Fluorescent Silica Nanoparticles to Label Metastatic Tumor Cells in Mineralized Bone Microenvironments.

During breast cancer bone metastasis, tumor cells interact with bone microenvironment components including inorganic minerals. Bone mineralization is a dynamic process and varies spatiotemporally as a function of cancer-promoting conditions such as age and diet. The functional relationship between skeletal dissemination of tumor cells and bone mineralization, however, is unclear. Standard histological analysis of bone metastasis frequently relies on prior demineralization of bone, while methods that maintain mineral are often harsh and damage fluorophores commonly used to label tumor cells. Here, fluorescent silica nanoparticles (SNPs) are introduced as a robust and versatile labeling strategy to analyze tumor cells within mineralized bone. SNP uptake and labeling efficiency of MDA-MB-231 breast cancer cells is characterized with cryo-scanning electron microscopy and different tissue processing methods. Using a 3D in vitro model of marrow-containing, mineralized bone as well as an in vivo model of bone metastasis, SNPs are demonstrated to allow visualization of labeled tumor cells in mineralized bone using various imaging modalities including widefield, confocal, and light sheet microscopy. This work suggests that SNPs are valuable tools to analyze tumor cells within mineralized bone using a broad range of bone processing and imaging techniques with the potential to increase the understanding of bone metastasis.

Overcoming Barriers Associated with Oral Delivery of Differently Sized Fluorescent Core-Shell Silica Nanoparticles.

Oral delivery, while a highly desirable form of nanoparticle-drug administration, is limited by challenges associated with overcoming several biological barriers. Here, the authors study how fluorescent and poly(ethylene glycol)-coated (PEGylated) core-shell silica nanoparticles sized 5 to 50 nm interact with major barriers including intestinal mucus, intestinal epithelium, and stomach acid. From imaging fluorescence correlation spectroscopy studies using quasi-total internal reflection fluorescence microscopy, diffusion of nanoparticles through highly scattering mucus is progressively hindered above a critical hydrodynamic size around 20 nm. By studying Caco-2 cell monolayers mimicking the intestinal epithelia, it is observed that ultrasmall nanoparticles below 10 nm diameter (Cornell prime dots, [C' dots]) show permeabilities correlated with high absorption in humans from primarily enhanced passive passage through tight junctions. Particles above 20 nm diameter exclusively show active transport through cells. After establishing C' dot stability in artificial gastric juice, in vivo oral gavage experiments in mice demonstrate successful passage through the body followed by renal clearance without protein corona formation. Results suggest C' dots as viable candidates for oral administration to patients with a proven pathway towards clinical translation and may generate renewed interest in examining silica as a food additive and its effects on nutrition and health.

Ultrasmall, Bright, and Photostable Fluorescent Core-Shell Aluminosilicate Nanoparticles for Live-Cell Optical Super-Resolution Microscopy.

Stochastic optical reconstruction microscopy (STORM) is an optical super-resolution microscopy (SRM) technique that traditionally requires toxic and non-physiological imaging buffers and setups that are not conducive to live-cell studies. It is observed that ultrasmall (<10 nm) fluorescent core-shell aluminosilicate nanoparticles (aC' dots) covalently encapsulating organic fluorophores enable STORM with a single excitation source and in a regular (non-toxic) imaging buffer. It is shown that fourfold coordinated aluminum is responsible for dye blinking, likely via photoinduced redox processes. It is demonstrated that this phenomenon is observed across different dye families leading to probes brighter and more photostable than the parent free dyes. Functionalization of aC' dots with antibodies allows targeted fixed cell STORM imaging. Finally, aC' dots enable live-cell STORM imaging providing quantitative measures of the size of intracellular vesicles and the number of particles per vesicle. The results suggest the emergence of a powerful ultrasmall, bright, and photostable optical SRM particle platform with characteristics relevant to clinical translation for the quantitative assessment of cellular structures and processes from live-cell imaging.