Salinomycin induces cell death and differentiation in head and neck squamous cell carcinoma stem cells despite activation of epithelial-mesenchymal transition and Akt

Abstract

BackgroundCancer stem cells (CSC) are believed to play a crucial role in cancer recurrence due to their resistance to conventional chemotherapy and capacity for self-renewal. Recent studies have reported that salinomycin, a livestock antibiotic, selectively targets breast cancer stem cells 100-fold more effectively than paclitaxel. In our study we sought to determine the effects of salinomycin on head and neck squamous cell carcinoma (HNSCC) stem cells.MethodsMTS and TUNEL assays were used to study cell proliferation and apoptosis as a function of salinomycin exposure in JLO-1, a putative HNSCC stem cell culture. MTS and trypan blue dye exclusion assays were performed to investigate potential drug interactions between salinomycin and cisplatin or paclitaxel. Stem cell-like phenotype was measured by mRNA expression of stem cell markers, sphere-forming capacity, and matrigel invasion assays. Immunoblotting was also used to determine expression of epithelial-mesenchymal transition (EMT) markers and Akt phosphorylation. Arrays by Illumina, Inc. were used to profile microRNA expression as a function of salinomycin dose.ResultsIn putative HNSCC stem cells, salinomycin was found to significantly inhibit cell viability, induce a 71.5% increase in levels of apoptosis, elevate the Bax/Bcl-2 ratio, and work synergistically with cisplatin and paclitaxel in inducing cell death. It was observed that salinomycin significantly inhibited sphere forming-capability and repressed the expression of CD44 and BMI-1 by 3.2-fold and 6.2-fold, respectively. Furthermore, salinomycin reduced invasion of HNSCC stem cells by 2.1 fold. Contrary to expectations, salinomycin induced the expression of EMT markers Snail, vimentin, and Zeb-1, decreased expression of E-cadherin, and also induced phosphorylation of Akt and its downstream targets GSK3-β and mTOR.ConclusionsThese results demonstrate that in HNSCC cancer stem cells, salinomycin can cause cell death and decrease stem cell properties despite activation of both EMT and Akt.

The impact of metformin and salinomycin on transforming growth factor β-induced epithelial-to-mesenchymal transition in non-small cell lung cancer cell lines

“…Although evidence for EMT-inhibitory effects of salinomycin exists (16), other literature also confirms the current data suggesting that escalating doses of salinomycin correlate with an upregulation of vimentin and downregulation of E-cadherin (27). These findings may be explained by a possible non-correspondence between EMT and certain cell abilities, such as invasion, in these cell lines (27). In EMT-transformed A549 cells treated with salinomycin, the present investigations of protein expression and migration revealed different results compared to those for HCC4006 cells.…”

Drug Transporter-Mediated Protection of Cancer Stem Cells From Ionophore Antibiotics

“…Eradication of these CSCs, however, has proven difficult, partly because several protection mechanisms are operative in these cells [11,25]. In the face of this challenge, the demonstration that IAs can target various CSC populations (including populations expressing ABCB1 and ABCG2) [3][4][5][6][7][8]12] was particularly remarkable. Despite this, a definite role of drug transporters in the response to IA-based treatment has not been established.…”

“…Based on the reported abilities of IAs to bear selectivity against epithelial and nonepithelial CSCs [3][4][5][6][7][8] and to overcome transporter-mediated drug resistance [12], we tested their effects on OvCa SP cells; however, using different cell lines expressing either ABCB1 or ABCG2, we found that-in contrast to non-SP cells-viability of SP cells was only marginally affected by salinomycin and nigericin (Fig. 3A, 3B) (data not shown).…”

“…Strikingly, their screen revealed significant CSCselective toxicity for two IAs (i.e., salinomycin and nigericin), indicating strong susceptibility of CSCs to this substance class. Specific anti-CSC activity of IAs was subsequently observed in other CSC populations [4][5][6][7][8]. Moreover, it was reported that salinomycin is able to overcome apoptosis resistance in cancer cells [9] and to interfere with Wnt signaling [10].…”

Salinomycin: A new paradigm in cancer therapy

“…45 Salinomycin with cisplatin or paclitaxel revealed strong synergism for antitumor activity in head and neck squamous cell carcinoma stem cells. 53 MCF-7 xenografts and salinomycin-loaded PEGb-PCL polymeric micelles combined with octreotide-modified paclitaxel-loaded PEG-b-PCL polymeric micelles showed stronger antitumor activity. 98 Lapatinib is an anticancer drug used in the treatment of breast cancer.…”