Background

Masitinib is an orally available inhibitor of the protein tyrosine kinase c-kit, which is expressed on cancer cells. Masitinib also inhibits PDGF and FGF receptors, and fyn and lyn kinases (Dubreuil et al., 2009). Masitinib interferes with the survival, migration, and activity of mast cells, and in this role has attracted attention for the treatment of neuroinflammatory and neurodegenerative disorders. Also relevant to Alzheimer’s, AB Science claims masitinib modulates microglia through inhibition of the macrophage colony stimulating factor receptor 1 kinase.

In preclinical work, chronic treatment with masitinib was reported to restore spatial learning and synaptic density in the hippocampus in the APP/PS1 mouse model of amyloidosis (Li et al., 2020).

Findings

From 2006 to 2009, AB Science conducted a Phase 2 trial comparing 3 and 6 mg/kg/day of masitinib or placebo, taken twice daily for six months as an add-on therapy to cholinesterase inhibitor and/or memantine treatment. Conducted at 12 centers in France, this trial enrolled 34 patients with mild to moderate Alzheimer's disease and used change in cognition as measured by the ADAS-cog as primary outcome. Masitinib was reported to have reduced cognitive decline in this study, with a claimed effect size of 6.8 and 7.6 at three and six months, respectively. Side effects including gastrointestinal disorders, edema, and rash occurred about twice as often with masitinib than placebo. Nineteen of 34 participants in the masitinib group withdrew before the study completed, compared with two of the eight placebo participants. Seven of the 19 withdrawals were reported as due to treatment-related adverse effects. The drug's tolerance was called acceptable in this report (Piette et al., 2011).

In 2012, a Phase 2b/3 trial began. Conducted in six European countries, it was to enroll 396 patients with mild to moderate Alzheimer's, comparing six months of 3 or 4.5 mg/kg daily, or placebo, as an add-on to cholinesterase and memantine treatment. In 2018, the study was enlarged to enroll 721 people from 118 sites in 21 mainly European countries, and added a dose escalation group receiving 4.5 mg/kg daily for three months, then 6 mg/kg, with a matching placebo group. The 3. 5 mg/kg group was discontinued. Cognition as measured by ADAS-cog and global function as measured by the ADCS-ADL were co-primary outcome measures.

In late 2020, the company announced that the study met its primary goal (Dec 2020 news). The 4.5 mg/kg treatment group improved on ADAS-cog and ADCS-ADL, while the placebo group declined. The ADAS-cog met the preset statistical threshold for success of p<0.025. Fewer drug- than placebo-treated participants progressed to severe dementia. No treatment effect was seen in the titration arm. Serious adverse events were twice as frequent in treated groups than placebo.

Masitinib was evaluated in Spain for amyotrophic lateral sclerosis as an add-on therapy to riluzole. This trial started in January 2013 as a Phase 2 with 45 patients but later was expanded into a Phase 3 study with 394 patients (see clinicaltrials.gov). The company reported that 48 weeks of 4.5 mg/kg/day slowed loss of motor abilities, except in patients with rapid progression (May 2017 news; Mora et al., 2019). Patients in the trial were eligible to continue masitinib. After six years, masitinib extended survival by two years in the subset of patients with mild symptoms at the start of treatment and who were not fast progressors (Mora et al., 2021). It did not affect survival in the overall study population. In October 2020, a confirmatory Phase 3 study began evaluating 48 weeks of 4.5 and 6 mg/kg or placebo in 495 participants with mild to moderate symptoms. It will run through 2022.

On June 1, 2021, AB Science announced a voluntary pause in recruitment and randomization for ongoing masitinib studies, including the ALS trial. Analysis of pooled results from unblinded, controlled trials identified a potential risk of ischemic heart disease that needs further investigation, the company said (see details). Dosing will continue for those already on treatment.

AB Science is also developing masitinib for multiple sclerosis, where it was reported to slow disease progression in a Phase 3 trial (2020 abstract). Clinical development for pancreatic cancer, asthma, mastocytosis, and COVID-19 disease is ongoing, as well. Masitinib has been tested in clinical trials for breast, colorectal, gastric, head and neck, liver, lung, and esophageal cancer, as well as glioblastoma, metastatic melanoma, multiple myeloma, and T cell lymphoma. The drug is available to treat cancer in veterinary medicine under the names Masivet or Kinavet.

For all trials of masitinib in Alzheimer's, see clinicaltrials.gov.

Clinical Trial Timeline