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Designing super selectivity in multivalent nano-particle binding.

ABSTRACT: A key challenge in nano-science is to design ligand-coated nano-particles that can bind selectively to surfaces that display the cognate receptors above a threshold (surface) concentration. Nano-particles that bind monovalently to a target surface do not discriminate sharply between surfaces with high and low receptor coverage. In contrast, "multivalent" nano-particles that can bind to a larger number of ligands simultaneously, display regimes of "super selectivity" where the fraction of bound particles varies sharply with the receptor concentration. We present numerical simulations that show that multivalent nano-particles can be designed such that they approach the "on-off" binding behavior ideal for receptor-concentration selective targeting. We propose a simple analytical model that accounts for the super selective behavior of multivalent nano-particles. The model shows that the super selectivity is due to the fact that the number of distinct ligand-receptor binding arrangements increases in a highly nonlinear way with receptor coverage. Somewhat counterintuitively, our study shows that selectivity can be improved by making the individual ligand-receptor bonds weaker. We propose a simple rule of thumb to predict the conditions under which super selectivity can be achieved. We validate our model predictions against the Monte Carlo simulations.

SUBMITTER: Martinez-Veracoechea FJ

PROVIDER: S-EPMC3131366 | biostudies-literature | 2011 Jul

REPOSITORIES: biostudies-literature

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Designing super selectivity in multivalent nano-particle binding.

Martinez-Veracoechea Francisco J FJ Frenkel Daan D

Proceedings of the National Academy of Sciences of the United States of America 20110620 27

A key challenge in nano-science is to design ligand-coated nano-particles that can bind selectively to surfaces that display the cognate receptors above a threshold (surface) concentration. Nano-particles that bind monovalently to a target surface do not discriminate sharply between surfaces with high and low receptor coverage. In contrast, "multivalent" nano-particles that can bind to a larger number of ligands simultaneously, display regimes of "super selectivity" where the fraction of bound p ...[more]

PMID: 21690358

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Project description:BACKGROUND: An approach to use multivalent dendrimer carriers for delivery of nucleoside signaling molecules to their cell surface G protein-coupled receptors (GPCRs) was recently introduced. RESULTS: A known adenosine receptor (AR) agonist was conjugated to polyamidoamine (PAMAM) dendrimer carriers for delivery of the intact covalent conjugate to on the cell surface. Depending on the linking moiety, multivalent conjugates of the N6-chain elongated functionalized congener ADAC (N6-[4-[[[4-[[[(2-aminoethyl)amino]carbonyl]methyl]anilino]carbonyl]methyl]phenyl]-adenosine) achieved unanticipated high selectivity in binding to the cytoprotective human A3 AR, a class A GPCR. The key to this selectivity of > 100-fold in both radioreceptor binding (Ki app = 2.4 nM) and functional assays (EC50 = 1.6 nM in inhibition of adenylate cyclase) was maintaining a free amino group (secondary) in an amide-linked chain. Attachment of neutral amide-linked chains or thiourea-containing chains preserved the moderate affinity and efficacy at the A1 AR subtype, but there was no selectivity for the A3 AR. Since residual amino groups on dendrimers are associated with cytotoxicity, the unreacted terminal positions of this A3 AR-selective G2.5 dendrimer were present as carboxylate groups, which had the further benefit of increasing water-solubility. The A3 AR selective G2.5 dendrimer was also visualized binding the membrane of cells expressing the A3 receptor but did not bind cells that did not express the receptor. CONCLUSION: This is the first example showing that it is feasible to modulate and even enhance the pharmacological profile of a ligand of a GPCR based on conjugation to a nanocarrier and the precise structure of the linking group, which was designed to interact with distal extracellular regions of the 7 transmembrane-spanning receptor. This ligand tool can now be used in pharmacological models of tissue rescue from ischemia and to probe the existence of A3 AR dimers.

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Designing super selectivity in multivalent nano-particle binding.

Publications

Designing super selectivity in multivalent nano-particle binding.

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