Complex Pharmacokinetics of a Humanized Antibody Against Human Amyloid Beta Peptide, Anti-Abeta Ab2, in Nonclinical Species

Anti-A beta Ab2 (Ab2) is a humanized monoclonal antibody against amino acids 3-6 of primate (but not rodent) amyloid beta (A beta) and is being evaluated for the treatment of Alzheimer's disease (AD). This study was conducted to predict the human pharmacokinetics of Ab2. In vivo PK profile of Ab2 in preclinical species and in vitro mechanistic studies in preclinical and human systems were used for pharmacokinetic predictions. In Tg2576 and PSAPP mice that have similar to 100-fold higher circulating levels of human A beta compared to humans, elimination of Ab2 was target-mediated, such that exposure was 5-10 fold lower compared to wild-type rodents or to PDAPP mice that have human A beta concentrations in plasma similar to humans. In cynomolgus monkeys, the t(1/2) of Ab2 was faster (< 2.5 days) compared to that of the control antibody (similar to 13 days). The fast elimination of Ab2 in cynomolgus monkeys was linked to off-target binding to cynomolgus monkey fibrinogen that was also causing incomplete recovery of Ab2 in cynomolgus monkey serum in blood partitioning experiments. Ab2 had significantly weaker to undetectable binding to human (and mouse) fibrinogen and had good recovery in human serum in blood partitioning experiments. These data predict that elimination of Ab2 in healthy or AD humans is expected to be slow, with t(1/2) similar to that observed for other humanized antibodies.