Heterotypic interactions between
tumor cells and macrophages can enable
tumor progression and hold potential for the development of therapeutic interventions. However, the communication between
tumors and macrophages and its mechanism are poorly understood. Here, we find that tumor-associated macrophages (TAM) from
tumor-bearing mice have high amounts of
lipid as compared to macrophages from
tumor-free mice. TAM also present high
lipid content in clinical human
gastric cancer patients. Functionally, TAM with high
lipid levels are characterized by polarized M2-like profiling, and exhibit decreased phagocytic potency and upregulated
programmed death ligand 1 (PD-L1) expression, blocking anti-
tumor T cell responses to support their immunosuppressive function. Mechanistically, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis identifies the specific PI3K pathway enriched within
lipid-laid TAM.
Lipid accumulation in TAM is mainly caused by increased uptake of extracellular
lipids from
tumor cells, which leads to the upregulated expression of gamma
isoform of
phosphoinositide 3-kinase (PI3K-γ) polarizing TAM to M2-like profiling. Correspondingly, a preclinical
gastric cancer model is used to show pharmacological targeting of PI3K-γ in high-
lipid TAM with a selective inhibitor, IPI549. IPI549 restores the functional activity of macrophages and substantially enhances the phagocytosis activity and promotes cytotoxic-T-cell-mediated
tumor regression. Collectively, this symbiotic
tumor-macrophage interplay provides a potential therapeutic target for
gastric cancer patients through targeting PI3K-γ in
lipid-laden TAM.