Effects of particle uptake, encapsulation, and localization in cancer cells on intracellular applications

• Endocytosis is affected by cell function, and likely malignancy.
• Particles endocytose into cells with reduced cell–cell interactions.
• Endocytosed particles may become unencapsulated by membranes with time.
• Endocytosis can safely be used to internalize particles for tracking.

Endocytosis is a normal process in living cells, often used to internalize drug-containing particles and probes for intracellular mechanics. The cell type, and especially malignancy, may affect particle internalization and transport. Specifically, membrane-encapsulation following internalization can affect particle interaction with the cell interior. Hence, particle-tracking measurements that reveal intracellular mechanics and dynamics require determination of effects of encapsulation. Here, we compare closely related, breast-cancer cell lines with high- and low-metastatic potential (MP) and benign, control cells. We evaluate time-dependent particle internalization, localization with endocytotic-pathway organelles, and membrane encapsulation at 2, 6, 24, and 48 h after initial cell exposure to particles. High MP cells internalize particles more rapidly and in larger amounts than low MP and benign cells. Moreover, while only cells at the edge of two-dimensional colonies of benign cells internalized particles, all cancer cells uniformly internalize particles. Particles mostly colocalize with late endosomes (>80%), yet surprisingly, overall membrane encapsulation decreases with time, indicating release into the cytoplasm; encapsulation at 48 h is <35% in all three cell types. We discuss implications to drug delivery and show that encapsulation does not significantly affect intracellular particle-tracking experiments, showing the applicability of endocytosis.