Modulating the tumor microenvironment (TME) to enhance anti tumor immunity using metabolic inhibitors

The tumor microenvironment (TME) presents a challenging setting for anti-tumor immunity due to its extreme metabolic features: nutrient deprivation, metabolite accumulation, acidity and hypoxia. Immune cells become dysfunctional under these unfavorable conditions resulting in diminished anti-tumor activity. Thus, strategies to address immunosuppressive conditions in the TME are warranted. We utilized metabolic inhibitors to modulate the TME and enhance anti-tumor immune responses. Neuroendocrine tumors (NETs) and chimeric antigen receptor (CAR)-T cells for somatostatin receptor 2 (SSTR2), a potential therapeutic target for NETs, were utilized as our experimental model. SSTR2 CAR-T cells were prepared from CD8 + T cells of healthy donors. To recapitulate T cell dysfunction in TME, CAR-T cells were cultured under unfavorable metabolic situations: acidic, hypoxic and low glucose conditions. The CAR-T cells exhibited dysfunctional phenotypes including decreased proliferation and viability and impaired cytotoxicity and cytokine production capacity. Additionally, exhaustion-related markers were significantly upregulated on CAR-T cells especially under acidic conditions. To modulate metabolism of NETs, we utilized inhibitors targeting lactate dehydrogenase A (LDHA) and mitochondrial complex I. LDH inhibitor NCI-006 reduced glucose consumption and lactate (Lac) production from NETs by inhibiting lactate fermentation, resulting in reduced extracellular acidification. However, NETs exhibited metabolic rewiring to oxidative phosphorylation (OXPHOS) after NCI-006 treatment. In contrast, Complex I inhibitor IACS-010759 treatment induced OXPHOS inhibition and rewiring to aerobic glycolysis. Combined treatment with these inhibitors successfully interrupted metabolic rewiring of NETs by blocking both aerobic glycolysis and OXPHOS. Hyperpolarized magnetic resonance imaging (HP-MRI) with 1-13C pyruvate (Pyr) and electron paramagnetic resonance (EPR) pO2 imaging were conducted to monitor in vivo metabolic activities in NET-derived xenograft tumors. Consistent to our in vitro findings, NCI-006 suppressed Lac production from Pyr, and IACS-010759 treatment resulted in elevated pO2 level in xenograft tumors. However, metabolic rewiring was also observed in xenograft model; NCI-006 treatment exacerbated hypoxia and IACS-010759 promoted Lac production from Pyr. To overcome the metabolic rewiring, we attempted combination treatment with NCI-006 and IACS-010759 on xenograft mice. The combination treatment effectively abrogated metabolic flexibility of NET-derived xenograft tumors. Metabolic stress resulted in CAR-T cell dysfunction, while NCI-006 and IACS-010759 showed potential to improve the extracellular environment of the TME. Further studies are warranted to test the feasibility and efficacy of metabolic inhibitors in combination with CAR-T therapy.