Funding opportunities

Screening and Development of Novel Therapeutics for Sickle Cell Disease and Thalassemia

Funding Type: 
Early Translational I
Grant Number: 
TR1-01255
Funds requested: 
$4 945 410
Funding Recommendations: 
Not recommended
Grant approved: 
No
Public Abstract: 
The hereditary anemias ß-thalassemia major and sickle cell disease are caused respectively by deficiency or dysfunction of ß-globin. Currently there may be more than 1,000,000 individuals living with one of the two diseases. They are found in a belt stretching from the Mediterranean and West Africa to Southeast Asia and South China, and also in areas like the US that have received immigration from endemic areas. ß-thalassemia mutations impair production of ß-globin and cause severe anemia; attempts to compensatory red blood cell production leads to massive expansion of marrow spaces, with consequent severe bony disfigurement, and an enormous metabolic load that causes growth failure, wasting, and eventually death. The current standard transfusion/chelation therapy treatment must be continued for life, and requires a well developed blood banking system. Bone marrow transplantation can be curative, but it is available to only a few. Most children born with ß-thalassemia major do not have access to anything more than rudimentary health care, and die in childhood having received little or no therapy. Sickle Cell Disease(SCD) is a devastating disorder leading to chronic and cumulative damage to multiple organs. Its manifestations are highly variable; comprehensive management is required to identify and treat complications as they arise, but this treatment is expensive and difficult. Bone marrow transplantation can be curative, but does not reverse organ damage, and the variability of the clinical syndrome makes it difficult to predict which patients are most likely to benefit from transplantation until organ damage has occurred. More than 1 in 375 African-Americans is born with SCD, and there are ~6,000 affected individuals in California and ~80,000 in the US. In sub-Saharan Africa the incidence is much higher. These disorders can be substantially improved by increased production of γ-globin, the closely related ß-like globin expressed in fetal-stage human red blood cells. This strategy presents the best hope for a therapy that can be applied widely and cheaply, as it must be if it is to benefit the great majority of affected children. Any agent that will effectively reverse γ-globin silencing must work on blood stem cells and early differentiating erythroblasts, because it is at this stage that the program of globin expression is set up. We have invented a screen for such compounds, and tested it with promising results. The compounds we have identified appear to be unique and distinct from all known compounds and therapeutics utilized to date. We aim to improve and expand our screen, and to develop the lead compounds it produces. We will perfect our screen by deriving new and more powerful reagents for chemical screening, screen chemical libraries of known drugs, and supplement them with compounds selected by computational methods. Lead compounds will be tested for activity in models relevant to the ß-hemoglobinopathies.
Statement of Benefit to California: 
The hereditary anemias ß-thalassemia major and sickle cell disease affect more than a million individuals. They occur in a belt stretching from the Mediterranean and West Africa to Southeast Asia and South China, and also in areas like the US that have received immigration from endemic areas. More than 1 in 375 African-Americans is born with SCD, and there are ~6,000 affected individuals in California and ~80,000 in the US. In sub-Saharan Africa the incidence is much higher. The numbers of ß-thalassemia cases are lower, but are rising as the US (and particularly California) receives more immigration from areas, particularly India and South China, where the disorder is common. ß-thalassemia major is a severe anemia that when untreated leads to major bony disfigurement, and an enormous metabolic load that causes growth failure, wasting, and eventually death. The current standard transfusion/chelation therapy treatment must be continued for life, and requires a well developed blood banking system. Bone marrow transplantation can be curative, but it is very expensive and available to only a few. Most children born with ß-thalassemia major do not have access to anything more than rudimentary health care, and die in childhood having received little or no therapy. Sickle Cell Disease(SCD) is a devastating disorder leading to chronic and cumulative damage to multiple organs. Its manifestations are highly variable; comprehensive management is required to identify and treat complications as they arise, but this treatment is expensive and difficult. Bone marrow transplantation can be curative, but does not reverse organ damage, and the variability of the clinical syndrome makes it difficult to predict which patients are most likely to benefit from transplantation until organ damage has occurred. Both diseases can