SAT0315 STRUCTURAL DAMAGE PROGRESSION OVER 4 YEARS OF SECUKINUMAB TREATMENT IN ANKYLOSING SPONDYLITIS: POST-HOC ANALYSIS OF MEASURE-1 TRIAL USING A LONGITUDINAL BAYESIAN MIXTURE MODEL

Background: Ankylosing spondylitis (AS) is an inflammatory disease resulting in progressive disability due to structural damage in the spine. The identification of predictors of progression would allow treating physicians to personalize treatments but requires an approach accounting for a relatively short follow-up of clinical studies, large between-patient variability, and low sensitivity of X-ray images which generate intra-patient variability when repeated measurements are taken. Objectives: 1) To identify patient characteristics predicting faster structural damage progression. 2) To quantify the progression over four years of secukinumab treatment, depending on dose/exposure. Methods: Data came from the phase 3 randomized placebo-controlled trial MEASURE 1 (NCT01358175)1 in which patients were treated with secukinumab (intravenous loading of 10 mg/kg at weeks 0, 2, and 4, followed by secukinumab subcutaneously at a dose of either 75 mg or 150 mg every 4 weeks) over 208 weeks. Only patients treated with secukinumab with at least two assessments of structural damage were included. We explored the effect of multiple baseline demographic traits, disease stage, severity, bone cartilage biomarkers as well as prior and current treatment on change in modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) using a longitudinal Bayesian mixture model with random effects, which accounted simultaneously for the probability of progression, magnitude of progression and inter-patient variability. Posterior predictive check was performed. Results: Out of 249 patients randomized to secukinumab, 167 had their structural damage assessed at least twice. These patients contributed in total 409 assessments of change in structural damage between weeks 0, 52, 104 and 208. Of the factors tested, a higher baseline BASMI score was associated with faster progression rate in a statistically significant way (+0.60 in mSASSS/year for each additional standard deviation of baseline BASMI (SD=1.74), 95% interval 0.03 to 1.14). Trends were also detected for association between faster mSASSS progression and younger age, prior exposure to TNFα inhibitor, HLA-B27 positivity, and higher osteocalcin levels. Increased exposure to secukinumab was associated with slower structural damage progression (-0.23 in mSASSS/year for each additional standard deviation in exposure, 95% interval -0.58 to 0.10). Model estimation suggested that secukinumab 150 mg was associated with a yearly progression of -0.2 (95% interval -1.2 to 0.8) in the first two years of treatment and 0.1 mSASSS (95% interval -0.8 to 1.0) in the third and fourth year of treatment. Analogously, secukinumab 75mg (currently not approved for clinical use) was associated with a progression of -0.2 mSASSS/year (95% interval -1.3 to 0.9) in the first two years of treatment and 0.5 mSASSS/year (95% interval -0.5 to 1.6) in the third and fourth year of treatment. Conclusion: Potential predictors of structural progression suggested by the model were higher baseline BASMI, younger age, prior exposure to TNFα inhibitor, HLA-B27 positivity, and higher osteocalcin at baseline, although only baseline BASMI showed statistical significance. Further analyses using larger, deeper and real-world data are needed to confirm these findings and to estimate progression rates in AS patients in daily practice. Reference [1] Baeten D, Sieper J, Braun J, et al. Secukinumab, an Interleukin-17A Inhibitor, in Ankylosing Spondylitis. N Engl J Med. 2015;373(26):2534-2548. Disclosure of Interests: Olivier Luttringer Shareholder of: Novartis, Employee of: Employee of Novartis Pharma AG, Todd Fox Employee of: Novartis, Brian Porter Shareholder of: Novartis, Employee of: Novartis, Abhijit Shete Shareholder of: Novartis Pharma AG, Employee of: Novartis Pharma AG, Hanno Richards Shareholder of: Novartis Pharma AG, Employee of: Novartis Pharma AG, Witold Wiecek Consultant for: Employee of CERTARA Strategic Consulting., Zuzanna Angehrn Shareholder of: Owns funds which might occassionaly invest in pharmaceutical companies’ stocks., Consultant for: Employee of CERTARA strategic consulting., Helene Karcher Consultant for: Former employee of Analytica Laser, a Certara company. Former independent consultant. Current employee of PAREXEL., Employee of: Former employee of Novartis., Billy Amzal Consultant for: Employee of CERTARA Strategic Consulting., Employee of: Former employee of Novartis.