Sanofi’s Principia purchase fails its first test

Just a day after Sanofi bought Kadmon, the French group got a reminder of the risks involved in acquisitions. Rilzabrutinib, one of the oral BTK inhibitors that Sanofi gained through its $3.7bn purchase of Principia, failed a phase 3 study in its lead indication, the skin disorder pemphigus.

Sanofi’s swoop for Principia always looked risky, and today’s news raises doubts about whether rilza will work in the various other indications that Sanofi is eyeing. The main focus of the buyout was the multiple sclerosis candidate tolebrutinib, however, which is still very much in play.

It will be a while before it becomes apparent whether Sanofi’s faith in tolebrutinib was justified, with the first of four pivotal MS studies set to yield data in 2023.

It should be remembered that mid-stage data from tolebrutinib were not clear cut, with questions about the use of a surrogate endpoint, the complex trial design and small patient numbers (Multiple sclerosis “win” makes the Principia shorts squirm, February 6, 2020).

As for rilza, its failure in pemphigus seems pretty definite. Sanofi did not give detailed data, but said the Pegasus trial did not show a difference between rilza and placebo on its primary endpoint, complete remission from week 29 to week 37. Patients were on “minimal doses” of corticosteroids, 10mg/day or less.

This outcome is not entirely surprising: when phase 2 data in pemphigus were released Evaluate Vantage flagged the lack of placebo arm and the possibility that background steroids could have been responsible for the responses seen.

There were also reasons to be cautious about phase 1/2 results in immune thrombocytopenia, where rilza is currently in a pivotal trial. Hopes cannot be high now in ITP, and the latest flop also does not bode well for Sanofi’s plan to evaluate rilza for a raft of other uses. 

The rilza setback could also be bad news for others developing BTK inhibitors for autoimmune diseases, banking on the theory that B cells have a major role in such disorders. MS is a big focus, and here Biogen recently licensed Innocare’s orelabrutinib to add to its own phase 1 asset, BIIB091.

Many MS BTK hopefuls have made much of their projects’ ability to cross the blood-brain barrier. But the more immediate question, underlined by rilza’s failure, is whether this mechanism is effective in autoimmune disease full stop.