Locking Peptides Into Shape: When Stapling Helps Cell-Penetrating Peptides Enter Cells Without Causing Damage | Research

The takeaway

Lactam stapling reduced membrane damage for most cell-penetrating peptides, but only improved cell entry for one of four tested, revealing that membrane-bound helical structure — not solution structure — predicts uptake.

1 of 4 improved
Only one of four cell-penetrating peptides (MAP-1) showed improved cell uptake after lactam stapling, though most showed reduced membrane toxicity

What the researchers found

Researchers tested whether lactam stapling — a chemical modification that locks peptides into a helical shape — improves cell-penetrating peptide (CPP) performance. The results were mixed: of four stapled peptides tested, only one (MAP-1) showed clear improvement. Stapling MAP-1 enhanced its helical structure in both water and lipid environments, eliminated membrane leakage (a proxy for toxicity), and maintained high cellular uptake in HEK293 and HeLa cells.

The other three peptides (DRIM, WWSP, KFGF) didn't improve with stapling. Critically, the study found that a CPP's ability to enter cells correlates with how helical it becomes when interacting with membranes — not how helical it is free in solution. Nearly all stapled peptides caused less membrane damage (less vesicle leakage, hemolysis, and bacterial lysis) than their linear versions.

Why it matters

Cell-penetrating peptides are key tools for delivering drugs into cells, but they often damage cell membranes in the process. This study shows that stapling can reduce toxicity, but its effect on cell entry depends heavily on the specific peptide. The finding that membrane-bound helicity (not solution helicity) predicts uptake efficiency is an important design principle for engineering better drug delivery peptides.

The numbers in context

4 stapled peptides vs 4 linear counterparts · MAP-1: eliminated leakage + maintained uptake · 3 other peptides: no improvement · Tested in HEK293 + HeLa cells · Reduced hemolysis across most stapled variants

How the study worked

In vitro comparison of four lactam-stapled cell-penetrating peptides against their linear (unstapled) counterparts. Measured membrane binding, conformational behavior (circular dichroism), vesicle leakage, hemolysis, bacterial lysis, and cellular uptake in HEK293 and HeLa cells. Correlated structural features with functional outcomes.

Who was studied

In vitro study using HEK293 cells, HeLa cells, artificial vesicles, red blood cells, and bacteria

What this study cannot tell us

In vitro study only — cell uptake in culture dishes may not predict in vivo drug delivery performance. Only four peptide systems tested, limiting generalizability. The success of stapling was peptide-dependent, making it hard to predict which CPPs will benefit from this modification without testing each one individually.

How to read the evidence

This is a preliminary-grade in vitro structure-activity study. While the experimental design is rigorous with multiple peptide systems and multiple readouts, the findings are limited to cell culture and artificial membrane systems without in vivo validation.

When this study was published

Published in 2017 in the Journal of Medicinal Chemistry, this study contributed to the growing understanding of when and how peptide stapling improves drug delivery, an area that has continued to evolve.

The bigger picture

Peptide stapling has been a hot topic in drug design because it can make peptides more stable and cell-permeable. This study adds important nuance — stapling doesn't universally improve CPPs. The finding that membrane-bound conformation matters more than solution conformation helps explain why some stapled peptides succeed in drug delivery applications while others don't, providing a more rational framework for future CPP design.

Questions still open

Can computational modeling predict which cell-penetrating peptides will benefit from stapling before synthesis?
Does the improved safety profile of stapled MAP-1 translate to better therapeutic index when delivering actual drug cargoes?
Would alternative stapling chemistries (hydrocarbon vs. lactam) produce different outcomes for the three peptides that didn't improve?

Common questions

What is peptide stapling and why is it used?

Peptide stapling is a chemical technique that creates a bridge (or 'staple') between two points on a peptide chain, locking it into a helical spiral shape. This can make peptides more stable, resistant to degradation, and better at entering cells. It's widely used in drug development to improve peptides that would otherwise be too floppy or fragile to work as medications.

What are cell-penetrating peptides used for?

Cell-penetrating peptides (CPPs) are short peptides that can cross cell membranes and carry cargo — like drugs, genes, or imaging agents — inside cells. They're important tools for drug delivery because many therapeutic molecules can't get into cells on their own. The challenge is making CPPs that enter cells efficiently without damaging the membranes they cross.

Read the original research

Lactam-Stapled Cell-Penetrating Peptides: Cell Uptake and Membrane Binding Properties.

Journal of medicinal chemistry, 60(19), 8071-8082

View on PubMed ↗Publisher’s paper ↗

Citation

Klein, Marco J; Schmidt, Samuel; Wadhwani, Parvesh; Bürck, Jochen; Reichert, Johannes; Afonin, Sergii; Berditsch, Marina; Schober, Tim; Brock, Roland; Kansy, Manfred; Ulrich, Anne S. (2017). Lactam-Stapled Cell-Penetrating Peptides: Cell Uptake and Membrane Binding Properties.. Journal of medicinal chemistry, 60(19), 8071-8082. https://doi.org/10.1021/acs.jmedchem.7b00813