FOR IMMEDIATE
RELEASE
6/3/2004
CONTACT: Dian Land, (608) 263-9893,
HYPERLINK "mailto:dj.land@hosp.wisc.edu" dj.land@hosp.wisc.edu
RESEARCHERS REPORT MAJOR ADVANCE IN GENE THERAPY TECHNIQUE
MADISON — Despite a roller-coaster ride of ups and downs during
the past 15 years, gene therapy has continued to attract many of the
world’s brightest scientists. They are tantalized by the enormous
potential that replacing missing genes or disabling defective ones
offers for curing diseases of many kinds.
One group, consisting of researchers from the University of
Wisconsin Medical School, the Waisman Center at UW-Madison and Mirus
Bio Corporation of Madison, Wis., now reports a critical advance
relating to one of the most fundamental and challenging problems of
gene therapy: how to safely and effectively get therapeutic DNA
inside cells.
The Wisconsin scientists have discovered a remarkably simple
solution. They used a system that is virtually the same as
administering an IV (intravenous injection) to inject genes and
proteins into the limb veins of laboratory animals of varying sizes.
The genetic material easily found its way to muscle cells, where it
functioned as it should for an extended period of time.
“I think this is going to change everything relating to gene
therapy for muscle problems and other disorders,” says Jon Wolff, a
gene therapy expert who is a UW Medical School pediatrics and
medical genetics professor based at the Waisman Center. “Our
non-viral, vein method is a clinically viable procedure that lets us
safely, effectively and repeatedly deliver DNA to muscle cells. We
hope that the next step will be a clinical trial in humans."
Wolff conducted the research with colleagues at Mirus, a
biotechnology company he created to investigate the gene delivery
problem. He will be describing the work on June 3 at the annual
meeting of the American Society of Gene Therapy in Minneapolis, and
a report will appear in a coming issue of Molecular Therapy. The
research has exciting near-term implications for muscle and blood
vessel disorders in particular.
Duchenne’s muscular dystrophy, for example, is a genetic disease
characterized by a lack of muscle-maintaining protein called
dystrophin. Inserting genes that produce dystrophin into muscle
cells could override the defect, scientists theorize, ensuring that
the muscles with the normal gene would not succumb to wasting.
Similarly, the vein technique can be useful in treating peripheral
arterial occlusive disease, often a complication of diabetes. The
disorder results in damaged arteries and, frequently, the subsequent
amputation of toes.
What’s more, Wolff says, with refinements the technique has the
potential to be used for liver diseases such as hepatitis, cirrhosis
and PKU (phenylketonuria).
In the experiments, the scientists did not use viruses to carry
genes inside cells, a path many other groups have taken. Instead,
they used “naked” DNA, an approach Wolff has pioneered. Naked DNA
poses fewer immune issues because, unlike viruses, it does not
contain a protein coat (hence the term “naked”), which means it
cannot move freely from cell to cell and integrate into the
chromosome. As a result, naked DNA does not cause antibody responses
or genetic reactions that can render the procedure harmful.
Researchers rapidly injected “reporter genes” into a vein in
laboratory animals. Under a microscope, these genes brightly
indicate gene expression. A tourniquet high on the leg helped keep
the injected solution from leaving the limb.
“Delivering genes through the vascular system lets us take
advantage of the access blood vessels have — through the capillaries
that sprout from them — to tissue cells,” Wolff says, adding that
muscle tissue is rich with capillaries. Rapid injection forced the
solution out of the veins into capillaries and then muscle tissue.
The injections yielded substantial, stable levels of gene
activity throughout the leg muscles in healthy animals, with minimal
side effects. “We detected gene expression in all leg muscle groups,
and the DNA stayed in muscle cells indefinitely,” notes Wolff.
In addition, the scientists were able to perform multiple
injections without damaging the veins. “The ability to do repeated
injections has important implications for muscle diseases since to
cure them, a high percentage of therapeutic cells must be
introduced,” he says.
The researchers also found that they could use the technique to
successfully administer therapeutically important genes and
proteins. When they injected dystrophin into mice that lacked it,
the protein remained in muscle cells for at least six months.
Similar lasting power occurred with the injection of erythropoietin,
which stimulates red blood cell production.
Furthermore, in an ancillary study, the researchers learned that
the technique could be used effectively to introduce molecules that
inhibit — rather than promote — gene expression, a powerful new
procedure called RNA interference.
“This could be very useful if you want to down-regulate a protein
that’s causing a muscle disorder, such as with myotonic dystrophy,”
says Wolff.
In the late 1980s, Wolff and his UW-Madison colleagues surprised
the scientific world with their discovery that they could get genes
to express in muscle cells simply by injecting naked DNA into rodent
muscle. The Wisconsin Alumni Research Foundation (WARF) licensed the
technology to Vical, a California biotechnology company.
Once Wolff created Mirus, a local company, he and his colleagues
turned their attention to the vascular system, a conduit to multiple
leg and arm muscles they felt would work more efficiently than
direct injection into muscle. WARF licensed the vascular technique
to Mirus, which now holds the patent and continues to commercialize
the technique.
In their first studies, the researchers focused on arteries, but
then began to concentrate on veins. “Injecting any substance into
arteries carries a degree of risk since, unlike veins, only one
artery feeds a whole limb,” notes Wolff.
In a related procedure, they experienced excellent results with
high-pressure injection of genes into the tail veins of rodents, a
technique that yielded extensive gene expression in the animals’
livers.
“We think the genes traveled from the capillaries through the
relatively large holes that exist in liver cells,” Wolff says,
adding that the technique has become a successful research tool for
many laboratories around the world.
“For delivering genes to limb muscles, the vein approach is so
simple,” he says. “We never expected it to work so well.”
Collaborating on the study were James Hagstrom, Julia Hegge, Mark
Nobel, David Lewis and Hans Herweijer, from Mirus Bio; and Guofeng
Zhang and Vladimir Budker, from the Waisman Center.