms by which statins‐induced cancer cell death, however, remain incompletely understood. In this study, we explored the anti‐tumour mechanisms of a lipophilic statin, lovastatin, in MCF‐7 breast cancer cells. Lovastatin inhibited cell proliferation and induced cell apoptosis. Lovastatin caused p21 elevation while reduced cyclin D1 and survivin levels. Lovastatin also increased p53 phosphorylation, acetylation and its reporter activities. Results from chromatin immunoprecipitation analysis showed that p53 binding to the survivin promoter region was increased, while Sp1 binding to the region was decreased, in MCF‐7 cells after lovastatin exposure. These actions were associated with liver kinase B1 (LKB1), AMP‐activated protein kinase (AMPK) and p38 mitogen‐activated protein kinase (p38MAPK) activation. Lovastatin's enhancing effects on p53 activation, p21 elevation and survivin reduction were significantly reduced in the presence of p38MAPK signalling inhibitor. Furthermore, LKB1‐AMPK signalling blockade abrogated lovastatin‐induced p38MAPK and p53 phosphorylation. Together these results suggest that lovastatin may activate LKB1‐AMPK‐p38MAPK‐p53‐survivin cascade to cause MCF‐7 cell death. The present study establishes, at least in part, the signalling cascade by which lovastatin induces breast cancer cell death.

Synthesis and Anticancer Activity of Tertiary Amides of Salinomycin and Their C20-oxo Analogues

The polyether ionophore salinomycin (SAL) has captured much interest because of its potent activity against cancer cells and cancer stem cells. Our previous studies have indicated that C1/C20 double-modification of SAL is a useful strategy to generate diverse agents with promising biological activity profiles. Thus, herein we describe the synthesis of a new class of SAL analogues that combine key modifications at the C1 and C20 positions. The activity of the obtained SAL derivatives was evaluated using primary acute lymphoblastic leukemia, human breast adenocarcinoma and normal mammary epithelial cells. One single- [N,N-dipropyl amide of salinomycin (5 a)] and two novel double-modified analogues [N,N-dipropyl amide of C20-oxosalinomycin (5 b) and piperazine amide of C20-oxosalinomycin (13 b)] were found to be more potent toward the MDA-MB-231 cell line than SAL or its C20-oxo analogue 2. When select analogues were tested against the NCI-60 human tumor cell line panel, 4 a [N,N-diethyl amide of salinomycin] showed particular activity toward the ovarian cancer cell line SK-OV-3. Additionally, both SAL and 2 were found to be potent ex vivo against human ER/PR⁺ , Her2^- invasive mammary carcinoma, with 2 showing minimal toxicity toward normal epithelial cells. The present findings highlight the therapeutic potential of SAL derivatives for select targeting of different cancer types.

Disruption of the NF-κB/IL-8 Signaling Axis by Sulconazole Inhibits Human Breast Cancer Stem Cell Formation

Breast cancer stem cells (BCSCs) are tumor-initiating cells that possess the capacity for self-renewal. Cancer stem cells (CSCs) are responsible for poor outcomes caused by therapeutic resistance. In our study, we found that sulconazole—an antifungal medicine in the imidazole class—inhibited cell proliferation, tumor growth, and CSC formation. This compound also reduced the frequency of cells expressing CSC markers (CD44^high/CD24^low) as well as the expression of another CSC marker, aldehyde dehydrogenase (ALDH), and other self-renewal-related genes. Sulconazole inhibited mammosphere formation, reduced the protein level of nuclear NF-κB, and reduced extracellular IL-8 levels in mammospheres. Knocking down NF-κB expression using a p65-specific siRNA reduced CSC formation and secreted IL-8 levels in mammospheres. Sulconazole reduced nuclear NF-κB protein levels and secreted IL-8 levels in mammospheres. These new findings show that sulconazole blocks the NF-κB/IL-8 signaling pathway and CSC formation. NF-κB/IL-8 signaling is important for CSC formation and may be an important therapeutic target for BCSC treatment.

STAT3 as a potential therapeutic target in triple negative breast cancer: a systematic review

Triple negative breast cancer (TNBC), which is typically lack of expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), represents the most aggressive and mortal subtype of breast cancer. Currently, only a few treatment options are available for TNBC due to the absence of molecular targets, which underscores the need for developing novel therapeutic and preventive approaches for this disease. Recent evidence from clinical trials and preclinical studies has demonstrated a pivotal role of signal transducer and activator of transcription 3 (STAT3) in the initiation, progression, metastasis, and immune evasion of TNBC. STAT3 is overexpressed and constitutively activated in TNBC cells and contributes to cell survival, proliferation, cell cycle progression, anti-apoptosis, migration, invasion, angiogenesis, chemoresistance, immunosuppression, and stem cells self-renewal and differentiation by regulating the expression of its downstream target genes. STAT3 small molecule inhibitors have been developed and shown excellent anticancer activities in in vitro and in vivo models of TNBC. This review discusses the recent advances in the understanding of STAT3, with a focus on STAT3’s oncogenic role in TNBC. The current targeting strategies and representative small molecule inhibitors of STAT3 are highlighted. We also propose potential strategies that can be further examined for developing more specific and effective inhibitors for TNBC prevention and therapy.

