Inhibition of phosphoribosylaminoimidazolecarboxamide transformylase by methotrexate and dihydrofolic acid polyglutamates

Inhibition of mitochondrial folate metabolism drives differentiation through mTORC1 mediated purine sensing

Supporting cell proliferation through nucleotide biosynthesis is an essential requirement for cancer cells. Hence, inhibition of folate-mediated one carbon (1C) metabolism, which is required for nucleotide synthesis, has been successfully exploited in anti-cancer therapy. Here, we reveal that mitochondrial folate metabolism is upregulated in patient-derived leukaemic stem cells (LSCs). We demonstrate that inhibition of mitochondrial 1C metabolism through impairment of de novo purine synthesis has a cytostatic effect on chronic myeloid leukaemia (CML) cells. Consequently, changes in purine nucleotide levels lead to activation of AMPK signalling and suppression of mTORC1 activity. Notably, suppression of mitochondrial 1C metabolism increases expression of erythroid differentiation markers. Moreover, we find that increased differentiation occurs independently of AMPK signalling and can be reversed through reconstitution of purine levels and reactivation of mTORC1. Of clinical relevance, we identify that combination of 1C metabolism inhibition with imatinib, a frontline treatment for CML patients, decreases the number of therapy-resistant CML LSCs in a patient-derived xenograft model. Our results highlight a role for folate metabolism and purine sensing in stem cell fate decisions and leukaemogenesis.

Exploring Psoriasis Inflammatory Microenvironment by NanoString Technologies

Psoriasis is a chronic inflammatory skin disease whose molecular mechanisms and microenvironment are poorly understood. We performed gene expression analysis through the nCounter® PanCancer Immune Profiling Panel (NanoString Technologies, Seattle, WA, USA) on 22 FFPE punch biopsies from 19 psoriasis-affected patients. A subset of five cases was analyzed before (T0) and after 6 months (T6) of treatment with dimethyl fumarate (DMF) to address immune microenvironment changes. Molecular comparisons according to biopsy site and age of onset showed a different distribution of innate immune cells (mast cells, macrophages, NK cells, and DC cells) and pathways (complement regulation and transporter functions). The analysis according to PASI (Psoriasis Area and Severity Index) led to non-significant results, suggesting no link between molecular expression profile and clinical amount of skin disease. In DMF-treated patients, we observed a strong immunomodulatory effect after treatment: A subversion of exhausted CD8 T cells, NK CD56dim cells, Tregs, neutrophils, CD45+ cells, T cells, B cells, and macrophages was reported between the two analyzed time-points, as well as the reduction in pro-inflammatory pathways and molecules, including cytotoxicity, pathogen defense, antigen processing, adhesion, cell cycle, chemokines, cytokines, and interleukins. The inflammatory psoriatic microenvironment can be modulated using DMF with encouraging results, achieving an immune-tolerant and non-inflammatory condition through the regulation of both innate and adaptive immunity.

Folate in maternal rheumatoid arthritis-filial autism spectrum disorder continuum

Rheumatoid Arthritis (RA) is an inflammatory autoimmune disease that affects women three times more than men. Epidemiological studies found that the incidence of Autism Spectrum Disorder (ASD), a neurological and developmental disorder, in children born to mothers suffering from RA is higher compared with the control population. Considering that the pathogenesis of ASD could be traced back to pregnancy and in uterine conditions, and the evidence of reduced folate levels in the brain of ASD-affected children, we aimed to study the role of folate, as an important nutritional factor during pregnancy, in associating maternal RA to ASD development in the offspring. Folate balance during RA could be influenced twice, initially during the immune activation associated with disease onset, and later during the treatment with anti-folate drugs, with a potential consequence of folate deficiency. Maternal folate deficiency during pregnancy could increase homocysteine levels, oxidative stress, and global DNA hypomethylation, all known risk factors in ASD pathogenesis. These effects could be intensified by genetic polymorphisms in the folate system, which were also found as genetic risk factors for both RA and ASD. The available evidence suggests that folate level as an important factor during RA, pregnancy and ASD could have pathological and therapeutical significance and should be carefully monitored and investigated in the RA-pregnancy-ASD axis.

AICAR promotes endothelium-independent vasorelaxation by activating AMP-activated protein kinase via increased ZMP and decreased ATP/ADP ratio in aortic smooth muscle

OBJECTIVES

AICAR, an adenosine analog, has been shown to exhibit vascular protective effects through activation of AMP-activated protein kinase (AMPK). However, it remains unclear as to whether adenosine kinase-mediated ZMP formation or adenosine receptor activation contributes to AICAR-mediated AMPK activation and/or vasorelaxant response in vascular smooth muscle.

METHODS AND RESULTS

In the present study using endothelium-denuded rat aortic ring preparations, isometric tension measurements revealed that exposure to 1 mM AICAR for 30 min resulted in inhibition of phenylephrine (1 μM)-induced smooth muscle contractility by ∼35%. Importantly, this vasorelaxant response by AICAR was prevented after pretreatment of aortic rings with an AMPK inhibitor (compound C, 40 µM) and adenosine kinase inhibitor (5-iodotubercidin, 1 µM), but not with an adenosine receptor blocker (8-sulfophenyltheophylline, 100 µM). Immunoblot analysis of respective aortic tissues showed that AMPK activation seen during vasorelaxant response by AICAR was abolished by compound C and 5-iodotubercidin, but not by 8-sulfophenyltheophylline, suggesting ZMP involvement in AMPK activation. Furthermore, LC-MS/MS MRM analysis revealed that exposure of aortic smooth muscle cells to 1 mM AICAR for 30 min enhanced ZMP level to 2014.9 ± 179.4 picomoles/mg protein (vs. control value of 8.5 ± 0.6; p<0.01), which was accompanied by a significant decrease in ATP/ADP ratio (1.08 ± 0.02 vs. 2.08 ± 0.06; p<0.01).

CONCLUSIONS

Together, the present findings demonstrate that AICAR-mediated ZMP elevation and the resultant AMPK activation in vascular smooth muscle contribute to vasorelaxation.

Methionine synthase supports tumour tetrahydrofolate pools

Mammalian cells require activated folates to generate nucleotides for growth and division. The most abundant circulating folate species is 5-methyl tetrahydrofolate (5-methyl-THF), which is used to synthesize methionine from homocysteine via the cobalamin-dependent enzyme methionine synthase (MTR). Cobalamin deficiency traps folates as 5-methyl-THF. Here, we show using isotope tracing that MTR is only a minor source of methionine in cell culture, tissues or xenografted tumours. Instead, MTR is required for cells to avoid folate trapping and assimilate 5-methyl-THF into other folate species. Under conditions of physiological extracellular folates, genetic MTR knockout in tumour cells leads to folate trapping, purine synthesis stalling, nucleotide depletion and impaired growth in cell culture and as xenografts. These defects are rescued by free folate but not one-carbon unit supplementation. Thus, MTR plays a crucial role in liberating THF for use in one-carbon metabolism.

