Current symptomatic pharmacotherapy for Alzheimer’s disease is primarily focused on acetylcholinesterase inhibitors and blocking of the NMDA receptor (N-methyl-D-aspartate). Tacrine, a molecule with both of the mechanisms of action, was withdrawn from the market in 2013 after 20 years of use due to the hepatotoxicity probably caused by its 7-hydroxytacrine metabolite. A rationale substitution of the tacrine molecule can potentially hinder the formation of a toxic species. The introduction of the methoxy or phenoxy group to position 7 led to 7-phenoxytacrine (7-PhO-THA) which we hypothesize to bypass the toxic metabolization via 7-OH tacrine and quinon methid. Furthermore, 7-PhO-THA was confirmed being of dual potency, i.e. potent and balanced inhibition of both AChE and NMDARs. We discovered that it selectively inhibits the GluN1/GluN2B subtype of NMDARs via an ifenprodil-binding site, in addition to its voltage-dependent inhibitory effect at both GluN1/GluN2A and GluN1/GluN2B subtypes of NMDARs. Furthermore, whereas NMDA-induced lesion of the dorsal hippocampus confirmed potent anti-excitotoxic and neuroprotective efficacy, behavioral observations showed that 7-PhO-THA manages to avoid side effects, symptoms of schizophrenia typical for NMDA antagonists.

Keywords: tacrine; hepatotoxicity; CYP450; biotransformation; quinon methid