Specific targeting of neurotoxic side effects and pharmacological profile of the novel cancer stem cell drug salinomycin in mice. J Mol Med (Berl). 2014;92:889-900. [PMID: 24770997 DOI: 10.1007/s00109-014-1155-0]

Calcium channels as therapeutic targets in head and neck squamous cell carcinoma: current evidence and clinical trials

Head and neck squamous cell carcinoma (HNSCC) originates from the mucosal epithelium of the oral cavity, pharynx, and larynx, and is marked by high rates of recurrence and metastasis. Calcium signaling is associated with the progression of HNSCC and the development of drug resistance. Changes in calcium ion flow can trigger severe pathophysiological processes, including malignant transformation, tumor proliferation, epithelial-mesenchymal transition, and apoptosis evasion. Calcium channels regulate and facilitate these processes. Remodeling of calcium signaling has become one of the most prevalent adaptive mechanisms in cancer cells. Preclinical and clinical evidence indicates that alterations in calcium signaling are crucial for the progression of HNSCC. This review examines the role of calcium channels in HNSCC development and evaluates current clinical trials targeting these channels to assess the feasibility of calcium signaling-based therapies for HNSCC.

Salinomycin, a potent inhibitor of XOD and URAT1, ameliorates hyperuricemic nephropathy by activating NRF2, modulating the gut microbiota, and promoting SCFA production

Long-term hyperuricemia can induce kidney damage, clinically referred to as hyperuricemic nephropathy (HN), which is characterized by renal fibrosis, inflammation, and oxidative stress. However, currently used uric acid-lowering drugs are not capable of protecting the kidneys from damage. Therefore, uric acid-lowering drugs that can also protect the kidneys are urgently needed. In this study, we first discovered that salinomycin, an antibiotic, can regulate uric acid homeostasis and ameliorate kidney damage in mice with HN. Mechanistically, salinomycin inhibited serum and hepatic xanthine oxidase (XOD) activities and downregulated renal urate transporter 1 (URAT1) expression and transport activity, thus exerting uric acid-lowering effects in mice with HN. Furthermore, we found that salinomycin promoted p-NRF2 Ser40 expression, resulting in increased nuclear translocation of NRF2 and activation of NRF2. More importantly, salinomycin affected the gut microbiota and promoted the generation of short-chain fatty acids (SCFAs) in mice with HN. In conclusion, our results revealed that salinomycin maintains uric acid homeostasis and alleviates kidney injury in mice with HN by multiple mechanisms, suggesting that salinomycin might be a desirable candidate for HN treatment in the clinic.

Exposure to salinomycin dysregulates interplay between mitophagy and oxidative response to damage the porcine jejunal cells

Salinomycin (SAL) has caused widespread pollution as a feed additive and growth promoter in livestock such as pigs, exerting a negative impact on public health. The toxicity mechanism of SAL has been widely studied in chickens, but the underlying mechanisms of SAL-induced toxicity to pigs and the ecosystem remain undefined. In this study, we explored the potential damage of SAL in IPEC-J2 cells to identify the effects of excessive SAL on the interplay between mitophagy and oxidative stress. The results showed that a concentration-dependent response was observed for SAL in altering cellular morphology and inducing cell death in IPEC-J2 cells, including the induction of cell cycle arrest and lactic dehydrogenase (LDH) release. Meanwhile, we found that excessive SAL led to oxidative damage by activating the Nrf2/Keap1/HO-1 pathway, accompanied by reactive oxygen species (ROS) elevation and the reduction of antioxidant enzyme activity. We also found that PINK1/Parkin-dependent mitophagy was activated by SAL exposure, particularly with mitochondrial membrane potential reduction. Interestingly, SAL-induced oxidative damages were prevented after the autophagy inhibitor 3-methyladenine (3-MA) treatment, and mitophagy was alleviated following ROS scavenger (N-acetylcysteine, NAC) treatment. Overall, our findings showed that SAL stimulated oxidative stress and mitophagy in IPEC-J2 cells resulting in cellular injury, and there was a strong connection between SAL-induced oxidative stress and mitophagy. Targeting ROS/PINK1/Parkin-dependent mitophagy and oxidative stress could be a novel protective mechanism in SAL-induced cell damage.

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.

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.