The folate antagonist methotrexate diminishes replication of the coronavirus SARS-CoV-2 and enhances the antiviral efficacy of remdesivir in cell culture models

The search for successful therapies of infections with the coronavirus SARS-CoV-2 is ongoing. We tested inhibition of host cell nucleotide synthesis as a promising strategy to decrease the replication of SARS-CoV-2-RNA, thus diminishing the formation of virus progeny. Methotrexate (MTX) is an established drug for cancer therapy and to induce immunosuppression. The drug inhibits dihydrofolate reductase and other enzymes required for the synthesis of nucleotides. Strikingly, the replication of SARS-CoV-2 was inhibited by MTX in therapeutic concentrations around 1 µM, leading to more than 1000-fold reductions in virus progeny in Vero C1008 (Vero E6) and ~100-fold reductions in Calu-3 cells. Virus replication was more sensitive to equivalent concentrations of MTX than of the established antiviral agent remdesivir. MTX strongly diminished the synthesis of viral structural proteins and the amount of released virus RNA. Virus replication and protein synthesis were rescued by folinic acid (leucovorin) and also by inosine, indicating that purine depletion is the principal mechanism that allows MTX to reduce virus RNA synthesis. The combination of MTX with remdesivir led to synergistic impairment of virus replication, even at 100 nM MTX. The use of MTX in treating SARS-CoV-2 infections still awaits further evaluation regarding toxicity and efficacy in infected organisms, rather than cultured cells. Within the frame of these caveats, however, our results raise the perspective of a two-fold benefit from repurposing MTX for treating COVID-19. Firstly, its previously known ability to reduce aberrant inflammatory responses might dampen respiratory distress. In addition, its direct antiviral activity described here would limit the dissemination of the virus.

Folate metabolism: a re-emerging therapeutic target in haematological cancers

Folate-mediated one carbon (1C) metabolism supports a series of processes that are essential for the cell. Through a number of interlinked reactions happening in the cytosol and mitochondria of the cell, folate metabolism contributes to de novo purine and thymidylate synthesis, to the methionine cycle and redox defence. Targeting the folate metabolism gave rise to modern chemotherapy, through the introduction of antifolates to treat paediatric leukaemia. Since then, antifolates, such as methotrexate and pralatrexate have been used to treat a series of blood cancers in clinic. However, traditional antifolates have many deleterious side effects in normal proliferating tissue, highlighting the urgent need for novel strategies to more selectively target 1C metabolism. Notably, mitochondrial 1C enzymes have been shown to be significantly upregulated in various cancers, making them attractive targets for the development of new chemotherapeutic agents. In this article, we present a detailed overview of folate-mediated 1C metabolism, its importance on cellular level and discuss how targeting folate metabolism has been exploited in blood cancers. Additionally, we explore possible therapeutic strategies that could overcome the limitations of traditional antifolates.

Folate Intake Alters Mutation Frequency and Profiles in a Tissue- and Dose-Specific Manner in MutaMouse Male Mice

BACKGROUND

While cancer is common, its incidence varies widely by tissue. These differences are attributable to variable risk factors, such as environmental exposure, genetic inheritance, and lifetime number of stem cell divisions in a tissue. Folate deficiency is generally associated with increased risk for colorectal cancer (CRC) and acute lymphocytic leukemia (ALL). Conversely, high folic acid (FA) intake has also been associated with higher CRC risk.

OBJECTIVE

Our objective was to compare the effect of folate intake on mutant frequency (MF) and types of mutations in the colon and bone marrow of mice.

METHODS

Five-week-old MutaMouse male mice were fed a deficient (0 mg FA/kg), control (2 mg FA/kg), or supplemented (8 mg FA/kg) diet for 20 wk. Tissue MF was assessed using the lacZ mutant assay and comparisons made by 2-factor ANOVA. LacZ mutant plaques were sequenced using next-generation sequencing, and diet-specific mutation profiles within each tissue were compared by Fisher's exact test.

RESULTS

In the colon, the MF was 1.5-fold and 1.3-fold higher in mice fed the supplemented diet compared with mice fed the control (P = 0.001) and deficient (P = 0.008) diets, respectively. This contrasted with the bone marrow MF in the same mice where the MF was 1.7-fold and 1.6-fold higher in mice fed the deficient diet compared with mice fed the control (P = 0.02) and supplemented (P = 0.03) diets, respectively. Mutation profiles and signatures (mutation context) were tissue-specific.

CONCLUSIONS

Our data indicate that dietary folate intake affects mutagenesis in a tissue- and dose-specific manner in mice. Mutation profiles were generally tissue- but not dose-specific, suggesting that altered cellular folate status appears to interact with endogenous mutagenic mechanisms in each tissue to create a permissive context in which specific mutation types accumulate. These data illuminate potential mechanisms underpinning differences in observed associations between folate intake/status and cancer.

Psoriasis

Psoriasis is a common, chronic papulosquamous skin disease occurring worldwide, presenting at any age, and leading to a substantial burden for individuals and society. It is associated with several important medical conditions, including depression, psoriatic arthritis, and cardiometabolic syndrome. Its most common form, chronic plaque or psoriasis vulgaris, is a consequence of genetic susceptibility, particularly in the presence of the HLA-C*06:02 risk allele, and of environmental triggers such as streptococcal infection, stress, smoking, obesity, and alcohol consumption. There are several phenotypes and research has separated pustular from chronic plaque forms. Immunological and genetic studies have identified IL-17 and IL-23 as key drivers of psoriasis pathogenesis. Immune targeting of these cytokines and of TNFα by biological therapies has revolutionised the care of severe chronic plaque disease. Psoriasis cannot currently be cured, but management should aim to minimise physical and psychological harm by treating patients early in the disease process, identifying and preventing associated multimorbidity, instilling lifestyle modifications, and employing a personalised approach to treatment.

Effects of germline DHFR and FPGS variants on methotrexate metabolism and relapse of leukemia

Methotrexate (MTX) during maintenance therapy is essential for curing acute lymphoblastic leukemia (ALL), but dosing strategies aiming at adequate treatment intensity are challenged by interindividual differences in drug disposition. To evaluate genetic factors associated with MTX metabolism, we performed a genome-wide association study in 447 ALL cases from the Nordic Society for Pediatric Haematology and Oncology ALL2008 study, validating results in an independent set of 196 patients. The intergenic single-nucleotide polymorphism rs1382539, located in a regulatory element of DHFR, was associated with increased levels of short-chain MTX polyglutamates (P = 1.1 × 10-8) related to suppression of enhancer activity, whereas rs35789560 in FPGS (p.R466C, P = 5.6 × 10-9) was associated with decreased levels of long-chain MTX polyglutamates through reduced catalytic activity. Furthermore, the FPGS variant was linked with increased relapse risk (P = .044). These findings show a genetic basis for interpatient variability in MTX response and could be used to improve future dosing algorithms.

SARS-CoV-2 hijacks folate and one-carbon metabolism for viral replication

The recently identified Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is the cause of the COVID-19 pandemic. How this novel beta-coronavirus virus, and coronaviruses more generally, alter cellular metabolism to support massive production of ~30 kB viral genomes and subgenomic viral RNAs remains largely unknown. To gain insights, transcriptional and metabolomic analyses are performed 8 hours after SARS-CoV-2 infection, an early timepoint where the viral lifecycle is completed but prior to overt effects on host cell growth or survival. Here, we show that SARS-CoV-2 remodels host folate and one-carbon metabolism at the post-transcriptional level to support de novo purine synthesis, bypassing viral shutoff of host translation. Intracellular glucose and folate are depleted in SARS-CoV-2-infected cells, and viral replication is exquisitely sensitive to inhibitors of folate and one-carbon metabolism, notably methotrexate. Host metabolism targeted therapy could add to the armamentarium against future coronavirus outbreaks.

