The ability of brain cells to take in substances from their surface is essential to the production of a key ingredient in Alzheimer's brain plaques, neuroscientists at Washington University School of Medicine in St. Louis have learned.
The researchers used a drug to shut down the intake process, known as endocytosis, in a mouse model of Alzheimer's disease. The change led to a 70 percent drop in levels of amyloid beta, the protein fragment that clumps together to form Alzheimer's plaques. Importantly, they also found that endocytosis' ability to increase amyloid beta was coupled to normal nerve cell communication called synaptic activity
Blocking endocytosis isn't a viable option for treatment because cells throughout the body, including brain cells, need endocytosis for healthy function," says first author John Cirrito, Ph.D., research instructor in neurology. "But we are starting to understand the origins of amyloid beta in more detail now, and what we’re learning is opening other options we can pursue to seek new treatments for Alzheimer's disease
While endocytosis is necessary for normal function of brain cells, Cirrito and others believe it may accidentally be causing the cells to take in the amyloid precursor protein (APP), which breaks down into amyloid beta. If so, a drug that reduces brain cells' intake of APP may help reduce amyloid beta production.
The results appear in the April 10 issue of Neuron.
Other research had shown previously that endocytosis might be important for amyloid beta production, and that amyloid beta is produced inside brain cells. In 2005, Cirrito and his colleagues linked increased communication between brain cells to higher amyloid beta levels.
Cirrito decided to test both endocytosis and brain cell activity in a coordinated fashion. He used a technique known as microdialysis that he had previously adapted for Alzheimer's research to monitor the results. In addition to allowing repeated sampling of the amyloid beta levels in the brains of live mice, the approach allows him to introduce drugs that reduce endocytosis and alter communication between brain cells.
When researchers gave mice the drug that stopped endocytosis, amyloid beta levels dropped by 70 percent. To see how much normal brain activity contributed to ongoing amyloid beta production in the absence of endocytosis, they then added a second drug that reduced brain cell communication. Amyloid beta levels did not decrease further.
When they reversed the experiment, reducing brain cell communication first, amyloid beta decreased by 60 percent. Adding the drug that stops endocytosis caused an additional small reduction in amyloid beta.
The results show that amyloid beta production requires both brain cell communication and endocytosis, but endocytosis is essential for a slightly larger share of amyloid beta. Basic nerve cell physiology may explain why.
The study focused on synapses, the region where nerve cells transmit messages by releasing chemicals from small compartments near the cell surface. To replenish those compartments, the nerve cell regularly takes them back in through endocytosis. The more active a brain cell is, the more often it has to bring these compartments back into the cell and refill them.
Endocytosis can be messy in that it brings lots of substances into the cell from the membrane it internalizes," Cirrito says. "I think APP may be an innocent bystander in this process -- it just happens to be present on the cell surface when nerve cell communication causes more endocytosis. If there is a functional reason APP has to participate in this process, no one has found it."
Activity isn't the only cause of endocytosis in brain cells. The cells have other reasons for bringing in materials through endocytosis, and this additional intake could account for the small share of amyloid beta production that requires endocytosis but doesn't need brain cell activity.
Cirrito conducted the research in the laboratories of co-senior authors David M. Holtzman, M.D., the Andrew B. and Gretchen P. Jones Professor and chair of the Department of Neurology at the School of Medicine, and neurologist-in-chief at Barnes-Jewish Hospital, and Steven J. Mennerick, Ph.D., associate professor of neurobiology and psychiatry.
Researchers already know several proteins on the surfaces of brain cells that bind to APP. They will be conducting follow-up studies to see if blocking these interactions can block APP endocytosis and reduce amyloid beta production.
Saturday, April 12, 2008
Protecting a Life-Saving Blood Product from Human Form of Mad Cow Disease
Amid concern that recipients of certain blood transfusions may risk infection with a deadly protein responsible for the human form of mad cow disease, researchers in Canada now report development of a special filter that quickly and effectively removes the protein from blood.
In addition to causing mad cow disease, these so-called prion proteins cause a variant form of the human neurological disorder, Creutzfeldt-Jakob disease. Termed variant Creutzfeldt-Jakob Disease (vCJD), its emergence triggered recent bans on exportation of beef from Europe. Variant CJD also can be transmitted in blood transfusions
“The use of the device will significantly decrease the risk of acquiring vCJD through blood transfusions,” co-author Patrick V. Gurgel, Ph.D., reported at the 235th national meeting of the American Chemical Society. The device has been approved for use in Europe “and has no competitor at the moment,” said Gurgel.
