Tag Archives: browne

Understanding migraines: The blind leading the…err…rats

Chances are that you have either suffered from migraine yourself or have a family member or close friend who have, after all about 1 in 8 of us will suffer from migraine at some stage in our lifetime, and some sufferers experience repeated debilitating episodes over many years . While headache on one side of the brain is typical other symptoms such as nausea are very common, indeed in some migraine victims nausea is the primary symptom of the disorder.  Through a combination of studies in animals and clinical research using techniques such as fMRI and PET scans scientists have learned a lot in recent years about what happens before and during migraine episodes but we do not yet fully understand what ultimately causes the attacks, and debate rages over the relative importance of some mechanisms originating deep in brain regions such as the hypothalamus and others that start in membranes that surround the brain, (1,2).  Current treatments can help prevent migraine, reduce suffering and hasten recovery they do not work for all patients, and a better understanding of what exactly is happening before and during a migraine attack will aid the development of really effective treatments and preventative measures.  A study published in Nature Neuroscience combines clinical research with studies of rats to provide clues about a key characteristic of migraines that has until now remained unexplained, the exacerbation of the pain experienced by sufferers by light (3).

The team, lead by Rami Burnstein of Beth Israel Deaconess Medical Centre in Boston, decided to concentrate of the role of a particular subset of nerve cells in the retina known as intrinsically photosensitive retinal ganglion cells (ipRGCs) which they knew from previous mouse research to be involved in eye functions that are not image forming, such as setting the biological clock to the day night cycle.  The ipRGCs are stimulated by light both indirectly via the rods and cones and directly through a pigment called melanopsin that they themselves contain.  In order to discover if the ipRCGs are important to light sensitivity in migraine they performed a very neat clinical study involving 20 blind patients who also suffered from migraine. Six of these patients lacked any light perception due to removal of their eyes or damage to the optic nerve, while in the remaining 14 the damage to the eyes was less total, affecting the rods and cones but not ipRGCs, so that while they were unable to see images they could detect light. The results were clear, blue and grey light made the headaches of those who retained light sensitivity worse, while having no effect on the six blind individuals who lacked light perception.

Determining that the ipRGCs are involved in the exacerbation of migraine headaches by light is of course only part of the story, and Professor Burnstein’s team next turned to tracing the nerve pathways that are responsible for the increased pain, knowledge that might help to develop new treatments.  This they could not do in human subjects because the available imaging techniques do not have the precision to determine the connections between individual neurons.  In a series of studies they injected labels including Green Fluorescent Protein into particular areas of the eyes and brain, and in some cases even individual nerve cells, of anesthetized rats with and followed the path of the neurons.  They were also able to use tiny electrodes to record the effect of light on the firing of individual nerves in the brain, something that cannot yet be done in human subjects. An exciting observation was that the ipRCGs connected to cells in a region of the brain known as the posterior thalamus, itself part of the trigeminovascular pathway that is strongly implicated in migraine headache through transmission of nerve signals from the irritated outer brain membranes to the deep brain. When they examined the electrical activity of these cells they discovered that the majority of the cells within the posterior thalamus that are involved in mediating migraine pain are also light sensitive.  Finally they demonstrated that the light-sensitive pain-mediating neurons of the posterior hypothalamus connect to nerve cells in several regions of the somatosensory region of the cortex, an intriguing discovery since abnormalities in this region have previously been seen in migraine patients. This discovery is likely to encourage scientists to study the role of the somatosensory cortex in migraine in more detail.

So how important is this study? Well it’s unlikely that this discovery will lead to any treatment breakthrough in the immediate future, though the discovery that grey light can exacerbate migraine headache is new and may help patients to avoid it.  Despite a perhaps natural tendency for the news media to look for “breakthroughs” the majority of scientific papers published are like this one, providing valuable new insights into biology that contribute to our overall understanding of how biological systems work and happens when they go awry but not indicating an easy fix.  I’ve no doubt that this and many similar basic science studies will contribute to better treatments for migraine in the future, but perhaps not tomorrow!

