FPGS

Gene Summary

Gene:FPGS; folylpolyglutamate synthase
Location:9q34.11
Summary:This gene encodes the folylpolyglutamate synthetase enzyme. This enzyme has a central role in establishing and maintaining both cytosolic and mitochondrial folylpolyglutamate concentrations and, therefore, is essential for folate homeostasis and the survival of proliferating cells. This enzyme catalyzes the ATP-dependent addition of glutamate moieties to folate and folate derivatives. Alternative splicing results in transcript variants encoding different isoforms. [provided by RefSeq, Jan 2014]
Databases:OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:folylpolyglutamate synthase, mitochondrial
Source:NCBIAccessed: 31 August, 2019

Ontology:

What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1994-2019)
Graph generated 31 August 2019 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Amino Acid Sequence
  • Base Sequence
  • Vorinostat
  • Polymerase Chain Reaction
  • Case-Control Studies
  • Acute Lymphocytic Leukaemia
  • Folic Acid
  • Survival Rate
  • Drug Resistance
  • Precursor T-Cell Lymphoblastic Leukemia-Lymphoma
  • Non-Small Cell Lung Cancer
  • Guanine
  • Colorectal Cancer
  • Lung Cancer
  • Membrane Transport Proteins
  • Methotrexate
  • DNA Methylation
  • Vincristine
  • Reduced Folate Carrier Protein
  • Risk Factors
  • Glutamates
  • Molecular Sequence Data
  • Promoter Regions
  • Antimetabolites, Antineoplastic
  • Messenger RNA
  • Peptide Synthases
  • Childhood Cancer
  • Pemetrexed
  • Genotype
  • Gene Expression Profiling
  • Cancer Gene Expression Regulation
  • Chromosome 9
  • Staging
  • Polyglutamic Acid
  • Folic Acid Antagonists
  • Enzymologic Gene Expression Regulation
  • Structure-Activity Relationship
  • Gene Expression
  • SEER Program
  • Single Nucleotide Polymorphism
Tag cloud generated 31 August, 2019 using data from PubMed, MeSH and CancerIndex

Specific Cancers (5)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: FPGS (cancer-related)

Taflin H, Odin E, Derwinger K, et al.
Relationship between folate concentration and expression of folate-associated genes in tissue and plasma after intraoperative administration of leucovorin in patients with colorectal cancer.
Cancer Chemother Pharmacol. 2018; 82(6):987-997 [PubMed] Free Access to Full Article Related Publications
PURPOSE: The aim of study was to investigate the relationship between folate concentration and expression of folate-associated genes in tumour, mucosa and plasma of patients with colorectal cancer, after intraoperative administration of bolus leucovorin (LV).
METHODS: Eighty patients were randomized into four groups to receive 0, 60, 200, or 500 mg/m
RESULTS: The folate concentration in tumour increased with increasing dosage of LV. Half of the patients treated with 60 mg/m
CONCLUSIONS: The results indicate the possibility of using the individual plasma 5-MTHF/LV ratio after LV injection as a surrogate marker for tissue folate concentration. Expression of several folate-associated genes is associated with folate concentration in tissue and plasma and may become useful when predicting response to LV treatment.

Yang L, Wu H, Gelder TV, et al.
SLCO1B1 rs4149056 genetic polymorphism predicting methotrexate toxicity in Chinese patients with non-Hodgkin lymphoma.
Pharmacogenomics. 2017; 18(17):1557-1562 [PubMed] Related Publications
AIM: To investigate the impact of polymorphisms in the FPGS, GGH and SLCO1B1 genes on high dose methotrexate (HD-MTX) related toxicity in Chinese patients with non-Hodgkin lymphoma (NHL).
MATERIALS & METHODS: We analyzed FPGS (rs10106), GGH (rs719235, rs10464903, rs12681874), SLCO1B1 (rs4149056) genetic polymorphisms in 105 Chinese patients with NHL treated with HD-MTX.
RESULTS: There was a statistically significant impact of the SLCO1B1 rs4149056 polymorphism on hepatotoxicity. Patients with TC and CC genotype had more hepatotoxicity than TT genotype (60 vs 32.94%, p = 0.025). After adjusting for disease stage, dosage, infusion time and therapy method, SLCO1B1 rs4149056 genotype remained significantly associated with hepatotoxicity (p = 0.028).
CONCLUSION: SLCO1B1 rs4149056 genetic variants can affect the HD-MTX-related toxicity in Chinese patients with NHL.

Mairinger FD, Vollbrecht C, Flom E, et al.
Folic acid phenotype (FAP) is a superior biomarker predicting response to pemetrexed-based chemotherapy in malignant pleural mesothelioma.
Oncotarget. 2017; 8(23):37502-37510 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Malignant pleural mesothelioma (MPM) is a rare tumor linked to a dismal prognosis. Even the most effective chemotherapeutical regime of pemetrexed combined with cisplatin leads to a remission-rate of only about 40%. The reasons for the rather poor efficacy remain largely unknown.
RESULTS: Phenotypes were significantly associated with progression (p=0.0279) and remission (p=0.0262). Cox-regression revealed significant associations between SLC19A1/TYMS-ratio (p=0.0076) as well as FPGS/TYMS-ratio (p=0.0026) and OS. For differentiation by risk-groups, COXPH identified a strong correlation (p=0.0008).
METHODS: 56 MPM specimens from patients treated with pemetrexed were used for qPCR analysis. Phenotypes and risk groups were defined by their expression levels of members of the folic acid metabolism and correlated to survival and objective response.
CONCLUSION: Our results indicate that the balance between folic acid uptake, activation and metabolism plays a crucial role in response to pemetrexed-based chemotherapy and the prognosis of MPM patients. Implementing this marker profile in MPM stratification may help to individualize MPM-therapy more efficiently.

Huang Z, Tong HF, Li Y, et al.
Effect of the Polymorphism of Folylpolyglutamate Synthetase on Treatment of High-Dose Methotrexate in Pediatric Patients with Acute Lymphocytic Leukemia.
Med Sci Monit. 2016; 22:4967-4973 [PubMed] Free Access to Full Article Related Publications
BACKGROUND The aim of this study was to investigate the association of the polymorphism of folylpolyglutamate synthetase (FPGS) with the dynamic plasma concentration of methotrexate (MTX) in pediatric patients with acute lymphocytic leukemia (ALL), as well as the prognosis. MATERIAL AND METHODS 57 ALL patients and 31 age and sex-matched children (control) were included in this study. Polymerase chain reaction-restriction fragment length polymorphism was performed for the analysis of the genotype of FPGS rs1544105 and high-performance liquid chromatography for measurement of MTX plasma concentration after 24-h and 44-h treatment. Overall survival was analyzed by Kaplan-Meier method. RESULTS No differences were observed between patients and controls regarding the distribution frequency of genotype and alleles of rs1544105. Patients carrying AA genotype had a significantly higher plasma concentration of MTX after 24 h than those carrying GG or GA (P<0.05) and no differences were found after 44 h. Kaplan-Meier survival analysis showed a longer median survival time in patients with AA than other genotypes with significant difference in overall survival. CONCLUSIONS Polymorphism of FPGS rs1544105 might be used as an effective approach for prediction of the treatment outcome of MTX.

