Synthetic inhibitors of pregnancy-associated plasma protein-A regulate IGF-1 signaling in vitro and in vivo

Dysregulation of insulin-like growth factor (IGF) signaling contributes to diverse human diseases. Therapeutic strategies have largely targeted the IGF-1 receptor, but the complexity of the IGF system has limited their clinical efficacy. Pregnancy-associated plasma protein-A (PAPP-A) is a secreted metalloproteinase that regulates local IGF signaling through proteolytic cleavage of IGF-binding proteins (IGFBPs) and represents an attractive therapeutic target. Here, we report the first synthetic PAPP-A inhibitors designed to target the enzyme active site using an IGFBP-5-derived anchor sequence. Replacing the scissile bond with phosphinate or phosphonate moieties yielded potent and selective PAPP-A inhibitors. Cryo-electron microscopy revealed the molecular basis of inhibition and key active-site interactions. The compounds inhibited cleavage of IGFBP-4 and IGFBP-5, two physiological PAPP-A substrates. They suppressed IGF-1 signaling in A549 lung cancer cells, with efficacy comparable to the endogenous PAPP-A inhibitor stanniocalcin-1. They also inhibited Papp-aa-dependent IGF signaling and cell proliferation in wild-type and stc1a-/- mutant zebrafish in vivo in a dose-dependent manner. Together, these findings establish the first class of synthetic, selective PAPP-A inhibitors capable of modulating IGF signaling. They provide new chemical tools for studying and modulating pathological IGF signaling and offer new directions for developing PAPP-A-targeted therapeutic strategies.