Background:
Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disease with very limited treatment options. A defining pathological hallmark in approximately 97% of People living with ALS (PlwALS) is nuclear depletion and cytoplasmic aggregation of TDP-43 in motor neurons (Brown et al., 2022; Ma et al., 2022). Loss of nuclear TDP-43 disrupts RNA splicing, including that of UNC13A, leading to transcript degradation and loss of protein. Because UNC13A is essential for synaptic transmission in the brain, spinal cord, and neuromuscular junction (Augustin et al., 1999), its depletion impairs circuit function and contributes to paralysis. Trace Neuroscience is developing therapeutics that restore UNC13A protein and synaptic function, thereby extending the promise of genomic medicine to PlwALS with TDP-43 pathology.
Objectives:
We conducted a comprehensive screening and optimization campaign to identify an antisense oligonucleotide (ASO), TRCN-1023, that specifically prevents UNC13A mis-splicing under conditions of TDP-43 nuclear depletion, thereby restoring normal UNC13A expression. TRCN-1023 was evaluated in human neurons and in novel humanized mouse models to assess the molecular and functional consequences of UNC13A splice correction upon TDP-43 depletion. Toxicity and pharmacokinetic studies were performed in rodents and non-human primates to support advancement toward human clinical testing.
Results:
Nearly 1,000 ASOs with varied sequence and chemistry were screened in human neurons for potency, selectivity, and off-target effects. TRCN-1023 emerged as a potent, dose-dependent splice modulator that restores correctly spliced UNC13A and reduces cryptic-exon–containing transcripts in neurons with reduced TDP-43. At doses several-fold higher than those anticipated for human efficacy, TRCN-1023 was safe and well tolerated in rodents and non-human primates. Pharmacokinetic studies demonstrated a long CNS tissue residence in the brain and spinal cord, supporting durable activity with infrequent dosing.
Conclusion:
These nonclinical data strongly support advancement of TRCN-1023 into an international, multicenter, randomized, double-blind, placebo-controlled Phase 1/2 trial (FUNCtion ALS).