Raz S, Stark M, Assaraf YG
Folylpoly-γ-glutamate synthetase: A key determinant of folate homeostasis and antifolate resistance in cancer.
Drug Resist Updat. 2016; 28:43-64 [PubMed] Related Publications
Mammalians are devoid of autonomous biosynthesis of folates and hence must obtain them from the diet. Reduced folate cofactors are B9-vitamins which play a key role as donors of one-carbon units in the biosynthesis of purine nucleotides, thymidylate and amino acids as well as in a multitude of methylation reactions including DNA, RNA, histone and non-histone proteins, phospholipids, as well as intermediate metabolites. The products of these S-adenosylmethionine (SAM)-dependent methylations are involved in the regulation of key biological processes including transcription, translation and intracellular signaling. Folate-dependent one-carbon metabolism occurs in several subcellular compartments including the cytoplasm, mitochondria, and nucleus. Since folates are essential for DNA replication, intracellular folate cofactors play a central role in cancer biology and inflammatory autoimmune disorders. In this respect, various folate-dependent enzymes catalyzing nucleotide biosynthesis have been targeted by specific folate antagonists known as antifolates. Currently, antifolates are used in drug treatment of multiple human cancers, non-malignant chronic inflammatory disorders as well as bacterial and parasitic infections. An obligatory key component of intracellular folate retention and intracellular homeostasis is (anti)folate polyglutamylation, mediated by the unique enzyme folylpoly-γ-glutamate synthetase (FPGS), which resides in both the cytoplasm and mitochondria. Consistently, knockout of the FPGS gene in mice results in embryonic lethality. FPGS catalyzes the addition of a long polyglutamate chain to folates and antifolates, hence rendering them polyanions which are efficiently retained in the cell and are now bound with enhanced affinity by various folate-dependent enzymes. The current review highlights the crucial role that FPGS plays in maintenance of folate homeostasis under physiological conditions and delineates the plethora of the molecular mechanisms underlying loss of FPGS function and consequent antifolate resistance in cancer.

Karube Y, Kobayashi S, Maeda S, et al.
Tumor-related gene expression levels in thymic carcinoma and Type B3 thymoma.
J Cardiothorac Surg. 2016; 11(1):85 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Thymic carcinoma (TC) is a rare type of malignant neoplasm that develops in the anterior mediastinum and associated with poor prognosis. Type B3 thymoma (B3) occasionally demonstrates malignant tumor characteristics, especially in the advanced stage. We investigated the expressions of tumor-related genes in resected TC and B3 specimens.
METHODS: TC and B3 specimens resected from 1999 through 2012 were investigated. Tumor segments were collected from the specimens by micro-dissection to extract mRNA, then RT-PCR was performed according to Dannenberg's tumor profile method for semi-quantitation of tumor-related gene mRNA. To compare with other types of cancer, data from lung cancer (LC) cases in our database were also examined.
RESULTS: The gene expression levels of thymidylate synthase were significantly higher in TC and B3 as compared to LC specimens (p < 0.02), while no difference were observed between TC and B3 tumors. The ratio of folypolyglutamyl synthase (FPGS) to gamma-glutamyl hydrolase (GGH) mRNA was significantly lower in TC than in B3 (p < 0.05), with lower FPGS/GGH in those tumors related to overall survival. Also, the gene expression of vascular endothelial growth factor (VEGF) was significantly higher in TC as compared to B3 (p = 0.04), with higher VEGF gene expression in TC and B3 specimens related to overall survival of affected patients. Epidermal growth factor receptor (EGFR) expression was significantly higher in B3 as compared to both TC and LC specimens (p < 0.01). However, there were no EGFR gene mutations detected in any of the specimens.
CONCLUSIONS: These results indicate that elevated expressions of the tumor-related genes FPGS/GGH and VEGF are correlated with malignancy of TC and B3 tumors. Additional examinations will be necessary to investigate their chemosensitivity.

Kim SE, Hinoue T, Kim MS, et al.
Effects of folylpolyglutamate synthase modulation on global and gene-specific DNA methylation and gene expression in human colon and breast cancer cells.
J Nutr Biochem. 2016; 29:27-35 [PubMed] Related Publications
Folylpolyglutamate synthase (FPGS) plays a critical role in intracellular folate homeostasis. FPGS-induced polyglutamylated folates are better substrates for several enzymes involved in the generation of S-adenosylmethionine, the primary methyl group donor, and hence FPGS modulation may affect DNA methylation. DNA methylation is an important epigenetic determinant in gene expression and aberrant DNA methylation is mechanistically linked cancer development. We investigated whether FPGS modulation would affect global and gene-specific promoter DNA methylation with consequent functional effects on gene expression profiles in HCT116 colon and MDA-MB-435 breast cancer cells. Although FPGS modulation altered global DNA methylation and DNA methyltransferases (DNMT) activity, the effects of FPGS modulation on global DNA methylation and DNMT activity could not be solely explained by intracellular folate concentrations and content of long-chain folylpolyglutamates, and it may be cell-specific. FPGS modulation influenced differential gene expression and promoter cytosine-guanine dinucleotide sequences (CpG) DNA methylation involved in cellular development, cell cycle, cell death and molecular transport. Some of the altered gene expression was associated with promoter CpG DNA methylation changes. In both the FPGS-overexpressed HCT116 and MDA-MB-435 cell lines, we identified several differentially expressed genes involved in folate biosynthesis and one-carbon metabolism, which might in part have contributed to the observed increased efficacy of 5-fluorouracil in response to FPGS overexpression. Our data suggest that FPGS modulation affects global and promoter CpG DNA methylation and expression of several genes involved in important biological pathways. The potential role of FPGS modulation in DNA methylation and its associated downstream functional effects warrants further studies.

Shimamoto Y, Nukatsuka M, Takechi T, Fukushima M
Association between mRNA expression of chemotherapy-related genes and clinicopathological features in colorectal cancer: A large-scale population analysis.
Int J Mol Med. 2016; 37(2):319-28 [PubMed] Free Access to Full Article Related Publications
To establish the individualized treatment of patients with colorectal cancer, factors associated with chemotherapeutic effects should be identified. However, to the best of our knowledge, few studies are available on this topic, although it is known that the prognosis of patients and sensitivity to chemotherapy depend on the location of the tumor and that the tumor location is important for individualized treatment. In this study, primary tumors obtained from 1,129 patients with colorectal cancer were used to measure the mRNA expression levels of the following genes associated with the effects of standard chemotherapy for colorectal cancer: 5-fluorouracil (5-FU)-related thymidylate synthase (TYMS), dihydropyrimidine dehydrogenase (DPYD) and thymidine phosphorylase (TYMP); folate-related dihydrofolate reductase (DHFR), folylpolyglutamate synthase (FPGS) and gamma-glutamyl hydrolase (GGH); irinotecan-related topoisomerase I (TOP1); oxaliplatin-related excision repair cross-complementing 1 (ERCC1); biologic agent-related vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR). Large-scale population analysis was performed to determine the association of gene expression with the clinicopathological features, in particular, the location of the colorectal cancer. From the results of our analysis of the mRNA expression of these 10 genes, we noted the strongest correlation between DPYD and TYMP, followed by TYMS and DHFR. The location of the colorectal cancer was classified into 4 regions (the right‑ and left-sided colon, rectosigmoid and rectum) and was compared with gene expression. A significant difference in all genes, apart from VEGF, was noted. Of the remaining 9 genes, the highest expression of TYMS and DPYD was observed in the right‑sided colon; the highest expression of GGH and EGFR was noted in the left-sided colon; the highest expression of DHFR, FPGS, TOP1 and ERCC1 was noted in the rectosigmoid, whereas TYMP expression was approximately equivalent in the right-sided colon and rectum, and higher than that in other locations. The data generated from this study may prove to be useful for the development of individualized chemotherapeutic treatments for patients with colorectal cancer, and will mean that the tumor location is taken into account.

