Abstract 5497: A novel bioactive approach to inhibit leptin-induced epithelial-mesenchymal transition in breast cancer.
Authors: Avtanski Dimiter B. , Nagalingam Arumugam , Kuppusamy Panjamurthy , Saxena Neeraj K. , Sharma Dipali 
Published: August 2014

Introduction: Molecular effects of obesity, a well-established risk factor for breast cancer progression, are mediated by adipocytokine leptin. Recent studies from our lab reveal that leptin induces epithelial-mesenchymal transition (EMT) and tumorsphere formation via concomitant activation of Akt/GSK3β and MTA1/Wnt1 signaling axes leading to β-catenin activation. Given the important role of leptin in breast cancer growth and metastasis, novel strategies to antagonize biological effects of leptin are much desired. We showed previously that honokiol (HNK), a bioactive polyphenol from Magnolia grandiflora, inhibits breast carcinogenesis. The present study provides first evidence for the efficacy of HNK against oncogenic effects of leptin including EMT.

Methods: Efficacy of HNK to inhibit oncogenic effects of leptin was evaluated by using clonogenicity, anchorage-independent growth, matrigel invasion and spheroid-migration assays. RT-PCR, Western blot and immunofluorescence analyses were used to examine the molecular changes associated with EMT as well as underlying molecular pathways. Functional importance of MTA1/Wnt1/β-catenin axis was examined by using overexpression, phospho-deficient constructs and specific inhibitors. Finally, mouse xenografts, immuniohistochemical, RT-PCR and Western blot analysis of tumors was used.

Results: HNK treatment circumvents leptin-induced EMT-associated phenotypic changes. A biochemical hallmark of EMT is loss of expression of epithelial markers with a concurrent increase in mesenchymal marker expression. HNK elicits increased expression of E-cadherin, occludin and cytokeratin-18 (epithelial markers) and decreased expression of vimentin, fibronectin and N-cadherin (mesenchymal markers) in leptin-treated cells providing molecular evidence for reversal of EMT. HNK also inhibits expression and nuclear translocation of transcriptional effectors of EMT: Snail, Slug, Zeb1 and Zeb2. Analysis of underlying molecular mechanisms reveals that HNK effectively inhibits leptin-induced MTA1/Wnt1/β-catenin axis. Furthermore, using nontoxic doses of HNK, we show that HNK treatment effectively inhibits leptin-induced breast tumorigenesis in vivo. Analysis of breast tumors show that HNK treatment reverses leptin-associated signaling (MTA1/Wnt1/β-catenin axis) along with decreased expression of mesenchymal markers and increased expression of epithelial markers.

Conclusions: In this study, we demonstrate for the first time that HNK is able to abolish leptin-induced EMT and provide in vitro and in vivo evidence for the integral role of a previously unrecognized crosstalk between honokiol and MTA1/Wnt1/ β catenin axis. Thus, HNK may be used as a non-toxic and non-endocrine rational therapeutic strategy for breast carcinoma in obese patients with high leptin levels.

Citation Format: Dimiter B. Avtanski, Arumugam Nagalingam, Panjamurthy Kuppusamy, Neeraj K. Saxena, Dipali Sharma. A novel bioactive approach to inhibit leptin-induced epithelial-mesenchymal transition in breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5497. doi:10.1158/1538-7445.AM2013-5497