Tag Archives: rodent

ERV blogs on GMO Herpes vs severe cancer pain

As gene therapy emerges as one of the hottest areas of medical research, one thing that is striking is how it employs viruses – sometimes very nasty viruses - to deliver the gene to where it is needed in the human body.

Yesterday virologist Abbie Smith discussed another excellent example of this on the ERV blog in a post entitled “GMO Herpes vs. severs cancer pain”, describing how scientists at the Universities of Michigen and Pittsburgh have used a genetically modified herpes virus to deliver the preproenkephalin gene – which produced a precursor to pain-killing opiates – to the nerve cells of terminal cancer patients who were suffering from severe pain.

Abbie remarks that “This was one of the most depressing, yet hopeful, papers I have ever read.”. It’s difficult to disagree, after all most of the patients participating in the trial died within 3 months of it starting. But to focus on this sobering statistic would miss the reason for this study, namely that the pain-relief available to patients with severe chronic pain is often inadequate, as the drugs are not specific enough and cause unacceptable side effects when used at the high doses often required for prolonged periods of time. By targeting the opiate molecules to the nerve ccells themselves these side effects can be avoided, and more effective pain relief provided.

The paper “Gene Therapy for Pain: Results of a Phase I Clinical Trial” is available for anyone to read in PubMed Central and makes it very clear that this is a therapy that was discovered, evaluated and refined in animal models of different types of pain before entering this first clinical trial. The first two paragraphs of the introduction noting that:

A significant limitation to the development of analgesic drugs is that off-target effects at doses below the maximal analgesic threshold restrict the ability to selectively interrupt nociceptive neurotransmission1. To address this limitation, we developed a series of replication defective HSV-based vectors to deliver gene expression cassettes directly to DRG neurons from skin inoculation 2, 3. The anatomically defined projection of DRG axons allows targeting of specific ganglia by injection into selected dermatomes. In preclinical studies, the release of anti-nociceptive peptides or inhibitory neurotransmitters in spinal dorsal horn from the central terminals of transduced DRG neurons effectively reduced pain-related behaviors in rodent models of inflammatory pain, neuropathic pain, and pain caused by cancer4-9.

The human PENK gene encodes for preproenkephalin, a precursor protein proteolytically cleaved to produce the endogenous opioid peptides met- and leu-enkephalin. In the spinal cord, enkephalin peptides inhibit pain signaling through actions at presynaptic opioid receptors located on central terminals of primary afferent nociceptors and postsynaptic opioid receptors on second order neurons involved in nociceptive neurotransmission10. HSV vectors expressing opioid peptides appear to be particularly effective in animal models of inflammatory and cancer pain4, 5, 8.”

And in the conclusion:

In preclinical animal studies, skin inoculation of HSV vectors expressing PENK reduce acute hyperalgesic responses27, and reduce pain-related behaviors in models of arthritis28, formalin injection4, peripheral nerve damage6 and bone cancer5. Because this was the first human trial employing HSV vectors to achieve gene transfer, we elected to carry out the phase 1 clinical trial for safety and dose-finding in patients with pain caused by cancer…This Phase I clinical trial primarily addressed the question of whether intradermal delivery of NP2 to skin would prove to be safe and well tolerated by subjects. The small number of patients and the absence of placebo controls warrant circumspect interpretation of the secondary outcome measures. But the observation that subjects in the low dose cohort had little change in the NRS or SF-MPQ while subjects in the higher dose cohorts reported substantial reduction in NRS and improvement in SF-MPQ is encouraging.”

Encouraging is possibly an understatement, seeing clear evidence of therapeutic benefits in a Phase I trial like this is very promising, or as Abbie puts it “A trial turning out this successful is a great starting point for optimizing this kind of therapy.”.

Paul Browne

p.s. Those interested in a more detailed account of the research that led to this clinical trial can find it in this review published in 2008 and available to read online for free.

