The Molecular Basis for Inhibition of Stemlike Cancer Cells by Salinomycin

Drug Repurposing of Selected Antibiotics: An Emerging Approach in Cancer Drug Discovery

Drug repurposing is a method of investigating new therapeutic applications for previously approved medications. This repurposing approach to "old" medications is now highly efficient, simple to arrange, and cost-effective and poses little risk of failure in treating a variety of disorders, including cancer. Drug repurposing for cancer therapy is currently a key topic of study. It is a way of exploring recent therapeutic applications for already-existing drugs. Theoretically, the repurposing strategy has various advantages over the recognized challenges of creating new molecular entities, including being faster, safer, easier, and less expensive. In the real world, several medications have been repurposed, including aspirin, metformin, and chloroquine. However, doctors and scientists address numerous challenges when repurposing drugs, such as the fact that most drugs are not cost-effective and are resistant to bacteria. So the goal of this review is to gather information regarding repurposing pharmaceuticals to make them more cost-effective and harder for bacteria to resist. Cancer patients are more susceptible to bacterial infections. Due to their weak immune systems, antibiotics help protect them from a variety of infectious diseases. Although antibiotics are not immune boosters, they do benefit the defense system by killing bacteria and slowing the growth of cancer cells. Their use also increases the therapeutic efficacy and helps avoid recurrence. Of late, antibiotics have been repurposed as potent anticancer agents because of the evolutionary relationship between the prokaryotic genome and mitochondrial DNA of eukaryotes. Anticancer antibiotics that prevent cancer cells from growing by interfering with their DNA and blocking growth of promoters, which include anthracyclines, daunorubicin, epirubicin, mitoxantrone, doxorubicin, and idarubicin, are another type of FDA-approved antibiotics used to treat cancer. According to the endosymbiotic hypothesis, prokaryotes and eukaryotes are thought to have an evolutionary relationship. Hence, in this study, we are trying to explore antibiotics that are necessary for treating diseases, including cancer, helping people reduce deaths associated with various infections, and substantially extending people's life expectancy and quality of life.

Selectivity of cation transport across lipid membranes by the antibiotic salinomycin

The ionophoric antibiotic salinomycin is in the phase of preclinical tests against several types of malignant tumors including breast cancer. Notwithstanding, the data on its ion selectivity, although being critical for its therapeutic activity, are rather scarce. In the present work, we studied the ability of salinomycin to exert cation/H+-exchange across artificial bilayer lipid membranes (BLM) by measuring electrical potential on planar BLM in the presence of a protonophore and fluorescence responses of the pH-sensitive dye pyranine entrapped in liposomes. The following order of ion selectivity was obtained by these two methods: K+ > Na+ > Rb+ > Cs+ > Li+. Measurements of the monovalent cation-induced quenching of fluorescence of thallium ions in methanol showed that salinomycin effectively binds potassium and calcium but poorly binds sodium and lithium ions. At high concentrations, salinomycin transports Ca2+ through membranes of liposomes and mitochondria, as measured by using the calcium-sensitive dye Fluo-5 N. The data obtained can be used in the mechanistic studies of the anti-tumor activity of salinomycin and its selective cytotoxicity towards cancer stem cells.

Salinomycin disturbs Golgi function and specifically affects cells in epithelial-to-mesenchymal transition

Epithelial-to-mesenchymal transition (EMT) gives rise to cells with properties similar to cancer stem cells (CSCs). Targeting the EMT program to selectively eliminate CSCs is a promising way to improve cancer therapy. Salinomycin (Sal), a K+/H+ ionophore, was identified as highly selective towards CSC-like cells, but its mechanism of action and selectivity remains elusive. Here, we show that Sal, similar to monensin and nigericin, disturbs the function of the Golgi. Sal alters the expression of Golgi-related genes and leads to marked changes in Golgi morphology, particularly in cells that have undergone EMT. Moreover, Golgi-disturbing agents severely affect post-translational modifications of proteins, including protein processing, glycosylation and secretion. We discover that the alterations induced by Golgi-disturbing agents specifically affect the viability of EMT cells. Collectively, our work reveals a novel vulnerability related to the EMT, suggesting an important role for the Golgi in the EMT and that targeting the Golgi could represent a novel therapeutic approach against CSCs.

Potent salinomycin C20-O-alkyl oxime derivative SAL-98 efficiently inhibits tumor growth and metastasis by affecting Wnt/β-catenin signal pathway

The dysregulation of Wnt/β-catenin signaling pathway is closely related to tumorigenesis, metastasis and cancer stem cell maintenance. Salinomycin is a polyether ionophore antibiotic that selectively eliminates cancer stem cells by inhibiting the Wnt/β-catenin signal pathway. Salinomycin selectively target cancer stem cells, but the toxicity limits its further use. In this study, we explore the anti-tumor mechanism of one most active salinomycin C20-O-alkyl oximederivative SAL-98 and found that SAL-98 exerts 10 times higher anti-tumor and anti-CSCs activities compared with salinomycin, which induces cell cycle arrest, ER stress and mitochondria dysfunction and inhibits Wnt/β-catenin signal pathway in vitro with high efficacy. Moreover, SAL-98 shows good anti-metastasis effect in vivo. In addition, SAL-98 demonstrates same anti-tumor activities as salinomycin with less 5 times concentration in vivo, the ER stress, autophagy and anti-CSCs effects were also confirmed in vivo. Mechanistically, SAL-98 inhibits the Wnt/β-catenin signaling pathway associated with CHOP expression induced by ER stress, the induced CHOP disrupts the β-catenin/TCF4 complex and represses the Wnt targeted genes. This study provides an alternative strategy for rational drug development to target Wnt/β-catenin signaling pathway.