About the size of a person’s hand, the device contains a specially-designed material that recognizes and binds to prions. “This technology adds a needed layer of protection against the transmission of vCJD through blood transfusion,” said Gurgel, senior research scientist at ProMetic Life Sciences in Mont-Royal, Quebec, Canada. “Our research shows that it works.”
The new filter can remove prions from red blood cell concentrate in less than an hour. Transfusions of red blood cells go to thousands of patients with chronic anemia resulting from kidney failure, cancer, gastrointestinal bleeding, and acute blood loss resulting from trauma.
The researchers needed five years to develop the device and are now working on ways to remove prion proteins from other blood components, including plasma and plasma proteins, Gurgel said.
In previous studies, the scientists showed that the device could successfully remove prions from the blood of infected hamsters and that the disinfected blood could be injected into healthy hamsters without causing disease. More recently, the researchers demonstrated that the device can also filter healthy human blood without damaging the red blood cells and other blood components, a finding that demonstrates that the technique is safe for use on human blood, they said.
Human clinical studies using the device, called the P-Capt® Prion Capture Filter, are now underway in Europe, where it has received approval for commercialization, the scientists say. The first commercialization will be in Ireland and the United Kingdom (UK) and is expected in mid 2008, in an effort to help safeguard blood supplies, Gurgel suggested
Experts believe that vCJD is acquired from eating beef from prion-infected cattle. As in cows, the disease is characterized by a slow destruction of the brain tissue, which results in nerve damage, paralysis, and eventually death. So far, vCJD has killed at least 200 people in Europe alone. Health officials are increasingly concerned that the disease may spread elsewhere, including the United States, through blood transfusions from infected individuals.
There is currently no reliable blood test for detecting the disease or a way of destroying the infectious prion proteins in blood. As a result, blood donation centers in the U.S. have imposed restrictions on blood donations from individuals who have lived in Europe for at least five years, particularly in the UK, where most vCJD cases have occurred.
In addition to causing mad cow disease, these so-called prion proteins cause a variant form of the human neurological disorder, Creutzfeldt-Jakob disease. Termed variant Creutzfeldt-Jakob Disease (vCJD), its emergence triggered recent bans on exportation of beef from Europe. Variant CJD also can be transmitted in blood transfusions
“The use of the device will significantly decrease the risk of acquiring vCJD through blood transfusions,” co-author Patrick V. Gurgel, Ph.D., reported at the 235th national meeting of the American Chemical Society. The device has been approved for use in Europe “and has no competitor at the moment,” said Gurgel.
About the size of a person’s hand, the device contains a specially-designed material that recognizes and binds to prions. “This technology adds a needed layer of protection against the transmission of vCJD through blood transfusion,” said Gurgel, senior research scientist at ProMetic Life Sciences in Mont-Royal, Quebec, Canada. “Our research shows that it works.”
The new filter can remove prions from red blood cell concentrate in less than an hour. Transfusions of red blood cells go to thousands of patients with chronic anemia resulting from kidney failure, cancer, gastrointestinal bleeding, and acute blood loss resulting from trauma.
The researchers needed five years to develop the device and are now working on ways to remove prion proteins from other blood components, including plasma and plasma proteins, Gurgel said.
In previous studies, the scientists showed that the device could successfully remove prions from the blood of infected hamsters and that the disinfected blood could be injected into healthy hamsters without causing disease. More recently, the researchers demonstrated that the device can also filter healthy human blood without damaging the red blood cells and other blood components, a finding that demonstrates that the technique is safe for use on human blood, they said.
Human clinical studies using the device, called the P-Capt® Prion Capture Filter, are now underway in Europe, where it has received approval for commercialization, the scientists say. The first commercialization will be in Ireland and the United Kingdom (UK) and is expected in mid 2008, in an effort to help safeguard blood supplies, Gurgel suggested
Experts believe that vCJD is acquired from eating beef from prion-infected cattle. As in cows, the disease is characterized by a slow destruction of the brain tissue, which results in nerve damage, paralysis, and eventually death. So far, vCJD has killed at least 200 people in Europe alone. Health officials are increasingly concerned that the disease may spread elsewhere, including the United States, through blood transfusions from infected individuals.