Animal research unleashes the power of human embryonic stem cells

For more than a decade now embryonic stem cell research has been one of the most high profile – and indeed controversial – areas of medical science, and it is an emerging field that owes a lot to animal studies performed by pioneers like Gail Martin of UCSF.

Recently the field has begun to live up to its promise with the announcement last year that the first patient had been enrolled in the first ever clinical trial of a human embryonic stem cells (hESCs), a trial that seeks to evaluate the safety of the hESC-derived oligodentrocyte progenitor cells in patients with spinal cord injury.  We discussed the role of animal research in the development of this therapy by Geron Corp in a post on this blog back in 2009.

In September of this year embryonic stem cells were in the news again with the announcement that clinical trials of retinal pigment epithelial cells (RPEs) derived from hESCs for the treatment of an inherited form of blindness known as Stargart’s Macular Dystrophy, are taking place at Moorfields Eye Hospital in London and the Jules Stein Eye Institute at UCLA. The development of this therapy was led by Professor Robert Lanza, Chief Scientific Officer at Advanced Cell Technology, and Adjunct Professor at Wake Forest University School of Medicine, and rests on animal studies which showed that RPE cells derived from hESCs were safe and could restore vision in rodent models of Stargart’s Macular Dystrophy, as a study publishes in the Journal Stem Cells in 2009 makes clear:

Assessments of safety and efficacy are crucial before human ESC (hESC) therapies can move into the clinic. Two important early potential hESC applications are the use of retinal pigment epithelium (RPE) for the treatment of age-related macular degeneration and Stargardt disease, an untreatable form of macular dystrophy that leads to early-onset blindness. Here we show long-term functional rescue using hESC-derived RPE in both the RCS rat and Elov14 mouse, which are animal models of retinal degeneration and Stargardt, respectively. Good Manufacturing Practice-compliant hESC-RPE survived subretinal transplantation in RCS rats for prolonged periods (>220 days). The cells sustained visual function and photoreceptor integrity in a dose-dependent fashion without teratoma formation or untoward pathological reactions. Near-normal functional measurements were recorded at >60 days survival in RCS rats. To further address safety concerns, a Good Laboratory Practice-compliant study was carried out in the NIH III immune-deficient mouse model. Long-term data (spanning the life of the animals) showed no gross or microscopic evidence of teratoma/tumor formation after subretinal hESC-RPE transplantation. These results suggest that hESCs could serve as a potentially safe and inexhaustible source of RPE for the efficacious treatment of a range of retinal degenerative diseases.”

Spinal Injury and Stargart’s Macular Dystrophy are only two of many diseases where hESC based treatments are offering hope of improvement, for more than a decade scientists have been investigating in animal models the use of embryonic stem cells to treat Parkinson’s disease, a degenerative disorder caused by the loss of nerve cells in the brain that produce the neurotransmitter dopamine and results in severe movement impairment. Now, a report in the Guardian newspaper describes how, after years of dedicated research, scientists have overcome a major of technical hurdle and paved the way for the evaluation of hESC therapy for Parkinson’s disease in human clinical trials. The Guardian report stresses the importance of studies in mice, rats and monkeys to evaluating the efficacy and safety of hESC-derived dopamine producing cells:

In a series of experiments, the team gave animals six injections of more than a million cells each, to parts of the brain affected by Parkinson’s. The neurons survived, formed new connections and restored lost movement in mouse, rat and monkey models of the disease, with no sign of tumour development. The improvement in monkeys was crucial, as the rodent brains required fewer working neurons to overcome their symptoms”

The study, which those with a subscription to Nature can read here, is very promising, and hopefully it won’t be very long until we are reading about the start of another clinical trial of hESC derived cells.