A new animal product free defined medium for 2D and 3D culturing of normal and cancer cells to study cell proliferation and migration as well as dose response to chemical treatment

Cell culturing methods are increasingly used to reduce and replace the use of live animals in biomedical research and chemical toxicity testing. Although live animals are avoided when using cell culturing methods, they often contain animal-derived components of which one of the most commonly used is foetal bovine serum (FBS). FBS is added to cell culture media among other supplements to support cell attachment/spreading and cell proliferation. The safety, batch-to-batch variation, and ethical problems with FBS are acknowledged and therefore world-wide efforts are ongoing to produce FBS free media. Here, we present the composition of a new defined medium with only human proteins either recombinant or derived from human tissues. This defined medium supports long-term culturing/routine culturing of normal cells and of cancer cells, and can be used for freezing and thawing of cells, i.e. for cell banking. Here, we show for our defined medium, growth curves and dose response curves of cells grown in two and three dimensions, and applications such as cell migration. Cell morphology was studied in real time by phase contrast and phase holographic microscopy time-lapse imaging. The cell lines used are human cancer-associated fibroblasts, keratinocytes, breast cancer JIMT-1 and MDA-MB-231 cells, colon cancer CaCo-2 cells, and pancreatic cancer MiaPaCa-2 cells as well as the mouse L929 cell line. In conclusion, we present the composition of a defined medium without animal-derived products which can be used for routine culturing and in experimental settings for normal cells and for cancer cells, i.e. our defined medium provides a leap towards a universal animal product free cell culture medium.

Up-Frameshift Suppressor 3 as a prognostic biomarker and correlated with immune infiltrates: A pan-cancer analysis

BACKGROUND

The mRNA expression of protein Up-Frameshift Suppressor 3 Homolog B (UPF3B) differ in different tumors. However, the clinical relevance of UPF3B in cancer patients, such as with prognosis, tumor stage, and levels of tumor-infiltrating immune cells remain unclear.

METHODS

We performed bioinformatics analysis of UPF3B with The Cancer Genome Atlas (TCGA) database (https://xenabrowser.net) and TIMER2.0 (Tumor Immune Estimation Resource 2.0, http://timer.comp-genomics.org/). UPF3B expression in 33 cancers versus counterpart normal tissues was analyzed using TCGA pan-cancer data. The influence of UPF3B in long-term prognosis was evaluated using Kaplan-Meier method, and the associations between UPF3B transcription levels and immune-related gene expression, immune cell infiltration, tumor microenvironment (TME) score are analyzed by spearman correlation analysis. Enrichment analysis of UPF3B was conducted using the R package "clusterProfiler."

RESULTS

The transcriptional level of UPF3B was dysregulated in the human pan-cancer dataset. A significant correlation was found between the expression of UPF3B and the pathological stage of Esophageal Carcinoma (ESCA), Kidney Chromophobe (KIHC), Liver Hepatocellular Carcinoma (LIHC), and Skin Cutaneous Melanoma (SKCM). Multiple cancer types with high transcriptional levels of UPF3B were associated with a significantly worse prognosis. The functions of expressed UPF3B gene are primarily related to ubiquitin mediated proteolysis, cell cycle, and mRNA surveillance pathway. Our results also show that immune cells infiltration and immunosuppressive markers such as CTLA-4, PD-1 and PD-L1 significantly correlate with UPF3B expression.

CONCLUSIONS

In the present study, we synthetically explored the expression status and prognostic significance of UPF3B, and the relationship with clinic characters and immune microenvironment across cancers. Our results may provide novel insights for UPF3B as an immunotherapeutic target and valuable prognostic biomarker in various malignant tumor.

Vitamin D3 and Salinomycin synergy in MCF-7 cells cause cell death via endoplasmic reticulum stress in monolayer and 3D cell culture

1α, 25, dihydroxyvitamin D₃ (1,25D), the active form of vitamin D₃, has antitumor properties in several cancer cell lines in vitro. Salinomycin (Sal) has anticancer activity against cancer cell lines. This study aims to examine the cytotoxic and antiproliferative effect of Sal associated with 1,25D on MCF-7 breast carcinoma cell line cultured in monolayer (2D) and three-dimensional models (mammospheres). We also aim to evaluate the molecular mechanism of Sal and 1,25D-mediated effects. We report that Sal and 1,25D act synergistically in MCF-7 mammospheres and monolayer causing G1 cell cycle arrest, reduction of mitochondrial membrane potential (MMP), and reactive oxygen species (ROS) overproduction with a long-lasting cytotoxic response represented by clonogenic and mammosphere assay. We observed the induction of cell death by apoptosis with upregulation in mRNA levels of apoptosis-related genes (CASP7, CASP9, and BBC3). Extensive cytoplasmic vacuolization, a morphological characteristic found in paraptosis, was also seen and could be triggered by endoplasmic reticulum stress (ER) as we found transcriptional upregulation of genes related to ER stress (ATF6, GADD153, GADD45G, EIF2AK3, and HSPA5). Overall, Sal and 1,25D act synergistically, inhibiting cell proliferation by activating simultaneously multiple death pathways and may be a novel and promising luminal A breast cancer therapy strategy.

Iron-Sensitive Prodrugs That Trigger Active Ferroptosis in Drug-Tolerant Pancreatic Cancer Cells

Persister cancer cells represent rare populations of cells resistant to therapy. Cancer cells can exploit epithelial-mesenchymal plasticity to adopt a drug-tolerant state that does not depend on genetic alterations. Small molecules that can interfere with cell plasticity or kill cells in a cell state-dependent manner are highly sought after. Salinomycin has been shown to kill cancer cells in the mesenchymal state by sequestering iron in lysosomes, taking advantage of the iron addiction of this cell state. Here, we report the chemo- and stereoselective synthesis of a series of structurally complex small molecule chimeras of salinomycin derivatives and the iron-reactive dihydroartemisinin. We show that these chimeras accumulate in lysosomes and can react with iron to release bioactive species, thereby inducing ferroptosis in drug-tolerant pancreatic cancer cells and biopsy-derived organoids of pancreatic ductal adenocarcinoma. This work paves the way toward the development of new cancer medicines acting through active ferroptosis.

Expeditive Synthesis of Potent C20-epi-Amino Derivatives of Salinomycin against Cancer Stem-Like Cells

As a continuation of our studies toward the development of small molecules to selectively target cancer stem cells (CSCs), a library of 18 novel derivatives of salinomycin (Sal), a naturally occurring polyether ionophore, was synthesized with a good overall yield using a one-pot Mitsunobu-Staudinger procedure. Compared to the parent structure, the newly synthesized products contained the mono- or disubstituted C20-epi-amine groups. The biological activity of these compounds was evaluated against human mammary mesenchymal HMLER CD24^low/CD44^high cells, a well-established model of breast CSCs, and its isogenic epithelial cell line (HMLER CD24^high/CD44^low) lacking CSC properties. Importantly, the vast majority of Sal derivatives were characterized by low nanomolar activities, comparing favorably with previous data in the literature. Furthermore, some of these derivatives exhibited a higher selectivity for the mesenchymal state compared to the reference Sal and ironomycin, representing a promising new series of compounds with anti-CSC activity.

