Effects of leptin inhibition on levels of proliferating cell nuclear antigen and cyclin D1. (a) MCF-7 breast cancer (BC) xenograft and (b) MDA-MB231 BC xenograft western blot results for proliferating cell nuclear antigen (PCNA) and cyclin D1 in tumor lysates from controls and SCID mice treated with leptin signaling antagonist (pegylated leptin peptide receptor antagonist 2 (PEG-LPrA2)). β-Actin was used as a loading control for western blot analysis. *P < 0.05, significant difference in mice treated with PEG-LPrA2 with respect to control mice receiving pegylated scrambled peptide. Data (mean ± standard error) show representative results (n = 10 tumors/treatment).