Chemoenzymatic Synthesis of a Rhamnose‐Functionalized Bispecific Nanobody as a Bispecific Antibody Mimic for Cancer Immunotherapy

Abstract Bispecific antibodies (BsAbs) are next‐generation therapeutics for complex cancer treatment. Herein, we developed a dual‐targeting non‐IgG format of bsAbs by using a bispecific nanobody (bsNb) that can simultaneously target EGFR and HER2 on tumor cells. Site‐specific modification of the anti‐EGFR‐HER2 bsNb was conducted using the rhamnose (Rha) hapten via sortase A‐mediated ligation to reconstitute the missing crystallizable fragment (Fc) effector biological functions. Functionally similar to bsAbs, bsNb‐Rha conjugates retained dual‐targeting activity and exerted potent anticancer effects via the Fc‐domain‐mediated engagement of endogenous anti‐Rha antibodies. Further, an optimized bsNb‐Rha conjugate exhibited markedly improved pharmacokinetics and efficient inhibitory effects against xenograft tumor growth in vivo. Our strategy provides a general and cost‐effective platform to generate a new bsAb format for cancer immunotherapy.