Ex Vivo Phenotypic Screening of Two Small Repurposing Drug Collections Identifies Nifuratel as a Potential New Treatment against Visceral and Cutaneous Leishmaniasis

Leishmaniases are vector-borne neglected diseases caused by single-celled parasites. The search for new antileishmanial drugs has experienced a strong boost thanks to the application of bioimaging to phenotypic screenings based on intracellular amastigotes. Mouse splenic explants infected with fluorescent strains of Leishmania are proven tools of drug discovery, where hits can be easily transferred to preclinical in vivo models. We have developed a two-staged platform for antileishmanial drugs. First, we screened two commercial collections of repurposing drugs with a total of 1769 compounds in ex vivo mouse splenocytes infected with an infrared emitting Leishmania infantum strain. The most active and safest compounds were scaled-up to in vivo models of chronic Leishmania donovani visceral leishmaniasis and Leishmania major cutaneous leishmaniasis. From the total of 1769 compounds, 12 hits with selective indices >35 were identified, and 4 of them were tested in vivo in a model of L. donovani visceral leishmaniasis. Nifuratel, a repurposed synthetic nitrofuran, when administered orally at 50 mg/kg bw once or twice a day for 10 days, caused >80% reduction in the parasitic load. Furthermore, the intralesional administration of nifuratel in a model of cutaneous leishmaniasis by L. major produced the parasitological cure. From the previous results we have deduced the great capacity of mouse splenic explants to identify new hits, a model which could be easily transferred to in vivo models, as well as the potential use of nifuratel as an alternative to the current treatment of cutaneous leishmaniasis.

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.

Ameliorative effects of deferiprone and tetraethylammonium salt of salinomycinic acid on lead-induced toxicity in mouse testes

In this study, we compare the effects of deferiprone (Def) and tetraethylammonium salt of salinomycinic acid (Sal) on lead (Pb)-induced toxicity in testes of Pb-exposed mice. Mature male ICR mice were allocated into four groups as follows: untreated control mice (ctrl)-received distilled water for 4 weeks; Pb-exposed mice (Pb)-subjected to 14-day Pb (II) nitrate administration at dose 80 mg/kg body weight (b.w.); Pb + Def group-Pb-exposed mice, treated with 20 mg/kg b.w. Def for 2 weeks; and Pb + Sal group-Pb-intoxicated mice, treated with 16 mg/kg b.w. Sal for 14 days. The results demonstrated that Pb exposure significantly increased blood and testicular Pb concentrations, decreased testicular calcium (Ca) content, significantly elevated testicular levels of magnesium (Mg), zinc (Zn), and selenium (Se) but did not significantly affect the endogenous contents of phosphorous (P) and iron (Fe) compared with untreated controls. Pb intoxication induced disorganization of the seminiferous epithelium. Def or Sal administration reduced blood Pb and testicular Pb concentrations in Pb-exposed mice compared with the Pb-intoxicated group. Mg, Zn, and Se concentrations in testes of Pb-exposed mice, treated with Def or Sal, remained higher compared with the untreated controls. Sal significantly increased testicular P concentration compared with untreated controls and significantly elevated the testicular Ca and Fe concentrations compared with the toxic control group. Both chelating agents improved testicular morphology to a great extent. The results demonstrate the potential of both compounds as antidotes for treatment of Pb-induced impairment of male reproductive function.

Emerging mechanisms and applications of ferroptosis in the treatment of resistant cancers

The development of chemotherapy drugs has promoted anticancer treatment, but the effect on tumours is not clear because of treatment resistance; thus, it is necessary to further understand the mechanism of cell death to explore new therapeutic targets. As a new type of programmed cell death, ferroptosis is increasingly being targeted in the treatment of many cancers with clinical drugs and experimental compounds. Ferroptosis is stimulated in tumours with inherently high levels of ferrous ions by a reaction with abundant polyunsaturated fatty acids and the inhibition of antioxidant enzymes, which can overcome treatment resistance in cancers mainly through GPX4. In this review, we focus on the intrinsic cellular regulators against ferroptosis in cancer resistance, such as GPX4, NRF2 and the thioredoxin system. We summarize the application of novel compounds and drugs to circumvent treatment resistance. We also introduce the application of nanoparticles for the treatment of resistant cancers. In conclusion, targeting ferroptosis represents a considerable strategy for resistant cancer treatment.

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.

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.

Salinomycin exerts anti-colorectal cancer activity by targeting the β-catenin/T-cell factor complex

BACKGROUND AND PURPOSE

Salinomycin is a well-known inhibitor of human cancer stem cells (CSCs). However, the molecular mechanism(s) by which salinomycin targets colorectal CSCs is poorly understood. Here, we have investigated underlying antitumour mechanisms of salinomycin in colorectal cancer cells and three tumour models.

EXPERIMENTAL APPROACH

The inhibitory effect of salinomycin on the Wnt/β-catenin pathway was analysed with the SuperTopFlash reporter system. The mRNA expression of Wnt target genes was evaluated with real-time PCR. Effects of salinomycin on β-catenin/TCF4E interaction were examined using co-immunoprecipitation and an in vitro GST pull-down assay. Cell proliferation was determined by BrdU incorporation and soft agar colony formation assay. The stemness of the cells was assessed by sphere formation assay. Antitumour effects of salinomycin on colorectal cancers was evaluated with colorectal CSC xenografts, APCmin/+ transgenic mice, and patient-derived colorectal tumour xenografts.

