Begacestat is a selective thiophene sulfonamide amyloid precursor protein gamma-secretase inhibitor (Aβ40,IC50=15 nM),and for the treatment of Alzheimer's disease.

Begacestat (GSI-953: 0, 2.5, 5, or 10 mg/kg, oral gavage, 3 h) results in a dose-dependent reversal of contextual fear conditioning deficits when compound is orally administered 3 h before training. Begacestat (5 mg/kg, p.o. in mice) treatment for 4 h significantly reduces the Aβ40 and Aβ42 in brain (37% lowering of brain Aβ40 and 25% lowering of Aβ40 observed)[1]. A dosage-related trend of slightly lower percentages of SP CD4+ cells in males at all dosages (SP CD4+ cells=~11% in controls compared with ~7% to ~9% in Begacestat-dosed animals) and females at 2000 mg/kg/day (SP CD4+ cells=~10% in controls compared with ~8% in Begacestat-dosed animals) is observed[2]. Significant deficits are observed after treatment with 2.5 mg/kg Begacestat, and there is some reversal of this at 5 mg/kg and full reversal at 10 mg/kg compared with vehicle-dosed Tg2576 mice[2].