Background: Macrophage migration inhibitory factor (MIF) has been proposed as a link between inflammation and tumorigenesis. Despite its potentially broad influence in tumour biology and prevalent expression, the value of MIF as a therapeutic target in cancer remains unclear. We sought to validate MIF in tumour models by achieving a complete inhibition of its expression in tumour cells and in the tumour stroma.
Methods: We used MIF shRNA-transduced B16-F10 melanoma cells implanted in wild-type and MIF-/- C57Bl6 mice to investigate the effect of loss of MIF on tumour growth. Cytokine detection and immunohistochemistry (IHC) were used to evaluate tumours ex vivo.
Results: Macrophage migration inhibitory factor shRNA inhibited expression of MIF protein by B16-F10 melanoma cells in vitro and in vivo. In vitro, the loss of MIF in this cell line resulted in a decreased response to hypoxia as indicated by reduced expression of VEGF. In vivo the growth of B16-F10 tumours was inhibited by an average of 47% in the MIF-/- mice compared with wild-type but was unaffected by loss of MIF expression by the tumour cells. Immunohistochemistry analysis revealed that microvessel density was decreased in tumours implanted in the MIF-/- mice. Profiling of serum cytokines showed a decrease in pro-angiogenic cytokines in MIF-/- mice.
Conclusion: We report that the absence of MIF in the host resulted in slower tumour growth, which was associated with reduced vascularity. While the major contribution of MIF appeared to be in the regulation of angiogenesis, tumour cell-derived MIF played a negligible role in this process.