Sanofi’s $3.7B Principia Buy Starts to Pay Off with Phase III Rilzabrutinib Win


Pictured: Sanofi's signage outside its office in Quebec, Canada/iStock, JHVEPhoto

Sanofi on Tuesday announced that its investigational BTK inhibitor rilzabrutinib met the primary endpoint in the Phase III LUNA 3 study, eliciting durable platelet response in adult patients with persistent or chronic immune thrombocytopenia.

The pharma did not disclose specific data in its announcement but said that significantly more patients on rilzabrutinib versus placebo achieved durable platelet response, which LUNA 3 defines as having a minimum platelet count of 50,000/µL for at least eight of the last 12 weeks.

Sanofi called LUNA 3’s results “clinically and statistically significant.” The study also achieved positive outcomes on key secondary endpoints.

Houman Ashrafian, head of research and development at Sanofi, in a statement said that LUNA 3’s results “reinforce rilzabrutinib’s potential to be a first-in-class oral, reversible BTK inhibitor that can provide clinically meaningful improvements for people living with severe immune-mediated disease,” including immune thrombocytopenia (ITP).

With these data, Sanofi is expecting to make U.S. and European Union regulatory submissions for rilzabrutinib in this indication by the end of 2024. In addition to ITP, the pharma is also developing rilzabrutinib for chronic spontaneous urticaria, prurigo nodularis, IgG4-related disease and warm autoimmune hemolytic anemia.

ITP is an acquired autoimmune blood disorder that arises when antibodies attack and destroy the body’s own platelets. Patients with ITP often have very low platelet counts—often dropping below 100,000/µL, whereas the normal range runs from 150,000/µL to 400,00/µL—which aggravates the risk of life-threatening bleeding complications, such as intracranial hemorrhages.

Patients with ITP also typically suffer from fatigue, cognitive problems and other quality-of-life issues.

According to Sanofi’s Tuesday announcement, rilzabrutinib’s “dual mechanisms of action” can address the underlying pathways in ITP and its complications.

Originally developed by Principia Biopharma, rilzabrutinib is an orally available and reversible covalent inhibitor of the BTK protein, which is commonly expressed in B cells, mast cells and other innate immune players, and which is a central player in the various inflammatory and immune-mediated pathways. Rilzabrutinib works by preventing platelet destruction by macrophages and lowering the production of disease-causing autoantibodies.

Sanofi obtained rilzabrutinib when it acquired Principia Biopharma in August 2020 for $3.68 billion.

Tuesday’s readout continues biopharma’s BTK winning streak. In March 2024, Novartis reported that its investigational BTK blocker remibrutinib aced a Phase IIb study in hidradenitis suppurativa, leading to a substantial reduction in abscesses and inflammatory nodules. A few days earlier, BeiGene’s BTK inhibitor Brukinsa (zanubrutinib) won the FDA’s accelerated approval for relapsed or refractory follicular lymphoma when combined with Genentech’s Gazyva (obinutuzumab).

Tristan Manalac is an independent science writer based in Metro Manila, Philippines. Reach out to him on LinkedIn or email him at or

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