be substantially improved by increased production of γ-globin, the closely related ß-like globin expressed in fetal-stage human red blood cells. This strategy presents the best hope for a therapy that can be applied widely and cheaply, as it must be if it is to benefit the great majority of affected children. Any agent that will effectively reverse γ-globin silencing must work on blood stem cells because it is at this stage of red blood cell development that the program of globin expression is set up. We are proposing to use innovative stem-cell based methods to identify compounds that can be developed into oral agents for the treatment of ß-thalassemia and sickle cell disease. Successful development of such an agent would broadly benefit the many affected individuals in California, who would for the first time be able to live free from the onerous complications of these diseases, and it would reduce the cost of providing health care to these individuals. It would also contribute to the development of the biotechnology and pharmaceutical industries in California, since the agent would be very likely to have a very large market around the world.
Review Summary: 
The goal of the proposed project is to advance the development of a potential candidate to treat β-hemoglobinopathies such as sickle cell disease and β-thalassemia, two disorders that result from mutations in the oxygen-binding protein β-globin and represent some of the most devastating diseases worldwide. To this end, the applicants propose to identify drugs that activate the expression of γ-globin, a fetal protein that is normally downregulated in mature tissues but can functionally compensate for β-globin. In the first aim, the applicants propose to develop mouse erythroleukemia (MEL) cell lines with humanized globin loci and a fluorescent reporter for γ-globin activation. In the second aim, these cells will be used to screen chemical libraries to identify those substances that antagonize the silencing of the γ-globin locus and therefore allow the message and protein to be expressed. As a complementary strategy, a secondary screen will be performed on differentiating erythroblasts derived from human CD34+ hematopoietic stem cells. For the third aim, computational methods will be used to virtually screen structural databases to optimize and refine leads, the most promising of which will be subjected to pharmacokinetic analyses. Finally, the applicants propose to develop relevant animal model systems to investigate the efficacy of candidate compounds, including a mouse model for sickle cell disease. The reviewers agreed that the proposed research addresses a critical need for the treatment of β-hemoglobinopathies, a common class of genetic disorders with an enormous impact on global health. Current therapies are far from ideal and are disproportionately unavailable to the poorest communities. As such, there is a strong desire for inexpensive, safe and more specific treatment options such as those represented by the described technology. In general, the reviewers were enthusiastic about the proposed methodology and considered the underlying rationale to be both meritorious and sound. The inclusion of the positive control and the use of human cells as a secondary model were thought to be considerable assets. Furthermore, the research team was described as capable and well assembled. Despite these strengths, however, the reviewers identified a number of weaknesses that were thought to limit the overall feasibility of this approach. First, the size of the proposed compound library was thought to be too small, given that the expected hit rate would likely be extremely low. With only a few promising leads, it seemed premature to embark on the computational modeling strategy for candidate refinement and optimization. Of greater concern, the selected compound concentrations were thought to be excessive, potentially leading to problems with toxicity and/or solubility. At the very least, such levels were generally thought to be inappropriate for clinical use. The reviewers also questioned whether the ambitious strategy for generating reporter lines could be readily accomplished within the limited time frame of this effort. The throughput of the FACS method was also of concern, with one reviewer suggesting that a luciferase reporter/plate reader approach might be a better choice for the assay. Finally, some reviewers were uncertain whether the readout depicted in the preliminary studies would be sufficiently convincing to move forward. In summary, the reviewers agreed that the proposed research addressed an important need, was of compelling rationale, and represented a logical and valid approach. While the investigators were judged to be excellent, a number of limitations in the experimental design were thought to diminish the feasibility of this effort. These weaknesses, combined with the relatively ambitious preliminary aims, raised concerns that the scope of the effort might have been significantly underestimated.
Conflicts: 

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