Interferon-γ lowers tumour growth by increasing glycolysis and lactate production in a nitric oxide-dependent manner: implications for cancer immunotherapy

Interferon-gamma (IFN-{gamma}), the sole member of the type-II interferon family, is well known to protect the host from infectious diseases as well as mount anti-tumour responses. The amounts of IFN-{gamma} in the tumour microenvironment determine the host responses against tumours; however, several tumours employ evasive strategies by responding to low IFN-{gamma} signalling. In this study, the response of various tumour cell lines to IFN-{gamma} was studied in vitro. IFN-{gamma}-activation increases glycolytic flux and reduces mitochondrial function in a nitric oxide (NO)- and reactive oxygen species (ROS)-dependent manner in the H6 hepatoma tumour cell line. The higher glycolysis further fuelled NO and ROS production, indicating a reciprocal regulation. These processes are accompanied by Hypoxia inducing factor (HIF)-1 stabilization and HIF-1-dependent augmentation of the glycolytic flux. The IFN-{gamma} enhancement of lactate production also occurred in other NO-producing cell lines: RAW 264.7 monocyte/macrophage and Renca renal adenocarcinoma. However, two other tumour cell lines, CT26 colon carcinoma and B16F10 melanoma, did not produce NO and lactate upon IFN-{gamma}-activation. HIF-1 stabilization upon IFN-{gamma}-activation led to lower cell growth of B16F10 but not CT26 cells. Importantly, the IFN-{gamma}-activation of both CT26 and B16F10 cells demonstrated significant cellular growth reduction upon metabolic rewiring by exogenous administration of potassium lactate. Clinical studies have shown the crucial roles of IFN-{gamma} for successful cancer immunotherapies involving checkpoint inhibitors and chimeric antigen receptor T cells. The positive implications of this study on the metabolic modulation of IFN-{gamma} activation on heterogeneous tumour cells are discussed.