Abstract A06: Obesity induces a metabolic switch toward aerobic glycolysis in breast cancer cells in vitro and in vivo
Authors: Cavazos David Antonio , Wheatly Karrie , Hursting Stephen 
Published: May 2015

Background: The prevalence of obesity is steadily increasing worldwide, impacting the incidence of a variety of diseases, including breast cancer (BCa). Although epidemiological studies show a strong association between elevated body mass index (BMI) and a heightened risk of postmenopausal BCa, the underlying etiology remains relatively unknown. One potential mechanism by which obesity contributes to BCa progression and recurrence is through induction of obesity-induced stress (OBIS). Reactive oxygen species (ROS) are byproducts of metabolism, and excessive production or accumulation of ROS is known to contribute to early tumor initiating events through redox modulation of p53 transcriptional activity.

Objectives: Recent studies indicate that p53 is a key regulator of glycolysis. As the obese state is known to promote aerobic glycolysis, the preferred mode of energy production by most transformed cells, and because approximately 40% of human breast cancers harbor p53 mutations, the aim of this study was to determine the impact of obesity on rates of glucose consumption and genotoxic stress in the context of p53 status.

Results: Using the MMTV-Wnt1 transgenic mouse model of spontaneous breast cancer harboring a heterozygous deletion mutation for p53, we determined the impact of diet-induced obesity (DIO) on markers of aerobic glycolysis and oxidative stress. Interestingly, thioredoxin interacting protein (TXNIP), a regulator of glucose homeostasis, was found to be induced in the normal mammary fat pad (MFP) of obese p53-heterozygous (p53-het) mice versus p53-wild type (p53-wt) MFPs. Conversely, MCF-7 breast cancer cells grown in vitro in serum from these obese mice showed a 50% decrease in TXNIP expression in comparison to cells cultured in serum from the non-obese mice. These findings are consistent with TXNIP's putative role as a tumor suppressor gene. Further, glucose transporter 1 (GLUT-1), a basal glucose transporter required to sustain cellular respiration, was upregulated 5-fold in the MFP of obese p53-het mice compared to MFP taken from non-obese p53-het mice, confirming that obesity regulates glucose uptake in the MFP independently of p53 status. Additionally, the obese p53-het mice displayed elevated serum levels of 8-isoprostane, a biomarker of oxidative stress. Additional in vitro studies demonstrate that MCF-7 cells cultured in serum derived from obese versus non-obese C57BL/6 mice (Ob-serum and non-Ob serum) displayed heightened levels of ROS and significant modulation of HIF-1α, a ROS-inducible transcription factor known to regulate glycolysis. Ob-serum also enhanced lactate dehydrogenase activity and inhibited expression of pyruvate dehydrogenase (PDH), concurrently promoting glycolysis and bypassing oxidative phosphorylation (OXPHOS). This metabolic shift was associated with the accumulation of γ-H2AX foci, a known indicator of DNA double-strand breaks (DSBs). Finally, we observed that a combined shRNA-mediated knockdown of TXNIP and p53 in MCF-7 cells resulted in a dramatic induction of DSBs, and this was exacerbated by exposure to Ob-serum.

Potential Impact: Based on these findings, we conclude that obesity may enhance the rate of metabolic reprogramming in breast cancer cells, resulting in OBIS and accumulation of ROS; thereby promoting disease progression by enhancing genotoxic stress in cells harboring a p53 mutation.

Citation Format: David Antonio Cavazos, Karrie Wheatly, Stephen Hursting. Obesity induces a metabolic switch toward aerobic glycolysis in breast cancer cells in vitro and in vivo. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Drug Sensitivity and Resistance: Improving Cancer Therapy; Jun 18-21, 2014; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(4 Suppl): Abstract nr A06.