Avid amyloid tracer hits target in Alzheimer's study

Sun Jul 11, 2010 7:30pm EDT

* Radioactive dye AV-45 lights up amyloid in brain-study

* Could be used with PET scans to detect early Alzheimer's

By Julie Steenhuysen

CHICAGO, July 11 (Reuters) - A new radioactive dye for PET scans showed that the same bits of a toxic protein that light up in the brain of people with Alzheimer's disease are present in an autopsy after they die, U.S. researchers said on Sunday, a finding that could lead to a new way to detect the disease at an earlier stage.

The study of Avid Radiopharmaceuticals' radioactive tracer AV-45 compared brain scans of people at the end of their lives with autopsy results after they died.

It showed that the dye is sticking to the right clumps of a protein called beta amyloid in the brain, researchers said at the Alzheimer's Association International Conference in Honolulu.

"The results are very encouraging. What they show is overall there is a very nice statistically significant correlation between how bright the scan is and how much amyloid there is at autopsy," said Dr. Michael Weiner of the University of California San Francisco, who has seen the results but is not involved in the study.

"There are some areas where there was a lot of amyloid on the scan and there was a lot of amyloid on the autopsy," said Weiner, who leads the National Institute on Aging's Alzheimer's Disease Neuroimaging Initiative, a five-year, $60 million study looking for early signs of Alzheimer's disease.

"This is certainly an important step toward the validation of AV-45 as a biomarker," he said in an interview.

Only an autopsy can confirm that a person has Alzheimer's disease. Short of that, doctors diagnose Alzheimer's by excluding other potential causes of memory loss, such as stroke, tumors and heavy drinking. They also can administer simple paper-and-pencil tests.

But several teams are looking for biological markers such as brain volume or measurements of proteins in spinal fluid to detect the disease early.

Dr. Reisa Sperling of Brigham and Women's Hospital in Boston, who has seen the results but did not take part in the autopsy study, said the results were not perfect but did show a high correlation between the presence of amyloid on the PET scan and amyloid in the brain.

"I think the evidence is convincing that they are binding fibular forms of the amyloid," Sperling said in an interview.

Academic researchers have been mixing up a different radioactive tracer called Pittsburgh Compound B or PIB to do similar studies for several years but the Avid tracer, also known as Florbetapir F18, is the first with the potential to be widely used to see amyloid plaques linked with Alzheimer's.

The difference is that PIB uses carbon 11 as its radioactive tracer, which has a half-life of just 20 minutes. That means it has to be made in a facility with a cyclotron, a kind of particle accelerator, then quickly injected into a patient. AV-45 uses fluoride 18, which has a two-hour half-life, long enough to be made at a different location and transported to imaging centers.

So far, Avid, a privately held Philadelphia company backed by Pfizer (PFE.N) and Eli Lilly (LLY.N), is about a year ahead in developing the tracer but larger rivals General Electric (GE.N) and Bayer (BAYGn.DE) also have fluoride 18 tracers in late-stage clinical trials.

The companies think the global market for the tracer could be worth anywhere from $1 billion to $5 billion but a lot of that depends on whether drug companies succeed in developing a successful treatment for Alzheimer's disease.

"I think there will be demand but it won't change the landscape for patients until we have something you can do about knowing you have amyloid," Sperling said.

Current Alzheimer's drugs only treat symptoms. So far no drugs can change the course of Alzheimer's, a mind-robbing form of dementia that affects more than 26 million people globally.

(Editing by Bill Trott)

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