3-Bromopyruvate Inhibits the Growth and Glucose Metabolism of TNBC Xenografts in Nude Mice by Targeting c-Myc.

BACKGROUND: Due to the lack of effective drug treatment, triple-negative breast cancer (TNBC) is prone to recurrence and metastasis after an operation. As a glycolytic inhibitor, 3-bromopyruvic acid (3-BrPA) can inhibit the proliferation and induce apoptosis of TNBC cells. However, whether it has similar effects in animal models remains unclear. OBJECTIVE: To observe the effect of 3-BrPA on the growth and glucose metabolism of human TNBC transplanted tumors in nude mice and to investigate the mechanism. METHODS: We constructed subcutaneous xenografts of human TNBC in nude mice and treated them with low, medium and high concentrations of 3-BrPA. After 15 days, nude mice were sacrificed to detect hexokinase (HK) activity and adenosine triphosphate (ATP) content in tumor tissues. Hematoxylin-eosin (HE) staining was used to detect the damage of transplanted tumors and liver and kidney in nude mice, which 3-BrPA caused. The expression of c-Myc in tumor tissues was detected by Immunohistochemistry (IHC). Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining was used to detect the apoptosis of tumor tissues. Besides, the expressions of Cytc, Bax, Bcl-2 and Caspase-9 were detected by Western blotting. RESULTS: Compared with the control group, intraperitoneal injection of 3-BrPA inhibited the growth of human TNBC transplant tumors, decreased HK activity and ATP production in tumor tissues, disrupted the tissue structure of transplant tumors, and did not significantly damage liver and kidney tissues. IHC staining and Western blotting showed that 3-BrPA could decrease the expression of c-Myc and Bcl-2, increase the expression of Cyt -c, Bax and Caspase-9 expression and promote apoptosis in tumor tissues. CONCLUSION: The above data indicate that 3-BrPA inhibits the growth of human TNBC transplanted tumors and promotes their apoptosis. Its anti-cancer mechanism might reduce HK activity by down-regulating c-Myc expression, eventually leading to decreased glycolytic pathway energy production and promoting apoptosis of transplanted tumors.

3-Bromopyruvic acid regulates glucose metabolism by targeting the c-Myc/TXNIP axis and induces mitochondria-mediated apoptosis in TNBC cells.

Aerobic glycolysis is commonly observed in tumor cells, including triple-negative breast cancer (TNBC) cells, and the rate of aerobic glycolysis is higher in TNBC cells than in non-TNBC cells. Hexokinase 2 (HK2) is a key enzyme in the glycolytic pathway and a target of the transcription factor c-Myc, which is highly expressed in TNBC and promotes aerobic glycolysis by enhancing HK2 expression. As an inhibitor of HK2, 3-bromopyruvic acid (3-BrPA) exhibits good therapeutic efficacy in intrahepatic and extrahepatic tumors and inhibits the proliferation of human tumor cells with high expression levels of c-Myc in vivo and in vitro. In addition, 3-BrPA combines with photodynamic therapy to inhibit TNBC cell migration. Thioredoxin-interacting protein (TXNIP) competes with c-Myc to reduce glucose consumption in tumor cells to restrain cell proliferation. A comparative analysis was performed in the present study in TNBC (HCC1143) and non-TNBC (MCF-7) cell lines to explore the effect of 3-BrPA on energy metabolism in TNBC cells and to investigate the possible mechanism of action. Cell viability and apoptosis were detected through Cell Counting Kit-8 and flow cytometry assays, respectively. Expression levels of HK2, glucose transporter 1, TXNIP, c-Myc and mitochondria-regulated apoptosis pathway proteins were measured through western blotting. 3-BrPA inhibited cell proliferation, downregulated c-Myc and HK2 expression, and upregulated TXNIP expression in TNBC cells, but it doesn't have the same effect on non-TNBC cells. Furthermore, 3-BrPA induced the typical manifestations of mitochondrial-mediated apoptosis such as decreasing Bcl-2 expression and increasing Bax, Cyt-C and Caspase-3 expression. The present results suggested that 3-BrPA promoted TXNIP protein expression and reduced HK2 expression in TNBC cells by downregulating c-Myc expression, inhibiting glycolysis including suppressing lactate generation, intracellular ATP generation and HK activity, inducing mitochondrial-mediated apoptosis and eventually suppressing TNBC cell proliferation. These findings may reveal a novel therapeutic target for the clinical treatment of TNBC.