Salinomycin increases chemosensitivity to the effects of doxorubicin in soft tissue sarcomas

Salinomycin induces apoptosis and potentiates the antitumor effect of doxorubicin against feline mammary tumor 2.5D organoids

Feline mammary tumors (FMT) are the third most common form of neoplasm in cats. The prognosis of FMT is poor due to its high malignancy and metastatic potential. The outcomes of treatment using the common anticancer drug doxorubicin (DOX) are unsatisfactory, with resistance inevitably leading to treatment failure and disease recurrence. Salinomycin (SAL), an antibiotic, has been reported to exert anticancer effects on both human and canine mammary tumors. To recapitulate the genetic and molecular imprints of the original tumor sample, we generated four strains of patient-derived FMT 2.5D organoids (FMTO) to examine the anti-tumor potential of SAL. Our results revealed that SAL decreased cell viability in a dose-dependent manner. Treatment of FMTO with SAL-induced cell apoptosis, represented by an upregulation of P21, Caspase-8, and Caspase-9, and increased activity of Caspase-3/7. The combination of low-dose SAL with DOX (SD) potentiated the cytotoxicity of the latter in both DOX-resistant and DOX-sensitive strains, promoting cell apoptosis and cell-cycle arrest. In vivo, experiments using FMTO-derived xenografts engrafted into mice revealed decreased tumor growth following SAL administration. In conclusion, SAL showed anticancer activity against FMTO and potentiated the anticancer effect of DOX by inhibiting cell proliferation and inducing apoptosis and cell cycle arrest. These results suggest that SAL may represent a new adjuvant treatment option for patients with FMT.

Concomitant Delivery of Pirarubicin and Salinomycin Synergistically Enhanced the Efficacy of Cancer Therapy and Reduced the Risk of Cancer Relapse

Pirarubicin attracted considerable attention in clinical studies because of its high therapeutic efficacy and reduced toxicity in comparison with other anthracyclines. Nevertheless, ~ 30% patients undergoing PIRA treatment still experience relapse and metastasis. Clinical advancements unveiled that cancer stem cells (CSCs) residing in the tumor constitutes a major factor for such limitations and subsequently are the reason for treatment failure. Consequently, eradicating CSCs alongside bulk tumor is a crucial undertaking to attain utmost therapeutic efficacy of the treatment. Nevertheless, majority of the CSCs inhibitors currently under examination lack specificity, show unsynchronized bioavailability with other primary treatments and exhibit notable toxicity in their therapeutic applications, which is primarily attributable to their inadequate tumor-targeting capabilities. Therefore, we have developed a biodegradable polylactic acid based blend block copolymeric NPs for concomitant delivery of CSCs inhibitor Salinomycin (SAL) & chemotherapeutic drug Pirarubicin (PIRA) with an aim to improve the efficacy of treatment and prevent cancer relapse. Prepared NPs showed < 100 nm size and excellent loading with sustained release for both the drugs. Also, PIRA:SAL co-loaded NPs exhibits synergistically enhanced cytotoxicity against cancer cell as well as CSCs. Most importantly, NPs mediated co-delivery of the drugs showed complete tumor eradication, without any reoccurrence throughout the surveillance period. Additionally, NPs treatment didn't show any histopathological alteration in vital organs confirming their non-toxic nature. Altogether, present study concludes that the developed PIRA:SAL NPs have excellent efficacy for tumor regression as well as prevention of cancer relapse, hence can be used as a potential combination therapy for cancer treatment.

miR-197-5p increases Doxorubicin-mediated anticancer cytotoxicity of HT1080 fibrosarcoma cells by decreasing drug efflux

