MS Treatment Breakthroughs: BTK Inhibitor Slows Progressive Disability in Landmark Trial
A sweeping review of 67 MS clinical trials reveals tolebrutinib's historic win in progressive MS while mapping the full frontier of repair therapies.
Summary
A 2025 review of 67 active or recently completed multiple sclerosis clinical trials maps the landscape of novel therapies across six categories: BTK inhibitors, remyelinating agents, immunomodulators, B-cell therapies, supplements/microbiome influencers, and cell-directed therapies. The headline finding is tolebrutinib's phase 3 success in nonrelapsing secondary progressive MS — the first drug ever to demonstrate statistically significant slowing of confirmed disability progression in this population. Conversely, simvastatin failed its phase 3 disability endpoint, and evobrutinib showed no advantage over teriflunomide. Remyelination remains elusive but multiple candidate drugs are in active trials. The review underscores that while relapsing MS is now highly treatable, progressive MS remains a frontier with cautious but growing optimism.
Detailed Summary
Multiple sclerosis has been transformed by decades of drug development for relapsing forms, yet progressive MS has stubbornly resisted treatment — until now. This 2025 review by Cree and Hartung, published in Current Opinion in Neurology, synthesizes 67 interventional clinical trials identified through a clinicaltrials.gov search to provide a comprehensive update on unapproved disease-modifying therapies across the MS spectrum.
The most consequential finding covered is tolebrutinib's phase 3 trial in nonrelapsing secondary progressive MS (nrSPMS). This Sanofi-sponsored study (NCT04411641, n=1131) met its primary endpoint by demonstrating a statistically significant reduction in confirmed disability progression (CDP) versus placebo — a first for any drug in this population. Tolebrutinib also showed confirmed disability improvement (CDI), adding further weight to its clinical relevance. However, its two parallel phase 3 trials in relapsing MS failed to show superiority over teriflunomide on relapse reduction, mirroring the earlier failure of evobrutinib (Merck Serono) in identical head-to-head designs. The authors suggest that CNS penetrance may be the key differentiator: tolebrutinib is highly CNS penetrant while evobrutinib is not, potentially explaining why only the former showed disability effects. Importantly, tolebrutinib carries a risk of potentially life-threatening drug-induced liver injury, necessitating intensive hepatic monitoring if approved. Ongoing phase 3 trials of fenebrutinib (Roche/Genentech) and remibrutinib (Novartis) in RMS are expected to complete in 2025–2026, though based on the track record of BTKIs on relapse endpoints, the authors are cautious about superiority over teriflunomide.
Remyelination remains one of the most compelling yet unfulfilled frontiers in MS therapeutics. Multiple agents that previously failed phase 3 trials include opicinumab (anti-LINGO-1), elezanumab (anti-RGMa), high-dose biotin (MD-1003), and bexarotene. Currently active phase 2 trials include clemastine fumarate (alone and combined with metformin), metformin monotherapy, bazedoxifene acetate in postmenopausal women, testosterone undecanoate in men, and PIPE-307 (a CNS-penetrant M1 muscarinic receptor antagonist). Metformin is of particular interest given its pro-regenerative effects on oligodendrocyte precursor cells and its broad safety profile. These trials use visual evoked potential latency and chronic inactive lesion volume as biomarkers rather than clinical disability alone.
Beyond BTKIs and remyelination, the review catalogs trials of immunomodulators (including CNS-targeting approaches), B-cell therapies (notably high-efficacy anti-CD20 agents and their successors), supplements and microbiome-influencing interventions, and cell-directed therapies including CAR-T and hematopoietic stem cell transplantation strategies. The simvastatin MS-STAT2 phase 3 trial in secondary progressive MS — a therapy with significant longevity and anti-inflammatory interest — failed to meet its primary disability endpoint, a notable setback given early phase 2 promise.
The review concludes with measured optimism: while the therapeutic landscape for relapsing MS is now rich, progressive MS is beginning to yield to targeted intervention. The authors highlight that microglial BTK signaling may be the key CNS mechanism underlying tolebrutinib's disability benefit, though this remains to be mechanistically confirmed. For longevity-focused readers, the overlapping biology of neuroinflammation, microglial activation, and progressive neurodegeneration makes these findings broadly relevant beyond MS.
Key Findings
- Tolebrutinib became the first drug to significantly slow confirmed disability progression in nonrelapsing secondary progressive MS in a phase 3 trial.
- Both evobrutinib and tolebrutinib failed to beat teriflunomide on relapse reduction in RMS, suggesting BTKIs may not excel at suppressing peripheral inflammation.
- Simvastatin failed its phase 3 MS-STAT2 trial, ending hopes for this widely studied neuroprotective agent in progressive MS.
- Remyelination remains clinically unproven; multiple phase 2 trials of clemastine, metformin, and PIPE-307 are actively ongoing.
- CNS penetrance of BTK inhibitors may be critical: tolebrutinib's high CNS penetrance correlates with its disability benefit absent from peripherally acting BTKIs.
Methodology
This is a narrative review based on a systematic clinicaltrials.gov search using the term 'multiple sclerosis' filtered for interventional trials that were not yet recruiting, recruiting, or active but not recruiting, yielding 517 trials reviewed by the authors. Sixty-seven trials of unapproved disease-modifying therapies were selected and categorized. No meta-analysis or pooled statistical analysis was conducted.
Study Limitations
As a narrative review, the paper is subject to author selection bias in trial inclusion and does not perform quantitative synthesis. Full trial data for several key studies (fenebrutinib, remibrutinib) are not yet available. Tolebrutinib's hepatotoxicity risk introduces a significant safety caveat that may limit real-world applicability pending post-marketing safety data.
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