Group component protein-derived macrophage activating factor stimulates macrophages that induce human breast cancer cell apoptosis.

Objectives: The vitamin D axis is involved in various aspects of human breast cancer. It is composed by vitamin D, vitamin D receptor (VDR) and group component (Gc) protein that is the precursor of the Gc protein-derived macrophage activating factor (GcMAF) (Eur Nephrol. 2011;5(1):15–9). It was demonstrated that administration of GcMAF to metastatic breast cancer patients yielded good clinical results (Int J Cancer. 2008 Jan 15;122(2):461-7). Here we demonstrate that GcMAF stimulates macrophages that attach to human breast cancer cells, induce their apoptosis and phagocytise them. Methods: Common reagents were from Sigma Aldrich. Purified, activity-tested GcMAF was from Immuno Biotech. Human breast cancer cell line MCF-7 was from the IZSLER. Macrophages (Raw 264.7) were from HPA Culture Collection. Morphology was studied by phase-contrast microscopy using an inverted microscope (Optika Microscopes). Results: When human breast cancer cells were co-cultured with macrophages that had been previously activated by GcMAF (100 ng/ml) for 72 h, macrophages attached to cancer cells and the chromatin in the nucleus of the cancer cells appeared fragmented and disorganized as expected in cells undergoing apoptosis. The cytoplasm appeared indented as if the macrophages attached to that region were deconstructing the cytoplasmic assembly of the cancer cell. The cytoplasm of macrophages appeared vacuolized suggesting active phagocytosis. Conclusions: These results are consistent with the observation that macrophages infiltrated experimental tumours implanted in mice after GcMAF injections, and open the way to further studies aimed at assessing the precise role and indications for GcMAF in the immunotherapy of breast cancer.