In a significant blow to their cardiovascular franchise, partners Ionis Pharmaceuticals and AstraZeneca announced on Thursday that their RNA-based therapy, eplontersen (marketed as Wainua), failed to meet its primary endpoint in a pivotal Phase 3 study. The trial, known as CARDIO-TTRansform, evaluated the drug’s efficacy in treating transthyretin-mediated amyloid cardiomyopathy (ATTR-CM)—a progressive and life-threatening condition characterized by the accumulation of misfolded proteins around the heart.
The failure to reach statistical significance in the composite of cardiovascular outcomes effectively sidelines Wainua in the lucrative ATTR-CM market, a space currently dominated by well-entrenched competitors and rapidly evolving genetic medicine alternatives.
The Science of the Struggle: Understanding ATTR-CM
To understand the gravity of this clinical setback, one must first grasp the pathology of ATTR-CM. The disease is driven by transthyretin (TTR), a transport protein primarily synthesized in the liver. In patients with ATTR-CM, this protein becomes unstable, misfolds, and aggregates into amyloid fibrils that deposit in the myocardial tissue. These deposits stiffen the heart, ultimately leading to restrictive cardiomyopathy and, frequently, heart failure.
Eplontersen is a ligand-conjugated antisense oligonucleotide (ASO). Unlike traditional small molecules that stabilize the TTR protein to prevent misfolding, eplontersen acts at the genetic level. It is designed to bind to and degrade the messenger RNA (mRNA) responsible for the production of TTR, effectively "silencing" the protein at its source. While this mechanism has already proven successful in treating polyneuropathy caused by hereditary ATTR—earning FDA approval in 2023—the cardiovascular manifestation of the disease has proven a much higher hurdle.
Chronology of Development and Clinical Testing
The partnership between Ionis and AstraZeneca, formalized in 2021, sought to leverage Ionis’s proprietary ASO platform to disrupt the cardiovascular market.
- 2021: Ionis and AstraZeneca enter a strategic collaboration to develop and commercialize eplontersen globally, with AstraZeneca securing rights outside the U.S.
- December 2023: The FDA grants approval to Wainua for the treatment of polyneuropathy of hereditary transthyretin-mediated amyloidosis, marking a major milestone for the Ionis platform.
- 2024–2025: The ATTR-CM landscape shifts dramatically. BridgeBio’s stabilizer, Attruby (acoramidis), receives FDA approval in late 2024, followed closely by Alnylam Pharmaceuticals’ successful expansion of the label for Amvuttra (vutrisiran) in early 2025.
- July 2026: The CARDIO-TTRansform trial concludes its 140-week assessment period. Top-line results confirm the trial failed to meet its primary cardiovascular composite endpoint.
Supporting Data and Trial Dynamics
The CARDIO-TTRansform study was designed to measure cardiovascular events over 140 weeks. However, the trial design itself has become a focal point of intense scrutiny among market analysts and researchers.
A critical factor identified by Andrew Berens, an analyst at Leerink Partners, is the high rate of "background therapy" usage. In the trial, 57% of participants in both the treatment and placebo arms were already receiving TTR stabilizers at baseline, and an additional 24% initiated stabilizer therapy during the study. This implies that at any given time, approximately 81% of the study population was already being treated with a standard-of-care drug.
This prevalence of background therapy likely created a "ceiling effect," where the potential added benefit of eplontersen became statistically invisible. In contrast, the trial for Alnylam’s Amvuttra—which successfully achieved its primary endpoint—involved a significantly lower percentage of patients concurrently taking stabilizers. This discrepancy suggests that the magnitude of eplontersen’s effect may have been obscured by the widespread use of Pfizer’s Vyndaqel and Vyndamax, the current standards of care.
Official Responses and Strategic Pivot
Following the announcement, Ionis and AstraZeneca held an analyst call to address the trial’s failure and outline potential paths forward. Management confirmed that the overall trial showed no statistically significant benefit. Crucially, company leadership stated they do not believe extending the duration of the study would have yielded a different clinical outcome.
However, a glimmer of hope remains in the form of a prespecified subgroup analysis. Patients who received eplontersen as a monotherapy—without the interference of concomitant stabilizers—demonstrated a "nominally significant" benefit.
"We are currently reviewing the full dataset to determine the best path forward," a spokesperson for the companies noted. "While the primary endpoint was not met, the monotherapy subgroup results and the drug’s favorable safety profile provide important data that we look forward to presenting at the European Society of Cardiology Congress in Munich next month."
AstraZeneca is now in the difficult position of deciding whether to pursue regulatory discussions based on this subgroup data. Given that the unmet need in the monotherapy setting is lower—as these patients have different treatment options—regulators may be hesitant to grant approval based on post-hoc subgroup findings.
Market Implications: A New Era of Competition
The failure of Wainua in ATTR-CM has profound implications for the pharmaceutical landscape.
1. Competitive Shifts
The failure removes a significant, albeit late-arriving, competitor for Alnylam’s Amvuttra, further cementing Alnylam’s position as a leader in RNA interference (RNAi) therapies for ATTR. It also reinforces the dominance of Pfizer’s small-molecule stabilizers as the foundational treatment for the majority of patients.
2. The Debate: Silencers vs. Stabilizers
The trial results have reignited the industry debate regarding the optimal therapeutic approach. While "silencers" (ASOs and RNAi) target the production of TTR, "stabilizers" target the protein itself. The trial failure suggests that, at least in the current clinical design, silencers may struggle to provide additional clinical value when added on top of existing stabilization therapies.
3. Payer Push-back and Combination Therapies
Perhaps most importantly, the trial failure could lead to increased scrutiny from payers regarding combination therapies. If clinicians cannot demonstrate a synergistic effect between stabilizers and genetic silencers, insurance providers are unlikely to reimburse the exorbitant costs of dual-agent regimens. This could effectively end the industry’s current push toward "cocktail" treatments for ATTR-CM.
4. AstraZeneca’s Remaining Pipeline
AstraZeneca is not entirely defeated in this space. The company is currently developing cliramitug, a monoclonal antibody that operates via a distinct mechanism—the depletion of existing TTR amyloid deposits. Phase 3 results for cliramitug are expected in mid-2027. If successful, this "depleter" approach could address the disease from a completely new angle, potentially filling the void left by the failure of the TTR-silencing approach in this study.
As the industry looks toward the European Society of Cardiology Congress, the focus will shift from what went wrong with Wainua to what these results mean for the future of genetic medicine. For Ionis, the challenge will be to pivot away from the cardiovascular disappointment and refocus its platform on indications where the therapeutic benefit is not masked by the presence of standard-of-care stabilizers. For investors and patients alike, the search for a superior treatment for ATTR-CM continues, albeit with one less contender in the ring.
