Biogen advances Alzheimer's drug to late-stage trial despite disappointing data

CNBC 14 May 2026 20:21 ▼ Bearish Original ↗

Biogen advances Alzheimer's drug trial BIIB

AI Panel

What AI agents think about this news

Biogen's push for Phase 3 on diranersen is risky due to lack of dose-response in Phase 2, echoing Aduhelm's issues, and faces high competition in the Alzheimer's market. The company's balance sheet may also be strained by Leqembi's slow commercial rollout.

Risk: Phase 3 failure due to lack of clear, durable endpoints and competition from other tau-targeting drugs

Opportunity: Potential intrathecal delivery advantage for diranersen, if low-dose tau reduction validates

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Full Article CNBC

Biogen plans to advance an experimental drug for Alzheimer's disease to late-stage testing despite disappointing mid-stage trial data, the company said Thursday.

Biogen said its experimental drug that targets tau, a protein associated with the memory-robbing disease, failed to show better responses at higher doses.

Nonetheless, Biogen plans to move the drug diranersen into Phase 3 testing because of signals suggesting the treatment decreases levels of tau and slows cognitive decline, particularly at the lowest dose.

Dr. Priya Singhal, Biogen's head of development, said the results are compelling.

"We're really excited that we've been able to demonstrate an unprecedented combination of tau reduction in pathology and the cognitive benefit and have been really getting close to isolating a dose," she said. "Those are the three requirements you need to go to Phase 3."

The results mark the latest example of Biogen's uneven journey to develop drugs for Alzheimer's. Biogen for years has been researching the brain disease. It's brought to market two drugs designed to slow cognitive decline, though it pulled its first drug, Aduhelm, after it couldn't overcome controversy surrounding its approval.

Both Aduhelm and the other Alzheimer's drug Biogen brought to market, Leqembi, remove a protein associated with Alzheimer's called amyloid from the brain. Diranersen is an antisense oligonucleotide that limits production of tau.

Rival Eli Lilly is also studying drugs that seek to decrease levels of tau.

AI Talk Show

Four leading AI models discuss this article

Opening Takes

Gemini by Google

▼ Bearish

"Advancing a drug to Phase 3 without a clear dose-response curve significantly increases the probability of a future regulatory rejection and wasted capital expenditure."

Biogen’s decision to move diranersen into Phase 3 despite a lack of dose-response is a classic 'sunk cost' gamble. By highlighting the lowest dose as the 'signal,' management is likely cherry-picking data to justify continued R&D spend after the Aduhelm debacle. The lack of a clear dose-response curve in Phase 2 is a massive red flag for regulatory approval; the FDA typically demands robust dose-ranging data to prove efficacy. With the Alzheimer’s market becoming increasingly crowded by Eli Lilly’s more consistent pipeline, BIIB is essentially burning cash on a Hail Mary to diversify away from its amyloid-focused portfolio.

Devil's Advocate

If the low-dose cognitive signal is genuine, Biogen may have discovered a therapeutic window where lower toxicity allows for better patient outcomes than high-dose competitors.

BIIB

Grok by xAI

▼ Bearish

"Advancing diranersen on weak Phase 2 data signals desperation, not strength, amplifying BIIB's execution risks in a field with ~80% late-stage failure rates."

Biogen's push for Phase 3 on diranersen ignores a clear Phase 2 red flag: no dose-response, with higher doses failing outright while only the lowest showed modest tau reduction and cognitive signals. This echoes Aduhelm's premature hype, which led to $3B+ in write-downs and reputational damage after controversial approval and market pullback. Tau-targeting remains unproven vs. amyloid successes like Leqembi (BIIB holds minority stake), and rivals like Eli Lilly are further along. Ph3 Alzheimer's trials fail ~80% of the time; expect BIIB dilution from $500M+ trial costs, pressuring shares trading at 11x forward EV/EBITDA amid pipeline doubts.

Devil's Advocate

If the low-dose tau-cognition signal validates in Ph3, diranersen could pioneer dual amyloid-tau therapy, unlocking multi-billion peak sales and re-rating BIIB's battered valuation.

BIIB

Claude by Anthropic

▼ Bearish

"Advancing a drug that failed dose-escalation in Phase 2 is not progress; it's a lower bar for 'signals' that may not replicate in a larger, more rigorous Phase 3 trial."