Metabolomic profiling of rare cell populations isolated by flow cytometry from tissues

Little is known about the metabolic regulation of rare cell populations because most metabolites are hard to detect in small numbers of cells. We previously described a method for metabolomic profiling of flow cytometrically isolated hematopoietic stem cells (HSCs) that detects 60 metabolites in 10,000 cells (Agathocleous et al., 2017). Here we describe a new method involving hydrophilic liquid interaction chromatography and high-sensitivity orbitrap mass spectrometry that detected 160 metabolites in 10,000 HSCs, including many more glycolytic and lipid intermediates. We improved chromatographic separation, increased mass resolution, minimized ion suppression, and eliminated sample drying. Most metabolite levels did not significantly change during cell isolation. Mouse HSCs exhibited increased glycerophospholipids relative to bone marrow cells and methotrexate treatment altered purine biosynthesis. Circulating human melanoma cells were depleted for purine intermediates relative to subcutaneous tumors, suggesting decreased purine synthesis during metastasis. These methods facilitate the routine metabolomic analysis of rare cells from tissues.

Perspectives of Methotrexate-Based Radioagents for Application in Nuclear Medicine

Methotrexate is a gold standard among disease modifying antirheumatic drugs and is also extensively used clinically in combination with oncological therapies. Thus, it is not surprising that nuclear medicine found an interest in methotrexate in the search for diagnostic and therapeutic solutions. Numerous folate-related radiopharmaceuticals have been proposed for nuclear medicine purposes; however, methotrexate radioagents represent only a minority. This imbalance results from the fact that methotrexate has significantly weaker affinity for folate receptors than folic acid. Nevertheless, radiolabeled methotrexate agents utilized as a tool for early detection and imaging of inflammation in rheumatoid arthritis patients gave promising results. Similarly, the use of multimodal MTX-release nanosystems may find potential applications in radiosynovectomy and theranostic approaches in folate receptor positive cancers.

In Silico Study Identified Methotrexate Analog as Potential Inhibitor of Drug Resistant Human Dihydrofolate Reductase for Cancer Therapeutics

Drug resistance is a core issue in cancer chemotherapy. A known folate antagonist, methotrexate (MTX) inhibits human dihydrofolate reductase (hDHFR), the enzyme responsible for the catalysis of 7,8-dihydrofolate reduction to 5,6,7,8-tetrahydrofolate, in biosynthesis and cell proliferation. Structural change in the DHFR enzyme is a significant cause of resistance and the subsequent loss of MTX. In the current study, wild type hDHFR and double mutant (engineered variant) F31R/Q35E (PDB ID: 3EIG) were subject to computational study. Structure-based pharmacophore modeling was carried out for wild type (WT) and mutant (MT) (variant F31R/Q35E) hDHFR structures by generating ten models for each. Two pharmacophore models, WT-pharma and MT-pharma, were selected for further computations, and showed excellent ROC curve quality. Additionally, the selected pharmacophore models were validated by the Guner-Henry decoy test method, which yielded high goodness of fit for WT-hDHFR and MT-hDHFR. Using a SMILES string of MTX in ZINC¹⁵ with the selections of 'clean', in vitro and in vivo options, 32 MTX-analogs were obtained. Eight analogs were filtered out due to their drug-like properties by applying absorption, distribution, metabolism, excretion, and toxicity (ADMET) assessment tests and Lipinski's Rule of five. WT-pharma and MT-pharma were further employed as a 3D query in virtual screening with drug-like MTX analogs. Subsequently, seven screening hits along with a reference compound (MTX) were subjected to molecular docking in the active site of WT- and MT-hDHFR. Through a clustering analysis and examination of protein-ligand interactions, one compound was found with a ChemPLP fitness score greater than that of MTX (reference compound). Finally, a simulation of molecular dynamics (MD) identified an MTX analog which exhibited strong affinity for WT- and MT-hDHFR, with stable RMSD, hydrogen bonds (H-bonds) in the binding site and the lowest MM/PBSA binding free energy. In conclusion, we report on an MTX analog which is capable of inhibiting hDHFR in wild type form, as well as in cases where the enzyme acquires resistance to drugs during chemotherapy treatment.

Overview of Dual-Acting Drug Methotrexate in Different Neurological Diseases, Autoimmune Pathologies and Cancers

Methotrexate, a structural analogue of folic acid, is one of the most effective and extensively used drugs for treating many kinds of cancer or severe and resistant forms of autoimmune diseases. In this paper, we take an overview of the present state of knowledge with regards to complex mechanisms of methotrexate action and its applications as immunosuppressive drug or chemotherapeutic agent in oncological combination therapy. In addition, the issue of the potential benefits of methotrexate in the development of neurological disorders in Alzheimer’s disease or myasthenia gravis will be discussed.

Methotrexate and its mechanisms of action in inflammatory arthritis

Despite the introduction of numerous biologic agents for the treatment of rheumatoid arthritis (RA) and other forms of inflammatory arthritis, low-dose methotrexate therapy remains the gold standard in RA therapy. Methotrexate is generally the first-line drug for the treatment of RA, psoriatic arthritis and other forms of inflammatory arthritis, and it enhances the effect of most biologic agents in RA. Understanding the mechanism of action of methotrexate could be instructive in the appropriate use of the drug and in the design of new regimens for the treatment of RA. Although methotrexate is one of the first examples of intelligent drug design, multiple mechanisms potentially contribute to the anti-inflammatory actions of methotrexate, including the inhibition of purine and pyrimidine synthesis, transmethylation reactions, translocation of nuclear factor-κB (NF-κB) to the nucleus, signalling via the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway and nitric oxide production, as well as the promotion of adenosine release and expression of certain long non-coding RNAs.

Transition of Methotrexate Polyglutamate Drug Monitoring Assay from Venipuncture to Capillary Blood-Based Collection Method in Rheumatic Diseases

Objective

Methotrexate (MTX) polyglutamate (MTXPG3) levels from isolated red blood cells (RBCs) collected by venipuncture have clinical utility in guiding MTX dosing for patients with rheumatoid arthritis (RA). Our objective was to transition this RBC-based therapeutic drug monitoring (TDM) assay to dried capillary blood collected by fingerstick.

Methods

Patients with RA treated with MTX were enrolled. Specimens were collected by fingerstick (volumetric absorptive microsampler) and venipuncture to measure MTXPG3 from dried capillary blood, total venous blood, and isolated RBCs. MTXPG3 levels from dried capillary blood were measured using LC-MS/MS, converted to RBC equivalent (nmol/L), and compared with those from isolated RBCs (reference method). Following transition to fingerstick collection, comparability in the distributions of dried capillary and venipuncture-based RBC MTXPG3 levels was assessed using the Kolmogorov–Smirnov (K-S) test.

Results

Intraday and interday precision ranged from 2.0% to 10.9% and 3.1% to 10.8%, respectively, at MTXPG3 concentrations ranging from 5 to 100 nmol/L. In 106 participants treated with MTX, MTXPG3 levels from total venous and dried capillary blood were comparable [slope = 0.97 (95% CI, 0.92–1.03); R2 = 0.92]. Dried capillary blood MTXPG3 converted to RBC equivalent was similar to levels from isolated RBCs (30 ± 18 nmol/L vs 33 ± 19 nmol/L; n = 106). After implementation in the clinical laboratory, RBC equivalents MTXPG3 from the fingerstick method were similar to levels from venipuncture [39 ± 22 nmol/L (n = 825) vs 39 ± 24 nmol/L (n = 47935)] (K-S test P = 0.09). Underexposure to MTX (MTXPG3 ≤5 nmol/L RBCs) was detected in 7.0% and 8.5% patient specimens collected using the fingerstick and venipuncture methods, respectively.

