D-K6L9 is a host defense-like peptide composed of six lysines and nine leucines, modified by the inclusion of D-amino acids to improve antimicrobial activity and resistance to degradation by proteases. D-K6L9 shows antimicrobial and antibiofilm activities against Pseudomonas aeruginosa from cystic fibrosis patients without inducing bacterial resistance. In addition to its antimicrobial properties, in animal models D-K6L9 is able to target and arrest the growth of aggressive and hormone-resistant primary human prostate and breast tumours and prevent metastasis, effects which are correlated with increased necrosis of the tumour cells and a decrease in the tumour microvessel density. The selectivity of D-K6L9 derives from specific binding to surface phosphatidylserine and the killing of the cancer cells via cytoplasmic membrane depolarization.
