Backbone Alterations in Cyclic Peptides Influence Both Membrane Permeability and Biological Activity

Cyclic peptides hold significant potential as disruptors of challenging targets such as protein–protein interactions, but their poor passive membrane permeability limits their use. In this study, we used a combination of cell-permeability assays and a target-agnostic cell-painting assay to observe how minimal structural changes affect membrane permeability and the biological activity of Sanguinamide A analogues. Significant differences in permeability were observed among the analogues, and for those that were permeable, NMR spectroscopy revealed conformational changes in response to environmental polarity. In the cell-painting assay, we observed that even though permeability generally correlated with overall morphological changes, distinct differences in specific activities were observed depending on the nature of the backbone modification. These findings highlight the importance of selecting the correct backbone modification when trying to balance both membrane permeability and biological activity, offering valuable insights for the development of cyclic peptides as therapeutic agents.