Investigational BACE inhibitors for the treatment of Alzheimer's disease

Introduction: The amyloid hypothesis of Alzheimer's disease (AD) states that brain accumulation of amyloid-beta (A beta) oligomers and soluble aggregates represents the major causal event of the disease. Several small organic molecules have been synthesized and developed to inhibit the enzyme (beta-site amyloid precursor protein cleaving enzyme-1 or BACE1) whose action represents the rate-limiting step in A beta production. Areas covered: We reviewed the pharmacology and clinical trials of major BACE1 inhibitors. Expert opinion: In transgenic mouse models of AD, BACE1 inhibitors dose-dependently lower A beta levels in brain and cerebrospinal fluid (CSF) but the evidence for attenuation or reversal cognitive or behavioral deficits is very scanty. In AD patients, BACE1 inhibitors robustly lower plasma and CSF A beta levels and reduce brain plaques but without cognitive, clinical, or functional benefit. To date, seventeen BACE1 inhibitors have failed in double-blind, placebo-controlled clinical trials in patients with mild-to-moderate or prodromal AD, or in cognitively normal subjects at risk of developing AD. Several of these studies were prematurely interrupted due to toxicity or cognitive and behavioral worsening compared to placebo-treated patients. Elenbecestat, the last BACE1 inhibitor remaining in late clinical testing for AD, was recently discontinued due to safety concerns.