Self-assembling, pH-responsive nanoflowers for inhibiting PAD4 and neutrophil extracellular trap formation and improving the tumor immune microenvironment

Self-assembling carrier-free nanodrugs are attractive agents because they accumulate at tumor by an enhanced permeability and retention (EPR) effect without introduction of inactive substances, and some nanodrugs can alter the immune environment. We synthesized a peptidyl arginine deiminase 4 (PAD4) molecular inhibitor, ZD-E-1M. It could self-assembled into nanodrug ZD-E-1. Using confocal laser scanning microscopy, we observed its cellular colocalization, PAD4 activity and neutrophil extracellular traps (NETs) formation. The populations of immune cells and expression of immune-related proteins were determined by single-cell mass cytometry. ZD-E-1 formed nanoflowers in an acidic environment, whereas it formed nanospheres at pH 7.4. Accumulation of ZD-E-1 at tumor was pH-responsive because of its pH-dependent differences in the size and shape. It could enter the nucleus and bind to PAD4 to prolong the intracellular retention time. In mice, ZD-E-1 inhibited tumor growth and metastasis by inhibiting PAD4 activity and NETs formation. Besides, ZD-E-1 could regulate the ratio of immune cells in LLC tumor-bearing mice. Immunosuppressive proteins like LAG3 were suppressed, while IFN-γ and TNF-α as stimulators of tumor immune response were upregulated. Overall, ZD-E-1 is a self-assembling carrier-free nanodrug that responds to pH, inhibits PAD4 activity, blocks neutrophil extracellular traps formation, and improves the tumor immune microenvironment.

Drug Repurposing Strategies for Non-Cancer to Cancer Therapeutics

Global efforts invested for the prevention and treatment of cancer need to be repositioned to develop safe, effective, and economic anticancer therapeutics by adopting rational approaches of drug discovery. Drug repurposing is one of the established approaches to reposition old, clinically approved off patent noncancer drugs with known targets into newer indications. The literature review suggests key role of drug repurposing in the development of drugs intended for cancer as well as noncancer therapeutics. A wide category of noncancer drugs namely, drugs acting on CNS, anthelmintics, cardiovascular drugs, antimalarial drugs, anti-inflammatory drugs have come out with interesting outcomes during preclinical and clinical phases. In the present article a comprehensive overview of the current scenario of drug repurposing for the treatment of cancer has been focused. The details of some successful studies along with examples have been included followed by associated challenges.

Undescribed polyether ionophores from Streptomyces cacaoi and their antibacterial and antiproliferative activities

Polyether ionophores represent a large group of naturally occurring compounds mainly produced by Streptomyces species. With previously proven varieties of bioactivity including antibacterial, antifungal, antiparasitic, antiviral and anti-tumor effects, the discovery of undescribed polyethers leading to development of efficient therapeutics has become important. As part of our research on polyether-rich Streptomyces cacaoi, we previously performed modification studies on fermentation conditions to induce synthesis of specialized metabolites. Here, we report four undescribed and nine known polyether compounds from S. cacaoi grown in optimized conditions. Antimicrobial activity assays revealed that four compounds, including the undescribed (6), showed strong inhibitory effects over both Bacillus subtilis and methicillin-resistant Staphylococcus aureus (MRSA) growth. Additionally, K41-A and its C15-demethoxy derivative exhibited significant cytotoxicity. These results signified that selectivity of C15-demethoxy K41-A towards cancer cells was higher than K41-A, which prompted us to conduct mechanistic experiments. These studies showed that this uninvestigated compound acts as a multitarget compound by inhibiting autophagic flux, inducing reactive oxygen species formation, abolishing proteasome activity, and stimulating ER stress. Consequently, the optimized fermentation conditions of S. cacaoi led to the isolation of undescribed and known polyethers displaying promising activities.

Cytotoxic and other bioactivities of a novel and known sesquiterpene lactones isolated from Vernonia leopoldi (Sch. Bip. ex Walp.) Vatke in breast cancer cell lines

Vernonia leopoldi (Sch. Bip. ex Walp.) Vatke (Asteraceae) is one of the widely used anti-cancer traditional medicinal plants in Ethiopia, despite the lack of data to support its therapeutic efficacy. Here we describe the isolation of compounds from the plant and the investigation of their cytotoxicity and other bioactivities. We identified the novel sesquiterpene lactone (SL) 11ß,13-dihydrovernodalol along with the three other SLs (vernomenin, vernolepin, and 11ß,13-dihydrovernodalin) and three flavonoids (apigenin, eriodyctiol, and luteolin) isolated from this plant for the first time. The structures of all the compounds were established based on extensive analysis of nuclear magnetic resonance spectroscopic data and confirmed by high-resolution electrospray ionization mass spectrometry. We then studied the biological activities of the SLs and found that all were cytotoxic at low μM ranges against MCF-7 and JIMT-1 breast cancer cells as well as against the normal-like MCF-10A breast epithelial cells evaluated in a spectrophotometric assay. All the SLs significantly reduced JIMT-1 cell migration after 72 h of treatment with 2 μM concentrations in a wound healing assay. Treatment with all SLs reduced the aldehyde dehydrogenase expressing cancer stem cell sub-population of the JIMT-1 cells significantly, evaluated by flow cytometry. Only 11ß,13-dihydrovernodalin resulted in a significant inhibition of tumor necrosis factor-α-induced translocation of nuclear factor κB to the cell nucleus. In addition, we show that the reporter fluorophore nitrobenzoxadiazole (NBD) can successfully be conjugated with an SL and that this SL-NBD conjugate is taken up efficiently in JIMT-1 cells. Therefore, the overall bioactivities of the SL compounds and specifically their effects against the stemness of breast cancer cells make them prime candidates for further in-depth investigation.

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Vernonia leopoldi (Sch. Bip. ex Walp.) Vatke is a traditional anticancer medicinal plant in Ethiopia.

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Sesquiterpene lactones (SLs) and flavonoids are isolated from V. leopoldi for the first time.

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A novel SL, named 11ß,13-dihydrovernodalol, was discovered.

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All the SLs reduce stemness and inhibit cell migration of cancer cells.

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A novel fluorophore-conjugated SL was synthesized for the study of SL uptake and localization in cells.