Doxorubicin (Dox) is one of the most used drugs in the treatment of Soft tissue sarcoma. However, acquired resistance linked with poor survival and numerous side effects are the major challenges. Meanwhile, miRNAs are reported to influence the chemotherapeutic responses. However, there is hardly any evidence on the involvement of tumor-suppressive miR-197 reported in our previous study in augmenting the sensitivity of fibrosarcoma cells to Dox. Therefore, in this study, we intend to decipher if miR-197-5p combined with Dox could increase the anticancer cytotoxicity. For this, we evaluated the antitumorigenic effects of Dox and miR-197-5p individually and in combination by performing a series of molecular assays. We noticed that the sub-lethal concentration of miR-197-5p markedly enhanced the sensitivity of HT1080 fibrosarcoma cells to Dox by promoting apoptosis and G2/M cell cycle arrest. We also observed miR-197-5p sensitizes HT1080 cells to Dox by increasing drug influx, possibly due to suppression of MDR genes (ABCC1, MVP). Moreover, we found that KIAA0101, a target of miR-197-5p is inhibited by Dox, which is further repressed when treated in combination with miRNA. We also observed a marked upregulation of p53, known to be negatively correlated with KIAA0101 in Dox and miR-197-5p combination treatment compared to Dox alone. Taken together, our study revealed that Dox chemotherapy in combination with miR-197-5p could overcome the problem of drug efflux and enhance its antitumor effects on fibrosarcoma.

Terrosamycins A and B, Bioactive Polyether Ionophores from Streptomyces sp. RKND004 from Prince Edward Island Sediment

Terrosamycins A (1) and B (2), two polycyclic polyether natural products, were purified from the fermentation broth of Streptomyces sp. RKND004 isolated from Prince Edward Island sediment. The one strain-many compounds (OSMAC) approach coupled with UPLC-HRMS-based metabolomics screening led to the identification of these compounds. The structure of 1 was determined from analysis of NMR, HRMS, and X-ray diffraction data. NMR experiments performed on 2 revealed the presence of two methoxy groups replacing two hydroxy groups in 1. Like other polyether ionophores, 1 and 2 exhibited excellent antibiotic activity against Gram-positive pathogens. Interestingly, the terrosamycins also exhibited activity against two breast cancer cell lines.

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

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

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.

Individualized doxorubicin sensitivity testing of undifferentiated soft tissue sarcoma (USTS) in a patient-derived orthotopic xenograft (PDOX) model demonstrates large differences between patients

Doxorubicin (DOX) is often first-line treatment of undifferentiated/unclassified soft tissue sarcoma (USTS). However, the DOX response rate for USTS patients is low. Individualized precision-medicine technology that could identify DOX responders as well as non-responders would be of high value to cancer patients. In the present study, we established 5 patient-derived orthotopic xenograft (PDOX) nude mouse models from 5 USTS patients and evaluated the efficacy of DOX in each PDOX model. USTS's were grown orthotopically in the right thigh of nude mice to establish the PDOX models. Two weeks after implantation, the mouse models were randomized into two groups of 8 mice each: untreated control; and DOX (3 mg/kg, i.p., once a week for 2 weeks). DOX showed significant growth inhibition in only 2 USTS PDOX models out of 5 (p = 0.0054, p = 0.0055, respectively) on day 14 after initiation. DOX was ineffective in the other 3 PDOX models. However, even in the DOX-sensitive cases, DOX could not regress the PDOX tumors responding to treatment. The present study has important implications since this is the first in vivo study to compare the DOX sensitivity for USTS on multiple patient tumors. We showed that only two of five USTS were responsive to DOX, despite DOX being first line chemotherapy for USTS. The 3 resistant cases should not be treated with DOX clinically, in order to spare the patients' unnecessary toxicity. This PDOX model is useful for precise individualized drug sensitivity testing, especially for rare heterogeneous recalcitrant sarcomas such as USTS.