Conclusion

Capillary blood MTXPG3 levels can be used to guide MTX dosing in TDM practice.

Baseline adenosine receptor mRNA expression in blood as predictor of response to methotrexate therapy in patients with rheumatoid arthritis

Methotrexate (MTX) reduces inflammation by increasing extracellular adenosine levels in rheumatoid arthritis (RA) patients. Adenosine acts via G-protein coupled receptors; ADORA1, ADORA2a, ADORA2b and ADORA3. We studied if baseline expression of whole blood adenosine receptors can predict response to MTX. RA patients [American College of Rheumatology/European-League-Against-Rheumatism (EULAR) 2010 criteria], Disease modifying anti-rheumatic drug (DMARD) naïve with active disease [Disease Activity Score 28 (DAS28) > 3.2] were enrolled. Blood samples were collected at baseline (n = 100) and at 4 months after therapy (n = 50). Patients were treated with MTX monotherapy. Based on EULAR response, patients were categorized into three groups i.e. good, moderate and non-responders. Adenosine receptors gene expression (ADORA1, ADORA2a, ADORA2b and ADORA3) in whole-blood RNA was measured using real-time PCR. HPRT1 was used as housekeeping gene. Receptor expression at baseline was correlated with response to MTX. All values are expressed as median (interquartile range). Hundred patients [87% females; age 40 (18) years]; duration of disease 24 (24.75) months; DAS28 4.7 (1.25) were enrolled. Fifty-one were classified as good, 28 moderate and 21 as non-responders. No expression of ADORA1 and ADORA2b was detected. Significant difference was observed in the expression levels of ADORA3 between good vs non-responder (P = 0.03) and moderate vs non-responder (P = 0.002). On ROC curve analysis, ADORA3 with cut-off value of less than - 0.60 (ΔCt) predicted non-response to MTX treatment (AUC: 0.7, P = 0.006). ADORA3 mRNA levels in whole blood may serve as a biomarker of response to MTX.

Clinical Implications of Methotrexate Pharmacogenetics in Childhood Acute Lymphoblastic Leukaemia

Background:

In the past two decades, a great body of research has been published regarding the effects of genetic polymorphisms on methotrexate (MTX)-induced toxicity and efficacy. Of particular interest is the role of this compound in childhood acute lymphoblastic leukaemia (ALL), where it is a pivotal drug in the different treatment protocols, both at low and high doses. MTX acts on a variety of target enzymes in the folates cycle, as well as being transported out and into of the cell by several transmembrane proteins.

Methods:

We undertook a structured search of bibliographic databases for peer-reviewed research literature using a focused review question.

Results:

This review has intended to summarize the current knowledge concerning the clinical impact of polymorphisms in enzymes and transporters involved in MTX disposition and mechanism of action on paediatric patients with ALL.

Conclusion:

In this work, we describe why, in spite of the significant research efforts, pharmacogenetics findings in this setting have not yet found their way into routine clinical practice.

Methotrexate disposition, anti-folate activity and efficacy in the collagen-induced arthritis mouse model

Methotrexate (MTX) efficacy in autoimmune arthritis is variable and unpredictable resulting in the need for the identification of biomarkers to guide drug therapy. This study utilizes the collagen-induced arthritis mouse model to investigate erythrocyte MTX disposition and anti-folate activity as biochemical markers of efficacy in autoimmune arthritis. Following induction of arthritis, DBA/1J mice were treated with once-weekly subcutaneous MTX at varying doses over a period of 40 days. At the completion of the study tissue samples were analyzed for MTX and folate content and assessed for their relationship with MTX efficacy. MTX treatment resulted in a reduction in disease activity that was variable and dose-dependent. Erythrocyte accumulation of MTX and its polyglutamate metabolites were dose proportionate, however, polyglutamate metabolites represented a mean ± S.E.M. of 8.9 ± 0.4% of total erythrocyte MTX, which is markedly lower than previously observed in humans and failed to display any significant association with MTX efficacy. MTX treatment resulted in reductions in erythrocyte 5-methyl-tetrahydrofolate (5mTHF) levels that were similar to those previously observed in human studies. Disease induction was associated with a decrease in liver 5mTHF and increased formyl-tetrahydrofolate (fTHF) that was normalized in MTX treated mice. MTX efficacy was associated with reductions in erythrocyte 5mTHF (P = 0.04) and increases in liver 5mTHF (P = 0.0001). Together, these findings demonstrate a relationship between alterations in tissue folate levels and MTX efficacy, and supports erythrocyte levels of 5mTHF as a marker of MTX efficacy in autoimmune arthritis.

Combined antitumoral effects of pretubulysin and methotrexate

Pretubulysin (PT), a potent tubulin-binding antitumoral drug, and the well-established antimetabolite methotrexate (MTX) were tested separately or in combination (PT+MTX) for antitumoral activity in L1210 leukemia cells or KB cervix carcinoma cells in vitro and in vivo in NMRI-nu/nu tumor mouse models. In cultured L1210 cells, treatment with PT or MTX displays strong antitumoral effects in vitro, and the combination PT+MTX exceeds the effect of single drugs. PT also potently kills the MTX resistant KB cell line, without significant MTX combination effect. Cell cycle analysis reveals the expected arrest in G1/S by MTX and in G2/M by PT. In both cell lines, the PT+MTX combination induces a G2/M arrest which is stronger than the PT-triggered G2/M arrest. PT+MTX does not change rates of apoptotic L1210 or KB cells as compared to single drug applications. Confocal laser scanning microscopy images show the microtubule disruption and nuclear fragmentation induced by PT treatment of L1210 and KB cells. MTX changes the architecture of the F-actin skeleton. PT+MTX combines the toxic effects of both drugs. In the in vivo setting, the antitumoral activity of drugs differs from their in vitro cytotoxicity, but their combination effects are more pronounced. MTX on its own does not display significant antitumoral activity, whereas PT reduces tumor growth in both L1210 and KB in vivo models. Consistent with the cell cycle effects, MTX combined at moderate dose boosts the antitumoral effect of PT in both in vivo tumor models. Therefore, the PT+MTX combination may present a promising therapeutic approach for different types of cancer.

