Replacing standard cysteine residues with stereochemical and structural variants in stapled peptides targeting the p53-MDM2 cancer pathway significantly altered binding affinity and target selectivity.
Significant affinity changes from cysteine editsReplacing standard L-cysteine with stereochemical variants (like D-cysteine) in the staple attachment points of cancer-targeting peptides produced measurable changes in target binding, revealing an overlooked optimization dimension.
What the researchers found
In stapled peptides targeting the p53-MDM2/MDMX interaction:
- Replacing L-cysteine residues with 'cysteine analogues' of different stereochemistry (D vs. L), side chain length, and beta-carbon substitution produced significant changes in binding affinity and target selectivity
- Some modifications, particularly incorporating two D-cysteine residues, favorably altered the positions of key functional amino acid side chains
- Computationally constructed homology models correlated with experimental surface plasmon resonance (SPR) binding data
- The approach demonstrates that the thiol-containing residue in cysteine-stapled peptides is not just a structural linker but actively influences target binding
This provides a new dimension for optimizing stapled peptide drug candidates beyond the staple chemistry itself.
Why it matters
The p53-MDM2 interaction is one of the most intensely pursued cancer drug targets — reactivating p53 could help treat over 50% of human cancers. Stapled peptides are among the most promising approaches, but optimizing their potency and selectivity has been challenging. This study reveals that a previously overlooked feature — the exact nature of the cysteine used for stapling — can dramatically tune drug properties. This gives medicinal chemists a new optimization tool that could accelerate the development of stapled peptide cancer therapeutics.
How the study worked
Researchers synthesized a series of perfluoroaryl-stapled peptides based on a p53-derived sequence with systematic variations in the cysteine residues used for cross-linking. Binding affinity to MDM2 and MDMX was measured by surface plasmon resonance (SPR). Target selectivity was assessed by comparing MDM2 vs. MDMX binding ratios. Computational homology modeling was used to rationalize the observed structure-activity relationships by predicting how cysteine modifications affected the positioning of functional amino acid side chains.
What this study cannot tell us
The study focused on a single target system (p53-MDM2/MDMX), and the generalizability of cysteine-editing effects to other stapled peptide targets is unknown. Only in vitro binding data were generated — no cellular activity, permeability, or in vivo efficacy was assessed. The number of cysteine variants tested was limited; more extensive exploration could reveal additional useful modifications. The computational models provide rationalization but may not fully capture the dynamic behavior of these peptides in solution. Manufacturing feasibility of non-standard cysteine analogs at scale was not addressed.
How to read the evidence
This is a medicinal chemistry study combining synthetic peptide design, biophysical measurement (SPR), and computational modeling. The approach is systematic and well-controlled, but limited to in vitro binding data without cellular or in vivo validation. It represents early-stage drug design research.
When this study was published
Published in 2019, this study is about 7 years old. The stapled peptide field has continued to advance, with several candidates progressing in clinical trials. The cysteine-editing concept has been incorporated into broader peptide design strategies.
The bigger picture
Stapled peptides represent a growing class of 'peptide drugs 2.0' — addressing the traditional limitations of peptide therapeutics (poor stability, membrane impermeability) by locking them into rigid, drug-like conformations. Several stapled peptides are in clinical trials for cancer. This study contributes to the fundamental design principles for this drug class, showing that every component of the staple — not just the linker chemistry but the individual amino acid residues forming the attachment points — influences therapeutic properties. The cysteine-editing approach could be broadly applicable to any cysteine-stapled peptide system.
Questions still open
- Can cysteine-editing be combined with other stapled peptide optimization strategies (e.g., N-methylation, backbone modifications) for additive improvements?
- Do the binding affinity changes translate to improved cellular activity and tumor growth inhibition?
- Could this approach be applied to stapled peptides targeting other cancer-relevant protein-protein interactions beyond p53-MDM2?
Common questions
What are stapled peptides and why are they important for cancer treatment?
How does changing the cysteine affect the drug?
Read the original research
Tuning the Binding Affinity and Selectivity of Perfluoroaryl-Stapled Peptides by Cysteine-Editing.
Chemistry (Weinheim an der Bergstrasse, Germany), 25(1), 177-182
Citation
Verhoork, Sanne J M; Jennings, Claire E; Rozatian, Neshat; Reeks, Judith; Meng, Jieman; Corlett, Emily K; Bunglawala, Fazila; Noble, Martin E M; Leach, Andrew G; Coxon, Christopher R. (2019). Tuning the Binding Affinity and Selectivity of Perfluoroaryl-Stapled Peptides by Cysteine-Editing.. Chemistry (Weinheim an der Bergstrasse, Germany), 25(1), 177-182. https://doi.org/10.1002/chem.201804163