Tools and Technologies II
About 43 million individuals in the US currently suffer from disabilities due to arthritis. The major source of pain in these patients is due to cartilage defects in the affected joints. Current treatments, whilst alleviating some of the clinical symptoms, prove insufficient to cure the underlying irreversible cartilage loss. Stem cells represent a unique source for restoration of the cartilage defects. Pre-clinical and clinical trials are currently pursued to investigate the potential of various types of stem cells and stem cell derived cartilage cells, which are transplanted into the cartilage defects, to repair arthritic joints and restore painless joint mobility. However, current challenges with this approach encompass loss of the transplanted cells from the transplantation site and cell death with clearance by the immune system. A major barrier for the development of successful stem cell therapies for arthritis treatment is our current inability to visualize the transplanted cells in the affected joints. Thus, successful or unsuccessful engraftment outcomes cannot be diagnosed directly, but have to be diagnosed months or years after the transplantation procedure via invasive or indirect measures (such as arthroscopies, biopsies or clinical evaluations). The goal of our project is to develop a non-invasive imaging technique, which would allow an early diagnosis of successful engraftment outcomes or detection of complications of the engraftment process within days to few weeks after the transplantation. Our imaging technique relies on an iron supplement drug (ferumoxytol, Feraheme), which is used in patients for the treatment of iron deficiency. This drug provides a strong signal on magnetic resonance (MR) images and, thus, can be used as a marker for stem cells. We will internalize ferumoxytol into stem cells and then depict the labeled cells after their implantation into cartilage defects with MR imaging in an animal model of arthritis. We predict that ferumoxytol-labeling will lead to long-term detection of stem cell transplants in cartilage defects on MR images and allow us to diagnose successful or unsuccessful stem cell transplant outcomes. We expect that loss of the ferumoxytol signal at the transplantation site indicates loss of the transplanted cells and that long term persistence of the ferumoxytol-signal on MR images indicates a successful cell engraftment. In a three-step approach, we will first optimize labeling of stem cells with ferumoxytol, then investigate long term signal characteristics of ferumoxytol-labeled cells in arthritic joints and finally, determine long term MR signal characteristics of successful and unsuccessful transplants. Since we use a clinically applicable cell marker and clinically applicable MR equipment, this imaging technique would be immediately accessible for monitoring stem-cell therapy outcomes in patients with arthritis. Results could be directly utilized to facilitate clinical trials.
Statement of Benefit to California:
Arthritis is the leading cause of disability in the United States, causing annual costs to our society in medical care and lost wages in the order of $95 billion. According to the California Department of Public Health, more than 46 million Americans and more than 5.3 million Californians suffer from arthritis (www.cdph.ca.gov). In California, 21% of adults are affected by arthritis; 3.3 million are women and over 2.0 million are men. Cartilage defects within the affected joints are the major source of pain and functional impairment in these patients. Unfortunately, cartilage is not capable of regenerating or repairing itself. Thus, current conventional treatments, whilst alleviating some of the clinical symptoms, prove insufficient to cure the underlying irreversible cartilage loss and resultant disabilities. Stem cell transplants provide a novel and unique source to create new cartilage with the capacity to repair cartilage defects and, thereby, the potential to cure arthritic joints and associated clinical symptoms. However, it is not yet clear, which cell type, how many cells, which added growth factors and which transplantation techniques provide optimal outcomes. To date, a large proportion of transplanted cells die and/or are cleared from the transplantation site by the immune system. We aim to develop an imaging technique that will allow us to depict the transplanted cells directly, non-invasively and repetitively in patients, without the need of performing an arthroscopy. This direct visualization of the transplanted cells by an imaging test will allow us to better understand factors that promote or impair successful transplant outcomes and help us to select the most promising techniques for clinical applications. Since we use clinically applicable cell markers and imaging equipment, our imaging technique would be in principle readily accessible to patients who undergo cell transplants for the treatment of arthritis. California is a leader in the development of stem-cell therapies for the treatment of arthritis with several ongoing clinical studies in major academic centers. Our imaging technique could be immediately applied to these ongoing clinical trials, could help to identify the most promising approaches, could thereby have an immediate impact on patient management and transplant outcomes, promote significant breakthroughs in the field and, ultimately, help to improve the quality of life of Californians affected by arthritis and other rheumatic conditions. The principles of our imaging technique can be also applied for non-invasive monitoring of other stem cell therapies, thereby providing an important, immediately clinically applicable key tool that may redirect and advance the entire field of stem cell therapies.
