POS0659 EFFICACY, SAFETY AND IMMUNOGENICITY OF THE PROPOSED TOCILIZUMAB BIOSIMILAR RGB-19, INTRAVENOUSLY ADMINISTERED TO PARTICIPANTS WITH ACTIVE RHEUMATOID ARTHRITIS: WEEK 24 DATA FROM A PHASE 3 STUDY

Background: RGB-19, a proposed biosimilar to tocilizumab, is a monoclonal antibody that competitively inhibits the binding of interleukin-6 (IL-6) to its receptor. Objectives: To demonstrate the clinical equivalence in efficacy, and compare serum concentration, pharmacodynamics (PD), safety and immunogenicity, of RGB-19 and reference tocilizumab (hereafter tocilizumab) in participants with rheumatoid arthritis (RA). Methods: This was a Phase 3, randomised, double-blind study in Japanese adults with active RA and an inadequate response to methotrexate, a baseline Disease Activity Score based on 28 joints with erythrocyte sedimentation rate (DAS28-ESR) of ≥3.2, and swollen/tender joints (≥6 from 66/68). Participants were assigned 1:1 to intravenous (IV) infusions of RGB-19 8 mg/kg or IV tocilizumab 8 mg/kg every 4 weeks to W (week) 52 and followed to W54. Primary endpoint was DAS28-ESR mean change from baseline (CfB) at W12 (equivalence margin: ±0.6 for the 2-sided 95% confidence interval of the pooled difference between groups), complemented by secondary efficacy, serum concentration, PD, immunogenicity and safety endpoints to W24. Results: Overall, 368 participants were randomised. A total of 182 (RGB-19) and 185 (tocilizumab) participants were included in the primary analysis. Median age (range) was 57 (20–75) years; most were female (76%) with Class I/II RA (86%) and median time (range) since first RA diagnosis of 2.95 (0.2–46.3) years. Baseline characteristics were balanced between groups. The analysis of covariance (ANCOVA) of the primary endpoint results showed equivalence in efficacy between RGB-19 and tocilizumab at W12 (adjusted mean CfB in DAS28-ESR: RGB-19 −3.62, tocilizumab −3.41; difference point estimate: −0.21 [95% confidence interval −0.43, 0.02]; Table 1). This was supported by the results of a sensitivity (tipping point) analysis and secondary endpoint analyses, including similar ACR, EULAR, CDAI, and SDAI achievement/response rates at W24 (Table 1). Median serum drug concentration, absolute neutrophil count, C-reactive protein level, and soluble IL-6 receptor values were similar for both treatments up to W24. Safety profiles were similar between treatments up to W24 (Table 2) with no new safety signals identified. Both treatments had similarly low immunogenicity (anti-drug antibody positive participants: RGB-19 5 [2.7%]; tocilizumab 8 [4.3%]); there were no treatment-related adverse events leading to death in either arm. Conclusion: Equivalence in efficacy was shown between RGB-19 and tocilizumab. Serum drug concentration, PD, safety, and immunogenicity profiles were similar between treatments. Additional, longer-term efficacy, safety and immunogenicity outcomes up to W52 are anticipated. REFERENCES: NIL . Acknowledgements: Study funded by Gedeon Richter and Mochida Pharmaceutical. Medical writing support provided by Timothy Davies, PhD, of Avalere Health, funded by Gedeon Richter. Disclosure of Interests: Ernest Choy has received research grants, speaking fees, consultancies or honoraria from Abbvie, Bio-Cancer, Biocon, Biogen, Chugai Pharma, Eli Lilly, Fresenius Kai, Galapagos, Gedeon Richter, Gilead, Janssen, Pfizer, Sanofi, UCB and Viatris, Paul Emery has provided expert advice to Abbvie, Activa, Astra-Zeneca, BMS, Boehringer Ingelheim, Galapagos, Gilead, Immunovant, Janssen, Lilly, and Novartis, and contributed to clinical trials of Abbvie, BMS, Lilly, Novartis, and Samsung, Hiroaki Matsuno has received honoraria and/or lecture fees from Chugai Pharmaceutical, Daiichi Sankyo, and Eli Lilly, and has received consulting fees from Mochida Pharmaceutical, and Nichi-Iko Pharmaceutical, Masato Okada has received speaking fees and/or honoraria from Astellas, Eli Lilly and Company, GSK, and Janssen, Zsofia Polgari is a Gedeon Richter employee, Karoly Horvát-Karajz is a Gedeon Richter employee, Gordana Dancer is a Gedeon Richter employee, Yusuke Karibe is a Mochida Pharmaceutical employee, Suguru Masuda is a Mochida Pharmaceutical employee, Joachim Kiefer is a Gedeon Richter employee, Gerd R. Burmester has received honoraria for lectures and consulting from Celltrion, Chugai, Fresenius, Gedeon Richter, and Sanofi. © The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.

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