Efficacy of Ixekizumab in Chinese Patients with Radiographic-Axial Spondyloarthritis by Baseline Inflammation Status on Magnetic Resonance Imaging

INTRODUCTION: We report an exploratory subgroup analysis of a Chinese phase 3 study to investigate the effect of baseline inflammation measured by magnetic resonance imaging (MRI) on ixekizumab efficacy in radiographic axial spondyloarthritis (r-axSpA). METHODS: Adults with r-axSpA were randomized (1:1) to receive ixekizumab 80 mg every 4 weeks (IXEQ4W) or placebo for 16 weeks. Endpoints analyzed by baseline Spondyloarthritis Research Consortium of Canada (SPARCC) MRI spine or sacroiliac joint (SIJ) inflammation score (< 2 or ≥ 2; elevated inflammation defined as score ≥ 2) were: Assessment of SpondyloArthritis International Society 40 (ASAS40); Bath Ankylosing Spondylitis Disease Activity Index 50 (BASDAI50); Ankylosing Spondylitis Disease Activity Score (ASDAS) < 2.1; ASDAS clinically important improvement (CII; change from baseline ≥ 1.1); Patient Global Assessment of Disease Activity (PtGA); spinal pain; nocturnal spinal pain; stiffness/inflammation; function; fatigue; Short Form-36 Physical Component Score (SF-36 PCS); European Quality of Life 5 Dimensions 5 Levels visual analog scale (EQ-5D-5L VAS). RESULTS: Overall, 145 patients were included. At Week 16, ASAS40 response rates were numerically improved with IXEQ4W versus placebo in the SPARCC MRI spine score < 2 subgroup (40.9% vs. 14.3%; p = 0.088) and significantly improved in the ≥ 2 subgroup (37.3% vs. 5.9%; p < 0.001). ASAS40 response rates were significantly improved in the SPARCC MRI SIJ score < 2 (34.4% vs. 8.6%; p < 0.05) and ≥ 2 (41.5% vs. 8.1%; p < 0.001) subgroups. Similar results were obtained on BASDAI50, ASDAS < 2.1, and ASDAS CII. IXEQ4W significantly improved PtGA, inflammation, and fatigue across all subgroups. Spinal and nocturnal spinal pain were significantly improved in the SPARCC MRI spine score ≥ 2 subgroup and both SPARCC MRI SIJ score subgroups. Function and SF-36 PCS were significantly improved in the SPARCC MRI spine score ≥ 2 subgroup. There were no significant differences in EQ-5D-5L VAS. CONCLUSION: These findings support IXEQ4W as an effective treatment for Chinese patients with r-axSpA, irrespective of baseline MRI inflammation. TRIAL REGISTRATION: ClinicalTrials.gov identifier, NCT04285229.