GRPR and Familial prostate cancer: Hofstetter and co-workers tethered a Gastrin Releasing Peptide receptor (GRPr) antagonist, D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2, to AAZTA5 via a 4-amino-1-carboxylmethyl-piperidine (Pip) spacer, for diagnostic imaging of GRPr-positive cancers (tested in an epithelial human prostate cancer cell line, PC3) [175].