Cinobufagin Inhibits Invasion and Migration of Non-Small Cell Lung Cancer via Regulating Glucose Metabolism Reprogramming in Tumor-Associated Macrophages

Abstract

Background: The immunosuppressive tumor microenvironment (TME) in lung cancer, driven in part by M2-polarized tumor-associated macrophages (TAMs), contributes to worse prognosis and supports tumor progression. Cinobufagin (CB), an active compound in cinobufotalin injections, has demonstrated potential antitumor effects by modulating macrophage activity. This study investigated the mechanism by which CB influences glucose metabolism and polarization in M2 TAMs by focusing on the regulation of HIF-1α.

Methods: Human THP-1 monocytes were differentiated into M2 macrophages by stimulation with interleukin-4 at 20 ng/mL and then treated with cinobufagin at 2 μM, either alone or together with the HIF-1α activator DMOG at 1 mM. HIF-1α hydroxylation and ubiquitination were evaluated by Western blot and co-immunoprecipitation. Glycolytic activity was determined by measuring uptake of the glucose analogue 2-NBDG, extracellular lactate levels and expression of GLUT1, PKM2, LDHA and MCT1. M2 polarization markers CD206, Arg-1 and IL-10 were quantified by qRT-PCR, and TGF-β and IL-10 secretion was measured by ELISA. PD-L1 expression was assessed by Western blot, immunofluorescence and chromatin immunoprecipitation. Finally, conditioned media from treated macrophages were applied to A549 cells to evaluate migration through wound-healing assays and invasion using Transwell inserts, and to HUVECs to quantify tube formation.

Results: Using DMOG, an HIF-1α activator, we stimulated glycolysis in M2 macrophages, promoting their immunosuppressive polarization and elevating PD-L1 expression, a checkpoint protein associated with immune evasion. CB treatment reversed this effect by increasing HIF-1α hydroxylation and ubiquitination, leading to decreased HIF-1α stability, glucose uptake, and lactate production in M2 macrophages. Additionally, CB pre-treatment of M2 macrophages reduced the secretion of the cytokines TGF-β and IL-10, thereby limiting lung cancer cell migration, invasion, and angiogenesis.

Conclusion: These findings suggest that CB suppresses M2 macrophage-mediated tumor support by targeting HIF-1α and glycolysis, thereby reprogramming the TME toward an anti-tumor state. This highlights CB's potential of CB in the treatment of lung cancer by countering immunosuppressive macrophage activity.

Keywords: TAMs; TME; cancer immunotherapy; lung cancer; metabolic reprogramming.

Figure 1

Effect of CB on Genes Related to M2 Macrophage Polarization. (A–C) Real-time quantitative PCR analysis of mRNA levels for CD206, Arg-1, and IL-10; n=3; **P<0.01 compared to M0; ^##P<0.01 compared to M2.

Figure 2

Effect of CB on Glycolysis in M2 Macrophages. (A) Fluorescence images of macrophages after uptake of 2-NBDG (400×); (B) Quantification of average fluorescence intensity; (C) Colorimetric measurement of lactate concentration. (D–G) Real-time quantitative PCR analysis of mRNA levels for GLUT1, PKM2, LDHA, and MCT1; (H–L) Western blot analysis of protein expression levels for GLUT1, PKM2, LDHA, and MCT1. n=3; *P<0.05, **P<0.01 compared to M0; ^#P<0.05, ^##P<0.01 compared to M2.

Figure 3

Effect of CB on the Transcription Factor HIF-1α in M2 Macrophages. (A) Real-time quantitative PCR analysis of HIF-1α mRNA levels; (B and C) Western blot analysis of HIF-1α protein expression; (D–F) Western blot analysis of HIF-1α and Hydroxy-HIF-1α protein expression; (G) Immunoprecipitation analysis of HIF-1α ubiquitination levels. n=3; *P<0.05, **P<0.01 compared to M0; ^#P<0.05 compared to M2; ^$P<0.05 compared to M2+DMOG.

Figure 4

Effect of CB on the Transcription Factor HIF-1α in M2 Macrophages. (A and B) Immunofluorescence analysis of HIF-1α nuclear translocation (400×); (C and D) Fluorescence images of macrophages after uptake of 2-NBDG (400×); (E) Colorimetric measurement of lactate concentration; (F–J) Western blot analysis of protein expression levels for GLUT1, PKM2, LDHA, and MCT1. n=3; *P<0.05 compared to M0; ^#P<0.05 compared to M2; ^$P<0.05 compared to M2+DMOG.

Figure 5

CB Targets HIF-1α to Regulate M2 Macrophage Polarization. (A–C) Real-time quantitative PCR analysis of mRNA levels for CD206, Arg-1, and IL-10; (D and E) ELISA measurement of TGF-β and IL-10 secretion levels. n=3; *P<0.05 compared to M0; ^#P<0.05 compared to M2; ^$P<0.01 compared to M2+DMOG.

Figure 6

CB Targets HIF-1α to Regulate PD-L1 Expression in M2 Macrophages. (A and B) Western blot analysis of PD-L1 protein expression; (C and D) Immunofluorescence analysis of PD-L1 fluorescence intensity (400×); (E and F) Agarose gel electrophoresis of Input, IgG, and ChIP results. n=3; *P<0.05 compared to M0; ^#P<0.05, ^##P<0.01 compared to M2; ^$P<0.05 compared to M2+DMOG.

Figure 7

Effect of CB-Treated Macrophage Conditioned Medium on A549 Cell Migration, Invasion, and Pro-Angiogenic Capacity. (A and B) Scratch wound healing assay to evaluate the effect of different treatments on A549 cell migration; scale bar = 200 µm; (C and D) Transwell invasion assay to assess the impact of different treatments on A549 cell invasion; scale bar = 1000 µm; (E-G) Tube formation assay to examine the effect of different treatments on A549 cell pro-angiogenic capacity; scale bar = 1000 µm. n=3; *P<0.05 compared to M0; ^#P<0.05 compared to M2; ^$P<0.05 compared to M2+DMOG.