Sanofi's Tolebrutinib Fails Phase 3 Trial in Primary Progressive Multiple Sclerosis
Key Insights
Sanofi's PERSEUS phase 3 study showed tolebrutinib failed to meet its primary endpoint of delaying disability progression in primary progressive multiple sclerosis (search) patients.
The company will not pursue regulatory registration for PPMS based on these results, though the drug remains under review for secondary progressive MS.
Tolebrutinib demonstrated a consistent safety profile with previous studies, with drug-induced liver injury (search) remaining an identified risk requiring monitoring.
Sanofi announced disappointing results from its PERSEUS phase 3 clinical trial, revealing that tolebrutinib failed to meet its primary endpoint in treating primary progressive multiple sclerosis (search) (PPMS). The global pharmaceutical company will not pursue regulatory registration for this indication based on the study outcomes.
The PERSEUS study evaluated tolebrutinib's ability to delay time to onset of 6-month composite confirmed disability progression (cCDP) compared to placebo in PPMS patients, who represent 10% of the overall multiple sclerosis (search) patient population. Despite the setback, Sanofi emphasized that the results will contribute to understanding multiple sclerosis disease biology.
"We are disappointed by today's results; however, we do believe that these results will improve our understanding of the underlying disease biology of multiple sclerosis (search)," said Houman Ashrafian, Executive Vice President, Head of Research & Development at Sanofi. "Our commitment to the multiple sclerosis community remains unchanged, as do our efforts to pursue novel advancements that address existing unmet needs and we remain confident in the value tolebrutinib can bring to those living with non-relapsing secondary progressive multiple sclerosis (search)."
Study Design and Patient Population
PERSEUS (NCT04458051) was designed as a global, double-blind, randomized phase 3 clinical study comparing tolebrutinib efficacy and safety against placebo in PPMS participants. The trial randomized patients 2:1 to receive either an oral daily dose of tolebrutinib or matching placebo for up to approximately 60 months.
The study included participants aged 18-55 years with a PPMS diagnosis according to 2017 revised McDonald criteria, an EDSS score ≥2.0 and ≤6.5 at screening, and positive cerebrospinal fluid findings. Patients also had either no access, intolerance, or perceived lack of efficacy to ocrelizumab.
The primary endpoint was six-month composite confirmed disability progression, defined as an increase over at least six months of ≥1.0 point from baseline EDSS score when baseline was ≤5.5, or ≥0.5 points when baseline EDSS was >5.5, or ≥20% from baseline T25-FW, or ≥20% from baseline 9-HPT.
Safety Profile and Regulatory Status
Preliminary analysis showed tolebrutinib's safety profile remained consistent with previous studies. Drug-induced liver injury (search) (DILI) continues to be an identified risk, requiring strict adherence to liver monitoring requirements and prompt management of liver enzyme elevations to mitigate risk.
Despite the PPMS trial failure, tolebrutinib maintains regulatory momentum in other indications. The drug received provisional approval in the United Arab Emirates in July 2025 for treating non-relapsing secondary progressive multiple sclerosis (search) and slowing disability accumulation independent of relapse activity in adults. It currently undergoes regulatory review in the EU and other jurisdictions worldwide, having previously received breakthrough therapy designation from the FDA in December 2024.
Mechanism and Unmet Medical Need
Tolebrutinib is an investigational, oral, brain-penetrant Bruton's tyrosine kinase (search) inhibitor specifically designed to target smoldering neuroinflammation, a key driver of disability progression in MS. This mechanism addresses progressive MS pathology by targeting inflammatory processes that contribute to neurodegeneration and disability accumulation.
PPMS presents as a slow, insidious neurologic decline, often with predominant spinal cord involvement, where symptoms gradually worsen over time without improvement periods. Addressing disability accumulation remains a significant unmet need in MS, as treatment options are limited.
Financial Impact
Sanofi will conduct an impairment test in accordance with IFRS (IAS 36) on the intangible asset value attached to tolebrutinib, with status provided alongside Q4 and FY 2025 results in January 2026. The company stated this outcome will have no impact on business net income or business EPS, with no changes to 2025 financial guidance.
Full safety and efficacy results from the PERSEUS study will be presented at an upcoming medical meeting, providing the scientific community with detailed data to better understand the trial outcomes and their implications for progressive MS treatment development.