Salinomycin and its derivatives - A new class of multiple-targeted "magic bullets"

The history of drug development clearly shows the scale of painstaking effort leading to a finished product - a highly biologically active agent that would be at the same time no or little toxic to human organism. Moreover, the aim of modern drug discovery can move from "one-molecule one-target" concept to more promising "one-molecule multiple-targets" one, particularly in the context of effective fight against cancer and other complex diseases. Gratifyingly, natural compounds are excellent source of potential drug leads. One of such promising naturally-occurring drug candidates is a polyether ionophore - salinomycin (SAL). This compound should be identified as multi-target agent for two reasons. Firstly, SAL combines a broad spectrum of bioactivity, including antibacterial, antifungal, antiviral, antiparasitic and anticancer activity, with high selectivity of action, proving its significant therapeutic potential. Secondly, the multimodal mechanism of action of SAL has been shown to be related to its interactions with multiple molecular targets and signalling pathways that are synergistic for achieving a therapeutic anticancer effect. On the other hand, according to the Paul Ehrlich's "magic bullet" concept, invariably inspiring the scientists working on design of novel target-selective molecules, a very interesting direction of research is rational chemical modification of SAL. Importantly, many of SAL derivatives have been found to be more promising as chemotherapeutics than the native structure. This concise review article is focused both on the possible role of SAL and its selected analogues in future antimicrobial and/or cancer therapy, and on the potential use of SAL as a new class of multiple-targeted "magic bullet" because of its multimodal mechanism of action.

MiR-451a suppressing BAP31 can inhibit proliferation and increase apoptosis through inducing ER stress in colorectal cancer

The global morbidity and mortality of colorectal cancer (CRC) are ranked the third among gastrointestinal tumors in the world. MiR-451a is associated with several types of cancer, including CRC. However, the roles and mechanisms of miR-451a in CRC have not been elucidated. BAP31 is a predicted target gene of miR-451a in our suppression subtractive hybridization library. Its relationship with miR-451a and function in CRC are unclear. We hypothesized that miR-451a could induce apoptosis through suppressing BAP31 in CRC. Immunohistochemistry and real-time PCR were used to measure BAP31 expressions in CRC tissues and pericarcinous tissues from 57 CRC patients and CRC cell lines. Dual-luciferase reporter assay was used to detect the binding of miR-451a to BAP31. The expression of BAP31 protein in CRC tissues was significantly higher than that in pericarcinous tissues, which was correlated with distant metastasis and advanced clinical stages of CRC patients. The expression of BAP31 was higher in HCT116, HT29, SW620, and DLD cells than that in the normal colonic epithelial cell line NCM460. The expression of BAP31 was absolutely down-regulated when over-expressing miR-451a in HCT116 and SW620 cells compared with control cells. Mir-451a inhibited the expression of BAP31 by binding to its 5'-UTR. Over-expressing miR-451a or silencing BAP31 suppressed the proliferation and apoptosis of CRC cells by increasing the expressions of endoplasmic reticulum stress (ERS)-associated proteins, including GRP78/BIP, BAX, and PERK/elF2α/ATF4/CHOP, which resulted in increased ERS, cytoplasmic calcium ion flowing, and apoptosis of CRC cells. These changes resulting from over-expressing miR-451a were reversed by over-expressing BAP31 with mutated miR-451a-binding sites. Over-expressing miR-451a or silencing BAP31 inhibited tumor growth by inducing ERS. The present study demonstrated that miR-451a can inhibit proliferation and increase apoptosis through inducing ERS by binding to the 5'-UTR of BAP31 in CRC.

Silibinin, A Natural Blend In Polytherapy Formulation For Targeting Cd44v6 Expressing Colon Cancer Stem Cells

Colon cancer stem cells have been attributed to poor prognosis, therapeutic resistance and aggressive nature of the malignancy. Recent reports associated CD44v6 expression with relapse, metastasis and reduced 5-year survival of colon cancer patients, thereby making it a potential therapeutic target. Thus, in this study, comprehensive prediction and screening of CD44v6 against 1674 lead compounds was conducted. Silibinin was identified as a potential compound targeting CD44v6. Inorder to substantiate these findings, the cytotoxic effect of 5FU, Silibinin and 5FU+ Silibinin was assessed on human colon carcinoma cell line HCT116 derived CD44+ subpopulation. 5FU+ Silibinin inhibited cell proliferation of CD44+ subpopulation at lower concentration than Silibinin standalone. Further, corresponding to CD44v6 knockdown cells, 5FU+ Silibinin treatment significantly decreased CD44v6, Nanog, CTNNB1 and CDKN2A expression whereas increased E-cadherin expression in HCT116 derived CD44+ cells. Moreover, synergistic effect of these drugs suppressed sphere formation, inhibited cell migration, triggered PARP cleavage and perturbation in mitochondrial membrane potential, thereby activating intrinsic apoptotic pathways and induced autophagic cell death. Importantly, 5FU+ Silibinin could inhibit PI3K/MAPK dual activation and arrest the cell cycle at G0/G1 phase. Thus, our study suggests that inhibition of CD44v6 attenuates stemness of colon cancer stem cells and holds a prospect of potent therapeutic target.

