PLATFORM TECHNOLOGY - Developing Novel Antisense Oligonucleotides for Neurodegenerative Diseases

INTRODUCTION

There have been significant advances in recent years in the development of RNA-targeting therapeutics for genetic diseases that have transformed the field and laid a strong foundation for future next-generation therapies. While gene therapies and gene-editing approaches such as CRISPR that target DNA are often highlighted for their potentially curative efficacy, clinical advances and product approvals of RNA-based therapies, such as antisense oligonucleotides (ASOs) and small interfering RNAs (siRNAs), have demonstrated that messenger RNA (mRNA) is a valid target for treating a range of genetic diseases, including rare neurode­generative diseases. Generally, these first-generation RNA-target­ing therapies involve one of two mechanisms: degrade RNA or modify its splicing. But researchers continue to learn more about how RNA is processed and develop new strategies to alter dys­functional RNA that drives many diseases to unlock the broader potential of RNA-based therapeutics. In this effort, Vico Thera­peutics is building on the clinical success of ASOs and siRNAs by expanding the number of ways we can modulate disease-causing RNA via multiple mechanisms of action, with the promise of ad­dressing wider patient populations.

A NEW PLATFORM TO EXPAND RNA MODULATION

Vico’s platform is to design ASOs to go beyond degradation or splicing modification alone. These ASOs are designed to mod­ulate RNA through multiple approaches, including inhibition of translation, modulation of splicing, editing, degradation, and ac­tivation. We use precision chemistry to identify an RNA modulator that achieves the desired target engagement and safety profile for different diseases to enable optimal ASO candidate selection. Modifications to the underlying disease-causing RNA are re­versible and transient in nature, without permanent changes to DNA code, which is a potential risk with some other therapeutic approaches that target DNA and RNA.

The flexibility of our platform offers the potential to target a broad range of diseases caused by underlying dysfunctional RNA that currently have limited or no therapeutic options. Our team of researchers has chosen to focus initially on severe, genetic neu­rodegenerative disorders, including Huntington’s disease and spinocerebellar ataxia type 1 (SCA1) and type 3 (SCA3). These are all categorized as polyglutamine (polyQ) diseases, a group of neurodegenerative disorders caused by expanded cytosine-adenine-guanine (CAG) RNA repeats encoding a long polyQ tract in the respective proteins. The translated polyQ tract results in mutant proteins that are toxic to nerve cells.¹ Research indicates that longer polyQ repeats are associated with increased toxicity and more severe disease with often an earlier age of onset.²

PROGRESS IN THE TREATMENT OF HUNTINGTON’S & SCA

With Huntington’s disease, the underlying cause is CAG trin­ucleotide repeat expansions in the coding region of exon 1 of the huntingtin (HTT) gene, which results in a mutant HTT (mHTT) pro­tein with an elongated polyQ tract at its N-terminus.³ This expanded polyQ tract leads to a toxic gain-of-function of mHTT protein that builds up in the brain and results in widespread neu­ronal death.

The disease is inherited, progressive, and ultimately fatal, with symptoms includ­ing movement disorders, cognitive impair­ment, dementia, and psychiatric manifestations, such as depression and psychosis. It affects approximately 10 to 15 people per 100,000.⁴ The age of onset is typically in the 30s to 40s, and the dis­ease progresses for about 10 to 15 years until it is ultimately fatal. Although the gene and mutation causing Huntington’s disease was identified 30 years ago, there are currently no approved therapies to delay disease onset or slow its progres­sion.⁵ Most available therapies alleviate some of the movement and psychiatric symptoms, and there remains a significant unmet need for disease-modifying thera­pies.

SCA is a group of rare, progressive hereditary genetic disorders that affects the cerebellum, brain stem, and spinal cord and has the same disease-causing muta­tion as Huntington’s disease. There are six types of SCAs, including SCA1 and SCA3, that are caused by translated CAG trinu­cleotide repeat expansions that encode mutant ataxin-1 (mATXN1) and mutant ataxin-3 (mATXN3) proteins, respectively. The presence of the elongated polyQ tract confers pathogenic properties to the result­ing protein through a dominant gain-of-function mechanism, resulting in degeneration of specific neuronal subpop­ulations that differ between the different SCA types. For SCA1 and SCA3 disease manifestation includes ataxia of gait, stance and limbs, dysarthria, and oculo­motor abnormalities. There are currently no approved therapies indicated for any form of SCA.

VO659 is an investigational allele-preferential ASO for the potential treat­ment of polyQ diseases, including Huntington’s disease, SCA1, and SCA3. VO659 is designed to target expanded CAG repeats in the mutant mRNA tran­script with two mechanisms of action: (1) inhibit mRNA translation of mHTT and mATXN1 or (2) modify splicing in mATXN3 pre-mRNA, both leading to reduction of the corresponding mutant polyQ protein, with the goal of halting or reversing dis­ease progression.

