Biogen plans phase 3 trial for Alzheimer’s drug diranersen

Biogen will advance Ionis’s tau-directed therapy diranersen into Phase 3 after Phase 2 data in early Alzheimer’s, where the 60 mg dose slowed clinical decline by 26% on CDR-SB (and 42% on ADAS-Cog13) versus placebo. However, the study did not meet the primary dose-response endpoint on CDR-SB at 18 months, and Ionis stock is down 34% over the past week. Despite the setback, Ionis reports 48% revenue growth and a 4.1 current ratio, while analysts have trimmed price targets for Ionis in response to a separate Wainua Phase 3 miss.

Analysis

The key market mechanism is not “Alzheimer’s success,” but a shift in the probability-weighted value of partner economics. For Biogen, advancing the program keeps tau as a cheap strategic call option, but the failed dose-response means the asset is still far from a de-risked franchise; any eventual label is likely to be narrower and slower to penetrate than amyloid-first therapies because intrathecal administration limits scale. For Ionis, the stock is reacting more to platform credibility than to direct economics, since the most valuable piece of any upside still sits with the partner; that makes the selloff more about sentiment reset than about a near-term cash-flow change.

Second-order, this is bad for any company marketing a pure biomarker story without a clean clinical hierarchy: if the market rewards a Phase 3 handoff despite ambiguous dose data, it raises the bar for competitors in antisense and CNS. But the overhang is that “biomarker positive” does not equal “commercially scalable,” especially when procedure burden and payer skepticism can cap uptake even after approval. The real catalyst path is the next 1-3 months of protocol clarity, enrollment pace, and whether the sponsor changes the dosing strategy; if that happens, the recent price move can retrace quickly.

Contrarian view: the market may be over-discounting Ionis because one partnered CNS readout does not impair the balance sheet or the broader platform, and the current ratio reduces dilution risk over the next year. The flip side is that investors may be underestimating how little of the ultimate economic upside accrues to Ionis relative to the headline clinical excitement. The thesis breaks if Biogen signals a materially stronger Phase 3 design or if Ionis’ next earnings show no cushion from milestones/partner revenue after the Wainua disappointment.

Key Decisions for Investors

• Long BIIB / short IONS as a 1-3 month relative-value trade: BIIB gets the higher-quality option on tau with limited capital at risk, while IONS still carries platform credibility damage from the broader pipeline; cover if IONS outperforms BIIB by >5% on protocol details or partner commentary.
• If already long IONS, reduce size into any relief rally and wait for the next earnings call and Phase 3 protocol disclosure; the upside is mostly sentiment-driven, while the downside reopens if milestones guidance or partner economics disappoint.
• Add BBIO vs IONS as a cleaner dispersion trade if you want exposure to the Alzheimer’s/biotech rerank: BBIO benefits from comparison dynamics and ongoing target revisions, while IONS faces a heavier burden of proof after the recent clinical miss.
• Watch for a reversal trigger in BIIB if the Phase 3 design turns into a high-burden intrathecal regimen with no dose simplification; that would cap the NPV and make the current enthusiasm fade within 1-2 quarters.