Propranolol inhibits glucose metabolism and 18F-FDG uptake of breast cancer through posttranscriptional downregulation of hexokinase-2

The advancement of breast cancer therapy is limited by the biologic behaviors of cancer cells, such as metastasis and recurrence. β-adrenoceptors (ADRB) are reported to be associated with the biologic behaviors of breast cancer and may influence glucose metabolism. Here, we sought to investigate the relationship between the activation of ADRB and the expression of glucose transporter (GLUT)-1 and hexokinase (HK)-2 and to clarify the impact of ADRB on (18)F-FDG PET imaging in breast cancer.

Methods: ADRB1/2 expression in 4T1, MDA-MB-231, and MCF-7 breast cancer cell lines was detected by Western blotting and immunofluorescence. ADRB-dependent regulation of GLUT-1 and HK-2 was determined by in vitro pharmacologic intervention. 4T1 breast cancer cells were treated with phosphate-buffered saline, isoproterenol, or propranolol, and the transcription and expression of GLUT-1 and HK-2 were measured by quantitative real-time polymerase chain reaction (RT-PCR) and Western blotting, respectively. ADRB1/2 was, respectively, blocked by small-interfering RNA to investigate the direct relationship between ADRB1/2 and HK-2. To evaluate the impact of ADRB on (18)F-FDG PET imaging, BALB/c mice bearing 4T1 tumors were injected with phosphate-buffered saline, isoproterenol, or propranolol, and (18)F-FDG PET imaging was performed. The tumor-to-nontumor (T/NT) values of tumors and brown adipose tissue were calculated by defining the liver as a reference. The in vivo expression of GLUT-1 and HK-2 was observed by immunohistochemical analysis and Western blotting.

Results: MDA-MB-231, MCF-7, and 4T1 breast cancer cells were positive for ADRB1/2 expression. The protein expression and posttranscriptional level of HK-2 were significantly decreased by treatment with propranolol in vitro, whereas GLUT-1 expression was not significantly altered by pharmacologic intervention. The expression of HK-2 could be reduced in ADRB2-blocked 4T1 cells. Mice in the propranolol-treated group exhibited lower T/NT values for the tumors and brown adipose tissue than the control group. Immunohistochemical analysis and Western blotting revealed reduced HK-2 expression in the tumors of propranolol-treated mice.

Conclusion: The expression of HK-2 was regulated by the activation of ADRB2 in 4T1 breast cancer cells primarily at the posttranscriptional level. Additionally, propranolol prevented glucose metabolism and (18)F-FDG PET imaging of 4T1 breast cancer tumors.