Advancements in Gene Therapy approaches for familial ALS cases – mAGENTA

Amyotrophic Lateral Sclerosis (ALS) is an incurable disorder, characterized by degeneration of motor neurons (MN) leading to progressive paralysis and death usually within 3 to 5 years after diagnosis. ALS is a rare disorder, however, a recent epidemiological study predicts that, along with aging of the population, ALS cases could increase by 69% in the upcoming years.
Over the past decade, a breakthrough for the treatment of neurological conditions was the demonstration that viral vectors, derived from Adeno-Associated Virus (AAV) can efficiently transduce cells in the central nervous system. Different applications for MN disorders followed this discovery and an AAV-mediated gene transfer approach has been tested in patients affected by Spinal Muscular Atrophy type 1, with encouraging results.
ALS is epidemiologically classified into sporadic (90%) and familial forms (10%, fALS). We recently developed an AAV-mediated gene therapy for fALS, caused by mutations in the SOD1 gene (representing about 20% of fALS cases). Several pre-clinical tests in rodent models overexpressing mutant forms of human SOD1 (hSOD1) have proven the efficacy of knockdown strategies for the treatment of SOD1-ALS. Furthermore, the intrathecal administration of antisense (AS) oligonucleotides against hSOD1 is under clinical trial in SOD1-ALS patients and various AAV-mediated silencing approaches are currently under pre-clinical development. Taking advantage of AAV serotype 10 vectors and the U7 small nuclear RNA particle, we designed and tested AS sequences inducing hSOD1 silencing through exon skipping (AAV10-U7-hSOD1). The result we obtained in SOD1G93A mice (model of SOD1-ALS) was reported as the most favorable therapeutic effect to date and the preclinical work aimed at the clinical translation of this approach to humans is undergoing.
The overall objective of this proposal is to advance the development of gene therapy strategies for fALS. To this aim, we intend to address the effects of the exon-skipping strategy on the silencing of the endogenous non-mutated hSOD1 gene (Objective 1). In addition, we plan to test a similar therapeutic approach for the most common genetic form of fALS and frontotemporal dementia (FTD), caused by hexanucleotide repeat expansion (HRE) in the C9 gene (Objective 2).
Objective 1- For the advancement of SOD1-silencing strategies is important to consider that the long-term removal of the SOD1 enzyme could be detrimental to cell physiology due to its essential role in protecting cells from oxidative stress. Furthermore, data from literature revealed that functional loss of SOD1 worsens ALS disease severity in animal models. Therefore, we propose to test in patient-derived cells the nonspecific silencing strategy based on the AAV10-U7-hSOD1 vector and to compare its effects with a newly generated vector that allows for both hSOD1 silencing (Erase) and re-expression of a functional wild-type hSOD1 (Replace). In parallel, we plan to assess the potential therapeutic effect of the Erase/Replace vector in SOD1G93A mice. The results of these experiments will be pivotal to predict outcomes of undergoing pre-clinical and clinical trials.
Objective 2- The HRE G4C2 in intron 1 of the C9 gene is responsible of ALS, FTD and ALS/FTD through three non-exclusive pathological mechanisms including loss of protein function, toxicity of nuclear HRE RNA and accumulation of dipeptide repeats. The potential therapeutic effect of AS oligonucleotides for the treatment of C9-ALS entered in a phase I/II clinical trial. The main goal here is to prove the therapeutic efficacy of an AAV-U7-mediated AS delivery for C9-ALS for durable and widespread transduction of affected tissues. We plan to test this approach in human cell models and in pre-clinical setting in vivo. The results of this study will be a prelude to the development of a pre-clinical therapeutic strategy for patients with ALS, FTD and ALS/FTD.