Bispecific antibodies are considered attractive bio-therapeutic agents owing to their ability to target two distinct disease mediators. Cross-arm avidity targeting of
antigen double-positive
cancer cells over single-positive normal tissue is believed to enhance the therapeutic efficacy, restrict major escape mechanisms and increase
tumor-targeting selectivity, leading to reduced systemic toxicity and improved therapeutic index. However, the interplay of factors regulating target selectivity is not well understood and often overlooked when developing clinically relevant bispecific
therapeutics. We show in vivo that dual targeting alone is not sufficient to endow selective
tumor-targeting, and report the pivotal roles played by the affinity of the individual arms, overall avidity and format valence. Specifically, a series of monovalent and bivalent bispecific IgGs composed of the anti-HER2
trastuzumab moiety paired with affinity-modulated VH and VL regions of the anti-EGFR
GA201 mAb were tested for selective targeting and eradication of double-positive human NCI-H358
non-small cell lung cancer target
tumors over single-positive, non-target NCI-H358-HER2 CRISPR knock out
tumors in nude mice bearing dual-flank
tumor xenografts. Affinity-reduced monovalent bispecific variants, but not their bivalent bispecific counterparts, mediated a greater degree of
tumor targeting selectivity, while the overall efficacy against the targeted
tumor was not substantially affected.