We decided to select some of the described peptides [27,28,31,40,41] bearing the mentioned substitutions and having affirmed affinity for GRP-R in the low nanomolar range, together with the original BBN (7-14), and use them as targeting moiety to deliver a cytotoxic payload, daunorubicin (Dau), to prostate and breast cancers. The gene discussed is GRPR; the disease is breast cancer.