Novartis AG reported that del-desiran missed its primary endpoint in the phase 3 Harbor trial, dealing a blow to the company's $12 billion acquisition of Avidity Biosciences last year.
The gene-silencing therapy showed no statistically significant benefit over placebo at improving video hand opening time (vHOT), the trial's primary measure of efficacy in patients with myotonic dystrophy type 1, a rare progressive muscle-wasting disease. The trial enrolled 159 patients and evaluated seven doses of del-desiran infused every eight weeks.
Del-desiran was widely regarded as the crown jewel of the Avidity deal. External revenue forecasts presented by Novartis projected peak annual sales of as much as $6 billion for the DM1 indication, making myotonic dystrophy type 1 the largest opportunity from the acquisition. Sales for the company's second Avidity-derived program in facioscapulohumeral muscular dystrophy (FSHD) were projected by some analysts to peak around $4 billion as of October.
The readout came as part of a rapid series of clinical results from Novartis in the second half of 2026. While the company secured a win for Rhapsido in relapsing multiple sclerosis, it also saw pelacarsen fail in a cardiovascular disease trial and now del-desiran stumble. The string of outcomes has drawn scrutiny from investors and analysts regarding the execution of Novartis's broader development strategy.
Guggenheim Securities analysts said the success of del-desiran had been "crucial" for validating the Avidity deal and that the results were "important for gaining confidence in Novartis' mid- and long-term sales potential."
Novartis acquired two other late-stage neuromuscular programs as part of the Avidity purchase: delpacibart zotadirsen, for which it has filed for accelerated approval in Duchenne muscular dystrophy, and delpacibart braxlosiran, which showed positive phase 1/2 data in FSHD and for which the company plans to meet with the FDA to discuss next steps.
Shreeram Aradhye, M.D., Novartis chief medical officer, said the company is committed "to identifying the most appropriate development path" as it analyzes the full del-desiran dataset and engages with health authorities.
In pre-market trading on Tuesday, Novartis shares fell 12.5% to $139.98, down from Friday's closing price of $159.99.
