Use of small organic molecules to enhance, control, and understand survival and self renewal of human embryonic stem cells in vitro
Overview of proposed research: Our long-term goals are to develop better defined media for in vitro culture of human embryonic stem cells (hESC) and to understand mechanisms regulating survival and self renewal of stem cells in vitro. Achievement of these goals is necessary to facilitate work with hESC and for future therapeutic applications of stem cells to human disease. Our specific strategy is to identify small organic molecules that promote survival and self renewal in hESC when added to culture media. We have already created a focused chemical library containing biologically active molecules that are effective at very low doses. Some of these molecules have growth factor activity when tested with human cells. The first molecule that we tested in this library acts as a potent growth factor for mouse ESC (mESC) cultured without fibroblast feeder cells or a protein substrate for cell attachment. Our goals in the proposed project are to screen our focused chemical library to identify additional chemicals that enhance survival and self renewal of hESC and to characterize the effect of each “hit” on attachment, growth, chromosomal stability, and pluripotency. We will meet these goals by first purchasing about 150 chemicals to augment our already existing focused chemical library. These chemicals will be structurally similar to those we already know to be highly biologically active. We will then screen our augmented focused library using hESC. Cells will be cultured in various doses of each chemical, and the effect on growth will be monitored after 24 hours by comparing cell number in control and treated groups. Chemicals that significantly increase cell number during 24 hours will be considered “hits”, and assays will then be performed on each “hit” to determine their effects on cell attachment, survival and growth, chromosomal stability, and pluripotency. In addition to our own focused library, we also have access to five diverse chemical libraries at our campus that we can screen in the unlikely event that no additional “hits” are found in our focused library. Potential contribution to therapies: There is a great need for developing better defined culture media for the growth and maintenance of hESC. Advances in this area are critical to development of hESC as biomedical tools for treatment of disease. Culture media that support growth without a layer of feeder cells and that are chemically defined are necessary to facilitate work in this field and for future therapeutic applications of stem cells to human disease. Improvements in culturing technology and maintenance of stability are necessary to advance research in this area and will potentially affect all applications of hESC to treatment of disease. In conducting our work, we expect to find multiple chemicals that will become valuable additives in hESC culture media and to contribute to our basic understanding of hESC survival and self renewal in culture.
Statement of Benefit to California:
In November 2004 the voters of California passed Proposition 71 by a large margin indicating the importance of stem cell technology to citizens of our state. Stem cell technology provides one of the most optimistic technologies in biomedical research for the future and has the potential to address treatments for many major diseases such as diabetes and Parkinson's disease. Our country has always been at the forefront of biomedical technology, and California now offers the promise of keeping our country in that position through funding of stem cell research. The development of better technologies for the growth and maintenance of hESC in culture is fundamental to any forward achievements in the application of stem cells to treatment of human disease. Before hESC can be used therapeutically, they will need to be cultured in media that support self renewal and at the same time maintain chromosomal stability and pluripotency. Ideally these media would not have animal products and feeder cells would not be used. Development of suitable media is a complex problem that needs to be explored from multiple perspectives. Improvements need to be thoroughly tested to ensure cells remain capable of self renewal, chromosomally stable, and pluripotent. Our proposed work builds off of our preliminary data that identified a small organic chemical capable of greatly enhancing survival and self renewal of mouse embryonic stem cells (mESC) grown in the absence of a feeder layer or protein attachment substrate. We propose to examine the ability of this and related chemicals to enhance growth, stability, and maintenance of pluripotency of hESC. The data obtained in our project should lead to identification and characterization of small organic molecules that can be added to hESC culture media to improve survival, growth, and maintenance of pluripotency. Addition of such chemicals to culture media will streamline media and make them more defined. Our work may also lead to improvements in methods for culturing other types of stem cells, such as adult stem cells. Moreover many of the chemicals that we will screen are considered safe and are already approved as additives to human consumer products. Improvements in hESC culture media are fundamental to any therapeutic work with stem cells. Data obtained on our project will improve the technology for culturing hESCs and thereby move us a step closer to being able to use stem cells to treat disease. The use of hESC therapeutically will be directly or indirectly extremely important to the citizens of California. Even young citizens who currently do not have major medical problems could benefit in the event of future illness or accidents. Development of hESC technologies and their application to medical problems will also contribute to the overall economy of the state by creating opportunities for the formation of new biotechnology companies and by stimulating growth of existing companies.
SYNOPSIS: The author proposes a chemical screen to identify small molecules that can enhance hESCs’ self renewal and survival. In their first attempt, the first molecule screened was endowed with a subset of such activity. Based on this, two specific aims are proposed. The first is to screen a focused chemical library and identify molecules that have high potency in hESC survival and self-renewal assays. The second specific aim will fully characterize the effect of each hit on the attachment, survival and growth, chromosomal stability, and maintenance of pluripotency of hESC. SIGNIFICANCE AND INNOVATION: Reviewer one: Detachment of hESC culture from xenotropic influences is a major step forward that affects both the basic research as well as potential clinical applications, and thus represents one of the highest priorities in hESC research and has tremendous significance. There is, however, no innovation as these types of screens have been performed in the past and are currently being performed, both in the academic as well as private sector. Reviewer two: The idea of using chemical compounds to understand the biology of cells and organisms is steadily gaining ground, but this proposal is still rather innovative. Identifying compounds that modulate the pluripotency of hES cells might help us to better understand the molecular pathways responsible for the maintenance of pluripotency and the capacity for differentiation in these cells and thus is highly significant. STRENGTHS: A young and talented group will undertake these experiments. UCR has excellent resources for chemical genomics, including a library of 42,000 compounds, and very good experience working mostly with MESCs. In addition, the inclusion of Dr. Noburu Sato as a collaborator clearly shows the commitment of the team to succeed. Dr. Sato is the co-discoverer of BIO, a small compound that maintains hESCs without feeder influences for small number of passages. In addition, the fact that the first compound assayed had activity has provided the group with the optimism required for this type of approach. WEAKNESSES: There are some shortcomings with the project. Among them is the fact that it is very difficult for academia to compete with the private sector in these types of high throughput approaches. The authors will start with a library of 50 compounds, to possibly be upgraded to 200 from the large UCR collection. This is not a lot, considering that robotic approaches using thousands of 384 plates are used in usual industrial settings, so luck will be a crucial and unreliable variable. In addition, one of the advantages of this type of chemical screen is that one can use the active compounds as probes to identify signaling pathways that underlie the biological activity. The author stops short of going this extra mile, however. Specific aim 2 is really a subpart of specific aim 1 and could have been recycled here to address biological targets of active compounds. Finally, the use of non-registry hESCs is not required for this project and thus it could have been funded by the NIH. While some preliminary data is presented in mouse ES cells, it is not clear that the researchers have a good definition (morpholical and molecular) of pluripotent versus differentiated cells. As any high-throughput screen ultimately succeeds or fails on the basis of what is being measured, in this instance the cellular phenotype assessed, it would have been nice to have a more extensive description of what molecular and morpholical criteria the investigators would use in their screens. DISCUSSION: Although the degree of innovation is not high and the size of the library relatively small, the initial success of this approach and the careful approach (for instance, testing multiple concentrations) and the quality of the young, dedicated researchers with experience in compound identification raised the enthusiasm of the reviewers for this proposal.