Detection of inflammatory cell function using 13 C magnetic resonance spectroscopy of hyperpolarized [6-13 C]-arginine

Abstract

Myeloid-derived suppressor cells (MDSCs) are highly prevalent inflammatory cells that play a key role in tumor development and are considered therapeutic targets. MDSCs promote tumor growth by blocking T-cell-mediated anti-tumoral immune response through depletion of arginine that is essential for T-cell proliferation. To deplete arginine, MDSCs express high levels of arginase, which catalyzes the breakdown of arginine into urea and ornithine. Here, we developed a new hyperpolarized 13 C probe, [6-13 C]-arginine, to image arginase activity. We show that [6-13 C]-arginine can be hyperpolarized, and hyperpolarized [13 C]-urea production from [6-13 C]-arginine is linearly correlated with arginase concentration in vitro. Furthermore we show that we can detect a statistically significant increase in hyperpolarized [13 C]-urea production in MDSCs when compared to control bone marrow cells. This increase was associated with an increase in intracellular arginase concentration detected using a spectrophotometric assay. Hyperpolarized [6-13 C]-arginine could therefore serve to image tumoral MDSC function and more broadly M2-like macrophages.