Biomedical Engineering Reference
In-Depth Information
instance, delivery systems make it possible to target therapeutic or contrast
agents directly to the desired organ or tissue using nanovectors. They typically
consist of a core decorated on the surface with targeting molecules and/
or solubilising agents and bearing inside therapeutic or imaging payloads
(Fig. 3.1).
Targeting unit
Drug moiety
Solubilising unit
Contrast agent
Figure 3.1
Schematic representation of nanovectors. See also Colour Insert.
They are, in fact, engineered to release the loaded units after having
reached the target and to carry out their activity with decreased side
effects. The recognition units are generally molecules, which are recognised
by receptors expressed (or in a favourable case overexpressed) on the
cell surface in tumour tissues. The targeting can be driven by an active
recognition, due to the presence of a special unit (active targeting), but can
also happen passively, because natural cellular uptake is, in this case, strictly
related to enhanced permeability and retention effect (EPR). EPR concerns
tumour angiogenesis, where blood vessels bear more numerous and larger
fenestrations than in normal tissues, because of the demands of a rapid
growth. The endothelium of cancer blood vessels is, in fact, characterised by
the presence of few pericytes and smooth muscle cells, with a consequent
different morphology of the vessel walls.
2
Moreover, in tumour tissue there
is usually a lack of lymphatic vessels, and these two characteristics, together
Search WWH ::
Custom Search