Tolebrutinib is an investigational drug. Its safety and efficacy have not been established and are being investigated in these phase III trials. Tolebrutinib has not been approved for the treatment of MS by any regulatory authority.
In the completed phase II study, 130 participants with relapsing forms of MS (not primary progressive MS or non-relapsing secondary progressive MS) took one of 4 doses of tolebrutinib for 12 weeks either before or after taking placebo for 4 weeks.
The primary purpose of the study was to compare the results of the different doses of tolebrutinib to help decide which dose to study in the phase III trials. Thirty-two of the 130 participants received the highest dose of tolebrutinib (same as used in current clinical trials), and 1 of those 32 withdrew consent because of the contraception requirement. Compared to the 4-week placebo period, the group that received the highest dose of tolebrutinib (same as used in current clinical trials) saw an 85% relative reduction in new gadolinium enhancing brain lesions, but because of the relatively small sample size per dosing group and a treatment period of only 12 weeks, this study was too short to assess effects on clinical outcomes such as relapses and disability.
The most frequent adverse events were headache (3 to 13%), upper respiratory tract infection (3 to 6%), and nasopharyngitis (3 to 9%). Of the 32 participants that received the highest dose of tolebrutinib, one had elevated alanine aminotransferase that exceeded three times the upper limit of normal, and one was hospitalized because of a MS relapse. The clinical significance of these data is under investigation.
Tolebrutinib is experimental (not approved by health authorities) and administered orally, once daily, as a coated tablet. It inhibits an enzyme called “Bruton’s tyrosine kinase (BTK)”. BTK is involved in the activation of B cells, which are immune cells that affect the cells in the brain and spinal cord contributing to MS. Tolebrutinib penetrates the brain and spinal cord and may inhibit the BTK involved in the activation of immune cells in the brain called microglia, which have been shown to be involved in MS disability progression. Tolebrutinib is still under investigation for the treatment of MS, and its efficacy and safety have not been established.
As we learn more about MS, it is becoming clear that there are pathways inside and outside the brain that are important for understanding multiple sclerosis. This video explores the role of immune cells inside and outside the brain to MS, including B cells and microglia, and their pathways of cell activation.
CNS: The central nervous system is represented by brain and spinal cord
B cells : A type of white blood cell that makes antibodies. These antibodies trap specific invading viruses and bacteria, helping the body to finish fighting most infections. B-cells also produce other substances with important role in the body immune response and inflammation.
Microglia: Microglia are specialized population of cells that reside in the brain and spinal cord. They remove damaged neurons and infections and are important for maintaining the health of the CNS.
Enzyme: An enzyme is a substance produced by the body to assist in breaking down chemicals.
Immune pathways involving cells compartmentalized in the CNS: Defense pathways which involve different type of cells which reside in the brain and spinal cord.
Immune and inflammatory mediators: substances with important role in the body defense against infections and in the inflammation.
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