Synthesis and anti-tumor activity evaluation of salinomycin C20-O-alkyl/benzyl oxime derivatives

Seventeen C20-O-alkyl/benzyl oxime derivatives were synthesized by a concise and effective method. Most of these derivatives showed tens to several hundred nanomolar IC₅₀ values against HT-29 colorectal, HGC-27 gastric and MDA-MB-231 breast cancer cells, whose antiproliferative activity is 15-240 fold better than that of salinomycin. The C20-oxime etherified derivatives can coordinate potassium ions, and further adjust the cytosolic Ca²⁺ concentrations in HT-29 cells. The significant improvement of the potency should be attributed to the better ion binding and transport ability of the modified derivatives. In addition, the C20-O-alkyl/benzyl oxime derivatives showed much better selectivity indexes (SI) than salinomycin, indicating that they present lower neurotoxic risk.

Rapid Access to Ironomycin Derivatives by Click Chemistry

Salinomycin, a natural carboxylic polyether ionophore, shows a very interesting spectrum of biological activities, including selective toxicity toward cancer stem cells (CSCs). Recently, we have developed a C20-propargylamine derivative of salinomycin (ironomycin) that exhibits more potent activity in vivo and greater selectivity against breast CSCs compared to the parent natural product. Since ironomycin contains a terminal alkyne motif, it stands out as being an ideal candidate for further functionalization. Using copper-catalyzed azide-alkyne cycloaddition (CuAAC), we synthesized a series of 1,2,3-triazole analogs of ironomycin in good overall yields. The in vitro screening of these derivatives against a well-established model of breast CSCs (HMLER CD24^low/CD44^high) and its corresponding epithelial counterpart (HMLER CD24^high/CD44^low) revealed four new products characterized by higher potency and improved selectivity toward CSCs compared to the reference compound ironomycin. The present study highlights the therapeutic potential of a new class of semisynthetic salinomycin derivatives for targeting selectively the CSC niche and highlights ironomycin as a promising starting material for the development of new anticancer drug candidates.

Gramicidin A accumulates in mitochondria, reduces ATP levels, induces mitophagy, and inhibits cancer cell growth

Here we revealed the spatiotemporal behavior of gramicidin A in cancer cells. Gramicidin A depolarizes both the plasma and mitochondrial membranes, inhibits ATP synthesis, and induces mitophagy, thereby causing potent inhibition of cell growth.

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.

Advances of nanomedicines in breast cancer metastasis treatment targeting different metastatic stages

Breast cancer is the most common tumor in women, and the metastasis further increases the malignancy with extremely high mortality. However, there is almost no effective method in the clinic to completely inhibit breast cancer metastasis due to the dynamic multistep process with complex pathways and scattered occurring site. Nowadays, nanomedicines have been evidenced with great potential in treating cancer metastasis. In this review, we summarize the latest research advances of nanomedicines in anti-metastasis treatment. Strategies are categorized according to the metastasis dynamics, including primary tumor, circulating tumor cells, pre-metastatic niches and secondary tumor. In each different stage of metastasis process, nanomedicines are designed specifically with different functions. At the end of the review, we give our perspectives on current limitations and future directions in anti-metastasis therapy. We expect the review provides comprehensive understandings of anti-metastasis therapy for breast cancer, and boosts the clinical translation in the future to improve women's health.

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.

Breast cancer cell line toxicity of a flavonoid isolated from Baccharis densiflora

Background

Flavonoids are compounds of interest in the search for new anti-cancer therapies. We have previously isolated the methoxyflavones 5,4′-dihydroxy-6,7,8,3′-tetramethoxyflavone (8-methoxycirsilineol), 5,4′-dihydroxy-6,7,8-trimethoxyflavone (xanthomicrol), and 5,4,'3′-trihydroxy-6,7,8-trimethoxyflavone (sideritoflavone) from Baccharis densiflora. Herein, we investigate the toxicity of these methoxyflavones in human breast-derived cell line. Our main aim was to focus on the cancer stem cell (CSC) sub-population of JIMT-1 breast cancer cells.

Methods

Initially, dose response experiments yielding inhibitory concentration 50 (IC₅₀) values were performed using MCF-7, HCC1937, and JIMT-1 breast cancer, and the MCF-10A normal-like breast cell lines to get an understanding of toxic ranges. Due to a clear difference in the toxicity of the flavones, only sideritoflavone was selected for further studies using the JIMT-1 cell line. Effects on the CSC sub-population was investigated using flow cytometry-based methods. A wound healing assay and digital holographic microscopy were used to investigate effects on cell movement. A reporter assay was used to study effects on signal transduction pathways and Western blot for protein expression.

Results

The dose response data showed that 8-methoxycirsilineol was non-toxic at concentrations below 100 μM, that the IC₅₀ of xanthomicrol was between 50 and 100 μM, while sideritoflavone was highly toxic with a single digit μM IC₅₀ in all cell lines. Treatment of the JIMT-1 cells with 2 μM sideritoflavone did not selectively effect the CSC sub-population. Instead, sideritoflavone treatment inhibited the proliferation of both the non-CSC and the CSC sub-populations to the same extent. The inhibition of cell proliferation resulted in an accumulation of cells in the G₂ phase of the cell cycle and the treated cells showed an increased level of γ-H2A histone family member X indicating DNA double strand breaks. Analysis of the effect of sideritoflavone treatment on signal transduction pathways showed activation of the Wnt, Myc/Max, and transforming growth factor-β pathways. The level of p65/nuclear factor kappa-light-chain-enhancer of activated Β cells was increased in sideritoflavone-treated cells. Cell movement was decreased by sideritoflavone treatment.

Conclusions

Altogether our data show that the methoxyflavone sideritoflavone has favourable anti-cancer effects that may be exploited for development to be used in combination with CSC specific compounds.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03349-4.

Aptamer and Peptide-Modified Lipid-Based Drug Delivery Systems in Application of Combined Sequential Therapy of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is known as the most common malignancy of the hepatobiliary system with a continued increase in incidence but limited therapeutic options. Nanomedicine has provided a promising strategy through engineered nanocarriers that are capable of targeting therapeutic agents specifically to tumor cells. In this research, two aptamer/peptide-modified lipid-based drug delivery systems (A54-PEG-SLN/OXA and A15-PEG-SLN/SAL) were developed as a sequential therapeutic strategy to conquer specific hepatocellular carcinoma. The nanomedicine A54-PEG-SLN/OXA was able to target specific hepatocellular carcinoma cell BEL-7402 and exhibited a strong targeting ability and antitumor efficiency both in vitro and in vivo. The A15-PEG-SLN/SAL could target and penetrate deeply to the spheroid composed of CD133+ cancer cells. In the study of developing a sequential therapeutic strategy, we demonstrated that A54-PEG-SLN/OXA could kill tumor cells and expose CD133+ cancer cells. After the administration of A15-PEG-SLN/SAL, the growth of the tumors was significantly inhibited. In conclusion, the aptamer/peptide-modified lipid-based drug delivery systems, A54-PEG-SLN/OXA and A15-PEG-SLN/SAL, could specifically target carcinoma cells and had an evident antitumor effect when administrated sequentially.

