Practical Design Guidelines for Synthetic Multivalent Nanoparticles as Targeted Biomedical Nanodevices.

Abstract

This dissertation explores the heterogeneity of synthetic nanoparticles and systematically investigates factors that regulate the multivalent binding avidity of these particles. We aim to establish parameters for designing multivalent nanoparticles, and define the role the heterogeneity of nanoparticles plays in this process from both structural and kinetic perspectives. In these studies, the kinetic and thermodynamic binding parameters of heterogeneous nanoparticle populations are identified and evaluated. We assess the effect of varied design parameters on the function of multivalent nanoparticles to provide these design guidelines. In the end, we prove the binding avidity of nanoparticles can be optimized using this approach. We first developed a novel method for evaluating the avidity distribution of nanoparticles. This involved the design and synthesis of a model multivalent nanoparticle system and a unique kinetic analysis to quantify the avidity distribution. We used mono-dispersed PAMAM dendrimers functionalized with ssDNA oligonucleotides as a platform, and used complementary oligonucleotides as targeted receptors to create this well-controlled model nanoparticle system and an SPR biosensor to evaluate their binding. We found the binding curves were characterized by heterogeneity, including fast- and slow-dissociation subpopulations. By using a parallel initial rate analysis and dual-Langmuir analysis, the avidity distribution of nanoparticles were determined and compared to the chemical diversity of ligand distribution. Second, we probed the avidity distributions resulting from a variety of parameters, including the number and the affinity of functionalized ligands. Based on both experimental and simulation results, we showed that multivalent interactions were dependent on these design parameters and developed strategies to enhance the binding avidity of ligand-functionalized nanoparticles and the frequency of high-avidity subpopulations in the heterogeneous nanoparticles. Finally, we tested the principles defined in our prior studies by synthesizing ligand-functionalized nanoparticles that demonstrated homogeneous high-avidity interactions with SPR surfaces. This was accomplished by using copper-free click chemistry, which allowed us to synthesize uniform and densely ligand-functionalized nanoparticles. As hypothesized, these nanoparticles demonstrated uniform binding to the targeted surface with pM-level avidity. This avidity is comparable to the avidity of antigen-antibody interaction, suggesting that these guidelines can be used in the design of nanoparticles in targeting drugs in vivo.