P5-06-10: Leptin Signaling Impacts Notch and Wnt Crosstalk in Breast Cancer.
Authors: McGlothen TZ , Gillespie C , Colbert L , Blaylock-Hogans D , Guo S , Gonzalez- Perez RR 
Published: June 2012

Abstract
Background: Triple negative breast cancer (TNBC: ER-, PR- and Her2/neu-) is an aggressive form of the disease that disproportionately affects women of color, has an early onset, and is associated with poor survival and a resistance to common therapeutic treatments. We have previously demonstrated an association between the adipocytokine leptin and Notch signaling pathways in breast cancer. Notch participates in a crosstalk relationship with many signaling pathways involved in carcinogenesis, including Wnt and leptin, which could in turn increase tumor burden and cell survival of MMTV-Wnt1 obese mice. We hypothesize that leptin signaling crosstalk with Notch and Wnt is instrumental in the development of drug-resistant features (increased survival and proliferation) of TNBC.
Objective: The aim of this study was to determine whether leptin mediated crosstalk of the Notch and Wnt pathways has a differential impact on TNBC compared to ER+ cells.
Materials & Methods: ER+ MCF-7 and TNBC-MDA MB-231 cells (96-well plate; 1×104 cells/well) were serum deprived for 24 hours and treated with varying doses of Doxorubicin and Cisplastin for 24h in conjunction with pharmacological doses of leptin, leptin peptide antagonist (LPrA2), Wnt agonist (Wnt-1) and antagonist (Wif-1). Cell proliferation was measured via WST assay. The effect of the various treatments on the activation of Wnt (total/pβ-catenin), Notch (Notch 1–4 and JAG1/Dll-4 and targets survivin/Hey2), and leptin (STAT3 and targets VEGF/VEGFR-2) signaling pathways were measured using western blot and ELISA. β-Catenin levels were also investigated by IHC in DMBA-breast cancer samples from lean and DIO (diet-induced obese mice) mice treated with LPrA2. Apoptosis was also measured.
Results: Leptin increased the levels of beta-catenin mainly in TNBC cells. This leptin-induced effect was also detected in breast tumors from DIO-mice. Interestingly, leptin increased survival (bcl-2 and Caspase-3 activation)/proliferation (cell number and Cyclin D1), expression of Notch and attenuated the detrimental effects of Doxorubicin and Cisplastin on breast cancer cells. Wnt-1 had similar but less pronounced effects compared to leptin. We also observed differences in Notch expression. Moreover, MDA MB-231 cells showed decreased response to Wnt1 in the presence of leptin.
Conclusions: Our findings suggest that leptin could play a negative role in TNBC by increasing drug-resistance through its crosstalk with Wnt and Notch signaling pathways. This may imply that obesity, characterized by elevated leptin levels, could negatively affect the outcome of TBNC treatment. Taken together, this data supports the theory that inhibition of leptin signaling could be a novel way to prevent and treat TBNC, particularly in the context of obesity and abnormal Wnt and Notch signaling. [This work was supported in part by NIH/NCI1SC1CA138658-02; NIH/ARRA/3SC1CA138658-02S1 and the Georgia Cancer Coalition Distinguished Cancer Scholar Award (to RRGP); CREDO (MSCR) 2R25RR017694-06A1 (to L.S.C); NIGMS506GM08248 and NCRR 5P20RR11104 (to T.Z.M); and facilities and support services at MSM (NIH RR03034 and 1C06 RR18386)].
Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-06-10.