Deregulation of folate pathway gene expression correlates with poor prognosis in acute leukemia

Glutathione levels are associated with methotrexate resistance in acute lymphoblastic leukemia cell lines

Introduction

Methotrexate (MTX), a folic acid antagonist and nucleotide synthesis inhibitor, is a cornerstone drug used against acute lymphoblastic leukemia (ALL), but its mechanism of action and resistance continues to be unraveled even after decades of clinical use.

Methods

To better understand the mechanisms of this drug, we accessed the intracellular metabolic content of 13 ALL cell lines treated with MTX by 1H-NMR, and correlated metabolome data with cell proliferation and gene expression. Further, we validated these findings by inhibiting the cellular antioxidant system of the cells in vitro and in vivo in the presence of MTX.

Results

MTX altered the concentration of 31 out of 70 metabolites analyzed, suggesting inhibition of the glycine cleavage system, the pentose phosphate pathway, purine and pyrimidine synthesis, phospholipid metabolism, and bile acid uptake. We found that glutathione (GSH) levels were associated with MTX resistance in both treated and untreated cells, suggesting a new constitutive metabolic-based mechanism of resistance to the drug. Gene expression analyses showed that eight genes involved in GSH metabolism were correlated to GSH concentrations, 2 of which (gamma-glutamyltransferase 1 [GGT1] and thioredoxin reductase 3 [TXNRD3]) were also correlated to MTX resistance. Gene set enrichment analysis (GSEA) confirmed the association between GSH metabolism and MTX resistance. Pharmacological inhibition or stimulation of the main antioxidant systems of the cell, GSH and thioredoxin, confirmed their importance in MTX resistance. Arsenic trioxide (ATO), a thioredoxin inhibitor used against acute promyelocytic leukemia, potentiated MTX cytotoxicity in vitro in some of the ALL cell lines tested. Likewise, the ATO+MTX combination decreased tumor burden and extended the survival of NOD scid gamma (NSG) mice transplanted with patient-derived ALL xenograft, but only in one of four ALLs tested.

Conclusion

Altogether, our results show that the cellular antioxidant defense systems contribute to leukemia resistance to MTX, and targeting these pathways, especially the thioredoxin antioxidant system, may be a promising strategy for resensitizing ALL to MTX.

The Emerging Role of MTHFD Family Genes in Regulating the Tumor Immunity of Oral Squamous Cell Carcinoma

Objective

To investigate the function and regulatory mechanisms of methylenetetrahydrofolate dehydrogenase (MTHFD) family genes in oral squamous cell carcinoma (OSCC), especially focus on their regulating role in tumor immunity.

Methods

The publicly available data from the TCGA database were used to investigate the expression pattern and regulatory role of MTHFD family genes in OSCC. More importantly, the involvement of MTHFD family genes in tumor immunity was investigated in terms of immune and stromal cell infiltration in tumor microenvironment, tumor-infiltrating immune cells, and immunomodulatory genes (e.g., immunoinhibitory genes and immunostimulatory genes). Statistical analysis was performed using R software packages and public web servers.

Results

MTHFD family genes were considerably upregulated in OSCC as compared with normal oral tissue. Patients with high MTHFD2 expression presented worse survival outcomes than those with low MTHFD2 expression. Functional enrichment analysis showed that the top 100 positively and negatively correlated genes of the MTHFD family genes were significantly enriched in several KEGG pathways, including cell cycle, spliceosome, DNA replication, and Th17 cell differentiation. As a result of tumor immunity analysis, MTHFD2L expression was found to be negatively related to the Estimate-Stromal-Immune score in OSCC; however, there was no statistical significance between the Estimate-Stromal-Immune score and MTHFD1, MTHFD1L, or MTHFD2 in OSCC. Additionally, MTHFD family genes were found to be significantly positively correlated with tumor-infiltrating immune cells, including Treg and Th17 cells. Moreover, MTHFD family genes were significantly correlated with several immune inhibitory genes such as CD274 and CTLA4 and several immune-stimulatory genes such as CXCL12, CXCR4, and TMIGD2.

Conclusion

Given the expression pattern, prognostic value, biological functions, and involvement in tumor immunity, MTHFD family genes could serve as potential therapeutic biomarkers in targeting tumor immunity in oral cancer.

Untargeted Metabolomics Showed Accumulation of One-Carbon Metabolites to Facilitate DNA Methylation during Extracellular Matrix Detachment of Cancer Cells

Tumor cells detached from the extracellular matrix (ECM) undergo anoikis resistance and metabolic reprogramming to facilitate cancer cell survival and promote metastasis. During ECM detachment, cancer cells utilize genomic methylation to regulate transcriptional events. One-carbon (1C) metabolism is a well-known contributor of SAM, a global substrate for methylation reactions, especially DNA methylation. DNA methylation-mediated repression of NK cell ligands MICA and MICB during ECM detachment has been overlooked. In the current work, we quantitated the impact of ECM detachment on one-carbon metabolites, expression of 1C regulatory pathway genes, and total methylation levels. Our results showed that ECM detachment promotes the accumulation of one-carbon metabolites and induces regulatory pathway genes and total DNA methylation. Furthermore, we measured the expression of well-known targets of DNA methylation in NK cell ligands in cancer cells, namely, MICA/B, during ECM detachment and observed low expression compared to ECM-attached cancer cells. Finally, we treated the ECM-detached cancer cells with vitamin C (a global methylation inhibitor) and observed a reduction in the promoter methylation of NK cell ligands, resulting in MICA/B re-expression. Treatment with vitamin C was also found to reduce global DNA methylation levels in ECM-detached cancer cells.