* 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 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
"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)