Title : From bench to preclinical evaluation: LL-37-derived peptides for combating orthopedic infections
Abstract:
Orthopedic implant-associated infections, frequently caused by Staphylococcus species, remain a major clinical concern due to biofilm formation and the growing threat of antimicrobial resistance. Antimicrobial peptides (AMPs), derived from the human cathelicidin LL-37, represent a promising alternative approach, offering potent antimicrobial activity and low susceptibility to resistance. This study aimed to design, characterize, and validate LL-37-derived synthetic peptides and their integration into silk fibroin–based biomaterials as delivery compounds to locally treat orthopedic infections.
Truncated analogues of LL-37 were synthesized and evaluated for antimicrobial activity against multi-drug resistant Staphylococcus aureus and Staphylococcus epidermidis reference and clinical strains. MIC, MBC, and biofilm eradication assays were conducted alongside cytotoxicity and hemolytic tests to determine efficacy and safety. The two most effective peptides, FK-16 and GF-17, were incorporated into silk fibroin (SF) and osteoinductive peptide–enriched silk fibroin (PSF) scaffolds. Structural and release characterizations, swelling behaviour, and time-kill assays were performed to analyse their delivery performance against methicillin-resistant Staphylococcus strains. Systemic in vivo toxicity studies were conducted in mice by intravenous injection of FK-16 and GF-17.
FK-16 and GF-17 exhibited potent antimicrobial and antibiofilm activities, with MIC values ranging from 2.34–18.75 μg/mL and a minimal cytotoxicity at concentrations below 75 μg/mL for GF-17 and 150 μg/mL for FK-16. Hemolytic activity was negligible (<1%) at antimicrobial doses. FK-16 showed superior release and bactericidal performance when incorporated into SF and PSF scaffolds, particularly against methicillin-resistant S. epidermidis. PSF matrices improved peptide retention and antibacterial efficacy relative to unmodified SF. In vivo systemic administration in mice revealed no signs of toxicity, confirming the safety of both peptides for further translational research. Importantly, a preclinical trial is currently underway in a rat model of septic nonunion infected with a clinical isolate of methicillin-resistant S. epidermidis to evaluate the therapeutic potential of FK-16–based local treatments.
LL-37-derived peptides, especially FK-16, display strong antimicrobial efficacy, low cytotoxicity, and successful integration into silk fibroin–based delivery systems. The combination of FK-16-loaded PSF scaffolds represents a promising strategy for localized prevention and treatment of multi-drug resistant orthopedic infections. The absence of systemic toxicity and ongoing preclinical evaluations in an infected nonunion model underscore the translational potential of this AMP-based therapeutic approach for the management of orthopedic infections.