Piwkham D, Siriboonpiputtana T, Beuten J, et al.
Mutation Screening and Association Study of the Folylpolyglutamate Synthetase (FPGS) Gene with Susceptibility to Childhood Acute Lymphoblastic Leukemia.
Asian Pac J Cancer Prev. 2015; 16(11):4727-32 [PubMed] Related Publications
BACKGROUND: Folylpolyglutamate synthetase (FPGS), an important enzyme in the folate metabolic pathway, plays a central role in intracellular accumulation of folate and antifolate in several mammalian cell types. Loss of FPGS activity results in decreased cellular levels of antifolates and consequently to polyglutamatable antifolates in acute lymphoblastic leukemia (ALL).
MATERIALS AND METHODS: During May 1997 and December 2003, 134 children diagnosed with ALL were recruited from one hospital in Thailand. We performed a mutation analysis in the coding regions of the FPGS gene and the association between single nucleotide polymorphisms (SNPs) within FPGS in a case-control sample of childhood ALL patients. Mutation screening was conducted by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and subsequently with direct sequencing (n=72). Association analysis between common FPGS variants and ALL risk was done in 98 childhood ALL cases and 95 healthy volunteers recruited as controls.
RESULTS: Seven SNPs in the FPGS coding region were identified by mutation analysis, 3 of which (IVS13+55C>T, g.1297T>G, and g.1508C>T) were recognized as novel SNPs. Association analysis revealed 3 of 6 SNPs to confer significant increase in ALL risk these being rs7039798 (p= 0.014, OR=2.14), rs1544105 (p=0.010, OR= 2.24), and rs10106 (p=0.026, OR= 1.99).
CONCLUSIONS: These findings suggested that common genetic polymorphisms in the FPGS coding region including rs7039789, rs1544105, and rs10106 are significantly associated with increased ALL risk in Thai children.

Miao C, Liu D, Zhang F, et al.
Association of FPGS genetic polymorphisms with primary retroperitoneal liposarcoma.
Sci Rep. 2015; 5:9079 [PubMed] Free Access to Full Article Related Publications
Primary retroperitoneal liposarcoma is generally regarded as a genetic disorder. We have retrospectively genotyped 8 single nucleotide polymorphisms (SNPs) in 6 candidate genes (MDM2, CDK4, CDC27, FPGS, IGFN1, and PRAMEF13) in 138 patients and 131 healthy control subjects to evaluate the effects of genetic factors on individual susceptibility to primary retroperitoneal liposarcoma in Chinese population. Three SNPs (rs2870820, rs1695147, rs3730536) of MDM2 showed significant differences in single-loci genotypes and allele frequencies between case and control groups (p < 0.05). The minor allele G of SNP rs10760502 in FPGS (folylpolyglutamate synthase) gene was significantly associated with increased risk for primary retroperitoneal liposarcoma, compared with major allele A. Our data suggest that FPGS variant in Chinese population may affect individual susceptibility to primary retroperitoneal liposarcoma.

Nowak D, Liem NL, Mossner M, et al.
Variegated clonality and rapid emergence of new molecular lesions in xenografts of acute lymphoblastic leukemia are associated with drug resistance.
Exp Hematol. 2015; 43(1):32-43.e1-35 [PubMed] Free Access to Full Article Related Publications
The use of genome-wide copy-number analysis and massive parallel sequencing has revolutionized the understanding of the clonal architecture of pediatric acute lymphoblastic leukemia (ALL) by demonstrating that this disease is composed of highly variable clonal ancestries following the rules of Darwinian selection. The current study aimed to analyze the molecular composition of childhood ALL biopsies and patient-derived xenografts with particular emphasis on mechanisms associated with acquired chemoresistance. Genomic DNA from seven primary pediatric ALL patient samples, 29 serially passaged xenografts, and six in vivo selected chemoresistant xenografts were analyzed with 250K single-nucleotide polymorphism arrays. Copy-number analysis of non-drug-selected xenografts confirmed a highly variable molecular pattern of variegated subclones. Whereas primary patient samples from initial diagnosis displayed a mean of 5.7 copy-number alterations per sample, serially passaged xenografts contained a mean of 8.2 and chemoresistant xenografts a mean of 10.5 copy-number alterations per sample, respectively. Resistance to cytarabine was explained by a new homozygous deletion of the DCK gene, whereas methotrexate resistance was associated with monoallelic deletion of FPGS and mutation of the remaining allele. This study demonstrates that selecting for chemoresistance in xenografted human ALL cells can reveal novel mechanisms associated with drug resistance.

Suthandiram S, Gan GG, Mohd Zain S, et al.
Genetic polymorphisms in the one-carbon metabolism pathway genes and susceptibility to non-Hodgkin lymphoma.
Tumour Biol. 2015; 36(3):1819-34 [PubMed] Related Publications
Corroborating evidence related to the role of aberrations on one-carbon metabolism (OCM) genes has been inconsistent. We evaluated the association between polymorphisms in 12 single nucleotide polymorphisms (SNPs) in 8 OCM genes (CBS, FPGS, FTHFD, MTRR, SHMT1, SLC19A1, TCN1, and TYMS), and non-Hodgkin lymphoma (NHL) risk in a multi-ethnic population which includes Malay, Chinese and Indian ethnic subgroups. Cases (N = 372) and controls (N = 722) were genotyped using the Sequenom MassARRAY platform. Our results of the pooled subjects showed a significantly enhanced NHL risk for CBS Ex9 + 33C > T (T versus C: OR 1.55, 95% CI 1.22-1.96, P = 0.0003), CBS Ex18-319G > A (A versus G: OR 1.15, 95% CI 1.14-1.83; P = 0.002), SHMT1 Ex12 + 236 T > C (T versus C: OR 1.44, 95% CI 1.15-1.81, P = 0.002), and TYMS Ex8 + 157C > T (T versus C: OR 1.29, 95% CI 1.06-1.57, P = 0.01). Haplotype analysis for CBS SNPs showed a significantly decreased risk of NHL in subjects with haplotype CG (OR 0.69, 95% CI 0.56-0.86, P = <0.001). The GG haplotype for the FTHFD SNPs showed a significant increased risk of NHL (OR 1.40, 95% CI 1.12-1.76, P = 0.002). For the TYMS gene, haplotype CAT at TYMS (OR 0.67, 95% CI 0.49-0.90, P = 0.007) was associated with decreased risk of NHL, while haplotype TAC (OR 1.29, 95% CI 1.05-1.58, P = 0.01) was found to confer increased risk of NHL. Our study suggests that variation in several OCM genes (CBS, FTHFD, SHMT1, TCN1, and TYMS) may influence susceptibility to NHL.