Small-Scale Preparation of Fluorescently Labeled Chemical Probes from Marine Cyclic Peptides, Kapakahines A and F

A number of bioactive marine natural products have been isolated so far, but it is still difficult to disclose their modes of action. In this study, we prepared fluorescently labeled chemical probes from the cytotoxic marine cyclic peptides kapakahines A (1) and F (2) to visualize their localization as the first step of the study of their modes of action. We used fluorescent dyes 3a or 3a/b (a 1:1 mixture of 3a and 3b) whose terminal N-hydroxysuccinimide (NHS) group can react with the free amino groups of kapakahines. The fluorescently labeled kapakahine A (Kap A-5-FL, 5a) stained P388 murine leukemia cells and HeLa human cervical cancer cells, while cells treated with fluorescently labeled kapakahine F (Kap F-5-FL, 6a) only weakly stained them. Further analysis of the confocal images of the stained cells with higher magnification (×100) indicated the localization of Kap A-5-FL (5a) in the cells. In this paper, we report the small-scale preparation and a new delivery method of fluorescent probes, as well as the application of these procedures to cell staining.

Ester derivatives of salinomycin efficiently eliminate breast cancer cells via ER-stress-induced apoptosis

The polyether ionophore salinomycin (SAL) has been found to selectively target breast cancer cells, including those with stem-like phenotype. On the other hand, SAL amides and esters obtained through derivatisation of the C1 carboxyl of the ionophore were found to exhibit anticancer properties, whilst reducing potential toxicity issues which often occur during standard chemotherapy. However, the studies on the activity and especially on the mechanisms of action of this class of semi-synthetic products against breast cancer cells are very limited. Therefore, in this work, we confirmed the anti-breast cancer activity of SAL, and further investigated the potential of its selected C1 amide and ester analogs to destroy breast cancer cells, including the highly aggressive triple-negative MDA-MB-231 cells. Importantly, SAL esters were found to be more potent than the native structure and their amide counterparts. Our data revealed that SAL ester derivatives, particularly compounds 5 and 7 (2,2,2-trifluoroethyl and benzotriazole ester of SAL, respectively), increase the level of p-eIF2α (Ser51) and IRE1α proteins. Additionally, an increased level of DNA damage indicators such as γH2AX protein and modified guanine (8-oxoG) was observed. These findings suggest that the apoptosis of MCF-7 and MDA-MB-231 cells induced by the most promising esters derived from SAL may result from the interaction between ER stress and DNA damage response mechanisms.

Photothermogenetic inhibition of cancer stemness by near-infrared-light-activatable nanocomplexes

Strategies for eradicating cancer stem cells (CSCs) are urgently required because CSCs are resistant to anticancer drugs and cause treatment failure, relapse and metastasis. Here, we show that photoactive functional nanocarbon complexes exhibit unique characteristics, such as homogeneous particle morphology, high water dispersibility, powerful photothermal conversion, rapid photoresponsivity and excellent photothermal stability. In addition, the present biologically permeable second near-infrared (NIR-II) light-induced nanocomplexes photo-thermally trigger calcium influx into target cells overexpressing the transient receptor potential vanilloid family type 2 (TRPV2). This combination of nanomaterial design and genetic engineering effectively eliminates cancer cells and suppresses stemness of cancer cells in vitro and in vivo. Finally, in molecular analyses of mechanisms, we show that inhibition of cancer stemness involves calcium-mediated dysregulation of the Wnt/β-catenin signalling pathway. The present technological concept may lead to innovative therapies to address the global issue of refractory cancers.

Cancer stem cells (CSCs) are known to induce chemotherapy resistance, and cause tumour relapse and metastasis. Here, the authors develop photoactive nanocarbon complexes with second near-infrared photothermal ability to target cancer cells overexpressing the receptor TRPV2 and show it to suppress CSCs through dysregulation of the Wnt/β-catenin signalling pathway.

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.

Salinomycin inhibits epigenetic modulator EZH2 to enhance death receptors in colon cancer stem cells

Drug resistance is one of the trademark features of Cancer Stem Cells (CSCs). We and others have recently shown that paucity of functional death receptors (DR4/5) on the cell surface of tumour cells is one of the major reasons for drug resistance, but their involvement in the context of in CSCs is poorly understood. By harnessing CSC specific cytotoxic function of salinomycin, we discovered a critical role of epigenetic modulator EZH2 in regulating the expression of DRs in colon CSCs. Our unbiased proteome profiler array approach followed by ChIP analysis of salinomycin treated cells indicated that the expression of DRs, especially DR4 is epigenetically repressed in colon CSCs. Concurrently, EZH2 knockdown demonstrated increased expression of DR4/DR5, significant reduction of CSC phenotypes such as spheroid formation in-vitro and tumorigenic potential in-vivo in colon cancer. TCGA data analysis of human colon cancer clinical samples shows strong inverse correlation between EZH2 and DR4. Taken together, this study provides an insight about epigenetic regulation of DR4 in colon CSCs and advocates that drug-resistant colon cancer can be therapeutically targeted by combining TRAIL and small molecule EZH2 inhibitors.

Mediating K+/H+ Transport on Organelle Membranes to Selectively Eradicate Cancer Stem Cells with a Small Molecule

Molecules that are capable of disrupting cellular ion homeostasis offer unique opportunities to treat cancer. However, previously reported synthetic ion transporters showed limited value, as promiscuous ionic disruption caused toxicity to both healthy cells and cancer cells indiscriminately. Here we report a simple yet efficient synthetic K⁺ transporter that takes advantage of the endogenous subcellular pH gradient and membrane potential to site-selectively mediate K⁺/H⁺ transport on the mitochondrial and lysosomal membranes in living cells. Consequent mitochondrial and lysosomal damages enhanced cytotoxicity to chemo-resistant ovarian cancer stem cells (CSCs) via apoptosis induction and autophagy suppression with remarkable selectivity (up to 47-fold). The eradication of CSCs blunted tumor formation in mice. We believe this strategy can be exploited in the structural design and applications of next-generation synthetic cation transporters for the treatment of cancer and other diseases related to dysfunctional K⁺ channels.