There is currently no reliable blood test for detecting the disease or a way of destroying the infectious prion proteins in blood. As a result, blood donation centers in the U.S. have imposed restrictions on blood donations from individuals who have lived in Europe for at least five years, particularly in the UK, where most vCJD cases have occurred.
Promising New Nanotechnology for Spinal Cord...
Promising New Nanotechnology for Spinal Cord Injury
A spinal cord injury often leads to permanent paralysis and loss of sensation below the site of the injury because the damaged nerve fibers can't regenerate. The nerve fibers or axons have the capacity to grow again, but don’t because they're blocked by scar tissue that develops around the injury.
Northwestern University researchers have shown that a new nano-engineered gel inhibits the formation of scar tissue at the injury site and enables the severed spinal cord fibers to regenerate and grow. The gel is injected as a liquid into the spinal cord and self -assembles into a scaffold that supports the new nerve fibers as they grow up and down the spinal cord, penetrating the site of the injury.
When the gel was injected into mice with a spinal cord injury, after six weeks the animals had a greatly enhanced ability to use their hind legs and walk.
The research is published today in the April 2 issue of the Journal of Neuroscience.
"We are very excited about this," said lead author John Kessler, M.D., Davee Professor of Stem Cell Biology at Northwestern University's Feinberg School of Medicine. "We can inject this without damaging the tissue. It has great potential for treating human beings.
"Kessler stressed caution, however, in interpreting the results. "It's important to understand that something that works in mice will not necessarily work in human beings. At this point in time we have no information about whether this would work in human beings."
"There is no magic bullet or one single thing that solves the spinal cord injury, but this gives us a brand new technology to be able to think about treating this disorder," said Kessler, also the chair of the Davee Department of Neurology at the Feinberg School. "It could be used in combination with other technologies including stem cells, drugs or other kinds of interventions."
“We designed our self-assembling nanostructures -- the building blocks of the gel -- to promote neuron growth,” said co-author Samuel I. Stupp, Board of Trustees Professor of Materials Science and Engineering, Chemistry, and Medicine and director of Northwestern’s Institute for BioNanotechnology in Medicine. “To actually see the regeneration of axons in the spinal cord after injury is a fascinating outcome.
”The nano-engineered gel works in several ways to support the regeneration of spinal cord nerve fibers. In addition to reducing the formation of scar tissue, it also instructs the stem cells --which would normally form scar tissue -- to instead to produce a helpful new cell that makes myelin. Myelin is a substance that sheaths the axons of the spinal cord to permit the rapid transmission of nerve impulses.
The gel's scaffolding also supports the growth of the axons in two critical directions -- up the spinal cord to the brain (the sensory axons) and down to the legs (the motor axons.) "Not everybody realizes you have to grow the fibers up the spinal cord so you can feel where the floor is. If you can't feel where the floor is with your feet, you can't walk," Kessler said.
Now Northwestern researchers are working on developing the nano-engineered gel to be acceptable as a pharmaceutical for the Food & Drug Administration.
If the gel is approved for humans, a clinical trial could begin in several years.
"It's a long way from helping a rodent to walk again and helping a human being walk again," Kessler stressed again. "People should never lose sight of that. But this is still exciting because it gives us a new technology for treating spinal cord injury."
A spinal cord injury often leads to permanent paralysis and loss of sensation below the site of the injury because the damaged nerve fibers can't regenerate. The nerve fibers or axons have the capacity to grow again, but don’t because they're blocked by scar tissue that develops around the injury.
Northwestern University researchers have shown that a new nano-engineered gel inhibits the formation of scar tissue at the injury site and enables the severed spinal cord fibers to regenerate and grow. The gel is injected as a liquid into the spinal cord and self -assembles into a scaffold that supports the new nerve fibers as they grow up and down the spinal cord, penetrating the site of the injury.
When the gel was injected into mice with a spinal cord injury, after six weeks the animals had a greatly enhanced ability to use their hind legs and walk.
The research is published today in the April 2 issue of the Journal of Neuroscience.
