Vigil's ALSP Drug Fails Phase 2 Trial, Sanofi Acquisition Proceeds

Vigil Neuroscience's experimental drug for a rare brain disease has failed to meet its primary endpoints in a phase 2 study, casting doubt on its future development. Despite this setback, the company's pending acquisition by pharmaceutical giant Sanofi remains unaffected.

Iluzanebart Falls Short in ALSP Trial

Vigil Neuroscience announced that iluzanebart, its TREM2 agonist, missed both biomarker and efficacy endpoints in a phase 2 study for adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP). The open-label proof-of-concept trial evaluated the drug's impact on brain volume loss, clinical measures of disease progression, and biomarkers of neurodegeneration.

While iluzanebart demonstrated a favorable safety, tolerability, and pharmacokinetic profile across both doses tested, it failed to show beneficial effects on the key outcome measures. As a result, Vigil has decided to halt a long-term extension trial of the compound.

William Blair analysts expressed little surprise at the outcome, noting that although the low dose had shown "early promising signals," there were concerns about iluzanebart's brain bioavailability and the reproducibility of results in an open-label study for ALSP.

Sanofi Acquisition Moves Forward

The failure of iluzanebart does not impact Sanofi's planned $470 million acquisition of Vigil Neuroscience, which was announced last month. As part of the deal, Vigil had already agreed to return the rights to iluzanebart to Amgen, allowing Sanofi to focus on VG-3927, a small-molecule TREM2 agonist.

The decision to exclude iluzanebart from the acquisition now appears prescient, with William Blair analysts noting that Vigil's willingness to relinquish the drug hinted at potential issues with its efficacy.

Amgen is set to regain control of iluzanebart before Sanofi completes the Vigil takeover, which is scheduled for the third quarter of this year. This arrangement ensures that the phase 2 failure will not affect the acquisition's progress or valuation.