The ionophore antibiotic gramicidin A inhibits pancreatic cancer stem cells associated with CD47 down-regulation

Abstract

Background Pancreatic 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. Methods Tumorsphere 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. Results GrA 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. Conclusions The 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.

Target c-Myc to treat pancreatic cancer

“…C-Myc also increases CD47 expression in pancreatic cancer. 119 C-Myc increases the transcription of CD47 in cancer cells. CD47 is located on the surface of cancer cells and interacts with signal-regulatory protein alpha (SIRP-α) to induce tolerance in immune cells, prevent cancer cells phagocytosis, and prolong cancer cells survival in pancreatic cancer.…”

Antimicrobial Peptides as New Combination Agents in Cancer Therapeutics: A Promising Protocol against HT-29 Tumoral Spheroids

“…GA is known to form ion channels, which can allow monovalent ion (Na + and K + ) diffusion, resulting in changes in intracellular osmolality, and finally in cell death [25]. Recently, its antitumoral effect on renal cell carcinoma [26,27], gastric cancer cells [28], or pancreatic cells [29] was reported. Moreover, it was shown that GA used in combination with curcumin kills the cells expressing the multidrug-resistance-linked ABCG2 transporter by stimulated depletion of ATP levels [30].…”

Strategies of Perturbing Ion Homeostasis for Cancer Therapy

“…Chloride influx Mitochondria-dependent apoptosis [40] Potassium Helical polypeptide Potassium efflux ER stress-mediated apoptosis [23] Valinomycin Potassium efflux Restoration of T cell immunity [31] Salinomycin Potassium efflux Suppression of Wnt pathway [6] Gramicidin A Potassium efflux Downregulation of CD47 [49] Calcium Helical polypeptide Calcium overload Mitochondria-dependent apoptosis [24] Calcium NPs Calcium overload Mitochondria-dependent apoptosis [59,[62][63][64] Tumor calcification [59,64] Zinc Clioquinol Zinc overload Inhibiton of NF-𝜅B pathways [ 68,115] Disulfiram Zinc overload Lysosomal disruption [69] Zinaamidole A Zinc overload Non-apoptotic cell death [11] Zinc NPs Zinc overload Oxidative stress-mediated apoptosis [ 71,73,74,77] PAC-1 Zinc depletion Autophagic cell death [ 75,116] Ferroptosis via disruption of iron homeostasis [76] VEGF inhibition [79] Manganese Manganese NPs Manganese overload Chemodynamic activity via Fenton-like reaction [84][85][86][87][88]117] MnO x nanospikes-nanovaccine Manganese overload Ferroptosis via Fenton-like reaction [89,90] Activation of cGAS/STING pathway [91] Ferroptosis-mediated ICD [90] Iron Tannic acid-based NP Iron overload Ferroptosis via Fenton reaction [21] Salinomycin analogue Iron overload Ferroptosis in cancer stem cells [9] Oxidized Starch Iron overload Ferroptosis via Fenton reaction [97] Iron NPs Iron overload Ferroptosis via Fenton reac...…”

“…[6] According to several reports, potassium ionophores are likely to activate antitumor immunity by pumping out intracellular potassium ions. [49] Gramicidin A has been used to reinforce antitumor immunity by suppressing an immune checkpoint. [49] The CD47 receptor is known as immune checkpoint that helps cancer cells prevent phagocytosis by antigen-presenting cells (APCs).…”