Raz S, Stark M, Assaraf YG
Binding of a Smad4/Ets-1 complex to a novel intragenic regulatory element in exon12 of FPGS underlies decreased gene expression and antifolate resistance in leukemia.
Oncotarget. 2014; 5(19):9183-98 [PubMed] Free Access to Full Article Related Publications
Polyglutamylation of antifolates catalyzed by folylpoly-γ-glutamate synthetase (FPGS) is essential for their intracellular retention and cytotoxic activity. Hence, loss of FPGS expression and/or function results in lack of antifolate polyglutamylation and drug resistance. Members of the TGF-β/Smad signaling pathway are negative regulators of hematopoiesis and deregulation of this pathway is considered a major contributor to leukemogenesis. Here we show that FPGS gene expression is inversely correlated with the binding of a Smad4/Ets-1 complex to exon12 of FPGS in both acute lymphoblastic leukemia cells and acute myeloid leukemia blast specimens. We demonstrate that antifolate resistant leukemia cells harbor a heterozygous point mutation in exon12 of FPGS which disrupts FPGS activity by abolishing ATP binding, and alters the binding pattern of transcription factors to the genomic region of exon12. This in turn results in the near complete silencing of the wild type allele leading to a 97% loss of FPGS activity. We show that exon12 is a novel intragenic transcriptional regulator, endowed with the ability to drive transcription in vitro, and is occupied by transcription factors and chromatin remodeling agents (e.g. Smad4/Ets-1, HP-1 and Brg1) in vivo. These findings bear important implications for the rational overcoming of antifolate resistance in leukemia.

Dy GK, Bogner PN, Tan W, et al.
Phase II study of perioperative chemotherapy with cisplatin and pemetrexed in non-small-cell lung cancer.
J Thorac Oncol. 2014; 9(2):222-30 [PubMed] Related Publications
INTRODUCTION: Pathologic complete response (pCR) with neoadjuvant chemotherapy is associated with improved survival in many solid tumors. We evaluated pCR rate of cisplatin with pemetrexed in non-small-cell lung cancer.
METHODS: Patients with stages IB to IIIA non-small-cell lung cancer, Eastern Cooperative Oncology Group performance status 0 to 1 were enrolled in this single-arm phase II trial using two-stage design with 90% power to detect pCR rate of more than or equal to 10%. Pretreatment mediastinal lymph node biopsy was required. Patients received three cycles of cisplatin 75 mg/m with pemetrexed 500 mg/m (day 1 every 21 days) preoperatively and additional two cycles within 60 to 80 days after surgery. The primary end point was pCR. Polymorphisms in FPGS, GGH, SLC19A1, and TYMS genes were correlated with treatment outcomes.
RESULTS: Thirty-eight patients were enrolled, with median age of 62.5 years. Preoperatively, 26% had squamous histology, and 34% had biopsy-proven N2 involvement. R0 resection was achieved in 94% of the 34 patients who underwent surgery, and 54% had documented N2 clearance. There was no pCR seen. Median disease-free survival (DFS) and overall survival of these patients have not yet been reached in contrast to median of 13.8 and 24.2 months, respectively, in patients with persistent N2 disease (p = 0.3241 and p = 0.1022, respectively). There was a statistically significant association between DFS and postoperative tumor, node, metastasis stage (p = 0.0429), SLC19A1 rs3788189 TT genotype (p = 0.0821), and viable tumor defined as less than or equal to 10% of resected specimen (p = 0.026).
CONCLUSION: The primary end point was not met. Patients with N2 clearance, less than or equal to 10% viable tumor in the resected specimen, and SLC19A1 rs3788189 TT genotype have favorable DFS outcomes.

Bienemann K, Staege MS, Howe SJ, et al.
Targeted expression of human folylpolyglutamate synthase for selective enhancement of methotrexate chemotherapy in osteosarcoma cells.
Cancer Gene Ther. 2013; 20(9):514-20 [PubMed] Related Publications
The antifolate methotrexate (MTX) is an important chemotherapeutic agent for treatment of osteosarcoma. This drug is converted intracellularly into polyglutamate derivates by the enzyme folylpolyglutamate synthase (FPGS). MTX polyglutamates show an enhanced and prolonged cytotoxicity in comparison to the monoglutamate. In the present study, we proved the hypothesis that transfer of the human fpgs gene into osteosarcoma cells may augment their MTX sensitivity. For this purpose, we employed the human osteocalcin (OC) promoter, which had shown marked osteosarcoma specificity in promoter studies using different luciferase assays in osteosarcoma and non-osteosarcoma cell lines. A recombinant lentiviral vector was generated with the OC promoter driving the expression of fpgs and the gene for enhanced green fluorescent protein (egfp), which was linked to fpgs by an internal ribosomal entry site (IRES). As the vector backbone contained only a self-inactivating viral LTR promoter, any interference of the OC promoter by unspecific promoter elements was excluded. We tested the expression of FPGS and enhanced green fluorescent protein (EGFP) after lentiviral transduction in various osteosarcoma cell lines (human MG-63 cells and TM 791 cells; rat osteosarcoma (ROS) 17/2.8 cells) and non-osteogenic tumor cell lines (293T human embryonic kidney cells, HeLa human cervix carcinoma cells). EGFP expression and MTX sensitivity were assessed in comparison with non-transduced controls. Whereas the OC promoter failed to enhance MTX sensitivity via FPGS expression in non-osteogenic tumor cell lines, the OC promoter mediated a markedly increased MTX cytotoxicity in all osteosarcoma cell lines after lentiviral transduction. The present chemotherapy-enhancing gene therapy system may have great potential to overcome in future MTX resistance in human osteosarcomas.

