Affinity of anti-insulin-like growth factor I receptor antibody binding to the receptor altered by plant lectins

The binding ability of anti-insulin-like growth factor. receptor (IGF-IR) single-chain variable fragments (scFvs) to IGF-IR was measured in the presence of plant lectins. Combinations of concanavalin A (Con A), wheat germ agglutinin (WGA), or peanut agglutinin (PNA) and 1H7 or 3B7 anti-IGF-IR scFv/phage antibodies that were previously produced and characterized were used. WGA inhibited binding of both scFvs proteins to the receptor. PNA slightly enhanced the binding of 1H7 scFv and phage antibody to the receptor. Con A led to enhancement of 3B7 scFv-binding but had no effect in a test of phage antibodies and determination of kinetic parameters. The effect of lectins differed for scFvs and phage antibodies, implying that affinity altered by lectins is dependent upon the molecular structure of the antibodies. Results indicated that animal lectins may affect the affinity of therapeutic antibodies targeting cell membrane receptors in vivo.