By combining two engineering strategies — backbone modification and stapling — researchers created peptide foldamers that penetrate cells, block disease-relevant protein interactions, and resist enzymatic breakdown nearly 100-fold better than standard stapled peptides.
~100x more resistant to breakdownThe stapled α/β-peptide foldamers resisted proteolytic degradation nearly 100-fold better than the parent stapled α-peptide, while maintaining the ability to enter cells and block target protein interactions.
What the researchers found
Researchers created α/β-peptide foldamers based on a stapled Bim BH3 peptide that could enter cells and block intracellular protein-protein interactions involved in apoptotic signaling — matching the function of the parent stapled α-peptide. Crucially, the α/β-peptide was nearly 100-fold more resistant to proteolytic degradation than the parent stapled α-peptide. This demonstrates that combining backbone modification (α/β substitution) with side chain cross-linking (stapling) produces synergistic benefits for peptide drug design.
Why it matters
One of the biggest barriers to using peptides as drugs is that the body breaks them down quickly and they can't get inside cells where many disease-relevant targets exist. This study shows that modifying the peptide backbone with β-amino acids while also using stapling technology solves both problems simultaneously — creating molecules that are dramatically more stable while still functioning inside living cells.
How the study worked
The researchers designed α/β-peptide variants of a stapled Bim BH3 α-peptide, incorporating β-amino acid residues into the backbone while maintaining the hydrocarbon cross-link (staple). They tested whether these foldamers could mimic the parent peptide's protein recognition, cell penetration, and ability to block apoptosis-related protein-protein interactions. Proteolytic stability was quantified by comparing degradation rates. Experiments included structural characterization, cell penetration assays, and functional tests in living cells including HCT116 human cancer cells.
Who was studied
In vitro and cell-based experiments using HCT116 human cancer cells and mouse-derived systems
What this study cannot tell us
This is a proof-of-concept study focused on a single protein-protein interaction target (Bim BH3/Bcl-2 family). Cell penetration was shown in certain cell types but may not generalize to all tissues. The study demonstrates the approach in cell-based assays but does not include in vivo animal efficacy data. The 100-fold proteolysis resistance was measured in vitro and may differ in whole-organism pharmacokinetics.
How to read the evidence
This is a preclinical proof-of-concept study published in the Journal of the American Chemical Society, demonstrating a new peptide engineering approach in cell-based assays. While the results are compelling for the field of peptide chemistry, this is early-stage research without in vivo animal data or clinical translation.
When this study was published
Published in 2015, this study established an important proof of concept for combining backbone modification with stapling. The α/β-foldamer approach has since been further developed by multiple research groups, making this a foundational paper in the field.
The bigger picture
Many high-value drug targets are protein-protein interactions inside cells — a class that traditional small-molecule drugs struggle to disrupt. This work represents a significant advance in peptide drug engineering by showing that backbone and side chain modifications work synergistically. The approach could enable an entirely new class of cell-penetrant, protease-resistant peptide therapeutics targeting previously "undruggable" intracellular interactions in cancer, autoimmune disease, and beyond.
Questions still open
- Can the α/β-peptide foldamer approach be generalized to target other intracellular protein-protein interactions beyond the Bcl-2 family?
- How do these foldamers perform in vivo — do they maintain their stability and cell penetration in animal models?
- What is the therapeutic window for these molecules, and could their increased stability lead to accumulation or off-target effects?
Common questions
What is a peptide foldamer and why does it matter for drug development?
What does 'stapling' a peptide mean?
Read the original research
α/β-Peptide Foldamers Targeting Intracellular Protein-Protein Interactions with Activity in Living Cells.
Journal of the American Chemical Society, 137(35), 11365-75
Citation
Checco, James W; Lee, Erinna F; Evangelista, Marco; Sleebs, Nerida J; Rogers, Kelly; Pettikiriarachchi, Anne; Kershaw, Nadia J; Eddinger, Geoffrey A; Belair, David G; Wilson, Julia L; Eller, Chelcie H; Raines, Ronald T; Murphy, William L; Smith, Brian J; Gellman, Samuel H; Fairlie, W Douglas. (2015). α/β-Peptide Foldamers Targeting Intracellular Protein-Protein Interactions with Activity in Living Cells.. Journal of the American Chemical Society, 137(35), 11365-75. https://doi.org/10.1021/jacs.5b05896