PENTOSE PHOSPHATE PATHWAY INHIBITION ACTIVATES MACROPHAGES TOWARDS PHAGOCYTIC LYMPHOMA CELL CLEARANCE

Introduction: Treatment response in lymphoma depends on the interaction of macrophages as important effector cells for tumor cell clearance by antibody-dependent cellular phagocytosis (ADCP). In the tumor microenvironment there is an altered supply of nutrients which implicates metabolic reprograming of immune cells such as diminished phagocytic capacity of macrophages. We aimed to identify metabolic pathways regulating macrophages to improve their effector cell function in lymphoma therapy. Methods: We addressed macrophage lymphoma cell co-cultures using macrophage cell lines, primary human and murine macrophages, humanized aggressive lymphoma cell model hMB, and primary CLL patient cells. For pathway inhibition specific compounds and shRNA-mediated knockdowns were used. Macrophages were studied by immunophenotyping, SeaHorse, (phospho)-proteomic and metabolomic assessment. Lymphoma bearing NSG and C57BL/6 mice were used for in vivo treatment with the pentose phosphate pathway inhibitor S3, analysis of macrophage reprogramming, and overall survival. Results: Inhibition of the pentose phosphate pathway (PPP) induced an increased therapeutic efficacy of lymphoma cell phagocytosis by macrophages. Under PPP inhibition, an increased metabolic activity and a pro-phagocytic reprogramming of macrophages was observed, accompanied by an increased pro-inflammatory cytokine secretion. PPP inhibition in macrophages reduced primary CLL cell survival support in co-culture. The increased lymphoma cell clearance and phenotypic alterations were also observed in PPP enzyme knockdown macrophages and by inhibiting the PPP in primary human macrophages. In a multiomics assessment, a connection between PPP inhibition, subsequent suppression of glycogen synthesis and a changed immune profile by modulation of the Stat1-Irg1-itaconate axis was identified and validated. In humanized lymphoma mouse model the addition of the PPP inhibitor S3 led to significant prolonged overall survival and an increased macrophage maturation, pro-inflammatory polarization and phagocytic activity. Conclusions: We have identified the PPP as therapeutic target for reprogramming macrophage activity towards lymphoma cell phagocytosis. This effect is driven by Stat1-Irg1-itaconate signalling axis, connecting metabolic activity and immune-phenotype of macrophages. We hypothesize the PPP as a key regulator of macrophage function determining the capacity of lymphoma cell clearance and propose PPP inhibition as a therapeutic booster of antibody dependent regimens in B cell lymphoma. The research was funded by: Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) KFO28 and SFB1530, Studentische Forschungsfoerderung/ Begabtenfoerderung of Koeln Fortune program Keywords: metabolism, microenvironment, targeting the tumor microenvironment No conflicts of interests pertinent to the abstract.