A Phase 3 Trial of Semagacestat for Treatment of Alzheimer's Disease

Alzheimer's disease is characterized by the presence of cortical amyloid-beta (Aβ) protein plaques, which result from the sequential action of β-secretase and γ-secretase on amyloid precursor protein. Semagacestat is a small-molecule γ-secretase inhibitor that was developed as a potential treatment for Alzheimer's disease.

We conducted a double-blind, placebo-controlled trial in which 1537 patients with probable Alzheimer's disease underwent randomization to receive 100 mg of semagacestat, 140 mg of semagacestat, or placebo daily. Changes in cognition from baseline to week 76 were assessed with the use of the cognitive subscale of the Alzheimer's Disease Assessment Scale for cognition (ADAS-cog), on which scores range from 0 to 70 and higher scores indicate greater cognitive impairment, and changes in functioning were assessed with the Alzheimer's Disease Cooperative Study-Activities of Daily Living (ADCS-ADL) scale, on which scores range from 0 to 78 and higher scores indicate better functioning. A mixed-model repeated-measures analysis was used.