SAT0189 Rapid Onset of Clinical Benefit in Patients with RA Treated with Mavrilimumab, A Fully Human Monoclonal Antibody Targeting GM–CSFR-ALPHA: Subanalysis of the Phase IIB Earth Explorer 1 Study

Background Macrophages are pivotal to the pathogenesis of rheumatoid arthritis (RA), and their inflammatory products drive many of the signs and symptoms of disease. Mavrilimumab inhibits macrophage activation and survival via blockade of granulocyte-macrophage colony-stimulating factor receptor-α (GM–CSFR-α) and has demonstrated sustained clinical benefit in patients with RA. 1 Objectives To examine time to onset of clinical response to mavrilimumab in the EARTH EXPLORER 1 study. Methods In a 24-week, Phase IIb study (NCT01706926), patients with adult-onset RA (18–80 years; Disease Activity Score 28 C-reactive protein [DAS28–CRP] >3.2; ≥4 swollen joints; inadequate response to ≥1 disease-modifying antirheumatic drugs [DMARDs]) receiving concomitant methotrexate were enrolled. Patients received mavrilimumab (150, 100, or 30 mg every other week [eow]) or placebo, administered subcutaneously with methotrexate (7.5–25.0 mg/week). Efficacy assessments included DAS28–CRP, American College of Rheumatology (ACR)20/50/70 responses, CRP, erythrocyte sedimentation rate (ESR), swollen joint count (SJC), tender joint count (TJC), and pain assessments. Results 326 patients with mean (SD) DAS28–CRP 5.8 (0.9) were randomized to mavrilimumab (150, 100, or 30 mg eow) or placebo (N=79, 85, 81, and 81, respectively). At Week 1 (first assessment), all mavrilimumab dosages demonstrated significant reductions from baseline in DAS28–CRP ( p p =0.003 to p Conclusions By targeting activated macrophages via inhibition of GM–CSFR-α, mavrilimumab substantially reduced patients9 RA disease activity early in their treatment, from first dose (Week 1) to final assessment for many patients, as evaluated by several clinical outcomes. References Burmester GR, et al. Ann Rheum Dis. 2013;72:1445–52. Acknowledgements Funded: MedImmune Ltd. Editorial assistance: N Panagiotaki, QXV Communications, UK Disclosure of Interest I. McInnes Grant/research support from: MedImmune (Research award to University of Glasgow), Consultant for: MedImmune, AstraZeneca, G. Burmester Grant/research support from: AbbVie, Pfizer, UCB, Roche, Consultant for: AbbVie, BMS, Novartis, MedImmune, MSD, Pfizer, UCB, Roche, Speakers bureau: AbbVie, BMS, Novartis, MSD, Pfizer, UCB, Roche, J. Kremer Shareholder of: Corrona, Grant/research support from: AbbVie, Amgen, Genentech, Lilly, Pfizer, Consultant for: AbbVie, Amgen, Genentech, Lilly, Pfizer, BMS, Employee of: Corrona, P. Miranda Grant/research support from: MedImmune (to support protocol), M. Korkosz: None declared, J. Vencovsky: None declared, A. Rubbert-Roth Grant/research support from: Pfizer, Chugai, Consultant for: MSD, UCB, Abbott, Pfizer, Roche, BMS, Chugai, Speakers bureau: Roche, Pfizer, UCB, E. Mysler Grant/research support from: MedImmune, Roche, BMS, Pfizer, D. Close Shareholder of: AstraZeneca, Employee of: MedImmune, M. Sleeman Shareholder of: AstraZeneca, Employee of: MedImmune, A. Godwood Shareholder of: AstraZeneca, Employee of: MedImmune, M. Albulescu Employee of: MedImmune, M. Weinblatt Grant/research support from: BMS, UCB, Crescendo Bioscience, Consultant for: MedImmune, AstraZeneca, Amgen, Abbvie, BMS, Crescendo bioscience, Lilly, Pfizer, UCB, Roche