Novartis’ Avidity Biosciences-acquired therapy, delpacibart etedesiran (del-desiran), has stumbled in a Phase III muscle wasting disorder study, dealing another blow to the company’s pipeline as it faces key patent expiries within its portfolio.
This late-stage miss stems from the HARBOR study (NCT06411288), in which Novartis was testing the efficacy and safety of del-desiran, an antibody-oligonucleotide conjugate (AOC), against placebo in 150 patients with myotonic dystrophy type 1 (DM1) over a 54-week period.
During the trial, intravenously administered del-desiran failed to significantly improve patient video hand opening times (vHOT) over placebo – missing the trial’s primary endpoint. vHOT is a clinical test used to measure the delay in a patient’s ability to relax their hand muscles after a forceful squeeze.
However, Novartis claims that del-desiran did demonstrate some signs of clinical activity in both secondary endpoints and exploratory analyses, though the company is yet to provide further details. According to a listing on ClinicalTrials.gov, HARBOR focused secondarily on del-desiran’s impact on hand grip strength and a patient’s ability to walk or run, as well as their overall muscle strength and daily functioning.
This outcome could represent a notable setback for patients with DM1, who currently rely on symptomatic and supportive treatments due to the absence of approved, disease-modifying drugs. Researchers estimate that the rare genetic disorder, characterised by progressive wasting of the skeletal muscles, currently impacts around 9.27 in every 100,000 – making it the most common form of muscular dystrophy in adults of European ancestry.
Though del-desiran missed its primary endpoint, Novartis’ CMO, Shreeram Aradhye notes that the Swiss pharma giant will “continue to explore the full HARBOR dataset” to determine next steps for the del-desiran programme.
Novartis originally acquired the rights to del-desiran through its $12bn takeover of Avidity Biosciences in 2025, which saw the company claim the rights to del-desiran, Duchenne muscular dystrophy (DMD) therapy, delpacibart zotadirsen (del-zota), and facioscapulohumeral muscular dystrophy (FSHD) candidate, delpacibart braxlosiran (del-brax).
Novartis pipeline rocked on recent Phase III blunders
Del-desiran’s Phase III HARBOR miss deals another blow to Novartis’ pipeline ambitions after the recent failure of its lipoprotein a Lp(a)-reducing drug, pelacarsen, in the closely watched Phase III Lp(a)HORIZON trial.
In a research note from July 2026, Jefferies analysts noted that the HARBOR trial “needed to deliver” to justify the $12bn price tag of this acquisition.
They also highlighted the relevance of the readout to the longer-term financial story for Novartis, as they believe that this late-stage flop could make it unlikely that the Swiss pharma company will be able to meet its mid-single digit growth aim up to 2030 without conducting further M&A deals.
A silver lining for Novartis, however, could be the recent resounding late-stage success of its Bruton’s tyrosine kinase (BTK) inhibitor, remibrutinib, in relapsing multiple sclerosis (RMS).
Novartis is looking to bolster its pipeline as it multiple key patent expiries within its branded portfolio loom closer, with blockbuster drugs like heart failure therapy, Entresto (sacubitril/valsartan) and autoimmune drug, Cosentyx (secukinumab) soon to lose their market exclusivity.
