ACHIEVEMENT OF LOW DISEASE ACTIVITY OVER 52 WEEKS IN PATIENTS WITH ACTIVE AXIAL SPONDYLOARTHRITIS ON BIMEKIZUMAB TREATMENT: RESULTS FROM THE PHASE 3 STUDIES BE MOBILE 1 AND BE MOBILE 2

X. Baraliakos, S. Ramiro, M. Magrey, M. Rudwaleit, N. Haroon, C. Fleurinck, U. Massow, N. De Peyrecave, T. Vaux, H. Marzo-Ortega, V. Navarro-CompánRuhr University Bochum, Rheumazentrum Ruhrgebiet Herne, Bochum, Germany Leiden University Medical Center, Department of Rheumatology, Leiden, Netherlands Case Western Reserve University, University Hospitals, Cleveland, United States of America University of Bielefeld, Klinikum Bielefeld, Bielefeld, Germany University of Toronto, University Health Network, Schroeder Arthritis Institute, Department of Medicine/Rheumatology, Toronto, Canada UCB Pharma, N/A, Brussels, Belgium UCB Pharma, N/A, Monheim am Rhein, Germany UCB Pharma, N/A, Slough, United Kingdom University of Leeds, NIHR Leeds Biomedical Research Centre, Leeds Teaching Hospitals NHS Trust and Leeds Institute of Rheumatic and Musculoskeletal Medicine, Leeds, United Kingdom La Paz University Hospital, Department of Rheumatology, IdiPaz, Madrid, Spain  Background Ankylosing Spondylitis (AS) Disease Activity Score (ASDAS) is the recommended instrument to assess disease activity in axial spondyloarthritis (axSpA). However, the Bath AS Disease Activity Index (BASDAI) remains commonly used in clinical practice. The recommended treatment target for axSpA is remission or low disease activity (LDA) according to ASDAS levels, while limited data exist to validate cut-offs for BASDAI. However, remission is difficult to achieve for many patients (pts), especially in established disease. Bimekizumab (BKZ) is a monoclonal IgG1 antibody that selectively inhibits interleukin (IL)-17F in addition to IL-17A. BKZ has demonstrated consistent and sustained efficacy up to Week (Wk) 52 in the BE MOBILE 1 and 2 phase 3 studies, including achievement of LDA according to ASDAS by >50% of pts with non-radiographic (nr-)axSpA and radiographic (r-)axSpA (i.e. AS). Objectives To report achievement of LDA, as assessed by either ASDAS <2.1, BASDAI <4, or both, to Wk 52 with BKZ across the spectrum of axSpA in two phase 3 studies. Methods BE MOBILE 1 (NCT03928704) and BE MOBILE 2 (NCT03928743) each comprised a 16-wk placebo (PBO)-controlled and 36-wk maintenance period. Pts with nr-axSpA in BE MOBILE 1 met Assessment of SpondyloArthritis international Society (ASAS) classification criteria and had objective inflammation as assessed by MRI and/or elevated C-reactive protein. Pts with r-axSpA included in BE MOBILE 2 met modified New York criteria and also fulfilled ASAS classification criteria. All pts had active disease (BASDAI ≥4 and spinal pain ≥4 as per BASDAI item 2) at baseline. Pts were randomised to subcutaneous BKZ 160 mg every 4 wks (Q4W) or PBO; all pts received BKZ 160 mg Q4W from Wk 16 onwards. The PBO arm is therefore referred to as PBO up to Wk 16, and PBO/BKZ at later timepoints. Here, we present the proportion of pts achieving LDA to Wk 52, as defined by either ASDAS <2.1, BASDAI <4, or both, using non-responder imputation. Results A total of 254 pts with nr-axSpA (BKZ: 128, PBO: 126) and 332 with r-axSpA (BKZ: 221, PBO: 111) were randomised. Most pts had high (ASDAS ≥2.1–≤3.5) or very high (ASDAS >3.5) disease activity at baseline (nr-axSpA: BKZ: 99.2%, PBO: 97.6%; r-axSpA: BKZ: 98.6%, PBO: 100%). In pts with nr-axSpA, a greater proportion of BKZ vs