Every Peptide

Peptide field guide

CYP9

A cyclic peptide engineered from an antimicrobial peptide scaffold (YD) that showed preclinical anti-fibrotic activity by suppressing TGF-β/Smad and MAPK pathway signaling in experimental models.

Evidence: emerging Safety: unknown Status: research Updated: March 25, 2026 PulmonaryCyclic peptideAnti-fibroticResearch peptide

What it is

CYP9 is a cyclic peptide reported in the medicinal chemistry literature as an optimized analog derived from an antimicrobial peptide scaffold referred to as YD.

The design goal was to improve the starting peptide’s drug-like properties (stability and exposure) while preserving or improving biological activity relevant to fibrosis.

Why people care about it

Pulmonary fibrosis involves persistent activation of fibroblasts and excess deposition of extracellular matrix, with signaling hubs such as transforming growth factor beta (TGF-β) playing a central role.

CYP9 is of interest because it is presented as a peptide that can modulate fibrosis-associated cellular programs and pathways in preclinical models, and because it illustrates a broader theme: peptide engineering (including cyclization and unnatural amino acids) can materially change what a peptide can do in vivo.

What we know vs what we do not know

What we know:

  • CYP9 is a cyclic peptide reported in Journal of Medicinal Chemistry (2026).
  • The authors report inhibition of fibrosis-relevant programs (e.g., myofibroblast activation and extracellular matrix synthesis) at nanomolar concentrations in cell assays.
  • The paper reports pathway-level inhibition of TGF-β/Smad and MAPK signaling.

What we do not know:

  • Whether CYP9’s effects are reproducible across fibrosis models and independent labs.
  • The direct molecular target (if any) and how specific the mechanism is.
  • Safety, tolerability, immunogenicity risk, and chronic dosing effects.
  • Whether the peptide can be manufactured reproducibly at scale with consistent activity.

Latest updates

  • 2026-03-26 (J Med Chem): A medicinal chemistry paper reported that cyclization and other modifications of an antimicrobial peptide (YD) yielded CYP9, a cyclic peptide with reported anti-fibrotic activity in preclinical models, including inhibition of TGF-β/Smad and MAPK signaling pathways.

Safety reality

CYP9 is not an approved drug. Any non-regulated product claiming to be CYP9 would carry substantial risks around identity, purity, and contaminants.

References

Zhang J, et al. Cyclization-Based Optimization of the Antimicrobial Peptide YD Yields a Nanomolar Inhibitor of Pulmonary Fibrosis. J Med Chem. (2026). https://pubmed.ncbi.nlm.nih.gov/41821216/ doi:10.1021/acs.jmedchem.6c00277