It has long been known that heat is an
effective weapon against tumor cells. However, it's difficult to heat
patients' tumors without damaging nearby tissues.
Now, MIT researchers have developed tiny gold particles that can home
in on tumors, and then, by absorbing energy from near-infrared light
and emitting it as heat, destroy tumors with minimal side effects.
Such particles, known as gold nanorods, could diagnose as well as treat
tumors, says MIT graduate student Geoffrey von Maltzahn, who developed
the tumor-homing particles with Sangeeta Bhatia, professor in the
Harvard-MIT Division of Health Sciences and Technology (HST) and in the
Department of Electrical Engineering and Computer Science, a member of
the David H. Koch Institute for Integrative Cancer Research at MIT and
a Howard Hughes Medical Institute Investigator.
Von Maltzahn and Bhatia describe their gold nanorods in two papers
recently published in Cancer Research and Advanced Materials.
von Maltzahn won the Lemelson-MIT Student Prize, in part for his work
with the nanorods.
Cancer affects about seven million people worldwide, and that number is
projected to grow to 15 million by 2020. Most of
those patients are
treated with chemotherapy and/or radiation, which are often effective
but can have debilitating side effects because it's difficult to target
With chemotherapy treatment, 99 percent of drugs administered typically
don't reach the tumor, said von Maltzahn. In contrast, the gold
nanorods can specifically focus heat on tumors.
"This class of particles provides the most efficient method of
specifically depositing energy in tumors," he said.
Wiping out tumors
Gold nanoparticles can absorb different frequencies of light, depending
on their shape. Rod-shaped particles, such as those used by von
Maltzahn and Bhatia, absorb light at near-infrared frequency; this
light heats the rods but passes harmlessly through human tissue.
In a study reported in the team's Cancer Research paper, tumors in mice
that received an intravenous injection of nanorods plus near-infrared
laser treatment disappeared within 15 days. Those mice survived for
three months with no evidence of reoccurrence, until the end of the
study, while mice that received no treatment or only the nanorods or
laser, did not.
Once the nanorods are injected, they disperse uniformly throughout the
bloodstream. Bhatia's team developed a polymer coating for the
particles that allows them to survive in the bloodstream longer than
any other gold nanoparticles (the half-life is greater than 17 hours).
In designing the particles, the researchers took advantage of the fact
0blood vessels located near tumors have tiny pores just large
enough for the nanorods to enter. Nanorods accumulate in the tumors,
and within three days, the liver and spleen clear any that don't reach
During a single exposure to a near-infrared laser, the nanorods heat up
to 70 degree Celsius, hot enough to kill tumor cells. Additionally,
heating them to a lower temperature weakens tumor cells enough to
enhance the effectiveness of existing chemotherapy treatments, raising
the possibility of using the nanorods as a supplement to those
The nanorods could also be used to kill tumor cells left behind after
surgery. The nanorods can be more than 1,000 times more precise than a
surgeon's scalpel, says von Maltzahn, so they could potentially remove
residual cells the surgeon can't get.
The nanorods' homing abilities also make them a promising tool for
diagnosing tumors. After the particles are injected, they can be imaged
using a technique known as Raman scattering. Any tissue that lights up,
other than the liver or spleen, could harbor an invasive tumor.
In the Advanced Materials paper, the researchers showed they could
enhance the nanorods' imaging abilities by adding molecules that absorb
near-infrared light to their surface. Because of this surface-enhanced
Raman scattering, very low concentrations of nanorods - to only a few
parts per trillion in water [gf1]- can be detected.
Another advantage of=2
0the nanorods is that by coating them with
different types of light-scattering molecules, they can be designed to
simultaneously gather multiple types of information - not only whether
there is a tumor, but whether it is at risk of invading other tissues,
whether it's a primary or secondary tumor, or where it originated.
Bhatia and von Maltzahn are looking into commercializing the
technology. Before the gold nanorods can be used in humans, they must
undergo clinical trials and be approved by the FDA, which von Maltzahn
says will be a multi-year process.
Other authors of the Advanced Materials paper are Andrea Centrone,
postdoctoral associate in chemical engineering; Renuka Ramanathan,
undergraduate in biological engineering; Alan Hatton, the Ralph Landau
Professor of Chemical Engineering; and Michael Sailor and Ji-Ho Park of
the University of California at San Diego.
Park and Sailor are also authors of the Cancer Research paper, along
with Amit Agrawal, former postdoctoral associate in HST; and Nanda
Kishor Bandaru and Sarit Das of the Indian Institute of Technology
The research was funded by the National Institutes of Health, the
Whitaker Foundation and the National Science Foundation.
supplied gold nanoparticles, gold nanowires and the precursor gold
nanorods used in this work.
ScienceDaily (May 5, 2009) —
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