GRP and cancer: To provide AO derivatives with specificity towards cancer cells, Paulo et al. have studied a covalent bioconjugation approach AO-containing Re(I)/99mTc(I) complexes carrying a bombesin sequence (BBN [7,8,9,10,11,12,13,14]) for the targeting of the gastrin releasing peptide receptor (GRPr) that is overexpressed in a variety of cancer cells (Figure 38).