2-Amino-3,4-dihydroquinazolines as Inhibitors of BACE-1 (β-Site APP Cleaving Enzyme): Use of Structure Based Design to Convert a Micromolar Hit into a Nanomolar Lead

Fragment-based discovery of BACE1 inhibitors using functional assays

Novel nonpeptidic inhibitors of beta-secretase (BACE1) have been discovered by employing a fragment-based biochemical screening approach. A diverse library of 20000 low-molecular weight compounds were screened and yielded 26 novel hits that were confirmed by biochemical and surface plasmon resonance secondary assays. We describe here fragment inhibitors cocrystallized with BACE1 in a flap open and flap closed conformation as determined by X-ray crystallography.

Measurement of cellular beta-site of APP cleaving enzyme 1 activity and its modulation in neuronal assay systems

Amyloid-beta peptide (Abeta), a putatively causative agent of Alzheimer's disease (AD), is proteolytically derived from beta-amyloid precursor protein (APP). Here we describe cellular assays to detect the activity of the key protease beta-site of APP cleaving enzyme 1 (BACE1) based on an artificial reporter construct containing the BACE1 cleavage site of APP. These methods allow identification of inhibitors and indirect modulators of BACE1. In primary neuronal cultures transfected with human APP constructs (huAPP), Abeta production was modified by BACE1 inhibitors similarly to the production of endogenous murine Abeta in wild-type cells and to that of different transgenic neurons. To further improve the assay, we substituted the extracellular domain of APP by secreted alkaline phosphatase (SEAP). SEAP was easily quantified in the cell culture supernatants after cleavage of SEAP-APP by BACE1 or alpha-secretases. To render the assay specific for BACE1, the alpha-secretase cleavage site of SEAP-APP was eliminated either by site-directed mutagenesis or by substituting the transmembrane part of APP by the membrane domain of the erythropoietin receptor (EpoR). The pharmacology of these constructs was characterized in detail in HEK293 cells (human embryonic kidney cell line), and the SEAP-APP-EpoR construct was also introduced into primary murine neurons and there allowed specific measurement of BACE1 activity.

Design, synthesis and biological evaluation of novel dual inhibitors of acetylcholinesterase and beta-secretase

To explore novel effective drugs for the treatment of Alzheimer's disease (AD), a series of dual inhibitors of acetylcholineterase (AChE) and beta-secretase (BACE-1) were designed based on the multi-target-directed ligands strategy. Among them, inhibitor 28 exhibited good dual potency in enzyme inhibitory potency assay (BACE-1: IC(50)=0.567 microM; AChE: IC(50)=1.83 microM), and also showed excellent inhibitory effects on Abeta production of APP transfected HEK293 cells (IC(50)=98.7 nM) and mild protective effect against hydrogen peroxide (H(2)O(2))-induced PC12 cell injury. Encouragingly, intracerebroventricular injection of 28 into amyloid precursor protein (APP) transgenic mice caused a 29% reduction of Abeta(1-40) production. Therefore, 28 was demonstrated as a good lead compound for the further study and more importantly, the strategy of AChE and BACE-1 dual inhibitors might be a promising direction for developing novel drugs for AD patients.

beta-Secretase as a therapeutic target for Alzheimer's disease

beta-Secretase (memapsin 2, BACE1) is an attractive target for the development of inhibitor drugs to treat Alzheimer's disease (AD). Not only does this protease function at the first step in the pathway leading to the production of amyloid-beta (Abeta), its gene deletion produces only mild phenotypes. In addition, beta-secretase is an aspartic protease whose mechanism and inhibition are well known. The development of beta-secretase inhibitors, actively pursued over the last seven years, has been slow, due to the difficulty in combining the required properties in a single inhibitor molecule. Steady progress in this field, however, has brought about inhibitors that contain many targeted characteristics. In this review, we describe the strategy of structure-based inhibitor evolution in the development of beta-secretase inhibitor drug. The current status of the field offers grounds for some optimism, in that beta-secretase inhibitors have been shown to reduce brain Abeta and to rescue the cognitive decline in transgenic AD mice, and an orally available beta-secretase inhibitor drug candidate is in clinical trial. With this knowledge base, it seems reasonable to expect that more drug candidates will be tested in human, and then successful disease-modifying drugs may ultimately emerge from this target.