Regards

Paul Browne

1)      Olesen J. et al “Origin of pain in migraine:evidence for peripheral sensitization” The Lancet Neurology Volume 8, Issue 7, Pages 679-690 (2009) doi:10.1016/S1474-4422(09)70090-0

2)      Alstadhaug K.B.  “Migraine and the hypothalamus” Cephalalgia Volume 29, Issue 8, Pages 809-817 doi: 10.1111/j.1468-2982.2008.01814.x

3)      Noseda R. et al. “A neural mechanism for exacerbation of headache by light” Nature neuroscience Advance Publication Online 10 January 2010 doi: 10.1038/nn.2475

Breakthrough of the Year (almost!)

As the year draws to a close it’s time to reflect on an exciting year of animal research, and there seems no better place to start than with the top 10 breakthroughs of the year as selected by the prestigious scientific journal Science. Science is of course a general science magazine, and the choices reflect this with research in diverse fields ranging from astronomy to paleontology.

Last year our sister organization in the United Kingdom reported that Science had selected cell reprogramming to produce induced pluripotent stem cells (iPS cells) as their breakthrough of the year.  Since then we have reported how the safety of iPS technology continues to improve while others have discussed exciting research which shows just how powerful the technique is by reprogramming fibroblast cells to generate healthy mice that can themselves produce offspring.

This year the top slot went to the discovery and study of Ardi, a 4.4 million year old ape who promises to shed a great deal of light on early human evolution, though it remains to be seem if she and her kind are a direct ancestor of modern humans.

We did have the consolation that one of the nine runner ups is an area of medicine to which animal research has made an enormous contribution , the return of gene therapy with Science claiming that  this year “… gene therapy turned a corner, as researchers reported success in treating several devastating diseases”. These diseases include X-Linked adrenoleukodystrophy, a usually fatal disease of the brain and nervous system, Leber’s congenital amaurosis, an inherited eye disorder that leads to blindness, and severe combined immunodeficiency (SCID) due to a lack of an enzyme called adenosine deaminase.

Only last month I wrote about the crucial role of research with mice in developing the gene therapy for X-Linked adrenoleukodystrophy, while both Anna Matynia and I have written about Leber’s congenital amaurosis.  However,  we have not yet had an opportunity to discuss the therapy developed for treating SCID  in patients whose immune system has collapsed because they lack an enzyme named adenosine deaminase (ADA) which is crucial for removing toxic metabolites from cells.

A clinical trial published in January by the New England Journal of Medicine (1) reported how an Italian team had successfully treated  children with SCID by harvesting bone marrow stem cells from the boys and treating these cells with a retroviral vector containing the ADA gene that produces adenosine deaminase, and then transplanting the modified cells back into them.  In 5 of the boys the therapy restored normal function and significant improvements in the function of the immune system were observed in the other 5.  This therapy has been a couple of decades in development and one of the key investigators involved in this effort, and indeed in the recent clinical trial,  has been Dr. Claudio Bordignon of the University of Milan. Dr. Bordignon developed techniques that enabled scientists to study the ability of retrovirus transformed bone marrow cells from patients with ADA-SCID  to restore immune function in  the NOD/SCID mice that lack a functioning immune system (2).  This enabled him and his team to develop retroviral vectors that could safely drive the production of adenosine deaminase in bone marrow stem cells that survived for long periods after transplantation and are suitable for use in ADA-SCID patients where they need to function for many years.

It’s great to see an area of medical research that we’ve been following closely over the past year receive this recognition from Science, and we hope that as with iPS cells in 2009 gene therapy continues to show what it can do in 2010.

Paul Browne

1)      Aiuti A. et al.”Gene therapy for immunodeficiency due to adenosine deaminase deficiency.” N Engl J Med. Volume 360(5), Pages 447-458 (2009) DOI:10.1056/NEJMoa0805817

2)      Ferrari G. et al “An in vivo model of somatic cell gene therapy for human severe combined immunodeficiency.” Science. Volume 251(4999), Pages 1363-1366 (1991) PubMed:1848369

Gene therapy on the brain

Hot on the heels of last weeks report of the successful use of gene therapy to treat the eye disease Leber’s congenital amaurosis comes a report that scientists lead by Nathalie Cartier and Patrick Aubourg of the French National Institute for Health and Medical Research have combined gene therapy and stem cell medicine to successfully treat two boys with the disease cerebral X-linked adrenoleukodystrophy (X-ALD).