KEY RESULTS

Salinomycin blocked β-catenin/TCF4E complex formation in colorectal cancer cells and in an in vitro GST pull-down assay, thus decreasing expression of Wnt target genes. Salinomycin also suppressed the transcriptional activity mediated by β-catenin/LEF1 or β-catenin/TCF4E complex and exhibited an inhibitory effect on the sphere formation, proliferation, and anchorage-independent growth of colorectal cancer cells. In colorectal tumour xenografts and APCmin/+ transgenic mice, administration of salinomycin significantly reduced tumour growth and the expression of CSC-related Wnt target genes including LGR5.

CONCLUSIONS AND IMPLICATIONS

Our study suggested that salinomycin could suppress the growth of colorectal cancer by disrupting the β-catenin/TCF complex and thus may be a promising agent for colorectal cancer treatment.

Salinomycin decreases feline sarcoma and carcinoma cell viability when combined with doxorubicin

BACKGROUND

Cancer is a significant health threat in cats. Chemoresistance is prevalent in solid tumors. The ionophore salinomycin has anti-cancer properties and may work synergistically with chemotherapeutics. The purpose of our study was to determine if salinomycin could decrease cancer cell viability when combined with doxorubicin in feline sarcoma and carcinoma cells.

RESULTS

We established two new feline injection-site sarcoma cell lines, B4 and C10, and confirmed their tumorigenic potential in athymic nude mice. B4 was more resistant to doxorubicin than C10. Dose-dependent effects were not observed until 92 μM in B4 cells (p = 0.0006) vs. 9.2 μM (p = 0.0004) in C10 cells. Dose-dependent effects of salinomycin were observed at 15 μM in B4 cells (p = 0.025) and at 10 μM in C10 cells (p = 0.020). Doxorubicin plus 5 μM salinomycin decreased viability of B4 cells compared to either agent alone, but only at supra-pharmacological doxorubicin concentrations. However, doxorubicin plus 5 μM salinomycin decreased viability of C10 cells compared to either agent alone at doxorubicin concentrations that can be achieved in vivo (1.84 and 4.6 μM, p < 0.004). In SCCF1 cells, dose-dependent effects of doxorubicin and salinomycin were observed at 9.2 (p = 0.036) and 2.5 (p = 0.0049) μM, respectively. When doxorubicin was combined with either 1, 2.5, or 5 μM of salinomycin in SCCF1 cells, dose-dependent effects of doxorubicin were observed at 9.2 (p = 0.0021), 4.6 (p = 0.0042), and 1.84 (p = 0.0021) μM, respectively. Combination index calculations for doxorubicin plus 2.5 and 5 μM salinomycin in SCCF1 cells were 0.4 and 0.6, respectively.

CONCLUSIONS

We have developed two new feline sarcoma cell lines that can be used to study chemoresistance. We observed that salinomycin may potentiate (C10 cells) or work synergistically (SCCF1 cells) with doxorubicin in certain feline cancer cells. Further research is indicated to understand the mechanism of action of salinomycin in feline cancer cells as well as potential tolerability and toxicity in normal feline tissues.

Novel silk fibroin nanoparticles incorporated silk fibroin hydrogel for inhibition of cancer stem cells and tumor growth

Background

A multi-drug delivery platform is needed as the intra-tumoral heterogeneity of cancer leads to different drug susceptibility. Cancer stem cells (CSCs), a small population of tumor cells responsible for tumor seeding and recurrence, are considered chemotherapy-resistant and have been reported to be sensitive to salinomycin (Sal) instead of paclitaxel (Ptx). Here we report a novel silk fibroin (SF) hydrogel-loading Sal and Ptx by incorporating drug-loaded silk fibroin nanoparticles (SF-NPs) to simultaneously kill CSCs and non-CSCs.

Methods

Using the method we have previously reported to prepare Ptx-loaded SF-NPs (Ptx-SF-NPs), Sal-loaded SF-NPs (Sal-SF-NPs) were fabricated under mild and non-toxic conditions. The drug-loaded SF-NPs were dispersed in the ultrasound processed SF solution prior to gelation.

Results

The resulting SF hydrogel (Sal-Ptx-NP-Gel) retained its injectable properties, exhibited bio-degradability and demonstrated homogeneous drug distribution compared to the non-NP incorporated hydrogel. Sal-Ptx-NP-Gel showed superior inhibition of tumor growth compared to single drug-loaded hydrogel and systemic dual drug administration in the murine hepatic carcinoma H22 subcutaneous tumor model. Sal-Ptx-NP-Gel also significantly reduced CD44⁺CD133⁺ tumor cells and demonstrated the least tumor formation in the in vivo tumor seeding experiment, indicating superior inhibition of cancer stem cells.

