Abstract
BackgroundPancreatic cancer stem cells (CSCs), a special population of cells, renew themselves infinitely and resist to various treatment. Gramicidin A (GrA), an ionophore antibiotic derived from microorganism, can form channels across the cell membrane and disrupt cellular ionic homeostasis, leading to cell dysfunction and death. As reported, the ionophore antibiotic salinomycin (Sal) has been proved to kill CSCs effectively. Whether GrA owns the potential as a therapeutic drug for CSCs still remains unknown. This study investigated the effect of GrA on pancreatic CSCs and the mechanism.MethodsTumorsphere formation assay was performed to assess pancreatic CSCs self-renewal potential. In vitro hemolysis assay was determined to test the borderline concentration of GrA. CCK-8 assay was used to detect pancreatic cancer cell proliferation capability. Flow cytometry was performed to detect cell apoptosis and mitochondrial membrane potential. Scanning and transmission electron microscopy was used to observe ultrastructural morphological changes on cell membrane surface and mitochondria, respectively. Western blot analysis was used to determine relative protein expression levels. Immunofluorescence staining was performed to observe CD47 re-distribution.ResultsGrA at 0.05 μM caused tumorspheres disintegration and decrease in number of pancreatic cancer BxPC-3 and MIA PaCa-2 cells. GrA and Sal both inhibited cancer cell proliferation. The IC50 values of GrA and Sal for BxPC-3 cells were 0.025 μM and 0.363 μM; while for MIA PaCa-2 cells were 0.032 μM and 0.163 μM, respectively. Compared on equal concentrations, the efficacy of GrA was stronger than that of Sal. GrA at 0.1 μM or lower did not cause hemolysis. GrA induced ultrastructural changes, such as the decrease of microvilli-like protrusions on cell surface membrane and the swelling of mitochondria. GrA down-regulated the expression levels of CD133, CD44, and CD47; in addition, CD47 re-distribution was observed on cell surface. Moreover, GrA showed synergism with gemcitabine in suppressing cancer cell proliferation.ConclusionsThe study found that GrA was highly active against pancreatic CSCs. It indicates that GrA exerts inhibitory effects against pancreatic CSCs associated with CD47 down-regulation, implying that GrA might play a positive role in modulating the interaction between macrophages and tumor cells.
Highlights
Pancreatic cancer stem cells (CSCs), a special population of cells, renew themselves infinitely and resist to various treatment
It is worth mentioning that Sal, an ionophore antibiotic isolated from Streptomyces albus, selectively targets tumorsphere initiation and the growth of CD133+ Pancreatic ductal adenocarcinoma (PDAC) CSCs and displays a synergistic effect when combined with gemcitabine (GEM) [13]
Our study aims at the action of Gramicidin A (GrA) on pancreatic CSCs and its mechanism
Summary
Pancreatic cancer stem cells (CSCs), a special population of cells, renew themselves infinitely and resist to various treatment. Recent studies demonstrate that self-renewing cancer stem cells (CSCs) contribute to metastatic dissemination and therapy failure, causing high mortality of PDAC. There are several potential targets to inhibit CSCs including pancreatic CSC-specific surface markers [7], stem-cell specific signaling pathways (e.g. Notch, Wnt and Hedgehog [6]), resistance mechanisms, the components of CSC niche [8], and mitochondria dysfunction [9, 10]. It is worth mentioning that Sal, an ionophore antibiotic isolated from Streptomyces albus, selectively targets tumorsphere initiation and the growth of CD133+ PDAC CSCs and displays a synergistic effect when combined with gemcitabine (GEM) [13]. Very few CSC-targeting drugs are currently available for clinical use; there is an urgent need for investigation of novel drugs with improved efficacy and reduced toxicity in CSC-targeting therapy
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