Philanthotoxin Analogues That Selectively Inhibit Ganglionic Nicotinic Acetylcholine Receptors with Exceptional Potency.

Philanthotoxin-433 (PhTX-433) is an active component of the venom from the Egyptian digger wasp, Philanthus triangulum. PhTX-433 nonselectively inhibits several excitatory ligand-gated ion channels, and we recently showed that its synthetic analogue, PhTX-343, exhibits strong selectivity for neuronal over muscle-type nicotinic acetylcholine receptors (nAChRs). Here, we examined the action of 17 analogues of PhTX-343 against ganglionic (α3β4) and brain (α4β2) nAChRs expressed in Xenopus oocytes by using a two-electrode voltage clamp at -100 mV. IC50 values for PhTX-343 inhibition of α3β4 and α4β2 receptors were 7.7 and 80 nM, respectively. All the studied analogues had significantly higher potency at α3β4 nAChRs with IC50 values as low as 0.16 nM and with up to 91-fold selectivity for α3β4 over α4β2 receptors. We conclude that PhTX-343 analogues displaying both a saturated ring and an aromatic moiety in the hydrophobic headgroup of the molecule demonstrate exceptional potency and selectivity for α3β4 nAChRs.