Antibacterial and Anticancer Activities of Pleurocidin-Amide, a Potent Marine Antimicrobial Peptide Derived from Winter Flounder, Pleuronectes americanus.

The extensive use of conventional antibiotics has led to the growing emergence of many resistant strains of pathogenic bacteria. Evidence suggests that cationic antimicrobial peptides (AMPs) have the greatest potential to serve as traditional antibiotic substitutes. Recent studies have also reported that certain AMPs have selective toxicity toward various types of cancer cells. The electrostatic attraction between the negatively charged membrane components and AMPs is believed to play a crucial role in the disruption of bacterial and cancer cell membranes. In the current study, we used a potent AMP called Pleurocidin (Ple) derived from winter flounder Pleuronectes americanus and its C-terminal-amidated derivative Pleurocidin-amide (Ple-a), and evaluated their antibacterial and anticancer activities. Our results indicated that both Ple and Ple-a exhibited significant antibacterial activity against a broad spectrum of Gram-positive and Gram-negative bacteria, especially marine pathogens, with MIC values ranging from 0.25 to 32 µg/mL. These peptides are also potent against several multidrug-resistant (MDR) bacterial strains, with MIC values ranging from 2 to 256 µg/mL. When used in combination with certain antibiotics, they exhibited a synergistic effect against MDR E. coli. Ple and Ple-a also showed notable cytotoxicity toward various cancer cell lines, with IC50 values ranging from 11 to 340 µM, while normal mouse fibroblast 3T3 cells were less susceptible to these peptides. Ple-a was then selected to study its anticancer mechanism toward A549 human lung adenocarcinoma cells. Western blot analysis and confocal microscopy showed that Ple-a could inhibit autophagy of A549 cells, and induce apoptosis 48 h after treatment. Our findings provided support for the future application of Ple-a as potential therapeutic agent for bacterial infections and cancer treatment.

Disulfide-cross-linked PEG-block-polypeptide nanoparticles with high drug loading content as glutathione-triggered anticancer drug nanocarriers.

The development of stimuli-responsive drug carrier systems enabling to deliver high doses of anti-cancer drugs to tumor tissues is still urgently needed. In this study, we report the preparation of reduction-responsive methoxypolyethylene glycol-block-(poly(l-lysine)-co-poly(l-tyrosine)) (mPEG-b-(PLL-co-PLY)) nanoparticles (NPs) exhibiting sizes smaller than 100 nm and high drug loading content (DLC) of doxorubicin (DOX) by selecting the Lys and Tyr residues as the polypeptide building blocks. The disulfide-cross-linked mPEG-b-(PLL-co-PLY) assemblies with sizes can be tuned by varying the polypeptide composition followed by subsequent disulfide-cross-linking. Cytotoxicity assays showed that the Dox-loaded NPs exhibited efficient cell internalization and proliferation inhibition toward cancer cells, whereas the copolymers exhibited low hemolysis to human red blood cells and excellent biocompatibility to both normal and cancer cells. The enhanced internalization and cytotoxicity of DOX-NPs can be possible due to their small size and their reduction-responsive property. Anticancer studies using C57BL/6 mice bearing LLC tumor model showed that the DOX-loaded NPs significantly suppressed tumor growth and prolonged the survival of tumor-bearing mice without obvious body weight loss and damage to major organs. This approach provides a platform for developing stimuli-responsive, polypeptide-based drug delivery systems with high DLC for cancer treatment.