Bimagrumab continues to be a enigma. We see flickering signs of good news – and then, inexplicably, it goes dark. The pattern repeated itself this week when news emerged that Lilly pulled the plug on a phase two study with bimagrumab and tirzepatide in persons with obesity and diabetes before it even enrolled a single patient.

Why? “Strategic business reasons” was the explanation Lilly gave. That’s biz-speak for buzz off.

A Two-Billion Dollar Asset with a Tortured History

This is a drug that has been in development for two decades. Novartis invented it with the intention of developing it for muscle weakness and wasting. FDA designated it as a potential breakthrough therapy for sporadic inclusion body myositis in 2013. But that indication didn’t work out, so Novartis took a shot at developing it for obesity treatment. A phase two study published in early 2021 showed promise, with patients losing 20% of body fat while actually gaining 3.6% in lean mass.

This sounded great, but Novartis walked away from it and spun the rights to it off to a startup called Versanis. At that point, explosive growth potential of the obesity market was not yet obvious to everyone.

So Versanis mounted a phase 2b study of bimagrumab in combination with semaglutide and then Lilly bought Versanis for roughly two billion dollars. Dazzling results from the semaglutide combination study came out in a presentation at the ADA Scientific Sessions in June.

But we have yet to see a full peer-reviewed publication of this study. If the devil is in the details, he’s playing a great game of hide and seek.

Caution or Trouble?

At this point it is hard to know if stopping the bimagrumab study in obesity and diabetes is a sign of wise caution or impending trouble for this promising drug. Lilly is still going ahead with a phase two study of bimagrumab and tirzepatide in persons with obesity but not diabetes. Results will be out next year with full completion of the study in 2027.

The concept of a drug that helps people lose fat while maintaining or even gaining muscle is fascinating. But it is uncharted territory with the potential for unpleasant surprises. Bimagrumab might be a breakthrough or it might be a dud.

The caution seems wise.

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