Mairinger F, Vollbrecht C, Halbwedl I, et al.
Reduced folate carrier and folylpolyglutamate synthetase, but not thymidylate synthase predict survival in pemetrexed-treated patients suffering from malignant pleural mesothelioma.
J Thorac Oncol. 2013; 8(5):644-53 [PubMed] Related Publications
BACKGROUND: Malignant mesothelioma is a highly aggressive tumor arising from mesothelial-lined surfaces, most often in the pleura cavities. Antifolates belong to the most effective cytotoxic drugs for malignant pleural mesothelioma (MPM) treatment. Pemetrexed is an antifolate inhibiting different folate pathway genes (thymidylate synthase [TS], dihydrofolate reductase, glycinamide ribonucleotide formyltransferase [GARFT], and aminoimidazole carboxamide ribonucleotide formyltransferase, [AICARFT]). Increased activity of pemetrexed occurs by folylpolyglutamate synthetase (FPGS), intracellular transport by reduced folate carrier (RFC). The aim of the study was to explore potential correlations between TS, GARFT, AICARFT, RFC, and FPGS levels in MPM and associations with clinical benefit from pemetrexed treatment.
METHODS: Samples from 63 patients were tested using immunohistochemistry (IHC) and quantitative polymerase chain reaction(qPCR) for expression levels of TS, GARFT, AICARFT, RFC, and FPGS. Clinical data were evaluated to determine associations between efficacy of pemetrexed and enzyme expression levels. Evaluation of expression levels was done through TaqMan-based qPCR, and IHC was evaluated semiquantitatively by using the H-score.
RESULTS: qPCR analysis showed no difference in expression pattern of GARFT and AICARFT. IHC analysis revealed a heterogeneous staining pattern for all the enzymes. No significant association was found between TS expression and survival or objective response of the tumors after pemetrexed treatment. FPGS (p = 0.0111) and RFC (p = 0.0088) mRNA expression levels were strongly associated with overall survival in these patients.
CONCLUSIONS: Our results reveal that in pemetrexed-treated MPMs TS expression levels have no influence on patient outcome. Furthermore, GARFT and AICARFT were homogeneously expressed in the patient samples. Folate uptake mechanisms by RFC and activation by FPGS were associated with clinical benefit from pemetrexed treatment.

Nagai H, Yasuda H, Hatachi Y, et al.
Nitric oxide (NO) enhances pemetrexed cytotoxicity via NO‑cGMP signaling in lung adenocarcinoma cells in vitro and in vivo.
Int J Oncol. 2012; 41(1):24-30 [PubMed] Related Publications
Pemetrexed (PEM) is a novel, multitargeted, antifolate, antineoplastic agent for the treatment of non-small cell lung cancer and malignant pleural mesothelioma. Additional effects of nitric oxide (NO) donors on the chemosensitivity of cancers have been reported. However, the effects of an NO donor on PEM-induced cytotoxicity remain unknown. In this study, we investigated the effects of the NO donors, NOC-18 on the cytotoxicity in A549 cells in vitro and of nitroglycerin (GTN), on the tumor growth of Lewis lung carcinoma cells in a murine syngraft model treated with PEM. The effects of NO donors on the expression of proteins associated with PEM metabolism, including thymidylate synthase (TS), reduced folate carrier 1 (RFC1), folylpolyglutamate synthase (FPGS), γ-glutamyl hydrolase (GGH) and multidrug resistance-related protein (MRP)5, and the effects of cyclic guanosine mono-phosphate (cGMP) signaling on these proteins were examined in A549 cells. Treatment with 100 nM NOC-18 for 3 days significantly enhanced PEM-induced cytotoxicity and increased the expression of RFC1 and FPGS in A549 cells. Treatment with 10 nM 8-bromo-cGMP (8-Br-cGMP) for 3 days also increased the expression of RFC1 and FPGS in A549 cells. 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 µm) significantly reversed the increase in RFC1 and FPGS expression induced by 100 nM NOC-18 in A549 cells. Combination therapy with GTN and PEM significantly reduced tumor growth compared with PEM alone in the syngraft model. The enhanced antitumor effect of GTN plus PEM was significantly reversed by the concomitant addition of ODQ. These findings suggest that NO donors, such as NOC-18 and GTN, enhance the anticancer effects of PEM by increasing the RFC1 and FPGS expression and stimulating cGMP signaling pathways in cancer cells.

Muhale FA, Wetmore BA, Thomas RS, McLeod HL
Systems pharmacology assessment of the 5-fluorouracil pathway.
Pharmacogenomics. 2011; 12(3):341-50 [PubMed] Free Access to Full Article Related Publications
AIM: To assess the impact of the 5-fluorouracil (5-FU) drug-pathway genes on cytotoxicity, and determine whether loss-of-function analyses coupled with functional assays can help prioritize pharmacogenomic candidate genes.
MATERIALS & METHODS: Dose-response experiments were used to quantify the phenotype of sensitivity to 5-FU following the specific knockdown of genes selected from the 5-FU PharmGKB drug pathway in three human colorectal cell lines. Changes in sensitivity were considered significant if the IC(50) for shRNA-exposed cells were three standard deviations outside the mean IC(50) for control-treated cells.
RESULTS: Of the 24 genes analyzed, 13 produced significant changes on the phenotype of sensitivity to 5-FU (DHFR, DPYS, DTYMK, DUT, FPGS, GGH, NME1, NT5C, RRM1, TYMS, UCK2, UNG and UMPS).
CONCLUSION: The RNAi screening strategy enabled prioritization of the genes from the 5-FU drug pathway. Further validation of the genes credentialed in this study should include gene activity or expression and mutation analyses of clinical samples.

Tsukioka S, Sakamoto E, Tsujimoto H, et al.
In vivo evidence for a significant role of folylpolyglutamate synthase in combined chemotherapy with oral fluoropyrimidine, UFT or S-1, and leucovorin.
Oncol Rep. 2011; 25(5):1407-12 [PubMed] Related Publications
Combined chemotherapy with 5-fluorouracil and leucovorin (LV) has been widely used for the treatment of patients with colorectal cancer. Given that LV effects are attributable to increased levels of reduced folate in cancer cells, we attempted here to show the in vivo role of folylpolyglutamate synthetase (FPGS), which stabilizes intracellular reduced folate, in the anticancer activities of oral fluoropyrimidines, UFT or S-1, combined with LV. To this end, HCT-15 human colon cancer cells were knocked down for FPGS expression by RNA interference. The cell line stably expressing FPGS shRNA (FPGS shRNA HCT-15) was cloned and transferred subcutaneously into nude mice fed a low-folate diet. FPGS shRNA HCT-15 tumors expressed a significantly lower level of FPGS at protein and mRNA levels than parental HCT-15 cells, and the levels of reduced folate in FPGS shRNA HCT-15 tumors became 57% of those in parent after a single administration of 10 mg/kg of LV. Notably, FPGS downregulation did not affect the tumor growth or sensitivity to fluoropyrimidine. Importantly, we observed that LV given for 14 days failed to enhance the anticancer effects of UFT and S-1 in FPGS shRNA HCT-15. This was in keeping with the results that LV did not increase the ternary complex of TS, FdUMP and reduced folate. In conclusion, the present results provide in vivo evidence that intratumor FPGS plays an important role in the efficacy of oral fluoropyrimidine plus LV therapy for colorectal cancer.