X-ALD is caused by mutations in the ABCD1 gene that plays a key role in the transport of fatty acids within cells, and lack of ABCD1 causes long-chain fatty acids to build up within cells known as microglia and oligodendrocytes in the brain. Affected microglial cells and oligodendrocytes eventually cease to maintain the insulating myelin sheath that is required for effective transmission of electrical impolses along nerve cells, leading to brain damage and ultimately death at an early age. The disease was made famous by the film “Lorenzo’s oil” which describes a dietary supplement that may delay the progression of the disease, though the only treatment that is currently considered truly effective is allogeneic hematopoietic cell transplantation where healthy bome marrow stem cells from a donor are transplanted into the X-ALD patient. Allogeneic hematopoietic cell transplantation works because the microglial gells and oligodendrocytes develop from cells that migrate to the brain from the bone marrow, so that healthy cells from the donor eventually replace some of the patient’s ABCD1 deficient cells and help maintain the myeline sheath. Unfortunately it is often difficult to identify a suitable donor, and even if one is found the procedure is risky due to problems such as graft-versus-host disease where immune cells in the donated bone marrow mount an immune response against the patient’s tissues.

Gene Therapy

MRIs of X-ALD patients over 24 months. The top line is untreated, the bottom is with gene therapy

Dr. Cartier and colleagues examined the possibility of using gene therapy to modify the patient’s own hematopoietic stem cells so that they express a functioning ABCD1 gene and then injecting these cells into the patient to replace their faulty bone marrow hematopoietic cells, thereby avoiding the problem of donor and host incompatability. Rather than attempt to genetically modify and transplant all types of human bone marrow stem cells they concentrated on a subset of cells called the CD34+ cells that give rise to many cells of the immune system. These have the great advantage that they can be isolated from the blood, avoiding the need for surgery to harvest bone marrow. To assess whether genetically modified CD34+ cells could develop into cells of the immune system when injected into the bone marrow they selected the NOD/SCID mouse that lacks a functioning immune system and is often used to assess human stem cell transplantation techniques and to study aspects of the human immune system. Initial results with retroviral vectors were disappointing but using the NOD/SCID mouse model they developed a lentiviral vector based on HIV-1 that enables the functioning ABCD1 gene to safely incorporate into the genome of a significant proportion of the cells and drive ABCD1 expression in immune system cells derived from them (1). What is more they found that as well as the expected range of immune cells the genetically modified CD34+ cells migrated to the brain and differentiated into microglial cells (2). Of course if the therapy is to prevent disease progression the vector needs not only to drive expression of ABCD1 but to do so reliably for many years,. To assess whether the lentiviral vector could do this they transplanted Sca-1+ cells, the mouse equivalent of human CD34+ cells, containing the ABCD1 expressing lentiviral vector into mice that lacked a functional ABCD1 gene, and found that even 12 months after transplantation almost a quarter of microglial cells in the mouse brain expressed ABCD1 (3).

These promising results in mice were enough to persuade Dr. Cartier and her colleagues that this therapy should proceed to a pilot study in human patients who are in the early stages of this desease. While it will take several years of observation and clinical trails involving larger numbers of patients before we can be sure that this therapy is a success, this exciting news is yet another sign that gene therapy is finally coming of age.

Regards

Paul Browne

1) Benhamida S. et al “Transduced CD34+ cells from adrenoleukodystrophy patients with HIV-derived vector mediate long-term engraftment of NOD/SCID mice.” Mol Ther. Volume 7(3), pages 317-324 (2003) PubMed: 12668127

2) Asheuer M. et al. “Human CD34+ cells differentiate into microglia and express recombinant therapeutic protein” Proc Natl Acad Sci U S A. Volume 101(10), pages 3557–3562 (2004) PubMed Central: PMC373501

3) Cartier N. et al. “Hematopoietic Stem Cell Gene Therapy with a Lentiviral Vector in X-Linked Adrenoleukodystrophy” Science Volume 326(5954), pages 818 – 823 DOI: 10.1126/science.1171242

Gene therapy for blindness – when dogged determination pays off!

