D - Oligonucleotide Therapeutics (including siRNAs, aptamers, antagomirs, miRNAs, shRNA, antisense, and splice switching oligos, plasmids)
1223: Divalent siRNA Therapy for Huntington's Disease Demonstrates Robust Safety and Efficacy in Pre-Clinical Assessment in an Ovine Model
Type: Poster Session
Poster Board Number: 1223
Presentation Details
Session Title: Thursday Posters: Oligonucleotide Therapeutics
Background: Huntington’s Disease (HD) poses a significant challenge as an autosomal dominant neurodegenerative disorder, resulting from the expansion of CAG repeats on chromosome 4. This expansion triggers the translation of a mutant huntingtin (mHTT) protein. Its chronic expression leads to protein aggregation in the central nervous system (CNS), and subsequent cell death. The severity and onset of HD correlate with the size of the CAG repeat, manifesting in various symptoms like choreiform movements, behavioral disturbances and dementia. Despite the absence of therapies capable of altering the onset or progression of the disease, there remains an urgent demand for safe and effective interventions. A prevailing hypothesis suggests that diminishing mHTT expression within the CNS could alleviate the pathological features of the disease and improve the overall clinical condition.
Methods: Our study addresses the therapeutic potential of a non-allele selective divalent small-interfering RNA (di-siRNA) scaffold designed to reduce normal huntingtin (HTT) and mHTT expression in the CNS. Utilizing this di-siRNA, notable efficacy was achieved in mice. However, acute seizures were noted, likely due to siRNA's negative charge. To address this issue we optimized the formulation to include calcium and magnesium cations and corrected the seizure phenotype. Advancing to a pre-clinical stage, safety and efficacy assessments were conducted in wild type sheep (n=28 divided in 7 cohorts) through intracranial ventricular (ICV) and intrathecal injections. Cohorts included a low ICV dose (25mg) and dose escalation groups (50, 75, and 100mg). Lumbar intrathecal injections offer an alternative less invasive route; therefore we tested a moderate 50mg dose. Safety and HTT knockdown (mRNA and protein) were analyzed 2-months and 6-months post-injection. Safety monitoring included real-time holter electroencephalography (EEG), histopathology and pre/post-MRI analysis.
Results: EEG revealed a dose-response toxicity: 25 and 50mg doses demonstrated safety, while 100mg resulted in seizures. Tissue analysis revealed efficacy in the striatum of sheep, one of the regions of the brain most severely affected by HD, demonstrated by HTT mRNA and protein reduction. The 50mg dose demonstrated superior efficacy compared to the baseline dose, revealing a notable reduction of approximately 50% in mRNA and an approximate 75% decrease in HTT expression. Intriguingly, doses >50mg did not increase knockdown further. After 6 months silencing in the cortex and hippocampus was evident, but not in the striatum.
Conclusion: Here we demonstrated the potential of a di-siRNA as a therapeutic approach for HD. The observed dose-dependent seizure phenotype emphasizes the necessity for meticulous safety EEG assessments. The long-term durability findings suggest a need for repetitive dosing <6 months to sustain the therapeutic efficacy in the striatum. Next, we will test the impact of repetitive dosing using the most effective and safe dose (50mg). Looking toward future clinical trials, we will also test magnesium-only formulation, addressing the unavailability of USP-grade calcium and magnesium buffers. These findings not only advance our understanding of HD treatment but also pave the way for future clinical trials.
Plain Language Summary
In our quest to tackle Huntington's Disease (HD), a devastating neurodegenerative disorder, we explored a promising avenue: a sophisticated genetic tool called the di-siRNA scaffold. This approach aims to reduce the expression of the problematic huntingtin protein within the brain, offering hope for mitigating HD's debilitating effects. Our experiments in mice demonstrated encouraging results, but challenges emerged. We fine-tuned our approach in a comprehensive study involving ovine models, carefully examining safety and efficacy through different dosing strategies. While we observed dose-dependent toxicity, especially at higher levels, our optimized 50mg dose showcased superior effectiveness, significantly reducing the abnormal protein. These discoveries underscore the importance of refining dosing strategies and formulation. As we delve deeper, ongoing histopathology analyses will unveil the intricate tissue-level effects, guiding us towards future clinical trials. This marks a substantial stride in developing targeted therapies for HD, bringing newfound optimism to patients and their families.
Hector Ribeiro Benatti1, Rachael Miller1, Toloo Taghian1, Dimas E Moreno1, Jillian Gallagher1, Erin F. Hall1, Abby McElroy1, Nathan K. Yingling1, Vania Anagnostakou1, Ellen Sapp2, Marian DiFiglia2, Anastasia Khvorova1, Heather L. Gray-Edwards1, Neil Aronin1
1UMass Chan Medical School, Worcester, MA,2MassGeneral Institute for Neurodegenerative Disease, Charlestown, MA"
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