Cystine deprivation triggers CD36-mediated ferroptosis and dysfunction of tumor infiltrating CD8+ T cells.

Cancer cells develop multiple strategies to evade T cell-mediated killing. On one hand, cancer cells may preferentially rely on certain amino acids for rapid growth and metastasis. On the other hand, sufficient nutrient availability and uptake are necessary for mounting an effective T cell anti-tumor response in the tumor microenvironment (TME). Here we demonstrate that tumor cells outcompete T cells for cystine uptake due to high Slc7a11 expression. This competition induces T-cell exhaustion and ferroptosis, characterized by diminished memory formation and cytokine secretion, increased PD-1 and TIM-3 expression, as well as intracellular oxidative stress and lipid-peroxide accumulation. Importantly, either Slc7a11 deletion in tumor cells or intratumoral cystine supplementation improves T cell anti-tumor immunity. Mechanistically, cystine deprivation in T cells disrupts glutathione synthesis, but promotes CD36 mediated lipid uptake due to dysregulated cystine/glutamate exchange. Moreover, enforced expression of glutamate-cysteine ligase catalytic subunit (Gclc) promotes glutathione synthesis and prevents CD36 upregulation, thus boosting T cell anti-tumor immunity. Our findings reveal cystine as an intracellular metabolic checkpoint that orchestrates T-cell survival and differentiation, and highlight Gclc as a potential therapeutic target for enhancing T cell anti-tumor function.

Fueling T-cell Antitumor Immunity: Amino Acid Metabolism Revisited.

T cells are the key players in eliminating malignant tumors. Adoptive transfer of tumor antigen-specific T cells and immune checkpoint blockade has yielded durable antitumor responses in the clinic, but not all patients respond initially and some that do respond eventually have tumor progression. Thus, new approaches to enhance the utility of immunotherapy are needed. T-cell activation and differentiation status are tightly controlled at the transcriptional, epigenetic, and metabolic levels. Amino acids are involved in multiple steps of T-cell antitumor immunity, including T-cell activation, proliferation, effector function, memory formation as well as functional exhaustion. In this review, we briefly discuss how amino acid metabolism is linked to T-cell fate decisions and summarize how amino acid deprivation or accumulation of certain amino acid metabolites within the tumor microenvironment diminishes T-cell functionality. Furthermore, we discuss potential strategies for immunotherapy via modulating amino acid metabolism either in T cells intrinsically or extrinsically to achieve therapeutic efficacy.

The intrinsic role and mechanism of tumor expressed-CD38 on lung adenocarcinoma progression.

It has been recently reported that CD38 expressed on tumor cells of multiple murine and human origins could be upregulated in response to PD-L1 antibody therapy, which led to dysfunction of tumor-infiltrating CD8+ T immune cells due to increasing the production of adenosine. However, the role of tumor expressed-CD38 on neoplastic formation and progression remains elusive. In the present study, we aimed to delineate the molecular and biochemical function of the tumor-associated CD38 in lung adenocarcinoma progression. Our clinical data showed that the upregulation of tumor-originated CD38 was correlated with poor survival of lung cancer patients. Using multiple in vitro assays we found that the enzymatic activity of tumor expressed-CD38 facilitated lung cancer cell migration, proliferation, colony formation, and tumor development. Consistently, our in vivo results showed that inhibition of the enzymatic activity or antagonizing the enzymatic product of CD38 resulted in the similar inhibition of tumor proliferation and metastasis as CD38 gene knock-out or mutation. At biochemical level, we further identified that cADPR, the mainly hydrolytic product of CD38, was responsible for inducing the opening of TRPM2 iron channel leading to the influx of intracellular Ca2+ and then led to increasing levels of NRF2 while decreasing expression of KEAP1 in lung cancer cells. These findings suggested that malignant lung cancer cells were capable of using cADPR catalyzed by CD38 to facilitate tumor progression, and blocking the enzymatic activity of CD38 could be represented as an important strategy for preventing tumor progression.

Direct inhibitory effect on viral entry of influenza A and SARS-CoV-2 viruses by azithromycin.

OBJECTIVES: Using strategy of drug repurposing, antiviral agents against influenza A virus (IAV) and newly emerging SARS-coronavirus 2 (SARS-CoV-2, also as 2019-nCoV) could be quickly screened out. MATERIALS AND METHODS: A previously reported engineered replication-competent PR8 strain carrying luciferase reporter gene (IAV-luc) and multiple pseudotyped IAV and SARS-CoV-2 virus was used. To specifically evaluate the pH change of vesicles containing IAV, we constructed an A549 cell line with endosomal and lysosomal expression of pHluorin2. RESULTS: Here, we identified azithromycin (AZ) as an effective inhibitor against multiple IAV and SARS-CoV-2 strains. We found that AZ treatment could potently inhibit IAV infection in vitro. Moreover, using pseudotyped virus model, AZ could also markedly block the entry of SARS-CoV-2 in HEK293T-ACE2 and Caco2 cells. Mechanistic studies further revealed that such effect was independent of interferon signalling. AZ treatment neither impaired the binding and internalization of IAV virions, nor the viral replication, but rather inhibited the fusion between viral and vacuolar membranes. Using a NPC1-pHluorin2 reporter cell line, we confirmed that AZ treatment could alkalize the vesicles containing IAV virions, thereby preventing pH-dependent membrane fusion. CONCLUSIONS: Overall, our findings demonstrate that AZ can exert broad-spectrum antiviral effects against IAV and SARS-CoV-2, and could be served as a potential clinical anti-SARS-CoV-2 drug in emergency as well as a promising lead compound for the development of next-generation anti-IAV drugs.

A ZEB1/p53 signaling axis in stromal fibroblasts promotes mammary epithelial tumours.

Accumulating evidence indicates that the zinc-finger transcription factor ZEB1 is predominantly expressed in the stroma of several tumours. However, the role of stromal ZEB1 in tumour progression remains unexplored. In this study, while interrogating human databases, we uncover a remarkable decrease in relapse-free survival of breast cancer patients expressing high ZEB1 levels in the stroma. Using a mouse model of breast cancer, we show that ZEB1 inactivation in stromal fibroblasts suppresses tumour initiation, progression and metastasis. We associate this with reduced extracellular matrix remodeling, immune cell infiltration and decreased angiogenesis. ZEB1 deletion in stromal fibroblasts increases acetylation, expression and recruitment of p53 to FGF2/7, VEGF and IL6 promoters, thereby reducing their production and secretion into the surrounding stroma. Importantly, p53 ablation in ZEB1 stroma-deleted mammary tumours sufficiently recovers the impaired cancer growth and progression. Our findings identify the ZEB1/p53 axis as a stroma-specific signaling pathway that promotes mammary epithelial tumours.