SP9 — Preclinical research guide.
SP9 is an engineered stapled peptide that blocks the rapid, calcium-triggered release of mucin from airway cells. Developed at Stanford Medicine to address the mucus plugs seen in asthma, COPD and cystic fibrosis, without disrupting the lung's normal baseline mucus production.
- Stapled peptide that blocks the interaction between synaptotagmin-2 (Syt2) and the SNARE complex, the molecular machinery airway cells use for rapid mucin release.
- Conjugated to a cell-penetrating carrier peptide (PEN-SP9) to reach airway epithelial cells.
- Selectively blocks the fast, stimulus-triggered mucin secretion pathway while leaving the slow, baseline secretion pathway intact.
- In an aerosolised mouse model, PEN-SP9 reduced mucin secretion and airway blockage without impairing normal lung function.
- Developed at Stanford Medicine (published in Nature, 2022); preclinical stage — not manufactured or sold commercially.
What is SP9?
SP9 is a short, chemically “stapled” peptide engineered to disrupt a specific protein-protein interaction inside airway goblet and secretory cells: the binding of synaptotagmin-2 (Syt2) to the SNARE protein complex. That interaction is the calcium-sensing trigger cells use to rapidly dump large amounts of mucin — the gel-forming glycoprotein that makes mucus thick and sticky — into the airway in response to an irritant or inflammatory signal. To reach cells inside the lung, SP9 is conjugated to a cell-penetrating carrier peptide, producing the combined molecule PEN-SP9.
How does it work?
Airway cells secrete mucin through two distinct pathways: a slow, continuous baseline release that keeps the airway surface properly lubricated, and a fast, calcium-triggered burst release that floods the airway with mucin during an asthma attack, infection or COPD flare. SP9 was designed to interrupt only the fast pathway by blocking the Syt2–SNARE interaction that senses the calcium signal, while leaving the SNARE machinery available for the slow, baseline pathway. In laboratory models this selectivity meant the treated airway kept its normal mucus lubrication while the excessive, plug-forming burst was suppressed.
What does the research show?
The mechanism was first confirmed in a reconstituted lab system showing SP9 disrupts calcium-triggered membrane fusion, then validated in cultured human airway epithelial cells using the cell-penetrating PEN-SP9 conjugate, where it inhibited rapid mucin secretion. A further study aerosolised PEN-SP9 and delivered it to a mouse model, confirming reduced mucin secretion and less airway blockage compared with untreated controls, while normal baseline secretion continued. The work, led by Stanford Medicine researchers together with collaborators at the University of Ulm and University of Alabama at Birmingham, was published in Nature in 2022. All results to date are from cell and animal models; no human trials have been reported.
Is SP9 available for research or purchase?
No. PEN-SP9 is an academic proof-of-concept compound rather than a manufactured or commercially available peptide. It has no assigned CAS number and is not offered by any peptide vendor. PeptideCompare covers it as an example of where mucus-targeted lung research is heading, not as something researchers can currently purchase.