It is worth noting that despite fierce opposition from its opponents, public support for human embryonic stem cell research remains very high, a level of support that owes much to the willingness of scientists and research charities such as the Michael J. Fox Foundation for Parkinson’s Research to speak out in support of this important work.  While polls indicate that a clear majority of Americans support animal research, that majority could be larger, and the lesson from the stem cell debate is that the public are willing to listen to the arguments put forward by scientist. It is up to all of us who value animal research to do our bit to ensure that the majority in favor of animal research grows; after all, it can’t be right that more Americans support hESC medicine than support the animal research on which it depends!

Paul Browne

Magic Bullets and Monoclonals: A Breakthrough in Bioscience

The Federation of American Societies for Experimental Biology (FASEB) is one of the world’s largest and most influential scientific organizations, representing as it does 23 independent scientific societies and over 90,000 individual scientists.  As a coalition that represents tens of thousands of US medical researchers FASEB has policies and positions on all kinds of issues which affect scientific research, from federal funding of research to the legal status of embryonic stem cells and human cloning, and you will probably not be altogether surprised to learn that FASEB has taken a very strong position in support of animal research and the scientists who undertake it.

FASEB also takes its responsibility to educate and inform members of the public about the role of biomedical research very seriously and has produced the excellent Breakthroughs in Bioscience, a series of essays written with the help of leading scientists on the research that led to important advances in medicine. While these essays do not of course focus solely on the role of animals in research, key discoveries have after all been made through approaches as disparate as clinical observations and X-ray crystallography,  they do illustrate how important animal research has been as an integral and frequently vital part of the research process.

The most recent essay entitled Magic Bullets and Monoclonals: An Antibody Tale is a great example of this;  I would encourage anyone who is interested in finding out how the role of antibodies in the immune system was first uncovered and how this eventually lead to the development of these “magic bullets” to read it.

A couple of years ago I wrote on the Pro-Test blog about the role of animal research in the development of the monoclonal antibody drug Lucentis that is used to treat the wet form of age-related macular degeneration, a common form of blindness , but it is only one example out of many.  The Breakthroughs in Bioscience essay focuses on the development other monoclonal antibody drugs including Rituximab, a treatment for cancers of the immune system such as non-Hodgkin lymphoma, infliximab, a treatment for autoimmune diseases such as rheumatoid arthritis, and trastuzumab, better known as Herceptin and used to treat breast cancer. While the essay discusses how animals were vital to the production of these monoclonal antibody drugs, the contribution of animal research to the development of these treatments went far beyond just that, as the following two examples illustrate.

Herceptin (1) targets the HER2/neu receptor, a protein whose normal function is to regulate the growth of cells but which is produced in excess in some breast cancers where it promotes tumor growth. HER2 was first discovered to have a role in cancer through studies of cancer in rats and mice, and scientists following up on this discovery then found that it was over-produced in some breast cancers.  Subsequently research in transgenic mice enabled scientists to understand how HER2 promoted tumor growth, while xenograft models where  immunodeficient mice wre injected with  of HER2 positive human breast cancer cells were used to screen candidate monoclonal antibodies, eventually identifying the antibody that was taken into successful human trials as trastuzumab.

The story was similar for infliximab, which works by blocking the action of a chemical messenger called Tumour Necrosis Factor-alpha (TNF-alpha) that promotes inflammation and is a key factor in the development of several autoimmune disorders.  Studies in rodents and dogs played a key role in the isolation and identification of TNF-alpha, and in subsequently animal research that demonstrated its role in both the normal immune system and in inflammatory and autoimmune diseases. This work included studies in transgenic mice which provided the definitive evidence that TNF-alpha plays a crucial role in the development of rheumatoid arthritis , which formed the basis for studies which demonstrated that a chimeric human/mouse monoclonal antibody against TNF-alpha could protect transgenic mice which produced human TNF-alpha from inflammation-induced cachexia (2). Follow up studies in transgenic mice expressing human TNF-alpha provided important pre-clinical information about the safety of infleximab (3).

