Development of Potent Fluorescent Polyamine Toxins
and Application in Labeling of Ionotropic Glutamate Receptors in Hippocampal
Neurons
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Abstract
The natural product argiotoxin-636
(ArgTX-636) found in the venom
of the Argiope lobata spider is a potent
open-channel blocker of ionotropic glutamate (iGlu) receptors, and
recently, two analogues, ArgTX-75 and ArgTX-48, were identified with
increased potency and selectivity for iGlu receptor subtypes. Here,
we have exploited these analogues as templates in the development
of fluorescent iGlu receptor ligands to be employed as unique tools
for dynamic studies. Eighteen fluorescent analogues were designed
and synthesized, and subsequently pharmacologically evaluated at three
iGlu receptor subtypes, which resulted in the discovery of highly
potent fluorescent iGlu receptor antagonists with IC<sub>50</sub> values
as low as 11 nM. The most promising ligands were further characterized
showing retention of their mechanism of action, as open-channel blockers
of iGlu receptors, as well as preservation of the photophysical properties
of the incorporated fluorophores. Finally, we demonstrate the applicability
of the developed probes for imaging of iGlu receptors in hippocampal
neurons
