Abstract 2686: Glycolysis-stimulated lactate production by tumor-associated macrophages promotes their M2-like phenotype

Abstract Tumor-associated macrophages (TAMs) are the predominant immune cells within the tumor microenvironment (TME), and their phenotypic modulation is influenced by environmental cues in the TME. In early tumors, TAMs adopt a pro-inflammatory M1-like phenotype, characterized by the secretion of immunogenic cytokines and the ability to kill cancer cells, thus opposing tumorigenesis. However, as tumors progress, TAMs mainly transition to an anti-inflammatory M2-like phenotype, promoting angiogenesis, suppressing anti-tumor immunity, and supporting metastasis. Importantly, a high M2-like/M1-like TAM ratio correlates with poor survival and decreased treatment responses.Despite the significance of TAMs, the molecular mechanisms driving their pro-tumorigenic M2-like phenotype remain unclear. One potential mechanism is metabolic reprogramming, where, traditionally, M1 macrophages favor glycolysis, and M2 macrophages rely on oxidative phosphorylation. However, this paradigm is primarily derived from in vitro experiments using well-defined polarization cocktails, which may not accurately replicate the complex TME. For instance, while in in vitro experiments IL4 and IL13 can induce oxidative phosphorylation and an M2-like phenotype, these cytokines do not seem essential for M2-like TAM polarization in vivo.Our studies reveal that, relative to M1-like TAMs, M2-like TAMs exhibit heightened glycolysis, intracellular lactate accumulation, and increased histone lysine lactylation - an epigenetic mark directly stimulated by lactate. Importantly, we demonstrate that TAM glycolysis and the M2-like phenotype are positively associated with hypoxia within a single tumor (GEM model and human tumors) and across various tumor types (syngeneic models). Inhibition of glycolysis-stimulated lactate production in TAMs through myeloid cell-specific deletion of lactate dehydrogenase A (mLdha-/-) reduces the M2-like:M1-like TAM ratio. This intervention increases tumor-infiltrating CD8+ T cells and reduces tumor growth in pre-clinical models, particularly in highly hypoxic environments. Moreover, to exclude the role of cancer cell-derived lactate on TAMs’ phenotypic changes, we reduced glycolysis in cancer cells by deleting pyruvate kinase muscle isozyme M2 (PKM2). This resulted in decreased lactate production and suppressed tumor growth. However, the M2/M1 ratio remained unaffected, suggesting that the intrinsic lactate production by TAMs is crucial for their phenotype modulation.Our findings underscore the pivotal role of hypoxia-induced glycolysis and lactate production in TAMs, shaping their M2-like phenotype and impacting tumor progression. This understanding not only advances our knowledge of macrophage metabolism and phenotype dynamics in the context of cancer but also in other diseases. Citation Format: Katarzyna Kurylowicz, Kasturi Chakraborty, Chang Cui, Gustavo Gastão Davanzo, Guolin Zhou, Xu Anna Tang, Kelly Q. Schoenfelt, Natalie Pulliam, Catherine A. Reardon, Swati Kulkarni, Tomas Vaisar, Pedro M. Moraes-Vieira, Yingming Zhao, Lev Becker. Glycolysis-stimulated lactate production by tumor-associated macrophages promotes their M2-like phenotype [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2686.