Studying the inhibitory effect of oxysterols on NK-92 metabolism and cytotoxicity

Abstract

NK cell-based immunotherapy has become a promising cancer treatment for cancer. One approach is the use of NK cell lines such as NK-92 as this overcomes many of the technical challenges associated with the use of human NK cells isolated from the blood. One of the major restrictions for the activity of NK cells against solid tumours are the conditions within the tumour microenvironment (TME) including adverse metabolic conditions. The Finlay lab has discovered that cellular metabolism is closely linked to NK cell anti-tumour functions, including NK cell cytotoxicity. However, little is known about the metabolic requirements for NK-92 to mediate anti-tumour cytotoxicity. This study investigated the metabolism of NK-92 cells and the importance for metabolic regulators, including mTORC1 and SREBP, in sustaining NK-92 cytotoxicity. Direct inhibition of metabolic pathways inhibited NK-92 cytotoxicity. While IL-2 signaling is required for NK92 cytotoxicity, the activity of the downstream signaling through mTORC1 and Srebp is dispensable. Interestingly, the oxidized cholesterol molecule 25-hydroxycholesterol (25-HC), a known inhibitor of SREBP activation, potentially inhibited NK-92 cytotoxicity, mitochondrial metabolism, along with observed distribution in membrane structure, seemed to occur independently of SREBP and LXR activation. 25-HC can be made by tumour associated macrophages (TAMs) that express cholesterol-25-hydroxylase. These data argue that 25-HC in the TME would inhibit NK-92 anti-tumour activity through modifying the membrane lipid order. Understanding NK92 cell metabolism will support designing better cell-based cancer therapeutic strategies in future. The data emerging from this project suggest that one strategy would be to engineer NK-92 cells to be resistant to the actions of 25-HC.