Cancer Stem Cells: Emergent Nature of Tumor Emergency

A functional analysis of 167 genes overexpressed in Krebs-2 tumor initiating cells was performed. In the first part of the study, the genes were analyzed for their belonging to one or more of the three groups, which represent the three major phenotypic manifestation of malignancy of cancer cells, namely (1) proliferative self-sufficiency, (2) invasive growth and metastasis, and (3) multiple drug resistance. 96 genes out of 167 were identified as possible contributors to at least one of these fundamental properties. It was also found that substantial part of these genes are also known as genes responsible for formation and/or maintenance of the stemness of normal pluri-/multipotent stem cells. These results suggest that the malignancy is simply the ability to maintain the stem cell specific genes expression profile, and, as a consequence, the stemness itself regardless of the controlling effect of stem niches. In the second part of the study, three stress factors combined into the single concept of "generalized cellular stress," which are assumed to activate the expression of these genes, were defined. In addition, possible mechanisms for such activation were identified. The data obtained suggest the existence of a mechanism for the de novo formation of a pluripotent/stem phenotype in the subpopulation of "committed" tumor cells.

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

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

Diverse effects of phospholipase A2 receptor expression on LNCaP and PC-3 prostate cancer cell growth in vitro and in vivo

Physiological and pathophysiological functions of the phospholipase A2 receptor 1 (PLA2R1) are still not completely understood. To elucidate PLA2R1’s function in prostate carcinoma, the receptor was ectopically overexpressed in LNCaP with silenced PLA2R1, and diminished in PC-3 cells with constitutively increased PLA2R1 expression relative to normal prostate epithelial cells. LNCaP cells were transfected to overexpress PLA2R1 (LNCaP-PLA2R1) and compared to control vector transfected cells (LNCaP-Ctrl). Alternatively, a CRISPR/Cas9-knockdown of PLA2R1 was achieved in PC-3 cells (PC-3 KD) and compared to the corresponding control-transfected cells (PC-3 Ctrl). The impact of PLA2R1 expression on proliferative and metastatic parameters was analysed in vitro. A pilot in vivo study addressed the effects of PLA2R1 in mice xenografted with transfected LNCaP and PC-3 cells. Cell viability/proliferation and motility were significantly increased in LNCaP-PLA2R1 and PC-3 Ctrl compared to LNCaP-Ctrl and PC-3 KD cells, respectively. However, levels of apoptosis, clonogenicity and cell invasion were reduced in LNCaP-PLA2R1 and PC-3 Ctrl cells. Gene expression analysis revealed an up-regulation of fibronectin 1 (FN1), TWIST homolog 1 (TWIST1), and cyclin-dependent kinase 6 (CDK6) in LNCaP-PLA2R1. In LNCaP xenografts, PLA2R1-dependent regulation of clonogenicity appeared to outweigh the receptor’s pro-oncogenic properties, resulting in decreased tumour growth, supporting the tumour-suppressive role of PLA2R1. Alternatively, PC-3 Ctrl xenografts exhibited faster tumour growth compared to PC-3 KD cells, suggesting a pro-oncogenic effect of endogenous PLA2R1 expression. The differential growth-regulatory effects of PLA2R1 may be mediated by FN1, TWIST1, and CDK6 expression, although further investigation is required.

Dynamism, Sensitivity, and Consequences of Mesenchymal and Stem-Like Phenotype of Cancer Cells

There are remarkable similarities in the description of cancer stem cells (CSCs) and cancer cells with mesenchymal phenotype. Both cell types are highly tumorigenic, resistant against common anticancer treatment, and thought to cause metastatic growth. Moreover, cancer cells are able to switch between CSC and non-CSC phenotypes and vice versa, to ensure the necessary balance within the tumor. Likewise, cancer cells can switch between epithelial and mesenchymal phenotypes via well-described transition (EMT/MET) that is thought to be crucial for tumor propagation. In this review, we discuss whether, and to which extend, the CSCs and mesenchymal cancer cells are overlapping phenomena in terms of mechanisms, origin, and implication for cancer treatment. As well, we describe the dynamism of both phenotypes and involvement of the tumor microenvironment in CSC reversion and in EMT.