Binding Strength, Not Valency, Dictates Accumulation and Penetration of Affinity Targeted Macromolecules into Solid Tumors

The efficacy of tumor-targeted therapeutics, engineered to engage specific cellular receptors to promote accumulation and penetration, is strongly influenced by the carrier's affinity for its target and the valency of binding molecules incorporated into the carrier. Previous research has primarily focused on improving targeting by augmenting the number of binding proteins on the carrier, inadvertently raising avidity without isolating the individual effects of binding strength and valency. Herein, we precisely evaluate the impact of multivalency on tumor targeting with a recombinant approach to independently control valency, avidity, and size. Our findings reveal that constructs with equivalent binding strength exhibit comparable receptor engagement and tumor extravasation, regardless of valency. Moreover, excessive avidity adversely affected tumor accumulation and penetration, with the highest-avidity construct showing diminished exposure. These results indicate that overall binding strength, not valency, is the primary determinant of tumor targeting, providing valuable insights for designing effective macromolecular drug carriers.