Down-Regulation of Hypoxia-Inducible Factor-1α and Downstream Glucose Transporter Protein-1 Gene by β-elemene Enhancing the Radiosensitivity of Lung Adenocarcinoma Transplanted Tumor

Abstract

Purpose: To study the effect of β-elemene on the radiosensitivity of A549 cell xenograft tumor and potential mechanisms by which β-elemene regulates the expression of hypoxia-inducible factor-1α (HIF-1α) and glucose transporter protein-1 (GLUT-1).

Methods: Using an A549 cell transplantation tumor model with male nude mice, we studied the effect of β-elemene on the radiosensitivity of non-small cell lung cancer (NSCLC). The expression of HIF-1α and GLUT-1 was detected by real-time PCR, Western blotting and immunohistochemistry. The relationship between the radiosensitivity of β-elemene and the expression of HIF-1α and GLUT-1 was analyzed.

Results: β-elemene and radiotherapy intervened in the growth of transplanted tumors in varying degrees. The enhancement factor (EF=2.44>1) was calculated; β-elemene at 45 mg/kg had the most significant enhanced effect on radiosensitivity. When β-elemene was used in combination with radiation, the expression of HIF-1α and GLUT-1 was significantly decreased, and there was a positive correlation between the two genes.

Conclusion: β-elemene exhibits a radiosensitizing effect on A549 cell xenograft tumor. The underlying molecular mechanism is probably associated with the down-regulation of HIF-1α and GLUT-1 expression, suggesting that β-elemene may directly or indirectly inhibit the expression of HIF-1α and GLUT-1. There is a positive significant correlation between expression of HIF-1α and GLUT-1. HIF-1α and downstream GLUT-1 could be used as a new target for the radiosensitization of NSCLC.

Keywords: GLUT-1; HIF-1α; radiosensitivity; transplanted tumor; β-elemene.

Figure 1

Growth curve and volume doubling time of transplanted tumors in each group. From the growth curve and the changes of transplanted tumor volume, which can be seen that both β-elemene and radiotherapy can effectively inhibit the growth of the transplanted tumor, and the combined effect of β-elemene and radiotherapy can significantly inhibit the growth of transplanted tumor (A). Display the volume doubling time of transplanted tumors in each group. The average volume of tumors in each group are the initial volume. The combined group showed the longest doubling time (B).

Figure 2

The melting curves of HIF-1α and GLUT-1 showed a single peak (A), which suggested that the amplification of PCR products was specific, and (B) shows its amplification curve.HIF-1α and GLUT-1 mRNA levels from the RT-PCR after diverse treatments were quantified by measuring the relative expression (C and D). The results represented the mean ± standard deviation (SD) of five nude mice in each group.

Figure 3

Transplanted tumors were assessed for the expression of HIF-1α and GLUT-1 by Western blot (A and C). HIF-1α and GLUT-1 protein levels of every group were quantified by measuring the relative optical density (OD). The OD in the treatment group was compared with the control group (P<0.01) (B and D). The results represented the mean ± SD of five nude mice in each group.

Figure 4

The immunohistochemical staining of HIF-1 α and GLUT-1 (A and B), and which the expression in every transplanted tumor (C–F). (A) HIF-1α; (B) GLUT-1. The results of Log₁₀ IOD and AOD in each experimental group were compared with those in the control group (P<0.01). The results represented the mean ± SD of five nude mice in each group.