Targeting of endoplasmic reticulum (ER) stress in gliomas

Gliomas remain a group of malignant brain tumors with dismal prognosis and limited treatment options with molecular mechanisms being constantly investigated. The past decade, extracellular stress and intracellular DNA damage have been shown to disturb proteostasis leading to Endoplasmic Reticulum (ER) stress that is implicated in the regulation of gene expression and the pathogenesis of several tumor types, including gliomas. Upon ER stress induction, neoplastic cells activate the adaptive mechanism of unfolded protein response (UPR), an integrated signaling system that either restores ER homeostasis or induces cell apoptosis. Recently, the manipulation of the UPR has emerged as a new therapeutic target in glioma treatment. General UPR activators or selective GRP78, ATF6 and PERK inducers have been detected to modulate cell proliferation and induce apoptosis of glioma cells. At the same time, target-specific UPR inhibitors and small molecule proteostasis disruptors, work in reverse to increase misfolded proteins and cause a dysregulation in protein maturation and sorting, thus preventing the growth of neoplastic cells. Herein, we discuss the pathogenic implication of ER stress in gliomas onset and progression, providing an update on the current UPR modifying agents that can be potentially used in glioma treatment.

Enhanced and Prolonged Antitumor Effect of Salinomycin-Loaded Gelatinase-Responsive Nanoparticles via Targeted Drug Delivery and Inhibition of Cervical Cancer Stem Cells

BACKGROUND

Cervical cancer stem cells (CCSCs) represent a subpopulation of tumor cells that possess self-renewal capacity and numerous intrinsic mechanisms of resistance to conventional chemotherapy and radiotherapy. These cells play a crucial role in relapse and metastasis of cervical cancer. Therefore, eradication of CCSCs is the primary objective in cervical cancer therapy. Salinomycin (Sal) is an agent used for the elimination of cancer stem cells (CSCs); however, the occurrence of several side effects hinders its application. Nanoscale drug-delivery systems offer great promise for the diagnosis and treatment of tumors. These systems can be used to reduce the side effects of Sal and improve clinical benefit.

METHODS

Sal-loaded polyethylene glycol-peptide-polycaprolactone nanoparticles (Sal NPs) were fabricated under mild and non-toxic conditions. The real-time biodistribution of Sal NPs was investigated through non-invasive near-infrared fluorescent imaging. The efficacy of tumor growth inhibition by Sal NPs was evaluated using tumor xenografts in nude mice. Flow cytometry, immunohistochemistry, and Western blotting were used to detect the apoptosis of CSCs after treatment with Sal NPs. Immunohistochemistry and Western blotting were used to examine epithelial-mesenchymal transition (epithelial interstitial transformation) signal-related molecules.

RESULTS

Sal NPs exhibited antitumor efficacy against cervical cancers by inducing apoptosis of CCSCs and inhibiting the epithelial-mesenchymal transition pathway. Besides, tumor pieces resected from Sal NP-treated mice showed decreased reseeding ability and growth speed, further demonstrating the significant inhibitory ability of Sal NPs against CSCs. Moreover, owing to targeted delivery based on the gelatinase-responsive strategy, Sal NPs was more effective and tolerable than free Sal.

CONCLUSION

To the best of our knowledge, this is the first study to show that CCSC-targeted Sal NPs provide a potential approach to selectively target and efficiently eradicate CCSCs. This renders them a promising strategy to improve the therapeutic effect against cervical cancer.

Echogenic PEGylated PEI-Loaded Microbubble As Efficient Gene Delivery System

BACKGROUND

Cancer stem cells (CSCs) are responsible for cancer therapeutic resistance and metastasis. To date, in addition to surgery, chemotherapy, and radiotherapy, gene delivery has emerged as a potential therapeutic modality for ovarian cancer. Efficient and safe targeted gene delivery is complicated due to the tumor heterogeneity barrier. Ultrasound (US)-stimulated microbubbles (MBs) have demonstrated a method of enabling non-invasive targeted gene delivery.

PURPOSE

The purpose of our study was to show the utility of poly(ethylene glycol)-SS-polyethylenimine-loaded microbubbles (PSP@MB) as an ultrasound theranostic and redox-responsive agent in a gene delivery system.

PATIENTS AND METHODS

PSP nanoparticles were conjugated to the MB surface through biotin-avidin linkage, increasing the gene-loading efficiency of MB. The significant increase in the release of genes from the PSP@MB complexes was achieved upon ultrasound exposure. The positive surface charge in PSP@MB can condense the plasmid through electrostatic interactions; agarose-gel electrophoresis further confirmed the ability of PSP@MB to condense plasmids. The morphology, particle sizes and zeta potential of PSP@MB were characterized by transmission electron microscopy and dynamic light scattering.

RESULTS

Laser confocal microscopy showed that the combination of ultrasound with PSP@MB could promote the cellular uptake of plasmids. Plasmids which encode enhanced green fluorescence protein (EGFP) reporter genes or luciferase reporter genes were delivered to CSCs in vitro and to subcutaneous xenografts in vivo via the combination of ultrasound with PSP@MB. Gene transfection efficiency was evaluated by fluorescence microscopy and In Vivo Imaging Systems. This study demonstrated that the combination of ultrasound with PSP@MB can remarkably promote gene delivery to solid tumors as well as diminishing the toxicity towards normal tissues in vivo. The combination of PSP@MB and the use of ultrasound can efficiently enhance accumulation, extravasation and penetration into solid tumors.

CONCLUSION

Taken together, our study showed that this novel PSP@MB and ultrasound-mediated gene delivery system could efficiently target CSCs.

