Experimental Treatments for SMA
Spinal muscular atrophy (SMA) is an inherited neurodegenerative disorder characterized by progressive muscle weakness. SMA patients do not produce enough of a protein called survival motor neuron (SMN), due to a mutation in the SMN1 gene. Another gene, SMN2, also can produce some SMN protein, but it is less stable.
A number of experimental therapies are in the pipeline for the potential treatment of SMA. These include treatments aimed at increasing SMN protein levels, enhancing residual SMN function, and compensating for its loss. Some of the therapies currently in development for SMA are summarized below.
Branaplam (also known as LMI070 or NVS-SM1) is a potential treatment being developed for babies newly diagnosed with SMA type 1. It is designed to increase the amount of functional SMN protein produced from the SMN2 gene. In mouse models of SMA, it was found to increase amounts of SMN protein, leading to improvements in body weight and survival of the animals. The potential therapy currently is being tested in a Phase 1/2 trial.
Olesoxime (TRO19622) is a neuroprotective agent being developed to treat SMA. Instead of targeting factors related to SMN gene expression or survival motor neuron (SMN) protein function, olesoxime instead binds to the mitochondrial permeability pore and blocks excessive permeability during times of intracellular stress.
Reldesemtiv (formerly CK-2127107) is an investigational therapy that may improve muscle function and physical performance in people with SMA or amyotrophic lateral sclerosis (ALS). It works by slowing the rate of calcium release from a group of proteins called the regulatory troponin complex, potentially increasing the capacity of skeletal muscles to contract. It has completed a Phase 2 trial with positive results.
Beta2-adrenoreceptor agonists have been shown to increase levels of SMN gene products both in vitro and in vivo. A study has shown that the beta2-adrenergic agonist salbutamol is a safe intervention even at high doses and that it may help certain SMA patients. The study also supported the idea that SMN may work as a reliable biomarker for SMA. This research represents the first longitudinal study that has monitored SMN levels in response to a drug that modulates gene expression.
Valproic acid has long been indicated for the treatment of seizures, mania, and migraine prophylaxis and has been used off-label for painful diabetic neuropathy, postherpetic neuralgia, and status epilepticus. Valproic acid is known to increase levels of the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA). However, this small molecule is also a histone deacetylase inhibitor. It is this mechanism of action that earned valproic acid the attention of SMA researchers.