The designation is supported by the positive outcomes from the double-blind Phase III HERCULES trial, where the therapy showed a 31% delay in the time to onset of six-month confirmed disability progression (CDP) versus placebo.
In the trial, tolebrutinib also showed promising outcomes in secondary endpoints. The proportion of subjects who saw confirmed disability improvement was nearly double at 10% with tolebrutinib, in contrast to 5% for those on placebo.
However, the trial also noted liver enzyme elevations, with 4.1% of the therapy recipients experiencing levels greater than three times the upper limit of normal (ULN) versus 1.6% in placebo arm.
Sanofi is currently finalising regulatory submissions for the therapy in the US and preparing for submissions in the European Union (EU).
Meanwhile, the Phase III study, PERSEUS in primary progressive MS is ongoing, with outcomes expected in the second half of next year.
Tolebrutinib is predicted to modulate B lymphocytes and disease-associated microglia due to its action as a BTK inhibitor. It is currently under clinical investigation, and its efficacy and safety have not yet been assessed by any regulatory authorities.
Sanofi Neurology Development global head Erik Wallström said: “This breakthrough therapy designation demonstrates the potential for tolebrutinib to delay disability progression, a critical unmet need for people living with multiple sclerosis.
“We look forward to working with the FDA during the regulatory review of this first of its kind medicine in non-relapsing secondary progressive multiple sclerosis where there are currently no approved treatments available.”