Research is being done every day to discover new or better ways to treat diseases and various medical conditions. In order to determine if these treatments will help patients, studies known as “clinical trials” need to be done before these methods of intervention can be safely and widely used in human patients. Clinical trials are regulated studies that involve volunteer human participants to test how safe and effective a potential new treatment.
Treatment interventions being tested can range from medical drugs, to medical devices, to introducing lifestyle changes (diet, exercise). Most clinical trials test new drugs by comparing them to no treatment, to an inactive version of a drug known as a “placebo”, or to a currently available approach. Clinical trials may take months to years to complete and are conducted in a series of steps, known as “phases”, described below.
Phase 1: Is the drug safe?
Healthy volunteers receive different doses of the drug and side effects are evaluated. Safe doses are chosen based on research performed prior to Phase 1, or “pre-clinical research”. The goal is to make sure the drug is not harmful. Usually lasts a few months.
Phase 2: Is the drug effective?
Similar to Phase 1, but the drug is given to a small group of volunteers affected by the medical condition it is intended to treat. This is commonly done by comparing how well participants do with the new drug compared to a placebo. Participants and doctors are typically “blinded”, or prevented from knowing whether the patient received the active drug or the placebo. This is meant to allow for unbiased observations of the participant’s health in response to the drug. Usually lasts a few months to years.
Phase 3: Is the drug still safe? Is it doing what is needed?
Testing becomes a bit more complex. The participant population is expanded while safety and efficacy of the drug continues to be tested. More detailed information about the drug as a treatment is gathered in this phase. Usually lasts several years.
Phase 4: The drug is approved and available on the market.
Long-term effects of the drug will continue to be monitored by pharmaceutical companies and compared to other available drugs and therapies for cost and efficacy.
Written by Terry Suk Edited by Dr. Hayley McLoughlin
In this classic article, researchers describe how CAG repeat number variation can inform differences in the way SCA3/MJD symptoms present.
Machado-Joseph Disease (MJD) was first described in the 1970’s in four families of Azorean descent. However, it was not initially clear that these families had the same disease, since the symptoms they displayed were highly variable. These symptoms included differing degrees of motor incoordination, muscular atrophy (i.e., loss of muscle mass), spasticity, and rigidity. Later, these four diseases were labeled using the single title of MJD due to their similar genetic inheritance and irregularly high symptom variability1.
In the early 1990’s, a group of French families were diagnosed with Spinocerebellar Ataxia Type III (SCA3), a disease that appeared similar to SCA1 and SCA2 but was shown to be caused by distinct genetic mutation. The symptoms of SCA3 were similar to those of MJD and, importantly, also showed a high degree of variability. The major differences between the two diseases, however, were mostly based on geographical origin (Azorean versus French descent) and family history. Thus, these were considered separate diseases, and very few (if any) ataxia researchers studied both.
Then, in 1994, MJD-1 was discovered to be the gene responsible for MJD. The disease-causing mutation in MJD-1 was found to be an expansion of a repetitive DNA sequence in the gene, described as “CAG repeats” (CAG = Cytosine, Adenine, and Guanine)2. Around this time, another research group narrowed down the location of the gene responsible for SCA33. Interestingly, this happened to reside in the same area of the genome as MJD‑1, which was appropriately named the “SCA3/MJD region” soon after. As mentioned above, both SCA3 and MJD patients displayed a wide variety of symptoms. This lead one group of researchers, Cancel and colleagues, to ask the following question in their 1995 publication: What is it about the SCA3/MJD region that leads SCA3 and MJD patients to exhibit such broad symptomatic variability?
Antisense Oligonucleotides (also known as ASOs or AONs) are small molecules that can be used to prevent or alter the production of proteins. Proteins are the workforce of the cell, taking care of most cellular processes. They are generally made in a two-step process: first, a specific protein-coding gene is converted into an instruction file, called the messenger RNA (mRNA). The mRNA carries the information from that gene to the compartment of the cell that builds proteins. There, the mRNA’s information then gets converted into the protein. ASOs are short single stranded pieces of DNA that match the complementary sequence of a specific mRNA. Based on the type of chemical modifications, the ASO can have two different effects on the mRNA. Some modifications of ASOs trigger the destruction of the mRNA. This will result in the loss of the corresponding protein. Other modifications can mask only certain parts of the mRNA leading to a modified version of the protein.
The majority of Spinocerebellar Ataxias (SCAs) are caused by the accumulation of toxic proteins in certain regions of the brain. The primary goal of ASO treatments for SCAs is therefore to prevent the production of the toxic protein altogether. One example is work from Dr. Harry Orr’s group at the University of Minnesota. His lab studies Spinocerebellar Ataxia Type 1 (SCA1), which is caused by the toxic accumulation of the Atxn1 protein. Injections of ASOs into a SCA1 animal model decreased Atxn1 levels and rescued the SCA1 motor incoordination symptoms. Another way of using ASOs as treatment for SCAs is the modification of the mRNAs information to produce a modified version of the protein. This approach has been tested in Spinocerebellar Ataxia Type 3 (SCA3), in which an expansion in the Atxn3 gene renders the Atxn3 protein toxic. The van Roon-Mom group from the Netherlands, for instance, used ASOs to only remove the expansion from Atxn3 while leaving the remaining protein structure and function intact.
