Arrowhead's under-the-skin RNAi drug cuts brain protein tau by 73% in early trial

Arrowhead Pharmaceuticals reported on 14 October 2026 that ARO-MAPT, an RNA interference drug injected under the skin, reduced levels of the protein tau by an average of 73% at 105 days in the highest dose group of an early trial in healthy volunteers ¹. Arrowhead said the data "provide clinical validation" of a platform designed to carry its drugs past the blood-brain barrier into the central nervous system ¹.

What the trial found

The study is an early-stage trial whose main purpose is safety, with a check on whether the drug acts as intended ¹. About 64 healthy volunteers were enrolled across three dose levels ¹. Two groups received a subcutaneous dose of 2.1 or 6.4 mg per kilogram of body weight on days one, eight and 15; the third received 12.8 mg per kilogram on days one and 15 ¹.

At day 105, tau fell by 40% in the 2.1 mg group and by 69% in the 6.4 mg group ¹. In the high-dose arm the average reduction was 73%, and Arrowhead said individual falls reached as much as 85% ¹. Reported side effects were mild: injection site reactions, bruising, respiratory infections and headaches ¹. The durability of the effect after two injections points to dosing once every three months ¹.

ARO-MAPT works by silencing the gene that leads to tau expression in the central nervous system ¹. Tau build-up is thought to play a part in how Alzheimer's progresses, which has made it a common target, but several candidate drugs aimed at it have struggled to show a clear benefit ¹.

What it means for the market

The main significance is delivery rather than Alzheimer's itself. Developers of RNA-modulating medicines have been looking for ways to reach targets outside the liver, a long-standing limit of the approach ¹. A drug given as an ordinary injection that reaches brain tissue in useful amounts would widen the range of neurological targets open to RNAi companies, and Arrowhead is presenting the result as proof that its platform can do this ¹.

Stifel analyst James Condulis wrote that the results "look compelling", and judged that with subcutaneous delivery they may compare well with other drugs built to cross the blood-brain barrier ¹. For companies working on brain shuttles and other routes into the central nervous system, that puts an under-the-skin option on the comparison table.

For Alzheimer's specifically, the commercial picture is set by the amyloid drugs approved in the early 2020s: Aduhelm, Leqembi and Kisunla ¹. Leqembi and Kisunla carry limits, including a warning against prescribing them to people on common blood thinners, and their benefits are modest ¹. Kisunla cleared nearly all amyloid lesions in most enrollees in a Phase 3 trial but did not stop disease progression ¹. A tau-lowering drug with quarterly injections would compete on a different mechanism, if it can show clinical benefit.

Arrowhead is also planning trials of ARO-MAPT in other tau-linked conditions, including frontotemporal dementia and progressive supranuclear palsy ¹.

Caveats

These are interim data from healthy volunteers in an early trial focused on safety, and they show only that the drug lowers its target ¹. Considerably more work is needed to show any effect on the disease ¹. Condulis noted that the drug is at a very early stage and that tau has not yet been clearly established as a good Alzheimer's target ¹. The remainder of the trial will enrol both healthy volunteers and people with mild Alzheimer's disease, who will receive up to five injections ¹.