Melittin suppresses tumor progression by regulating tumor-associated macrophages in a Lewis lung carcinoma mouse model

Abstract

Abstract Tumor-associated macrophages (TAM) are a major component of tumor stroma. It has been reported that TAMs have M2-like phenotype and facilitate tumor progression by promoting angiogenesis and immunosuppression. Melittin, a major polypeptide of bee venom, has been widely studied as an anti-cancer drug due to its cytotoxicity to malignant cells. However, very little is known regarding the effect of melittin on immune cells in the tumor microenvironment. We demonstrated here that melittin inhibited the rapid tumor growth compared to the control in vivo. Melittin increased the M1/M2 ratio of TAMs by selectively reducing the number of CD206+ M2-like TAMs, while not affecting the number of CD86+ M1-like TAMs. Melittin also preferentially bound to CD11b+ cells and this binding was not associated with phagocytosis. Gene expression of vascular endothelial growth factor (Vegf) and mannose receptor C type 1 (Mrc1/CD206) was reduced in M2-like bone marrow-derived macrophages by melittin treatment, but there was no significant change in the gene level of Vegf and FMS-like tyrosine kinase 1 (Flt1/VEGFR1) in tumor cells. Additionally, the levels of VEGF and CD31, markers of angiogenesis, were significantly decreased by melittin treatment in tumor tissues. This study revealed a novel role for melittin in tumor treatment and suggested that melittin could be a promising therapeutic agent for targeting M2-like TAMs.