Rational Design of Thrombin-Derived VFR12 Analogs with Enhanced Antimicrobial, Antibiofilm, and Anti-inflammatory Properties

The worsening crisis of antibiotic resistance demands innovative therapies to combat multidrug-resistant pathogens. In this study, we report the rational design and optimization of VFR12 (VFRLKKWIQKVI), a thrombin C-terminus-derived 12-mer peptide, via systematic amino acid substitutions and stereochemical modifications. A series of 12-mer analogs were synthesized and assessed for antimicrobial activity, cell selectivity, biofilm disruption, and immunomodulatory effects. Six lead candidates (VFR12-a7, VFR12-a8, VFR12-a7(L), VFR12-a8(L), VFR12-a7(L)-d, VFR12-a8(L)-d) demonstrated potent, broad-spectrum antimicrobial activity against both Gram-positive and Gram-negative bacteria, including multidrug-resistant Pseudomonas aeruginosa , while exhibiting minimal hemolytic activity. Notably, D-amino acid variants VFR12-a7(L)-d and VFR12-a8(L)-d showed significantly improved therapeutic indices, complete resistance to proteolysis, and enhanced serum stability compared to their L-isomers. These peptides effectively inhibited biofilm formation and disrupted preformed biofilms while maintaining excellent biocompatibility. Furthermore, anti-inflammatory assessments revealed a significant suppression of LPS-induced production of TNF-α, IL-6, and nitric oxide, along with strong endotoxin neutralization. Among the analogs, VFR12-a8(L)-d emerged as the most promising candidate, combining potent antimicrobial activity with excellent safety and multifaceted therapeutic properties. These findings provide a valuable framework for the development of next-generation host defense peptides with integrated antimicrobial, antibiofilm, and anti-inflammatory properties, offering a multifaceted approach to tackling antibiotic resistance and sepsis.