Conclusion

These results suggest that SF-NPs incorporated SF hydrogel is a promising drug delivery platform, and Sal-Ptx-NP-Gel could be a novel and powerful locoregional tumor treatment regimen in the future.

Salinomycin, as an autophagy modulator-- a new avenue to anticancer: a review

Since Salinomycin (Sal) emerged its ability to target breast cancer stem cells in 2009, numerous experiments have been carried out to test Sal’s anticancer effects. What deserve to be mentioned is that Sal can efficiently induce proliferation inhibition, cell death and metastasis suppression against human cancers from different origins both in vivo and in vitro without causing serious side effects as the conventional chemotherapeutical drugs on the body. There may be novel cell death pathways involving the anticancer effects of Sal except the conventional pathways, such as autophagic pathway. This review is focused on how autophagy involves the effects of Sal, trying to describe clearly and systematically why autophagy plays a vital role in predominant anticancer effects of Sal, including its distinctive characteristic. Based on recent advances, we present evidence that a dual role of Sal involving in autophagy may account for its unique anticancer effects - the preference for cancer cells. Further researches are required to confirm the authenticity of this suppose in order to develop an ideal anticancer drug.

Suramin-Induced Neurotoxicity: Preclinical Models and Neuroprotective Strategies

Suramin is a trypan blue analogon originally developed to treat protozoan infections, which was found to have diverse antitumor effects. One of the most severe side effects in clinical trials was the development of a peripheral sensory-motor polyneuropathy. In this study, we aimed to investigate suramin-induced neuropathy with a focus on calcium (Ca²⁺) homeostasis as a potential pathomechanism. Adult C57Bl/6 mice treated with a single injection of 250 mg/kg bodyweight suramin developed locomotor and sensory deficits, which were confirmed by electrophysiological measurements showing a predominantly sensory axonal-demyelinating polyneuropathy. In a next step, we used cultured dorsal root ganglia neurons (DRGN) as an in vitro cell model to further investigate underlying pathomechanisms. Cell viability of DRGN was significantly decreased after 24-hour suramin treatment with a calculated IC₅₀ of 283 µM. We detected a suramin-induced Ca²⁺ influx into DRGN from the extracellular space, which could be reduced with the voltage-gated calcium channel (VGCC) inhibitor nimodipine. Co-incubation of suramin and nimodipine partially improved cell viability of DRGN after suramin exposure. In summary, we describe suramin-induced neurotoxic effects on DRGN as well as potentially neuroprotective agents targeting intracellular Ca²⁺ dyshomeostasis.

Tumor acidosis enhances cytotoxic effects and autophagy inhibition by salinomycin on cancer cell lines and cancer stem cells

Sustained autophagy contributes to the metabolic adaptation of cancer cells to hypoxic and acidic microenvironments. Since cells in such environments are resistant to conventional cytotoxic drugs, inhibition of autophagy represents a promising therapeutic strategy in clinical oncology. We previously reported that the efficacy of hydroxychloroquine (HCQ), an autophagy inhibitor under clinical investigation is strongly impaired in acidic tumor environments, due to poor uptake of the drug, a phenomenon widely associated with drug resistance towards many weak bases. In this study we identified salinomycin (SAL) as a potent inhibitor of autophagy and cytotoxic agent effective on several cancer cell lines under conditions of transient and chronic acidosis. Since SAL has been reported to specifically target cancer-stem cells (CSC), we used an established model of breast CSC and CSC derived from breast cancer patients to examine whether this specificity may be associated with autophagy inhibition. We indeed found that CSC-like cells are more sensitive to autophagy inhibition compared to cells not expressing CSC markers. We also report that the ability of SAL to inhibit mammosphere formation from CSC-like cells was dramatically enhanced in acidic conditions. We propose that the development and use of clinically suitable SAL derivatives may result in improved autophagy inhibition in cancer cells and CSC in the acidic tumor microenvironment and lead to clinical benefits.

Unbiased screen identifies aripiprazole as a modulator of abundance of the polyglutamine disease protein, ataxin-3

No disease-modifying treatment exists for the fatal neurodegenerative polyglutamine disease known both as Machado-Joseph disease and spinocerebellar ataxia type 3. As a potential route to therapy, we identified small molecules that reduce levels of the mutant disease protein, ATXN3. Screens of a small molecule collection, including 1250 Food and Drug Administration-approved drugs, in a novel cell-based assay, followed by secondary screens in brain slice cultures from transgenic mice expressing the human disease gene, identified the atypical antipsychotic aripiprazole as one of the hits. Aripiprazole increased longevity in a Drosophila model of Machado-Joseph disease and effectively reduced aggregated ATXN3 species in flies and in brains of transgenic mice treated for 10 days. The aripiprazole-mediated decrease in ATXN3 abundance may reflect a complex response culminating in the modulation of specific components of cellular protein homeostasis. Aripiprazole represents a potentially promising therapeutic drug for Machado-Joseph disease and possibly other neurological proteinopathies.

