Myeloid-Specific Acly Deletion Alters Macrophage Phenotype In Vitro and In Vivo without Affecting Tumor Growth

Why and how citrate may sensitize malignant tumors to immunotherapy

Immunotherapy, either alone or in combination with chemotherapy, has demonstrated limited efficacy in a variety of solid cancers. Several factors contribute to explaining primary or secondary resistance. Among them, cancer cells, whose metabolism frequently relies on aerobic glycolysis, promote exhaustion of cytotoxic immune cells by diverting the glucose in the tumor microenvironment (TME) to their own profit, while secreting lactic acid that sustains the oxidative metabolism of immunosuppressive cells. Here, we propose to combine current treatment based on the use of immune checkpoint inhibitors (ICIs) with high doses of sodium citrate (SCT) because citrate inhibits cancer cell metabolism (by targeting both glycolysis and oxidative metabolism) and may active anti-tumor immune response. Indeed, as showed in preclinical studies, SCT reduces cancer cell growth, promoting cell death and chemotherapy effectiveness. Furthermore, since the plasma membrane citrate carrier pmCIC is mainly expressed in cancer cells and low or not expressed in immune and non-transformed cells, we argue that the inhibition of cancer cell metabolism by SCT may increase glucose availability in the TME, thus promoting functionality of anti-tumor immune cells. Concomitantly, the decrease in the amount of lactic acid in the TME may reduce the functionality of immunosuppressive cells. Preclinical studies have shown that SCT can enhance the anti-tumor immune response through an enhancement of T cell infiltration and activation, and a repolarization of macrophages towards a TAM1-like phenotype. Therefore, this simple and cheap strategy may have a major impact to increase the efficacy of current immunotherapies in human solid tumors and we encourage testing it in clinical trials.

Acetyl-CoA metabolism in cancer

Few metabolites can claim a more central and versatile role in cell metabolism than acetyl coenzyme A (acetyl-CoA). Acetyl-CoA is produced during nutrient catabolism to fuel the tricarboxylic acid cycle and is the essential building block for fatty acid and isoprenoid biosynthesis. It also functions as a signalling metabolite as the substrate for lysine acetylation reactions, enabling the modulation of protein functions in response to acetyl-CoA availability. Recent years have seen exciting advances in our understanding of acetyl-CoA metabolism in normal physiology and in cancer, buoyed by new mouse models, in vivo stable-isotope tracing approaches and improved methods for measuring acetyl-CoA, including in specific subcellular compartments. Efforts to target acetyl-CoA metabolic enzymes are also advancing, with one therapeutic agent targeting acetyl-CoA synthesis receiving approval from the US Food and Drug Administration. In this Review, we give an overview of the regulation and cancer relevance of major metabolic pathways in which acetyl-CoA participates. We further discuss recent advances in understanding acetyl-CoA metabolism in normal tissues and tumours and the potential for targeting these pathways therapeutically. We conclude with a commentary on emerging nodes of acetyl-CoA metabolism that may impact cancer biology.

Control of tumor-associated macrophage responses by nutrient acquisition and metabolism

Metazoan tissue specification is associated with integration of macrophage lineage cells in sub-tissular niches to promote tissue development and homeostasis. Oncogenic transformation, most prevalently of epithelial cell lineages, results in maladaptation of resident tissue macrophage differentiation pathways to generate parenchymal and interstitial tumor-associated macrophages that largely foster cancer progression. In addition to growth factors, nutrients that can be consumed, stored, recycled, or converted to signaling molecules have emerged as crucial regulators of macrophage responses in tumor. Here, we review how nutrient acquisition through plasma membrane transporters and engulfment pathways control tumor-associated macrophage differentiation and function. We also discuss how nutrient metabolism regulates tumor-associated macrophages and how these processes may be targeted for cancer therapy.

ATP-citrate lyase (ACLY) inhibitors as therapeutic agents: a patenting perspective

INTRODUCTION

ATP citrate lyase (ACLY) is a key enzyme in cellular metabolism, being the main source of acetyl-Coenzyme A, an important precursor for fatty acid, cholesterol and isoprenoid biosynthesis, and it is also involved in protein acetylation. Its expression changes are related to hyperlipidemia and cardiovascular diseases. Other studies have shown that ACLY is closely related to the occurrence of cancer: the increase in lipid synthesis provides the necessary building blocks for cell growth and division. Therefore, finding effective ACLY inhibitors has very important application prospects for lipid-related pathologies and cancer.

AREAS COVERED

: This review covers patents concerning ACLY inhibitors and alternative strategies to modulate ACLY activity, with their potential therapeutic applications.

EXPERT OPINION

In recent years ACLY as a drug target has become a hot spot in the research of innovative drugs for disorders of glucose and lipid metabolism. Many types of small-molecule ACLY inhibitors have been discovered, but few ACLY inhibitors proved to be highly effective in vitro and in vivo, since their main limitations were low cell penetration and low affinity to ACLY. The search for new effective ACLY inhibitors is of great significance and has broad application prospects for the treatment of hyperlipidemia and cancer.

Contradictory roles of lipid metabolism in immune response within the tumor microenvironment

Complex interactions between the immune system and tumor cells exist throughout the initiation and development of cancer. Although the immune system eliminates malignantly transformed cells in the early stage, surviving tumor cells evade host immune defense through various methods and even reprogram the anti-tumor immune response to a pro-tumor phenotype to obtain unlimited growth and metastasis. The high proliferation rate of tumor cells increases the demand for local nutrients and oxygen. Poorly organized vessels can barely satisfy this requirement, which results in an acidic, hypoxic, and glucose-deficient tumor microenvironment. As a result, lipids in the tumor microenvironment are activated and utilized as a primary source of energy and critical regulators in both tumor cells and related immune cells. However, the exact role of lipid metabolism reprogramming in tumor immune response remains unclear. A comprehensive understanding of lipid metabolism dysfunction in the tumor microenvironment and its dual effects on the immune response is critical for mapping the detailed landscape of tumor immunology and developing specific treatments for cancer patients. In this review, we have focused on the dysregulation of lipid metabolism in the tumor microenvironment and have discussed its contradictory roles in the tumor immune response. In addition, we have summarized the current therapeutic strategies targeting lipid metabolism in tumor immunotherapy. This review provides a comprehensive summary of lipid metabolism in the tumor immune response.

The multifaceted therapeutic value of targeting ATP-citrate lyase in atherosclerosis

ATP-citrate lyase (Acly) is the target of the new class low-density lipoprotein-cholesterol (LDL-C)-lowering drug bempedoic acid (BA). Acly is a key metabolic enzyme synthesizing acetyl-CoA as the building block of cholesterol and fatty acids. Treatment with BA lowers circulating lipid levels and reduces systemic inflammation, suggesting a dual benefit of this drug for atherosclerosis therapy. Recent studies have shown that targeting Acly in macrophages can attenuate inflammatory responses and decrease atherosclerotic plaque vulnerability. Therefore, it could be beneficial to extend the application of Acly inhibition from solely lipid-lowering by liver-specific inhibition to also targeting macrophages in atherosclerosis. Here, we outline the possibilities of targeting Acly and describe the future needs to translate these findings to the clinic.