Enhanced cellular uptake of CpG DNA by α-helical antimicrobial peptide Kn2-7: Effects on macrophage responsiveness to CpG DNA

Differences in Phage Recognition and Immunogenicity Contribute to Divergent Human Immune Responses to Escherichia coli and Klebsiella pneumoniae Phages

Bacteriophages (phages) are emerging as a viable adjunct to antibiotics for the treatment of multidrug-resistant (MDR) bacterial infections. While intravenous phage therapy has proven successful in many cases, clinical outcomes remain uncertain due to a limited understanding of host response to phages. In this study, we conducted a comprehensive examination of the interaction between clinical-grade phages used to treat MDR Escherichia coli and Klebsiella pneumoniae infections, and human peripheral blood immune cells. Using whole transcriptome as well as proteomic approaches, we identified a strong inflammatory response to E. coli phage vB_EcoM-JIPh_Ec70 (herein, JIPh_Ec70) that was absent upon exposure to K. pneumoniae phage JIPh_Kp127. We confirmed that JIPh_Ec70's DNA recognition by the STING pathway was principally responsible for the activation of NF-kB and the subsequent inflammatory response. We further show that monocytes and neutrophils play a dominant role in phage uptake, primarily through complement-mediated phagocytosis. Significant differences in complement-mediated phagocytosis of JIPh_Kp127 and JIPh_Ec70 were observed, suggesting that reduced recognition, phagocytosis, and immunogenicity all contribute to the significantly decreased response to JIPh_Kp127. Our findings contribute to the progress of our understanding of the innate immune response to therapeutic phages and offer potential insights into how to improve the safety and effectiveness of phage therapy.

High amphipathicity of α-helical peptides enhances unmethylated CpG DNA-induced activation of mouse macrophage-like RAW264.7 cells

The α-helical antimicrobial peptide Kn2-7 enhances the activation of mouse macrophage-like RAW264.7 induced by DNA containing unmethylated cytosine-guanine motifs (CpG DNA). This enhancement is related to increased cellular uptake of DNA by Kn2-7, but the relevant properties of Kn2-7 are unknown. Physicochemical property analysis revealed that Kn2-7 has high amphipathicity. In contrast, the α-helical antimicrobial peptide L5, which increases the cellular uptake of CpG DNA but does not enhance CpG DNA-induced activation, has low amphipathicity. Kn2-7 derivatives with decreased amphipathicity but the same amino acid composition as Kn2-7 did not enhance CpG DNA-induced activation. On the other hand, L5 derivatives with high amphipathicity but the same amino acid composition as L5 enhanced CpG DNA-induced activation. Cellular uptake of DNA was not increased by the L5 derivatives, indicating that high amphipathicity does not affect DNA uptake. Furthermore, α-helical peptides with reversed sequences relative to the Kn2-7 and L5 derivatives with high amphipathicity were synthesized. The reversed-sequence peptides, which had the same amphipathicity but different amino acid sequences from their counterparts, enhanced CpG DNA-induced activation. Taken together, these observations indicate that the high amphipathicity of α-helical peptides enhances the CpG DNA-induced activation of RAW264.7.

The Contribution of Antimicrobial Peptides to Immune Cell Function: A Review of Recent Advances

The development of novel antimicrobial agents to replace antibiotics has become urgent due to the emergence of multidrug-resistant microorganisms. Antimicrobial peptides (AMPs), widely distributed in all kingdoms of life, present strong antimicrobial activity against a variety of bacteria, fungi, parasites, and viruses. The potential of AMPs as new alternatives to antibiotics has gradually attracted considerable interest. In addition, AMPs exhibit strong anticancer potential as well as anti-inflammatory and immunomodulatory activity. Many studies have provided evidence that AMPs can recruit and activate immune cells, controlling inflammation. This review highlights the scientific literature focusing on evidence for the anti-inflammatory mechanisms of different AMPs in immune cells, including macrophages, monocytes, lymphocytes, mast cells, dendritic cells, neutrophils, and eosinophils. A variety of immunomodulatory characteristics, including the abilities to activate and differentiate immune cells, change the content and expression of inflammatory mediators, and regulate specific cellular functions and inflammation-related signaling pathways, are summarized and discussed in detail. This comprehensive review contributes to a better understanding of the role of AMPs in the regulation of the immune system and provides a reference for the use of AMPs as novel anti-inflammatory drugs for the treatment of various inflammatory diseases.

