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Nanoparticles Block Radiation Damage

May 7, 2010
Written by: , Filed in: Nuclear Medicine
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Tiny particles covered with melanin and injected into the body may protect bone marrow from damage during radiation therapy for cancer, judging from the results of experiments on mice.

Scientists at Albert Einstein College of Medicine of Yeshiva University in New York described their research in the International Journal of Radiation Oncology•Biology•Physics.

Melanin, the pigment that gives skin and hair its color, also protects against radiation. So the researchers coated incredibly tiny particles of sand, just 20 nanometers in diameter (a sheet of paper is about 100,000 nanometers thick) with several layers of synthesized melanin pigments.

The particles had to be small so they would not get trapped by the lungs, liver, or spleen. When injected into mice, they successfully lodged in the bone marrow.

“A technique for shielding normal cells from radiation damage would allow doctors to administer higher doses of radiation to tumors, making the treatment more effective,” said Ekatherina Dadachova, PhD, senior author of the study. She is associate director of nuclear medicine and of microbiology and immunology and the Sylvia and Robert S. Olnick Faculty Scholar in Cancer Research at Einstein College.

“We wanted to devise a way to provide protective melanin to the bone marrow,” Dr. Dadachova said. “That’s where blood is formed, and the bone-marrow stem cells that produce blood cells are extremely susceptible to the damaging effects of radiation.”

The researchers injected the melanized nanoparticles into one group of mice, then exposed those mice and a second, noninjected group of mice to whole-body radiation. For the next 30 days, researchers checked the mice’s blood for signs of bone marrow damage, such as a reduced count of white blood cells and platelets.

The melanin-protected mice fared much better. Ten days after irradiation, for example, platelet levels had dropped by 60 percent in untreated mice but only 10 percent in mice that had received the nanoparticles.

In a second experiment, researchers determined that the melanized nanoparticles protected the bone marrow without also infiltrating and protecting tumors.

Arturo Casadevall, MD, PhD, is professor of medicine and of microbiology and immunology and the Leo and Julia Forchheimer Chair in Microbiology and Immunology at Einstein College and a coauthor of the study.  He said:

The ability to protect the bone marrow will allow physicians to use more extensive cancer-killing radiation therapies, and this hopefully will translate into greater tumor response rates.

In previously published research, Dr. Dadachova and colleagues showed how melanin’s radiation protection works. Melanin, they found, helps prevent the formation of free radicals (atoms or molecules with single unpaired electrons in an outer shell; they’re highly reactive and can cause chemical damage within the body). Melanin also scavenges free radicals that do form.

The study’s authors said melanin might be able to shield other radiation-sensitive body tissues as well. Dr. Dadachova said clinical trials on humans could begin within three years. She said melanized nanoparticles also might be able to protect workers cleaning up after a nuclear accident, astronauts exposed to radiation in space, or even the general public following a nuclear attack.

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