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Synthesis of (6R)- and (6S)-5,10-dideazatetrahydrofolate oligo-gamma-glutamates: kinetics of multiple glutamate ligations catalyzed by folylpoly-gamma-glutamate synthetase.

ABSTRACT: Folylpoly-gamma-glutamate synthetase (FPGS, EC 6.3.2.17) catalyzes the ATP-dependent ligation of glutamic acid to reduced folates including (6S)-5,6,7,8-tetrahydrofolate (H4PteGlu), as well as to anticancer drugs such as 5,10-dideaza-5,6,7,8-tetrahydrofolate ((6R)-DDAH4PteGlu1, (6R)-DDATHF, Lometrexol). Synthesis of unlabeled mono- and polyglutamates, DDAH4PteGlu(n) (6R, n = 1-6; 6S, n = 1-2), as well as (6R)-DDAH4Pte[14C]Glu1, was effected from (6R)- or (6S)-5,10-dideazatetrahydropteroyl azide and glutamic acid, H-Glu-gamma-Glu(n)-gamma-Glu-OH (n = 0-4), or [14C]glutamic acid, respectively. These compounds were evaluated as FPGS substrates to determine steady-state kinetic constants. Michaelis-Menten kinetics were observed for (6R)-DDAH4PteGlu1, the isomer corresponding to H(4)PteGlu, whereas marked substrate inhibition was observed for (6S)-DDAH4PteGlu(n) (n = 1-2) and (6R)-DDAH4PteGlu(n) (n = 2-5), but not (6R)-DDAH4PteGlu6. Multiple ligation of glutamate renders a quantitative analysis of these data difficult. However, approximate values of K(M) = 0.65-1.6 microM and K(I) = 144-417 microM for DDAH4PteGlu(n) were obtained using a simple kinetic model.

SUBMITTER: Tomsho JW

PROVIDER: S-EPMC1989673 | biostudies-literature | 2005 Sep

REPOSITORIES: biostudies-literature

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Synthesis of (6R)- and (6S)-5,10-dideazatetrahydrofolate oligo-gamma-glutamates: kinetics of multiple glutamate ligations catalyzed by folylpoly-gamma-glutamate synthetase.

Tomsho John W JW McGuire John J JJ Coward James K JK

Organic & biomolecular chemistry 20050815 18

Folylpoly-gamma-glutamate synthetase (FPGS, EC 6.3.2.17) catalyzes the ATP-dependent ligation of glutamic acid to reduced folates including (6S)-5,6,7,8-tetrahydrofolate (H4PteGlu), as well as to anticancer drugs such as 5,10-dideaza-5,6,7,8-tetrahydrofolate ((6R)-DDAH4PteGlu1, (6R)-DDATHF, Lometrexol). Synthesis of unlabeled mono- and polyglutamates, DDAH4PteGlu(n) (6R, n = 1-6; 6S, n = 1-2), as well as (6R)-DDAH4Pte[14C]Glu1, was effected from (6R)- or (6S)-5,10-dideazatetrahydropteroyl azide ...[more]

PMID: 16132101

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Project description:BACKGROUND: Expression of folylpoly-gamma-glutamate synthetase (FPGS) gene is two- to three-fold higher in B-precursor ALL (Bp- ALL) than in T-lineage ALL (T-ALL) and correlates with intracellular accumulation of methotrexate (MTX) polyglutamates and lymphoblast sensitivity to MTX. In this report, we investigated the molecular regulatory mechanisms directing FPGS gene expression in Bp-ALL and T-ALL cells. METHODS: To determine FPGS transcription rate in Bp-ALL and T-ALL we used nuclear run-on assays. 5'-RACE was used to uncover potential regulatory regions involved in the lineage differences. We developed a luciferase reporter gene assay to investigate FPGS promoter/enhancer activity. To further characterize the FPGS proximal promoter, we determined the role of the putative transcription binding sites NFY and E-box on FPGS expression using luciferase reporter gene assays with substitution mutants and EMSA. RESULTS: FPGS transcription initiation rate was 1.6-fold higher in NALM6 vs. CCRF-CEM cells indicating that differences in transcription rate led to the observed lineage differences in FPGS expression between Bp-ALL and T-ALL blasts. Two major transcripts encoding the mitochondrial/cytosolic and cytosolic isoforms were detected in Bp-ALL (NALM6 and REH) whereas in T-ALL (CCRF-CEM) cells only the mitochondrial/cytosolic transcript was detected. In all DNA fragments examined for promoter/enhancer activity, we measured significantly lower luciferase activity in NALM6 vs. CCRF-CEM cells, suggesting the need for additional yet unidentified regulatory elements in Bp-ALL. Finally, we determined that the putative transcription factor binding site NFY, but not E-box, plays a role in FPGS transcription in both Bp- and T-lineage. CONCLUSION: We demonstrated that the minimal FPGS promoter region previously described in CCRF-CEM is not sufficient to effectively drive FPGS transcription in NALM6 cells, suggesting that different regulatory elements are required for FPGS gene expression in Bp-cells. Our data indicate that the control of FPGS expression in human hematopoietic cells is complex and involves lineage-specific differences in regulatory elements, transcription initiation rates, and mRNA processing. Understanding the lineage-specific mechanisms of FPGS expression should lead to improved therapeutic strategies aimed at overcoming MTX resistance or inducing apoptosis in leukemic cells.

Project description:Pemetrexed-based chemotherapy represents the standard of care in first-line treatment of advanced malignant pleural mesothelioma (MPM). However, there are no established predictors of clinical benefit. Pemetrexed inhibits multiple enzymes involved in pyrimidine and purine synthesis, but the main target is thymidylate synthase (TS). After cellular uptake pemetrexed is converted into more effective polyglutamated forms by folylpoly-?-glutamate synthetase (FPGS). We hypothesized that FPGS and TS protein expressions are associated with clinical outcome after pemetrexed-based chemotherapy.Pretreatment tumor samples from 84 patients with histologically confirmed MPM, who received pemetrexed combined with platinum (79 of 84) or single-agent pemetrexed (5 of 84) as first-line treatment, were retrospectively analyzed. FPGS and TS protein expressions were semiquantitatively assessed by using the Hybrid (H)-scoring system (range, 0-300). H-scores were correlated with radiological response according to modified Response Evaluation Criteria in Solid Tumors, progression-free survival (PFS) and overall survival (OS).Median H-score of the entire cohort was 230 for FPGS (range, 100-300), and 210 for TS (range, 100-300). High FPGS protein expression was significantly associated with longer PFS (pCOX = 0.0337), better objective tumor response (partial response versus stable disease + progressive disease; pKW = 0.003), and improved disease-control rate (partial response + stable disease versus progressive disease; pKW = 0.0208), but not with OS. In addition, high TS protein expression was associated with progressive disease under pemetrexed-based therapy (p = 0.0383), and shorter OS (pCOX = 0.0071), but no association with PFS was observed.FPGS and TS expressions were associated with clinical response and outcome to pemetrexed-based first-line chemotherapy in MPM. Prospective evaluation of FPGS and TS expressions and their prognostic/predictive power in MPM patients is warranted.

Dataset Information

Synthesis of (6R)- and (6S)-5,10-dideazatetrahydrofolate oligo-gamma-glutamates: kinetics of multiple glutamate ligations catalyzed by folylpoly-gamma-glutamate synthetase.

Publications

Synthesis of (6R)- and (6S)-5,10-dideazatetrahydrofolate oligo-gamma-glutamates: kinetics of multiple glutamate ligations catalyzed by folylpoly-gamma-glutamate synthetase.

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