We have completed a study where mouse breast tumour cells were injected intracerebrally into our eGFP monocyte/macrophage mice and the generated metastases were analysed at days 7, 14, and 21. These animals were also imaged using gadolinium enhanced MRI and these images were registered with histological images of the eGFP positive cells within the brain. The eGFP positive cells were detected at all timepoints and correlated with blood-brain barrier breakdown detected using MRI. We also found that the amount of eGFP positive cell infiltration increased significantly before significant changes could be seen in the vasculature within the metastases.
The phenotype of the eGFP positive cells in the brain metastases was analysed for iNOS (pro-inflammatory marker) and Arg1 (anti-inflammatory marker) expression to determine the initial phenotype any changes that occurred during growth of the lesion. The phenotype of the infiltrated GFP positive cells was initial a mixed phenotype of pro- and anti-inflammatory but leaning towards anti-inflammatory, which then shifted to a more predominantly anti-inflammatory phenotype at the later time points.
In vitro studies were performed where mouse macrophages were stimulated with either be pro-inflammatory, anti-inflammatory or left unstimulated and then co-cultured with mouse breast tumour cells in a transwell plate system that allows us to measure the invasiveness of the tumour cells. We found that tumour cells cultured with anti-inflammatory macrophages were more invasive than those that were cultured with pro-inflammatory macrophages.
We are currently conducting a study using miniature pumps loaded with PBS (a control), Macrophage Inhibitory Peptide (TKP, a general inhibitor of macrophage activation) or a CSF-1R neutralizing antibody (inhibits the anti-inflammatory expansion of macrophages) to modulate the function of blood-derived monocytes and macrophages and evaluate the how these different inhibitors affect the metastases’ growth. This study has been delayed due to poor breeding performance of our mouse colony.
