A Quantitative Assessment of Nanoparticle−Ligand Distributions: Implications for Targeted Drug and Imaging Delivery in Dendrimer Conjugates

Abstract

Functional nanoparticles often contain ligands including targeting molecules, fluorophores, and/or active moieties such as drugs. Characterizing the number of these ligands bound to each particle, and the distribution of nanoparticle-ligand species, is important for understanding the nanomaterial’s function. In this study, the amide coupling methods commonly used to conjugate ligands to poly(amidoamine) (PAMAM) dendrimers were examined. A skewed Poisson distribution was observed and quantified using HPLC for two sets of dendrimer-ligand samples prepared using the amine terminated form of the PAMAM dendrimer and a partially acetylated form of the PAMAM dendrimer that has been used for targeted in vivo drug delivery. The prepared samples had an average number of ligands per dendrimer ranging from 0.4 to 13. Distributions identified by HPLC are in excellent agreement with the mean ligand/dendrimer ratio, measured by 1H NMR, gel permeation chromatography (GPC), and potentiometric titration. These results provide insight into the heterogeneity of distributions that are obtained for many classes of nanomaterials to which ligands are conjugated and belie the use of simple cartoon models that present the “average” number of ligands bound as a physically meaningful representation for the material.

Particle-by-Particle Charge Analysis of DNA-Modified Nanoparticles Using Tunable Resistive Pulse Sensing

“…When using nanoparticle systems a mean population zeta potential will not allow the true measure of the ligand distribution across all of the particles to be interpreted, and in a typical reaction the ligand density would follow a poisson distribution [33][34][35] . The spread of the population can have an effect on the reaction kinetics, stability and sensitivity of nanoparticle based assays [36][37][38] .…”

Bifunctional Phosphorus Dendrimers and Their Properties

“…In many cases, a stochastic functionalization on the surface of the dendrimer is carried out to have multiple types of functions [114]. This approach is paradoxical, as the synthesis of dendrimers aims at obtaining pure compounds, whereas the stochastic functionalization in the last step affords a mixture of compounds, which in particular can induce inconsistencies in biological responses [115].…”

Polymer-Drug Nanoconjugate – An Innovative Nanomedicine: Challenges and Recent Advancements in Rational Formulation Design for Effective Delivery of Poorly Soluble Drugs

“…Therefore it has been difficult to satisfy the drug product quality and regulatory requirements including the metabolic fate of the conjugates relative to traditional formulations. Current literature is replete with research efforts on quantitative techniques to evaluate homogeneity of the drug and ligand distribution in the preparation of PAMAM dendrimers (42,43) and the effect of physical instability (aggregation) of HPMA-folate conjugate on folate receptor-mediated uptake (44). Sophisticated analytical techniques such as small angle neutron scattering (SANS), 2D 1 H NOESY and TOCSY NMR and pulsed gradient NMR have been used to characterize polymer-drug nanoconjugates (45,46).…”