The centerpiece of Novartis’ $12 billion Avidity acquisition missed the HARBOR primary endpoint in DM1, days after pelacarsen’s Phase 3 cardiovascular failure.
Key Takeaways
- Delpacibart etedesiran (del-desiran) failed to significantly improve video hand opening time versus placebo in the Phase 3 HARBOR trial for myotonic dystrophy type 1 (DM1).
- HARBOR evaluated 159 patients over 54 weeks, with del-desiran administered once every eight weeks. Novartis reported signs of activity across secondary and exploratory endpoints but has not disclosed the full dataset.
- The setback followed the Phase 3 failure of pelacarsen only days earlier. Novartis shares fell more than 13% by late Tuesday morning on September 8, intensifying scrutiny of its pipeline and recent dealmaking. (BioPharma Dive)
Data Snapshot
| Item | Details |
|---|---|
| Candidate | Delpacibart etedesiran (del-desiran) |
| Disease | Myotonic dystrophy type 1 |
| Modality | Antibody-oligonucleotide conjugate |
| Molecular target | DMPK mRNA |
| Delivery target | Transferrin receptor 1 (TfR1) |
| Phase 3 trial | HARBOR |
| Patients evaluated | 159 |
| Treatment period | 54 weeks |
| Dosing | Every 8 weeks |
| Primary endpoint | Video hand opening time (vHOT) |
| Result | Primary endpoint not met |
| Development status | Full dataset under review |
Del-desiran is a TfR1-targeted antibody-oligonucleotide conjugate designed to deliver small interfering RNA into muscle and degrade toxic DMPK mRNA. HARBOR, however, did not demonstrate a statistically significant benefit on its primary functional endpoint. (Novartis HARBOR update)
What Happened
Novartis reported on September 8 that its global Phase 3 HARBOR trial failed to meet its primary endpoint in people with DM1.
The trial measured video hand opening time (vHOT), which evaluates how quickly a patient can relax the hand after making a fist. The test is designed to quantify myotonia, one of the hallmark manifestations of DM1.
After seven doses administered once every eight weeks, del-desiran was not statistically superior to placebo on vHOT. Novartis said it observed evidence of clinical activity across secondary endpoints and exploratory analyses and will review the full dataset before discussing the program’s next steps with regulators.
The result is particularly significant because del-desiran was the most advanced DM1 asset acquired through Novartis’ $12 billion acquisition of Avidity Biosciences—approximately KRW 16.7 trillion at an exchange rate of KRW 1,390 per U.S. dollar. Analysts had viewed the HARBOR readout as a crucial test of the strategic value behind the acquisition. (Fierce Biotech)
Why It Matters
The HARBOR failure came only days after another important Novartis Phase 3 setback.
On September 4, pelacarsen substantially lowered lipoprotein(a), or Lp(a), in the Lp(a)HORIZON trial but failed to significantly reduce major cardiovascular events. Del-desiran has now become the company’s second major Phase 3 failure within days. (Fierce Biotech pelacarsen coverage)
The market reaction reflects more than disappointment in a single drug. Investors are also reassessing whether Novartis’ external pipeline investments can deliver the growth expected from them beyond 2030.
DM1 remains a competitive development field despite having no approved disease-modifying therapy.
| Candidate | Company | Approach | Development status | Key distinction |
|---|---|---|---|---|
| Del-desiran | Novartis / Avidity | TfR1-targeted siRNA against DMPK mRNA | Phase 3 HARBOR missed its primary endpoint | Degrades toxic DMPK RNA |
| Zeleciment basivarsen (z-basivarsen; formerly DYNE-101) | Dyne Therapeutics | TfR1-targeted antisense oligonucleotide against DMPK RNA | Phase 3 HARMONIA | Reduces toxic nuclear DMPK RNA through targeted muscle and CNS delivery |
| PGN-EDODM1 | PepGen | Peptide-conjugated oligonucleotide targeting expanded CUG repeats | Phase 2 FREEDOM2-DM1 | Releases MBNL1 without degrading DMPK RNA |
Dyne began the approximately 150-patient Phase 3 HARMONIA trial in March 2026. Notably, HARMONIA uses the five-times sit-to-stand test as its primary endpoint, while vHOT is a secondary endpoint. PepGen, meanwhile, is continuing dose escalation in Phase 2 FREEDOM2-DM1. (Dyne HARMONIA update, PepGen FREEDOM2-DM1 update)
HARBOR therefore has implications beyond Novartis. It raises a broader question for the DM1 field: Was the failure driven by insufficient molecular correction, uneven drug delivery, endpoint variability—or the difficulty of translating RNA-splicing correction into measurable functional improvement?
The Science Behind Del-desiran
DM1 is caused by expanded CUG-repeat DMPK RNA, which traps muscleblind-like, or MBNL, proteins and disrupts alternative RNA splicing across multiple tissues.
Del-desiran was designed to intervene upstream by reducing the toxic RNA itself.
Why did a strong molecular rationale fail to produce a positive Phase 3 primary endpoint?
Read the BP Science explainer:
How Toxic RNA Drives DM1—and Why Del-desiran Was Designed to Silence It
BP View
The most immediate consequence of HARBOR is that it weakens the commercial case for the centerpiece of Novartis’ Avidity acquisition. The company has not abandoned del-desiran, and the secondary endpoints may still influence its regulatory or development strategy. But once a pivotal trial misses its prespecified primary endpoint, supportive signals must be unusually consistent and clinically persuasive to preserve a credible path forward.
The timing magnifies the damage. Pelacarsen and del-desiran represented two important late-stage opportunities in different therapeutic areas, and both failed their primary Phase 3 objectives within days. That sequence helps explain why Novartis’ share-price reaction was considerably larger than would normally be expected from a single rare-disease readout.
The Avidity platform itself is not necessarily invalidated. Novartis is still advancing delpacibart zotadirsen (del-zota) in Duchenne muscular dystrophy and delpacibart braxlosiran (del-brax) in facioscapulohumeral muscular dystrophy. Their biological targets, clinical endpoints and required levels of molecular correction differ from those of del-desiran.
HARBOR may also become an endpoint-selection lesson for the broader DM1 field. Dyne placed the five-times sit-to-stand test—not vHOT—at the center of its confirmatory Phase 3 trial. If del-desiran produced molecular or multisystem improvements that vHOT failed to capture reliably, the full HARBOR dataset could influence how future DM1 trials define clinically meaningful benefit.
The practical question is now whether Novartis can identify a sufficiently coherent benefit across the complete dataset to preserve a path for del-desiran—and whether the remaining AOC programs can independently demonstrate that antibody-guided oligonucleotide delivery translates molecular correction into meaningful patient benefit.
Related Post
For the other recent Novartis Phase 3 setback, read my previous analysis of pelacarsen and the Lp(a)HORIZON cardiovascular outcome failure.
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Biopharma Perspective (BP) explains global biopharma news through strategic, clinical and market perspectives.
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