Abstract
The International Consortium of Stem Cell Networks’ (ICSCN) Workshop Towards Clinical Trials Using Stem Cells for Amyotrophic Lateral Sclerosis (ALS)/Motor Neuron Disease (MND) was held on 24–25 January 2011. Twenty scientific talks addressed aspects of cell derivation and characterization; preclinical research and phased clinical trials involving stem cells; latest developments in induced pluripotent (iPS) cell technology; industry involvement and investment. Three moderated panel discussions focused on unregulated ALS/MND treatments, and the state of the art and barriers to future progress in using stem cells for ALS/MND. This review highlights the major insights that emanated from the workshop around the lessons learned and barriers to progress for using stem cells for understanding disease mechanism, drug discovery, and as therapy for ALS/MND. The full meeting report is only available in the online version of the journal. Please find this material with the following direct link to the article: http://www.informahealthcare.com/als/doi/10.3109/17482968.2011.590992.
Introduction
The Workshop Towards Clinical Trials Using Stem Cells for Amyotrophic Lateral Sclerosis (ALS)/Motor Neuron Disease piloted a series of international meetings intended to bring together global stem cell researchers to catalyze broad discussions in disease areas where expertise is limited in any one country. The meeting was organized and cosponsored by The ALS Association, the MND Association, The New York Stem Cell Foundation, the UK National Stem Cell Network, and the Stem Cell Network (Canada). The international contingent of 63 participants hailed from 14 countries and included representation from a variety of universities, associations, foundations, institutes, hospitals/centers, biopharmaceutical companies and the regulatory field. Each scientific session included three to five invited speakers and the moderated sessions opened with discourse from two to three panel members followed by a plenary discussion.
Overview of ALS/MND
The introductory presentations described ALS/MND as a complex disease where the interaction between genetic and environmental susceptibility factors contributes to a clinical and pathological spectrum of disease phenotypes. Key to unraveling this complexity is the discovery of more genes, better biomarkers, better models that replicate disease, and large environmental studies that assess several of the exposures occurring throughout one's lifetime, including occupations, nutrition, exercise and electromagnetic fields. One of the main opportunities for embryonic (ES) and induced pluripotent (iPS) stem cells lies in their ability to mimic disease in a dish, thus offering human in vitro models for understanding disease mechanism, facilitating drug discovery, and providing cell-based therapy to treat ALS/MND.
Stem cells for understanding disease mechanism
Critical to the development of robust human in vitro models to study ALS/MND is to identify the best strategies for creating stem cell derived motor neuron lines and, in so doing, provide models to address the fundamental question of what leads a neuron to become a motor neuron (). Importantly, benchmarking against ES-derived lines has shown no obvious signature that sets iPS lines apart from ES lines. Both make motor neurons with similar efficiencies, but the unique property of iPS lines is that they carry the genetics of the ALS patient. The motor neuron subtypes generated are diverse, can be shifted upon changing culture conditions, and can be distinguished by the region they innervate and the expression of different transcription factors, such as Hoxa5, Wnt and FGF. Future in vitro assays should take stock of whether ALS is purely a disorder of motor neurons and also what happens to motor neurons post-mitotically, given that ALS is an age-related disease.
Table I. Barriers to future progress in using stem cells for ALS/MND.
Stem cells for drug discovery
Because the iPS cell model can be patient specific, it offers considerable hope for drug development. Significant advances have been made in developing drug screens based on ES- and iPS-derived cell lines, with the advantage that they can be differentiated into astrocytes and motor neurons, the cells at risk in ALS. A trophic survival assay established at the French company Trophos tested over 50,000 compounds on pure rat embryonic motor neurons, leading to the identification of a compound that may target mitochondrial function and prove promising to patients. The compound is currently being tested in clinical trials in Europe and results are anticipated later this year. Presenters cautioned that one must consider the purity of the assays, the variation in motor neurons derived from different patients, ongoing neurogenesis in cultures and the epigenetic memory of iPS cells with regard to location of origin. Industry contributions to stem cells for drug discovery are also advancing, with the development of iPierian's large (200,000+) chemical library for testing on iPS lines from ALS patients, and Pfizer's chemogenomic library (750+) for identifying small molecules that differentiate iPS cells into motor neurons or glia.
