Inhibition of the electron transport chain increases cell dependence on purine transport and salvage

Research Background

The electron transport chain (ETC) is a key mechanism in mitochondria responsible for energy generation, playing an important role in maintaining cellular homeostasis and growth. However, it remains unclear how cells adjust their metabolism to cope with ETC dysfunction. Metabolic disorders due to mutations in cancer cells and inborn errors of metabolism (IEMs) are common, involving multiple metabolic pathways such as glycolysis, amino acid oxidation, and the urea cycle. These pathological mechanisms share commonalities between cancer and IEMs, and studying metabolic reprogramming in these contexts might provide new insights into cross-domain pathological mechanisms.

Source and Authors

This article was published in “Cell Metabolism” and written by Zheng Wu and team members Divya Bezwada, Feng Cai, Robert C. Harris, and others. The authors are affiliated with research institutions such as the University of Texas Southwestern Medical Center and the University of Chicago. The article was published on July 2, 2024.

Research Objectives and Questions

The study aims to explore the metabolic responses of human cells when the ETC function is impaired, particularly in relation to changes in purine metabolism. The study investigates whether ETC defects lead cells to shift from de novo purine synthesis towards purine salvage and examines whether this metabolic reprogramming could provide new therapeutic targets for tumors.

Research Methods

Research Process

1. Metabolomics Analysis: Researchers used metabolomics to analyze fibroblasts from patients with various mitochondrial diseases and cancer cells with blocked ETC.
2. Stable Isotope Tracing Experiment: Used stable isotope tracing technology to verify the impact of ETC defects on the purine synthesis pathway.
3. Molecular Biochemical Experiments: Measured the levels of various metabolites in ETC-deficient cells and the relationship between enzymes relevant to purine synthesis and purine precursors in the culture medium.
4. Gene Knockout Experiments: Using gene knockout technology, examined the role of the purine salvage enzyme HPRT1 in ETC dysfunction.
5. Mouse Model Experiments: Verified the effects of drugs on purine metabolism in vivo using mouse models.

Specific Experimental Steps

1. Metabolomics and Isotope Tracing Experiment: Analyzed the levels of purine metabolites using fibroblasts from patients with ETC dysfunction. Subsequently, tracked changes in purine synthesis pathways in cells using stable isotopes (such as 13C-labeled glucose and 15N-labeled glutamine).

2. Drug Treatment and Cell Experiment: Treated human non-small cell lung cancer (NSCLC) cells H460 with IACS-010759 inhibitor, observed changes in purine synthesis and cell growth.

3. Gene Knockout Experiment: Investigated the dependence of ETC-deficient cells on purine salvage through HPRT1 gene knockout and the cells’ growth performance after drug treatment.

4. Mouse In Vivo Experiment: Implanted H460 cells in mice and treated with IACS-010759, detected changes in purine metabolites in captured tumors.

Special Algorithms and Tools

1. Metabolomics Analysis: Used Metabolite Set Enrichment Analysis (MSEA) to analyze disturbances in specific metabolite pathways.
2. Stable Isotope Tracing: Based on mass spectrometry analysis of the distribution of labeled isotopes in metabolites to quantify pathway conversion.
3. Bioinformatics Tools: Used the DepMap cancer dependency map for analyzing the co-essentiality of purine metabolism-related genes.

Research Results

Main Results

1. ETC Defect Inhibits De Novo Purine Synthesis: The study found that ETC dysfunction obstructed de novo purine synthesis pathways, significantly reducing the abundance of purine isomers.
2. Purine Metabolism Reprogramming: When the ETC is inhibited, the expression of the purine salvage enzyme HPRT1 increases, enriching the abundance of metabolites like purine monophosphates (e.g., IMP) in the salvage pathway.
3. Supportive Role of Purine Salvage on Cell Growth: Introducing HPRT1 inhibition in cells, maintaining cellular NAD+/NADH balance, and supplementing intermediate metabolites significantly mitigates growth inhibition due to ETC suppression.
4. Contribution of Purine Salvage to Tumor Growth In Vivo: Mouse experiments showed that inhibiting the expression of purine salvage enzymes (such as HPRT1) significantly reduced tumor growth in vivo, notably when ETC function was compromised.

Data Support

Concentration of metabolites and isotope labeling distributions in the various experiments were obtained via high-resolution mass spectrometry and validated using appropriate statistical methods like two-tailed unpaired T-tests and two-tailed one-way ANOVA.

Research Conclusions

Main Conclusions and Significance

ETC dysfunction reduces the cell’s ability for de novo purine synthesis, forcing the cell to rely on the purine salvage pathway to meet metabolic demands. This metabolic reprogramming is crucial for the growth of cancer cells, particularly under hypoxic conditions or mitochondrial dysfunction. This study not only reveals a novel tumor metabolic vulnerability but also suggests that HPRT1 and related metabolic pathways could become important targets for future cancer treatments.

Research Highlights

1. Identification of Purine Metabolism Reprogramming Due to ETC Defect: This phenomenon reveals mechanisms of cellular adaptation to metabolic stress.
2. Significance of HPRT1 in ETC Inhibition: Offers a new potential target for cancer therapy.
3. Comprehensive Analysis of Purine Metabolism Changes Using Multiple Technologies: Achieved a thorough understanding of metabolic reprogramming.
4. In Vivo Validation in Mouse Models: Further strengthened the reliability of the research results, supporting clinical treatment strategies.

Other Important Information

This study provides strong scientific evidence for future exploration of metabolic responses to ETC dysfunction under various pathological conditions, and calls on the academic community and pharmaceutical industry to pay attention to cellular adaptation mechanisms in purine metabolism and develop corresponding therapeutic approaches. As stated in the article, the ETC inhibitor IACS-010759 shows increased purine metabolites in clinical trials, further corroborating the clinical relevance of the research findings.