Folate Metabolism and Cancer: Biological Mechanisms and Therapeutic Strategies

Product Manager: Harrison Michael

Folate is a water-soluble B-vitamin that cannot be synthesized in mammals and must be obtained from the diet, including leafy green vegetables, citrus fruits, and fortified grains. The folate metabolic cycle is crucial for normal cell growth, DNA synthesis, and methylation modifications, particularly in rapidly proliferating tissues and cancer cells. The core metabolic form, tetrahydrofolate (THF), undergoes a series of redox reactions in the body and serves as a one-carbon donor for the synthesis of purines, thymidylate, and methionine.

I. Core Mechanisms of Folate Metabolism

Dietary folate is initially reduced by dihydrofolate reductase (DHFR, EC 1.5.1.3) into dihydrofolate (DHF) and then further reduced to tetrahydrofolate (THF). THF serves as the starting substrate for multiple one-carbon metabolism pathways and is converted into various folate derivatives through enzymatic reactions catalyzed by methylenetetrahydrofolate dehydrogenase (MTHFD1, EC 1.5.1.5) and other enzymes. These molecules play a key role in cellular growth:

1. Synthesis of Purines and Pyrimidines

Thymidylate synthase (TS, EC 2.1.1.45) utilizes 5,10-methylene-THF to catalyze the conversion of deoxyuridine monophosphate (dUMP) into deoxythymidine monophosphate (dTMP), a process essential for DNA synthesis and repair.

2. De Novo Purine Synthesis

Glycinamide ribonucleotide transformylase (GAR, EC 2.1.2.2) and aminoimidazole carboxamide ribonucleotide transformylase (AICAR, EC 2.1.2.3) catalyze purine base synthesis, ensuring normal DNA replication and RNA transcription.

3. Methylation Reactions

5-Methyl-THF, through methionine synthase (MS, EC 2.1.1.13), catalyzes the conversion of homocysteine to methionine, which is further converted into S-adenosylmethionine (SAM), a key methyl donor for DNA, RNA, and protein methylation.

II. Folate Metabolism and Cancer

Cancer cells exhibit rapid proliferation and have a high demand for nucleotides, making folate metabolism highly active in tumors. Inhibiting folate metabolism has become an important anti-cancer strategy by disrupting purine and thymidine synthesis, thereby impairing DNA replication and cell proliferation.

1. Anti-Tumor Effects of Folate Metabolism Inhibitors

1.Dihydrofolate Reductase Inhibitors

·MTX: A folate analog that competitively inhibits DHFR, preventing the conversion of DHF to THF, thereby blocking pyrimidine and purine synthesis and inhibiting cancer cell growth.

·Pemetrexed: A multi-target antifolate inhibitor that simultaneously inhibits DHFR, TS, and MTHFD1 and is widely used in the treatment of lung cancer and malignant pleural mesothelioma.

2.Thymidylate Synthase Inhibitors

·Raltitrexed: Directly inhibits TS, preventing dUMP conversion to dTMP and thereby affecting DNA synthesis. It is commonly used in colorectal cancer treatment.

3.Novel Folate Metabolism Inhibitors

·Trimetrexate: Unlike classical folate analogs, it can penetrate cell membranes directly and inhibit DHFR, showing potential efficacy against drug-resistant tumors.

2.Dual Role of Folate Metabolism: Cancer Therapy and Genetic Stability

While folate metabolism inhibitors effectively treat cancer, folate deficiency may lead to genomic instability. Studies have shown that insufficient folate intake causes DNA strand breaks and hypomethylation, increasing mutation risks. For example, hypomethylation of specific sequences in the tumor suppressor gene p53 is associated with folate deficiency, and p53 mutations are found in 30%-50% of human cancers.

III. Experimental Studies on Folate in Cancer Research

1. Role of Folate in Cancer Cell Proliferation

In cancer research, scientists use in vitro cell culture experiments to assess the impact of folate on cancer cell proliferation. For instance, colorectal cancer (HCT116), breast cancer (MCF-7), or lung cancer (A549) cells are cultured in varying folate concentrations to observe changes in proliferation rates. Studies have shown that high folate levels promote DNA synthesis, accelerating cancer cell growth, while folate deficiency leads to cell cycle arrest in the S or G1 phase, inhibiting tumor progression.

Experimental Methods:

·CCK-8 or MTT cell proliferation assay

·Flow cytometry for cell cycle analysis

2. Folate Metabolism and Oncogene Regulation

Folate influences DNA methylation, indirectly regulating oncogenes and tumor suppressor genes. For instance, under folate-deficient conditions, tumor suppressor genes such as p53 and BRCA1 may exhibit abnormal expression due to hypomethylation, whereas oncogenes like c-Myc may be upregulated due to excessive methylation.

Experimental Methods:

·Methylation-specific PCR (MSP)

·ChIP-qPCR to detect gene methylation status influenced by folate

3. Anti-Cancer Experiments with Folate Metabolism Inhibitors

To study the mechanism by which folate metabolism inhibitors (e.g., MTX) kill cancer cells, scientists use in vitro cell models and animal experiments. For example, following MTX treatment, levels of DNA damage markers such as γ-H2AX increase, indicating impaired DNA synthesis.

Experimental Methods:

·Western blot to detect DNA damage protein expression

·Annexin V-FITC/PI apoptosis assay

Conclusion

Folate metabolism plays a dual role in cancer initiation, progression, and treatment. While it serves as a necessary nutrient for cancer cell proliferation, it is also a crucial target for cancer therapy. By further investigating the mechanisms of folate metabolism in tumors and developing more effective folate metabolism inhibitors, future cancer treatments may achieve significant breakthroughs.

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