Advanced Science | Targeting Cystine Metabolism Enhances Immune Checkpoint Inhibition in Lung Cancer

This study reveals that cysteine and cystine levels are significantly elevated in lung cancer patients' tumor tissues, and targeting cystine metabolism promotes macrophage polarization toward antitumor M1 phenotypes while upregulating PD-L1 expression. Combining cystine-targeted interventions with PD-L1 antibody treatment markedly inhibits subcutaneous tumor growth in mice, offering a novel strategy for lung cancer immunotherapy combined with metabolic regulation.

 

Literature Overview
The article "Targeting Cystine Metabolism in the Lung Cancer Environment Enhances the Efficacy of Immune Checkpoint Inhibition", published in Advanced Science, reviews the critical role of cystine metabolism in lung cancer immune microenvironment and its potential synergy with PD-L1 antibody therapy.

Background Knowledge
Non-small cell lung cancer (NSCLC) accounts for 80-85% of all lung cancer cases. Although immune checkpoint inhibitors (ICIs) like PD-1/PD-L1 antibodies have improved survival outcomes for advanced NSCLC patients in recent years, the overall response rate remains only 20-30%. Metabolic reprogramming within the tumor microenvironment (TME) has emerged as a key factor influencing immunotherapy efficacy. Amino acid metabolism profoundly affects tumor cell survival, proliferation, migration, and immune cell function regulation. For instance, arginine is essential for T cell viability and effector functions, while tumor-associated macrophages (TAMs) suppress T cell activity by upregulating arginase to degrade arginine. Glutamine serves as a primary energy source for T cells and NK cells, and its deficiency reduces IFN-γ expression. However, the specific roles of cysteine and cystine in lung cancer immunotherapy remain incompletely understood.

 

 

Research Methods and Experiments
This study first conducted metabolomic analysis on tumor tissues and paired adjacent normal tissues from 28 NSCLC patients, identifying significant upregulation of cysteine and cystine. KEGG pathway enrichment analysis revealed that the "cysteine-methionine metabolic pathway" was the most enriched. Flow cytometry and magnetic bead sorting techniques were then employed to detect system xc- (xCT) expression across different cell types, showing highest xCT expression in TAMs. Subsequently, murine peritoneal macrophages were cultured in cystine-free medium (CFM) for RNA-seq analysis of gene expression changes. A subcutaneous LLC tumor model in mice was established to evaluate tumor growth, oxidative stress marker MDA, PD-L1 expression, and immune cell infiltration under cystine-free diet (CFD) or PD-L1 antibody treatment. Molecular mechanisms of cystine deficiency-induced PD-L1 upregulation were further investigated using GSH supplementation and NF-κB inhibition approaches.

Key Conclusions and Perspectives

• Cysteine and cystine levels in NSCLC tumor tissues were significantly higher than in adjacent tissues, with cysteine-methionine metabolism identified as the most enriched pathway in TME.
• Cystine deficiency induced M1 polarization in both murine and human THP-1-derived macrophages, promoting secretion of antitumor factors including TNF-α, CXCL9, and CXCL10.
• Cystine depletion or system xc- inhibition (e.g., erastin) specifically upregulated PD-L1 expression in macrophages but not tumor cells.
• In mice receiving CFD or IKE treatment, combination with PD-L1 antibody significantly suppressed tumor growth, enhanced CD8+ T cell infiltration, and increased IFN-γ, granzyme B, and perforin expression.
• Mechanistically, cystine deficiency reduced GSH levels, decreasing glutathionylation of p65 and promoting its phosphorylation and nuclear translocation, thereby activating the NF-κB pathway to enhance M1 and PD-L1 gene expression.
• In clinical cohorts, NSCLC patients responding favorably to PD-1 immunotherapy showed significantly lower serum GSH levels than non-responders, suggesting GSH as a potential biomarker for treatment response.

Research Significance and Prospects
This research elucidates the pivotal role of cystine metabolism in TAM functional reprogramming, proposing a therapeutic strategy combining cystine metabolic targeting with PD-L1 inhibition to address immunotherapy resistance in lung cancer. Future studies should investigate this metabolic regulation in other tumor types, assess clinical translational feasibility, and develop more specific cystine transporter inhibitors to optimize therapeutic outcomes.

 

 

Conclusion
In summary, this study demonstrates cystine's critical regulatory role in lung cancer immune microenvironment through metabolomic analysis, cell functional assays, and animal models. Targeting cystine metabolism induces macrophage polarization toward antitumor M1 phenotypes and enhances PD-L1 expression, suggesting synergistic effects when combined with PD-L1 antibodies. Mechanistically, cystine deficiency reduces GSH levels, activating the NF-κB signaling pathway to promote PD-L1 and M1 gene expression. Clinical data further validate the correlation between low GSH levels and PD-1 inhibitor efficacy. This work provides a novel metabolic intervention strategy for lung cancer immunotherapy, highlighting cystine metabolic regulation as a potential approach to enhance ICIs effectiveness.

 

Yun Xu, Shumin Li, Jiaji Wu, Peng Xiao, and Kai Wang. Targeting Cystine Metabolism in the Lung Cancer Environment Enhances the Efficacy of Immune Checkpoint Inhibition. Advanced Science.