Osteoarthritis is a major debilitating condition characterized by the degeneration of joint (articular) cartilage. There is considerable interest in developing cell replacement therapies based on the use of stem cell-derived cartilage cells (chondrocytes). A significant impediment to progress in developing such therapies is the current lack of a non-invasive imaging modality to track cell engraftment outcomes in a timely manner. To overcome this bottleneck, the applicants intend to demonstrate the utility of two ultra-small superparamagnetic iron oxide nanoparticle (USPIO) compounds for in vivo imaging of stem cells following transplantation into sites of articular cartilage defects. One of the compounds, ferumoxytol, is FDA-approved for a different indication. The applicants will first optimize the labeling of human embryonic stem cells (hESCs), human mesenchymal stem cells (hMSCs) and murine MSC (mMSC) with USPIOs. Then, the applicants will evaluate the magnetic resonance (MR) signal characteristics of USPIO-labeled stem cell-derived chondrocyte transplants in preclinical models of arthritis. Finally, in order to assess the feasibility of diagnosing the viability of transplanted cells in vivo, the applicants will determine if the MR signal characteristics of viable and apoptotic chondrocyte transplants differ. The reviewers agreed that this application addresses a critical bottleneck. If successful, this new imaging approach would have significant impact on facilitating the development of stem cell-based treatments for cartilage defects. However, reviewers felt the proposed approach lacked innovation, unless the use of ferumoxytol in this setting was to be considered novel. Similar studies on tracking stem cells and cartilage repair have been performed before. Reviewers raised several criticisms regarding the experimental approach. Although hMSC-derived chondrocytes are likely to retain sufficient USPIO label, reviewers doubted that this would be the case for hESC-derived chondrocytes, since undifferentiated hESCs will continue to proliferate as they transition through various stages of differentiation before becoming mature chondrocytes. This will dilute the label and, consequently, the strength of the MR signal. Reviewers also expressed strong concern regarding the hESC differentiation protocol, which leads to the formation of fibrocartilage, rather than articular cartilage. The preliminary data show the presence of mineralized tissue in hESC-derived cartilage, which is not a desirable outcome in articular cartilage. Since the applicants only assessed cartilage markers, the source of the mineralized tissue remains unclear. Furthermore, while the applicants provide preliminary data simulating MR imaging of live versus dead cells in vitro, reviewers questioned whether this approach would enable a similar distinction in vivo as additional cellular processes such as continued proliferation and macrophage clearance may affect MR signal strength. Finally, reviewers felt that the proposed mMSC studies were neither justified nor scientifically sound. Taken together, these issues undermined confidence in the feasibility of the proposed studies. The track record of the Principal Investigator (PI) is directly relevant to the imaging and arthritis aspects of this proposal, but lack of expertise in stem cell biology and cartilage development raised some concern. This is only partially alleviated by the team members at the applicant institution. The team also includes a Partner-PI who has imaging, cell differentiation and preclinical model expertise, as well as access to the second USPIO compound. Reviewers observed a certain redundancy in the experiments performed by the two groups, but some considered this a strength in terms of data validation. In summary, the applicants propose to use iron oxide nanoparticles to track stem cells after engraftment for the treatment of osteoarthritis. Although success would overcome an important bottleneck, reviewers’ enthusiasm for this application was diminished by several critical flaws in experimental design. Thus, the application was not recommended for funding.