Panetta JC, Sparreboom A, Pui CH, et al.
Modeling mechanisms of in vivo variability in methotrexate accumulation and folate pathway inhibition in acute lymphoblastic leukemia cells.
PLoS Comput Biol. 2010; 6(12):e1001019 [PubMed] Free Access to Full Article Related Publications
Methotrexate (MTX) is widely used for the treatment of childhood acute lymphoblastic leukemia (ALL). The accumulation of MTX and its active metabolites, methotrexate polyglutamates (MTXPG), in ALL cells is an important determinant of its antileukemic effects. We studied 194 of 356 patients enrolled on St. Jude Total XV protocol for newly diagnosed ALL with the goal of characterizing the intracellular pharmacokinetics of MTXPG in leukemia cells; relating these pharmacokinetics to ALL lineage, ploidy and molecular subtype; and using a folate pathway model to simulate optimal treatment strategies. Serial MTX concentrations were measured in plasma and intracellular MTXPG concentrations were measured in circulating leukemia cells. A pharmacokinetic model was developed which accounted for the plasma disposition of MTX along with the transport and metabolism of MTXPG. In addition, a folate pathway model was adapted to simulate the effects of treatment strategies on the inhibition of de novo purine synthesis (DNPS). The intracellular MTXPG pharmacokinetic model parameters differed significantly by lineage, ploidy, and molecular subtypes of ALL. Folylpolyglutamate synthetase (FPGS) activity was higher in B vs T lineage ALL (p<0.005), MTX influx and FPGS activity were higher in hyperdiploid vs non-hyperdiploid ALL (p<0.03), MTX influx and FPGS activity were lower in the t(12;21) (ETV6-RUNX1) subtype (p<0.05), and the ratio of FPGS to γ-glutamyl hydrolase (GGH) activity was lower in the t(1;19) (TCF3-PBX1) subtype (p<0.03) than other genetic subtypes. In addition, the folate pathway model showed differential inhibition of DNPS relative to MTXPG accumulation, MTX dose, and schedule. This study has provided new insights into the intracellular disposition of MTX in leukemia cells and how it affects treatment efficacy.

Adjei AA, Salavaggione OE, Mandrekar SJ, et al.
Correlation between polymorphisms of the reduced folate carrier gene (SLC19A1) and survival after pemetrexed-based therapy in non-small cell lung cancer: a North Central Cancer Treatment Group-based exploratory study.
J Thorac Oncol. 2010; 5(9):1346-53 [PubMed] Free Access to Full Article Related Publications
PURPOSE: To correlate polymorphisms in genes involved in the transport, activation, and inactivation of pemetrexed with the outcome of patients with advanced non-small cell lung cancer (NSCLC) treated with pemetrexed.
EXPERIMENTAL DESIGN: Data from a phase II NSCLC trial evaluating the optimal schedule of gemcitabine and pemetrexed were used. All patients with available DNA were genotyped for polymorphisms in FPGS, GGH, and SLC19A1 genes. Patients with various genotypes were compared for efficacy and adverse events resulting from pemetrexed.
RESULTS: Fifty-four patients had genotype results for all polymorphisms studied. Patients with the homozygous variant genotypes for SLC19A1 IVS4(2117) C>T, IVS5(9148) C>A, and wild-type genotype for exon6(2522) C>T had a significantly better overall survival compared with their counterparts (median overall survival in months: 8.9 [CC] versus 14.0 [CT] versus 16.7 [TT]; 9.4 [CC] versus 10.3 [CA] versus 22.7 [AA]; and 22.7 [CC] versus 10.3 [CT] versus 9.4 [TT] respectively; all log rank p = 0.03). Patients with the heterozygous TC genotype for GGH IVS5(1042) T>C had greater rates of confirmed response + stable disease compared with the TT genotype (85% versus 60%; odds ratio = 4.0; p = 0.06). A greater risk for grade 3/4 SGPT (ALT) elevation was observed in patients heterozygous (GA) for the FPGS IVS1 (28) G>A polymorphism compared with the GG genotype (43% versus 13%; odds ratio = 5.0, p = 0.07). All results were largely consistent within patients with nonsquamous (n = 40) histology.
CONCLUSION: Polymorphisms in SLC1A91 seem to predict for survival differences in pemetrexed-treated NSCLC. Additionally, polymorphisms in GGH and FPGS have marginal associations with response and adverse event. These results should be validated in larger prospective studies using pemetrexed.

Leclerc GJ, Mou C, Leclerc GM, et al.
Histone deacetylase inhibitors induce FPGS mRNA expression and intracellular accumulation of long-chain methotrexate polyglutamates in childhood acute lymphoblastic leukemia: implications for combination therapy.
Leukemia. 2010; 24(3):552-62 [PubMed] Related Publications
Children with acute lymphoblastic leukemia (ALL) diagnosed with resistant phenotypes, and those who relapse, have a dismal prognosis for cure. The antifolate methotrexate (MTX), a universal component of ALL therapies, is metabolized by folylpoly-gamma-glutamate synthetase (FPGS) into long-chain polyglutamates (MTX-PG(3-7)), resulting in enhanced cytotoxicity from prolonged inhibition of dihydrofolate reductase (DHFR) and thymidylate synthetase (TS). Using DNaseI assays, we identified a hypersensitive site upstream from exon-1, suggesting chromatin remodeling could alter FPGS expression. We demonstrated that histone deacetylase-1 (HDAC1) is recruited by NFY and Sp1 transcription factors to the FPGS promoter in ALL cell lines. We examined the effect of histone deacetylase inhibitors (HDACIs) sodium butyrate and suberoylanilide hydroxamic acid (SAHA) on the expression of FPGS and other folate-related genes. HDACIs increased FPGS mRNA expression by 2- to 5-fold, whereas DHFR and TS mRNA expression was decreased. Combination treatment with MTX plus SAHA significantly increased cytotoxicity and apoptosis in B- and T-ALL cell lines as compared with each drug alone (CI

Figueiredo JC, Levine AJ, Lee WH, et al.
Genes involved with folate uptake and distribution and their association with colorectal cancer risk.
Cancer Causes Control. 2010; 21(4):597-608 [PubMed] Free Access to Full Article Related Publications
Folate status is an important predictor of colorectal cancer risk. Common genetic variants in genes involved in regulating cellular folate levels might also predict risk, but there are limited data on this issue. We conducted a family-based case-control association study of variants in four genes involved in folate uptake and distribution: FOLR1, FPGS, GGH and SLC19A1, using 1,750 population-based and 245 clinic-based cases of pathologically confirmed colorectal cancer and their unaffected relatives participating in the Colon Cancer Family Registries. Standardized questionnaires, administered to all participants, collected information on risk factors and diet. Standard molecular techniques were used to determine microsatellite instability (MSI) status on cases. tagSNPs (n = 29) were selected based on coverage as assessed by pairwise r2. We found no evidence that tagSNPs in these genes were associated with risk of colorectal cancer. For the SLC19A1-rs1051266 (G80A, Arg27His) missense polymorphism, the A/A genotype was not associated with risk of colorectal cancer using population-based (OR = 1.00; 95% CI = 0.81-1.23) or clinic-based (OR = 0.75; 95% CI = 0.44-1.29) families compared to the G/A and G/G genotypes. We found no evidence that the association between any tagSNP and CRC risk was modified by multivitamin use, folic acid use and dietary folate intake and total folate intake. The odds ratios were similar, irrespective of MSI status, tumor subsite and family history of colorectal cancer. In conclusion, we found no significant evidence that genetic variants in FOLR1, GGH, FPGS and SLC19A1 are associated with the risk of colorectal cancer.

