High-throughput screening and proteomic characterization of compounds targeting myeloid-derived suppressor cells

Myeloid-derived suppressor cells are a heterogeneous cell population of incompletely differentiated immune cells. They are known for suppressing T cell activity and are implicated in multiple chronical diseases, which makes them an attractive drug target for the pharmaceutical industry. Here, we differentiated mouse MDSC from a progenitor cell line and used quantitative (phospho)proteomics to quantify more than 7,000 proteins and phosphorylation sites that enable the characterization of MDSC on a molecular level. Based on this differentiation protocol, we investigated the effects of the well-studied MDSC drugs Entinostat and Mocetinostat on a proteomewide level and established a high-throughput drug screening platform. We assessed the effects on T cell proliferation and INF-γ secretion of ~21,000 small molecules in a MDSC/T cell coculture setup. The most promising candidates were further validated in a screening setup using human MDSC. Finally, a proteomics experiment showed the significant upregulation of several proteins associated with the reduction of reactive oxygen species, suggesting the potential mode of action of this compound.