Spheroid-based 3D cell cultures identify salinomycin as a promising drug for the treatment of chondrosarcoma

Chondrosarcoma (CS) is a cartilage malignancy of adulthood that is treated by surgery alone, since chemotherapy is considered ineffective. Unfortunately, a large proportion of patients with CS develop lung metastases, and several die of the disease. In this study, we compared 3D-spheroid cultures and conventional cell monolayer models in order to identify the best way to select anticancer agents that could be effective for the systemic control of CS. Using SW1353 cells, we developed a three-dimensional (3D) in vitro culture model to mimic in vivo features of CS microenvironment and evaluated the efficacy of different drugs to modulate CS cell proliferation and survival in 2D versus 3D-cultures. Doxorubicin (DXR) and cisplatin, that are widely employed in sarcomas, were less effective on 3D-CS spheroids when compared to standard monolayer models, whereas treatment with the ionophore salinomycin (SAL) had a strong cytotoxic effect both on 2D and 3D-cultures. Furthermore, as demonstrated by the reduced viability and the enhanced DXR nuclear localization, SAL enhanced DXR cytotoxicity in 3D-CS spheroids also at sub-lethal doses. SAL activity on 3D-CS spheroids was mediated by a significant induction of apoptosis via caspase activation. This study demonstrates that preclinical tests significantly differ in monolayer and 3D cultures of CS cells. Using this approach, SAL, alone or, at sub-lethal concentrations, in combination with DXR, represents a promising agent for the systemic treatment of CS. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Influence of salinomycin treatment on division and movement of individual cancer cells cultured in normoxia or hypoxia evaluated with time-lapse digital holographic microscopy

Most studies on new cancer drugs are based on population-derived data, where the absence of response of a small population may pass unnoticed. Thus, individual longitudinal tracking of cells is important for the future development of efficient cancer treatments. We have used digital holographic microscopy to track individual JIMT-1 human breast cancer cells and L929 mouse fibroblast cultivated in normoxia or hypoxia. In addition, JIMT-1 cells were treated with salinomycin, a cancer stem cell targeting compound. Three-day time-lapse movies were captured and individual cells were analysed with respect to cell division (cell cycle length) and cell movement. Comparing population-doubling time derived from population-based growth curves and individual cell cycle time data from time-lapse movies show that the former hide a sub-population of dividing cells. Salinomycin treatment increased the motility of cells, however, this motility did not result in an increased distant migration i.e. the cells increased their local movement. MCF-7 breast cancer cells showed similar motility behaviour as salinomycin-treated JIMT-1 cells. We suggest that combining features, such as motility and migration, can be used to distinguish cancer cells with mesenchymal (JIMT-1) and epithelial (MCF-7) features. The data clearly emphasize the importance of longitudinal cell tracking to understand the biology of individual cells under different conditions.

Potassium as a pluripotency-associated element identified through inorganic element profiling in human pluripotent stem cells

Despite their well-known function in maintaining normal cell physiology, how inorganic elements are relevant to cellular pluripotency and differentiation in human pluripotent stem cells (hPSCs) has yet to be systematically explored. Using total reflection X-ray fluorescence (TXRF) spectrometry and inductively coupled plasma mass spectrometry (ICP-MS), we analyzed the inorganic components of human cells with isogenic backgrounds in distinct states of cellular pluripotency. The elemental profiles revealed that the potassium content of human cells significantly differs when their cellular pluripotency changes. Pharmacological treatment that alters cell membrane permeability to potassium affected the maintenance and establishment of cellular pluripotency via multiple mechanisms in bona fide hPSCs and reprogrammed cells. Collectively, we report that potassium is a pluripotency-associated inorganic element in human cells and provide novel insights into the manipulation of cellular pluripotency in hPSCs by regulating intracellular potassium.