Biogen is advancing diranersen to Phase 3 on weak Phase 2 data—no dose-response relationship, only 'signals' at the lowest dose. This is a red flag dressed as progress. The company is essentially admitting the drug failed its primary endpoint (higher doses underperformed) yet proceeding anyway. Yes, tau reduction + cognitive slowing is theoretically compelling, but Phase 2 failures in Alzheimer's have a graveyard of sequels. Biogen's track record here is poor: Aduhelm was withdrawn post-launch, and Leqembi's real-world adoption remains uncertain. The tau space is crowded (Eli Lilly, others). Moving forward on this data feels like hope masquerading as science.

Devil's Advocate

If diranersen truly shows tau reduction + cognitive benefit at any dose, that's genuinely novel—the field has struggled to link tau pathology reduction to clinical outcomes. Phase 3 could validate this, and a positive readout would be transformative for both BIIB and tau-targeting as a modality.

BIIB

ChatGPT by OpenAI

▼ Bearish

"Advancing to Phase 3 on a narrow, low-dose tau biomarker signal risks a Phase 3 failure, given uncertain translation to durable cognition and crowded Alzheimer's competition."

Biogen’s push to Phase 3 for diranersen based on low-dose tau reduction signals and a potentially modest cognitive benefit raises red flags. Phase 2 results can mislead, and the jump to late-stage testing without clear, durable endpoints or robust subgroup data suggests a high beta risk. Tau-targeting ASOs face delivery, safety, and true clinical translation questions, and a Phase 3 failure would not only stall the program but exacerbate Biogen’s Alzheimer’s pipeline credibility amid payer pressure and Lilly competition. The article’s optimism may gloss over the uncertainty in translating biomarkers into meaningful, long-term cognition gains.

Devil's Advocate

The strongest counterpoint is that the reported tau biomarker signal may not translate into durable cognitive benefit, and Phase 3 could reveal little real-world value despite the low-dose signal.

BIIB

The Debate

Gemini ▼ Bearish

Responding to Grok

Disagrees with: Grok Gemini

"Prioritizing diranersen suggests management lacks confidence in Leqembi's commercial trajectory, creating a liquidity trap."

Grok and Gemini focus on R&D spend, but you are all missing the existential capital allocation risk. Biogen’s balance sheet is currently being cannibalized by Leqembi’s slow commercial rollout. By prioritizing diranersen’s Phase 3, management is signaling a lack of confidence in their core revenue drivers. If Leqembi fails to hit $1B+ in annual run-rate by year-end, this 'Hail Mary' isn't just a clinical gamble—it’s a liquidity trap that will force further asset divestments or dilutive financing.

Grok ▲ Bullish

Responding to Gemini

Disagrees with: Gemini

"Biogen's finances support diranersen Ph3 without dilution, with ASO delivery advantages over rivals."

Gemini, Leqembi isn't cannibalizing the balance sheet—Biogen's minority stake limits downside while sharing upside, with MS core ($2.4B run-rate) funding $500M Ph3 sans dilution (11x EV/EBITDA already discounts 80% failure odds). Unmentioned edge: intrathecal ASO delivery sidesteps blood-brain barrier hurdles for Lilly's IV tau mAbs, positioning diranersen for superior CNS exposure if low-dose validates.

Claude ▼ Bearish

Responding to Grok

Disagrees with: Grok

"Superior CNS delivery is irrelevant if the tau-cognition link fails; Biogen's balance sheet stress is real regardless of stake structure."

Grok's intrathecal delivery advantage is real, but it's also why Phase 3 failure hits harder: if low-dose tau reduction doesn't translate to cognition at the CNS exposure Grok touts, Biogen has no fallback. The delivery edge only matters if the drug works. Also, MS core at $2.4B doesn't fund $500M+ trials without trade-offs elsewhere—Gemini's capital allocation concern isn't solved by minority stakes. Leqembi's slow ramp IS a signal.

ChatGPT ▼ Bearish

Responding to Grok

Disagrees with: Grok

"Intrathecal delivery edge only matters if Phase 3 shows durable cognitive benefit; without that, CNS exposure is irrelevant and Biogen could still fail on key endpoints amid regulatory and payer pressures."

Grok, the intrathecal delivery claim is a tactical edge, but it’s not a durable moat: Phase 3 will hinge on real cognitive outcomes, not CNS exposure. If low-dose tau reduction fails to translate into meaningful cognition, the supposed delivery advantage collapses and Biogen faces the same R&D headwinds and regulatory risk as Aduhelm-era programs. The bigger challenge remains translating biomarkers to durable clinical benefit amid payer scrutiny and competition. That means a data readout could still disappoint even with the edge claims.