Leber’s congenital amaurosis is a progressive disorder that affects about 3,000 Americans, and hundreds of thousands worldwide, and causes a progressive loss of vision that usually results in blindness. The disease, for which there has until now been no effective treatment, is caused by a mutation in the encoding RPE65, an enzyme which is crucial to the production of the chemical 11-cis retinal that photoreceptor cells in the eye need so that they can respond to light.

In one of my first posts for Speaking of Research last year I discussed on this blog how two teams of scientists at Moorfields hospital in the UK and the University of Pennsylvania had used gene therapy to introduce a functioning RPE65 gene into the eye of patients with Leber’s congenital amaurosis, and only last month Anna Matynia discussed how this treatment employs adenovirus-based vectors that have been developed through years of research in rodents and dogs. While the results of those trials were promising the benefits to most of the patients were modest, which was not all that surprising since the scientists doing the trials knew from their studies of Briard dogs with naturally occurring mutations in the RPE65 gene that the therapy needed to begin early in the course of the disease for maximum benefit. For this reason, and because the therapy appeared safe in the first adult human trials, the team at Pennsylvania decided to include children with Leber’s congenital amaurosis in their next study group.

Briard_dog

Briard Dog

The early results of that study have been announced following publication in the medical journal The Lancet, and as expected the greatest benefits have been seen in the children, one of whose eyesight improved to nearly normal, though adults in the study also experienced significant improvement. While this particular therapy will benefit a relatively small number of patients its success and that of early trials of gene therapy for Parkinson’s disease are an indication how gene therapy, a field of medicine that has seen its fair share of hope and disappointment over the past couple of decades, is maturing as scientists have learned from both animal studies and human trials about how to harness this powerful therapeutic approach.

The insights gained through the study of the Briard dog with naturally occurring mutations in the RPE65 gene are a good example of the increasingly close ties between clinical and veterinary medicine, a collaboration that is exemplified by the Comparative Oncology Trials Program which brings together veterinary and clinical oncologists under the leadership of the National Cancer Institute to study cancers that affects both dogs and humans, with a dozen trails of new anti-cancer medications already underway. In the future such trials may play an important role bridging the gap between in vitro and rodent studies in the lab that rely on a relatively limited range of cancer cell lines and the far more diverse cancers seen in the clinic. It is hardly surprising that antivivisectionist groups are opposed to these trials, as our colleagues at Understanding Animal Research point out they are quite happy to put dogma ahead of dogs, but fortunately the majority of veterinarians have a much more positive attitude to animal research.

Regard

Paul Browne

Mending a Broken Heart

An interesting item in the news today about research on repairing the damage to the heart caused by a heart attack. The report in PNAS can be read by those with a subscription at:

While there have been several attempts to bioengineer cardiac tissue for transplant  in vitro using starting from cells seeded onto a scaffold, so far these efforts have been hampered by difficulties in getting the capillaries necessary to supply blood to enable the muscles in the tissue patch to grow properly.  Due to these difficulties engrafted heart patches have until now had limited benefits on heart function in animal models of heart attack, and consequently this approach has not yet been assessed in human clinical trials.

A cross-section of the new tissue with functional blood vessels (the hollow ovals) containing red blood cells

A cross-section of the new tissue with functional blood vessels (the hollow ovals) containing red blood cells

In this project the scientists at Ben-Gurion University started with  a similar approach to that used previously by other scientists. They grew the patch of tissue from neonatal rat heart cells which were seeded in scaffolds designed to allow cardiac cell organization and blood vessel penetration after transplantation, and supplemented them with a mixture of growth factors that encourage cell survival and blood vessel growth. After the cells had been cultured in vitro for 24 hours to allow initial organization of the cells within the scaffold  they introduced a new step, implanting the patch into the rat omentum, an abdominal tissue that is particularly rich in blood vessels, in the hope that the interaction with the blood vessels of the omentum would encourage the development of mature blood vessels in the heart patch.

