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Objective: Fenebrutinib (GDC‐0853) is a noncovalent, oral, and highly selective inhibitor of Bruton's tyrosine kinase (BTK). The efficacy, safety, and pharmacodynamics of fenebrutinib in systemic lupus erythematosus (SLE) were assessed in this phase II, multicenter, randomized, placebo‐controlled study. Methods: Patients who had moderately to severely active SLE while receiving background standard therapy were randomized to receive placebo, fenebrutinib 150 mg once daily, or fenebrutinib 200 mg twice daily. Glucocorticoid taper was recommended from weeks 0 to 12 and from weeks 24 to 36. The primary end point was the SLE Responder Index 4 (SRI‐4) response at week 48. Results: Patients (n = 260) were enrolled from 44 sites in 12 countries, with the majority from Latin America, the US, and Western Europe. The SRI‐4 response rates at week 48 were 51% for fenebrutinib 150 mg once daily (P = 0.37 versus placebo), 52% for fenebrutinib 200 mg twice daily (P = 0.34 versus placebo), and 44% for placebo. British Isles Lupus Assessment Group–based Combined Lupus Assessment response rates at week 48 were 53% for fenebrutinib 150 mg once daily (P = 0.086 versus placebo), 42% for fenebrutinib 200 mg twice daily (P = 0.879 versus placebo), and 41% for placebo. Safety results were similar across all arms, although serious adverse events were more frequent with fenebrutinib 200 mg twice daily. By week 48, patients treated with fenebrutinib had reduced levels of a BTK‐dependent plasmablast RNA signature, anti–double‐stranded DNA autoantibodies, total IgG, and IgM, as well as increased complement C4 levels, all relative to placebo. Conclusion: While fenebrutinib had an acceptable safety profile, the primary end point, SRI‐4 response, was not met despite evidence of strong pathway inhibition. [ABSTRACT FROM AUTHOR]

Objective: To evaluate fenebrutinib, an oral and highly selective noncovalent inhibitor of Bruton's tyrosine kinase (BTK), in patients with active rheumatoid arthritis (RA). Methods: Patients with RA and an inadequate response to methotrexate (MTX) (cohort 1; n = 480) were randomized to receive fenebrutinib (50 mg once daily, 150 mg once daily, or 200 mg twice daily), adalimumab (40 mg every other week), or placebo. Patients with RA and an inadequate response to tumor necrosis factor inhibitors (cohort 2; n = 98) received fenebrutinib (200 mg twice daily) or placebo. Both cohorts continued MTX therapy. Results: In cohort 1, the percentages of patients in whom American College of Rheumatology 50% improvement criteria (ACR50) was achieved at week 12 were similar in the fenebrutinib 50 mg once daily and placebo groups, and were higher in the fenebrutinib 150 mg once daily group (28%) and 200 mg twice daily group (35%) than in the placebo group (15%) (P = 0.016 and P = 0.0003, respectively). Fenebrutinib 200 mg twice daily and adalimumab (36%) were comparable (P = 0.81). In cohort 2, ACR50 was achieved in more patients receiving fenebrutinib 200 mg twice daily (25%) than placebo (12%) (P = 0.072). The most common adverse events in the fenebrutinib groups included nausea, headache, anemia, and upper respiratory tract infections. Fenebrutinib had significant effects on myeloid and B cell biomarkers (CCL4 and rheumatoid factor). Fenebrutinib and adalimumab caused overlapping as well as distinct changes in B cell and myeloid biomarkers. Conclusion: Fenebrutinib demonstrates efficacy comparable to adalimumab in patients with an inadequate response to MTX, and safety consistent with existing immunomodulatory therapies for RA. These data support targeting both B and myeloid cells via this novel mechanism for potential efficacy in the treatment of RA. [ABSTRACT FROM AUTHOR]

GDC‐0853 is a small molecule inhibitor of Bruton's tyrosine kinase (BTK) that is highly selective and noncovalent, leading to reversible binding. In double‐blind, randomized, and placebo‐controlled phase I healthy volunteer studies, GDC‐0853 was well tolerated, with no dose‐limiting adverse events (AEs) or serious AEs. The maximum tolerated dose was not reached during dose escalation (≤600 mg, single ascending dose (SAD) study; ≤250 mg twice daily (b.i.d.) and ≤500 mg once daily, 14‐day multiple ascending dose (MAD) study). Plasma concentrations peaked 1–3 hours after oral administration and declined thereafter, with a steady‐state half‐life ranging from 4.2–9.9 hours. Independent assays demonstrated dose‐dependent BTK target engagement. Based on pharmacokinetic/pharmacodynamic (PK/PD) simulations, a once‐daily dosing regimen (e.g., 100 mg, q.d.) is expected to maintain a high level of BTK inhibition over the dosing interval. Taken together, the safety and PK/PD data support GDC‐0853 evaluation in rheumatoid arthritis, lupus, and other autoimmune or inflammatory indications. [ABSTRACT FROM AUTHOR]