Metabolism of Immune Cells in the Tumor Microenvironment

Immunometabolism in cancer: basic mechanisms and new targeting strategy

Maturing immunometabolic research empowers immune regulation novel approaches. Progressive metabolic adaptation of tumor cells permits a thriving tumor microenvironment (TME) in which immune cells always lose the initial killing capacity, which remains an unsolved dilemma even with the development of immune checkpoint therapies. In recent years, many studies on tumor immunometabolism have been reported. The development of immunometabolism may facilitate anti-tumor immunotherapy from the recurrent crosstalk between metabolism and immunity. Here, we discuss clinical studies of the core signaling pathways of immunometabolism and their inhibitors or agonists, as well as the specific functions of these pathways in regulating immunity and metabolism, and discuss some of the identified immunometabolic checkpoints. Understanding the comprehensive advances in immunometabolism helps to revise the status quo of cancer treatment. An overview of the new landscape of immunometabolism. The PI3K pathway promotes anabolism and inhibits catabolism. The LKB1 pathway inhibits anabolism and promotes catabolism. Overactivation of PI3K/AKT/mTOR pathway and IDO, IL4I1, ACAT, Sirt2, and MTHFD2 promote immunosuppression of TME formation, as evidenced by increased Treg and decreased T-cell proliferation. The LKBI-AMPK pathway promotes the differentiation of naive T cells to effector T cells and memory T cells and promotes anti-tumor immunity in DCs.

Mesenchymal Stem Cells Increase Drug Tolerance of A431 Cells Only in 3D Spheroids, Not in 2D Co-Cultures

Mesenchymal stem cells (MSCs) are an integral part of the tumor microenvironment (TME); however, their role is somewhat controversial: conflicting reports suggest that, depending on the stage of tumor development, MSCs can either support or suppress tumor growth and spread. Additionally, the influence of MSCs on drug resistance is also ambiguous. Previously, we showed that, despite MSCs proliferating significantly more slowly than cancer cells, there are chemotherapeutic drugs which proved to be similarly toxic to both cell types. Here we established 2D co-cultures and 3D co-culture spheroids from different ratios of GFP-expressing, adipose tissue-derived MSCs and A431 epidermoid carcinoma cells tagged with mCherry to investigate the effect of MSCs on cancer cell growth, survival, and drug sensitivity. We examined the cytokine secretion profile of mono- and co-cultures, explored the inner structure of the spheroids, applied MSC-(nutlin-3) and cancer cell-targeting (cisplatin) treatments separately, monitored the response with live-cell imaging and identified a new, double-fluorescent cell type emerging from these cultures. In 2D co-cultures, no effect on proliferation or drug sensitivity was observed, regardless of the changes in cytokine secretion induced by the co-culture. Conversely, 3D spheroids developed a unique internal structure consisting of MSCs, which significantly improved cancer cell survival and resilience to treatment, suggesting that physical proximity and cell-cell connections are required for MSCs to considerably affect nearby cancer cells. Our results shed light on MSC-cancer cell interactions and could help design new, better treatment options for tumors.

Analyzing the impact of metabolism on immune cells in tumor microenvironment to promote the development of immunotherapy

Tumor metabolism and tumor immunity are inextricably linked. Targeting the metabolism of tumors is a point worth studying in tumor immunotherapy. Recently, the influence of the metabolism of tumors and immune cells on the occurrence, proliferation, metastasis, and prognosis of tumors has attracted more attention. Tumor tissue forms a specific tumor microenvironment (TME). In addition to tumor cells, there are also immune cells, stromal cells, and other cells in TME. To adapt to the environment, tumor cells go through the metabolism reprogramming of various substances. The metabolism reprogramming of tumor cells may further affect the formation of the tumor microenvironment and the function of a variety of cells, especially immune cells, eventually promoting tumor development. Therefore, it is necessary to study the metabolism of tumor cells and its effects on immune cells to guide tumor immunotherapy. Inhibiting tumor metabolism may restore immune balance and promote the immune response in tumors. This article will describe glucose metabolism, lipid metabolism, amino acid metabolism, and immune cells in tumors. Besides, the impact of metabolism on the immune cells in TME is also discussed for analyzing and exploring tumor immunotherapy.

Tumor microenvironment and cellular senescence: Understanding therapeutic resistance and harnessing strategies

The tumor microenvironment (TME) is a major contributor to cancer malignancy including development of therapeutic resistance, a process mediated in part through intercellular crosstalk. Besides diverse soluble factors responsible for pro-survival pathway activation, immune evasion and extracellular matrix (ECM) remodeling further promote cancer resistance. Importantly, therapy-induced senescence (TIS) of cells in the TME is frequently observed in anticancer regimens, an off-target effect that can generate profound impacts on disease progression. By conferring the resistance and fueling the repopulation of remaining cancerous cells, TIS is responsible for tumor relapse and distant metastasis in posttreatment stage. This pathological trajectory can be substantially driven by the pro-inflammatory feature of senescent cells, termed as the senescence-associated secretory phenotype (SASP). Targeting strategies to selectively and efficiently remove senescent cells before they exert non-autonomous but largely deleterious effects, are emerging as an effective solution to prevent drug resistance acquired from a treatment-remodeled TME. In this review, we summarize the TME composition and key activities that affect tissue homeostasis and support treatment resistance. Promising opportunities that allow TME-manipulation and senescent cell-targeting (senotherapy) are discussed, with translational pipelines to overcome therapeutic barriers in clinical oncology projected.