Serum albumin-binding VHHs with variable pH sensitivities enable tailored half-life extension of biologics
Open Access
- 1 June 2020
- journal article
- research article
- Published by Wiley in The FASEB Journal
- Vol. 34 (6), 8155-8171
- https://doi.org/10.1096/fj.201903231R
Abstract
Prolonged serum half-life is required for the efficacy of most protein therapeutics. One strategy for half-life extension is to exploit the long circulating half-life of serum albumin by incorporating a binding moiety that recognizes albumin. Here, we describe camelid single-domain antibodies (V(H)Hs) that bind the serum albumins of multiple species with moderate to high affinity at both neutral and endosomal pH and significantly extend the serum half-lives of multiple proteins in rats from minutes to days. We serendipitously identified an additional VHH (M75) that is naturally pH-sensitive: at endosomal pH, binding affinity for human serum albumin (HSA) was dramatically weakened and binding to rat serum albumin (RSA) was undetectable. Domain mapping revealed that M75 bound to HSA domain 1 and 2. Moreover, alanine scanning of HSA His residues suggested a critical role for His247, located in HSA domain 2, in M75 binding and its pH dependence. Isothermal titration calorimetry experiments were suggestive of proton-linked binding of M75 to HSA, with differing binding enthalpies observed for full-length HSA and an HSA domain 1-domain 2 fusion protein in which surface-exposed His residues were substituted with Ala. M75 conferred moderate half-life extension in rats, from minutes to hours, likely due to rapid dissociation from RSA during FcRn-mediated endosomal recycling in tandem with albumin conformational changes induced by M75 binding that prevented interaction with FcRn. Humanized V(H)Hs maintained in vivo half-life extension capabilities. These V(H)Hs represent a new set of tools for extending protein therapeutic half-life and one (M75) demonstrates a unique pH-sensitive binding interaction that can be exploited to achieve modest in vivo half-life.This publication has 53 references indexed in Scilit:
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