Tools and Technologies II
Autism Spectrum Disorders (ASDs) are a heritable group of neuro-developmental disorders characterized by language impairments, difficulties in social integrations, and the presence of stereotyped and repetitive behaviors. There are no treatments for ASDs, and very few targets for drug development. Recent evidence suggests that some types of ASDs are caused by defects in calcium signaling during development of the nervous system. We have identified cellular defects in neurons derived from induced pluripotent stem cells (iPSCs) from patients with Timothy Syndrome (TS), caused by a rare mutation in a calcium channel that leads to autism. We propose to use cells carrying this mutant calcium channel to identify drugs that act on calcium signaling pathways that are involved in ASDs. Our research project has three aims. First, we will determine whether known channel modulators reverse the cellular defects we observe in cells from TS patients. It is possible that we will find that existing drugs already approved for use in humans might be effective for treating this rare but devastating disorder. Our second aim is to determine whether screens using neuronal cells derived from ASD patients can be used to identify calcium signaling modulators. A bottleneck to therapy development for ASDs has been the lack of appropriate in vitro models for these disorders, and we would like to determine whether our studies could serve as the basis for a new type of screen in human neurons. Our third aim is to identify signaling molecules that might be affected in patients with ASDs, which could be targets for future drug discovery. There is increasing evidence that several types of ASDs are caused by defects in neuronal activity and calcium signaling. More specifically, the CaV1.2 calcium channel that we are studying has been implicated in syndromic and non-syndromic forms of autism, and also in schizophrenia and bipolar disorder. One of the more exciting aspects of our screen of neurons with a mutation in CaV1.2 is that it gives us a tool to explore calcium-mediated signaling pathways that are defective in ASDs. We will try to modify calcium signaling in neurons from ASD patients by changing the expression of proteins that are known to affect calcium signaling in other contexts. These experiments will identify targets that are active in human neurons and that affect cellular phenotypes that are defective in ASD. In summary, the work described in this proposal constitutes a critical step to fulfilling the promise that reprogramming of patient-specific cells offers for the treatment of neuropsychiatric disorders such as autism. Our studies will identify lead compounds that could be tested in the clinic for a rare form of autism, and novel molecular targets for therapeutic development in the future. Importantly, these studies will provide a proof of principle that iPSC-derived cells are valuable for drug discovery for neuropsychiatric disorders.
Statement of Benefit to California:
Autism Spectrum Disorders (ASDs) affect approximately 1 in 110 children in California. In addition to the devastating effects that ASDs have on the families of affected individuals, treating and educating people with ASDs imposes a heavy economic burden on the state. In 2007, almost 35,000 individuals with autism were receiving services from the California Regional Centers, and the number was expected to rise to 50,000 by last year. Recent estimates suggest that the lifetime cost of caring for an individual with an ASD can exceed $3 million. In spite of their impact on our society, there are currently no effective therapies for ASDs. Our lack of cellular and molecular tools to study these disorders means that there are no good targets for drug screening, so there are very limited prospects for developing effective pharmacological treatments in the near future. New drug discovery paradigms are needed to help develop therapies for these neuropsychiatric conditions. The research described in this proposal could have a dramatic impact on drug discovery methods for ASDs. First, we hope to identify drugs that are effective in treating Timothy Syndrome, a rare form of autism caused by an electrophysiological defect in a calcium channel. Second, we aim to develop new tools to explore calcium-mediated signaling pathways that are defective in ASDs. If successful, our research will identify a family of molecular targets that will be useful for developing therapies for ASDs in the future.