Low Dose of Doxorubicin Potentiates the Effect of Temozolomide in Glioblastoma Cells

Glioblastoma (GBM) is an aggressive brain tumor with temozolomide (TMZ)-based chemotherapy as the main therapeutic strategy. Doxorubicin (DOX) is not used in gliomas due to its low bioavailability in the brain; however, new delivery strategies and low doses may be effective in the long term, especially as part of a drug cocktail. Our aim was to evaluate the chronic effects of low doses of DOX and TMZ in GBM. Human U87-ATCC cells and a primary GBM culture were chronically treated with TMZ (5 μM) and DOX (1 and 10 nM) alone or combined. DOX resulted in a reduction in the number of cells over a period of 35 days and delayed the cell regrowth. In addition, DOX induced cell senescence and reduced tumor sphere formation and the proportion of NANOG- and OCT4-positive cells after 7 days. Low doses of TMZ potentiated the effects of DOX on senescence and sphere formation. This combined response using low doses of DOX may pave the way for its use in glioma therapy, with new technologies to overcome its low blood-brain barrier permeability.

Salinomycin: A new paradigm in cancer therapy

The primary hurdle in the treatment of cancer is acquisition of resistance by the tumor cells toward multiple drugs and selectively targeting the cancer stem cells. This problem was overcome by the chemotherapeutic property of recently discovered drug salinomycin. Exact mechanism of action of salinomycin is not yet known, but there are multiple pathways by which salinomycin inhibits tumor growth. Salinomycin decreases the expression of adenosine triphosphate-binding cassette transporter in multidrug resistance cells and interferes with Akt signaling pathway, Wnt/β-catenin, Hedgehog, and Notch pathways of cancer progression. Salinomycin selectively targets cancer stem cells. The potential of salinomycin to eliminate both cancer stem cells and therapy-resistant cancer cells may characterize the compound as a novel and an efficient chemotherapeutic drug.

Evaluation of growth inhibitory response of Resveratrol and Salinomycin combinations against triple negative breast cancer cells

Resveratrol (RSVL) a dietary phytochemical showed to enhance the efficacy of chemotherapeutic drugs. Recently, Salinomycin (SAL) has gained importance as cancer therapeutic value for breast cancer (BC), however, its superfluxious toxicity delimits the utility. Taking the advantage of RSVL, the therapeutic efficacy of RSVL and SAL combination was studied in vitro and in vivo system. Firstly, the synergistic combination dose of RSVL and SAL was calculated and further, the efficacy was examined by wound healing, and Western blots analysis. Further, in vivo study was performed to confirm the effect of colony formation and apoptosis detection by flow cytometry based assays. Further, the molecular mode of action was determined at both transcript and translational level by quantitative Real Time PCR combination in Ehrlich ascitic carcinoma model.The combination of IC20 (R20) of RSVL and IC10 (S10) dose of SAL showed best synergism (CI<1) with ∼5 fold dose advantage of SAL. Gene expression results at mRNA and protein level revealed that the unique combination of RSVL and SAL significantly inhibited epithelial mesenchymal transition (Fibronectin, Vimentin, N-Cadherin, and Slug); chronic inflammation (Cox2, NF-kB, p53), autophagy (Beclin and LC3) and apoptotic (Bax, Bcl-2) markers. Further, i n vivo study showed that low dose of SAL in combination with RSVL increased life span of Ehrlich ascitic mice. Overall, our study revealed that RSVL synergistically potentiated the anticancer potential of SAL against triple negative BC.

Consecutive salinomycin treatment reduces doxorubicin resistance of breast tumor cells by diminishing drug efflux pump expression and activity

Chemoresistance is a major challenge for the successful therapy of breast cancer. The discovery of salinomycin as an anticancer stem cell drug provides progress in overcoming chemoresistance. However, it remains to be elucidated whether salinomycin treatment is able to sensitize cancer cells to chemotherapeutic drugs. In the present study, we consecutively treated epithelial MCF-7 and BT-474 breast cancer cells as well as mesenchymal MDA-MB 231 and MDA-MB 436 cells with salinomycin, and analyzed the gene expression of the two prominent multiple drug resistance (MDR) genes, MDR1 and BCRP1. We found that repeated treatment with salinomycin generated resistance against this drug in all cell lines and increased the chemosensitivity towards doxorubicin. Drug efflux pump gene expression and pump activity of MDR1 and BCRP1 were downregulated in almost all cell lines, except for MDR1 in the MDA-MB 231 cells. Consequently, the intracellular doxorubicin accumulation was increased compared to the respective parental cells. Our findings suggest a novel treatment option for MDR tumors by sensitizing these tumors via salinomycin pretreatment.

