Pharmacokinetics, Pharmacodynamics, Bioavailability, and Immunogenicity of Obexelimab Following Subcutaneous Administration in Healthy Japanese and Non-Japanese Volunteers

Obexelimab is an investigational, bifunctional, non-depleting, humanized monoclonal antibody that binds CD19 and FcγRIIb to inhibit B cells, plasmablasts, and CD19-expressing plasma cells. In clinical trials, intravenous (IV) administration of obexelimab has been well-tolerated, and demonstrated clinical activity in patients with rheumatoid arthritis, systemic lupus erythematosus, and immunoglobulin G4-related disease. This study was performed to evaluate the pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity of obexelimab following subcutaneous (SC) administration, and compare PK/PD profiles between healthy Japanese and non-Japanese volunteers.

This was a Phase I, open-label, parallel group, multiple-dose study. Participants were randomized to five cohorts to receive three doses of obexelimab as 125 mg SC every 14 days (q14d), 250 mg SC q14d, 375 mg SC q14d, 250 mg IV q14d, and 125 mg SC every 7 days, then monitored during a 28-day safety follow-up period. PK/PD assessments were performed after the first and third doses.

A total of 50 healthy volunteers (25 Japanese and 25 non-Japanese) were enrolled and distributed evenly between dose cohorts. All SC dosing regimens were well-tolerated. Dose-proportional PK was observed following SC doses with a bioavailability of approximately 60%. No clinically meaningful differences in PK parameters were found between healthy Japanese and non-Japanese participants. Antidrug antibodies (ADA) were detected in 6/50 (12%) participants after dosing. ADA had no or minimal impact on PK in all six ADA positive participants. Near-complete CD19 receptor occupancy and an absolute B-cell count nadir of approximately 50% baseline levels were maintained for the duration of the study in both populations.

Obexelimab SC administration demonstrated favorable bioavailability, was well-tolerated, and showed no clinically meaningful ethnic differences in PK/PD. These results support further clinical development of SC obexelimab to treat B-cell mediated autoimmune diseases.

NCT02867098.