“9.61x6.69” b2815 Tissue Engineering and Nanotheranostics
Delivering Nanoparticles to Cancer Cells 219
In addition to penetrating and destroying tumor cells, nanoparti
cles within a cell can readily be located externally, either by magnetics
or by photons emitted by the particle. In this way, nanoparticles can
image tumors and thus assist in surgery and/or radiation.
Imaging with nanoparticles is often conducted using quantum
dots and nanoshells. Quantum dots are small particles no more than
10 nm in major dimension and nanoshells are gold covered nanopar
ticles. Gold nanoparticles can pass through the blood brain barrier.^1
Small magnetic nanoparticles (<30 nm) can have their magnetism
blocked so that they are no longer magnetic, but then become mag
netic when in a magnetic field. Such particles are said to be “super
paramagnetic”.^46 This blocking of the magnetism prevents the
particles from clustering together before they reach a tumor target.
Despite the promising observations in the foregoing paragraphs,
there is still not an effective and reliable method for getting nano
particles into the cells of tumors. Although the use of nanoparticles
to treat tumors is believed to have some advantages over conven
tional chemotherapy the difficulties with chemotherapy are also
inherited by the injection of therapeutic nanoparticles into the blood
stream.
The principal source of the difficulty is the vasculature (blood ves
sel geometry) leading up to, surrounding, and supplying tumors.
Tumor blood vessels have structural abnormalities with evidence of
uncontrolled growth. Some have even described the tumor vascula
ture as “architectural anarchy”.^11
Most tumor cells with their rapid growth are oxygen deprived.
Therefore they recruit blood vessels which in turn tend to increase
in diameter to accommodate the demand for blood supply. Large
diameter blood vessels, however, have high back pressure keeping
the supply of therapeutic chemicals and particles from reaching all
the tumor cells.11,47–48
In addition to these structural deficiencies of the vasculature the
blood vessels themselves can become malignant. They can leak,^11
again allowing many malignant cells to escape therapy.
There are other difficulties with blood injected nanoparticles:
(1) The particles are quickly removed from the blood vessels47–48;