Nannizzi S, Veal GJ, Giovannetti E, et al.
Cellular and molecular mechanisms for the synergistic cytotoxicity elicited by oxaliplatin and pemetrexed in colon cancer cell lines.
Cancer Chemother Pharmacol. 2010; 66(3):547-58 [PubMed] Free Access to Full Article Related Publications
PURPOSE: Oxaliplatin effect in the treatment of colorectal cancer is improved upon combination with thymidylate synthase (TS) inhibitors. Pemetrexed is polyglutamated by the folylpolyglutamate synthase (FPGS) and blocks folate metabolism and DNA synthesis by inhibiting TS, dihydrofolate reductase (DHFR) and glycinamide ribonucleotide formyltransferase (GARFT). The present study evaluates the pharmacological interaction between oxaliplatin and pemetrexed in colorectal cancer cells.
METHODS: Human HT29, WiDr, SW620 and LS174T cells were treated with oxaliplatin and pemetrexed. Drug interaction was studied using the combination index method, while cell cycle was investigated with flow cytometry. The effects of drugs on Akt phosphorylation and apoptosis were studied with ELISA and fluorescence microscopy, respectively. RT-PCR analysis was performed to assess whether drugs modulated the expression of pemetrexed targets and of genes involved in DNA repair (ERCC1 and ERCC2). Finally, platinum-DNA adduct levels were detected by ultra-sensitive multi-collector inductively coupled plasma mass spectrometry (ICP-MS).
RESULTS: A dose-dependent inhibition of cell growth was observed after drug exposure, while a synergistic interaction was detected preferentially with sequential combinations. Oxaliplatin enhanced cellular population in the S-phase. Drug combinations increased apoptotic indices with respect to single agents, and both drugs inhibited Akt phosphorylation. RT-PCR analysis showed a correlation between the FPGS/(TS x DHFR x GARFT) ratio and pemetrexed sensitivity, as well as a downregulation of ERCC1, ERCC2, TS, DHFR and GARFT after drug exposure. In addition, pretreatment with pemetrexed resulted in an increase of oxaliplatin-DNA adducts.
CONCLUSION: These data demonstrate that oxaliplatin and pemetrexed synergistically interact against colon cancer cells, through modulation of cell cycle, inhibition of Akt phosphorylation, induction of apoptosis and modulation of gene expression.

Adjei AA, Mandrekar SJ, Dy GK, et al.
Phase II trial of pemetrexed plus bevacizumab for second-line therapy of patients with advanced non-small-cell lung cancer: NCCTG and SWOG study N0426.
J Clin Oncol. 2010; 28(4):614-9 [PubMed] Free Access to Full Article Related Publications
PURPOSE: To evaluate the efficacy and toxicity of pemetrexed combined with bevacizumab as second-line therapy for patients with advanced non-small-cell lung cancer (NSCLC) and to correlate allelic variants in pemetrexed-metabolizing genes with clinical outcome.
PATIENTS AND METHODS: Patients with previously treated NSCLC received pemetrexed (500 mg/m(2) intravenous) combined with bevacizumab (15 mg/kg intravenous) every 3 weeks. The primary end point, evaluated using a one-stage Fleming design for detecting a true success rate of at least 70%, was the proportion of patients who were progression free and on treatment at 3 months. Polymorphisms in genes responsible for pemetrexed transport (reduced folate carrier [SLC19A1]) and metabolism (folylpolyglutamate synthase [FPGS] and gamma-glutamyl hydrolase [GGH]) evaluated in germline DNA (blood) were correlated with treatment outcome.
RESULTS: Forty-eight evaluable patients (14 females and 34 males) received a median of four cycles (range, one to 20 cycles). The most common grade 3 or 4 nonhematologic adverse events (AEs) were fatigue (13%), dyspnea (10%), and thrombosis (10%). Grade 3 or 4 hematologic AEs were neutropenia (19%) and lymphopenia (13%). Twenty-four (57%; 95% CI, 41% to 72%) of the first 42 patients met the success criteria. Median overall survival (OS) and progression-free survival (PFS) times were 8.6 and 4.0 months, respectively. The exon 6 (2522)C-->T polymorphism in SLC19A1 correlated with 3-month progression-free status (P = .01) and with PFS (P = .05). The IVS1(1307)C-->T polymorphism in GGH correlated with OS (P = .04).
CONCLUSION: The study did not meet its primary end point. However, the median PFS time of 4 months is promising. Pharmacogenetic studies in larger cohorts are needed to definitively identify polymorphisms that predict for survival and toxicity of pemetrexed.

Ozasa H, Oguri T, Uemura T, et al.
Significance of thymidylate synthase for resistance to pemetrexed in lung cancer.
Cancer Sci. 2010; 101(1):161-6 [PubMed] Related Publications
Pemetrexed (MTA) is a multitargeted antifolate with promising clinical activity in lung cancer. We exposed the small cell lung cancer cell line PC6 to stepwise-increasing pemetrexed concentrations of 0.4, 1.6, and 4.0 microm, and established three pemetrexed-resistant lung cancer cell lines: PC6/MTA-0.4, PC6/MTA-1.6, and PC6/MTA-4.0 cells. To investigate the mechanisms of acquired resistance to pemetrexed, we measured the expression levels of the thymidylate synthase (TS), reduced folate carrier (RFC), and folylpoly-gamma-glutamate synthetase (FPGS) genes. TS gene expression was significantly increased in PC6/MTA-1.6 and PC6/MTA-4.0 cells relative to parental cells in a pemetrexed dose-dependent manner. In contrast, the levels of RFC gene expression in PC6/MTA-0.4 cells and FPGS in PC6/MTA-1.6 cells were significantly decreased, whereas the levels of both genes were restored in PC6/MTA-4.0 cells. Knockdown of TS expression using siRNA enhanced pemetrexed cytotoxicity in PC6/MTA-4.0 cells. The expression level of the TS gene was significantly correlated with the concentration of pemetrexed for 50% cell survival (IC(50)) in 11 non-small cell lung cancer cell lines. These results suggest that the alteration of molecular pharmacological factors in relation with pemetrexed resistance is dose-dependent, and that up-regulation of the expression of the TS gene may have an important role in the acquired resistance to pemetrexed. In addition, TS may be a predictive marker for pemetrexed sensitivity in lung cancer.