This unique dual mechanism of action of VO659 enables potent target engage­ment across multiple disease models. In preclinical studies, significant and dose-dependent reductions of mHTT protein and improvement in motor function were observed in vivo in disease mouse models of Huntington’s disease.3 Allele-preferen­tial reductions of mHTT were also ob­served in vitro in Huntington’s disease patient cell models. Preclinical data also showed VO659 induced a significant re­duction of mATXN1 and mATXN3 protein levels in vivo in disease mouse models and in vitro in patient cell models of SCA1 and SCA3, respectively.⁶ Preclinical supportive data were recently presented at the CHDI Foundation’s 18th Annual Huntington’s Disease Therapeutics Conference in April 2023.

VO659 is now being evaluated in a Phase 1/2 clinical trial, a multi-center, open-label basket study designed to as­sess the safety and tolerability of multiple ascending doses of VO659 (up to five dose levels) administered intrathecally in participants with early manifest Hunting­ton’s disease or mild to moderate SCA1 or SCA3. The trial is expected to enroll up to 71 participants ages 25 to 60 years with a clinical diagnosis of Huntington’s disease, SCA1 or SCA3, with genetic confirmation of increased CAG repeat length via ge­netic testing.

Exploratory endpoints include the as­sessment of pharmacodynamic biomark­ers (mHTT, total HTT, mATXN3, total ATXN3, and neurofilament light chain) in cerebrospinal fluid, plasma pharmacoki­netics, and clinical outcome measures. The trial will take place over approximately 42 weeks, including a screening period of up to 6 weeks, a 13-week dosing period, and a 23-week post-dosing period.

APPLYING THE PLATFORM TO OTHER GENETIC DISEASES

Our platform is modular in nature, meaning it has the potential to be used to develop multiple ASOs generally using similar principal components. In addition to VO659, researchers at Vico are also ex­ploring potential product candidates for the treatment of Rett syndrome and famil­ial Alzheimer’s disease.

Rett syndrome is another rare, genetic neurodevelopmental disorder, affecting brain development and characterized by severe mental and physical disability. Ap­proximately one in 10,000 to 15,000 girls are affected each year, with cases rarely seen in boys.⁷ Initial symptoms include re­gression of early developmental mile­stones, such as speech and purposeful hand motions, followed by severe motor abnormalities, including respiration, and premature death, typically by age 40. Af­fected boys generally have more severe forms of the disease, often succumbing before 2 years of age.

The underlying genetic defect is a mu­tation in the gene encoding the global transcriptional regulator, methyl-CpG-binding protein 2 (MECP2), located on the X chromosome, which is why girls are gen­erally more affected than boys. MECP2 is a global transcriptional regulator that is essential for normal nerve development and function and acts as one of the many biochemical switches that can either in­crease gene expression or direct other genes when to turn off and stop producing their own unique proteins. There are cur­rently no disease-modifying therapies for Rett syndrome, with available treatments that can only help alleviate symptoms. Vico’s therapeutic strategy is based on ASO-mediated RNA editing to repair mu­tant MECP2 and reverse symptoms.

Alzheimer’s disease is a highly preva­lent, well-known progressive neurological disease for which there are multiple ther­apies in development and clinical ad­vances, including a recent landmark FDA drug approval. But the disease is highly complex, and researchers continue to try to better understand the underlying patho­physiology to develop new effective treat­ment options. There are early and late-onset forms of the disease, both which have a genetic component, and ultimately lead to devastating impacts on cognition, memory, behavior, and motor function.⁸

Early onset Alzheimer’s disease is rare, representing less than 5% of all Alzheimer’s cases and generally occurs in people age 30 to 60. Some cases of early onset Alzheimer’s have no known cause, but most cases are inherited, a type known as familial Alzheimer’s disease (FAD).⁸ Re­search indicates that Alzheimer’s does not have a single genetic cause but rather can be influenced by multiple genes, in com­bination with lifestyle and environmental factors. Of the known genetic variants as­sociated with Alzheimer’s disease, three disease-causing variants are known: amy­loid precursor protein (APP) on chromo­some 21, presenilin 1 (PSEN1) on chromosome 14, and presenilin 2 (PSEN2) on chromosome 1.⁹ If a parent carries a disease-causing genetic variant of one of these three genes then their child has a 50/50 chance of inheriting the mutant form of the gene and developing early onset Alzheimer’s.

Our team of researchers is focused on the PSEN1 inherited form of FAD, with a therapeutic approach in early develop­ment stages based on allele preferential ASO-mediated RNA degradation of the mutant PSEN1 RNA to try to address the root cause of the condition. There is much more work to be done, and additional therapeutic approaches will be required to effectively treat the underlying genetic de­fects associated with different forms of Alzheimer’s disease. But development ef­forts are underway and collectively, re­searchers are taking important steps in the right direction.