The examples above show just how important animal research is to both basic research which seeks to understand what is going on in normal physiology and disease, and translational research which seeks to take that knowledge and apply it to developing treatments that can be used effectively in the clinic.  We’re delighted by the work that FASEB is doing to ensure that the public is aware of how all types of research contribute to medical progress, and hope that they continue these efforts for many years to come.

Paul Browne

1)      Pegram M. and Ngo D. “Application and potential limitations of animal models utilized in the development of trastuzumab (HerceptinR): A case study”  Advanced Drug Delivery Reviews Volume 58, Pages 723-734 (2006) DOI:10.1016/j.addr.2006.05.003

2)      Siegel S.A. et al. “The Mouse/Human Chimeric Monoclonal Antibody cA2 Neutralizes TNF In Vitro and Protects Transgenic Mice from Cachexia and TNF Lethality In Vivo” Cytokine Volume 7(1), Pages 15-25 (1995) DOI:10.1006/cyto.1995.1003

3)      European Medicines Agency report http://www.ema.europa.eu/humandocs/PDFs/EPAR/Remicade/190199en6.pdf

A new era for embryonic stem cells

As the new president takes office and the scientific community eagerly awaits the announcement of the reversal of the ban on federal funding of most research involving human embryonic stem cells (hESC’s), there’s news that the FDA has approved the first ever trial of a treatment based on hESC’s for severe spinal cord injury.

This is a very welcome development; for a decade now hopes have been raised about the potential for hESC’s to treat a range of serious illnesses, particularly brain and spinal injuries,  but despite excellent work by organizations such as the Christopher and Dana Reeve Foundation no treatments have yet reached clinical trials in patients.  This is not a criticism of hESC’s, underneath the hype is the reality that hESC research is a very new science. After all the first hESC’s were produced by Professor James Thomson and colleagues at the University of Wisconsin-Madison a mere ten years ago, and a lot of work has been necessary to ensure that hESC therapies are safe and effective enough to justify human trials.

The treatment developed by Geron uses a type of cell known as an oligodendrocyte progenitor cell (OPC) that was derived by growing  hESC’s  under carefully controlled conditions. OPC’s  in their turn develop into oligodendrocytes, cells that forms a sheath around the nerve cells and are vital to the proper function of the nervous system.  In rat studies the scientists at Geron showed that OPC treatment could restore the ability to move after severe spinal injury.  Subsequent safety studies in rodents indicated that the injected cells remained within the nervous system and did not produce teratomas, a type of tumour produced by stem cells that have not been adequately processed to ensure they have differentiated into a more mature cell type suitable for transplantation. An important observation made during Geron’s animal studies of OPC therapy was that the therapy worked when the cells were injected 7 days after injury but not when treatment was delayed until 10 months after injury (1) indication that early treatment was vital, and leading to the decision to treat patients 7-14 days after injury in this phase I clinical trial.

If you take a look through the Geron and Christopher and Dana Reeve Foundation websites you will see that there are many other hESC based treatments under development, and appreciate the undeniable importance of animal research to this work. With a new president who appreciates the importance of hESC research we will no doubt see more announcements of this sort, but it’s also worth remembering that animal research is crucial to other types of stem cell research, including the iPS approach we’ve discussed here and other methods we discussed earlier this week on our sister blog in the UK.

Could this be the dawn of a new era in medicine?

Update 21 February 2011: After being put on hold for over a year due to potential problems with cyst formation identified in an animal study, additional animal studies have proved reassuring and the FDA gave its approval for the trial to go ahead. Geron recently announced the enrollment of  the first patient into their phase I study of hESC based therapy for spinal injury.

Regards

Paul Browne

1) Keirstead H.S. et al. “Human embryonic stem cell-derived oligodendrocyte progenitor cell transplants remyelinate and restore locomotion after spinal cord injury” J Neurosci., Volume 25(19), Pages 4694-4705 (2005) doi:10.1523/JNEUROSCI.0311-05.

2005