Abstract: The binding interactions between herstatin, or the intron 8-encoded receptor binding domain (RBD Int8) thereof, and several receptors were analyzed. According to aspects of the present invention, herstatin and the intron 8-encoded domain bind with high affinity (e.g., nM concentrations) to all four of the ErbB receptors: EGFR (HER-1, erbB-1); HER-2 (erbB-2); HER-3 (erbB-3); and HER-4 (erbB-4), as well as to ?EGFR and the IGF-1 receptor, and such binding has utility to modulate signaling mediated by these receptors. Herstatin inhibited target receptor-mediated activation of intracellular signaling pathways ((e.g., PI3/Akt, IRS-2, etc., pathways) that are important in cell survival, and further inhibited target receptor-mediated (e.g., IGF-1/IGF-1R-mediated) survival of cancer cells.