Comparative effects of meso-2,3- dimercaptosuccinic acid, monensin, and salinomycin on cadmium-induced brain dysfunction in cadmium-intoxicated mice

Cadmium (Cd) is a risk factor for neurodegenerative diseases. The purpose of this study was to compare the effects of meso-2,3-dimercaptosuccinic acid (DMSA) and the polyether ionophorous antibiotics monensin and salinomycin on Cd-induced neurodegenerative alterations in mice. The results show that subacute intoxication of mice with Cd (II) acetate (20 mg/kg body weight (BW) for 14 days) caused a significant accumulation of cadmium (Cd) in the brain. Treatment of Cd-exposed mice with DMSA (20 mg/kg BW for 14 days) significantly increased the Cd concentration in the brains compared to those of the Cd-treated group. However, administration of monensin (20 mg/kg BW for 14 days) or salinomycin (20 mg/kg BW for 14 days) significantly reduced the Cd concentration in the brains of Cd-treated mice compared to the toxic control group. Histopathological analysis of brain tissues from the Cd-treated mice revealed that Cd induced neuronal necrosis, characterized by many shrunken, darkly stained pyknotic neurons with prominent perineuronal spaces. Whereas monensin and salinomycin significantly reduced the adverse effects of Cd on brain morphology of Cd-treated mice, DMSA did not. Monensin slightly increased the copper and iron endogenous levels in the brains of Cd-exposed mice compared to those of the untreated mice. Salinomycin did not affect the concentrations of biometal ions in the brain of Cd-exposed mice compared to untreated controls. The results demonstrated salinomycin to be a better potential chelating agent for treatment of Cd-induced brain injury compared to DMSA and monensin.

Salinomycin overcomes acquired tamoxifen resistance through AIB1 and inhibits cancer cell invasion in endocrine resistant breast cancer

Salinomycin is a monocarboxylic polyether ionophore isolated from Streptomyces albus. It has been widely used as an antibiotic in veterinary medicine in poultry. A recent study demonstrated that salinomycin selectively inhibits human breast cancer stem cells; one possible mechanism of tamoxifen resistance. Our results show that salinomycin is effective in inhibiting MCF-7/LCC2 and MCF-7/LCC9 cell lines which are well-established endocrine resistant cells and has a synergistic effect in combination with tamoxifen using MTT proliferation assay. The inhibitory effect of salinomycin on the reduction of critical ER co-activator; amplified breast 1 (AIB1) mRNA and protein expression is overcoming tamoxifen resistance. Moreover, salinomycin significantly inhibits cell invasion in Matrigel invasion assay. The effect was mediated at least in part by the decrease of matrix metalopeptidase 9 (MMP-9) which is one critical enzyme facilitated in the cell invasion process. In conclusion, salinomycin should be developed as a novel agent used alone or in combination for endocrine-resistant breast cancer.

A novel preventive therapy for paclitaxel-induced cognitive deficits: preclinical evidence from C57BL/6 mice

Chemotherapy-induced central nervous system (CNS) neurotoxicity presents an unmet medical need. Patients often report a cognitive decline in temporal correlation to chemotherapy, particularly for hippocampus-dependent verbal and visuo-spatial abilities. We treated adult C57Bl/6 mice with 12 × 20 mg kg^-1 paclitaxel (PTX), mimicking clinical conditions of dose-dense chemotherapy, followed by a pulse of bromodesoxyuridine (BrdU) to label dividing cells. In this model, mice developed visuo-spatial memory impairments, and we measured peak PTX concentrations in the hippocampus of 230 nm l^-1, which was sevenfold higher compared with the neocortex. Histologic analysis revealed a reduced hippocampal cell proliferation. In vitro, we observed severe toxicity in slowly proliferating neural stem cells (NSC) as well as human neuronal progenitor cells after 2 h exposure to low nanomolar concentrations of PTX. In comparison, mature post-mitotic hippocampal neurons and cell lines of malignant cells were less vulnerable. In PTX-treated NSC, we observed an increase of intracellular calcium levels, as well as an increased activity of calpain- and caspase 3/7, suggesting a calcium-dependent mechanism. This cell death pathway could be specifically inhibited with lithium, but not glycogen synthase kinase 3 inhibitors, which protected NSC in vitro. In vivo, preemptive treatment of mice with lithium prevented PTX-induced memory deficits and abnormal adult hippocampal neurogenesis. In summary, we identified a molecular pathomechanism, which invokes PTX-induced cytotoxicity in NSC independent of cell cycle status. This pathway could be pharmacologically inhibited with lithium without impairing paclitaxel's tubulin-dependent cytostatic mode of action, enabling a potential translational clinical approach.

