Multivalent ligands can in principle enhance binding affinity and functional activity with respect to their monomers.[1] While this multivalency effect has been observed at GPCRs[2] and integrin receptors[3], little information has been gained at ion channel receptors to date. Given the broad interest in discovering and/or designing potent and selective ion channel ligands we chose α-conotoxin ImI (α-ImI), a potent blocker of α7-nicotinic receptor as the model peptide to investigate multivalency effects on ion channel receptors. Homogenous di- and tetravalent dendrimers incorporating α-ImI with polyethylene glycol spacers were designed and synthesized via a copper-catalyzed azide-alkyne cycloaddition (CuAAc), coupling the azide-modified α-ImI to an alkyne-modified polylysine dendron. NMR and CD structural analysis confirmed that each α-ImI moiety in both dendrimers had the same 3D structure as native α-ImI. Binding affinity of the α-ImI dendrimers to the binding protein Ac-AChBP was measured by surface plasmon resonance and revealed enhanced affinity. Quantitative electrophysiology showed that the α-ImI dendrimers had ~100-fold enhanced potency at human α7 nAChRs (IC50 = 4 nM) compared to native α-ImI (IC50 = 440 nM). Importantly, when compared to native α-ImI, no significant potency enhancement was observed at heteromeric hα3β2 and hα9α10 nAChRs. These multivalent peptide constructs represent a promising approach to enhancing potency and selectivity of ligands for homomeric ion channels.
[1] Handl H. L., J. Vagner, H. Y. Han, E. Mash, V. J. Hruby, R. J. Gillies, Expert. Opin. Ther. Tar., 2004, 8, 565-586.
[2] Kuil J., T. Buckle, J. Oldenburg, H. S. Yuan, A. D. Borowsky, L. Josephson, F. W. B. van Leeuwen, Mol. Pharmaceut., 2011, 8, 2444-2453.
[3] Wangler C., S. Maschauer, O. Prante, M. Schafer, R. Schirrmacher, P. Bartenstein, M. Eisenhut, B. Wangler, Chembiochem, 2010, 11, 2168-2181.