Sadahiro S, Suzuki T, Maeda Y, et al.
Molecular determinants of folate levels after leucovorin administration in colorectal cancer.
Cancer Chemother Pharmacol. 2010; 65(4):735-42 [PubMed] Related Publications
PURPOSE: Oral leucovorin (LV) is used with uracil/tegafur (UFT) in the treatment of colorectal cancer (CRC). In order to find the factors related to the efficacy of LV in enhancing the antitumour effect of UFT, we investigated the relationships between the reduced folate levels in the CRC tissue after LV administration and the gene-expression levels of folate-metabolizing enzymes and folate transporters.
METHODS: The subjects were 60 CRC patients, scheduled to undergo surgery. The control group (n = 30) did not receive LV. Three groups (n = 10 for each) received a single dose of oral LV at 25 mg, 4, 12 or 18 h before surgery (LV 4 h, LV 12 h or LV 18 h groups, respectively). The reduced folate levels in plasma and tissues were measured by high-performance liquid chromatography (HPLC) or a thymidylate synthase-FdUMP binding assay, respectively. The intratumoral expression levels of 34 genes were quantitatively evaluated with a real-time polymerase chain reaction (RT-PCR) assay.
RESULTS: The reduced folate levels persisted for a longer period of time in the CRC tissue than in the plasma after LV administration. A multivariate logistic regression analysis revealed that high folylpolyglutamate synthase (FPGS) gene expression, low gamma-glutamyl hydrolase (GGH) gene expression and low ATP-binding cassette sub-family C, number 1 (ABCC1) gene expression in CRC tissues were predictive factors for a high reduced folate level after LV administration.
CONCLUSIONS: The expression level of FPGS, GGH and ABCC1 in CRC tissues could predict the reduced folate level after LV administration, and these factors may determine the efficacy of LV treatment.

Fotoohi AK, Assaraf YG, Moshfegh A, et al.
Gene expression profiling of leukemia T-cells resistant to methotrexate and 7-hydroxymethotrexate reveals alterations that preserve intracellular levels of folate and nucleotide biosynthesis.
Biochem Pharmacol. 2009; 77(8):1410-7 [PubMed] Related Publications
In vitro treatment of human T-cell leukemia cells with 7-hydroxymethotrexate, the major metabolite of methotrexate resulted in acquired resistance as a result of the complete loss of folypolyglutamate synthetase (FPGS) activity. This was in contradistinction to the major modality of antifolate resistance of impaired drug transport in leukemia cells exposed to methotrexate. To identify the genes associated with methotrexate and 7-hydroxymethotrexate resistance, we herein explored the patterns of genome-wide expression profiles in these antifolte-resistant leukemia sublines. mRNA levels of the reduced folate carrier, the primary influx transporter of folates and antifolates, were down-regulated more than two-fold in methotrexate-resistant cells. The dramatic loss of FPGS activity in 7-hydroxymethotrexate-resistant cells was associated with alterations in the expression of various genes aimed at preserving reduced folates and/or enhancing purine nucleotide biosynthesis, e.g. methylene tetrahydrofolate reductase, glycinamide ribonucleotide formyltransferase, adenosine deaminase, cystathionine beta synthase, as well as the ATP-dependent folate exporters BCRP/ABCG2 and MRP1/ABCC1. The observed changes in gene expression were generally not paralleled by acquired DNA copy numbers alterations, suggesting transcriptional regulatory mechanisms. Interestingly, gene expression of DNA/RNA metabolism and transport genes were more profoundly altered in methotrexate-resistant subline, whereas in 7-hydroxymethotrexate-resistant cells, the most profoundly affected groups of genes were those encoding for proteins involved in metabolism and cellular proliferation. Thus, the present investigation provides evidence that 7-hydroxymethotrexate induces gene expression alterations and an antifolate resistance modality that are distinct from its parent drug methotrexate.

Stark M, Wichman C, Avivi I, Assaraf YG
Aberrant splicing of folylpolyglutamate synthetase as a novel mechanism of antifolate resistance in leukemia.
Blood. 2009; 113(18):4362-9 [PubMed] Related Publications
Folylpoly-gamma-gluatamate synthetase (FPGS) catalyzes the polyglutamylation and thus intracellular retention of folates and antifolates (eg, methotrexate; MTX) through the addition of multiple glutamate equivalents to their gamma-carboxyl residue. Since polyglutamylation of antifolates is crucial for their pharmacological activity in leukemia, loss of FPGS function results in decreased cellular levels of polyglutamylation-dependent antifolates and consequent drug resistance. Whereas resistance to pulse exposure to antifolates is frequently associated with loss of FPGS activity, the underlying molecular mechanism remains elusive. Here we explored the molecular basis of antifolate resistance in human MTX-resistant leukemia cell lines displaying marked loss of FPGS activity. We demonstrate that these MTX-resistant cells exhibit impaired splicing of FPGS mRNA based on intron retention and/or exon skipping, thereby resulting in loss of FPGS function due to premature translation termination. Furthermore, analysis of FPGS transcripts in blood or bone marrow specimens from patients with acute lymphoblastic leukemia revealed exon 12 skipping, both at diagnosis and at relapse, the latter of which occurs after high-dose MTX-containing chemotherapy. These results constitute the first demonstration of the loss of FPGS function via aberrant mRNA splicing, thereby resulting in loss of antifolate retention and drug resistance. The clinical ramifications of these novel findings are discussed.

Ifergan I, Assaraf YG
Molecular mechanisms of adaptation to folate deficiency.
Vitam Horm. 2008; 79:99-143 [PubMed] Related Publications
Folic acid is an essential vitamin for a wide spectrum of biochemical reactions; however, unlike bacteria and plants, mammals are devoid of folate biosynthesis and thus must obtain this cofactor from exogenous sources. Therefore, folate deficiency may impair the de novo biosynthesis of purines and thymidylate and thereby disrupt DNA and RNA metabolism, homocysteine remethylation, methionine biosynthesis, and subsequent formation of S-adenosylmethionine (the universal methyl donor) which in turn may lead to altered methylation reactions. This impaired folate-dependent intracellular metabolism can lead to several key pathologies including, for example, megaloblastic anemia, homocysteinemia, cardiovascular disease, embryonic defects, in particular neural tube defects (NTDs), congenital heart defects, and possibly cancer. The current review presents and evaluates the up-to-date knowledge regarding the molecular mechanisms underlying cellular survival and/or adaptation to folate deficiency or insufficiency. These mechanisms of adaptation to folate deficiency generally associated with folate uptake, intracellular folate retention, folate-dependent metabolism, and active folate efflux specifically include: (a) Up- or downregulation of various folate-dependent enzymes like dihydrofolate reductase (DHFR) and thymidylate synthase (TS), (b) Cellular retention of folates via polyglutamylation by the enzyme folylpoly-gamma-glutamate synthetase (FPGS), (c) Overexpression of folate influx systems including the reduced folate carrier (RFC), folate receptor (FR) as well as the proton-coupled folate transporter (PCFT), a recently identified intestinal folate influx transporter optimally functioning at the acidic microclimate of the upper intestinal epithelium, (d) Downregulation of ATP-driven folate efflux transporters of the multidrug resistance protein (MRP; ABCC) family and breast cancer resistance protein (BCRP; ABCG2) that belong to the multidrug resistance (MDR) efflux transporters of the ATP-binding cassette (ABC) superfamily. Moreover, the intricate interplay between various components of the adaptive response to folate deprivation is also discussed.

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