17β-Estradiol Augments ¹⁸F-FDG Uptake and Glycolysis of T47D Breast Cancer Cells via Membrane-Initiated Rapid PI3K–Akt Activation

Abstract

Use of 18 F-FDG uptake as a surrogate marker of therapeutic response requires the recognition of biologic factors that influence cancer cell glucose metabolism. Estrogen is a potent stimulator of breast cancer proliferation, a process that requires sufficient energy, which is likely met by increased glycolysis. We thus explored the effect of estrogen on 18 F-FDG uptake in responsive breast cancer cells and investigated the mediating molecular mechanisms. Methods: T47D breast cancer cells were stimulated with 17b-estradiol (E 2 ) or bovine serum albumin (BSA)-E 2 and measured for 18 F-FDG uptake, lactate release, and mitochondrial hexokinase activity. The effects of antiestrogens, cycloheximide, and major protein kinase inhibitors were investigated. Immunoblots were performed for membrane glucose transporter type 1, phosphorylated phosphatidylinositol 3-kinase (PI3K), and Akt. Results: E 2 augmented T47D cell 18 F-FDG uptake in a dose-and time-dependent manner that preceded and surpassed its proliferative effect. With exposure to 10 nM E 2 , protein content-corrected 18 F-FDG uptake reached 172.7% 6 6.6% and 294.4% 6 9.5% of controls by 24 and 48 h, respectively. Lactate release reached 110.9% 6 7.3% and 145.2% 6 10.5% of controls at 24 and 48 h, and mitochondrial hexokinase activity increased to 187.1% 6 31.6% at 24 h. Membrane glucose transporter type 1 expression was unaltered. The effect was absent in estrogen receptor (ER)-negative breast cancer cells and was abrogated by ICI182780, indicating ER dependence. The E 2 effect was not blocked by tamoxifen and was mimicked by membrane-impermeable BSA-E 2 , consistent with nongenomic membrane-initiated E 2 action. Inhibition by cycloheximide demonstrated the requirement of a new protein synthesis. Immunoblots displayed rapid phosphorylation of PI3K and Akt within minutes of E 2 treatment, and the specific PI3K inhibitors wortmannin and LY294002 abolished the ability of E 2 to elevate 18 F-FDG uptake. Conclusion: Estrogen augments breast cancer cell 18 F-FDG uptake by stimulating glycolysis and hexokinase activity via membrane-initiated E 2 action that activates the PI3K-Akt pathway. These findings yield important insight into our understanding of the biology of breast cancer metabolism and may have potential implications for 18 F-FDG uptake as a surrogate marker of therapeutic response.

Estradiol Stimulates Glucose Metabolism via 6-Phosphofructo-2-kinase (PFKFB3)

“…PFKFB3 Expression, F26BP, Glucose Uptake, and Glycolysis Are Induced by E2 in MCF-7 Cells-Given that E2 increases the glucose uptake of ER ϩ breast cancer cells in vitro and in vivo (6,7) and that the PFKFB3 promoter has putative EREs (14), we postulated that ER and its ligand, E2, might regulate PFKFB3 mRNA expression. Initially, we examined PFKFB3 mRNA expression by real-time RT-PCR after exposure to EtOH (vehicle control), or 10 or 100 nM E2 for 1, 3, 6, and 24 h. We observed a marked increase in PFKFB3 mRNA levels after only 1 h of exposure to either 10 or 100 nM E2 (Fig.…”

“…The observation that the PFKFB3 promoter contains putative ER response elements (ERE) (14) prompted us to determine whether PFKFB3 is a direct transcriptional target of ER. Considering previous research showing that E2 increases glucose uptake in vivo and in vitro (6,7), together with the glycolysisactivating function of PFKFB3, we postulated that PFKFB3 may be a downstream effector of E2 that serves to activate the energetic and anabolic pathways required for the survival and growth of breast cancer cells.…”

Metabolomics and Transcriptional Responses in Estrogen Receptor Positive Breast Cancer Cells

“…To further demonstrate this estrogen dependence, it was seen that when the ER+ T47D cells were pretreated with the pure antiestrogen ICI182,780 (fulvestrant), the glucose uptake was totally abrogated. Unlike fulvestrant, the partial antiestrogen tamoxifen was incapable of blocking this estrogen response (Ko et al, 2010). Comparison of metabolic and morphological differences between normal breast and ER+ breast cancer cells gave insights into the adaptive responses adaptive responses which enable cancer cells to better utilize cellular energy resources.…”

Targeting metabolism in breast cancer: How far we can go?

“…Increased MYC expression often indicates increased dependency on glutamine and glucose for survival, may have a correlation with drug resistance in breast cancer cells and inhibition of MYC could reverse the drug resistance [50][51][52] . In antiestrogen resistant breast cancer cells, MYC could activate an unfolded protein response through glucoseregulated protein-78 (GRP78/HSP5A/BiP) and inositolrequiring enzyme-1α (IRE1α/ΕRΝ1) and increase cJun N-terminal kinase activation and spliced X-box protein-1 to support cell survival [45] . The inhibition of MYC was shown to decrease glutaminase activity, although there were different results in drug resistant breast cancer cells and other cells [50,53,54] .…”

“…mTOR inhibitor rapamycin may inhibit cancer cell glucose metabolism by downregulating pyruvate kinase M2 and restoring the susceptibility of breast cancer cells to tamoxifen treatment effectively may be one mechanism of rapamycin [45] . On the other hand, estrogen-induced HIF-1 accumulation in breast cancer cells stimulates glucose uptake via the PI3K/Akt signaling pathway [19,46] which also leads to increased mTOR phosphorylation [47] .…”