Magainin II

Objective:Magainin II belongs to a family of antimicrobial peptides and has been shown to exhibit antibiotic activity in a wide range of organisms. Recent studies have also reported a significant antitumor effect of magainin II against various cancer cell lines and tumor mice models. In this study, we evaluated the cytotoxic and antiproliferative potency of magainin II in bladder tumor cells and normal fibroblasts.Methods:The antiproliferative and cytotoxic effect of magainin II was quantified by colorimetric WST-1-, bromodeoxyuridine (BrdU)-, and lactic dehydrogenase (LDH) assays in three bladder cancer cell lines (RT4, 647V, and 486P) and in the murine fibroblast cell line 3T3 as well as in a primary culture from human fibroblasts. The median inhibitory concentration (IC50) values were determined for each assay, representing the concentration at which cell viability was reduced by 50%. Scanning electron microscopy (SEM) was used to visualize the morphologic effects of magainin II on bladder tumor cells and fibroblasts.Results:Magainin II inhibited cell proliferation of bladder cancer cells in a dose-dependent manner. The average IC50 of magainin II against all bladder cancer cell lines was 198.1 microM (range, 52.4-484.03 microM) for the WST-1 assay and 75.2 microM (range, 31.0-135.3 microM) for the BrdU assay. The normal murine and human fibroblast cell lines were not affected by magainin II and their IC50 could not be determined at the concentrations of magainin II tested. LDH release was increased in all bladder tumor cell lines in the presence of magainin II, whereas normal fibroblasts showed no cell lysis. SEM demonstrated lethal membrane perforation by peptide pore formation in bladder cancer cells, but not in fibroblasts.Conclusion:Magainin II peptide exerts cytotoxic and antiproliferative efficacy by pore formation in bladder cancer cells but has no effect on normal murine or human fibroblasts. Magainin II may offer a novel therapeutic strategy in the treatment of bladder cancer with potentially low cytotoxic effects on normal cells.

Background:Antibiotic residues can cause antibiotic resistance in livestock and their food safety-related issues have increased the consumer demand for products lacking these residues. Hence, developing safe and effective antibiotic alternatives is important to the animal feed industry. With their strong antibacterial actions, antimicrobial peptides have potential as antibiotic alternatives.Results:We investigated the antibacterial and immunomodulatory activities and the mechanisms of action of an antimicrobial peptide. The hybrid antimicrobial peptide magainin II-cecropin B (Mag II-CB) gene was transformed into the medicinal Cordyceps militaris fungus. Recombinant Mag II-CB exhibited broad-spectrum antibacterial activity in vitro and its antibacterial and immunomodulatory functions were evaluated in BALB/c mice infected with Escherichia coli (ATCC 25922). Histologically, Mag II-CB ameliorated E. coli-related intestinal damage and maintained the integrity of the intestinal mucosal barrier by up-regulating tight junction proteins (zonula occludens-1, claudin-1 and occludin). The intestinal microbial flora was positively modulated in the Mag II-CB-treated mice infected with E. coli. Mag II-CB treatment also supported immune functioning in the mice by regulating their plasma immunoglobulin and ileum secreted immunoglobulin A levels, by attenuating their pro-inflammatory cytokine levels, and by elevating their anti-inflammatory cytokines levels. Moreover, directly feeding the infected mice with the C. militaris mycelium producing Mag II-CB further proofed the antibacterial and immunomodulatory functions of recombinant hybrid antimicrobial peptide.Conclusion:Our findings suggest that both purified recombinant AMPs and C. militaris mycelium producing AMPs display antibacterial and immunomodulatory activities in mice. And C. militaris producing AMPs has the potential to become a substitute to antibiotics as a feed additive for livestock in future.

Polydiacetylene (PDA) micelles have been widely used to deliver anticancer drugs in the treatment of a variety of tumours and for imaging living cells. In this study, we developed an effective strategy to directly conjugate magainin II (MGN-II) to the surface of PDA micelles using a fluorescent dye. These stable and well-defined PDA micelles had high cytotoxicity in cancer cell lines, and were able to reduce the tumour size in mice. The modified PDA micelles improved the anticancer effects of MGN-II in the A549 cell line only at a concentration of 16.0 μg mL(-1) (IC50). In addition, following irradiation with UV light at 254 nm, the PDA micelles gave rise to an energy transfer from the fluorescent dye to the backbone of PDA micelles to enhance the imaging of living cells. Our results demonstrate that modified PDA micelles can not only be used in the treatment of tumors in vitro and in vivo in a simple and directed way, but also offer a new platform for designing functional liposomes to act as anticancer agents.