SUMMARY

There are many neurodegenerative diseases, rare and common, including Huntington’s disease, SCA1, SCA3, Rett syndrome, Alzheimer’s disease and others with an underlying RNA component that drives each disease. But there is no one-size-fits-all approach to cor­recting disease-causing mutations at the RNA level. It is important to explore a breadth of RNA manipulations and therapeutic ap­proaches to identify the optimal mechanism that will deliver safe, potentially disease-modifying and curative treatments. It will also be essential to continue efforts to better understand the natural history and pathophysiology of genetic diseases and the role of RNA mutations to identify promising biologic targets. We are hopeful that our novel platform for targeting disease-causing RNA with multiple modulating approaches will lead to major ad­vances in treating genetic disease and improving the lives of pa­tients and their families in the years ahead.

REFERENCES

1. Fan, HC., et al. Polyglutamine (PolyQ) diseases: genetics to treatments. Cell Transplant. 2014;23(4-5):441-58. doi: 10.3727/096368914X678454. PMID: 24816443.
2. Paulson, H. L., Bonini, N. M. and Roth, K.A. Polyglutamine disease and neu­ronal cell death. 2000 Oct 31;97 (24) 12957-12958. Doi: 10.1073/pnas.210395797
3. Datson, N.A., et al. The expanded CAG repeat in the huntingtin gene as target for therapeutic RNA modulation throughout the HD mouse brain. PLoS One. 2017 Feb 9;12(2):e0171127. doi: 10.1371/journal.pone.0171127. eCollec­tion 2017.
4. Ross, C.A. and Tabrizi, S.J. Huntington’s disease: from molecular pathogenesis to clinical treatment. Lancet Neurol. 2011 Jan;10, 83–98. doi: 10.1016/S1474-4422(10)70245-3.
5. MacDonald, M.E., et al. A novel gene containing a trinucleotide repeat that is expanded and unstable on Huntington’s disease chromosomes. The Hunting­ton’s Disease Collaborative Research Group. Cell. 1993 Mar 26;72(6):971-83. doi: 10.1016/0092-8674(93)90585-e.
6. Kourkouta, E., et al. Suppression of Mutant Protein Expression in SCA3 and SCA1 Mice Using a CAG Repeat-Targeting Antisense Oligonucleotide. Mol Ther Nucleic Acids. 2019 Sep 6;17:601-614. doi: 10.1016/j.omtn.2019.07.004. Epub 2019 Jul 19.
7. Rett Syndrome, Cleveland Clinic, May 6, 2021, https://my.clevelandclinic.org/health/articles/6089-rett-syndrome.
8. Alzheimer’s Disease Genetics: Fact Sheet, NIH Publication No. 11-6424, June 2011, https://adrccares.org/wp-content/uploads/2016/01/AD-Genetics-Fact-Sheet.pdf.
9. Alzheimer’s Disease Genetics Fact Sheet, NIH National Institute on Aging, March 1, 2023, https://www.nia.nih.gov/health/alzheimers-disease-genetics-fact-sheet.

Dr. Scott Schobel serves as Chief Medical Officer at Vico Therapeutics. Previously, he was Group Medical Director at Roche and the Clinical Science Leader of tominersen and gantenerumab clinical development programs. At Roche, he pioneered the development of clinical endpoints in Huntington’s disease research, co-chaired a task force that generated a new research-based disease staging framework for Huntington’s disease based on underlying biology, and clinically led the first ever huntingtin-lowering therapy Phase 3 program with tominersen. Prior to Roche, he was an Assistant Professor of Clinical Psychiatry at Columbia University Medical Center focused on studying hippocampal dysfunction across neurological and psychiatric diseases using a cross-species neuroimaging approach. He was also Medical Director of Columbia University Medical Center’s Center of Prevention and Evaluation (COPE), a clinical service dedicated to the treatment and longitudinal study of teenagers and young adults at high risk for psychotic disorders. He earned a BA in Japanese from the University of Minnesota, an MD from the University of North Carolina, and an MS from Columbia University.

Dr. Nicole Datson serves as Chief Scientific Officer at Vico Therapeutics and is responsible for discovery and non-clinical drug development. She has more than 20 years of experience in preclinical research in both academia and industry, of which the last 10 years has been in the field of RNA modulating ASOs. Prior to joining Vico, she served as Senior Director Drug Discovery and Early Preclinical Development at BioMarin Nederland B.V. from 2015-2019 and as head of preclinical development at Prosensa Therapeutics B.V. from 2013-2015. She has a strong background in molecular neuroscience and was member of the international Huntington’s Disease Collaborative Research Group that cloned the gene for Huntington’s disease in 1993. She earned her PhD in Molecular Genetics from Leiden University, The Netherlands and held research staff positions as assistant professor at the Department of Medical Pharmacology and Human Genetics at Leiden University and Leiden University Medical Centre (LUMC) from 2005-2013. During her academic career she obtained several prestigious research grants and headed a research group in the field of molecular neuroscience, focusing on identification of genes and pathways controlled by stress hormones in the brain as potential drug targets for treatment of stress-related brain disorders. She is the author of over 70 publications in peer-reviewed scientific journals in the field of molecular genetics, molecular biology, molecular neuroscience and RNA modulation.