Masitinib

AB Science is a small Paris-listed company. Masitinib is its lead drug and has been tested in many diseases; in 2026 the company dropped several of those programmes to focus on ALS and one cancer drug. It has relied on repeated small share sales and debt deferrals for funding, and it changed chief executive in July 2026. In September 2026 inspectors from three European regulators carried out a "for cause" inspection of how it runs clinical trials.

Masitinib blocks signalling enzymes (kinases) in immune cells called mast cells and microglia. In ALS these cells may become overactive and keep up inflammation that harms motor neurons. The idea is that calming them slows nerve damage. In 2026 the company reported a blood marker linked to inflamed microglia that it wants to test in the Phase 3 trial, but has not named it.

The confirmatory Phase 3 trial AB23005 (about 408 people, 48 weeks) was cleared by the FDA and several European countries in 2025, but no patient has been enrolled. In April 2026 the company paused all European trials after regulators raised questions about its resources, and EU regulators listed AB23005 as suspended. After a regulatory inspection in September 2026, the company said it now aims to restart the trial in the fourth quarter of 2027, subject to health authority approval.

In the earlier AB10015 trial, people progressing at a "normal" rate (losing under 1.1 points a month) lost 9.2 ALSFRS-R points on high-dose masitinib plus riluzole versus 12.6 on placebo plus riluzole over 48 weeks. This group was defined by a mid-trial change to the plan, and there was no clear benefit in the whole group treated or on survival. Serious side effects were more common on masitinib (31% vs 18%). European regulators found problems with how the study was run and did not consider the data reliable. Later company analyses of narrower subgroups are post hoc and partly unreviewed preprints.

This is the most favourable result reported. See all key studies for the full picture.

The Phase 3 trial is designed for people with ALS whose decline is under 1.1 ALSFRS-R points a month and who still score at least 1 on every item of the ALSFRS-R (no function completely lost). The company says this is about three-quarters of people with ALS. US participants may also take edaravone.

AB Science said on 29 September 2026 that it must first finish a new quality management system and have it audited by the end of 2026, then pass a new inspection, before resuming the ALS trial in the fourth quarter of 2027. The final inspection report is expected before the end of 2026.

No masitinib ALS trial is enrolling. The EU trial record (2024-511244-12-01) lists the study as suspended in the countries that had approved it. We did not find an active expanded access programme for ALS.

• AB23005 (Phase 3) (NCT07174492) suspended · Planned in EU, USA, Argentina, Serbia