Anticancer Properties of Triptolide: Inhibition of Tumor‐associated Macrophages Differentiation and Cytokine Production
Authors: Sun Lixin , Li Han , Zhang Luyong , Zhou Huiping 
Published: November 2023

Macrophages play significant roles in the immune response to various pathogens and in tissue homeostasis. Macrophages can be activated and differentiated into multiple subtypes depending on the microenvironment, including classically activated (M1) and alternatively activated (M2) macrophages. Tumor‐associated macrophages (TAMs), which generally exhibit an M2‐like phenotype, play a critical role in tumor progression, angiogenesis, actual metastasis and immunosuppression. Triptolide, a diterpenoid isolated from the plant Tripterygium wilfordii Hook. F, exerts a unique bioactive spectrum of anti‐inflammatory and anticancer activities. Our previous studies showed that triptolide selectively inhibited the production of cytokines/chemokines in macrophages. But the effect of triptolide on TAMs remains unknown. The aim of this study was to determine if triptolide has any effect on the activation of TAMs and production of proinflammatory cytokines and other tumor‐promoting mediators.

Methods

The selective cytotoxic effect of triptolide on macrophages derived from blood monocytes (TAMs model in vitro), neutrophils, lymphocytes purified from BALB/c mouse and 4T1 mammary carcinoma cells was assessed by CCK‐8 assay. The effects of triptolide on the viability of macrophage polarization were examined by flow cytometry. The azoxymethane/dextran sulfate sodium (AOM/DSS)‐induced colon tumor ICR‐1 mice were used to elucidate the role of macrophage targeting in the antitumor activity of triptolide in vivo. BALB/c mice co‐inoculated with 4T1 cells and M2‐polarized RAW264.7 cells (control or pretreated with triptolide) were used to further examine whether triptolide's inhibitory effect on tumor progression is mediated by the targeting of TAMs. Real‐time PCR, Western blot analysis, immunofluorescence staining and flow cytometry were performed to determine the expression of cell surface markers and cytokine production.

Results

Macrophages were found more highly susceptible to triptolide than neutrophils, lymphocytes and tumor cells. M2‐polarized macrophages were more susceptible than M0/M1‐polarized macrophages. Triptolide inhibited macrophage differentiation toward the M2 phenotype, which was correlated with the reduction of tumors in AOM/DSS‐treated mice. In addition, triptolide abolished the M2 macrophage‐mediated tumor progression in cancer co‐inoculated Xenograft mouse models. Furthermore, triptolide inhibited the expression of the M2 markers, such as CD206, Arginase 1, CD204, and CD163, and inhibited both in vitro and in vivo the secretion of the anti‐inflammatory cytokines, transforming growth factor β1 (TGFβ1) and interleukin (IL)‐10.

Conclusions

Our study indicated that triptolide selectively inhibited the functions of M2‐polarized macrophages and TAMs. The inhibitory effect of triptolide on TAMs viability, differentiation, and cytokine production may elucidate the major underlying mechanisms of its antitumor activity. Our findings provide important information for the potential clinical application of triptolide in cancer therapy.

Support or Funding Information

This work was supported by grants from the National Natural Science Foundation of China (No. 81102887, No. 81320108029, No. 81102887, No.81173651, No. 81274146 and No. 81303301)