Voluntary Wheel Running Modulates Tumour-Associated Macrophage Polarization in Breast Cancer Lung Metastases of Old BALB/C Mice, in a Dose-dependent Manner

Introduction Tumour-associated macrophages (TAMs) are highly plastic immune cells that polarize into tumour killing M1-like or tumour promoting M2-like macrophages depending on signals in the tumour microenvironment (TME). Exercise training may induce TAMs towards M1-like phenotypes to slow cancer progression and metastasis. In this study, we explored the effects of wheel running in tumour-challenged mice by analysing immune cell expression in metastatic tissues. Methods Archival breast cancer lung metastases tissues of old BALB/c mice were subjected to multiplex immunofluorescence (mIHC) to quantify immune cell subsets. The immune cell expressions were then analysed against the primary mammary tumour mass, metastatic lung tissue area, as well as distance ran before and after tumour implant for the exercise mice. Results Based on the mIHC results from control (n=9) and exercise (n=10) mice tissues, wheel running did not significantly alter immune cell expressions relative to lung metastases or mammary tumour. Correlations between immune cell expression and the metastatic foci area revealed significant trends. Of note, F4/80 + CD163 + or M2-like macrophage expression is positively correlated for both control (r=0.835, p =0.005) and exercise (r=0.669, p =0.034). The F4/80 + cells or overall macrophage expression was only positively correlated in the control (r=0.764, p =0.017) group. Likewise, the mammary tumour mass was positively correlated in the control group (r=0.834, p =0.010) but not in the exercise group. Interestingly, F4/80 + CD86 + or M1-like macrophage cells (r=0.758, p =0.011) and M1/M2 ratio (r=0.642, p =0.045) were only significantly correlated with mean distances ran after tumour implant. Conclusion Voluntary wheel running may shift the expression of metastatic TAMs towards anti-tumour M1-like macrophages in a dose-dependent manner after tumour challenge. This study demonstrates the importance and potential of implementing exercise training in combination with immunotherapy to treat metastatic breast cancer.