Effects of salinomycin and niclosamide on small cell lung cancer and small cell lung cancer circulating tumor cell lines

Tumor dissemination and recurrence is attributed to highly resistant cancer stem cells (CSCs) which may constitute a fraction of circulating tumor cells (CTCs). Small cell lung cancer (SCLC) constitutes a suitable model to investigate the relation of CTCs and CSCs due to rapid tumor spread and a high number of CTCs. Expansion of five SCLC CTC lines (BHGc7, 10, 16, 26 and UHGc5) in vitro at our institution allowed for the analysis of CSC markers and cytotoxicity of the CSC-selective drugs salinomycin and niclosamide against CTC single cell suspensions or CTC spheroids/ tumorospheres (TOS). Salinomycin exerted dose-dependent cytotoxicity against the SCLC lines but, with exception of BHGc7 TOS, there was no markedly enhanced activity against TOS. Similarly, niclosamide exhibits high activity against BHGc7 TOS and UHGc5 TOS but not against the other CTC spheroids. High expression of the CSC marker CD133 was restricted to three SCLC tumor lines and the BHGc10 CTC line. All SCLC CTCs are CD24-positive but lack expression of CD44 and ABCG2 in contrast to the SCLC tumor lines which show a phenotype more similar to that of CSCs. The stem cell marker SOX2 was found in all CTC lines and SCLC GLC14/16, whereas elevated expression of Oct-3/4 and Nanog was restricted to BHGc26 and UHGc5. In conclusion, the SCLC CTCs established from patients with relapsed disease lack a typical CSC phenotype in respect to chemosensitivity to CSC-selective drugs, surface markers, expression of pluripotent stem cell and transcription factors.

Impaired Mitochondrial ATP Production Downregulates Wnt Signaling via ER Stress Induction

Wnt signaling affects fundamental development pathways and, if aberrantly activated, promotes the development of cancers. Wnt signaling is modulated by different factors, but whether the mitochondrial energetic state affects Wnt signaling is unknown. Here, we show that sublethal concentrations of different compounds that decrease mitochondrial ATP production specifically downregulate Wnt/β-catenin signaling in vitro in colon cancer cells and in vivo in zebrafish reporter lines. Accordingly, fibroblasts from a GRACILE syndrome patient and a generated zebrafish model lead to reduced Wnt signaling. We identify a mitochondria-Wnt signaling axis whereby a decrease in mitochondrial ATP reduces calcium uptake into the endoplasmic reticulum (ER), leading to endoplasmic reticulum stress and to impaired Wnt signaling. In turn, the recovery of the ATP level or the inhibition of endoplasmic reticulum stress restores Wnt activity. These findings reveal a mechanism that links mitochondrial energetic metabolism to the control of the Wnt pathway that may be beneficial against several pathologies.

Measurements of Ion Binding to Lipid-Hosted Ionophores by Affinity Chromatography

The binding affinity between antibiotic ionophores and alkali ions within supported lipid bilayers was evaluated using affinity chromatography. We used zonal elution and frontal analysis methods in nanovolume liquid chromatography to characterize the binding selectivity of the carrier and channel ionophores valinomycin and gramicidin A within different phosphatidylcholine bilayers. Distinct binding sensitivity to the lipid phase, both in affinity and selectivity, is observed for valinomycin, whereas gramicidin is less sensitive to changes in a membrane environment, behavior that is consistent with ion binding occurring within the interior of an established channel. There is good agreement between the chromatographic retention and the reported binding selectivity measured by other techniques. Surface potential near the binding site affects ion retention and the apparent association binding constants, but not the binding selectivity or enthalpy measurements. A model accounting for the surface potential contributions of retained ions during frontal analyses yields values close to intrinsic binding constants for gramicidin A (K_A for K⁺ between 70 and 120 M^-1) using reasonable estimates of the initial potential that is postulated to arise from the underlying silica.

Chemical Syntheses and Chemical Biology of Carboxyl Polyether Ionophores: Recent Highlights

A central goal of chemical biology is to develop molecular probes that enable fundamental studies of cellular systems. In the hierarchy of bioactive molecules, the so-called ionophore class occupies an unflattering position in the lower branches, with typical labels being "non-specific" and "toxic". In fact, the mere possibility that a candidate molecule possesses "ionophore activity" typically prompts its removal from further studies; ionophores-from a chemical genetics perspective-are molecular outlaws. In stark contrast to this overall poor reputation of ionophores, synthetic chemistry owes some of its most amazing achievements to studies of ionophore natural products, in particular the carboxyl polyethers renowned for their intricate molecular structures. These compounds have for decades been academic battlegrounds where new synthetic methodology is tested and retrosynthetic tactics perfected. Herein, we review the most exciting recent advances in carboxyl polyether ionophore (CPI) synthesis and in addition discuss the burgeoning field of CPI chemical biology.

Doxycycline, salinomycin, monensin and ivermectin repositioned as cancer drugs

Chemotherapy is one of the standard methods for the treatment of malignant tumors. It aims to cause lethal damage to cellular structures, mainly DNA. Noteworthy, in recent years discoveries of novel anticancer agents from well-known antibiotics have opened up new treatment pathways for several cancer diseases. The aim of this review article is to describe new applications for the following antibiotics: doxycycline (DOX), salinomycin (SAL), monensin (MON) and ivermectin (IVR) as they are known to show anti-tumor activity, but have not yet been introduced into standard oncological therapy. To date, these agents have been used for the treatment of a broad-spectrum of bacterial and parasitic infectious diseases and are widely available, which is why they were selected. The data presented here clearly show that the antibiotics mentioned above should be recognised in the near future as novel agents able to eradicate cancer cells and cancer stem cells (CSCs) across several cancer types.

BCL11A enhances stemness and promotes progression by activating Wnt/β-catenin signaling in breast cancer

Background: Breast cancer has become the most common malignant disease threatening women’s health. The cancer stem cell (CSC) has been recognized as a small subpopulation of cancer cells possesses stem cell properties, which is crucial in tumorigenicity, tumor invasion, drug resistance, and metastasis. The BCL11A plays a crucial role in breast cancer progression. To investigate the effect of BCL11A, a functional oncogene, we focused on its maintenance ability of stemness in breast cancer stem cells.

Methods: We assessed the BCL11A expression level in tumor and non-tumor tissues using RT-qPCR and IHC. We subsequently established BCL11A-modulating breast cancer cell lines MDA-MB-231 and MCF-7. CCK8, colony formation assays, and xenograft model were used to determine the effect of BCL11A on tumorigenicity. Transwell assay and lung metastasis model in vivo were conducted to validate its function in metastasis. Its effect on stemness was assessed by flow cytometry and mammosphere formation. Western blot further characterized the importance of Wnt/β-catenin signaling in BCL11A-regulated cancer cell stemness.