Effects of salinomycin and 17‑AAG on proliferation of human gastric cancer cells in vitro

The aim of the present study was to investigate the effects and mechanisms of 17-AAG combined with salinomycin treatment on proliferation and apoptosis of the SGC-7901 gastric cancer cell line. An MTT assay was used to detect the proliferation of SGC-7901 cells. Morphological alterations of cells were observed under inverted phase-contrast and fluorescence microscopes. Cell cycle and apoptosis were assessed by flow cytometry analysis. The protein expression of nuclear factor (NF)-κB p65 and Fas-ligand (L) were evaluated by immunocytochemistry. Salinomycin with a concentration range of 1–32 µmol/l was demonstrated to inhibit growth of SGC-7901 cells effectively, affect the morphology and apoptosis rate of cells, and arrest SGC-7901 cells in S phase. Furthermore, salinomycin significantly increased the protein expression of Fas-L and decreased the protein expression of NF-κB p65. The alterations in SGC-7901 cells co-treated with salinomycin and 17-AAG were more significant compared with cells treated with one drug only. In conclusion, the individual use of salinomycin and combined use with 17-AAG may significantly inhibit SGC-7901 gastric cancer cell proliferation and induce cell apoptosis. The potential mechanisms may be associated with upregulation of Fas-L and downregulation of NF-κB. These results provide a basis for the potential use of salinomycin in gastric cancer treatment.

Multidrug-resistant cancer cells and cancer stem cells hijack cellular systems to circumvent systemic therapies, can natural products reverse this?

Chemotherapy is one of the most effective and broadly used approaches for cancer management and many modern regimes can eliminate the bulk of the cancer cells. However, recurrence and metastasis still remain a major obstacle leading to the failure of systemic cancer treatments. Therefore, to improve the long-term eradication of cancer, the cellular and molecular pathways that provide targets which play crucial roles in drug resistance should be identified and characterised. Multidrug resistance (MDR) and the existence of tumor-initiating cells, also referred to as cancer stem cells (CSCs), are two major contributors to the failure of chemotherapy. MDR describes cancer cells that become resistant to structurally and functionally unrelated anti-cancer agents. CSCs are a small population of cells within cancer cells with the capacity of self-renewal, tumor metastasis, and cell differentiation. CSCs are also believed to be associated with chemoresistance. Thus, MDR and CSCs are the greatest challenges for cancer chemotherapy. A significant effort has been made to identify agents that specifically target MDR cells and CSCs. Consequently, some agents derived from nature have been developed with a view that they may overcome MDR and/or target CSCs. In this review, natural products-targeting MDR cancer cells and CSCs are summarized and clustered by their targets in different signaling pathways.

Cellular acidification as a new approach to cancer treatment and to the understanding and therapeutics of neurodegenerative diseases

During the last few years, the understanding of the dysregulated hydrogen ion dynamics and reversed proton gradient of cancer cells has resulted in a new and integral pH-centric paradigm in oncology, a translational model embracing from cancer etiopathogenesis to treatment. The abnormalities of intracellular alkalinization along with extracellular acidification of all types of solid tumors and leukemic cells have never been described in any other disease and now appear to be a specific hallmark of malignancy. As a consequence of this intracellular acid-base homeostatic failure, the attempt to induce cellular acidification using proton transport inhibitors and other intracellular acidifiers of different origins is becoming a new therapeutic concept and selective target of cancer treatment, both as a metabolic mediator of apoptosis and in the overcoming of multiple drug resistance (MDR). Importantly, there is increasing data showing that different ion channels contribute to mediate significant aspects of cancer pH regulation and etiopathogenesis. Finally, we discuss the extension of this new pH-centric oncological paradigm into the opposite metabolic and homeostatic acid-base situation found in human neurodegenerative diseases (HNDDs), which opens novel concepts in the prevention and treatment of HNDDs through the utilization of a cohort of neural and non-neural derived hormones and human growth factors.

Induction of G1 Cell Cycle Arrest in Human Glioma Cells by Salinomycin Through Triggering ROS-Mediated DNA Damage In Vitro and In Vivo

Chemotherapy has always been one of the most effective ways in combating human glioma. However, the high metastatic potential and resistance toward standard chemotherapy severely hindered the chemotherapy outcomes. Hence, searching effective chemotherapy drugs and clarifying its mechanism are of great significance. Salinomycin an antibiotic shows novel anticancer potential against several human tumors, including human glioma, but its mechanism against human glioma cells has not been fully elucidated. In the present study, we demonstrated that salinomycin treatment time- and dose-dependently inhibited U251 and U87 cells growth. Mechanically, salinomycin-induced cell growth inhibition against human glioma was mainly achieved by induction of G1-phase arrest via triggering reactive oxide species (ROS)-mediated DNA damage, as convinced by the activation of histone, p53, p21 and p27. Furthermore, inhibition of ROS accumulation effectively attenuated salinomycin-induced DNA damage and G1 cell cycle arrest, and eventually reversed salinomycin-induced cytotoxicity. Importantly, salinomycin treatment also significantly inhibited the U251 tumor xenograft growth in vivo through triggering DNA damage-mediated cell cycle arrest with involvement of inhibiting cell proliferation and angiogenesis. The results above validated the potential of salinomycin-based chemotherapy against human glioma.

