We observed in vitro neuroprotective and AMPA/kainate receptor antagonist effects of the new 2,3-benzodiazepine derivative EGIS-8332 (R, S-1-(4-aminophenyl)-7,8-methylenedioxy-4-cyano-4-methyl-3-N-acetyl-5H-3,4-dihydro-2,3-benzodiazepine) using the lactate dehydrogenase (LDH) release assay and patch clamp recordings on primary cultures of rat embryonic telencephalon neurons exposed to AMPA/kainate receptor agonists.
EGIS-8332 potently decreased alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and quisqualate induced LDH release (IC50 = 5.2 ± 0.4 and 7.4 ± 1.3 μM, respectively) from the cells.
Whole-cell patch clamp studies carried out on the ionotropic glutamate receptors N-methyl d-aspartate (NMDA), as well as AMPA (and kainate) in cultured telencephalon neurons verified that EGIS-8332 blocked steady state responses to AMPA and kainate (IC50 = 1.7 ± 0.4 and 6.2 ± 1.6 μM, respectively), but hardly influenced currents evoked by NMDA. EGIS-8332 also inhibited kainate-evoked response in CHO cells expressing the flop variant of GluR1 receptor and, in cerebellar Purkinje cells at similar efficiency. The stereoselectivity of the inhibitory site is established by the clearly dissimilar inhibitory potency of the enantiomer components of EGIS-8332 differing in the configuration of methyl and cyano substituents on carbon C4: the R(−) enantiomer was found to be the efficient species. This finding suggests that the inhibitory interaction between the channel protein and drug is promoted by presence of the C4 methyl group.
The inhibition of the AMPA/kainate ion channels by EGIS-8332 is non-competitive, not use dependent, and depends neither on the closed/open state of the channel, nor the membrane potential. These findings suggest an allosteric mechanism for the inhibition.
These in vitro observations suggest that the compound might be useful in the treatments of certain acute and chronic neurological syndromes initiated by derangements of ionotropic glutamate receptor function.