The 70th Annual American Academy of Neurology meeting, held in Los Angeles last week, provided an opportunity to check in on antisense therapies and the continued dividends from The ALS Association’s early investment in the technology.
Antisense oligonucleotide therapies are designed to prevent the production of disease proteins, saving the body of toxicity. Despite initial skepticism about the concept, The ALS Association took the lead in developing antisense therapies in 2004. As we learned in Los Angeles, that decision has contributed significantly to the progress made in the fight against ALS.
In December 2016, the Food and Drug Administration approved the first ever antisense drug, Spinraza. Spinraza targets spinal muscular atrophy (SMA), a common neuromuscular disease, which is the leading cause of genetic death in infants and toddlers. This is the first approved treatment for this disorder. This success provides hope for the future of antisense therapies targeting ALS.
Currently, there are more than 20 antisense drugs in preclinical stages or in clinical trials. This includes an ongoing trial to test antisense oligonucleotides that target SOD1, the second most common cause of ALS. That trial is currently in phase I/II. Also, work is being done to prepare the upcoming C9orf72 antisense clinical trial, slated to start in the near future (see more below). The C9orf72 mutation is the most common mutation associated with inherited ALS.
During the American Academy of Neurology Meeting in Los Angeles, experts from multiple neurodegenerative diseases came together to give an overview of ASO therapy past and present. Here is a short summary of the antisense technology presentations.
What are antisense oligonucleotides (ASOs)?
Antisense technology is a way to prevent the production of proteins involved in disease, like SOD1 and C9orf72, with the aim to provide therapeutic benefits to people living with ALS.
In short, ASOs are single-stranded DNA molecules that once they are taken up by cells, ASOs selectively target and bind to messenger RNA (mRNA), the instruction book to make protein. Instead, of the mRNA being made into protein, ASOs direct the mRNA to be degraded in the cells, thereby preventing toxic proteins from being made. Without the mutated protein being created, the cells have a better chance to remain healthy. Thus, the goal for antisense drugs is to slow or even to stop ALS disease progression.
Dr. Frank Bennet from Ionis Pharmaceuticals gave an overview on how ASOs work and how they are classified. Their company and others have worked diligently to improve antisense technology to optimize antisense drug design and delivery to the central nervous system.
ASOs are delivered directly to the central nervous system by direct spinal cord injection into the cerebral spinal fluid, since they do not readily cross the blood-brain-barrier, the central nervous system’s protective barrier. They distribute broadly into the spinal cord and brain tissue following cerebral spinal fluid delivery. The injection lasts on average for months and has efficient target reduction. The ASOs are cleared from the body through normal pathways via the liver.
ASOs Targeting Spinal Muscular Atrophy (SMA)
Dr. Richard Finkel from Nemours Children’s Hospital and Dr. John Day from Stanford University gave case presentations on the challenges and considerations of treatments for spinal muscular atrophy (SMA) and rare neurodegenerative diseases using real-life patient examples.
Since Spinraza’s FDA approval in 2016, there are real world data emerging from commercially treated patients. In general, Spinraza is safe and well tolerated. They are finding that pre-symptomatic treatment is optimal (< 6 weeks of age) and earlier treatment has the most robust response. Also, they are understanding that disease stabilization is a response to the drug.
It is also important to identify different types of patients and how they would best respond. For example, older type 1 and 2 patients with more advanced disease, patients with spinal fusion that makes injection difficult, and high-functioning, ambulant adults, all require further consideration.
Questions to still consider when treating SMA remain. Some examples include:
- Who to treat and when?
- What is the sustainability and stability of response?
- Is there a possible need to treat non-central nervous system tissues?
- Can a dose be personalized for optimal response?
- Are there measures to determine an individual’s best dosing schedule?
- Is there an age limit for treatment?
- Can antisense drugs be further optimized?