Both studies as well as other studies performed for additional SCAs are highlighting the potential use of ASOs as therapeutics for SCAs. While ASO research for SCA is mostly in the pre-clinical phase, ASO treatment for other diseases, including Duchenne muscular dystrophy and spinal muscular atrophy, have already gained approval by the US Food and Drug Administration (FDA). Further clinical trials will need to be performed to measure the therapeutic benefit of ASOs in SCA patients.
If you would like to learn more about antisense oligonucelotides, take a look at this article in HDBuzz about ASOs in development for Huntington’s Disease.
Snapshot written by Larissa Nitschke edited by Dr. Hayley McLoughlin
Written by Carrie A. Sheeler Edited by Dr. Marija Cvetanovic
Group 1 p21-associated kinases (PAKs) present a new avenue for SCA1 research.
Spinocerebellar ataxia type 1 (SCA1) is caused by a specific mutation in the Ataxin1 gene, which causes the protein that’s made from that gene (also called Ataxin1) to have an abnormally elongated polyglutamine (polyQ) tract. This leads to dysfunction and death in the affected cells of the brain (predominantly Purkinje neurons in the cerebellum), which causes symptoms in patients that include a progressive worsening of coordination and balance. While there is currently no cure for SCA1, several studies suggest that lowering the amount of Ataxin1 protein in the brain may delay the onset of the disease and decrease the severity of symptoms. This leads us to an important question: how do we most effectively decrease the amount of Ataxin1 in SCA1 patients? One paper recently published by Bondar and colleagues suggests that a multi-pronged approach could be the most effective means of reducing this toxic protein.
The amount of any specific protein in the body can be altered by either decreasing the amount of protein produced or increasing the rate at which cells break those proteins down. Proteins are made using messenger RNA (mRNA), which is created following specific instructions found in DNA. Decreasing the production or stability of mRNA decreases the amount of corresponding protein made. One way to target the mRNA that causes production of a specific protein is with antisense oligonucleotides (ASOs). ASOs are designed to target specific mRNA sequences by binding to them directly. Binding of ASOs to mRNA causes those molecules to be marked for destruction within the cell. Proteins in the body are also regularly recycled, but without the blueprints to build a new protein, cells cannot replenish the protein supply it loses over time. So, if Ataxin1 mRNAs are targeted and destroyed by ASO treatment, the amount of Ataxin1 in our cells would theoretically decrease.
Some proteins can also be altered by other proteins, creating another way that their stability, shape, and function can be regulated. This leads us to the other way we can alter the amount of a specific protein in a cell: regulating the regulators. In terms of SCA1, this could mean removing a protein that helps stabilize Ataxin1 or increasing the production of a protein that breaks Ataxin1 down. Previous research has identified several proteins of interest that regulate Ataxin1 protein stability, including several kinases. Kinases are a class of proteins that transfer a phosphate group from adenosine triphosphate (ATP) to another protein in the cell. The addition of this phosphate group acts as an energy source to the receiving protein, altering its stability or how it interacts with other molecules in the cell (usually by causing it to change its shape). Recently, Bondar and colleagues have identified a new potential regulator of Ataxin1: a group of proteins known as p21-activated kinases (PAKs) (Bondar et al 2018).
One of the most important features of neurons (Purkinje cells, for example), is that they are capable of electrical communication. Think of the last time you saw a TV intro or movie montage with a depiction of the brain on a microscopic level – though it’s technically invisible to the naked eye, that ‘spark’ you can see traveling down a portion of the neuron is actually not too far from reality. One of the most common ways to describe an active neuron, in fact, is to say that it’s “firing.” Essentially, when a neuron is activated, it ‘fires off’ an electrical impulse that is transmitted down a long, slender extension known as the axon. The axon ends where the next neuron in the circuit begins, and when the impulse arrives at that point, it initiates a series of events that allows the signal to jump to the next cell.
This electrical signal is made possible by molecular machines known as ion channels. These proteins span the cell membrane, which is the barrier between the interior and exterior of the cell. When they receive a certain signal, the channel opens, allowing ions – atoms that carry an electrical charge, such as sodium, potassium, and calcium – to pass through. There are many types of proteins that allow the transport of small molecular components, but the source of a neuron’s electrical capabilities is that its channels specifically allow ions to pass into or out of the cell. Though a single ion’s charge is quite small, the large number of ions that are exchanged when a neuron’s channels open makes for a significant electrical effect – enough to produce an electrical signal that allows neurons to communicate with one another, giving us the ability to think, move, and interact with our environment.
Though the mutations that cause SCAs typically occur in genes that are expressed in every cell of the body, disease is usually restricted to the brain. One theory about why this is the case is that these SCA-related genes are necessary for the health and maintenance of ion channels in certain brain tissues – namely, the cerebellum and brainstem. At any rate, there is evidence that the electrical activity of these brain regions is abnormal in many SCAs, which strongly suggests that ion channels play a critical role in these disorders.