Discussing New Bimekizumab, Risankizumab Data in PsA, With Peter Nash, MBBS

New positive topline results have been released from the BE BOLD trial, a head-to-head study evaluating bimekizumab (Bimzelx) against risankizumab (Skyrizi) in adults with active psoriatic arthritis (PsA) by UCB.^1,2

Bimekizumab, the first and only approved medication to selectively inhibit both interleukin (IL)-17A and IL-17F, was described as having attained statistically significant superiority on the study’s ACR50 primary efficacy endpoint at Week 16. ACR50 represents a 50% or greater improvement from the point of baseline in the American College of Rheumatology’s response criteria.

During BE BOLD, bimekizumab’s safety was also consistent with prior findings, as the treatment was generally well tolerated with a lack of new safety signals. Peter Nash, MBBS, FRACP, FQAAS, from the School of Medicine at Griffith University in Brisbane, Australia, spoke in a Q&A about these findings and their significance:

Rheumatology Live: How clinically meaningful is the ACR50 advantage seen with bimekizumab at Week 16?

Nash: I think of ACR20, which was used in previous trials as a primary outcome measure, as the minimal clinically important improvement needed to separate a drug from placebo. By contrast, ACR50 requires a 50% improvement in joint tenderness and swelling, along with a 50% improvement in other outcomes such as pain, physical function, and both patient and physician global assessments. It therefore represents a clear, noticeable, moderate-to-major improvement.

With so many therapies now available, modern clinicians are demanding at least this level of response for their patients. In some countries, including mine, if at least a 50% improvement is not achieved by 16 weeks, the patient cannot continue to access reimbursed therapy.

Rheumatology Live: Did improvements in joint symptoms correlate with skin clearance in the BE BOLD population?

Nash: So far, we only have a limited press release, and important questions like this will need to await formal presentation of the data, hopefully at the next major meeting, followed by publication in a peer-reviewed paper. Anecdotally, from our trial experience, patients who did well clinically from a joint perspective also tended to do well from a psoriasis perspective, although, of course, we were blinded to the treatment arm.

Rheumatology Live: Were there notable differences in outcomes across PsA domains such as enthesitis or dactylitis?

Nash: Those domain-specific findings have not yet been publicly disclosed. We plan to share the full results at an upcoming medical congress.

Rheumatology Live: What does this head-to-head trial suggest about the relative roles of the IL-17 and IL-23 pathways in psoriatic arthritis?

Nash: We know, from a pathophysiological perspective, that both pathways are important and that both are effective therapeutic targets in psoriatic disease. IL-23 is the upstream regulator that drives the process— initiating and sustaining it, if you like— whereas IL-17 is more directly responsible for the clinical effects, executing the inflammation and damage.

Rheumatology Live: Do the results support earlier use of dual IL-17A/IL-17F inhibition in patients with both skin and joint disease?

Nash: Whilst there is suggestive evidence from other trials to support this, the BE-BOLD trial did not stratify by disease duration. However, provided there are sufficient numbers of patients with early disease (e.g. <2 years) and established disease (e.g. >2 years), a post hoc analysis should help shed light on this question.

Rheumatology Live: Where might bimekizumab fit in treatment sequencing as clinicians choose between IL-17, IL-23, and TNF inhibitors?

Nash: Thus far, head-to-head trials in PsA have compared IL-17 inhibition with TNF inhibition, and this is the first trial to compare IL-17A and IL-17F inhibition directly with IL-23 inhibition. It will provide important evidence for treatment algorithms based on direct efficacy and safety data, rather than on network meta-analyses.

References

1. BIMZELX[®]▼(bimekizumab) superior to SKYRIZI[®] (risankizumab) in BE BOLD: first head-to-head study in active psoriatic arthritis (PsA) to demonstrate superiority in ACR50. UCB. March 11, 2026. Accessed March 24, 2026. https://www.ucb.com/newsroom/press-releases/article/bimzelxrvbimekizumab-superior-to-skyrizir-risankizumab-in-be-bold-first-head-to-head-study-in-active-psoriatic-arthritis-psa-to-demonstrate-superiority-in-acr50.

2. UCB announces U.S. FDA approvals for BIMZELX for the treatment of psoriatic arthritis, non-radiographic axial spondyloarthritis, and ankylosing spondylitis. Press release. UCB. September 23, 2024. Accessed March 24, 2026. https://www.prnewswire.com/news-releases/ucb-announces-us-fda-approvals-for-bimzelx-bimekizumab-bkzx-for-the-treatment-of-psoriatic-arthritis-non-radiographic-axial-spondyloarthritis-and-ankylosing-spondylitis-302255482.html.