Astatine-211

At-211 delivers a single, clean high-LET alpha per decay near 6.8 MeV. Alpha tracks are dense, so the radiolytic yield per unit energy is high, and At-211 is administered at high activity for an alpha emitter, in the hundreds of megabecquerels. That combination gives it a substantial absolute peroxide burden, delivered on a short 7.2-hour clock, unlike Ac-225, whose far smaller activity is carried across a roughly 10-day chain to a higher accumulated peak.

That burden is concentrated into a 7.2-hour half-life. The peroxide climbs fast and steeply while the source is live (high-LET intensity at high activity), and the source itself decays away within a day. A short, intense clock is the At-211 signature: a lower peak than Ac-225's, reached in hours rather than across a roughly 10-day chain.

DuraRad lines the vial wall with a sol-gel coating that holds immobilized manganese superoxide dismutase and catalase. Both enzymes are fixed in the coating, not dissolved into the drug product, so they are not an ingredient in the dose. The dense alpha tracks split water throughout the solution, generating superoxide and hydrogen peroxide at random points and in every direction. As those species diffuse to the wall, the immobilized manganese SOD converts superoxide into hydrogen peroxide and oxygen, and the catalase decomposes that hydrogen peroxide into water and oxygen. The coating therefore acts as a distributed sink at the wall, lowering the steady-state concentration of superoxide and peroxide in the vial. Clearing that superoxide and peroxide at the wall keeps their concentration low in the vial and lowers the oxidative burden on the drug.

At-211 carries a substantial absolute peroxide burden for an alpha emitter, because one high-LET alpha per decay meets an administered activity in the hundreds of megabecquerels. That burden rises and falls on a 7.2-hour clock, which is still many multiples of the minutes-scale turnover time the immobilized enzymes need to consume the superoxide and peroxide reaching the wall, so the modeled suppression is large. It is smaller than for the multi-day therapeutics, since a sub-day source gives the enzymes fewer cycles of steady-state operation, and hydroxyl radical and singlet oxygen are not enzyme substrates, so any reduction in those is indirect rather than a direct scavenging. The Q4 2026 radioactive validation at Washington University in St. Louis is designed to confirm this modeled behavior.