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

Abstract

is an active component of the venom from the Egyptian digger wasp, Philanthus triangulum. PhTX-433 non-selectively inhibits several excitatory ligandgated 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 seventeen analogues of PhTX-343 against ganglionic (α3β4) and brain (α4β2) nAChRs expressed in Xenopus oocytes by using two-electrode voltage-clamp at 100 mV. IC50 values for PhTX-343 inhibition of α3β4 and α4β2 receptors were 7.7 nM and 80 nM, respectively. All of the studied analogues had significantly higher potency at α3β4 nAChRs with IC50 values as low as 0.16 nM and with up to a 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.

Philanthotoxin-343 attenuates retinal and optic nerve injury, and protects visual function in rats with N-methyl-D-aspartate-induced excitotoxicity

“…In this regard, philanthotoxin (PhTX) is a potential candidate. PhTX, a low-molecular-weight toxin from wasps, has been shown to block both NMDA and nicotinic acetylcholine receptor channels non-competitively [ 18 – 20 ]. PhTX-433 is the natural compound isolated from the venom sac of the female wasp, Philanthus triangulum , mainly found in the Sahara Desert.…”

“…The compound, first discovered by T. Piek and colleagues, contains a butyryl/tyrosyl/polyamine structure and exerts glutamate receptor-blocking properties including antagonism towards the NMDA receptors [ 21 – 23 ]. Subsequently, its analogue, known as PhTX-343 (numerals denote the number of methylenes between the amino group of the spermine moiety from left to right) was synthesized and shown to retain the pharmacological properties [ 18 , 20 , 24 , 25 ]. The present study aimed to assess the inhibitory effects of PhTX-343 against NMDA receptor-mediated excitotoxicity resulting in neuroprotective effects in rat retinas.…”

The Effects of Structural Alterations in the Polyamine and Amino Acid Moieties of Philanthotoxins on Nicotinic Acetylcholine Receptor Inhibition in the Locust, Schistocerca gregaria

“…In contrast, it was not envisaged that Cha-PhTX-343 would be only slightly (and not statistically significantly) more potent than PhTX-343 for the 1 s current; moreover, Cha-PhTX-343 proved less potent (p = 0.0075) than PhTX-12. Previously, Cha-PhTX-343 was reported to be a particularly strong antagonist of nAChRs, with IC 50 values in the low nanomolar range against rat subtypes α4β2 and α3β4, nAChRs [5], and >100 and >10 times more potent than PhTX-343 and PhTX-12, respectively, against human muscle-type nAChRs [25]. Interestingly, the potency of Cha-PhTX-12 has not previously been assessed with any nAChR subtype and, as expected, combination of both the above structural modifications proved to have a synergistic effect on its potency, resulting in a 471-fold (for 1 s current) increased potency compared to that of PhTX-343.…”

“…The modular structure of PhTX-433 (Figure 1a) facilitates the development of novel synthetic analogues that can be made specific against particular ionotropic receptors [2]. PhTX-433 and its synthetic analogues are non-competitive antagonists of ionotropic glutamate receptors of vertebrate nervous systems and insect muscles, as well as of nicotinic acetylcholine receptors (nAChR), expressed by the cells of a variety of organisms, including human muscles [3,4], the mammalian central nervous system (CNS) [5][6][7], and the insect CNS [8].…”

“…Structure-activity studies of PhTX-343, a synthetic model compound for PhTX-433, have shown that each moiety plays a role in determining the potency of PhTXs towards ionotropic receptors [4,5,[21][22][23][24][25][26][27]. In particular, a certain degree of hydrophobicity of the headgroup (Figure 1a, Regions I and II) is important for high potency toward nAChRs [5,22], while removal of the secondary amines from the polyamine moiety (Figure 1a, Region III) of PhTX-343 (to give PhTX-12) increases potency toward human muscle-type nAChRs [3,27], albeit this alteration greatly reduces potency toward some insect nAChRs [22,28]. For vertebrate nAChRs, voltage-dependence studies have revealed that, in addition to different potencies, PhTX-343 and PhTX-12 have different binding sites and modes of action.…”