MTHFR C677T polymorphism increases MTX sensitivity via the inhibition of S-adenosylmethionine and de novo purine synthesis

Objective: Currently, no guidelines are established for pharmacogenomic testing involving folate metabolic genes in long-term disease-modifying antirheumatic drugs' (DMARD) therapies. We carefully investigated how common genetic variations in methylenetetrahydrofolate reductase (MTHFR) influence cellular metabolic kinetics in response to methotrexate (MTX). Designs: Two distinct cell models: HepG2 with stabilized MTHFR inhibition using shRNA delivered by a Lentiviral vector; and Epstein-Barr virus transformed human lymphoblasts expressing MTHFR polymorphic allele 677C and 677T were used. Disease activity and DMARD use were compared between MTHFR-677CC, CT and TT rheumatoid arthritis (RA) patients in a cross-sectional study (n=120). Results: Compared with MTHFR-CC, MTHFR-TT carriers had lower mean weakly MTX dose (9.8 ± 3.3 compared with 12.1 ± 3.5, P<0.05). More MTHFR-TT carriers (8/11, 73%) reported MTX-related side effects compared with MTHFR-677CC (32/57, 56%) and MTHFR-677CT (30/51, 59%). No genotypic difference was found in other DMARDs. At the same dose of MTX, lymphoblasts were more sensitive in cell survival, protein and thymidine syntheses whereas HepG2 models were more susceptible to the inhibition of S-adenosylmethionine (adoMet) synthesis. MTHFR-C677T altered protein turnover and folate mediated 1-carbon metabolic fluxes in lymphoblasts with and without MTX. MTHFR function significantly affected transmethylation fluxes and adoMet homeostasis but not nucleotide biosyntheses in MTX-treated HepG2 cell-lines. Conclusion: Combining cell models, kinetic studies, and genetic tests in humans, the present study gives insight on how MTHFR effects hepatic transmethylation homeostasis during MTX therapy. We provide platforms that help predict the genetic impact on antifolate drugs, and further delineate tissue-specific target pathway in DMARD therapies. We suggest that genetic factors should be taken into account in clinical practice.

Nicotinamide Phosphoribosyltransferase Deficiency Potentiates the Antiproliferative Activity of Methotrexate through Enhanced Depletion of Intracellular ATP

Lower plasma nicotinamide phosphoribosyltransferase (NAMPT) levels are associated with improved response to methotrexate (MTX) in patients with juvenile idiopathic arthritis. Cell-based studies confirmed that reduced cellular NAMPT activity potentiates the pharmacologic activity of MTX; however, the mechanism of this interaction has yet to be defined. Therefore, in this study, we investigate the mechanism of enhanced pharmacologic activity of MTX in NAMPT-deficient A549 cells. Small interfering RNA-based silencing of NAMPT expression resulted in a greater than 3-fold increase in sensitivity to MTX (P < 0.005) that was completely reversed by supplementation with folinic acid. Despite a 68% reduction in cellular NAD levels in NAMPT-deficient cells, no change in expression or activity of dihydrofolate reductase was observed and uptake of MTX was not significantly altered. MTX did not potentiate the depletion of cellular NAD levels, but NAMPT-deficient cells had significant elevations in levels of intermediates of de novo purine biosynthesis and were 4-fold more sensitive to depletion of ATP by MTX (P < 0.005). Supplementation with hypoxanthine and thymidine completely reversed the antiproliferative activity of MTX in NAMPT-deficient cells and corresponded to repletion of the cellular ATP pool without any effect on NAD levels. Together, these findings demonstrate that increased MTX activity with decreased NAMPT expression is dependent on the antifolate activity of MTX and is driven by enhanced sensitivity to the ATP-depleting effects of MTX. For the first time, these findings provide mechanistic details to explain the increase in pharmacological activity of MTX under conditions of reduced NAMPT activity.

Discovery of N-(6-Fluoro-1-oxo-1,2-dihydroisoquinolin-7-yl)-5-[(3R)-3-hydroxypyrrolidin-1-yl]thiophene-2-sulfonamide (LSN 3213128), a Potent and Selective Nonclassical Antifolate Aminoimidazole-4-carboxamide Ribonucleotide Formyltransferase (AICARFT) Inhibitor Effective at Tumor Suppression in a Cancer Xenograft Model

A hallmark of cancer is unbridled proliferation that can result in increased demand for de novo synthesis of purine and pyrimidine bases required for DNA and RNA biosynthesis. These synthetic pathways are frequently upregulated in cancer and involve various folate-dependent enzymes. Antifolates have a proven record as clinically used oncolytic agents. Our recent research efforts have produced LSN 3213128 (compound 28a), a novel, selective, nonclassical, orally bioavailable antifolate with potent and specific inhibitory activity for aminoimidazole-4-carboxamide ribonucleotide formyltransferase (AICARFT), an enzyme in the purine biosynthetic pathway. Inhibition of AICARFT with compound 28a results in dramatic elevation of 5-aminoimidazole 4-carboxamide ribonucleotide (ZMP) and growth inhibition in NCI-H460 and MDA-MB-231met2 cancer cell lines. Treatment with this inhibitor in a murine based xenograft model of triple negative breast cancer (TNBC) resulted in tumor growth inhibition.

Folylpoly-γ-glutamate synthetase: A key determinant of folate homeostasis and antifolate resistance in cancer

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.

Reduction in Serum Uric Acid May Be Related to Methotrexate Efficacy in Early Rheumatoid Arthritis: Data from the Canadian Early Arthritis Cohort (CATCH)

OBJECTIVES

The mechanism of action of methotrexate in rheumatoid arthritis (RA) is complex. It may increase adenosine levels by blocking its conversion to uric acid (UA). This study was done to determine if methotrexate lowers UA in early RA (ERA).

METHODS

Data were obtained from Canadian Early Arthritis Cohort, an incident ERA cohort. All ERA patients with serial UA measurements were included, comparing those with methotrexate use vs. no methotrexate exposure (controls). Analyses were exploratory. Patients with concomitant gout or taking UA-lowering therapies were excluded.

RESULTS

In total, 49 of the 2,524 ERA patients were identified with data available for both pre-methotrexate UA levels and post-methotrexate UA levels (300 µmol/L and 273 µmol/L, respectively; P = 0.035). The control group not taking methotrexate had a mean baseline UA level of 280 µmol/L and a follow-up level of 282 µmol/L (P = 0.448); mean change in UA with methotrexate was −26.8 µmol/L vs. 2.3 µmol/L in the no methotrexate group (P = 0.042). Methotrexate users with a decrease in UA had a disease activity score of 2.37 for 28 joints when compared with the controls (3.26) at 18 months (P = 0.042). Methotrexate users with decreased UA had a lower swollen joint count (SJC) of 0.9 at 18 months, whereas methotrexate users without lowering of UA had an SJC of 4.5 (P = 0.035). Other analyses were not significant.

CONCLUSIONS

Methotrexate response is associated with lowering of serum UA in ERA compared to nonusers. This may be due to changes in adenosine levels. Methotrexate response is associated with lower UA and fewer swollen joints compared to nonresponders.

Methotrexate reduces HbA1c concentration but does not produce chronic accumulation of ZMP in patients with rheumatoid or psoriatic arthritis

OBJECTIVES

The mechanism by which methotrexate (MTX) improves glucose homeostasis in patients with rheumatoid (RA) and psoriatic arthritis (PsA) remains undetermined. Animal studies indicate a role for intracellular accumulation of 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranosyl 5'-monophosphate (ZMP) but this has not been directly demonstrated in humans. We explored whether accumulation of ZMP is associated with improvements in glucose homeostasis during MTX therapy.

METHOD

MTX-naïve, non-diabetic RA (n = 16) and PsA (n = 10) patients received uninterrupted MTX treatment for 6 months. To evaluate whether ZMP accumulated during MTX therapy, we measured the concentration of ZMP in erythrocytes and the concentration of its dephosphorylated derivative 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) in urine using liquid chromatography mass spectrometry (LC-MS/MS). To assess glucose homeostasis, we determined the concentration of glycated haemoglobin (HbA1c) and homeostasis model assessment of insulin resistance [HOMA-IR: fasting glucose (mmol/L) × fasting insulin (μU/mL)/22.5].

