Masitinib is a tyrosine kinase inhibitor (TKI) being developed by AB Science to treat symptoms of amyotrophic lateral sclerosis (ALS).

The treatment is advancing in clinical trials as a possible therapeutic for numerous disorders, from cancer and inflammatory diseases to those of the central nervous system, such as ALS.

How masitinib works

Masitinib is an oral therapy that targets cells of the immune system called the mast cells and macrophages. It works by blocking the activation of proteins called tyrosine kinases, which play a role in inflammation and chronic inflammatory states.

A recent study in rats published in The Journal of Clinical Investigation suggests that mast cells and neutrophils may be involved in motor neuron degeneration. A follow-up study supported these findings and showed that masitinib inhibited these cells and prevented neuronal damage.

Data presented at the 2019 Muscular Dystrophy Association clinical and scientific conference showed that macrophages, neutrophils, mast cells, and Schwann cells are involved in peripheral neurodegeneration, and that masitinib is able to inhibit all four types of cells.

Masitinib in clinical trials

Masitinib was recently evaluated in a Phase 2/3 clinical trial (NCT02588677) that compared the safety and efficacy of the treatment combined with an approved ALS medication called Rilutek (riluzole), against a placebo plus Rilutek.

The study included 394 ALS patients who were randomized to receive 4.5 mg per kg per day of masitinib and Rilutek, 3 mg per kg per day of masitinib and Rilutek, or a placebo and Rilutek, for up to 48 weeks.

The study’s primary objective was to measure changes in patients’ scores on the revised ALS functional rating scale (ALSFRS-R), which measures abilities such as walking, speech, hand control, and breathing. A secondary objective was to determine patients’ progression-free survival, which researchers defined as a deterioration of less than nine points in the ALSFRS-R score.

AB Science announced in March 2017 that the Phase 2/3 clinical trial met its main goal of improving the functioning of ALS patients. The results showed that masitinib administered at 4.5 mg per kg per day in combination with Rilutek improved patients’ quality of life and survival.

The company also provided results in May 2017, which showed that patients treated with 3 mg per kg per day of masitinib and Rilutek also showed improvements in ALSFRS, progression-free survival, and quality of life scores compared with those given a placebo and Rilutek. Masitinib was found to be safe, and no major adverse effects were reported. Results from this study were presented at the 2017 European Network for the Cure of ALS conference in Ljubljana, Slovenia.

A new Phase 3 trial (NCT03127267) is scheduled to begin in May 2019 to assess masitinib in combination with Rilutek, against a placebo-with-Rilutek combination, in about 400 ALS patients.

Other information

AB Science submitted a marketing application to the European Medicines Agency (EMA) in September 2016 using interim results from the Phase 2/3 trial. The final safety data from the study were not available until February 2018 and therefore not included in the application. The EMA’s Committee for Human Medicinal Products issued a negative opinion on the application in April 2018. AB Science decided not to pursue reexamination of the EMA’s decision since the company would not be able to submit the new safety data.

The U.S. Food and Drug Administration designated masitinib an orphan drug in 2015, a designation that provides incentives to companies to advance the development of potential treatments for rare diseases.

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