Red-light modulated <i>ortho</i> -chloro azobenzene photoswitch for peptide stapling <i>via</i> aromatic substitution

Abstract

The application of peptide stapling using photoswitchable linkers has gained notable interest for potential therapeutic applications. However, many existing methodologies of photoswitching still rely on the use of tissue-damaging and weakly skin-penetrating UV light. Herein, we describe the development of a tetra-<i>ortho</i>-chloro azobenzene linker that was successfully used for cysteine-selective peptide stapling <i>via</i> S_NAr. This linker facilitates precise photocontrol of peptide structure <i>via trans</i> to <i>cis</i> isomerisation under red light irradiation. As a proof-of-concept, we applied the developed peptide stapling platform to a modified PMI peptide, targeting the inhibition of MDM2/p53 protein-protein interaction (PPI). Biophysical characterisation of the photoswitchable peptide by competitive fluorescence polarisation showed a significant difference in affinity between the <i>trans</i> and <i>cis</i> isomer for the p53-interacting domain of the human MDM2. Remarkably, the <i>cis</i> isomer displayed a >240-fold higher potency. To the best of our knowledge, this is the highest reported difference in binding affinity between isoforms of a photoswitchable therapeutic peptide. Overall, our findings demonstrate the potential of this novel photoswitchable peptide stapling system for tuneable, selective modulation of PPIs <i>via</i> visible-light isomerisation with deeply-tissue penetrating red light.