Biomedical Engineering Reference
In-Depth Information
depends on the size effect, because tumor tissues have a larger intercellular
space than normal tissues, while active targeting refers to the specific
recognition between functional components of carriers and cancer cells. The
details are discussed as follows.
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5.3.2.1 Passive Targeting
Owing to their rapid growth, many tumor tissues exhibit fenestrated
vasculature and poor lymphatic drainage, thus leading to the EPR effect,
which allows nanoparticles to accumulate nonspecifically at the tumor site, as
shown in Figure 5.6. This is often referred to as passive targeting.
Nanoparticles such as HBP self-assemblies primarily depend on the size effect
to accumulate at the specific tumor tissues. In the human body, the equilibrium
is involved in pharmacokinetics between (i) elimination of the polymeric drug
delivery system from the blood by the kidneys, liver, and other organs and (ii)
extravasation of the drug out of the blood vasculature into the tumor tissues.
Polymeric delivery systems whose hydrodynamic diameters have a size
comparable to the pores of the kidney are inclined to be eliminated; by
Figure 5.6
Schematic representation of the EPR effect: passive targeting to tumor
tissue is achieved by extravasation of polymers through the increased
permeability of the tumor vasculature and ineffective lymphatic drainage.
Passively targeted polymer drug conjugates are taken up by cancer cells
through pinocytosis and processed by endosomes and lysosomes (inset).
(Reproduced from Fox et al.
42
with permission from the American
Chemical Society.)
