Myelin Repair Strategy for MS Hits Snag in Phase 2 Clinical Trial
August 30, 2021
Published results from a phase 2 clinical trial of oral bexarotene in people with MS reveal that there were some signs that the drug could help restore the myelin coating on nerve fibers damaged by MS, but the key MRI outcome measured in the trial was not met and people taking the drug experienced serious side effects. The researchers suggest that they will not conduct further trials of this drug, but that similar agents that are more selective may still hold promise.
- Background: MS causes damage to the myelin coating on nerve fibers in the brain and spinal cord, leaving the nerve fibers exposed to injury. There is an unmet need in MS for therapies that can restore function by repairing myelin to improve nerve signaling and protect nerve fibers. Bexarotene is a drug used to treat a form of skin cancer. Previous research in the lab found that drugs like bexarotene that target docking sites in the brain (called retinoid X receptors – or RXR) can encourage cells called oligodendrocytes to produce myelin.
- Study: Researchers at the University of Cambridge and collaborators conducted the placebo-controlled trial with funding from the Multiple Sclerosis Society of the United Kingdom. Fifty-two people with relapsing-remitting MS who were taking the MS disease-modifying therapy, dimethyl fumarate, were recruited. While staying on dimethyl fumarate, half received bexarotene and half received placebo for 6 months.
- Results: All participants treated with bexarotene experienced hypothyroidism (under-active thyroid gland) and most had high levels of triglycerides (a type of fat which at high levels is linked to heart disease). Although there was no change in the primary MRI outcome measure, there were other hints of increased myelin repair in MS lesions in specific parts of the brain and in measures of visual nerve signal conduction.
- Conclusion: The investigators suggest that finding a compound that more specifically targets the version of RXR that showed promise in lab models may still have potential as a myelin repair strategy in MS. Read more about MS research on nervous system repair
These results were originally announced at ECTRIMS Virtual 2020 conference and they are now published in Lancet Neurology
(2021; 20: 709–20): “Safety and efficacy of bexarotene in patients with relapsing-remitting multiple sclerosis (CCMR One): a randomised, double-blind, placebo-controlled, parallel-group, phase 2a study
,” by J William L Brown, Nick G Cunniffe, Alasdair J Coles and others.