RESULTS

Erythrocyte ZMP and urinary AICAR concentrations did not increase during 6 months of MTX therapy. HbA1c concentration was reduced from 5.80 ± 0.29% at baseline to 5.51 ± 0.32% at 6 months (p < 0.001), while HOMA-IR remained unaltered. Reduction in HbA1c concentration was not associated with increased ZMP or AICAR concentrations.

CONCLUSIONS

MTX therapy probably does not produce a chronic increase in erythrocyte ZMP or urinary AICAR concentrations. Collectively, our data do not support the hypothesis that MTX improves glucose homeostasis through chronic accumulation of ZMP.

Assessment of the relationship between methotrexate polyglutamates in red blood cells and clinical response in patients commencing methotrexate for rheumatoid arthritis

BACKGROUND AND OBJECTIVES

Therapeutic drug monitoring in patients with rheumatoid arthritis (RA) receiving methotrexate (MTX, MTXGlu1) has not been established. In this study, we aim to explore the relationship between red blood cell (RBC) concentrations of MTX and its polyglutamate metabolites (MTXGlu(n); n = 2, 3, 4, 5) and clinical response in RA patients commencing MTX.

METHODS

The binding activity of MTXGlu(n) to three putative enzymes involved in the MTX mechanism of action—dihydrofolate reductase, thymidylate synthase, and 5-aminoimidazole-4-carboxamide ribonucleotide transformylase—was simulated. RBC MTXGlu(n) concentrations that gave the highest inhibition activity across all three enzymes were linked with the disease activity score DAS28-3v (C-reactive protein [CRP]). A population pharmacokinetic-pharmacodynamic model was developed to describe the relationship between RBC MTX polyglutamate concentrations and clinical response in 12 RA patients commencing MTX.

RESULTS

The highest inhibition activity was with RBC MTXGlu(3-5). These polyglutamates were further evaluated for their relationship with DAS28-3v (CRP). Three of the 12 patients had a high DAS28-3v (CRP) at baseline (mean = 6.1) and showed a delayed response to MTX treatment. The remaining nine patients with a lower DAS28-3v (CRP) baseline (mean = 3.6) showed an immediate response. The developed MTX pharmacokinetic-pharmacodynamic model provided an acceptable description of the observed DAS28-3v (CRP) across all patients.

CONCLUSIONS

The developed model describes a longitudinal relationship between RBC MTXGlu(3-5) concentrations and DAS28-3v (CRP) in patients with RA commencing MTX. Further work is required to determine whether measurement of RBC MTX polyglutamates might be useful for dose individualisation in patients with RA.

Outcomes related to methotrexate dose and route of administration in patients with rheumatoid arthritis: a systematic literature review

OBJECTIVES

Methotrexate (MTX) is considered the 'anchor drug' in the therapy of rheumatoid arthritis (RA), yet many physicians do not optimise MTX regimens in spite of high RA disease activity. The recent development of an auto-injector for the subcutaneous (subQ) administration of MTX has prompted re-evaluation of MTX utilisation. The purpose of this systematic literature review is to determine the optimal dose, drug level, and route of administration for MTX in the context of relevant pharmacokinetics and pharmacogenomics.

METHODS

A systematic literature review was performed in Medline searching specifically for randomised controlled trials, systematic reviews, case control and cohort studies evaluating outcomes related to MTX dose and route of administration. Articles fulfilling these inclusion criteria were reviewed. Data on MTX dose, route of administration, clinical response, drug levels and adverse events were evaluated.

RESULTS

Our search identified 420 articles of which 6 were eligible for inclusion using the above criteria. These included 2 systematic reviews, 2 randomised open label trials, one longitudinal study and one retrospective cohort study.

CONCLUSIONS

Efficacy and toxicity for MTX appear related to absorbed dose of MTX, not to route of administration. While bioavailability is greater for parenteral MTX, there is no evidence yet that splitting the oral dose of MTX is less advantageous, less safe or less tolerable than administering parenteral MTX. However, there appear to be modest benefits in beginning with higher doses of MTX, and switching to parenteral MTX when the clinical response to an oral dose is inadequate.

High folic acid consumption leads to pseudo-MTHFR deficiency, altered lipid metabolism, and liver injury in mice

BACKGROUND

Increased consumption of folic acid is prevalent, leading to concerns about negative consequences. The effects of folic acid on the liver, the primary organ for folate metabolism, are largely unknown. Methylenetetrahydrofolate reductase (MTHFR) provides methyl donors for S-adenosylmethionine (SAM) synthesis and methylation reactions.

OBJECTIVE

Our goal was to investigate the impact of high folic acid intake on liver disease and methyl metabolism.

DESIGN

Folic acid-supplemented diet (FASD, 10-fold higher than recommended) and control diet were fed to male Mthfr(+/+) and Mthfr(+/-) mice for 6 mo to assess gene-nutrient interactions. Liver pathology, folate and choline metabolites, and gene expression in folate and lipid pathways were examined.

RESULTS

Liver and spleen weights were higher and hematologic profiles were altered in FASD-fed mice. Liver histology revealed unusually large, degenerating cells in FASD Mthfr(+/-) mice, consistent with nonalcoholic fatty liver disease. High folic acid inhibited MTHFR activity in vitro, and MTHFR protein was reduced in FASD-fed mice. 5-Methyltetrahydrofolate, SAM, and SAM/S-adenosylhomocysteine ratios were lower in FASD and Mthfr(+/-) livers. Choline metabolites, including phosphatidylcholine, were reduced due to genotype and/or diet in an attempt to restore methylation capacity through choline/betaine-dependent SAM synthesis. Expression changes in genes of one-carbon and lipid metabolism were particularly significant in FASD Mthfr(+/-) mice. The latter changes, which included higher nuclear sterol regulatory element-binding protein 1, higher Srepb2 messenger RNA (mRNA), lower farnesoid X receptor (Nr1h4) mRNA, and lower Cyp7a1 mRNA, would lead to greater lipogenesis and reduced cholesterol catabolism into bile.

CONCLUSIONS

We suggest that high folic acid consumption reduces MTHFR protein and activity levels, creating a pseudo-MTHFR deficiency. This deficiency results in hepatocyte degeneration, suggesting a 2-hit mechanism whereby mutant hepatocytes cannot accommodate the lipid disturbances and altered membrane integrity arising from changes in phospholipid/lipid metabolism. These preliminary findings may have clinical implications for individuals consuming high-dose folic acid supplements, particularly those who are MTHFR deficient.

In silico analysis of glycinamide ribonucleotide transformylase inhibition by PY873, PY899 and DIA

In humans, purine de novo synthesis pathway consists of multi-functional enzymes. Nucleotide metabolism enzymes are potential drug targets for treating cancer and autoimmune diseases. Glycinamide ribonucleotide transformylase (GART) is one of the most important trifunctional enzymes involved in purine synthesis. Previous studies have demonstrated the role of folate inhibitors against tumor activity. In this present study, three components of GART enzyme were targeted as receptor dataset and in silico analysis was carried out with folate ligand dataset. To accomplish the task, Autodock 4.2 was used for determining the docking compatibilities of ligand and receptor dataset. Taken together, it has been suggested that folate ligands could be potentially used as inhibitors of GART.

