Very High Plasma Concentrations of a Monoclonal Antibody against the Human Insulin Receptor Are Produced by Subcutaneous Injection in the Rhesus Monkey

Brain penetration of recombinant protein drugs is possible following the re-engineering of the drug as an IgG fusion protein. The IgG domain is a monoclonal antibody (mAb) against an endogenous blood-brain barrier (BBB) receptor transporter, such as the insulin receptor. One such mAb targets the human insulin receptor (HIR) and is active in Rhesus monkeys. Prior work has measured the plasma pharmacokinetics of HIRMAb-derived fusion proteins following intravenous (IV) infusion. However, an alternative method of administration for chronic treatment of brain disease is the subcutaneous (SQ) route. The extent to which an antibody against the insulin receptor undergoes systemic distribution and clearance is unknown. Therefore, in the present study, the rate of plasma clearance of the HIRMAb is measured in Rhesus monkeys following IV or SQ administration of 3, 10, and 30 mg/kg doses of the antibody. The HIRMAb is readily absorbed into the systemic circulation following SQ injection with a 42% plasma bioavailability. The rate of plasma clearance of the antibody, 0.04-0.06 mL/min/kg, is the same following either IV or SQ administration. Owing to the slow rate of plasma clearance of the antibody, high concentrations of the HIRMAb are sustained in plasma for days after the SQ injection. The plasma concentration of the HIRMAb exceeds 0.8 mg/mL, which is 9% of the entire plasma IgG pool in the primate, after the SQ injection of the high dose, 30 mg/kg, of the antibody. In summary, the pharmacokinetics of plasma clearance of the HIRMAb are such that HIRMAb-derived fusion proteins can be developed as protein therapeutics for the brain with chronic SQ administration on a weekly or twice-weekly regimen.