Discovery, bioactivity assessment, mechanisms study and rational design of naturally-occurring peptides from frog skin secretion with dual antimicrobial and anticancer potential

Guided by helix–hinge–helix optimisation and C-terminal truncation, several analogues were generated, among which P19 retained the antimicrobial potency of the parent peptide while displaying notably-reduced cytotoxicity and haemolysis. Mechanistic studies confirmed rapid membrane permeabilisation and depolarisation, alongside low resistance induction.<br><br>Chapter 4 reports the identification of QUB-2522, another dermaseptin peptide, from the skin secretion of Phyllomedusa tarsius.

While the native peptide exhibited only moderate antimicrobial activity, rational design yielded two distinct analogues. Charge-enhanced derivative, 17K, showed dramatically-improved antimicrobial, antifungal, and anticancer activities, rapid killing kinetics, low haemolysis, and minimal resistance development. In contrast, LS, with adjusted hydrophobic amino acids, lost its biological activity.

Mechanistic assays confirmed that 17K exerts its effects through membrane disruption coupled with DNA-binding capability, indicating a dual mechanism of action.<br><br>In Chapter 5, a phylloseptin peptide annotated in UniProt and designated, PT-1, was selected through database mining and evaluated alongside six designed analogues. PT-1 displayed broad antibacterial activity and moderate tumour-cell inhibition. Structure–activity analysis revealed that the conserved N-terminal motif and intact hydrophobic face are the primary determinants of biological function.

PT-H and PT-HH showed enhanced anticancer potency but increased haemolysis, whereas PT-HA successfully reduced toxicity while retaining partial bioactivity. Excessive histidine or arginine incorporation (PT-3H, PT-RHH) compromised the therapeutic window. All active peptides retained the canonical membrane-permeabilising mechanism of phylloseptins.<br><br>In summary, this work has successfully-identified two previously-unreported functional peptides derived from frogs.

A third peptide was subsequently screened from databases, and comprehensive bioactivity assessments alongside investigations into their antimicrobial mechanisms, were conducted for all three peptides and their analogues. The findings demonstrate that preservation of key structural elements—particularly hydrophobic-face continuity and conserved N-terminal motifs—is essential for maintaining antimicrobial and anticancer efficacy.

The optimised analogues P19, 17K, and PT-HA represent promising lead molecules with enhanced selectivity and therapeutic potential. Overall, this work highlights the value of amphibian skin secretions as a natural reservoir of drug-like peptides and provides a foundation for the rational development of next-generation antimicrobial and anticancer peptide therapeutics.<br><br><i>Thesis is embargoed until 31 July 2031.</i>