17β-estradiol augments ¹⁸F-FDG uptake and glycolysis of T47D breast cancer cells via membrane-initiated rapid PI3K-Akt activation

Use of ¹⁸F-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 ¹⁸F-FDG uptake in responsive breast cancer cells and investigated the mediating molecular mechanisms. Methods: T47D breast cancer cells were stimulated with 17β-estradiol (E₂) or bovine serum albumin (BSA)-E₂ and measured for ¹⁸F-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 ¹⁸F-FDG uptake in a dose- and time-dependent manner that preceded and surpassed its proliferative effect. With exposure to 10 nM E₂, protein content-corrected ¹⁸F-FDG uptake reached 172.7% ± 6.6% and 294.4% ± 9.5% of controls by 24 and 48 h, respectively. Lactate release reached 110.9% ± 7.3% and 145.2% ± 10.5% of controls at 24 and 48 h, and mitochondrial hexokinase activity increased to 187.1% ± 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 E₂ effect was not blocked by tamoxifen and was mimicked by membrane-impermeable BSA-E₂, consistent with nongenomic membrane-initiated E₂ action. Inhibition by cycloheximide demonstrated the requirement of a new protein synthesis. Immunoblots displayed rapid phosphorylation of PI3K and Akt within minutes of E₂ treatment, and the specific PI3K inhibitors wortmannin and LY294002 abolished the ability of E₂ to elevate ¹⁸F-FDG uptake. Conclusion: Estrogen augments breast cancer cell 18F-FDG uptake by stimulating glycolysis and hexokinase activity via membrane-initiated E₂ 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 ¹⁸F-FDG uptake as a surrogate marker of therapeutic response.