Identification of novel glycoproteins expressed on human macrophage surface using glycoproteomics

Prostate cancer is a leading cause of cancer-related deaths of men in the U.S. While localized disease is highly treatable by surgical resection and radiation, cancer that has metastasized remains incurable. Immune cells that primarily scavenge debris, promote prostate cancer angiogenesis and wound repair are M2 Macrophages. They are phenotypically similar to M2 tumor-associated macrophages (M2-TAMs) have been reported to associate with solid tumors and aide in proliferation, metastasis, and resistance to therapy. As an invasive species within the tumor microenvironment, this makes M2-TAMs an ideal therapeutic target in prostate cancer. To identify novel surface antigens expressed on M2-macrophages, we developed a novel method of creating homogenous populations of human macrophages from human CD14+ monocytes in vitro. These homogenous M1 macrophages secrete pro-inflammatory cytokines and our M2 macrophages secrete anti-inflammatory cytokines as well as Vascular Endothelial Growth Factor (VEGF). To identify enriched surface glycoproteins, we then performed solid-phase extraction of N-linked glycopeptides (SPEG) followed by liquid chromatography-tandem Mass Spectrometry (LC-MS/MS) on our homogenous macrophage populations. We discovered novel glycoproteins that are enriched exclusively on human M2-macrophages relative to human M1 macrophages and human CD14+ monocytes. Lastly, we determined if these surface antigens, found enriched on M2 macrophages, were also expressed in human metastatic castrate-resistant prostate cancer (mCRPC) tissues. Using mCRPC tissues from rapid autopsies, we were able to determine M2-macrophage infiltration by using immunohistochemistry and flow cytometry. These findings highlight the presence of macrophage infiltration in human mCRPC but also surface antigens that could be used for prognosis of localized disease and for targeting strategies.