Neuroprotective derivatives of tacrine that target NMDA receptor and acetyl cholinesterase - Design, synthesis and biological evaluation.

The complex and multifactorial nature of neuropsychiatric diseases demands multi-target drugs that can intervene with various sub-pathologies underlying disease progression. Targeting the impairments in cholinergic and glutamatergic neurotransmissions with small molecules has been suggested as one of the potential disease-modifying approaches for Alzheimer's disease (AD). Tacrine, a potent inhibitor of acetylcholinesterase (AChE) is the first FDA approved drug for the treatment of AD. Tacrine is also a low affinity antagonist of N-methyl-D-aspartate receptor (NMDAR). However, tacrine was withdrawn from its clinical use later due to its hepatotoxicity. With an aim to develop novel high affinity multi-target directed ligands (MTDLs) against AChE and NMDAR, with reduced hepatotoxicity, we performed in silico structure-based modifications on tacrine, chemical synthesis of the derivatives and in vitro validation of their activities. Nineteen such derivatives showed inhibition with IC50 values in the range of 18.53 ± 2.09 - 184.09 ± 19.23 nM against AChE and 0.27 ± 0.05 - 38.84 ± 9.64 µM against NMDAR. Some of the selected compounds also protected rat primary cortical neurons from glutamate induced excitotoxicity. Two of the tacrine derived MTDLs, 201 and 208 exhibited in vivo efficacy in rats by protecting against behavioral impairment induced by administration of the excitotoxic agent, monosodium glutamate. Additionally, several of these synthesized compounds also exhibited promising inhibitory activitiy against butyrylcholinesterase. MTDL-201 was also devoid of hepatotoxicity in vivo. Given the therapeutic potential of MTDLs in disease-modifying therapy, our studies revealed several promising MTDLs among which 201 appears to be a potential candidate for immediate preclinical evaluations.

Protection of α-CaMKII from Dephosphorylation by GluN2B Subunit of NMDA Receptor Is Abolished by Mutation of Glu96 or His282 of α-CaMKII.

Interaction of CaMKII and the GluN2B subunit of NMDA receptor is essential for synaptic plasticity events such as LTP. Synaptic targeting of CaMKII and regulation of its biochemical functions result from this interaction. GluN2B binding to the T-site of CaMKII leads to changes in substrate binding and catalytic parameters and inhibition of its own dephosphorylation. We find that CaMKIINα, a natural inhibitor that binds to the T-site of CaMKII, also causes inhibition of dephosphorylation of CaMKII similar to GluN2B. Two residues on α-CaMKII, Glu96 and His282, are involved in the inhibition of CaMKII dephosphorylation exerted by binding of GluN2B. E96A-α-CaMKII is known to be defective in GluN2B-induced catalytic modulation. Data presented here show that, in both E96A and H282A mutants of α-CaMKII, GluN2B-induced inhibition of dephosphorylation is impaired.