Bong-Ho Ko

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: E2 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.

Mitogen-Activated Protein Kinase Signaling Enhances Sodium Iodide Symporter Function and Efficacy of Radioiodide Therapy in Nonthyroidal Cancer Cells

Although the success of sodium/iodide symporter (NIS) gene–based cancer therapy is critically dependent on the level of radioiodide accumulation attained, recent evidence indicates that successful therapy relies not solely on NIS amount but also crucially on its functional activity. In this study, we investigated the role of kinase-linked signaling on the regulation of NIS function in cancer cells. Methods: T47D human breast cancer and PC-12 rat pheochromocytoma cells were transduced with the human NIS genes via an adenoviral vector. Cells were measured for 125I uptake, and the effects of activation or inhibition of protein kinase C (PKC) and mitogen-activated protein (MAP) kinase pathways were evaluated. Membrane localization of NIS was evaluated by biotinylation-immunoblotting and confocal microscopy. 131I-mediated cancer cell killing was evaluated by clonogenic assays. Results: NIS function was acutely reduced by short stimulation with the PKC activator phorbol 12-myristate 13-acetate and increased by its inhibition with staurosporine or prolonged phorbol 12-myristate 13-acetate exposure. Surprisingly, epidermal growth factor (EGF) caused a strong dose-dependent augmentation of radioiodide transport, accompanied by extracellular signal-regulated kinase (ERK)-1/2 activation. Both effects were completely abrogated by specific MAP kinase kinase (MEK) inhibitors, which also reduced basal NIS function. Hence, radioiodide uptake levels could differ 24-fold, depending on ERK activity. Biotinylation-immunoblotting and confocal microscopy revealed that EGF increases plasma membrane–localized NIS without affecting total cellular levels. EGF stimulation was sufficient to enhance the killing effect of 131I on the cancer cells. Conclusion: Thus, PKC and ERK signaling play important roles in the regulation of NIS function, and control of these signaling pathways may help enhance the efficacy of radioiodide cancer therapy.

Effects of theophylline on radioiodide uptake in MCF-7 breast cancer and NIS gene-transduced SNU-C5 colon cancer cells.

BACKGROUND We investigated whether theophylline has the potential to increase radioiodide uptake in nonthyroidal cancer cells. MATERIALS AND METHODS MCF-7 cells that express endogenous sodium/iodide symporter (NIS) and SNU-C5 cells adenovirally transduced with the human NIS gene (SNU-C5/NIS) were treated with 10(-7)-2x10(-4) mol/L theophylline for 24 hours before incubation with (125)I, and then, radioiodide uptake and retention were measured. NIS expression was assessed by immunohistochemistry and Western blot analysis, using an antihuman NIS monoclonal antibody. RESULTS Theophylline at 10(-6)-2x10(-4) mol/L significantly and dose dependently augmented radioiodide uptake in MCF-7 cells and at 10(-6)-10(-5) mol/L in SNU-C5/NIS cells, without affecting radioiodide efflux. Abrogation by KClO(4)(-) demonstrated that the effect of theophylline occurred through specific iodide transport. Immunohistochemistry revealed dose-dependent increases of NIS staining in MCF-7 and SNU-C5/NIS cells by 10(-6)-10(-4) and 10(-6)-10(-5) mol/L theophylline, respectively. Western blot analysis demonstrated similar findings, showing increased expression of NIS on the membrane of SNU-C5/NIS and MCF-7 cells by theophylline treatment. CONCLUSIONS Theophylline can augment radioiodide uptake in breast cancer cells and NIS gene-transduced cancer cells through the upregulation of NIS expression. Therefore, further investigations are warranted to explore the potential utility of this phenomenon for enhancing radioiodide-based imaging and therapies of NIS gene-transduced cancer cells.