Pharmacological and immunological targeting of tumor mesenchymalization

Controlling the spread of carcinoma cells to distant organs is the foremost challenge in cancer treatment, as metastatic disease is generally resistant to therapy and is ultimately incurable for the majority of patients. The plasticity of tumor cell phenotype, in which the behaviors and functions of individual tumor cells differ markedly depending upon intrinsic and extrinsic factors, is now known to be a central mechanism in cancer progression. Our expanding knowledge of epithelial and mesenchymal phenotypic states in tumor cells, and the dynamic nature of the transitions between these phenotypes has created new opportunities to intervene to better control the behavior of tumor cells. There are now a variety of innovative pharmacological approaches to preferentially target tumor cells that have acquired mesenchymal features, including cytotoxic agents that directly kill these cells, and inhibitors that block or revert the process of mesenchymalization. Furthermore, novel immunological strategies have been developed to engage the immune system in seeking out and destroying mesenchymalized tumor cells. This review highlights the relevance of phenotypic plasticity in tumor biology, and discusses recently developed pharmacological and immunological means of targeting this phenomenon.

Structure-activity & structure-toxicity relationship study of salinomycin diastereoisomers and their benzoylated derivatives

Salinomycin diastereoisomers and their benzoylated derivatives were synthesized and evaluated for both antiproliferative activity and neurotoxicity in vitro. The results indicated that the stereoscopic configurations of the spiro C17 and C21 atoms as well as the benzoyl groups of O-20 on the rigid B/C/D spiro-ketal structures are crucial for biological activity and neural toxicity. In general, there are some positive correlations between the antiproliferative activity and neurotoxicity in these salinomycin derivatives, indicating possibly similar mechanisms of action.

Nanomedicine strategies for sustained, controlled, and targeted treatment of cancer stem cells of the digestive system

Cancer stem cells (CSCs) constitute a small proportion of the cancer cells that have self-renewal capacity and tumor-initiating ability. They have been identified in a variety of tumors, including tumors of the digestive system. CSCs exhibit some unique characteristics, which are responsible for cancer metastasis and recurrence. Consequently, the development of effective therapeutic strategies against CSCs plays a key role in increasing the efficacy of cancer therapy. Several potential approaches to target CSCs of the digestive system have been explored, including targeting CSC surface markers and signaling pathways, inducing the differentiation of CSCs, altering the tumor microenvironment or niche, and inhibiting ATP-driven efflux transporters. However, conventional therapies may not successfully eradicate CSCs owing to various problems, including poor solubility, stability, rapid clearance, poor cellular uptake, and unacceptable cytotoxicity. Nanomedicine strategies, which include drug, gene, targeted, and combinational delivery, could solve these problems and significantly improve the therapeutic index. This review briefly summarizes the ongoing development of strategies and nanomedicine-based therapies against CSCs of the digestive system.

Cancer stem cell drugs target K-ras signaling in a stemness context

Cancer stem cells (CSCs) are considered to be responsible for treatment relapse and have therefore become a major target in cancer research. Salinomycin is the most established CSC inhibitor. However, its primary mechanistic target is still unclear, impeding the discovery of compounds with similar anti-CSC activity. Here, we show that salinomycin very specifically interferes with the activity of K-ras4B, but not H-ras, by disrupting its nanoscale membrane organization. We found that caveolae negatively regulate the sensitivity to this drug. On the basis of this novel mechanistic insight, we defined a K-ras-associated and stem cell-derived gene expression signature that predicts the drug response of cancer cells to salinomycin. Consistent with therapy resistance of CSC, 8% of tumor samples in the TCGA-database displayed our signature and were associated with a significantly higher mortality. Using our K-ras-specific screening platform, we identified several new candidate CSC drugs. Two of these, ophiobolin A and conglobatin A, possessed a similar or higher potency than salinomycin. Finally, we established that the most potent compound, ophiobolin A, exerts its K-ras4B-specific activity through inactivation of calmodulin. Our data suggest that specific interference with the K-ras4B/calmodulin interaction selectively inhibits CSC.

