2021 saw advances in a number of projects sponsored by the AHC organizations. Here is an update of where we are today in each of them:
We are continuing to assess our AAV mediated gene therapy at the Jackson Laboratory. Behavioral testing in mice has been underway for the last two years. We are now on our third pilot study.
So far, the results are compelling, especially in terms of two important measures: survival and hypothermia-induced dystonia. We are seeing early data from the third pilot now, and tests will continue for the next couple of weeks.
We are running four tests and analyses on our mice in our third pilot. We are measuring:
Pilot 2 showed some important data for the efficacy of our vector, particularly in the hypothermia induced dystonia test. When AHC mice are placed in cold water, their body temperature decreases and the mice all develop dystonia. Some even die. This is a clinically-relevant phenotype, and it was discovered and reported previously by other scientists in other AHC mice. We confirmed this phenotype in our AHC mice at Jax. It is severe and fully penetrant—every single AHC mouse shows it. In an important finding, several AHC mice that had been injected with our AAV vector either did not develop cold-induced dystonia or demonstrated a milder version of it. This was an exciting result, and we hope to see more hypothermia-induced dystonia data in Pilot 3.
While our collaborating scientists have real confidence that the therapy is working, the fragile mice are difficult to keep alive in sufficient numbers. Achieving statistical significance is difficult because a number of mice do not survive until testing can begin. Stress from laboratory tests can also cause death in the mice. However, the pilot studies have been designed to allow some comparisons between pilots, and this combined data also adds additional reason for confidence.
Looking forward, the next phase in the project will look ahead to the approval process for new treatments at the FDA. We will need to present a compelling case that gene therapy is a viable clinical option for AHC, and satisfy the specific requirements of the FDA. Objectives for the next phase at the Jackson Laboratory will consequently include collating existing data and filling gaps, with a particular emphasis on dosing and achieving statistical significance where possible.
David Liu’s lab at the Harvard-MIT Broad Institute has just completed the first year of their gene editing project. Under the capable leadership of David and Alex Sousa, the team has made encouraging progress.
Earlier in the project, the team determined that prime editing, a highly versatile and programmable mammalian cell gene editing technology invented by the Liu group, would be the most appropriate gene editing technique to directly correct the AHC D801N mutation. Alex and his team began the process of designing the optimal prime editor. Through a great deal of careful design and iterated development of prime editing systems tailor-made to correct the D801N mutation, the team achieved high-efficiency correction of this mutation with minimal editing byproducts in cultured cells.
The team is in the process of completing in vitro studies before testing their most promising prime editing systems on our AHC mouse model. Testing on mice will occur in the next phase of the project, either at Harvard or at the Jackson Laboratory. The Liu lab will deliver the prime editor to the neurons of the central nervous system. Instead of delivering extra functional copies of ATP1A3, as in the AAV project, the lab will deliver the optimized prime editor system to correct the DNA.
The gene editing project and the AAV project benefit from considerable technical overlap. We are sharing as much information as possible on animal husbandry, procedural details, and behavioral tests from the AAV project. We hope that the lessons learned about the fragility of the mice, especially their propensity to die from stress, and the challenges to keeping them alive, can help the Liu team as they move forward.
AHC is one of the first diseases that the Liu lab is attempting to treat with prime editing. The team is excited to use AHC as a testing ground to apply and further advance knowledge of prime editing technologies, using their experience with AHC to “write the book” on prime editing, a metaphor Alex described last week. AHC is thus at the forefront of the most advanced tool for genetic medicine with the Liu lab, and it is incredibly exciting both for the AHC community, and for the future of rare disease treatment.
We are also considering a third area of research stemming from our previously funded research at Northwestern University: Antisense oligonucleotides (ASOs). We are in a very early exploratory stage of this effort. This area of AHC research may be the least mature, but the technology has received FDA approval for other diseases.
ASOs are short synthetic chains of nucleotides that are designed to block the translation of mRNA molecules to prevent expression—and the negative effects—of the mutant ATP1A3 gene.
The project could eventually include the design and testing of ASOs to knock down the AHC-associated mutant copy of ATP1A3 gene in AHC. As a first step, we plan to explore in vitro testing to assess whether elimination of the disease-causing copy of the gene rescues the neuronal defects associated with AHC. This work will be done in neurons that were generated using AHC patient cells, so findings from this experiment are clinically translatable, relevant, and specific. Subsequent testing in our mouse model will allow us to determine if we can rescue the behavioral phenotype on an organismal level (in vivo).
A secondary approach to ASOs may also hold promise. We may also explore the use of ASOs to enhance or up-regulate expression of ATP1A1 and ATP1B1, which could help compensate for the loss of ATP1A3 functionality that occurs with AHC.
At this preliminary stage of the project, we are exploring proposals and contracts at Northwestern and Charles River to design and test the ASOs.
If we move forward further, we will pursue the ASO project with the same careful, measured approach that we have applied to the other research projects underway: we will phase all research with deliberate decision points where we can decide to proceed with, or halt, the project.
We are pursuing several complementary strategies to develop therapy for AHC by addressing the root cause of it: correcting or supplementing the deficiencies in ATP1A3 gene. The projects are in different stages, but each holds promise for our patients. In theory, our patients may be able to benefit from all of these therapies. In short, we are pursuing each of the best identified potential treatments for AHC.
While the projects are separate, we are encouraged by the overlap between them and by the shared enthusiasm of the researchers working on them. Scientists from the different projects are collaborating, learning from the other projects, and developing ideas for future approaches and assays.
A portfolio of promising projects, enthusiasm and collaboration from our scientists, a careful funding approach—we believe this combination will translate into the best possible outlook for patients.