In order to investigate the signal transduction pathways involved in leptin-induced proliferation and the inhibitory effect of OB3 on leptin’s action, ovarian cancer cells were treated with 10 nM leptin, 10 μM OB3 or their combination (Fig. 4) in the presence or absence of inhibitors of ERK1/2 (PD98059) and PI3K (LY294002). This evidence concerns the gene LEP and ovarian carcinoma.