Kinetics of human serum butyrylcholinesterase inhibition by a novel experimental Alzheimer therapeutic, dihydrobenzodioxepine cymserine.

Cholinergic loss is the single most replicated neurotransmitter deficiency in Alzheimer's disease (AD) and has led to the use of acetylcholinesterase inhibitors (AChE-Is) and unselective cholinesterase inhibitors (ChE-Is) as the mainstay of treatment. AChE-Is and ChE-Is, however, induce dose-limiting adverse effects. Recent studies indicate that selective butyrylcholinesterase inhibitors (BuChE-Is) elevate acetylcholine (ACh) in brain, augment long-term potentiation, and improve cognitive performance in rodents without the classic adverse actions of AChE-Is and ChE-Is. BuChE-Is thereby represent a new strategy to ameliorate AD, particularly since AChE activity is depleted in AD brain, in line with ACh levels, whereas BuChE activity is elevated. Our studies have focused on the design and development of cymserine analogues to induce selective time-dependent brain BuChE inhibition, and on the application of innovative and quantitative enzyme kinetic analyses to aid selection of drug candidates. The quantitative interaction of the novel inhibitor, dihydrobenzodioxepine cymserine (DHBDC), with human BuChE was characterized. DHBDC demonstrated potent concentration-dependent binding with BuChE. The IC(50) and specific new kinetic constants, such as K(T50), P(PC), K(T1/2) and R(I), were determined at dual substrate concentrations of 0.10 and 0.60 mM butyrylthiocholine and reaction times, and are likely attainable in humans. Other classical kinetic parameters such as K(ia), K(ma), V(ma) and V(mi) were also determined. In synopsis, DHBDC proved to be a highly potent competitive inhibitor of human BuChE in comparison to its structural analogue, cymserine, and represents an interesting drug candidate for AD.