Stem cells as therapy
Researchers have hypothesized that ALS is not cell autonomous, and that mutant motor neurons can be saved by providing a better neighborhood of astrocytes that might mitigate rapid disease progression. Researchers and industry based in California and funded by The Californian Institute of Regenerative Medicine (CIRM) are collaborating towards developing an ES-derived astrocyte cell line to take forward in a clinical trial planned for 2014 in which the astrocytes will be injected into the cervical or lumbar spinal cord of ALS patients. Other avenues being explored include testing whether clinical grade human neural progenitor cells can improve respiratory output in the SOD1-G93A rat model of ALS. Preliminary results show that GDNF-secreting human progenitor cells protect dying motor neurons in rats at 105 days, but the lack of functional effect despite excellent cell body survival has been attributed to axonal pullback (inability to repair the neuromuscular junction). The nuances around surgery, safety, accuracy and tolerability were profiled during the presentation of three phase I clinical trials for ALS patients who received neural stem cells derived from human fetal spinal cord or mesenchymal stem cells. A phase I clinical trial for intrathecal injections of modified mesenchymal stem cells into ALS/MND patients has also been recently approved. Because neurosurgery is extremely risky, presenters voiced the need to define what is considered meaningful for patients in order to assess the acceptable levels of morbidity.
Moderators’ summary
During the workshop, participants identified a number of barriers to progress for clinical trials using stem cells for ALS/MND (). Despite the shared belief that it might someday be possible to implant and rebuild neural circuitry, in the case of motor neurons with meter-long axons needing to appropriately reconnect with denervated muscles, this currently seemed an impossible task. Most of the workshop discussion focused on other kinds of cell therapy, ranging from transplanting neural progenitors to engineered neuroprogenitors, astrocytes and mesenchymal stem cells. The common theme centered on providing a local source of trophic factors or astrocytes to detoxify the motor neuron environment. Neurotrophic factors alone have not been successful, perhaps owing to incorrect combinations of factors, delivery, or dosing issues.
There is great appeal in using iPS-derived cells for cell based therapies or for modeling ALS to test drugs on patient-specific lines in order to identify the best therapeutics for different subgroups. A stumbling block to the progress is heterogeneity, observed both at the level of the disease itself and also among individual ES and iPS cells. Such marked heterogeneity demands the collection of a large number of patient lines to determine which would be most representative of the disease for drug screening. The Harvard Stem Cell Institute (HSCI) Core Facility houses a wide variety of published control cell lines as well as four ALS iPS lines, with two distinct SOD1 genotypes (11b-29e). These cell lines have been specifically expanded for broad distribution to the research community and are available upon request to http://www.hsci.harvard.edu/ipscore/node/3. In addition, the iPS lines below may be obtained, on a pre-publication and collaborative basis, through Kevin Eggan by contacting him directly at [email protected].
25b SOD1D90A (59/F)
39b SOD1A4V (43/F)
36a TDP43Q343R (53/M)
47a TDP43G298S (43/M)
In terms of developing future in vitro models for drug screening, it will be important for the field to improve cell survival towards developing long-term cultures. Moving forward, it is likely that a few models with the most relevant phenotypes will be selected for screening. Participants discussed the problems of administration, manufacturing and unknown endpoints associated with using cells for therapeutics. In response to the fundamental question of whether one can model late-onset disease, some participants reasoned that an accelerated disease phenomenon may be observed under the right circumstances. Standardization of lines so that they can be used across laboratories is crucial. The IPS Consortium established by the National Institute of Neurological Disorders and Stroke (NINDS) aims to address many of these issues, and the development of new tools that predict stem cell behavior will also be of tremendous benefit to the field.
The efforts by Neuralstem to inject stem cells into patients in the FDA-approved clinical trial are extremely important in moving the clinical aspects of stem cells towards a treatment for ALS.
It is clear that new surgical techniques will help to refine current parameters used in the trial, such as injection points, the rate of diffusion, and differentiation of stem cells. The sensitivity for detecting foreign cells is crucial, and there are efforts in industry to develop a platform to detect foreign cells using a collection of pre-clinical and clinical biomarker approaches. It will also be necessary to devise ways to track autologous cells.
Conclusion
The meeting highlighted the exciting advances being made, the importance of standardization, global collaboration, and the significant work outstanding to realize the potential of iPS and ES cell lines as effective tools for drug screening. An important issue raised was the need for more collaboration and better communication between the scientific and patient communities regarding the advances of stem cell research and the validity of some of the treatment approaches being offered.
http://www.informahealthcare.com/doi/abs/10.3109/17482968.2011.590992
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