Tumor-specific drug release through controlled endosomal escape
Protein-based drugs must be transported into cells in a way
that prevents their immediate degradation. A new approach is intended to
ensure that they remain intact only in certain cells, such as cancer
cells. In the journal Angewandte Chemie, a Japanese research team
has introduced a nanocarrier that can “escape” from endosomes before its
cargo is destroyed there. This ability to escape is only triggered
within the endosomes of certain tumor cells.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
The uptake of nanocarriers into cells occurs by
endocytosis: when a nanocarrier lands on the cell surface, the cell
membrane folds in and encloses it in a bubble, called an endosome, which
then drifts into the cell interior. In its late phase, the endosome
merges with lysosomes that contain enzymes, forming an endolysosome.
Within this structure, the enzymes break down both material from the
body and foreign material. A protein-based drug can only become active if it
“escapes” the endolysosome before being broken down. This is known as
“endosomal escape”. Some nanocarriers can open the endo/lysosomal
membrane and thus have endosomal escape ability.
Led by Kazunori Kataoka and Horacio Cabral, the team aims
to take this a step further by producing nanocarriers for which
endosomal escape is only triggered when they enter very specific cells,
such as tumor cells. This would protect healthy cells. The researchers
exploit the fact that different types of cells have very different
endolysomomal enzyme activities. For example, the activity of the
protease cathepsin B (CTSB) is especially high in cancer cells.
With the use of special fluorescence probe molecules, the
team from The University of Tokyo and the Kawasaki Institute of
Industrial Promotion initially studied CTSB activity and protein
degradation in endosomes. They determined that in cancer cells with
highly acidic endosomes, CTSB activity is already very high in their
early phase—significantly before protein degradation ramps up. The
researchers take advantage of this time window by using nanocarriers
whose endosomal escape ability is triggered by the CTSB in cancer cells.
The team constructed poly(ethylene glycol)-based
nanocarriers with diaminoethane groups capable of “tearing open”
endo/lysosomal membranes. Using a linker, they then attached antibodies
to act as a model for a protein drug. The nanocarrier shields the
“tearing tools” so that they are initially inactive. The linker is
designed to be split by the CTSB in the endolysosomes. This separates
the cargo from the carrier, activating the tearing tools. They open the
endo/lysosomal membrane and release intact antibodies into the cell
interior—but only in tumor cells that have elevated endosomal CTSB
activity.
This method could represent a new strategy for the
cell-specific release of drugs through stimulus-responsive nanocarriers
with controlled endosomal escape.
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About the Author
Dr Horacio Cabral is an Associate Professor at The
University of Tokyo with appointments in Bioengineering and Materials
Engineering. His main specialty is biomaterials and drug delivery, with
a major focus on developing innovative therapies for intractable
diseases.
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