Identification of circulating neuropilin-1 and dose-dependent elevation following anti-neuropilin-1 antibody administration.

Neuropilin-1 (NRP1) acts as a co-receptor for class 3 semaphorins and vascular endothelial growth factor and is an attractive angiogenesis target for cancer therapy. In addition to the transmembrane form, naturally occurring soluble NRP1 proteins containing part of the extracellular domain have been identified in tissues and a cell line. We developed ELISAs to study the existence of circulating NRP1 and to quantify it in serum.