Your white blood cells carry a tool for dissolving things. A single protein circulating in your blood is what stops it from dissolving you.

The tool is neutrophil elastase, an enzyme that neutrophils release to break down bacteria and cellular debris. The brake is alpha-1 antitrypsin, made in the liver and carried to the lungs. In alpha-1 antitrypsin deficiency, the brake is missing or misfolded, the elastase runs unchecked, and it goes to work on elastin, the protein that gives the air sacs their spring. The result is emphysema, often in people in their forties who have never smoked. Somewhere between 50,000 and 80,000 Americans are thought to be affected.

On August 11, Mereo BioPharma granted Sentynl Therapeutics, a Zydus subsidiary, US commercial and global manufacturing rights to alvelestat. Mereo takes a non-refundable option fee, then $40 million in upfront and research payments if Sentynl exercises the option, up to $435 million in milestones, and double-digit tiered royalties on US sales. Mereo will run the global Phase 3. It acquired alvelestat from AstraZeneca in 2017 for $5 million upfront.

The current treatment is augmentation therapy: weekly intravenous infusions of alpha-1 antitrypsin purified from donated human plasma. It replaces what is missing, which is the obvious approach, and it comes with the obvious costs. A lifetime of infusions, and a supply chain that depends on how many people show up to donate plasma.

Alvelestat comes at the problem from the other end. It is a neutrophil elastase inhibitor, so it leaves the brake alone and goes after the thing the brake was holding back. That has a consequence beyond convenience. A small molecule can be made by chemical synthesis in whatever quantity is needed and swallowed as a tablet. If approved, alvelestat would be the first oral treatment for the condition.

AstraZeneca developed alvelestat and then let it go for a sum that would not cover a mid-sized Phase 2 trial. The easy reading is that AstraZeneca misjudged the drug, but the real story is about what large pharmaceutical companies are built to do. A programme aimed at 50,000 to 80,000 patients cannot win an internal argument against one aimed at millions, so it gets dropped. A smaller company, for which that same programme is the entire business, picks it up and carries it through the stages that remove the uncertainty.

The gap between $5 million in 2017 and up to $475 million now is mostly the price of that de-risking. It is also worth reading the structure rather than the headline: $475 million is the number if everything goes right. The money Mereo can count on today is an option fee.

The mechanism is the part worth carrying away. When a protein is missing, the reflex is to replace it. Alvelestat suggests it is sometimes easier to disable whatever that protein was holding back. Fit a governor to the engine instead of rebuilding the brakes, and in doing so, turn a plasma-limited biologic into a pill.

Sources: Mereo BioPharma and Sentynl Therapeutics option and license agreement announcement (GlobeNewswire, 11 August 2026); BioSpace.