LD-aminopterin in the canine homologue of human atopic dermatitis: a randomized, controlled trial reveals dosing factors affecting optimal therapy

Background

Options are limited for patients with atopic dermatitis (AD) who do not respond to topical treatments. Antifolate therapy with systemic methotrexate improves the disease, but is associated with adverse effects. The investigational antifolate LD-aminopterin may offer improved safety. It is not known how antifolate dose and dosing frequency affect efficacy in AD, but a primary mechanism is thought to involve the antifolate-mediated accumulation of 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR). However, recent in vitro studies indicate that AICAR increases then decreases as a function of antifolate concentration. To address this issue and understand how dosing affects antifolate efficacy in AD, we examined the efficacy and safety of different oral doses and schedules of LD-aminopterin in the canine model of AD.

Methods and Findings

This was a multi-center, double-blind trial involving 75 subjects with canine AD randomized to receive up to 12 weeks of placebo, once-weekly (0.007, 0.014, 0.021 mg/kg) or twice-weekly (0.007 mg/kg) LD-aminopterin. The primary efficacy outcome was the Global Score (GS), a composite of validated measures of disease severity and itch. GS improved in all once-weekly cohorts, with 0.014 mg/kg being optimal and significant (43%, P<0.01). The majority of improvement was seen by 8 weeks. In contrast, GS in the twice-weekly cohort was similar to placebo and worse than all once-weekly cohorts. Adverse events were similar across all treated cohorts and placebo.

Conclusions

Once-weekly LD-aminopterin was safe and efficacious in canine AD. Twice-weekly dosing negated efficacy despite having the same daily and weekly dose as effective once-weekly regimens. Optimal dosing in this homologue of human AD correlated with the concentration-selective accumulation of AICAR in vitro, consistent with AICAR mediating LD-aminopterin efficacy in AD.

6-thioguanine: a drug with unrealized potential for cancer therapy

Sixty years ago, 6-thioguanine (6-TG) was introduced into the clinic. We suggest its full potential in therapy may not have been reached. In this paper, we contrast 6-TG and the more widely used 6-mercaptopurine; discuss 6-TG metabolism, pharmacokinetics, dosage and schedule; and summarize many of the early studies that have shown infrequent but nevertheless positive results with 6-TG treatment of cancers. We also consider studies that suggest that combinations of 6-TG with other agents may enhance antitumor effects. Although not yet tested in man, 6-TG has recently been proposed to treat a wide variety of cancers with a high frequency of homozygous deletion of the gene for methylthioadenosine phosphorylase (MTAP), often codeleted with the adjacent tumor suppressor CDKN2A (p16). Among the cancers with a high frequency of MTAP deficiency are leukemias, lymphomas, mesothelioma, melanoma, biliary tract cancer, glioblastoma, osteosarcoma, soft tissue sarcoma, neuroendocrine tumors, and lung, pancreatic, and squamous cell carcinomas. The method involves pretreatment with the naturally occurring nucleoside methylthioadenosine (MTA), the substrate for the enzyme MTAP. MTA pretreatment protects normal host tissues, but not MTAP-deficient cancers, from 6-TG toxicity and permits administration of doses of 6-TG that are much higher than can now be safely administered. The combination of MTA/6-TG has produced substantial shrinkage or slowing of growth in two different xenograft human tumor models: lymphoblastic leukemia and metastatic prostate carcinoma with neuroendocrine features. Further development and a clinical trial of the proposed MTA/6-TG treatment of MTAP-deficient cancers seem warranted.

Molecular basis for pharmacokinetics and pharmacodynamics of methotrexate in rheumatoid arthritis therapy

  Methotrexate (MTX) is a derivative of folic acid (folate) and commonly used as an anchor drug for the treatment of rheumatoid arthritis (RA). The pharmacokinetics (PK) and pharmacodynamics (PD) of MTX entirely depends on the function of specific transporters that belong to the two major superfamilies, solute carrier transporters and ATP-binding cassette transporters. Several transporters have been identified as being able to mediate the transport of MTX, and suggested to be involved in the disposition in the body and in the regulation of intracellular metabolism in target cells, together with several enzymes involved in folate metabolism. Thus, drug-drug interactions through the transporters and their genetic polymorphisms may alter the PK and PD of MTX, resulting in an interpatient variability of efficacy. This review summarizes the PK and PD of MTX, particularly in relation to RA therapy and focuses on the roles of transporters involved in PK and PD with the aim of facilitating an understanding of the molecular basis of the mechanism of MTX action to achieve its effective use in RA therapy.

Methotrexate treatment causes early onset of disease in a mouse model of Ross River virus-induced inflammatory disease through increased monocyte production

Part of the Togaviridae family, alphaviruses, including chikungunya virus (CHIKV), Sindbis virus (SINV) and Ross River virus (RRV), are able to cause significant inflammatory pathologies ranging from arthritis to encephalitis. Following symptomatic infection with arthritis-associated alphaviruses, patients often experience severe joint pain, affecting distal and small joints, which can last six months or longer. Recently, methotrexate (MTX), a disease modifying anti-rheumatic drug (DMARD), was used to treat patients experiencing chronic rheumatic symptoms following infection with CHIKV. Here, the effect of MTX on Ross River virus disease (RRVD) in mice was examined to better understand its therapeutic potential for alphaviral-induced musculoskeletal disease and to further our knowledge of the development of alphaviral pathologies. Using a mouse model, we analyzed the effect of MTX on RRVD. RRV disease pathogenesis in response to MTX treatment was determined by measuring levels of proinflammatory factors, cellular infiltrates, viral titer and histological analysis of infected tissues. RRV-infected mice receiving MTX treatment rapidly developed musculoskeletal disease, which correlated with a significant influx of inflammatory cell infiltrates into the skeletal muscle tissue. Although no difference was observed in the level of proinflammatory cytokines and chemokines, the viral load increased at early time points post infection in the serum and quadriceps of MTX treated mice, possibly contributing to disease pathogenesis. Results suggest that MTX treatment of acute RRVD in mice provides no therapeutic benefit and underline the importance of inflammatory monocytes in alphaviral induced arthritides.

Low-dose methotrexate results in the selective accumulation of aminoimidazole carboxamide ribotide in an erythroblastoid cell line

Therapeutic and toxic response to low-dose methotrexate (MTX) in the treatment of autoimmune disease continues to be highly variable, resulting in a critical need to identify predictive biomarkers of response. Biomarker development has been hampered by an incomplete understanding of the molecular pharmacology of low-dose MTX. To address this issue, accumulation of the substrates for aminoimidazole carboxamide ribonucleotide transformylase (AICART) and thymidylate synthase (TS) was measured as markers of pharmacological activity of MTX in an erythroblastoid cell line. A 115-fold increase in the AICART substrate and anti-inflammatory mediator, 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranosyl 5'-monophosphate (ZMP), was observed following exposure to 10 nM MTX but subsequently decreased with increasing MTX concentrations, declining to baseline levels with 1000 nM MTX. In contrast, the TS substrate, 2'-deoxyuridine 5'-monophosphate disodium salt (dUMP), displayed concentration-dependent accumulation, increasing 29-, 342-, and 471-fold over baseline with 10, 100, and 1000 nM MTX, respectively. Cellular levels of dUMP correlated with levels of the parent drug (MTX-PG1; r = 0.66, P < 0.001) and its polyglutamates (MTX-PG2-6) (r = 0.81, P < 0.001), whereas cellular levels of ZMP were only moderately correlated with MTX-PG1 (r = 0.34, P < 0.01). In contrast, accumulation of ZMP at 10 nM MTX was associated with a 2.9-fold increase in the AICART inhibitor dihydrofolate (DHF), represented primarily by long-chain DHF polyglutamates. Selectivity, defined as the ratio of ZMP to dUMP, was maximal following exposure to 6 nM MTX. Characterizing the range of MTX concentrations that selectively promote ZMP accumulation while preserving pyrimidine biosynthesis may lead to optimization of low-dose MTX therapy.