Autism spectrum disorders (ASDs) are neuropsychiatric disorders that have been difficult targets for therapeutic drug development due to the lack of validated animal or cellular models of disease and the lack of validated molecular targets in human neurons. Utilization of induced pluripotent stem cell (iPSC) technology allows for the development of in vitro neuropsychiatric disease models in which patient specific iPSC-derived cells display disease specific molecular and cellular phenotypes. Such a model has been developed for Timothy Syndrome (TS), a rare ASD that results from a mutation in a L-type voltage gated calcium channel (LTC). The goal of this application is to utilize the TS iPSC disease model to develop iPSC-based screening tools and to identify novel LTC molecular drug targets. The applicant suggests that although TS is rare, development of the described tools and elucidation of LTC molecular drug targets could be more broadly applicable, as mutations leading to LTC dysfunction have been implicated in both bipolar disorder and schizophrenia. In Aim 1, the applicant will determine whether LTC blockers that are currently in clinical use can reverse the cellular phenotype observed in TS iPSC-derived neurons. In Aim 2, the applicant will design a medium-throughput screen that measures the calcium responses of TS iPSC-derived neuronal precursor cells and identify disease-modifying compounds. In Aim 3, the applicant will conduct an RNAi (RNA interference) screen to identify proteins involved in LTC signaling and affecting the cellular phenotype observed in TS iPSC-derived neurons in order to identify novel therapeutic targets for ASDs, biopolar disorder, and schizophrenia. Reviewers agreed that the lack of appropriate cell-based models is a major hurdle in the development of effective treatments for ASD and other neuropsychiatric disorders. Successfully utilization of iPSC-based modeling of TS to identify therapeutic drug candidates or molecular drug targets would represent a major breakthrough with possible impact to other ASDs, bipolar disorder, and schizophrenia patient populations. Although the reviewers agreed the application’s rationale was excellent and clearly presented, they raised some reservations regarding the level of innovation inherent in the applicant’s approach. Reviewers felt it was not clear whether an entirely novel tool would be developed or if an existing technology would be used to identify phenotypes for the iPSC screen. However, these concerns were minor when compared to the potential impact of a possible therapeutic advance. The reviewers were generally enthusiastic about this application. Reviewers believed the first two aims were thoroughly described, supported by preliminary data, and appeared entirely feasible with good success criteria. The impressive preliminary data supported the applicant’s ability develop the cell lines and assays necessary conduct the proposed screens. Reviewers expressed some concern that beyond mentioning that control lines had been derived, the applicant paid very little attention to control cell lines or describing their kinship to the disease lines and missed the opportunity to create a rescued TS line that would provide a perfectly matched control cell line. However, the strength of the preliminary data describing the applicant’s ability to generate iPSC-derived neurons displaying distinguishable disease phenotypes to some extent negated this concern. Reviewers were less enthusiastic about Aim 3 and considered this aim to be the major weakness of the proposal. Reviewers commented that the feasibility of Aim 3 is insufficiently supported by preliminary data and the experimental plan is poorly described. For example, the applicant does not provide any detail describing how the RNAi screen will be performed nor which genes will be selected and how they will be prioritized. The scientific approach is logical, but reviewers felt it difficult to assess the significance of this aim without further elaboration. Reviewers noted the other flaw in this proposal is the lack of alternate plans or discussion of potential pitfalls. One reviewer stated that regardless of an applicant’s confidence in his/her abilities to complete a set of proposed goals, an applicant must address this section for a reviewer to feel confidence in the feasibility of the proposed experiments. Despite these concerns, the reviewers maintained their enthusiasm about the application given the excellent preliminary data and sound scientific rationale. The principal investigator (PI) is an outstanding scientist who is the foremost expert in the proposed area of research. The applicant has a stellar list of publications and has an outstanding track and funding record. The applicant institution is excellent and has the necessary facilities to help accomplish the proposed research. The research team is comprised entirely of members from the applicant’s research group, and the applicant states that his/her group has the collective expertise to complete this project. However, it was noted that the publication records of all the key personnel on the proposal do not entirely support this so one must take the applicant’s word for this claim. In summary, while reviewers were enthusiastic regarding the potential impact, the strong PI, and the overall feasibility of this application; their enthusiasm was somewhat tempered by concerns regarding Aim 3 and the lack of alternative plans.
- A motion was made to move this application into Tier 1, Recommended for Funding. No specific programmatic reason was identified. The motion carried.