Acelyrin Flags CRO Errors in Izokibep Program After Late-Stage Failure

Vials_iStock, NikiLitov

Pictured: Syringe drawing from a series of vials/iStock, NikiLitov

Acelyrin on Monday announced that it will conduct a sweeping review of the development program for its investigational IL-17A inhibitor izokibep after it discovered crucial dosing errors committed by contract research organization Fortrea.

The announcement comes more than two months after izokibep missed its primary efficacy endpoint in one part of a Phase IIb/III study in hidradenitis suppurativa. In a September 2023 data drop, Acelyrin said that its candidate was unable to significantly outperform placebo in terms of 16-week HiSCR75 score, a measure that represents at least a 75% reduction in disease markers.

Shortly after the readout, Acelyrin’s shares dropped by as much as 64%.

The clinical trial “execution errors” disclosed Monday by Acelyrin affected a psoriatic arthritis trial of izokibep, which included four dosing arms: 160-mg weekly, 160-mg every other week (Q2W), 80-mg every four weeks (Q4W) and placebo. However, a vendor engaged by the contract research organization (CRO) had incorrectly programmed the proper dosing sequence, an error that further went undetected during the testing process.

As a result of the CRO and the vendor’s oversight, “some patients in the 160mg Q2W and 80mg Q4W arms received placebo and active treatment in random order rather than in an alternating pattern as intended,” Acelyrin noted in Monday’s announcement.

At the same time, however, the dosing error poses “no risk to patient safety” and “no patient received more active treatment than was already included in the protocol,” the biotech said.

Acelyrin revealed in a Nov. 26 SEC filing that the CRO in question is Fortrea.

The programming error has been rectified and Acelyrin is now currently working to “determine the implications” on the affected treatment groups but believes that the placebo and once-weekly izokibep arms are unaffected.

Acelyrin will also contract an independent, third-party auditor to review Fortrea’s work and izokibep’s clinical trial program, scrutinizing not only the psoriatic arthritis study but also the hidradenitis suppurativa trial that returned disappointing results in September 2023. The biotech likewise said that it will no longer work with Fortrea on any future trials.

In May 2023, the California-based biotech closed its initial public offering and raised $540 million, largely buoyed by the promise of izokibep.

Acelyrin will decide on the best path forward for izokibep based on the findings of the independent audit. The company expects to release topline data from the psoriatic arthritis early next year, also pending the completion of the audit.

Tristan Manalac is an independent science writer based in Metro Manila, Philippines. He can be reached at or

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