Abstract

Therapeutic fragmented antibodies show a poor pharmacokinetic profile that leads to frequent high-dose administration. In the current study, for the first time, a novel proline, alanine, serine (PAS) repeat sequence called PAS#208 was designed to extend the plasma half-life of a nanosized anti–vascular endothelial growth factor-A single-domain antibody. Polyacrylamide gel electrophoresis, circular dichroism, dynamic light scattering, and electrophoretic light scattering were used to assess the physicochemical properties of the newly designed PAS sequence. The effect of PAS#208 on the biologic activity of a single-domain antibody was studied using an in vitro proliferation assay. The pharmacokinetic parameters, including terminal half-life, the volume of distribution, elimination rate constant, and clearance, were determined in mice model and compared with the native protein and PAS#1(200) sequence. The novel PAS repeat sequence showed comparable physicochemical, biologic, and pharmacokinetic features to the previously reported PAS#1(200) sequence. The PAS#208 increased the hydrodynamic radius and decreased significantly the electrophoretic mobility of the native protein without any change in zeta potential. Surprisingly, the fusion of PAS#208 to the single-domain antibody increased the binding potency. In addition, it did not alter the biologic activity and did not show any cytotoxicity on the normal cells. The PAS#208 sequence improved the terminal half-life (14-fold) as well as other pharmacokinetic parameters significantly. The simplicity as well as superior effects on half-life extension make PAS#208 sequence a novel sequence for in vivo pharmacokinetic enhancement of therapeutic fragmented antibodies.