Tumour-associated macrophages as a novel target of VEGI-251 in cancer therapy

Tumour-associated macrophages (TAMs), which possess M2-like characters and are derived from immature monocytes in the circulatory system, represent a predominant population of inflammatory cells in solid tumours. TAM infiltration in tumour microenvironment can be used as an important prognostic marker in many cancer types and is a potential target for cancer prevention or treatment. VEGI-251 not only is involved in the inhibition of tumour angiogenesis, but also participates in the regulation of host immunity. This work aimed to investigate the involvement of VEGI-251 in the regulation of specific antitumour immunity. We found that recombinant human VEGI-251(rhVEGI-251) efficiently mediated the elimination of TAMs in tumour tissue in mice, and induced apoptosis of purified TAMs in vitro. During this process, caspase-8 and caspase-3 were activated, leading to PARP cleavage and apoptosis. Most importantly, we further elucidated the mechanism underlying VEGI-251-triggered TAM apoptosis, which suggests that ASK1, an intermediate component of the VEGI-251, activates the JNK pathway via TRAF2 in a potentially DR3-dependent manner in the process of TAM apoptosis. Collectively, our findings provide new insights into the basic mechanisms underlying the actions of VEGI-251 that might lead to future development of antitumour therapeutic strategies using VEGI-251 to target TAMs.