They also tackled using antisense therapies in rare diseases, such as Ataxia telangiectasia (A-T), a genetic, immunodeficiency disorder of children that impacts a number of different organs in the body. An immunodeficiency disease is one that causes the immune system to break down, allowing the body susceptible to disease. Here Dr. Day presented a case of one person (“n of 1”) with A-T that was treated with antisense therapy. Issues that need to be considered is not only can “n of 1” treatments could be developed efficiently, but what will the FDA demand regarding efficacy and toxicity testing for the specific antisense drug? Also, what kind of disease models will be required for drug approval?
ASOs Targeting a Rare Disease
Next, Dr. John Berk from Boston University School of Medicine presented work of antisense therapies targeting another rare, fatal, genetic disorder called, Hereditary Amyloid Transthyretin (hATTR) Amyloidosis, where treatment options are limited. In disease, there is a buildup of misfolded tranthyretin (TTR) in vital organs, causing amyloid (i.e. clumps of protein) deposition in nerves and cardiac tissues. This leads to neurologic and cardiac impairment, resulting in progressive decline in quality of life, severely impacting daily living, and limiting a person’s independence.
Inotersen, an ASO drug, was developed by Ionis Pharmaceuticals to specifically target TTR mRNA, preventing its toxic protein production, thus eliminating the bad amyloid protein in cells. Here, Dr. Berk reviewed a phase 3 NEURO-TTR clinical trial, that required subcutaneous injections of the drug once-weekly. The patient population was diverse with stages ranging from one to four, with some having heart impairment, and most having considerable impairment.
The team reported that Inotersen significantly inhibited neurologic disease progression, and importantly, improved quality of life in patients. The extended drug experience in the open label extension is continuing to demonstrate benefit with long term dosing of the drug. The regulatory approval process is advancing under priority review, with a decision expected soon.
Update on ALS C9orf72 ASO Studies
Dr. Robert Brown from the University of Massachusetts Medical School gave an update on the ALS C9orf72 (C9) ASO preclinical studies, which are leading up to a clinical trial. The C9orf72 expansion mutation is the most common cause of inherited ALS. They are working with Wave Life Sciences, Inc. to optimize the antisense therapy using special chemistry methods to improve the ASO selectivity and potency. In mice models, the team was able to preferentially knock down only the repeat-containing transcripts, leaving the normal C9 protein alone. They confirmed selectivity and potency in these models and achieved significant reduction in targeted C9 protein.
Currently toxicology for the C9 ASO drug is ongoing. The clinical trial is anticipated to begin enrolling in Q4 of 2018.
Dr. Lindsey Hayes and team from Johns Hopkins University presented their work to explore the need for strand-specific ASOs to treat ALS, with a focus on the C9 expansion mutation.
DNA is double-stranded, made up of a sense and antisense strand, which are complementary to each other. Messenger RNA (mRNA) is made from a cellular process, called transcription, using one of the DNA strands as a template. The formed single-stranded mRNA transcript is identical to the other DNA strand (not the template). ASOs target specific sequences on the mRNA.
Previous work shows that ASOs targeting the sense strand in C9 animal models demonstrated protective effects. On the other hand, RNA foci and protein aggregates (clumps of protein) are also made up of the antisense C9 strand that have been found both in patient tissue and animal models, which have also conferred toxicity.
Here, the team tested whether strand-specific ASOs targeting both the antisense and sense strand mRNA transcripts are needed to reduce disease toxicity.
They found that strand-specific ASO treatment shows targeted knockdown of sense and antisense repeat transcripts and rescued toxicity in motor neurons derived from induced pluripotent cells (iPSC) obtained from C9 ALS patients. This suggests that both strands make a significant contribution to disease pathways associated with C9 ALS and are important for clinical trial ASO drug design.
For more in-depth information about this session, visit our partner, the ALS Research Forum, article that is coming soon.
Session S25: Advances in ALS abstracts here.
Session N2: Neuroscience in the Clinic: Antisense Oligonucleotide (ASO) Therapy abstracts here.