New Enzyme-Free Method Could Make Cyclic Peptide Drugs Much Cheaper to Produce | Research

The takeaway

Researchers developed a simple, enzyme-free chemical method to produce cyclic peptides from natural or engineered proteins under mild conditions, potentially slashing production costs for this important class of drug molecules.

1 reagent, no enzymes
New method cyclizes peptides under mild aqueous conditions using a single readily available chemical, eliminating the need for expensive enzymes or solid-phase synthesis

What the researchers found

The researchers demonstrated enzyme-free biochemical cyclization of peptides under mild aqueous conditions using a single, readily available chemical reagent:

- Successfully produced a 17-mer cyclic peptide from wild-type human eye lens γ-crystallin protein

- Produced a set of 10-residue cyclic peptides from recombinantly expressed polypeptide precursors

- The method works without disulfides, using only canonical amino acids

- Products were identified via complex mass spectrometry fragmentation patterns

- Linear and cyclic peptide forms were chromatographically separated

- The approach works with both natural protein sources and recombinantly expressed precursors

Why it matters

Cyclic peptides are among the most promising classes of peptide drugs because their ring structure makes them more stable and resistant to degradation than linear peptides. However, the gold standard production method (solid-phase synthesis) is expensive, limiting their use to high-value pharmaceutical applications. This enzyme-free method could make cyclic peptides accessible for a much wider range of uses, potentially reducing drug costs and enabling new applications.

How the study worked

The researchers developed a chemical cyclization protocol using mild aqueous conditions and a single reagent. They tested the method on natural protein (human γ-crystallin) and recombinant polypeptide precursors. They systematically investigated how reaction conditions and amino acid sequence changes affect cyclization efficiency. Products were verified using mass spectrometry fragmentation analysis and chromatographic separation of linear from cyclic forms.

What this study cannot tell us

This is a preprint (bioRxiv), meaning it has not yet undergone peer review. The method has been demonstrated at laboratory scale but scalability to industrial production is unproven. The efficiency and yield of the cyclization reaction across diverse peptide sequences needs broader characterization. The study does not assess whether the cyclic peptides produced retain the biological activity needed for specific therapeutic applications.

How to read the evidence

This is a preprint (not peer-reviewed) demonstrating proof-of-concept for a new peptide production method. The chemistry is well-characterized with mass spectrometry verification, but scalability, reproducibility across diverse sequences, and practical application have not been fully validated.

When this study was published

Published as a 2025 preprint on bioRxiv, this represents cutting-edge research in peptide chemistry. As a preprint, it has not yet undergone peer review, and findings should be considered preliminary until published in a peer-reviewed journal.

The bigger picture

Cyclic peptides represent a frontier in drug development — they combine the specificity of biological molecules with the stability approaching small-molecule drugs. Companies like Bicycle Therapeutics are building entire drug platforms around cyclic peptides. This production breakthrough could accelerate the field by removing a major bottleneck: manufacturing cost. If scaled, it could enable mass production of cyclic peptide drugs and even make diverse cyclic peptide libraries feasible for drug screening.

Questions still open

Can this enzyme-free cyclization method be scaled to industrial production volumes while maintaining efficiency?
How does the bioactivity of peptides produced by this method compare to those made by traditional solid-phase synthesis?
Could this approach enable rapid, low-cost screening of large cyclic peptide libraries for drug discovery?

Common questions

What are cyclic peptides and why are they important as drugs?

Cyclic peptides are peptide molecules whose ends are joined to form a ring. This ring structure makes them much more stable than regular (linear) peptides — they resist degradation by digestive enzymes, can penetrate cell membranes better, and often bind their targets more tightly. Many naturally occurring antibiotics and immunosuppressants (like cyclosporine) are cyclic peptides, and the pharmaceutical industry is actively developing new ones.

Why are cyclic peptides currently expensive to produce?

The standard method (solid-phase peptide synthesis) builds peptides one amino acid at a time on a solid support, then cyclizes them through additional chemical steps. Each step requires expensive reagents and careful quality control. For cyclic peptides specifically, the cyclization step can be particularly challenging and low-yielding. This new enzyme-free approach could bypass much of this complexity by cyclizing peptides in solution using a single reagent.

Read the original research

Enzyme-free biochemical production of seamlessly N-to-C cyclized peptides from natural or recombinant proteins.

bioRxiv : the preprint server for biology

View on PubMed ↗Publisher’s paper ↗

Citation

Behboodian, Ali; Serebryany, Eugene. (2025). Enzyme-free biochemical production of seamlessly N-to-C cyclized peptides from natural or recombinant proteins.. bioRxiv : the preprint server for biology. https://doi.org/10.1101/2025.07.31.667801