They observed that the blood vessels of the omentum connected with those developing in the heart patch, encouraging blood vessel development and growth of cardiac muscle. The real test came when they compared the ability of omentum-grown heart patches to repair tissue damage in rats which had undergone experimentally incuced heart attacks 7 days earlier, with that of heart patches that had been grown in vitro.  The result was clear, the omentum-grown heart patches had better blood vessel and muscle quality than the in-vitro grown patches and integrated more strongly into the heart.  When they examined several parameters of heart  function they found that the hearts of those rats which had received omentum-grown patches worked better than those of control rats and those which had received in-vitro grown patches.

So what does this mean for the treatment of heart attacks? The authors point out this is a relatively straightforward procedure that could be assessed in human trials, but also caution that the extra surgery required to grow the heart patch on the omentum would be to risky for many elderly or ill patients so it is a procedure suitable for only a minority of heart attack patients.  What the authors suggest is the development of in vitro bioengineering techniques that mimic the influence of the omentum on the growth of blood vessels and muscle within the heart patch, and with this study they have begun to determine what the requirements of such in vitro systems are.

Needless to say as such in vitro techniques for stimulating heart tissue growth are developed they will need to be assessed in animal models of heart injury before they can enter clinical trials in human patients.

Regards

Dr. Paul Browne

Scientists discover AIDS in Chimpanzees

The discovery of the human immunodeficiency virus (HIV) by the French scientists Luc Montagnier and Françoise Barré-Sinoussi in 1983, and the, and the subsequent confirmation by the American scientist Robert Gallo that it caused AIDS was a shock to doctors and scientists around the globe, and begged the question as to whether or not similar viruses existed in other species. They did not have to wait long, in 1985 a virus was identified that caused AIDS in Rhesus macaques. Analysis of the new virus showed that it was a retrovirus closely related to HIV and it was christened simian immunodeficiency virus (SIV). Since then more than 40 different strains of SIV have been identified in a number of African primate species but a curious pattern was quickly noted; individual SIV strains rarely cause disease in their natural host, for example SIVsmm naturally infects sooty mangabeys but does not cause AIDS in them. On the other hand Asian macaques in the laboratory are infected by a strain of SIV closely related to SIVsmm they develop AIDS. It is thought that over thousands of years natural hosts of SIV have evolved ways of restricting the spread of SIV in their bodies and limiting the damage it can do. If we can identify the mechanisms through which primates limit virus infection we might be able to order to develop treatments that work along similar principles for those of us not fortunate to have natural resistance, and perhaps develop powerful new anti-viral medicines. Five years ago scientists found that some of the variability between species in the ability to restrict HIV or SIV is due in part to differences in the structure of a protein known as TRIM5alpha that prevents the virus from reproducing within the cell, the structure of TRIM5alpha in African monkey species makes it an efficient blocker of SIV and HIV but different structures in macaque TRIM5alpha mean that it has a low blocking effect against SIVmac while human TRIM5alpha only weakly blocks HIV (1,2). With greater understanding of the differences in TRIM5alpha structure between species and how this effects function we may be able to develop new drugs that replicate its action and block HIV in humans.

Chimpanzees - Handout photo provided by Nature magazine

Chimpanzees - Handout photo provided by Nature magazine

So are humans the only primate in which naturally occurring retroviral infection causes AIDS? Until this week the answer would have been “probably”, because no one knew for sure whether the SIV found in chimpanzees, SIVcpz causes AIDS. There had been reports that it might but no firm evidence one way or the other. In this week’s issue of Nature an international team of scientists from institutions including the, Yerkes National Primate Research Centre and the Jane Goodall Institute and lead by Dr Beatrice Hahn of the University of Alabama at Birmingham report that SIVcpz does cause AIDS in a subspecies of chimpanzee found in Gombe National Park in Tanzania (3). In infected animals it was associated with a 10-16 fold higher risk of that, lower than that seen in humans infected with HIV-1, the main cause of the AIDS pandemic, but higher than that seen in humans infected with HIV-2. Comparison of the number of CD4+ T-lymphocytes, the same immune cells killed by HIV in humans, in SIVcpz infected monkeys with that in uninfected humans and chimpanzees showed that SIVcpz infection lowered CD4+ T-lymphocyte dramatically. By contrast they found that in sooty mangabeys infected with SIVsmm the CD4+T-lymphocyte count stayed high and there was no progression to AIDS.

