Intracellular Delivery of Colloidal Drug Aggregates

Donders, Eric (1, 2); Ganesh, Ahil (1,2); Shoichet, Brian (3); Shoichet, Molly (1,2,4)

  1. Department of Chemical Engineering and Applied Chemistry, University of Toronto

  2. Institute of Biomaterials and Biomedical Engineering, University of Toronto

  3. School of Pharmacy, University of California, San Francisco

  4. Department of Chemistry, University of Toronto

Some small molecule drugs form colloidal aggregates above a critical aggregation concentration. This behaviour has been traditionally seen as a nuisance, as it causes false positive hits in enzyme inhibition assays. Furthermore, colloid-bound drugs are unable to pass through cellular membranes, leading to suboptimal cytotoxicity in cell-based assays. However, we hypothesized that these colloidal drug aggregates could be useful for drug delivery owing to their high drug content. To address the inability of colloids to enter cells, we functionalized their surface with targeting proteins, then examined their cell uptake and cytotoxicity.
Colloidal drug aggregates of clinically relevant cancer drugs such as fulvestrant were formulated by solvent-shift self-assembly, and then coated with different macromolecules including amphiphilic polymers and proteins such as transferrin or trastuzumab. These stabilized colloidal drug aggregates were characterized by dynamic light scattering and transmission electron microscopy. We then assessed the cell uptake of the colloids by flow cytometry, intracellular distribution of colloids using confocal microscopy, and cytotoxicity of the colloids against relevant cancer cell lines.
We found that colloidal drug aggregates with size ranging from 100-300 nm and dispersity less than 0.2 could be reliably formulated using our method. These formulations were stable against precipitation and growth in buffer at physiological temperature. Colloids that were functionalized with targeting proteins were taken up to a greater extent than colloids coated with non-targeting moieties. Through labelling of specific cell organelles, we found that internalized colloids were trafficked through the endo-lysosomal pathway. Ultimately, colloidal formulations that were endocytosed were also more cytotoxic than non-endocytosed formulations.
The self-assembly of active pharmaceutical ingredients to form colloidal aggregates presents an opportunity to deliver drugs using these constructs. We investigate the interactions with this novel class of materials with cells and demonstrate methods for enhancing their intracellular delivery.