Iterative optimization yields Mcl-1-targeting stapled peptides with selective cytotoxicity to Mcl-1-dependent cancer cells

Proc Natl Acad Sci U S A. 2018 Jan 30;115(5):E886-E895. doi: 10.1073/pnas.1712952115. Epub 2018 Jan 16.


Bcl-2 family proteins regulate apoptosis, and aberrant interactions of overexpressed antiapoptotic family members such as Mcl-1 promote cell transformation, cancer survival, and resistance to chemotherapy. Discovering potent and selective Mcl-1 inhibitors that can relieve apoptotic blockades is thus a high priority for cancer research. An attractive strategy for disabling Mcl-1 involves using designer peptides to competitively engage its binding groove, mimicking the structural mechanism of action of native sensitizer BH3-only proteins. We transformed Mcl-1-binding peptides into α-helical, cell-penetrating constructs that are selectively cytotoxic to Mcl-1-dependent cancer cells. Critical to the design of effective inhibitors was our introduction of an all-hydrocarbon cross-link or "staple" that stabilizes α-helical structure, increases target binding affinity, and independently confers binding specificity for Mcl-1 over related Bcl-2 family paralogs. Two crystal structures of complexes at 1.4 Å and 1.9 Å resolution demonstrate how the hydrophobic staple induces an unanticipated structural rearrangement in Mcl-1 upon binding. Systematic sampling of staple location and iterative optimization of peptide sequence in accordance with established design principles provided peptides that target intracellular Mcl-1. This work provides proof of concept for the development of potent, selective, and cell-permeable stapled peptides for therapeutic targeting of Mcl-1 in cancer, applying a design and validation workflow applicable to a host of challenging biomedical targets.

Keywords: BH3 mimetic; Mcl-1; apoptosis; inhibitor; stapled peptide.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Binding Sites
  • Cell Line
  • Cell Survival
  • Circular Dichroism
  • Crystallography, X-Ray
  • Cytoplasm / metabolism
  • Drug Design
  • Humans
  • Hydrophobic and Hydrophilic Interactions
  • Inhibitory Concentration 50
  • Mice
  • Mutation
  • Myeloid Cell Leukemia Sequence 1 Protein / metabolism*
  • Neoplasms / metabolism*
  • Peptides / chemistry*
  • Protein Binding
  • Protein Interaction Mapping
  • Spectrometry, Fluorescence


  • MCL1 protein, human
  • Mcl1 protein, mouse
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Peptides

Associated data

  • PDB/5W89
  • PDB/5W8F