Solid-phase synthesis and biological evaluation of Joro spider toxin-4 from Nephila clavata.

Polyamine toxins from orb weaver spiders are attractive pharmacological tools particularly for studies of ionotropic glutamate (iGlu) receptors in the brain. These polyamine toxins are biosynthesized in a combinatorial manner, providing a plethora of related, but structurally complex toxins to be exploited in biological studies. Here, we have used solid-phase synthetic methodology for the efficient synthesis of Joro spider toxin-4 (JSTX-4) (1) from Nephila clavata, providing sufficient amounts of the toxin for biological evaluation at iGlu receptor subtypes using electrophysiology. Biological evaluation revealed that JSTX-4 inhibits iGlu receptors only in high µM concentrations, thereby being substantially less potent than structurally related polyamine toxins.

Subtype-Specific Agonists for NMDA Receptor Glycine Binding Sites.

A series of analogues based on serine as lead structure were designed, and their agonist activities were evaluated at recombinant NMDA receptor subtypes (GluN1/2A-D) using two-electrode voltage-clamp (TEVC) electrophysiology. Pronounced variation in subunit-selectivity, potency, and agonist efficacy was observed in a manner that was dependent on the GluN2 subunit in the NMDA receptor. In particular, compounds 15a and 16a are potent GluN2C-specific superagonists at the GluN1 subunit with agonist efficacies of 398% and 308% compared to glycine. This study demonstrates that subunit-selectivity among glycine site NMDA receptor agonists can be achieved and suggests that glycine-site agonists can be developed as pharmacological tool compounds to study GluN2C-specific effects in NMDA receptor-mediated neurotransmission.

Structure-activity relationship studies of argiotoxins: selective and potent inhibitors of ionotropic glutamate receptors.

Argiotoxin-636 (ArgTX-636), a natural product from the spider Argiope lobata, is a potent but nonselective open-channel blocker of ionotropic glutamate (iGlu) receptors. Here, three series of analogues were designed to exploit selectivity among iGlu receptors, taking advantage of a recently developed solid-phase synthetic methodology for the synthesis of ArgTX-636 and analogues. Initially, the importance of secondary amino groups in the polyamine chain was studied by the synthesis of systematically modified ArgTX-636 analogues, which were evaluated for pharmacological activity at NMDA and AMPA receptors. This led to the identification of two compounds with preference for NMDA and AMPA receptors, respectively. These were further elaborated by systematically changing the aromatic headgroup and linker amino acid leading to compounds with increased potency and selectivity for NMDA and AMPA receptors, respectively. Thus, the first structure-activity relationship study of ArgTX-636 has been carried out and has provided lead compounds for probing the ion channel region of iGlu receptors.

General synthesis of ß-alanine-containing spider polyamine toxins and discovery of nephila polyamine toxins 1 and 8 as highly potent inhibitors of ionotropic glutamate receptors.

Certain spiders contain large pools of polyamine toxins, which are putative pharmacological tools awaiting further discovery. Here we present a general synthesis strategy for this class of toxins and prepare five structurally varied polyamine toxins. Electrophysiological testing at three ionotropic glutamate receptor subtypes reveals that two of these, Nephila polyamine toxins 1 (NPTX-1) and 8 (NPTX-8), comprise intriguing pharmacological activities by having subnanomolar IC(50) values at kainate receptors.