Metformin and salinomycin as the best combination for the eradication of NSCLC monolayer cells and their alveospheres (cancer stem cells) irrespective of EGFR, KRAS, EML4/ALK and LKB1 status

The presence of cancer stem cells (CSCs) is linked to preexisting or acquired drug resistance and tumor relapse. Therefore, targeting both differentiated tumor cells and CSCs was suggested as an effective approach for non-small cell lung cancer (NSCLC) treatment. After screening of chemotherapeutic agents, tyrosine kinase inhibitors (TKIs) or monoclonal antibody in combination with the putative stem cell killer Salinomycin (SAL), we found Metformin (METF), which modestly exerted a growth inhibitory effect on monolayer cells and alveospheres/CSCs of 5 NSCLC cell lines regardless of their EGFR, KRAS, EML4/ALK and LKB1 status, interacted synergistically with SAL to effectively promote cell death. Inhibition of EGFR (AKT, ERK1/2) and mTOR (p70 s6k) signaling with the combination of METF and SAL can be augmented beyond that achieved using each agent individually. Phospho-kinase assay further suggested the multiple roles of this combination in reducing oncogenic effects of modules, such as ß-catenin, Src family kinases (Src, Lyn, Yes), Chk-2 and FAK. Remarkably, significant reduction of sphere formation was seen under combinatorial treatment in all investigated NSCLC cell lines. In conclusion, METF in combination with SAL could be a promising treatment option for patients with advanced NSCLC irrespective of their EGFR, KRAS, EML4/ALK and LKB1 status.

Co-Eradication of Breast Cancer Cells and Cancer Stem Cells by Cross-Linked Multilamellar Liposomes Enhances Tumor Treatment

The therapeutic limitations of conventional chemotherapeutic drugs have emerged as a challenge for breast cancer therapy; these shortcomings are likely due, at least in part, to the presence of the cancer stem cells (CSCs). Salinomycin, a polyether antibiotic isolated from Streptomyces albus, has been shown to selectively inhibit cancer stem cells; however, its clinical application has been hindered by the drug's hydrophobility, which limits the available administration routes. In this paper, a novel drug delivery system, cross-linked multilamellar liposomal vesicles (cMLVs), was optimized to allow for the codelivery of salinomycin (Sal) and doxorubicin (Dox), targeting both CSCs and breast cancer cells. The results show that the cMLV particles encapsulating different drugs have similar sizes with high encapsulation efficiencies (>80%) for both Dox and Sal. Dox and Sal were released from the particles in a sustained manner, indicating the stability of the cMLVs. Moreover, the inhibition of cMLV(Dox+Sal) against breast cancer cells was stronger than either single-drug treatment. The efficient targeting of cMLV(Dox+Sal) to CSCs was validated through in vitro experiments using breast cancer stem cell markers. In accordance with the in vitro combination treatment, in vivo breast tumor suppression by cMLV(Dox+Sal) was 2-fold more effective than single-drug cMLV treatment or treatment with the combination of cMLV(Dox) and cMLV(Sal). Thus, this study demonstrates that cMLVs represent a novel drug delivery system that can serve as a potential platform for combination therapy, allowing codelivery of an anticancer agent and a CSC inhibitor for the elimination of both breast cancer cells and cancer stem cells.