Results: A higher level of BCL11A was detected in clinical breast cancer samples. BCL11A promoted tumor formation, cancer cell mobility, spheroid forming, and epithelial-mesenchymal transition by activating the Wnt/β-catenin signaling. In addition, BCL11A was associated with lung metastasis and increased the breast cancer cells stemness. BCL11A high expression (BCL11A^high) cancer cells exhibited stem cell-like properties compared with BCL11A^low cells, including a higher percentage of CD24^low/CD44^high subpopulation, self-renewal spheroids formation, and higher tumorigenicity. Our studies demonstrated that the Wnt/β-catenin signaling activated by BCL11A plays a potential role in the initiation of the renewal of breast cancer stem cells.

Conclusions: BCL11A not only functions in breast cancer carcinogenesis but also enhanced the stemness of breast cancer through activating Wnt/β-catenin signaling, and may become a potential target for breast cancer treatment.

Nucleolin Is a Functional Binding Protein for Salinomycin in Neuroblastoma Stem Cells

The aim of this study is to illuminate a novel therapeutic approach by identifying a functional binding target of salinomycin, an emerging anticancer stem cell (CSC) agent, and to help dissect the underlying action mechanisms. By utilizing integrated strategies, we identify that nucleolin (NCL) is likely a salinomycin-binding target and a critical regulator involved in human neuroblastoma (NB) CSC activity. Salinomycin markedly suppresses NB CD34 expression and reduces CD34+ cell population in an NCL-dependent manner via disruption of the interaction of NCL with CD34 promoter. The elevated levels of NCL expression in NB tumors are associated with poor patient survival. Altogether, these results indicate that NCL is likely a novel functional salinomycin-binding target that exhibits the potential to be a prognostic marker for NB therapy.

Extracellular and intracellular small-molecule galectin-3 inhibitors

Galectin-3 is a carbohydrate binding protein which has important roles in cancer and immunity. Potent galectin-3 inhibitors have been synthesized, for experimental purposes and potential clinical use. As galectin-3 is implicated in both intra- and extracellular activities, permeability of galectin-3 inhibitors is an important parameter determining biological effects. We compared the cellular uptake of galectin-3 inhibitors and their potency in the intracellular or extracellular space. The inhibitors differed in their polar surface area (PSA), but had similar affinities for galectin-3. Using a well-established permeability assay, we confirmed that the uptake was significantly higher for the inhibitor with the lowest PSA, as expected. To analyze intracellular activity of the inhibitors, we developed a novel assay based on galectin-3 accumulation around damaged intracellular vesicles. The results show striking differences between the inhibitors intracellular potency, correlating with their PSAs. To test extracellular activity of the inhibitors, we analyzed their potency to block binding of galectin-3 to cell surfaces. All inhibitors were equally able to block galectin-3 binding to cells and this was proportional to their affinity for galectin-3. These inhibitors may serve as useful tools in exploring biological roles of galectin-3 and may further our understanding of intracellular versus extracellular roles of galectin-3.

Salinomycin: Anti-tumor activity in a pre-clinical colorectal cancer model

Objectives

Salinomycin is a polyether antibiotic with selective activity against human cancer stem cells. The impact of salinomycin on patient-derived primary human colorectal cancer cells has not been investigated so far. Thus, here we aimed to investigate the activity of salinomycin against tumor initiating cells isolated from patients with colorectal cancer.

Methods

Primary tumor-initiating cells (TIC) isolated from human patients with colorectal liver metastases or from human primary colon carcinoma were exposed to salinomycin and compared to treatment with 5-FU and oxaliplatin. TICs were injected subcutaneously into NOD/SCID mice to induce a patient-derived mouse xenograft model of colorectal cancer. Animals were treated either with salinomycin, FOLFOX regimen, or salinomycin and FOLFOX. Human colorectal cancer cells were used to delineate an underlying molecular mechanism of salinomycin in this tumor entity.

Results

Applying TICs isolated from human patients with colorectal liver metastases or from human primary colon carcinoma, we demonstrated that salinomycin exerts increased antiproliferative activity compared to 5-fluorouracil and oxaliplatin treatment. Consistently, salinomycin alone or in combination with FOLFOX exerts superior antitumor activity compared to FOLFOX therapy in a patient-derived mouse xenograft model of colorectal cancer. Salinomycin induces apoptosis of human colorectal cancer cells, accompanied by accumulation of dysfunctional mitochondria and reactive oxygen species. These effects are associated with expressional down-regulation of superoxide dismutase-1 (SOD1) in response to salinomycin treatment.

Conclusion

Collectively, the results of this pre-clinical study indicate that salinomycin alone or in combination with 5-fluorouracil and oxaliplatin exerts increased antitumoral activity compared to common chemotherapy.

MFG-E8 overexpression is associated with poor prognosis in breast cancer patients

BACKGROUND

MFG-E8(Milk fat globule-EGF factor 8), a secreted glycoprotein, plays an exceptional role in various diseases. MFG-E8 overexpression is found in a variety of cancers. However, it remains unclear whether MFG-E8 overexpression is associated with the clinicopathological characteristics and prognosis of human breast cancer.

MATERIALS AND METHODS

In this study, we detected the expression and localization of MFG-E8 protein in breast cancer and cancer-adjacent tissues using immunohistochemical staining, Western blot analysis and immunofluorescence. We analyzed the association between MFG-E8 expression and clinical characteristics and outcomes of breast cancer patients with different HR and HER2 statuses.

RESULTS

Our results confirmed that MFG-E8 expression increased significantly in breast cancer compared with cancer-adjacent tissues by immunohistochemical staining (P <  0.001). Similarly, the Western blot results further confirmed the increased expression of MFG-E8 in breast cancer compared with cancer-adjacent tissues (P =  0.001). Immunofluorescence staining showed that MFG-E8 was mainly localized in the cytoplasm and membrane of tumor cells, consistent with the immunohistochemical staining results. The high expression levels of MFG-E8 showed a greater association with lymph node metastasis, TNM stage and histological grade (P < 0.001). Moreover, high MFG-E8 expression was related to a shortened overall survival (OS) (P <  0.001) and disease-free survival (DFS) (P <  0.001). Bioinformatics analysis with a Kaplan-Meier plotter also demonstrated a strong association of MFG-E8 mRNA overexpression with a short OS and DFS compared with low MFG-E8 expression (P =  0.040, P =  0.005).

CONCLUSIONS

Our findings indicate that MFG-E8 may be a potential marker for poor prognosis and survival in breast cancer.