Tumor Reliance on Cytosolic versus Mitochondrial One-Carbon Flux Depends on Folate Availability

Lee, Won Dong; Pirona, Anna Chiara; Sarvin, Boris; Stern, A. A.; Nevo‐Dinur, Keren; Besser, Elazar; Sarvin, Nikita; Lagziel, Shoval; Mukha, Dzmitry; Raz, Shachar; Aizenshtein, É. M.; Shlomi, Tomer

doi:10.1016/j.cmet.2020.12.002

Cited by 39 publications

(33 citation statements)

References 45 publications

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“…In fact, PF382 methotrexate resistant cells had a decreased expression of SLC19A but a two-fold decrease in IC 50 of RZ-2994. This may be related to a decrease in folate entry and increased dependency on SHMT1 48 . Thus, it is possible that resistance to inhibition of the one-carbon folate pathway may be overcome with novel inhibitors of this pathway though further in vivo testing is necessary.…”

Section: Discussionmentioning

confidence: 99%

Targeting serine hydroxymethyltransferases 1 and 2 for T-cell acute lymphoblastic leukemia therapy

et al. 2021

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Despite progress in the treatment of acute lymphoblastic leukemia (ALL), T-cell ALL (T-ALL) has limited treatment options, particularly in the setting of relapsed/refractory disease. Using an unbiased genome-scale CRISPR-Cas9 screen we sought to identify pathway dependencies for T-ALL which could be harnessed for therapy development. Disruption of the one-carbon folate, purine and pyrimidine pathways scored as the top metabolic pathways required for T-ALL proliferation. We used a recently developed inhibitor of SHMT1 and SHMT2, RZ-2994, to characterize the effect of inhibiting these enzymes of the one-carbon folate pathway in T-ALL and found that T-ALL cell lines were differentially sensitive to RZ-2994, with the drug inducing a S/G2 cell cycle arrest. The effects of SHMT1/2 inhibition were rescued by formate supplementation. Loss of both SHMT1 and SHMT2 was necessary for impaired growth and cell cycle arrest, with suppression of both SHMT1 and SHMT2 inhibiting leukemia progression in vivo. RZ-2994 also decreased leukemia burden in vivo and remained effective in the setting of methotrexate resistance in vitro. This study highlights the significance of the one-carbon folate pathway in T-ALL and supports further development of SHMT inhibitors for treatment of T-ALL and other cancers.

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Section: Discussionmentioning

confidence: 99%

Targeting serine hydroxymethyltransferases 1 and 2 for T-cell acute lymphoblastic leukemia therapy

et al. 2021

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“…As SHMT2 is essential not only in cancer pathology, but also in normal physiology, the mitochondria-specific inhibition of SHMT2 activity remains challenging [68,69]. However, one should acknowledge that anti-cancer models that disrupt SHMT2 as a proxy for drug treatment likely overestimate the undesirable impact of SHMT2 targeting.…”

Section: Discussionmentioning

confidence: 99%

Metformin Is a Pyridoxal-5′-phosphate (PLP)-Competitive Inhibitor of SHMT2

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et al. 2021

Cancers

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The anticancer actions of the biguanide metformin involve the functioning of the serine/glycine one-carbon metabolic network. We report that metformin directly and specifically targets the enzymatic activity of mitochondrial serine hydroxymethyltransferase (SHMT2). In vitro competitive binding assays with human recombinant SHMT1 and SHMT2 isoforms revealed that metformin preferentially inhibits SHMT2 activity by a non-catalytic mechanism. Computational docking coupled with molecular dynamics simulation predicted that metformin could occupy the cofactor pyridoxal-5′-phosphate (PLP) cavity and destabilize the formation of catalytically active SHMT2 oligomers. Differential scanning fluorimetry-based biophysical screening confirmed that metformin diminishes the capacity of PLP to promote the conversion of SHMT2 from an inactive, open state to a highly ordered, catalytically competent closed state. CRISPR/Cas9-based disruption of SHMT2, but not of SHMT1, prevented metformin from inhibiting total SHMT activity in cancer cell lines. Isotope tracing studies in SHMT1 knock-out cells confirmed that metformin decreased the SHMT2-channeled serine-to-formate flux and restricted the formate utilization in thymidylate synthesis upon overexpression of the metformin-unresponsive yeast equivalent of mitochondrial complex I (mCI). While maintaining its capacity to inhibit mitochondrial oxidative phosphorylation, metformin lost its cytotoxic and antiproliferative activity in SHMT2-null cancer cells unable to produce energy-rich NADH or FADH2 molecules from tricarboxylic acid cycle (TCA) metabolites. As currently available SHMT2 inhibitors have not yet reached the clinic, our current data establishing the structural and mechanistic bases of metformin as a small-molecule, PLP-competitive inhibitor of the SHMT2 activating oligomerization should benefit future discovery of biguanide skeleton-based novel SHMT2 inhibitors in cancer prevention and treatment.

