OPTIMIZATION OF THE PHARMACOKINETIC (PK) AND PHARMACODYNAMIC (PD) PROPERTIES OF AN ANTI-ABETA ANTIBODY M266 FAB FRAGMENT VARIANT BY SITE-SPECIFIC PEGYLATION

Antibodies are increasingly being tested as therapeutics in many diseases including Alzheimer’s disease. Potential limitations for biologic treatment of CNS disease states include difficulty crossing the blood brain barrier (BBB), potential for Fc mediated inflammatory responses, and long half-life of antigen:antibody complexes. The utilization of an engineered Fab fragment with an optimal half-life may mitigate these challenges. The Abeta antibody m266, which recognizes only soluble monomer Abeta, is currently being investigated for the ability to alter CNS to plasma Abeta equilibria for enhanced net clearance to the periphery. It has previously been demonstrated that attachment of varying sized PEG moieties to biomolecules can result in altered pharmacokinetics. We generated m266 Fab fragment variants with differing size PEG moieties attached (5kD, 10kD or 20kD PEG) and subsequently characterized the PK/PD responses in transgenic mice and non-transgenic rats after peripheral administration of single doses or subcutaneous pump infusions of the Fab constructs. An important target engagement biomarker after peripheral injection of central domain antibodies is the accumulation of plasma Abeta as part of an immunocomplex. We demonstrate that the monovalent binding affinity of the Fab toward soluble Abeta remained extremely high regardless of the attachment of the various PEG moieties. Additionally, we show that attachment of increasing sized PEG moieties resulted in increased plasma half-life that was correlative to the PEG size. The peripheral target engagement of plasma Abeta likewise paralleled the enhanced exposure times with the increasing PEG size. Time course studies following single peripheral injection in rats demonstrated a size dependent alteration of blood-brain barrier permeability for the Fab-PEG constructs (smaller equated to better penetration). We demonstrate the ability to alter the PK/PD relationships for an anti-Abeta Fab antibody when coupled to varying sized PEG moieties. Based upon these results, we can select an ideal Fab-PEG construct that balances the desired plasma half-life and yet maintains adequate blood-brain barrier permeability. The PK/PD relationship was consistent between rodent species (mouse and rat) and may be useful in tailoring antibodies for human therapeutics.