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Radioactive Cocaine Analogue Sheds Light on Brain
story behind the diagnostic drug that could someday lead to
a cure for Parkinson's disease has all the elements of an international
thriller: A Penn scientist flies to Asia without telling most of his colleagues.
Once there, he injects himself with a radioactive cocaine-like substance
based on a formula that he and his team of researchers have just developed.
Then he puts his head in an imaging machine -- a SPECT scanner, as it's
called -- and makes a picture of his brain.
Competing researchers around the country gnash their
teeth. The Federal Drug Administration, which has no jurisdiction over
such activities in foreign countries, fires off some testy letters to
the University, which in turn is less than amused -- especially after
it is sued by a former radiation-safety officer who claims that he was
axed for reporting that the scientist had skirted federal regulations
and University policy. (Penn argues vigorously that the officer was fired
for other reasons.)
But the Society of Nuclear Medicine hails that
cerebral self-portrait as the "image of the year." The European
Journal of Nuclear Medicine presents its annual award for Best Science
Paper to the scientist who developed the image-enhancing drug. And the
drug itself, known as TRODAT-1, appears to have the potential to play
an extremely important role in the diagnosis of Parkinson's disease and
other dopamine-related disorders -- and to offer insights into certain
cerebral differences between men and women. It has also since been approved
by the FDA.
The scientist's name is Dr. Hank F. Kung, chief of radiopharmaceutical
chemistry at Penn. TRODAT is a tropane, a close cousin of cocaine or cocaine
analogue. Like cocaine, TRODAT follows the flow of dopamine -- a chemical
messenger known as a neurotransmitter -- to the dopamine transporters
in the basal ganglia, which one researcher defines as "strategic
relay centers that help different parts of the brain coordinate the execution
of complex cognitive and motoric functions."
brain of a healthy 66-year-old man, left, shows a far higher concentration
of dopamine transporters than does the brain of a 63-year-old man
with Parkinson's disease, right.
Since Parkinson's patients
have a dramatic loss of dopamine transporters, finding a safe drug that
can illuminate them is of profound importance for diagnosing the disease.
TRODAT, which contains an atom of radioactive technetium-99m, can be imaged
by a SPECT (Single Photon Emission Computational Tomography) scanner,
which operates by emitting photons (the component of light). But unlike
the tropanes being developed by other researchers, TRODAT is cheap, safe,
and highly effective as an imaging agent.
Dr. David Mozley, associate professor of radiology and
psychiatry, has collaborated with Kung and has been using TRODAT to measure
the concentration of dopamine transporters in Parkinson's patients and
other people. While he doubts that TRODAT will ever prove to be a financial
gold mine for the University, he acknowledges that there has been an "intense
competition" to develop the drug and a "lot of prestige"
in getting it patented.
"Labeling a receptor compound with technetium has
been a Holy Grail of radiochemists for a long time," he says. "It's
a remarkably difficult feat to accomplish."
TRODAT has already attracted considerable interest
from pharmaceutical companies, though it has not yet received a patent.
According to Dr. Peter B. Kramer, director of licensing in physical sciences
at Penn's Center for Technology Transfer, the CTT has licensed the patent
rights to a company (whose identity he would not disclose) in exchange
for option payments and other considerations.
"I think TRODAT is a significant compound that
will be useful in diagnosing Parkinson's disease," says Kramer. "Early
results indicate that the drug passes through the blood-brain barrier,
even though it's been labeled with technetium, and that's a difficult
feat. Hank Kung has accomplished something quite remarkable."
"Right now, it's more or less a chicken-and-egg
situation," explains Kung. "It's very difficult for a drug company
to develop a neurodegenerative detection agent, because they could not
open up everybody's brain. Neurodegenerative disease is a very slow process,
hard to evaluate. By making this readily available, it will provide a
very useful tool for developing a drug that will fight neurodegenerative
diseases such as Parkinson's."
In addition to demonstrating TRODAT's diagnostic value
for Parkinson's disease, Mozley's current research also indicates that
men in general have slightly higher concentrations of dopamine transporters
than women, and that women have different concentrations depending on
the stage of their menstrual cycle. In fact, he says, the highest concentration
of dopamine transporters he has seen was in a woman who was still lactating,
shortly after the cessation of breast-feeding.
