Abstract
Inorganic nanoparticles (NPs) are studied as drug carriers, radiosensitizers and imaging agents, and characterizing nanoparticle biodistribution is essential for evaluating their efficacy and safety. Tracking NPs at the single-cell level with current technologies is complicated by the lack of reliable methods to stably label particles over extended durations in vivo. Here we demonstrate that mass cytometry by time-of-flight provides a label-free approach for inorganic nanoparticle quantitation in cells. Furthermore, mass cytometry can enumerate AuNPs with a lower detection limit of ∼10 AuNPs (3 nm core size) in a single cell with tandem multiparameter cellular phenotyping. Using the cellular distribution insights, we selected an amphiphilic surface ligand-coated AuNP that targeted myeloid dendritic cells in lymph nodes as a peptide antigen carrier, substantially increasing the efficacy of a model vaccine in a B16-OVA melanoma mouse model. This technology provides a powerful new level of insight into nanoparticle fate in vivo.
Highlights
We show that mass cytometry overcomes challenges in fluorescence-based analysis of autofluorescent tissue cells, and illustrate the value of combined single cell NP detection with antibody-based phenotyping, using insights derived from mass cytometer analysis to select a nanoparticle composition that accumulates in dendritic cells for vaccination
We first synthesized AuNPs with comparable inorganic core diameters but three different surface chemistries expected to have distinct biodistributions and cellular uptake in vivo (Fig. 1a): 3-mercapto1-propanesulfonate (MPSA) NPs, coated by a dense layer of short sulfonate-terminated ligands that strongly interact with water; 11-mercapto-1-undecanesulfonate/1-octanethiol (MUS/OT) NPs bearing an amphiphilic mixed ligand shell, which are water soluble but strongly interact with cell membranes;[33,34] and poly(ethylene glycol) NPs sterically stabilized by PEG to reduce opsonization by serum components[35]
Gold uptake by macrophages was clearly detectable by mass cytometry across this entire concentration range, whereas NPs at concentrations of 0.1 mg ml À 1 or lower were not detected in cells using flow cytometry (Fig. 2a,b)
Summary
Using the cellular distribution insights, we selected an amphiphilic surface ligand-coated AuNP that targeted myeloid dendritic cells in lymph nodes as a peptide antigen carrier, substantially increasing the efficacy of a model vaccine in a B16-OVA melanoma mouse model This technology provides a powerful new level of insight into nanoparticle fate in vivo. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) enables quantitation of metal contents at the single-cell level with additional insights on sub-cellular localization of NPs, this image-based method suffers from low throughput (tens to hundreds of cells typically analysed) and relatively low sensitivity (requiring millions of atoms per cell)[15,16,17]. Such highly multiparametric detection has offered new insights into the complexity of biology, in applications ranging from deep phenotyping of tumours to immune system signalling pathways[26,27]
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