Macrophages are Activated Toward Phagocytic Lymphoma Cell Clearance by Pentose Phosphate Pathway Inhibition

Medicine Biochemistry Cell Biology Oncology Life Sciences Immunology
macrophages lymphoma pentose phosphate pathway immune regulation metabolic modulation

Academic Background

The tumor microenvironment (TME) is a critical area in cancer research, where tumor cells interact with surrounding non-tumor cells to influence disease progression and therapeutic responses. Tumor-associated macrophages (TAMs) play a pivotal role in tumor growth, angiogenesis, and immune suppression. Recently, the role of metabolic regulation in macrophage function has gained attention, particularly the impact of glucose and mitochondrial metabolism on macrophage polarization and activity. However, the function of the pentose phosphate pathway (PPP) in TAMs and its effects on immune regulation remain understudied.

This study, conducted by Anna C. Beielstein and colleagues, aims to investigate the impact of PPP inhibition on the ability of macrophages to phagocytose lymphoma cells and to uncover the underlying metabolic and immune regulatory mechanisms. The research team, affiliated with the University Hospital of Cologne, the Cologne Excellence Cluster for Cellular Stress Responses in Aging-Associated Diseases (CECAD), and other institutions, published their findings on December 17, 2024, in Cell Reports Medicine.

Research Process and Experimental Design

1. Metabolic Inhibition Screening

The study began with a metabolic inhibition screening to assess the effects of different metabolic pathways on the phagocytic ability of macrophages. Various metabolic inhibitors were used, including glycolysis inhibitors (2-deoxy-D-glucose), AMPK inhibitors (BML-275), mitochondrial ATP production inhibitors (oligomycin), and PPP inhibitors (6-aminonicotinamide and oxythiamine). The phagocytic ability of macrophages under metabolic inhibition was evaluated using antibody-dependent cellular phagocytosis (ADCP) assays.

2. Validation of PPP Inhibition

To further validate the effects of PPP inhibition on macrophage function, the research team employed multiple PPP inhibitors (e.g., physcion and p-hydroxyphenylpyruvate) and repeated the phagocytosis assays in the human monocyte cell line THP1. Additionally, ADCP assays were conducted under hypoxic conditions to mimic the physiological state of the tumor microenvironment.

3. Macrophage Polarization and Metabolic Activity Analysis

Using flow cytometry and fluorescence microscopy, the team assessed the impact of PPP inhibition on macrophage polarization and morphology. Seahorse metabolic analysis was also performed to measure glycolysis and mitochondrial activity in macrophages, revealing that PPP inhibition significantly enhanced macrophage metabolic activity.

4. Multi-Omics Analysis

To uncover the molecular mechanisms underlying the effects of PPP inhibition on macrophage function, the team conducted proteomics, phosphoproteomics, and metabolomics analyses. The results showed that PPP inhibition shifted macrophages toward a pro-inflammatory polarization and significantly altered the expression of proteins involved in immune regulation.

5. In Vivo Experiments

The effects of PPP inhibition were validated in a mouse model. Using the PPP inhibitor S3, the study found that PPP inhibition significantly improved survival rates and enhanced the phagocytic ability of macrophages against lymphoma cells.

Key Findings

  1. PPP Inhibition Enhances Macrophage Phagocytic Ability: The study demonstrated that PPP inhibition significantly increased the ability of macrophages to phagocytose lymphoma cells, particularly in ADCP assays.

  2. PPP Inhibition Alters Macrophage Polarization: PPP inhibition induced a shift toward pro-inflammatory (M1-like) polarization in macrophages, reducing the expression of anti-inflammatory (M2-like) and tumor-associated macrophage (TAM) markers.

  3. PPP Inhibition Affects Immune Regulation via Metabolic Modulation: The study revealed that PPP inhibition modulates glycogen metabolism and the UDPG-STAT1-IRG1-itaconate axis, influencing macrophage immune regulation. PPP inhibition led to decreased glycogen levels, suppressed STAT1 activity, and reduced expression of the immunosuppressive gene IRG1, ultimately enhancing macrophage phagocytic ability.

  4. PPP Inhibition Enhances Anti-Tumor Effects In Vivo: In a mouse model, the PPP inhibitor S3 significantly prolonged survival and enhanced the phagocytic ability of macrophages against lymphoma cells.

Conclusions and Significance

This study highlights the critical role of PPP inhibition in regulating macrophage function, demonstrating that PPP inhibition can enhance macrophage phagocytic ability and reduce their supportive role in tumor cells through metabolic and immune regulatory mechanisms. These findings provide new insights into the treatment of B-cell lymphoma, particularly when combined with antibody therapy, potentially improving therapeutic outcomes and extending patient survival.

Highlights

  1. PPP Inhibition Enhances Macrophage Phagocytosis: The study systematically revealed the role of PPP inhibition in promoting macrophage phagocytosis of lymphoma cells.
  2. Link Between Metabolism and Immune Regulation: The study identified the molecular mechanism by which PPP inhibition regulates macrophage function through the UDPG-STAT1-IRG1-itaconate axis.
  3. In Vivo Validation of Therapeutic Efficacy: The study validated the therapeutic efficacy of PPP inhibition in a mouse model, showing significant extension of survival in lymphoma-bearing mice.

Research Value

The scientific value of this study lies in its revelation of the critical role of PPP inhibition in macrophage function regulation, offering a new target for tumor immunotherapy. Its application value is evident in the potential combination of PPP inhibitors with existing antibody therapies to enhance the treatment of B-cell lymphoma, with promising clinical prospects.

Additional Valuable Information

The research team also noted that PPP inhibition may affect other immune cells, such as T cells, opening new avenues for future research. Additionally, the low toxicity and high efficacy of PPP inhibitors make them promising candidates for clinical applications.

Summary

Through systematic metabolic inhibition screening and multi-omics analysis, this study revealed the critical role of PPP inhibition in regulating macrophage function and validated its potential application in the treatment of B-cell lymphoma. This discovery provides new insights into tumor immunotherapy, with significant scientific and clinical implications.