"We know that this receptor is the one that seems
to be the most sensitive to the effects of estrogen," he explains,
and high concentrations of the transporters appear to affect not just
cognitive and physical tasks but also mood. "We know that women who
are breast-feeding think a little bit differently," he adds. "Anecdotal
observation for millennia suggests that they're more difficult to perturb,
harder to rattle, when they're breast-feeding. And we come up with all
kinds of psychological mumbo-jumbo to explain that -- some of which is
probably true, at least at some core level, but there also are some biological
correlates of that which have not been really explored."
Mozley points out that originally, the Penn group "never
even imagined" using TRODAT to evaluate a drug that could cure Parkinson's,
and notes that the funding for its development came from the National
Institute on Drug Abuse. (TRODAT is likely to be a useful tool in studying
certain drug addictions.) He also acknowledges that TRODAT's primary use
for Parkinson's patients is as a diagnostic tool, not a cure in itself,
and that some neurologists will say "it's not going to do a bloody
thing for people."
But since in his opinion, shared by some other
neuroscientists, early intervention "not only retards the development
of symptoms but actually may slow the progression of the disease,"
TRODAT's early-diagnostic abilities could be of critical importance. Mozley
also notes that a new Brazilian drug known as Sygen is now being tested
by colleagues at Thomas Jefferson University Hospital in Philadelphia
and has shown promising results thus far. He and his Penn colleagues are
now conducting studies using TRODAT to determine whether Sygen really
does produce beneficial changes in the brain.
Some three years ago, in order to test TRODAT, Kung
flew to Korea and tried it on himself and a colleague, former Penn researcher
Dr. Hee-Joung Kim of the Asan Medical Center in South Korea. (The University
notes that "no radioactive materials were transported by Dr. Kung
to Korea.") While the notion of injecting a close relative of cocaine
into one's bloodstream sounds rather adventuresome for a highly regarded
scientist, neither Kung nor anyone else could come close to getting high
from the 20 millicuries of TRODAT.
"For a layman, it sounds very exciting," Kung
acknowledges, "but the chemical amount is probably one millionth
of what is required for a pharmaceutical effect."
By acting as his own guinea pig in a foreign country,
Kung avoided the FDA's restrictions on testing a drug on humans before
it has been proven safe. Although there is a robust debate over the merits
of testing a drug on oneself before it has been approved by the FDA, Kung's
colleagues -- and many other scientists -- believe that it is actually
a thoroughly ethical thing to do.
"For an investigator to inject himself first with
his compound," says Mozley, "is highly ethical."
That sensitive issue became even more sensitive in the
wake of the University's firing of Dr. Mark Selikson, a former radiation
safety officer, in February 1997. Selikson has since sued Penn for wrongful
dismissal, claiming that he had been fired for alerting the FDA and the
Nuclear Regulatory Commission about Kung's activities -- "utilizing
radioactive compounds for human experimentation in a manner that violated
federal regulations and University policy," in the words of the suit.
The suit also charged that Penn, "seeking to protect its pecuniary
interest in the fruits of the unlawful experimentation, responded by leveling
a number of baseless allegations against Dr. Selikson" in order to
justify the firing.
Penn strongly disputes the claim that he was
fired for whistle-blowing, and says that Selikson was dismissed for other
reasons, most of which had to do with his having allegedly defied University
policy by doing consulting work for an outside firm and using University
resources while doing so.
"We believe [the lawsuit] is without merit,"
said Kenneth Wildes, Penn's director of news and public affairs, "and
we will defend [the firing of Selikson] vigorously."
Kung describes himself as "sort of a victim"
of Selikson's lawsuit: "It had nothing to do with me, but I got dragged
But the medical possibilities of TRODAT, he says, should
make up for all the trouble.
"We are quite happy where we are," he said
recently, "and I'm hopeful that this agent will be commercially available
and will help various types of patients. And that's what makes all the
headaches and troubles worthwhile in the end."
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Gazette Last modified 2/17/99