C-terminal PEGylation improves SAAP-148 peptide's immunomodulatory activities

Synthetic antibacterial and anti-biofilm peptide (SAAP)-148 was developed to combat bacterial infections not effectively treatable with current antibiotics. SAAP-148 is highly effective against antimicrobial-resistant (AMR) bacteria without inducing resistance, however challenges for further development of SAAP-148 include its cytotoxicity and short circulation half-life. To circumvent these drawbacks a library of SAAP-148 linked to polyethylene glycol (PEG) groups of various lengths was screened for in vitro antibacterial activity and hemolytic activity. Results indicated that PEGylated SAAP-148 variants combine antibacterial activities with reduced hemolysis compared to SAAP-148. Interestingly, pro-inflammatory immunomodulatory activities of SAAP-148 were enhanced upon C-terminal PEGylation, with SAAP-148-PEG27 showing most effect. SAAP-148-PEG27 enhanced SAAP-148’s capacity to chemoattract human neutrophils and was able to more efficiently (re)direct M-CSF-induced monocyte-macrophage differentiation towards type 1 macrophages compared to SAAP-148. Furthermore, dendritic cells with a stronger mature expression profile were produced if monocytes were exposed to SAAP-148-PEG27 during monocyte-immature dendritic cell differentiation in comparison to SAAP-148. Parameters that influenced the immunomodulatory activities of the peptide-PEG conjugate include i) the length of the PEG-group, ii) the position of PEG conjugation, and iii) the peptide sequence. Together, these results indicate that SAAP-148-PEG27 is highly effective in redirecting monocyte-macrophage differentiation towards a proinflammatory phenotype and promoting monocyte-mature dendritic cells development. Therefore, SAAP-148-PEG27 may be a promising agent to modulate inadequate immune responses in case of tumors and chronically infected wounds

Encapsulation of SAAP-148 in Octenyl Succinic Anhydride-Modified Hyaluronic Acid Nanogels for Treatment of Skin Wound Infections

Chronic wound infections colonized by bacteria are becoming more difficult to treat with current antibiotics due to the development of antimicrobial resistance (AMR) as well as biofilm and persister cell formation. Synthetic antibacterial and antibiofilm peptide (SAAP)-148 is an excellent alternative for treatment of such infections but suffers from limitations related to its cationic peptidic nature and thus instability and possible cytotoxicity, resulting in a narrow therapeutic window. Here, we evaluated SAAP-148 encapsulation in nanogels composed of octenyl succinic anhydride (OSA)-modified hyaluronic acid (HA) to circumvent these limitations. SAAP-148 was efficiently (>98%) encapsulated with high drug loading (23%), resulting in monodispersed anionic OSA-HA nanogels with sizes ranging 204–253 nm. Nanogel lyophilization in presence of polyvinyl alcohol maintained their sizes and morphology. SAAP-148 was sustainedly released from lyophilized nanogels (37–41% in 72 h) upon reconstitution. Lyophilized SAAP-148-loaded nanogels showed similar antimicrobial activity as SAAP-148 against planktonic and biofilm-residing AMR Staphylococcus aureus and Acinetobacter baumannii. Importantly, formulated SAAP-148 showed reduced cytotoxicity against human erythrocytes, primary human skin fibroblasts and human keratinocytes. Additionally, lyophilized SAAP-148-loaded nanogels eradicated AMR S. aureus and A. baumannii colonizing a 3D human epidermal model, without inducing any cytotoxicity in contrast to SAAP-148. These findings indicate that OSA-HA nanogels increase SAAP-148′s therapeutic potential for treatment of skin wound infections