Cyclic gomesin as a scaffold for stabilising anticancer peptides and targeting melanoma cells

Cyclic peptides are increasingly recognised as a therapeutic modality for modulating intracellular protein–protein interactions (PPIs), including those considered ‘undruggable’ by small molecules or biologics. Cyclic gomesin (cGm), an 18-residue β-hairpin peptide containing two disulfide bonds and a cyclised backbone, combines high chemical stability with amphipathic character that promotes selective interaction with negatively charged cancer cell membranes. We previously showed that cGm enters cancer cells at non-toxic concentrations by endocytosis and direct membrane partitioning, outperforming established cell-penetrating peptides, and that it can be engineered to incorporate a sequence that inhibits PPIs involved in lactate dehydrogenase-5 tetramerisation. Here, we further assess its grafting capacity by incorporating bioactive loop sequences of varying size, charge and hydrophobicity into the cGm framework. Structural and biophysical analyses confirmed that grafted analogues retained the three-dimensional fold and had membrane-binding features, anticancer activity, melanoma selectivity and low toxicity toward non-cancerous cells. These findings demonstrate the tolerance of cGm to sequence variation and support its development as a modular scaffold for designing intracellularly active cyclic peptide therapeutics.