The analogue D-Ser (H-(D)Ser-Glu-Nva-Val-Ala-Leu-Ser-(N-Me)Arg-βAla-NH2), incorporating in the peptide chain a D-amino acid to prevent BBB penetration, efficiently inhibited leptin-induced growth in colon adenocarcinoma HT29 and breast cancer MCF7 cells at 1 nM concentration without any partial agonistic activity in the absence of the exogenous leptin [122]. This evidence concerns the gene LEP and breast cancer.