Abstract 1849: The role of leptin signaling in the promotion of obesity-associated tumorigenesis and cancer stem cell characteristics in a transgenic mouse model of basal-like breast cancer
Authors: Khatib Subreen A. , Bowers Laura W. , Rossi Emily L. , McDonell Shannon B. , Lineberger Claire G. , Cavazos David A. , deGraffenried Linda A. , Hursting Stephen D. 
Published: July 2017

Background: Epidemiological studies have linked obesity to a greater risk of breast cancer-specific mortality. This association may be mediated in part by enhanced cancer stem cell (CSC) enrichment, as CSCs are thought to be the primary drivers of tumor initiation, growth, and metastasis. We and others have have demonstrated that obesity promotes CSC enrichment in pre-clinical models of basal-like breast cancer, but only when leptin signaling is present. These findings, coupled with evidence that elevated serum leptin and breast tumor leptin receptor expression are linked to a worse breast cancer prognosis, suggest that leptin-induced CSC enrichment may be a key contributor to obesity-associated breast cancer progression.

Methods: MMTV-Wnt-1 transgenic mice, which develop spontaneous basal-like mammary tumors, were fed a control diet (10% kcal from fat) or a diet-induced obesity regimen (DIO, 60% kcal from fat). Mice were euthanized when tumors reached 1.5 cm in diameter. RNA sequencing was performed on 4 tumors/diet group. Serum hormones and cytokines were measured via luminex-based assay. ALDH activity, a putative CSC marker, was quantified by an ALDH Activity Assay Kit (abcam). Quantitative RT-PCR was used to determine expression of CSC-related genes, leptin, and the leptin receptor. Two mammary tumor cell lines isolated from the MMTV-Wnt-1 model (M-Wnt and E-Wnt cells) and human MDA-MB-231 were exposed in vitro to pooled serum from DIO or control mice (2% concentration), and cell viability, migration, invasion and expression of CSC related genes were measured.

Results: Tumor incidence and growth rate were greater in DIO versus control mice. RNA sequencing revealed an upregulation in a CSC gene signature in tumors from DIO versus control mice. Significant upregulation in several of these genes, including aldh1a, oct4, twist1, twist2, and akt3, was confirmed by qRT-PCR (P &lt; 0.05). ALDH activity in the DIO (relative to control) tumors was also significantly increased (P &lt; 0.05). Serum levels and mammary tissue expression of leptin and tumor expression of the leptin receptor were significantly elevated in DIO versus control mice (P &lt; 0.05). Exposure to serum from DIO mice significantly increased (relative to control) M-Wnt, E-Wnt, and MDA-MB-231 cell viability, migration, invasion, and expression of CSC-related genes in vitro (P &lt; 0.05). The role of leptin signaling in these effects and in vitro measures of CSC enrichment will be explored through additional in experiments.

Conclusions: Obesity promotes MMTV-Wnt-1 mammary tumor incidence and growth rate, possibly via CSC enrichment. Preliminary findings suggest increased leptin signaling may underlie obesity-associated CSC enrichment and may contribute to the breast cancer burden in obese women.

Citation Format: Subreen A. Khatib, Laura W. Bowers, Emily L. Rossi, Shannon B. McDonell, Claire G. Lineberger, David A. Cavazos, Linda A. deGraffenried, Stephen D. Hursting. The role of leptin signaling in the promotion of obesity-associated tumorigenesis and cancer stem cell characteristics in a transgenic mouse model of basal-like breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1849. doi:10.1158/1538-7445.AM2017-1849