Background: Expansion of short sequences of genetic code, called microsatellite repeats, to sometimes upwards of thousands of copies, results in a number of human diseases, including Huntington's disease and myotonic dystrophy. One of these types of mutations, located in the C9ORF72 gene, was identified in 2011 as the most common cause of both familial and sporadic amyotrophic lateral sclerosis (ALS). ALS is a devastating disorder that causes the death of specific nerve cells in the brain and spinal cord that control muscle movement. The disease, which results in paralysis, usually strikes people between the ages of 40 and 70. Currently there are no effective treatment strategies for ALS or any of the more than forty other microsatellite disorders.

Research in the laboratory of Dr. Laura Ranum has identified key mechanisms that play an important role in C9ORF72 ALS (C9-ALS). First Dr. Ranum demonstrated using another microsatellite repeat expansion disease, called spinocerebellar ataxia type 8 (SCA8), that repeat expansions can be bidirectionally transcribed. Transcription of a gene into RNA was previously thought to occur in one direction but when bidirectional transcription occurs transcripts are made in both directions, resulting in two transcripts harboring the repeat expansion mutation instead of just one. Second, Dr. Ranum discovered a new process by which the expansion RNAs can be translated into proteins without the need for what was thought to be a critical signal, an ATG start codon. As opposed to normal translation, which results in expression in a single reading frame that contains an ATG start codon and in which one gene makes one protein, Dr. Ranum demonstrated that this new process, called repeat-associated non-ATG (RAN) translation, results in the production of protein from all three reading frames regardless of the presence of an ATG-codon. The resulting RAN proteins have now been shown to be toxic to cells and to accumulate in the brains of patients with C9-ALS and a growing number of microsatellite expansion diseases.

Approach: As part of their research into C9-ALS, the Ranum lab has generated a mouse model that mimics the neuromuscular, neurological, and molecular features of ALS in patients. They have also demonstrated that inhibiting the protein kinase R (PKR) pathway, which responds to RNA produced during viral infections, can reduce RAN translation and the production of toxic RAN proteins. They have generated preliminary data showing that different approaches to altering the PKR pathway not only reduces the accumulation of RAN proteins but also reduces disease symptoms in their C9-ALS mouse model. Additionally, they have identified an FDA-approved drug, metformin, as a potential modulator of the PKR pathway, which can also reduce disease symptoms in their mouse model. The proposal will explore the mechanisms associated with the therapeutic potential of PKR inhibition, including the mode of action of metformin in combating ALS and the potential development of more potent derivatives of metformin.

Scientific Objective: The objective of this proposal is to explore the mechanism and therapeutic potential of PKR inhibition, including the use of the FDA-approved drug metformin and metformin-like derivatives on C9ORF72 ALS.

Clinical Application and Patient Impact: This treatment approach will be applicable to all ALS patients with the C9ORF72 repeat expansion, which is the most common cause of ALS. Since metformin is already FDA-approved and has a long safety history in the general population, this approach may provide a fast, inexpensive, and effective treatment for ALS that directly targets a key disease mechanism by reducing C9ORF72 RAN proteins. In addition to ALS, there is potential that this strategy could benefit a large number of additional repeat expansion disorders.

Time for Patient-Related Outcomes: Preclinical data generated will help to identify safety and dosing issues related to the use of metformin and the C9ORF72 expansion mutation and should pave the way for the development of additional, more effective second-generation drugs. It is possible that patient trials could begin in 3-6 months and patient-related outcomes within the next year given that metformin is already FDA-approved and has a long history of safe use in a large percentage of the general population.

Contribution to Therapeutic Development: This study has the potential to advance to the clinic within a short period of time as a readily available, cost-effective, and safe treatment option for C9-ALS patients that advances beyond the currently available and modestly effective treatment options. Additionally, because the approach explores and exploits a specific pathway that contributes to disease, it has the potential to open up additional targets for therapeutic intervention, not only in C9-ALS but also potentially in over 40 other expansion diseases.