Renal Cancer Stem Cells: Characterization and Targeted Therapies

Renal cell carcinoma (RCC) is a major neoplasm with high incidence in western countries. Tumors are heterogeneous and are composed of differentiated cancer cells, stromal cells, and cancer stem cells (CSCs). CSCs possess two main properties: self-renewal and proliferation. Additionally, they can generate new tumors once transplanted into immunodeficient mice. Several approaches have been described to identify them, through the expression of cell markers, functional assays, or a combination of both. As CSCs are involved in the resistance mechanisms to radio- and chemotherapies, several new strategies have been proposed to directly target CSCs in RCC. One approach drives CSCs to differentiate into cancer cells sensitive to conventional treatments, while the other proposes to eradicate them selectively. A series of innovative therapies aiming at eliminating CSCs have been designed to treat other types of cancer and have not been experimented with on RCC yet, but they reveal themselves to be promising. In conclusion, CSCs are an important player in carcinogenesis and represent a valid target for therapy in RCC patients.

Glucose starvation-mediated inhibition of salinomycin induced autophagy amplifies cancer cell specific cell death

Salinomycin has been used as treatment for malignant tumors in a small number of humans, causing far less side effects than standard chemotherapy. Several studies show that Salinomycin targets cancer-initiating cells (cancer stem cells, or CSC) resistant to conventional therapies. Numerous studies show that Salinomycin not only reduces tumor volume, but also decreases tumor recurrence when used as an adjuvant to standard treatments. In this study we show that starvation triggered different stress responses in cancer cells and primary normal cells, which further improved the preferential targeting of cancer cells by Salinomycin. Our in vitro studies further demonstrate that the combined use of 2-Fluoro 2-deoxy D-glucose, or 2-deoxy D-glucose with Salinomycin is lethal in cancer cells while the use of Oxamate does not improve cell death-inducing properties of Salinomycin. Furthermore, we show that treatment of cancer cells with Salinomycin under starvation conditions not only increases the apoptotic caspase activity, but also diminishes the protective autophagy normally triggered by the treatment with Salinomycin alone. Thus, this study underlines the potential use of Salinomycin as a cancer treatment, possibly in combination with short-term starvation or starvation-mimicking pharmacologic intervention.

Synthesis and biological activity evaluation of 20-epi-salinomycin and its 20-O-acyl derivatives

20-epi-Salinomycin and six 20-O-acylated analogs were synthesized and tested for their biological activity.

Early effects of the antineoplastic agent salinomycin on mitochondrial function

Salinomycin, isolated from Streptomyces albus, displays antimicrobial activity. Recently, a large-scale screening approach identified salinomycin and nigericin as selective apoptosis inducers of cancer stem cells. Growing evidence suggests that salinomycin is able to kill different types of non-stem tumor cells that usually display resistance to common therapeutic approaches, but the mechanism of action of this molecule is still poorly understood. Since salinomycin has been suggested to act as a K(+) ionophore, we explored its impact on mitochondrial bioenergetic performance at an early time point following drug application. In contrast to the K(+) ionophore valinomycin, salinomycin induced a rapid hyperpolarization. In addition, mitochondrial matrix acidification and a significant decrease of respiration were observed in intact mouse embryonic fibroblasts (MEFs) and in cancer stem cell-like HMLE cells within tens of minutes, while increased production of reactive oxygen species was not detected. By comparing the chemical structures and cellular effects of this drug with those of valinomycin (K(+) ionophore) and nigericin (K(+)/H(+) exchanger), we conclude that salinomycin mediates K(+)/H(+) exchange across the inner mitochondrial membrane. Compatible with its direct modulation of mitochondrial function, salinomycin was able to induce cell death also in Bax/Bak-less double-knockout MEF cells. Since at the concentration range used in most studies (around 10 μM) salinomycin exerts its effect at the level of mitochondria and alters bioenergetic performance, the specificity of its action on pathologic B cells isolated from patients with chronic lymphocytic leukemia (CLL) versus B cells from healthy subjects was investigated. Mesenchymal stromal cells (MSCs), proposed to mimic the tumor environment, attenuated the apoptotic effect of salinomycin on B-CLL cells. Apoptosis occurred to a significant extent in healthy B cells as well as in MSCs and human primary fibroblasts. The results indicate that salinomycin, when used above μM concentrations, exerts direct, mitochondrial effects, thus compromising cell survival.

Overcoming EMT-driven therapeutic resistance by BH3 mimetics

Epithelial-mesenchymal transition (EMT) contributes to the progression of cancer through enhanced invasion and stem-like properties of cancer cells. Additionally, EMT confers resistance towards many chemotherapeutics. We recently described a mechanism that mediates EMT-driven chemoresistance through augmented levels of Bcl-xL, an anti-apoptotic member of the Bcl-2 family (Keitel et al., Oncotarget, in press). Here, we elaborate on how these findings pertain to cancer cells dispersed in the tumor-adjacent stroma of breast cancer tissues, and how BH3-mimetics may provide a therapeutic strategy to eliminate cancer cell populations that have passed through an EMT.