capsules could one day be used to deliver cancer drugs
with pinpoint accuracy Reported by RACHEL NOWAK, MELBOURNE
NANOSCALE polymer capsules could one day be used to
deliver chemotherapy direct to tumours, leaving adjacent
The capsules would be designed to rupture when heated
by a low-energy laser pulse, delivering their payload
right where it is needed. Anti-cancer drugs would be
more effective, and the side effects less severe, if
they could home in on a tumour and be delivered in a
single burst. This would allow the drug to reach the
concentrations needed to kill cancer cells, while minimising
damage to surrounding tissue.
So Frank Caruso and his team
at the University of Melbourne, Australia, are developing
an ingenious way of doing this, they report in the
journal Advanced Materials (vol 16, p 2184). Their
trick is to enclose the drug in polymer capsules that
are peppered with gold nanoparticles and attached
to tumour-seeking antibodies. When injected into the
bloodstream, the capsules will concentrate inside
tumours. When enough capsules have gathered there,
a pulse from an near-infrared laser will melt the
gold, which strongly absorbs near-infrared wavelengths.
This will rupture the plastic
capsules and release their contents. To make the capsules,
the researchers repeatedly add the polymer to a suspension
of drug particles around 1 micrometre wide until the
polymer forms multi-layered spheres containing the
They then add gold particles
around 6 nanometres in diameter to the mix, which
become embedded in the polymer. Finally they add a
lipid, which forms an outer layer, and the antibodies
that will target tumour cells (see Graphic). In lab
tests, the capsules were ruptured by a 10-nanosecond
pulse from a near-infrared laser. While bulk gold
has a melting point of 1064 °C, gold nanoparticles
melt at far lower temperatures- between 600 and 800
°C. The brief pulse was enough to melt the nanoparticles,
which could be seen under an electron microscope to
swell to up to 50 nanometres in diameter as they coalesced.
The pulse was too short to damage the contents of
the capsule. Caruso showed that a lysozyme enzyme
did not lose its activity after being released from
the capsules in this way.
In clinical use, the laser
would be able to penetrate a few millimetres of tissue.
It could be shone through the skin, or be beamed inside
the body via an endoscope. The 100 millijoules per
square centimetre of infrared energy that would be
needed to rupture the capsules is well within safety
"It's way below that used
to remove tattoos," Caruso says.
Clinical use is still some
way off, however, and even animal tests are several
years away. The next refinement will be to make the
capsules a lot smaller. Caruso plans to shrink them
from around 1 micrometre in diameter to a couple of
hundred nanometres by starting with smaller drug particles.
Caruso thinks his team's key innovation has been in
making the capsules react to a laser that is harmless
to the body. Gold usually absorbs light from the visible
to ultraviolet part of the electromagnetic spectrum,
which can burn tissue. But electromagnetic interactions
between the gold nanoparticles in the capsules change
the properties of the metal, making it absorb light
from the near infrared instead. This light is the
most transparent to tissue. Observers are impressed.
"This work is tremendously
cool," says Matt Trau of the Nanotechnology and
Biomaterials Centre at the University of Queensland
in Brisbane. Photo-activating the capsules without
damaging surrounding tissue is the particularly innovative
part, he says.
Link : http://www.newscientist.com