"We are very excited about this," said lead author John Kessler, M.D., Davee Professor of Stem Cell Biology at Northwestern University's Feinberg School of Medicine. "We can inject this without damaging the tissue. It has great potential for treating human beings.
"Kessler stressed caution, however, in interpreting the results. "It's important to understand that something that works in mice will not necessarily work in human beings. At this point in time we have no information about whether this would work in human beings."
"There is no magic bullet or one single thing that solves the spinal cord injury, but this gives us a brand new technology to be able to think about treating this disorder," said Kessler, also the chair of the Davee Department of Neurology at the Feinberg School. "It could be used in combination with other technologies including stem cells, drugs or other kinds of interventions."
“We designed our self-assembling nanostructures -- the building blocks of the gel -- to promote neuron growth,” said co-author Samuel I. Stupp, Board of Trustees Professor of Materials Science and Engineering, Chemistry, and Medicine and director of Northwestern’s Institute for BioNanotechnology in Medicine. “To actually see the regeneration of axons in the spinal cord after injury is a fascinating outcome.
”The nano-engineered gel works in several ways to support the regeneration of spinal cord nerve fibers. In addition to reducing the formation of scar tissue, it also instructs the stem cells --which would normally form scar tissue -- to instead to produce a helpful new cell that makes myelin. Myelin is a substance that sheaths the axons of the spinal cord to permit the rapid transmission of nerve impulses.
The gel's scaffolding also supports the growth of the axons in two critical directions -- up the spinal cord to the brain (the sensory axons) and down to the legs (the motor axons.) "Not everybody realizes you have to grow the fibers up the spinal cord so you can feel where the floor is. If you can't feel where the floor is with your feet, you can't walk," Kessler said.
Now Northwestern researchers are working on developing the nano-engineered gel to be acceptable as a pharmaceutical for the Food & Drug Administration.
If the gel is approved for humans, a clinical trial could begin in several years.
"It's a long way from helping a rodent to walk again and helping a human being walk again," Kessler stressed again. "People should never lose sight of that. But this is still exciting because it gives us a new technology for treating spinal cord injury."
Drug makers chase cancer stem cells
As evidence implicating stem cells in cancer mounts, drug makers are taking notice. GlaxoSmithKline (GSK) in December formed a strategic alliance worth up to $1.4 billion with OncoMed Pharmaceuticals, of Redwood City, California. The deal gives GSK an option to license four of OncoMed's antibody candidates developed to target cancer stem cells, one of which is scheduled to enter clinical trials in June.The GSK-OncoMed pact is the first major deal focused on cancer stem cell R&D, which is undergoing explosive growth. John Bates, the director of Biopharm Reports, in Cambridge, UK, says the number of companies devoted to this research has grown from 17 in April 2007 to nearly 40 today. What's more, patents covering developments in cancer stem cells doubled to about 70 in 2007, he adds. The problem is that not everyone even believes that targeting cancer stem cells will yield therapeutic benefits.
George Schreiner, CEO with Raven Biotechnologies in San Francisco, attributes the burst of commercial interest to recent evidence of cancer stem cells in solid tumors. Scientists have suspected since the 1950s that the cells play a role in blood tumors, such as acute myeloid leukemia, but their existence in solid tumors became evident only in 2003. That's when Michael Clarke, currently associate director of Stanford University's Institute for Stem Cell and Regenerative Medicine, and his then post-doc, Mohamed Al-Hajj, claimed to find cancer stem cells in breast tumors. The cells had two markers that are now synonymous with cancer stem cells: high expression of the antigen CD44 and low expression of antigen CD24. Isolated on the basis of these markers, the human cells were cultured and introduced into immunocompromised mice. Clarke and Al-Hajj found that only a few of the cells could spawn aggressive, metastatic tumors in the animals. Those findings bolstered a theory that solid tumors arise from a small population of cancer stem cells that, like normal stem cells, have the capacity for self-renewal. Clarke and his colleague Max Wicha, the director of the University of Michigan Comprehensive Cancer Center, founded OncoMed to pursue clinical opportunities in cancer stem cells in 2004. They now sit on the company's scientific advisory board.
