*Correspondence, Darren Shu Jeng Ting: ting.darren@gmail.com

Background/Aim Infectious keratitis (IK) is a major cause of corneal blindness worldwide. This study aimed to develop potent human-derived hybrid host defense peptides (HyHDPs) with broad-spectrum antimicrobial activities for IK.

Methods HyHDPs were rationally designed through combination of human cathelicidin (LL-37) and human-beta-defensins (HBDs), and with guidance from molecular dynamics (MD) simulations. Efficacy of HyHDPs was determined against a range of bacteria, fungi and Acanthamoeba. Risk of antimicrobial resistance (AMR) was evaluated using multipassage AMR assay. Pre-clinical murine studies were performed to examine the in vivo efficacy and safety of HyHDPs in methicillin-resistant S. aureus (MRSA)-related keratitis.

Results Hybridisation of LL-37 and HBD-2 led to the development of HDP23, which demonstrated good efficacy against S. aureus and MRSA [minimum inhibitory concentration (MIC)=12.5–25.0 µm/ml], but not against fungi or Acanthamoeba. MD simulations provided atomistic insights into the key membrane-active residues and accelerated the discovery of HDP56. Compared to HDP23, HDP56 exhibited 4–32 times improved efficacy against S. aureus, MRSA, Pseudomonas aeruginosa, and Fusarium solani (MIC=3.1–6.3 µm/ml). At 100 µm/ml, HDP56 exhibited good anti-Acanthamoeba trophozoites efficacy (99.8%) and anti-encystation efficacy (80.9%). S. aureus did not develop any AMR against HDP56 after 15 treatment passages/days but developed significant AMR (32 times increase in MIC) against levofloxacin after 13 passages/days. Pre-clinical murine studies demonstrated strong efficacy and safety of HDP56 (0.5 mg/ml) in treating MRSA-related keratitis (93% reduction in bacteria, which was equally effective to levofloxacin (5 mg/ml).

Conclusion Rational hybridisation of HDPs, with guidance from MD simulations, has enabled the development of a novel HDP-based therapy for IK.