PBO-treated pts achieved LDA at Wk 16 according to ASDAS <2.1 (BKZ: 46.1%, PBO: 19.8%), BASDAI <4 (BKZ: 52.3%, PBO: 31.7%), and both (BKZ: 43.8%, PBO: 19.0%). Separation from PBO was apparent from first post-baseline assessment for ASDAS <2.1 and both ASDAS <2.1 and BASDAI <4 (Figure 1). Results were similar for pts with r-axSpA (Figure 1). Across continuous BKZ-treated pts and PBO/BKZ switchers, achievement of LDA, according to ASDAS <2.1, BASDAI <4, and both, was sustained or improved in both studies to Wk 52 (Figure 1). Proportion of pts achieving BASDAI <4 was consistently higher compared with achievement of ASDAS <2.1, regardless of treatment arm. Conclusion Across the full axSpA disease spectrum, dual inhibition of IL-17A and IL-17F with BKZ resulted in rapid achievement of LDA vs PBO to Wk 16, as assessed by ASDAS <2.1, BASDAI <4, or both. Proportion of pts achieving LDA increased to Wk 52. These data suggest that ASDAS <2.1 is a more stringent criteria for LDA than BASDAI <4, and the majority of pts who achieved ASDAS <2.1 also achieved BASDAI <4. This is relevant for the consideration of BKZ in the context of a potential treat-to-target approach for pts with axSpA in daily practice. References [1] Smolen J. Ann Rheum Dis. 2018;77:3–17; [2] Kwon OC. Rheumatology (Oxford). 2022;61:2369–74; [3] Chen Y-H. Front Med (Lausanne). 2022;9:856654; [4] Boel A. Ann Rheum Dis. 2019;78:1545–9; [5] Baraliakos X. Arthritis Rheumatol. 2022;74(Suppl 9). Image/graph: Acknowledgements This study was funded by UCB Pharma. Medical writing support was provided by Costello Medical, funded by UCB Pharma. Disclosure of Interests Xenofon Baraliakos Speakers bureau: AbbVie, BMS, Chugai, Eli Lilly, Galapagos, Gilead, MSD, Novartis, Pfizer, and UCB Pharma, Paid instructor for: AbbVie, BMS, Chugai, Eli Lilly, Galapagos, Gilead, MSD, Novartis, Pfizer, and UCB Pharma, Consultant of: AbbVie, BMS, Chugai, Eli Lilly, Galapagos, Gilead, MSD, Novartis, Pfizer, and UCB Pharma, Sofia Ramiro Consultant of: AbbVie, Eli Lilly, Novartis, Pfizer, Sanofi, and UCB Pharma, Grant/research support from: AbbVie, Galapagos, MSD, Novartis, Pfizer, and UCB Pharma, Marina Magrey Consultant of: AbbVie, Eli Lilly, Novartis, Pfizer, and UCB Pharma, Grant/research support from: AbbVie and UCB Pharma, Martin Rudwaleit Speakers bureau: AbbVie, BMS, Boehringer Ingelheim, Chugai, Eli Lilly, Janssen, Novartis, Pfizer, and UCB Pharma, Consultant of: AbbVie, Eli Lilly, Novartis, and UCB Pharma, Nigil Haroon Consultant of: AbbVie, Eli Lilly, Janssen, Novartis, and UCB Pharma, Carmen Fleurinck Employee of: UCB Pharma, Ute Massow Employee of: UCB Pharma, Natasha de Peyrecave Employee of: UCB Pharma, Thomas Vaux Employee of: UCB Pharma, Helena Marzo-Ortega Speakers bureau: AbbVie, Biogen, Eli Lilly, Janssen, Moonlake, Novartis, Pfizer, Takeda and UCB Pharma, Consultant of: AbbVie, Biogen, Eli Lilly, Janssen, MoonLake, Novartis, Pfizer, Takeda, and UCB Pharma, Grant/research support from: Janssen, Novartis, and UCB Pharma, Victoria Navarro-Compán Speakers bureau: AbbVie, Eli Lilly, Janssen, MSD, Novartis, Pfizer, and UCB Pharma, Consultant of: AbbVie, Eli Lilly, Galapagos, MoonLake, MSD, Novartis, Pfizer, and UCB Pharma, Grant/research support from: AbbVie and Novartis. Keywords: Spondyloarthritis, Clinical trials, Treat to target DOI: 10.1136/annrheumdis-2023-eular.833Citation: , volume 82, supplement 1, year 2023, page 875Session: Spondyloarthritis - treatment (Poster View)