Acute and progressive injuries or diseases that affect the human brain are very serious personal and societal problems. Usually the quality of life of afflicted individuals is substantially compromised. Yet even a small amount of recovery in affected areas of the brain can induce a major enhancement in lifestyle. This is the promise of stem cell therapy. But our development of suitable therapeutic candidates still exists in the developmental stage. Many problems governing the widespread successful use of stem cell based therapy must be overcome. A set of these problems can be defined as bottlenecks to translation. Such bottlenecks greatly restrict the successful implementation of what should be very beneficial therapy. We have identified two of these bottlenecks, and we propose methods to overcome them.
The first bottleneck is due to the propensity of stem cells to die in huge numbers when they are undergoing expansion and differentiation in the laboratory. Such cell death is a normal event in the growth and development of the human brain, but is of no use and a serious problem in the laboratory. We plan to delineate the pathway to death during stem cell expansion and differentiation, and develop compounds that prevent this unwanted demise.
Paradoxically, the very act of expanding these populations of stem cells can lead to grafts that contain expanding cores of undifferentiated cells, which can be tumorigenic. Thus, excessive proliferation after transplantation of stem cell-derived neural progenitors represents a major bottleneck for therapeutic applications. We plan to overcome this unwanted proliferation of cells by developing compounds that preserve the desirable neuronal character of transplants without unwanted proliferation.
Our objective is to overcome these bottlenecks by identifying FDA-approved drugs or dietary supplements that substantially overcome these blocks. This research route to discovering suitable drugs is greatly enhanced by the fact that these compounds have already been administered to humans and are therefore very well characterized and development ready. Thus our approach has a the potential benefit of providing greater quantities of correctly programmed stem cells without the long wait for approval of novel drugs.
Statement of Benefit to California:
Future stem cell-based therapies will likely be patient-specific and application-tailored. In contrast to basic research, where established neural cell lines represent a “one size fits all” solution, a large variety of new hESCs and iPSC lines need to be created and used for differentiation. Large amounts of viable and multipotent neural progenitors are a prerequisite for all human ES or iPS cell-based therapies for neurodegeneration and for the in vitro testing of polymorphism-sensitive drugs. Extensive cell death, however, dramatically reduces the numbers of desirable neural progenitors. Contrary to the in vitro situation, excessive proliferation after transplantation of human ES cell-derived neural progenitors represents a major problem for the therapeutic applications of hESC, and likely, iPS-derived neural cells. Independent of the particular future stem cell-based CNS therapies/repair, efficient derivation of NPCs is a necessary requirement. Similarly, independently of any specific differentiation protocol, the transplantation of NPCs must be safeguarded from uncontrolled proliferation of transplanted cells and tumor development. Our proposal will help to resolve both critical issues currently hindering progress towards stem cell based therapies.
An effective, straightforward, and understandable way to describe the benefits to the citizens of the State of California that will flow from the stem cell research we propose to conduct is to couch it in the familiar business concept of “Return on Investment”. The novel therapies and reconstructions that will be developed and accomplished as a result of our research program and the many related programs that will follow will provide direct benefits to the health of California citizens. In addition, this program and its many complementary programs will generate potentially very large, tangible monetary benefits to the citizens of California. These financial benefits will derive directly from two sources. The first source will be the sale and licensing of the intellectual property rights that will accrue to the state and its citizens from this and the many other stem cell research programs that will be financed by the CIRM. The second source will be the many different kinds of tax revenues that will be generated from the increased bio-science and bio-manufacturing businesses that will be attracted to California by the success of the CIRM.
The present proposal addresses two perceived bottlenecks to advancing stem cell based therapies for acute or progressive neurodegenerative diseases into the clinic. Firstly, the extensive cell death that occurs during differentiation of stem cell populations severely limits current protocols for their expansion. Secondly, excessive proliferation and potential teratoma formation after transplantation of human embryonic stem cells (hESC) derived neural progenitors represents a major bottleneck for the therapeutic applications of hESC, and likely, induced pluripotent stem cell (iPSC)-derived neural cells. This proposal seeks to overcome these two bottlenecks by 1) determining the mechanisms of cell death during hESC expansion and differentiation to neuronal progenitor cells (NPCs), 2) screening focused compound libraries to identify molecules that prevent this death, 3) screening the same libraries to identify molecules that prevent unwanted proliferation of implanted NPCs, and 4) validate candidates in vivo following transplantation of NPCs into mice. In order to achieve the above mentioned aims, the applicants plan to take advantage of libraries of FDA-approved drugs and dietary supplements that have already been administered to humans and are therefore very well characterized and development ready, i.e. well positioned for rapid IND submission.
In terms of impact, one of the reviewers mentioned that this project’s impact would be in the control of the quantity of NPCs for transplantation and the stability of a transplant. That said, most reviewers questioned the scientific rationale for the proposal, asking whether cell death in hESC cultures is something that should necessarily be prevented. It seems likely in many cases that this death is not due to failure of target recognition (as is the case in vivo during development) but instead to chromosomal abnormalities or pathological changes in the cultured cells. Those reviewers pointed out that transplanting such cells could have deleterious effects and therefore had strong reservations about the logic and the impact of the application. Most reviewers raised questions about the feasibility of the research plan. They were concerned by the relatively small number of compounds to be screened, describing ~6,500 as “a good start” but suggesting that the applicant’s estimated hit rate of almost 1% may be unreasonably optimistic. Preliminary data demonstrating that this hit rate is achievable, using the proposed mouse embryonic carcinoma cell line, for example, would have strengthened the proposal. One reviewer suggested that alternative additional libraries should have been planned to be available in case no good compounds are identified. Another reviewer commented that the proposal is under ambitious and the cell-based screens are too narrowly focused, particularly the second screen for neural differentiation, which focuses on a single target. A reviewer wondered if the proposed mouse carcinoma cell line was the best choice for primary screening in Aim 1 and whether a human reporter cell line could be used. The testing of NPCs in a mouse model of stroke was also questioned, with one reviewer calling it “over elaborate”. This reviewer thought that neonatal brain would be a better, more permissive environment to test integration of hESC-derived neurons and glia, in contrast to the stroke brain where evidence for integration remains extremely poor.
Reviewers praised the experience of the applicant and the excellence of the assembled research team in the areas of cell death and high-throughput screening technologies. However, one reviewer was concerned about a lack of neuroscience expertise in the proposed team. The resources and research environment were judged to be excellent. One reviewer commented that the budget is very high.
Overall, despite the assembly of a great team and the experience of the PI, most reviewers had concerns about the logic of the proposed research, and consequently on its impact in terms of advancing SC-derived therapies neurodegenerative diseases into the clinic. Reviewers also found the research plan to be too narrowly focused and questioned its feasibility.