Sanofi (SNY) Stock: Falls After MS Drug Suffers Double Blow

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Sanofi announced this week that its experimental multiple sclerosis drug tolebrutinib failed a major clinical trial. The company said it will abandon plans to seek regulatory approval for the treatment in one form of the disease.

Sanofi, SNY

The pharmaceutical giant revealed that its PERSEUS phase 3 study did not meet its primary goal. The trial tested whether tolebrutinib could delay disability progression in patients with primary progressive multiple sclerosis, or PPMS.

The study specifically looked at 6-month composite confirmed disability progression as its main measure. Tolebrutinib failed to show it could slow this progression compared to a placebo.

Company Drops Plans for Regulatory Approval

Following the disappointing results, Sanofi said it will not pursue regulatory registration for tolebrutinib in primary progressive MS. This means the company will not ask health authorities like the FDA to approve the drug for this specific patient group.

Houman Ashrafian, Executive Vice President at Sanofi, addressed the outcome in a statement. He expressed disappointment with the results but said the data still provides value for understanding MS biology.

The setback comes at the same time as another problem for the drug. The FDA has delayed its decision on tolebrutinib, creating a double blow for Sanofi’s MS program.

Primary progressive MS affects about 10 to 15 percent of all MS patients. Unlike other forms of the disease, PPMS causes steady worsening of symptoms from the start without periods of relapse and remission.

Development Continues for Other MS Forms

Despite the failure in primary progressive MS, Sanofi is not giving up on tolebrutinib entirely. The company said it remains committed to developing the drug for non-relapsing secondary progressive multiple sclerosis.

Secondary progressive MS is a different form of the disease that develops in people who initially had relapsing-remitting MS. In the non-relapsing form, patients experience gradual worsening without clear relapses.

Sanofi told investors that the failed trial will not impact its main profit measures. The company also said the news does not change its financial guidance for 2025.

The market has reacted negatively to the news. Sanofi shares have fallen 15 percent so far this year following the announcement.

Tolebrutinib belongs to a class of drugs called BTK inhibitors. These medications work by blocking an enzyme called Bruton’s tyrosine kinase, which plays a role in immune system activation.

Multiple sclerosis is an autoimmune disease where the immune system attacks the protective covering of nerve fibers. This damage disrupts communication between the brain and the rest of the body.

The PERSEUS study enrolled patients with primary progressive MS to test whether tolebrutinib could help slow their disease progression. Researchers measured disability progression over a 6-month period as the primary way to judge the drug’s effectiveness.

Sanofi continues to analyze the data from the PERSEUS trial. The company has not announced a timeline for sharing detailed results from the study.

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