DISCOVERY OF NOVEL ANTI-SERUM ALBUMIN VHH AS A BUILDING BLOCK FOR PK PROLONGATION

Abstract Background The serum half-life of endogenous albumin is approximately 19 days in humans and 1.5-2.5 days in rodents. This extended half-life in vivo is primarily due to effective recycling upon internalization mediated by the neonatal Fc receptor (FcRn). Many protein therapeutics smaller than 60 kD have short serum half-life, which can be extended by fusing the proteins of interest with an anti-albumin antibody. The fusion proteins then take advantage of FcRn-mediated recycling. Single domain antibody (VHH) molecules (around 15 kD), derived from camelid heavy-chain-only IgG, are attracting increased attention globally in the field of antibody-based therapies due to several features including small size, high stability, low immunogenicity, good tissue penetration and cost effectiveness in manufacturing. Methods an anti-human/cynomolgus monkey/murine/canine/feline serum albumin VHH lead was discovered from a proprietary, large native phage-displayed VHH library, which was then humanized, and affinity matured. The optimized VHH was fused to bispecific and trispecific antibodies for in vivo PK studies. Results An anti-human serum albumin VHH Ab was discovered, and it also bound to cyno and mouse serum albumin with high affinity without affecting the interaction of HSA with FcRn. The VHH showed good developability and, once fused to protein therapeutics, long half-life and anti-tumor activity in rodents. Conclusions a novel VHH against serum albumin of different species was discovered from native VHH libraries, and it can be easily assembled into bispecific Abs and multispecific Abs to prolong the molecules’ PK profile.