Mitochondrial uncouplers turn off serine metabolism and breast cancer lung metastasis
image: Mitochondrial uncoupling inhibits serine catabolism through FTO activation in metastatic breast cancer. Left: The m6A RNA demethylase, FTO, utilizes α-KG as a substrate. Under the Warburg effect, the reduced NAD+:NADH ratio leads to conversion of α-KG to 2-HG. 2-HG, which is structurally similar to α-KG, acts as a competitive inhibitor of FTO. This inhibition results in the accumulation of m6A on target RNAs, including target RNAs encoding the MSCP pathway enzymes, SHMT2, MTHFD2, and MTHFD1L. The resulting upregulation of these enzymes, which are essential for de novo purine biosynthesis, thereby fulfills the metabolic demands of metastatic breast cancer cell proliferation. Right: Mitochondrial uncouplers, a class of compounds that dissipate the proton gradient across the inner mitochondrial membrane, can activate electron transport chain activity and alleviate reductive stress. This activation of the electron transport chain restores the NAD+:NADH ratio, reverses the Warburg effect, and lowers 2-HG levels. Consequently, FTO activity is recovered, leading to decreased m6A methylation on MSCP gene transcripts, reduced expression of the corresponding enzymes, and suppressed metastasis. α-KG, α-ketoglutarate; 2-HG, 2-hydroxyglutarate; m6A, N6-methyladenosine; FTO, fat mass and obesity-associated protein; SHMT2, serine hydroxymethyltransferase 2; MTHFD2, methylenetetrahydrofolate dehydrogenase 2; MTHFD1L, methylenetetrahydrofolate dehydrogenase 1-like.
Credit: Cancer Biology & Medicine
Metastatic breast cancer remains challenging to treat because tumor cells rewire metabolism to survive and spread. This study shows that a class of drugs known as mitochondrial uncouplers, which reactivates respiration, suppresses the mitochondrial serine catabolic pathway (MSCP) and de novo purine synthesis. The researchers found that uncouplers lower key MSCP enzymes through fat mass and obesity-associated protein (FTO)-dependent N⁶-methyladenosine (m⁶A) demethylation, thereby linking mitochondrial metabolism to RNA modification. In mouse models, dietary mitochondrial uncoupling significantly reduced breast cancer lung metastasis. The work suggests that reactivating respiration to target serine catabolism may offer a new therapeutic strategy for metastatic breast cancer and identifies a druggable metabolic–epitranscriptomic axis. Together, these findings highlight a new way to target cancer epitranscriptome.
Mitochondrial serine catabolic pathway (MSCP), also called serine, glycine, and one-carbon metabolism, is essential for cancer cells to produce amino acids, one-carbon units, and reducing equivalents. The pathway is frequently upregulated in tumors: serine hydroxymethyltransferase 2 (SHMT2) and methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) are among the most overexpressed metabolic enzymes in human cancers, and their activity supports cancer cell proliferation, redox balance, and metastasis. Cancer cells rely on MSCP when the electron transport chain (ETC) is impaired, yet no effective therapy selectively targets this pathway. Fat mass and obesity-associated protein (FTO), an m⁶A demethylase, can be inhibited by 2-hydroxyglutarate (2-HG). FTO expression is associated with favorable prognosis and is downregulated in breast cancer, yet there is currently no effective way to reactivate FTO in cancer.Given these challenges, there is a need for in-depth research on therapies that safely reactivate respiration and target MSCP in metastatic breast cancer.
Researchers at Stanford University School of Medicine, with collaborators at The Second Hospital of Jilin University and Agilent Technologies, published (DOI: 10.20892/j.issn.2095-3941.2025.0444) the study in Cancer Biology & Medicine. The team, led by Jiangbin Ye, used uniformly ¹³C-labeled serine (U-¹³C-serine) tracing, immunoblotting, methylated RNA immunoprecipitation quantitative polymerase chain reaction (MeRIP-qPCR), and mouse metastasis models to test whether mitochondrial uncouplers such as niclosamide ethanolamine (NEN) and BAM15 suppress MSCP activity and breast cancer metastasis.
