Bufalin suppresses tumour microenvironment-mediated angiogenesis by inhibiting the STAT3 signalling pathway

Kai Fang,Ruiqiu Zhu,Zeting Yuan,Min Sun,Peihao Yin,Yueping Zhan,Xin Liang,Yanyan Qiu,Chengqi Wu,Yuqian Wang,Ke Xu

doi:10.1186/s12967-021-03058-z

Abstract

BackgroundAntiangiogenic therapy has increasingly become an important strategy for the treatment of colorectal cancer. Recent studies have shown that the tumour microenvironment (TME) promotes tumour angiogenesis. Bufalin is an active antitumour compound whose efficacy has been indicated by previous studies. However, there are very few studies on the antiangiogenic effects of bufalin.MethodsHerein, human umbilical vein endothelial cell (HUVEC) tube formation, migration and adhesion tests were used to assess angiogenesis in vitro. Western blotting and quantitative PCR were used to detect relevant protein levels and mRNA expression levels. A subcutaneous xenograft tumour model and a hepatic metastasis model were established in mice to investigate the influence of bufalin on angiogenesis mediated by the TME in vivo.ResultsWe found that angiogenesis mediated by cells in the TME was significantly inhibited in the presence of bufalin. The results demonstrated that the proangiogenic genes in HUVECs, such as VEGF, PDGFA, E-selectin and P-selectin, were downregulated by bufalin and that this downregulation was mediated by inhibition of the STAT3 pathway. Overexpression of STAT3 reversed the inhibitory effects of bufalin on angiogenesis. Furthermore, there was little reduction in angiogenesis when bufalin directly acted on the cells in the tumour microenvironment.ConclusionOur findings demonstrate that bufalin suppresses tumour microenvironment-mediated angiogenesis by inhibiting the STAT3 signalling pathway in vascular endothelial cells, revealing that bufalin may be used as a new antiangiogenic adjuvant therapy medicine to treat colorectal cancer.

Highlights

Antiangiogenic therapy has increasingly become an important strategy for the treatment of colorectal cancer
Bufalin suppresses angiogenesis induced by cells in the tumour microenvironment To clarify the effects of bufalin on angiogenesis caused by TME cells, we collected the supernatants of CT26 cells, Cancer-associated fibroblast (CAF) and Tumour-associated macrophage (TAM) as TME-conditioned media (CMs)
We found that the Signal transducer and activator of transcription 3 (STAT3)-OE plasmid (See figure on page.) Fig. 5 Bufalin inhibits Colorectal cancer (CRC) cell growth via an antiangiogenic mechanism in vivo. a Scheme and schedule of imaging and treatments. b Tumour volumes from day 0 to day 28. c Tumour growth was visualized by an in vivo imaging system from day 7 to day 28. d Tumour weights and images. e IHC analysis of CD31 and Ki67 in tumours. f VEGF expression level in serum. g Immunofluorescence analysis of CD31 and p-STAT3 in tumours. **P < 0.01, ***P < 0.001

Summary

Introduction

Antiangiogenic therapy has increasingly become an important strategy for the treatment of colorectal cancer. It has been reported that antiangiogenic therapy can effectively improve the survival rate of CRC patients, which. Many studies have demonstrated that the TME including the cancer-associated fibroblasts (CAFs) and tumourassociated macrophages (TAMs) contained within it, promotes tumour angiogenesis [8,9,10]. The tumour microenvironment, which is termed the tumour mesenchyme or tumour stroma, includes CAFs, TAMs, blood vessels and extracellular matrix and substantially influences the initiation, growth and dissemination of CRC [3]. It was reported that the TME activates STAT3 signalling in human umbilical vein endothelial cells [13], and that the tumour microenvironment may affect angiogenesis through the STAT3 signalling pathway. The STAT3 pathway in blood vessels may become a target for the treatment of angiogenesis

Methods

Results

Discussion

Conclusion