Cell

Nanotechnology

Biology

Pharmacokinetics

Internalization

Radiochemistry

Chemistry

Materials science

In vitro

Biodistribution

Labelling

Cell biology

Extracellular vesicles

Biochemistry

Medicine

Pharmacology

Advanced Drug Delivery Reviews

There is a large interest in developing nanoparticles and extracellular vesicles for delivery of therapeutics or imaging agents. Regulatory approval of such products requires knowledge about their biodistribution, metabolism and excretion. We here discuss possibilities and challenges of methods used for such studies, which most often are performed after labelling with radioactive isotopes or fluorescent molecules. It is important to evaluate if the labelled and unlabeled products can be expected to behave similarly in the body. Furthermore, one needs to critically consider whether the labels are still associated with the product at the time of analyses. We discuss advantages and disadvantages of different imaging modalities such as PET, SPECT, MRI, CT, ultrasound and optical imaging for whole-body biodistribution, and describe how to estimate the amount of labelled product in harvested organs and tissue. Microscopy of cells and tissues and various mass spectrometry methods are also discussed in this review.

Biodistribution, pharmacokinetics and excretion studies of intravenously injected nanoparticles and extracellular vesicles: Possibilities and challenges