This report is important for a number of reasons. First of all SIVcpz is the strain of SIV most closely related to HIV-1, indeed phylogenetic analysis indicates that it is the direct ancestor of HIV-1. The scientists involved in this study hope that by studying the course of SIVcpz infection and comparing how it interacts with the chimpanzee immune system with the behavior of HIV in humans and other SIV strains in monkeys they can gain a better understanding that will lead to improved treatments and the development of effective vaccines. Secondly SIV is thought to have crossed into chimpanzees from monkeys that they eat only about 500 years ago, so the observation that it still causes disease in chimpanzees will be of great interest to those studying the evolution of resistance to viruses. This brings us on to the third reason why this study is important, chimpanzees are an endangered species and this disease is a threat they could do without, so scientists are keen to determine whether infection with SIVcpz leads to AIDS in other chimpanzee subspecies, and whether it has a significant impact on the overall number of chimpanzees. If the threat is found to be serious than perhaps we should be thinking about developing a vaccine against SIVcpz as well as against HIV.

Regards

Paul Browne

1) Stremlau M. et al. “The cytoplasmic body component TRIM5alpha restricts HIV-1 infection in Old World monkeys” Nature Vol. 427, Pages 848-853 (2004) PubMed: 14985764
2) Song B. Et al.“Retrovirus Restriction by TRIM5alpha Variants from Old World and New World Primates” Journal of Virology Vol. 79, No.7, Pages 3930-3937 (2005) PubMed: 15767395
3) Keele B. et al. “Increased mortality and AIDS-like immunopathology in wild chimpanzees infected with SIVcpz” Nature, Vol. 460, Pages 515-519 (2009) DOI:10.1038/nature0820

From Science Fiction to Science Fact

The ability to regrow limbs lost through accident or the action of their nemesis is a power usually thought of as belonging only to comic-book heroes, but in nature the ability to regenerate tissues and even whole limbs is surprisingly widespread across the plant and animal kingdoms. While in the womb mammals such as humans have a powerful ability to repair and regenerate tissues, but this ability has only been observed to a limited extent in young children, who partially grow back the tips of fingers that have been lost in accidents, and is rarely seen in adults. The ability of mammals, including humans, to repair damaged tissues is rather paltry* when compared to the ability of the axolotl, a species of salamander, which can regrow an entire limb if the limb is amputated anywhere between the shoulder and hand (1). Since the axolotl, an amphibian, shares much of the basic wound healing machinery with mammals scientists study it to gain a better understanding of how wound healing and tissue regeneration take place, and through understanding why wounds heal differently in mammals and they hope to develop new treatment that improve healing and decrease scarring in patients who have suffered serious injuries. Ultimately it is hoped that this knowledge will help scientists to engineer tissues and organs for transplant, and perhaps someday to replace limbs list in automobile accidents and conflict.

Axolotl
This week the science journal Nature reports that a team of scientists working in Dresden and Florida have made a significant discovery concerning the limb regeneration process in the axolotl (2). Very early in the regeneration process a clump of cells known as the blastema forms at the site of injury, and this clump of apparently identical cells gives rise to all parts of the regenerated limb such as cartilage, muscle, nerves and skin. Until now it has generally been assumed that the blastema is composed of uniform pluripotent cells that can develop into a wide range of tissues. To examine if this was indeed the case Martin Kragl and colleagues used transgenic technology to label specific tissues in the axolotl with Green Fluorescent Protein (GFP). They found that when they transplanted GFP-labeled cells from a particular tissue at the injury site they could watch these cells became blastema cells and later develop into new tissue in the regrown limb. The interesting finding was that cells could only produce cells of the original tissue type, muscle cells became blastema cells and then developed into new muscle, and nerve cells became blastema cells and then developed into new nerve tissue. The one exception was cells from a layer of skin known as the dermis, which contributed to both the dermal layer of the new skin and to new bone. This basic research discovery that the cells of the blastema are not in fact pluripotent despite taking on many of the characteristics of stem cells, and the implication that the blastema needs to include cells from a range of tissues for proper regeneration to occur, is of critical importance to scientists who are seeking to reproduce blastema conditions in mammals.

