Structure‐Enabled Discovery of a Stapled Peptide Inhibitor to Target the Oncogenic Transcriptional Repressor TLE1

TLE1 is an oncogenic transcriptional co‐repressor that exerts its repressive effects through binding of transcription factors. Inhibition of this protein–protein interaction represents a putative cancer target, but no small‐molecule inhibitors have been published for this challenging interface. Herein, the structure‐enabled design and synthesis of a constrained peptide inhibitor of TLE1 is reported. The design features the introduction of a four‐carbon‐atom linker into the peptide epitope found in many TLE1 binding partners. A concise synthetic route to a proof‐of‐concept peptide, cycFWRPW, has been developed. Biophysical testing by isothermal titration calorimetry and thermal shift assays showed that, although the constrained peptide bound potently, it had an approximately five‐fold higher K d than that of the unconstrained peptide. The co‐crystal structure suggested that the reduced affinity was likely to be due to a small shift of one side chain, relative to the otherwise well‐conserved conformation of the acyclic peptide. This work describes a constrained peptide inhibitor that may serve as the basis for improved inhibitors.