Screening of new huprines-Inhibitors of acetylcholinesterases by electrospray ionization ion trap mass spectrometry

Acetylcholinesterase inhibitors (AChEI) are one of the drugs families validated for clinical use in the treatment of Alzheimer's disease (AD). For this reason, finding new more potent and more selective AChEIs is always of interest. Since 1961, the inhibitory activity of AChEI is evaluated through the Ellman's method. Herein, we reported a MS-based evaluation of potential new AChEI with the determination of their inhibitory activity (IC50 and KI). Compared to the Ellman's method, that uses the substrate analog acetylthiocholine, the electrospray ionization ion trap mass spectrometry (ESI-IT-MS) consists in monitoring the conversion ratio of a low concentration of the natural substrate - acetylcholine to choline. We present here the inhibition activity of huprine X and six of its derivates (bearing different functional groups at position 9) towards the recombinant human (rhAChE) and Electrophorus electricus acetylcholinesterase (EelAChE). Mechanisms of action of selected inhibitors were evaluated by means of Lineweaver-Burk plot analysis. The Michaelis-Menten constants (KM), inhibitory constants (KI) were examined as well as the IC50 to allow classifying a series of huprine derivatives by inhibition potency by a comparison with a reference (huprine X). Our results demonstrate that these drugs are very potent AChE inhibitors, especially (±)-huprine 6 with an inhibitory activity on recombinant human AChE (rhAChE) in the picomolar range. This study reveals the interest of huprine compounds in the treatment of AD.