Endostar enhances the antitumor effects of radiation by affecting energy metabolism and alleviating the tumor microenvironment in a Lewis lung carcinoma mouse model

Abstract

Lung cancer is a leading cause of morbidity and mortality. Previous studies have identified that an improvement in treatment efficacy was achieved using Endostar; however, the role of Endostar in lung cancer remains poorly understood. The present study investigated whether the enhanced antitumor effects of Endostar in combination with radiation involved changes in the metabolism and microenvironment in non-small cell lung cancer. A Lewis lung carcinoma mouse model was used, including the control, Endostar (ES), radiotherapy (RT) and Endostar plus radiotherapy (ES + RT) groups. The tumor inhibition rates and growth were described based on changes in tumor volume. In addition, ultraviolet enzymatic analysis was performed to determine the lactate level and reverse transcription-polymerase chain reaction was used to measure the mRNA expression of lactate dehydrogenase (LDH). A Meph-3 pH meter was used to detect the ranges of tumor interstitial tissue pH, and immunohistochemical analysis was adopted to examine hypoxia within the tumor microenvironment. The tumor inhibition rate of the ES + RT group was significantly higher compared with the other three groups (P<0.05). Following treatment, the lactate levels decreased in all three treatment groups compared with the control, particularly in the ES + RT group (P<0.05). Reduced LDH expression and hypoxic fraction in the tumor microenvironment were also observed in the ES + RT group (P<0.05). Furthermore, changes from acidic to alkaline pH in the tumor microenvironment were detected in the ES + RT group. The present study suggested that Endostar is involved in the regulation of metabolism and tumor microenvironment hypoxia, which may be responsible for the enhanced antitumor effect of Endostar in combination with radiotherapy.

Keywords: endostar; hypoxia; lactate; lung cancer; radiotherapy.

Figure 1.

Tumor samples of Lewis lung carcinoma samples from the four different groups between days 2 and 12. (A) Control; (B) Endostar; (C) radiotherapy and (D) Endostar + radiotherapy groups.

Figure 2.

Changes in the tumor volumes, LDH levels and pH following treatment. (A) Growth curve of tumor in the Lewis lung adenocarcinoma mouse model. Tumor volumes were measured following separation of tumors. (B) Changes of lactate levels in the tumors, which were detected between day 2 and day 12 in all the groups. (C) LDH mRNA levels in tumor tissues on different days. Tumor samples were prepared and kept in −80°C. The expression of lactate mRNA was measured using reverse transcription-polymerase chain reaction between day 0 and day 12. (D) pH values of tumor tissues on different days. Groups: NC, normal control; RT, radiotherapy; ES, Endostar; ES + RT, Endostar + radiotherapy. LDH, lactate dehydrogenase.

Figure 3.

Immunohistochemical analysis of hypoxic cell samples collected (A-D) at day 10 and (E-H) at day 12, in each group (hematoxylin and eosin stain; magnification, ×400). Groups: (A and E) normal control; (B and F), radiotherapy; (C and G) Endostar; (D and H) Endostar + radiotherapy.

Figure 4.

Proportion of hypoxic cells following treatment with Endostar and/or radiation. The hypoxic cells were marked using immunohistochemistry and the percentage of hypoxic cells was observed under a microscope. Groups: NC, normal control; RT, radiotherapy; ES, Endostar; ES + RT, Endostar + radiotherapy.