Identification and functional study of peptides from the skin secretion of Phyllomedusa azurea

Analogues with enhanced cationicity apparently improved potency and therapeutic indices, whereas reduced hydrophobicity or loss of C-terminal amidation attenuated activity. PS-12 displayed moderate antibacterial activity, with MIC values ranging from 2–64 µM across tested strains. Rational modification of cationicity and α-helical propensity generated more potent analogues, with PS-12-1 showing improved activity (MIC = 1–4 µM against S. aureus and E. coli).

However, excessive hydrophobicity or structural disruption reduced selectivity. Hydrocarbon stapling (PS-12-5) enhanced resistance to proteolytic degradation but resulted in reduced antimicrobial potency (MIC ≥64 µM), highlighting a trade-off between stability and activity. For the dermaseptin DRS-01, activity was robust across bacterial species but markedly-compromised by trypsin digestion, whereas the N-terminal Nal-modified analogue DRS-N preserved both potency and partial protease resistance.

Modifications aimed at sequence shortening or charge redistribution generated apparent loss of activity.<br><br>Across all peptide families, mechanistic assays demonstrated rapid bactericidal effects mediated by membrane perturbation, including outer- and inner-membrane permeabilisation, depolarisation, and time-dependent disruption consistent with a carpet-like mode of action. Several analogues exhibited reduced haemolytic activity and improved antiproliferative effects against cancer cell lines, underscoring the tunability of bioactivity profiles.

Resistance-development assays revealed minimal MIC shifts over serial passaging, indicating a low propensity for resistance induction.<br><br>Collectively, these studies have established QUB-2480, PS-12, DRS-01, and their optimised analogues, as promising membrane-active AMPs, and provide detailed structure–activity insights to guide the rational design of next-generation antimicrobial therapeutics with improved stability, potency, and safety.<br><br><i>Thesis is embaragoed until 31 July 2031.</i>