Intratumoral delivery of brachytherapy and immunotherapy by a thermally triggered polypeptide depot

Biomaterial-based approaches for a combination of radiotherapy and immunotherapy can improve outcomes in metastatic cancer through local delivery of both therapeutic modalities to the primary tumor to control local tumor growth and distant metastases. This study describes an injectable depot for sustained intratumoral (i.t.) delivery of an iodine-131 (¹³¹I) radionuclide and a CpG oligodeoxynucleotide immunostimulant, driven by the thermally sensitive phase transition behavior of elastin-like polypeptides (ELPs). We synthesized and characterized an ELP with an oligolysine tail (ELP-K₁₂) that forms an electrostatic complex with CpG for delivery from an ELP depot and evaluated the ability of the complex to enhance local and systemic tumor control as a monotherapy and in combination with ¹³¹I-ELP brachytherapy. I.t delivery of CpG from an ELP-K₁₂ depot dramatically prolongs i.t. retention to more than 21 days as compared to soluble CpG that is only retained within the tumor for <24 h. ELP-K₁₂ also enhances CpG delivery by increasing cellular uptake of CpG to generate greater toll-like receptor 9 (TLR9) activation than CpG alone. I.t. treatment with an ELP-K₁₂/CpG depot slows primary tumor growth and reduces lung metastases in a poorly immunogenic 4 T1 syngeneic breast cancer model whereas i.t treatment of CpG alone has no significant effect on primary tumor growth or metastases. Notably, a combination of ¹³¹I-ELP brachytherapy and ELP-K₁₂/CpG delivered i.t. inhibited 4 T1 tumor growth and strongly decreased the development of lung metastases, leading to a synergistic improvement in mouse survival. These preclinical results demonstrate that injectable ELP depots may provide a useful approach for the delivery of combination radio- and immuno-therapy to treat metastatic disease.

Antimicrobial Peptide Modifications against Clinically Isolated Antibiotic-Resistant Salmonella

Antimicrobial peptides are promising molecules to address the global antibiotic resistance problem, however, optimization to achieve favorable potency and safety is required. Here, a peptide-template modification approach was employed to design physicochemical variants based on net charge, hydrophobicity, enantiomer, and terminal group. All variants of the scorpion venom peptide BmKn-2 with amphipathic α-helical cationic structure exhibited an increased antibacterial potency when evaluated against multidrug-resistant Salmonella isolates at a MIC range of 4–8 µM. They revealed antibiofilm activity in a dose-dependent manner. Sheep red blood cells were used to evaluate hemolytic and cell selectivity properties. Peptide Kn2-5R-NH₂, dKn2-5R-NH₂, and 2F-Kn2-5R-NH₂ (variants with +6 charges carrying amidated C-terminus) showed stronger antibacterial activity than Kn2-5R (a variant with +5 charges bearing free-carboxyl group at C-terminus). Peptide dKn2-5R-NH₂ (d-enantiomer) exhibited slightly weaker antibacterial activity with much less hemolytic activity (higher hemolytic concentration 50) than Kn2-5R-NH₂ (l-enantiomer). Furthermore, peptide Kn2-5R with the least hydrophobicity had the lowest hemolytic activity and showed the highest specificity to Salmonella (the highest selectivity index). This study also explained the relationship of peptide physicochemical properties and bioactivities that would fulfill and accelerate progress in peptide antibiotic research and development.