Meanwhile a technique that might once have seemed like science fiction, the use of high-energy ultrasound beams to heat and destroy tumors, has been in the news after a successful clinical trial for the treatment of prostate cancer in the UK. While the use of ultrasound in medicine is something most of us are familiar with, being frequently used to produce images of the developing fetus during pregnancy, high intensity focused ultrasound (HIFU) is less well known, despite being under development for more than fifty years. The earliest research on the use of HIFU was performed by ultrasound pioneer William Fry who used it to produce lesions deep in the brains of cats and monkeys (3), technique that was subsequently used in the treatment of Parkinson’s disease. Technological limitations however impeded the development of the technique, and it was not until the development of technologies such as magnetic resonance imaging (MRI) , used to identify the targets for the beams and monitor their destruction, that HIFU became a practical technique.

Reproduced from European Journal of Ultrasound 9, 19-29, 1999

Reproduced from European Journal of Ultrasound 9, 19-29, 1999

From the late 1970’s until the early 1990’s a series of experiments (3,4) in rodent models of cancer showed that HIFU could be used to safely kill tumor cells, and in the early 1990s studies undertaken by Dr. Albert Gelet and colleagues in Lyon and Prof. Francis J. Fry at the Indiana University Medical Center demonstrated that it was possible to precisely destroy small regions within the dog prostate without harming the surrounding tissue using a probe inserted in the rectum and guided by MRI (5,6). These studies led directly to successful clinical trials of this technique in humans, and to the introduction of a treatment that is now gaining acceptance as a safe and effective alternative to invasive surgery or radiation in the treatment of prostate cancer. Animal research was crucial to the development and evaluation of HIFU over the past decades and continues to play a key role in ongoing work to adapt HIFU to treat other types of cancer, including cancers of the kidney and liver.

* An exception to this rule is deer, which regularly regrow antlers containing skin, bone and blood vessels.

Regards

Paul Browne

1) Gurtner G.C. et al. “Wound repair and regeneration” Nature, Volume 453, Pages 314-321 (2008) DOI: 10.1038/nature07039
2) Kragl M. et al. “Cells keep a memory of their tissue origin during axolotl limb regeneration” Nature, Volume 460, Pages 60-65 (2009) DOI:10.1038/naure08152
3) Kennedy J.E. et al. “High intensity focused ultrasound: surgery of the future?” The British Journal of Radiology, Volume 76, Pages 590-599 (2003) DOI:10.1259/bjr/17150274
4) Acher P.L. “High-intensity focused ultrasound for treating prostate cancer” BJU International, Volume 99(1), Pages 28-32 (2007) DOI: 10.1111/j.1464-410X.2006.06523.x
5) Gelet A. et al. “Prostatic tissue destruction by high-intensity focused ultrasound: experimentation on canine prostate” Journal of endourology, Volume 7(3), Pages 249-253 (1993) PubMed: 8358423
6) Foster R.S. “Production of prostatic lesions in canines using transrectally administered high-intensity focused ultrasound.” European urology, Volume 23(2), Pages 330-336 (1993) PubMed: 7683997

Can we protect the brain against tumor metastasis?

Brain metastasis that affect at least 20% of cancer patients are a serious problem for doctors seeking to treat cancer and kill thousands of patients every year, being particularly difficult to treat because many anti-cancer drugs cannot cross the blood-brain barrier and because surgery to remove the tumor can often be difficult and risky.  Patients suffering from breast, lung and skin cancer run a relatively high risk that their cancer will spread to the brain, a worrying fact considering that these are amongst the most common of cancers .  As a consequence of this scientists are very keen to understand how cancer spreads to the brain, with the ultimate aim of preventing that spread.

It has long been thought that brain metastasis is due to interactions between cells that are shed by the primary tumor and the nerve cells of the brain, but real evidence of this from living animals and humans for that theory has been hard to find, and in recent years observations made in animal models of cancer have suggested that blood vessels in the brain rather than nerve cells are the site of the early growth of tumor cells during brain metastasis.  This week a paper in the open access journal PLoS One reports on work done by scientists at Oxford University that confirms that during brain metastasis tumor cells do indeed bind to blood vessels and form tumors before spreading into the surrounding nerve tissue, a result of huge importance to the future treatment and prevention of brain metastasis.

