IRG1/itaconate axis modulates lung tumor microenvironment via pentose phosphate pathway [sav25]

Tumor-associated macrophages (TAMs) are an important component of the immune milieu within the lung tumor microenvironment (TME) and have both tumor-promoting and tumor-inhibiting functions. However, the exact mechanisms underlying TAM-mediated inhibition of tumor development are still unknown. Itaconate is one of the main metabolites produced by the enzyme immune responsive gene 1 (IRG1) during a pro-inflammatory response. Single cell RNA-seq studies show that macrophages are the major immune cells for Irg1 expression in human and mouse lung tumors. Both Irg1-deficient mice and transplantation of Irg1-depleted bone marrow resulted in increased development of lung tumors in Kras and orthotopic mouse models, suggesting the anti-tumor function of Irg1-associated macrophages. On the other hand, 4-octyl-itaconate (octyl-Ita) reduces lung tumor development in lung cancer cell lines in vitro, in vivo models of lung cancer, and ex vivo using human tumor precision-cut lung slices. Mechanistically, IRG1/itaconate induces a metabolic shift in cancer cells and pro-tumor macrophages, specifically through inhibition of the pentose phosphate pathway (PPP). An integrative analysis of metabolomics, transcriptomics and proteomics identified glucose-6-phosphate dehydrogenase (G6PD) as the primary target for the antiproliferative effect of IRG1/itaconate. IRG1/Itaconate inhibited G6PD activity without affecting G6PD expression in Irg1-deficient mice and octyl Ita-treated lung cancer models. The novel inhibitory effects of IRG1/Itaconate and Octyl Ita on G6PD activity and PPP metabolism can not only suppress cancer cell proliferation in a non-cell-autonomous manner, but also re-educate pro-tumor macrophages into anti-tumor macrophages in a cell-autonomous manner. Our results suggest that octyl Ita is an effective anti-tumor metabolite with potential therapeutic application in lung cancer.