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“…Our observed change in metabolic gene expression in MDA-MB-231 (but not M-Wnt) tumors in response to FA restriction indicates MDA-MB-231 cells can compensate for the loss of folate-bound one-carbon transfer by enhancing the flux of the groups into the folate pool (elevation of MTHFD1 and SHMT1) or by re-directing them to specific metabolic pathways (elevation of MTHFR, ALDH1L1, and GNMT). There is substantial diversity among cancer cells in the utilization of cytosolic verses mitochondrial folate pathways, in response to reduced FA supply [ 51 ]. SHMT1/2 are two main sources of one-carbon groups for folate metabolism [ 1 ] and the two enzymes can compensate for each other [ 49 ].…”

Section: Discussionmentioning

confidence: 99%

Metabolic Response of Triple-Negative Breast Cancer to Folate Restriction

et al. 2021

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Background: Triple-negative breast cancers (TNBCs), accounting for approximately 15% of breast cancers, lack targeted therapy. A hallmark of cancer is metabolic reprogramming, with one-carbon metabolism essential to many processes altered in tumor cells, including nucleotide biosynthesis and antioxidant defenses. We reported that folate deficiency via folic acid (FA) withdrawal in several TNBC cell lines results in heterogenous effects on cell growth, metabolic reprogramming, and mitochondrial impairment. To elucidate underlying drivers of TNBC sensitivity to folate stress, we characterized in vivo and in vitro responses to FA restriction in two TNBC models differing in metastatic potential and innate mitochondrial dysfunction. Methods: Metastatic MDA-MB-231 cells (high mitochondrial dysfunction) and nonmetastatic M-Wnt cells (low mitochondrial dysfunction) were orthotopically injected into mice fed diets with either 2 ppm FA (control), 0 ppm FA, or 12 ppm FA (supplementation; in MDA-MB-231 only). Tumor growth, metabolomics, and metabolic gene expression were assessed. MDA-MB-231 and M-Wnt cells were also grown in media with 0 or 2.2 µM FA; metabolic alterations were assessed by extracellular flux analysis, flow cytometry, and qPCR. Results: Relative to control, dietary FA restriction decreased MDA-MB-231 tumor weight and volume, while FA supplementation minimally increased MDA-MB-231 tumor weight. Metabolic studies in vivo and in vitro using MDA-MB-231 cells showed FA restriction remodeled one-carbon metabolism, nucleotide biosynthesis, and glucose metabolism. In contrast to findings in the MDA-MB-231 model, FA restriction in the M-Wnt model, relative to control, led to accelerated tumor growth, minimal metabolic changes, and modest mitochondrial dysfunction. Increased mitochondrial dysfunction in M-Wnt cells, induced via chloramphenicol, significantly enhanced responsiveness to the cytotoxic effects of FA restriction. Conclusions: Given the lack of targeted treatment options for TNBC, uncovering metabolic vulnerabilities that can be exploited as therapeutic targets is an important goal. Our findings suggest that a major driver of TNBC sensitivity to folate restriction is a high innate level of mitochondrial dysfunction, which can increase dependence on one-carbon metabolism. Thus, folate deprivation or antifolate therapy for TNBCs with metabolic inflexibility due to their elevated levels of mitochondrial dysfunction may represent a novel precision-medicine strategy.

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Tumor Reliance on Cytosolic versus Mitochondrial One-Carbon Flux Depends on Folate Availability

Cited by 39 publications

References 45 publications

Targeting serine hydroxymethyltransferases 1 and 2 for T-cell acute lymphoblastic leukemia therapy

Targeting serine hydroxymethyltransferases 1 and 2 for T-cell acute lymphoblastic leukemia therapy

Metformin Is a Pyridoxal-5′-phosphate (PLP)-Competitive Inhibitor of SHMT2

Metabolic Response of Triple-Negative Breast Cancer to Folate Restriction

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