Brain Metastasis From Lung Cancer

Brain Metastasis From Lung Cancer

To demonstrate this Dr Shawn Carbonel and colleagues (1) injected breast and skin tumor cells into the bloodstream or fat tissue of mice and then after several days humanely killed the mice determined where in the brain the micrometastases, small colonies of tumor cells that later grow into tumors, were forming, and found that almost all were associated with the blood vessels. There was no sign of any new blood vessel growth, which indicated that the metastases were associating with the blood vessels, and that it wasn’t simply the case that they were promoting the growth of new blood vessels in the vicinity of the growing tumor. To confirm that this is also true in humans they examined tissue samples that been donated following neurosurgery or autopsy and found that almost all metastases were associated with blood vessels, a finding that supported the results of their experiments in mice.

Now they had to answer a new question; were the micrometastases associated with the blood vessels because they have a preference for interacting with the cells of the blood vessel, or simply because the first part of the brain they come to is that adjecent to the blood vessel?  To answer this the Oxford scientists injected tumor cells that were labelled with green fluorescent protein directly into an area of the brain allowing equal access to both blood vessels and nerve cells, and using a cranial window in the skulls of the mice were able to observe where the GFP-labelled tumor cells ended up.  They observed that the GLF-labelled cells associated almost exclusively with blood vessels, and that the tumors subsequently grow into the surrounding brain tissue.

The tumor cells bind to a blood vessel structure called the vascular basement membrane (VBM), but what the Oxford scientists really wanted to know was what caused the tumor cells to bind to the VBM. Once again using mice with cranial windows fitted they found that an enzyme named focal adhesion kinase was highly active where the tumor cells were interacting with the VBM. Focal adhesion kinase is part of a pathway through which a  class of proteins known as the integrins control the interaction between many cells and either other cells or extracellular proteins such as the components of the vascular basement membrane, an observation which suggested that an integrin plays a key role in the binding of tumor cells to the VBM. They next found that a particular integren named Beta 1 integrin is present on all the tumor cell lines they were studying, and that antibodies blocking it could prevent the tumor cells from binding components of the VBM in vitro and to blood vessels in human brain tissue slices.

But would the anti-Beta 1 integrin blocking antibody prevent tumor metastasis in living animals? The answer was yes, the antibodies greatly reduced the growth tumors from human breast tumor cells that were injected directly into the brains of mice. To further emphasize the importance of Beta 1 integrin in brain metastasis they found that when mouse lymphoma cells that had been genetically engineered to lack Beta 1 integrin were injected into mouse brains they formed far smaller tumors than non-GM lymphoma cells.
This  study changes the way we look at the process of brain metastasis, and more importantly in Beta 1 integrin it identifies a target for new drugs, perhaps monoclonal antibodies, that block the binding of tumor cells to blood vessels and prevent brain metastasis.  With this in mind it is useful to note that studies in mice have found that while Beta 1 integrin is crucial during embryonic development prolonged anti-Beta 1 therapy in adult animals did not produce any overt evidence of toxicity (2), indicating that it should also be possible to inhibit it safely in human patients during anti-cancer chemotherapy.

It’s a very nice paper, my only gripe being that they didn’t examine if anti-Beta 1 integrin blocking antibody therapy could prevent tumor cells injected into the mouse bloodstream from producing micrometastases in the blood vessels of the brain rather than just looking at the growth of tumor cells injected directly into the brain, though I expect that those experiments are now being done and will soon be reported.  There will certainly be a lot of interest in this paper in the cancer research world, and scientists will seek to reproduce these results (a vital part of the scientific process) and then expand on them with their own studies of the safety and efficacy of this approach before clinical trials in humans can begin.

Regards

Paul Browne

1) Carbonell W.S. et al. “The vascular basement membrane as “soil” in brain metastasis.” PLoS ONE Volume 4(6):e5857 (2009) DOI:10.1371/journal.pone.0005857

2) Park C.C. et al. “Beta1 integrin inhibitory antibody induces apoptosis of breast cancer cells, inhibits growth, and distinguishes malignant from normal phenotype in three dimensional cultures and in vivo.”Cancer Res. Volume 66(3), Pages 1526-1535 (2006) DOI:10.1158/0008-5472.CAN-05-3071