PNNL scientists take on cancer with isotopes

By Annette Cary, Herald staff writerAugust 29, 2010 

RICHLAND -- Researchers worldwide have access to promising and newly available medical isotopes to advance cancer treatment thanks to Pacific Northwest National Laboratory.

Both isotopes, thorium 227 and radium 223, emit alpha radiation, which holds promise to treat cancer that has spread from the main tumor. The high energy released by the alpha particles, with their short range and short half-life, can destroy cancerous cells with minimal damage to healthy tissue.

However, alpha-emitting isotopes have been expensive and difficult for researchers to obtain, limiting the development of their use in treating cancer.

"We have reversed that trend," said Darrell Fisher, leader of the isotope sciences program for the Department of Energy's national lab in Richland. "We can make it on demand and ship it anywhere."

It began shipping the isotopes June 1 for research into new drugs or other products.

The lab starts with the isotope actinium 227, which is a natural decay product of uranium 235. However, it's present in such small amounts naturally that it's been made in reactors, including Hanford's defunct Fast Flux Test Facility.

However, the actinium 227 being used for PNNL's program originally was made in France, was transferred to the oil industry and then sent to Hanford for disposal when it was no longer needed.

PNNL claimed the actinium 227, the only supply in the nation, for use in its isotopes program, which recycles and purifies unwanted radioisotopes for research use. A radioisotope is a form of a radioactive element, and they're used not only in medicine but also in industry.

The lab had a strong program in medical isotope research in the 1990s, developing a way to produce the isotope yttrium 90 from nuclear waste. The process was so successful that production of yttrium 90 was commercialized in the late '90s and no longer is done at the lab.

The isotope is used in a drug that treats lymphoma.

Since 2000, PNNL has been rebuilding its isotope program, first by providing technical help to Tri-City companies such as Isoray Medical and Advanced Medical Isotope.

It also has rejoined the DOE isotope program, doing work such as supplying strontium 90 worldwide on behalf of DOE. It's a byproduct left from the production of plutonium for nuclear weapons. PNNL supplies it for yttrium 90 production, but it also can be used to treat the wet form of macular degeneration, an eye disease.

For the lab's two new isotope products, it's borrowed Russian technology to separate thorium 227 and radium 223 from its supply of actinium 227.

"We've developed a brand new chemical separation approach for pulling these out very purely so they can be used in medicine," Fisher said.

He has been interested in the potential of radium 223 for cancer treatment since 1989, in part because it has a lot of energy and is an isotope that could be made inexpensively in a reactor. Half of its radiation decays in 11 days, which is a practical time frame for cancer treatment.

A Norwegian company also has pursued radium 223 for cancer treatment, developing and marketing the drug AlphaRadin for treatment of bone cancer that has spread from breast and prostate cancer, Fisher said. Radium seeks out bone in the body.

Now that radium 223 has been successful in treating bone cancer, there should be increased demand for research to try it on other cancers, Fisher said.

However, ways to deliver its radiation to cancer tumors, including cancer cells that have spread from the main cancer, need to be developed.

Thorium 227 can be attached to an antibody that seeks out and attaches to cancer cells to bombard them with radiation from the medical isotope.

But nanoscience may yield newer and better ways to deliver medical isotopes such as radium 223 and thorium 227, Fisher believes. One or two dozen atoms could be placed inside nanoparticles that would link up to cancer cells.

"It's the difference between a bus and a motorcycle," he said.

Instead of linking up individual isotopes to a tumor, the nanoparticle could deliver many at once, including a mix of isotope types that could include alpha radiation for killing cancer cells and gamma radiation to allow imaging of what's occurring at the tumor.

* Annette Cary: 509-582-1533; acary@tricityherald.com.

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