Oridonin inhibits BxPC-3 cell growth through cell apoptosis

Oridonin, an ent-kaurene diterpenoid extracted from the traditional Chinese herb Rabdosia rubescens, has multiple biological and pharmaceutical functions and has been used clinically for many years. While the antitumor function of oridonin has been corroborated by numerous lines of evidence, its anticancer mechanism has not been well documented. In this study, the pancreatic cancer cell line BxPC-3 was used as a model to investigate a possible anticancer mechanism of oridonin through examining its effects on cell viability. The results showed that oridonin affected cell viability in a time- and dose-dependent manner. After exposure to different oridonin concentrations, growth rates and cell cycle arrest of BxPC-3 cells were significantly reduced compared with untreated cells, suggesting its effects on proliferation inhibition. Detailed signaling pathway analysis by western blot analysis revealed that low-dose oridonin treatment inhibited BxPC-3 cell proliferation by up-regulating p53 and down-regulating cyclin-dependent kinase 1 (CDK1), which led to cell cycle arrest in the G2/M phase. A high-dose oridonin not only arrested BxPC-3 cells in the G2/M phase but also induced cell accumulation in the S phase, presumably through γH2AX up-regulation and DNA damage. In addition, our results showed that a cell subpopulation was stained with propidium iodide after oridonin treatment. Protein quantification showed that cleaved poly(ADP-ribose) polymerase (PARP) expression was increased after a high-dose oridonin treatment, especially after long-term exposure. Accompanied by the increased level of deactivated PARP in BxPC-3 cells, the apoptosis initiators caspase-3 and caspase-7 expressions were also significantly increased, suggesting that caspase-mediated apoptosis contributed to cell death.

A case of myxoid liposarcoma of the retroperitoneum: a challenging tumour for diagnosis and treatment

Retroperitoneal sarcomas are rare neoplasms that account for only 1%-2% of all solid tumors and liposarcomas represent the most frequent histological type. We describe the case of a 44-year-old female with a retroperitoneal myxoid liposarcoma of 22 × 19 × 8 cm in size. The only symptoms were persistent pain and progressive tenderness of the abdomen lasting for two months. The mass was radically excised during laparotomy. CT and MRI were useful to clarify the site of origin of the tumor, relationships with other organs, and planning surgery but final diagnosis was based on histological findings. Here we review the literature about the challenging diagnosis, treatment, and prognostic factors of this disease.

Triggering of erythrocyte cell membrane scrambling by salinomycin

Salinomycin, a polyether ionophore antibiotic effective against a variety of pathogens, has been shown to trigger apoptosis of cancer cells and cancer stem cells. The substance is thus considered for the treatment of malignancy. Salinomycin compromises tumour cell survival at least in part by interference with mitochondrial function. Erythrocytes lack mitochondria but may undergo apoptosis-like suicidal cell death or eryptosis, which is characterized by scrambling of the cell membrane with phosphatidylserine exposure at the erythrocyte surface. Signalling involved in the triggering of eryptosis includes activation of oxidant-sensitive Ca(2+) permeable cation channels with subsequent increase in cytosolic Ca(2+) activity ([Ca(2+)]i). This study explored whether salinomycin stimulates eryptosis. Phosphatidylserine-exposing erythrocytes were identified by measurement of annexin-V binding, cell volume was estimated from forward scatter, haemolysis determined from haemoglobin release, [Ca(2+)]i quantified utilizing Fluo3-fluorescence and oxidative stress from 2',7' dichlorodihydrofluorescein diacetate (DCFDA) fluorescence in flow cytometry. A 48-hr exposure to salinomycin (5-100 nM) was followed by a significant increase in Fluo3-fluorescence, DCFDA fluorescence and annexin-V binding, as well as a significant decrease in forward scatter (at 5-10 nM, but not at 50 and 100 nM). The annexin-V binding after salinomycin treatment was significantly blunted but not abrogated in the nominal absence of extracellular Ca(2+) or in the presence of antioxidant n-acetyl cysteine (1 mM). Salinomycin triggers cell membrane scrambling, an effect at least partially due to oxidative stress and entry of extracellular Ca(2+).