Findings in other laboratories have since suggested cancer stem cells exist in various tumors, including those of the brain, head and neck, prostate, and colon. Scientists further postulate that cancer stem cells resist current drug therapies and repair DNA after radiation treatment more efficiently than their differentiated, daughter cells. That explains why solid tumors often recur after treatment, Schreiner explains. "What happens is the stem cells survive and repopulate to form a new tumor," he says. "And because they transmit their resistance to daughter cells, the new tumors are much harder to treat." Some researchers now believe the only way to cure cancer is by killing the stem cells that give rise to it.
OncoMed is one of a handful of companies preparing to test compounds against cancer stem cells in the clinic. In the GSK deal, OncoMed receives an undisclosed, up-front payment in cash and equity investment, with $1.4 billion more tied to achieving milestones. Royalties on product sales would follow. OncoMed's lead candidate, a humanized monoclonal antibody (mAb) OMP-21M18, targets "a cancer stem cell pathway with broad applicability across multiple solid tumors," says Paul Hastings, the company's CEO.
Other companies preparing for clinical trials this year include Arius Research in Toronto, whose lead humanized IgG1 mAb targets a variant form of CD44 found in leukemia, breast, colon and prostate cancer cells. Also, Raven Biotechnologies has two mAbs in preclinical development: RAV17 (which targets the pancreatic assigned tumor marker PAN), which Schreiner says targets prostate as well as pancreatic cancer cells, and RAV18 (which targets ADAM-9), for colon and lung cancer. Raven is now preparing to merge with VaxGen, a San Francisco-based vaccine manufacturer, picking up needed cash reserves from a company with a depleted pipeline but plenty of manufacturing assets. Reflecting a broader trend in cancer drug development, most compounds targeting cancer stem cells are monoclonal antibodies, Bates says (see Table 1). MAbs predominate because they target antigens on the cell surface rather than processes inside the cell as small molecules do.
The chief safety concern with targeting cancer stem cells, Clarke warns, is that these mAbs might also attack normal stem cells that replenish damaged tissues. "The main thing is to ensure that we eliminate the malignant cancer stem cells only without affecting the normal stem cells," he says. "Whether we'll be able to do this is the billion dollar question that everyone wants to answer."
Meanwhile, as commercial entities grow up around it, skeptics question the validity of targeting cancer stem cells. Current thinking holds that a tiny population of stem cells can explain why cancers recur even when existing treatments kill off up to 99% of a given tumor. According to Bert Volgestein, a professor of oncology at Johns Hopkins University in Baltimore, tumors can be completely eradicated only if those small—and presumably drug-resistant—stem cell fractions are destroyed.
The tumor fraction contributed by stem cells ranges from a low of 0.1% to a high of 40%, and some reports have described tumors made entirely of stem cells. But Vogelstein also admits that if a tumor containing a large fraction of stem cells were almost completely eliminated by treatment, this would undermine the logic of targeting stem cells as the last, drug-resistant holdouts from which aggressive metastatic tumors would likely emerge refractive to treatment.
GSK's interest in OncoMed comes from a desperation "to tap into oncology space, an area in which it is particularly weak," says Sho Matsubara, an analyst with London-based Standard and Poor's Equity Research Division. Also, GSK's sales are assumed to decline in coming years, due to generic competition (Matsubara estimates a 7% drop annually for the next five years). It does have a compound of its own that may have shrunk breast tumors by attacking cancer stem cells. According to evidence described at the San Antonio Breast Cancer Symposium on December 17, six weeks' treatment with GSK's Tyverb (lapatinib), a small molecule used in conjunction with Xeloda (capecitabine) for late-stage breast cancer, slashed the number of stem cells by more than half among 30 women studied. Two-thirds of the women were reportedly cancer-free after follow-up treatment.
But others remain cautious as, in some instances, claims pointing to the existence of cancer stem cells have turned out to be wrong upon closer inspection. "More studies are needed to confirm that cancer stem cells were in fact targeted by Tyverb," Bates notes. "We need further evidence to show that cancer stem cells in humans have been fully characterized. And we need ways to demonstrate that a particular subpopulation of cells has been reduced by treatment," he notes.
Ultimately, the best evidence will come from more studies that show killing cancer stem cells improves patient survival, Bates says. For fast-moving cancers such as pancreatic tumors, the evidence may come sooner. In the case of slow-moving cancers, such as prostate, accumulating the necessary evidence could take more time, he points out.
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