[Editors] MIT: Targeting tumors using tiny gold particles

[Elizabeth Thomson]

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MIT: Targeting tumors using tiny gold particles
--Gold nanorods could detect, treat cancer
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For Immediate Release
MONDAY, MAY. 4, 2009

Contact: Elizabeth A. Thomson, MIT News Office
E: thomson at mit.edu, T: 617-258-5402

Photo Available

CAMBRIDGE, Mass.--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. In  
March, 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 tumor tissue.

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  
that blood 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  
the tumor.

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  
treatments.

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.

Finding tumors

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 — can be detected.

Another advantage of the 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  
Madras.

The research was funded by the National Institutes of Health, the  
Whitaker Foundation and the National Science Foundation. Nanopartz  
Inc. supplied gold nanoparticles, gold nanowires and the precursor  
gold nanorods used in this work.

--END--


Written by Anne Trafton, MIT News Office
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