Validation of NRP-1 as a receptor for the CGFYWLRSC peptide. (A) Phage binding to recombinant rat NRP-1/Fc chimera (rrNRP-1/Fc) or to control GP130-Fc protein was assessed. Results shown are averages of 3 independent assays. ***P < .001. (B-D) Flow cytometry analysis of cell-surface expression of NRP-1 on K562 (B), OCI-AML3 (C), and MOLT-4 (D) leukemia cell lines. Cells were stained as follows: control rabbit IgG and FITC-goat anti–rabbit IgG (green), rabbit anti–human NRP-1 and FITC-goat anti–rabbit IgG (violet). (E) Binding of the CGFYWLRSC phage to OCI-AML3 cells transfected with NRP-1-targeting siRNA or with the nontargeting control siRNA. Untransfected wild-type cells and insertless phage were used as controls. **P < .01; ***P < .001.