Using U-¹³C-serine tracing, the researchers found that NEN and BAM15 did not change serine uptake but sharply reduced glycine and purine nucleotides labeling, indicating lower MSCP and de novo purine synthesis flux. Uncouplers increased oxygen consumption and the NAD⁺ (nicotinamide adenine dinucleotide): NADH (reduced nicotinamide adenine dinucleotide) ratio, confirming ETC activation and alleviated reductive stress. Prolonged treatment downregulated mitochondrial enzymes SHMT2, MTHFD2, and methylenetetrahydrofolate dehydrogenase 1-like (MTHFD1L) proteins in triple-negative breast cancer (TNBC) and pancreatic cancer cells, while cytosolic enzyme serine hydroxymethyltransferase 1 (SHMT1) protein remained unaffected. Surprisingly, mRNA levels of SHMT2, MTHFD2, and MTHFD1L were unchanged or elevated, pointing to post-transcriptional control. Both pharmacologic or genetic inhibition of FTO restored MSCP enzyme expression. Uncoupler treatment reduced 2-HG and global m⁶A levels; L-2-HG supplementation increased m⁶A and MSCP enzymes, whereas α-KG (alpha-ketoglutarate) supplementation decreased them. In mice, a 2000 ppm NEN diet significantly reduced breast cancer lung metastasis. Low FTO expression was associated with poorer relapse-free survival in breast cancer patients, while SHMT2 was overexpressed in metastatic samples. Given that FTO is an α-KG-dependent dioxygenase and 2-HG acts as a competitive inhibitor, these findings suggest that, by lowering 2-HG, uncoupling restores FTO activity and reduces m⁶A marks on MSCP transcripts.
The authors said the findings reframe the Warburg effect as a targetable metabolic state. They said reactivating the electron transport chain (ETC) with mitochondrial uncouplers restores the NAD⁺:NADH balance, lowers 2-HG, and releases FTO to demethylate m⁶A on MSCP transcripts. In their view, this makes mitochondrial uncoupling a promising way to attack metabolic vulnerabilities that metastatic breast cancer cells rely on. They emphasized that the mechanism links metabolism, epitranscriptome, and metastasis in one axis.
The study points to mitochondrial uncouplers as potential therapeutics for metastatic breast cancer, especially tumors with high SHMT2 expression. Niclosamide, the parent of NEN, is approved as an antiparasitic drug but has shown limited oncology efficacy, possibly due to poor bioavailability or a narrow therapeutic window. BAM15 and next-generation uncouplers with broader dosing windows may be better candidates. Future work should test these agents in clinical trials, and determine whether combining uncoupling with existing therapies can delay or prevent metastasis. Combining metabolic therapy with standard treatments may further improve outcomes and help turn this metabolic strategy into a practical treatment option.
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References
DOI
10.20892/j.issn.2095-3941.2025.0444
Original Source URL
https://doi.org/10.20892/j.issn.2095-3941.2025.0444
Funding information
This work was supported by the Stanford Maternal and Child Health Research Institute Faculty Scholar Award (2020), the American Cancer Society Research Scholar Grant (Grant No. RSG-20–036–01), and the Agilent University Relations SIRA program (Grant ID #4792) to J.Y.
About Cancer Biology & Medicine
Cancer Biology & Medicine (CBM) is a peer-reviewed open-access journal sponsored by China Anti-cancer Association (CACA) and Tianjin Medical University Cancer Institute & Hospital. The journal monthly provides innovative and significant information on biological basis of cancer, cancer microenvironment, translational cancer research, and all aspects of clinical cancer research. The journal also publishes significant perspectives on indigenous cancer types in China. The journal is indexed in SCOPUS, MEDLINE and SCI (IF 12.4), with all full texts freely visible to clinicians and researchers all over the world.