Bexarotene was investigated in laboratory and clinical trials for its potential to repair myelin.
- Bexarotene targets the retinoid X receptor on oligodendrocytes and stimulates myelin production.
- In laboratory studies, bexarotene showed the potential to repair myelin.
- An early stage clinical trial showed some indication of myelin repair, but the dose required led to serious side effects.
- Side effects of bexarotene include increased levels of fats in the blood (cholesterol and triglycerides), reduced numbers of white blood cells, lower levels of thyroid hormones (hypothyroidism), itchy rash, headaches, vomiting and diarrhoea.
- No further clinical trials are planned.
Myelin is a fatty protein that forms a sheath around the axons of nerve cells - the part of the cell that transmits messages to other nerve cells. Myelin acts as insulation to the axon and helps maintain the speed of transmission of messages. In the central nervous system, myelin is produced by cells called oligodendrocytes.
Damage to myelin (or demyelination) caused by multiple sclerosis interrupts or blocks nerve messages. In the earlier stages of MS, oligodendrocytes can often repair areas of damaged myelin - a process known as remyelination. As MS becomes more established, these cells stop functioning or are killed off and myelin is not repaired, resulting in increasing disability.
Bexarotene binds to special locations (receptors), called retinoid X receptors, on oligodendrocytes. Laboratory studies have found that drugs which act on these receptors can encourage oligodendrocytes to remyelinate, offering the potential to reverse damage caused by MS and improve symptoms.
Bexarotene is currently used as a treatment for certain types of skin cancer.
Bexarotene is taken as tablets, once daily.
Laboratory studies have identified a role for the retinoid X receptor in the control of myelin repair. Animal studies suggested that bexarotene, a drug which acts on these receptors, may promote remyelination, offering the potential to reverse damage caused by MS and improve symptoms.
52 people with relapsing remitting MS and taking Tecfidera also took either bexarotene or placebo for six months.
Although the main measure of the study found that bexarotene was no more effective than placebo, there were some hints of increased myelin repair in MS lesions in specific parts of the brain and in visual evoked potential measures. However, the dose required led to serious side effects, including thyroid problems and dangerous levels of fats in the blood. The researchers concluded that bexarotene would not be suitable for further study but safer drugs that work in a similar way could be studied in the future.
In a series of blogs and vlogs, Hellie, a person with MS, chronicles her journey taking part in this clinical trial.
The most common side effects of bexarotene include:
- changes in levels of fats in the blood (cholesterol and triglycerides)
- reduced numbers of white blood cells
- lower levels of thyroid hormones (hypothyroidism)
- itchy rash