Fibroblasts from methotrexate-sensitive mice accumulate methotrexate polyglutamates but those from methotrexate-resistant mice do not

OBJECTIVES

We and others have previously demonstrated that methotrexate (MTX) mediates its anti-inflammatory effects through an increase in cellular release of adenosine. Consistent with this observation, there is no increase in adenosine from exudates of mouse strains resistant to MTX. Because intracellular MTX polyglutamates inhibit AICAR transformylase (ATIC) activity and thereby promote adenosine release we determined whether there is any difference in the capacity of cells from MTX-resistant mice to accumulate MTX polyglutamates.

METHODS

Dermal fibroblasts (DF) from BALBc, MTX-sensitive, and DBA/1J, MTX-resistant, mice were cultured in the presence or absence of MTX. Adenosine concentration in the supernatant and intracellular MTX polyglutamate (MTXPG1-5) concentrations were measured by liquid chromatography. ATIC activity in DF was monitored spectrophotometrically by the formation of formytetrahydrofolate.

RESULTS

MTX (1 μM) increased adenosine production by DF from BALBc sensitive-mice from 269±40 nM to 446±4 nM. No adenosine production was found in supernates of cultured DF from DBA/1J mice regardless of MTX treatment. Intracellular MTX polyglutamates (MTXPG2-4) were detected only in BALBc DFs, not in DBA/1J DF. Further investigation demonstrated that ATIC activity was inhibited following MTX treatment in DF from BALBc mice.

CONCLUSIONS

These data suggest that resistance to the anti-inflammatory effects of MTX could be due to diminished MTX polyglutamate accumulation resulting in diminished ATIC inhibition and adenosine accumulation.

Pharmacokinetics, pharmacodynamics and toxicities of methotrexate in healthy and collagen-induced arthritic rats

Methotrexate (MTX) is an anchor drug used to treat rheumatoid arthritis (RA), but responsiveness is variable in effectiveness and toxicity. Methotrexate and its polyglutamate conjugates (MTXPG(n)) in red blood cells (RBC) have been associated with patient response. In the current study, 13 collagen-induced arthritic (CIA) rats and 12 healthy rats were given subcutaneous doses of either saline or 0.3 or 1.5 mg/kg per 2 days of MTX from day 21 to 43 post-induction. Blood samples were obtained at various times to measure MTX in plasma, and MTX and MTXPG(n) in RBC. Effects on disease progression were indicated by body weight and paw size. After multiple-doses, RBC MTX reached steady-state (82.4 nm) within 4 days. The MTXPG(2) and MTXPG(3) in RBC kept increasing until the end of the study, attaining 12.5 and 17.7 nm. Significant weight loss was observed after dosing with 1.5 mg/kg/2 days, whereas moderate effectiveness was observed after dosing with 0.3 mg/kg/2 days. A pharmacokinetic/pharmacodynamic/disease (PK/PD/DIS) model with indirect mechanisms and transduction components incorporating plasma MTX, RBC MTX and RBC MTXPG(n) concentrations, and paw size was developed using naïve data pooling and ADAPT 5. The PK/PD in CIA rats dosed at 0.3 mg/kg/2 days were captured well by our proposed model. Methotrexate showed modest (I(maxd) = 0.16) but sensitive (IC(50d) = 0.712 nm) effectiveness on paw edema. The higher dose produced toxicity. The proposed model offers improved understanding of the effects of methotrexate on rheumatoid arthritis.

AMPK: opposing the metabolic changes in both tumour cells and inflammatory cells?

AMPK (AMP-activated protein kinase) is a sensor of cellular energy status that appears to have arisen during early eukaryotic evolution. In the unicellular eukaryote Saccharomyces cerevisiae, the AMPK orthologue is activated by glucose starvation and is required for the switch from glycolysis (fermentation) to oxidative metabolism when glucose runs low. In mammals, rapidly proliferating cells (including tumour cells) and immune cells involved in inflammation both tend to utilize rapid glucose uptake and glycolysis (termed the Warburg effect or aerobic glycolysis) rather than oxidative metabolism to satisfy their high demand for ATP. Since mammalian AMPK, similar to its yeast orthologue, tends to promote the more energy-efficient oxidative metabolism at the expense of glycolysis, it might be expected that drugs that activate AMPK would inhibit cell proliferation and and hence cancer, as well as exerting anti-inflammatory effects. Evidence supporting this view is discussed, including our findings that AMPK is activated by the classic anti-inflammatory drug salicylate.

In silico analysis of the amido phosphoribosyltransferase inhibition by PY873, PY899 and a derivative of isophthalic acid

Selectively decreasing the availability of precursors for the de novo biosynthesis of purine nucleotides is a valid approach towards seeking a cure for leukaemia. Nucleotides and deoxynucleotides are required by living cells for syntheses of RNA, DNA, and cofactors such as NADP(+), FAD(+), coenzyme A and ATP. Nucleotides contain purine and pyrimidine bases, which can be synthesized through salvage pathway as well. Amido phosphoribosyltransferase (APRT), also known as glutamine phosphoribosylpyrophosphate amidotransferase (GPAT), is an enzyme that in humans is encoded by the PPAT (phosphoribosyl pyrophosphate amidotransferase) gene. APRT catalyzes the first committed step of the de novo pathway using its substrate, phosphoribosyl pyrophosphate (PRPP). As APRT is inhibited by many folate analogues, therefore, in this study we focused on the inhibitory effects of three folate analogues on APRT activity. This is extension of our previous wet lab work to analyze and dissect molecular interaction and inhibition mechanism using molecular modeling and docking tools in the current study. Comparative molecular docking studies were carried out for three diamino folate derivatives employing a model of the human enzyme that was built using the 3D structure of Bacillus subtilis APRT (PDB ID; 1GPH) as the template. Binding orientation of interactome indicates that all compounds having nominal cluster RMSD in same active site's deep narrow polar fissure. On the basis of comparative conformational analysis, electrostatic interaction, binding free energy and binding orientation of interactome, we support the possibility that these molecules could behave as APRT inhibitors and therefore may block purine de novo biosynthesis. Consequently, we suggest that PY899 is the most active biological compound that would be a more potent inhibitor for APRT inhibition than PY873 and DIA, which also confirms previous wet lab report.

Old drugs, old problems: where do we stand in prediction of rheumatoid arthritis responsiveness to methotrexate and other synthetic DMARDs?

Methotrexate (MTX) is the central drug in the management of rheumatoid arthritis (RA) and other immune mediated inflammatory diseases. It is widely used either in monotherapy or in association with other synthetic and biologic disease modifying anti-rheumatic drugs (DMARDs). Although comprehensive clinical experience exists for MTX and synthetic DMARDs, to date it has not been possible to preview correctly whether or not a patient will respond to treatment with these drugs. Predicting response to MTX and other DMARDs would allow the selection of patients based on their likelihood of response, thus enabling individualized therapy and avoiding unnecessary adverse effects and elevated costs. However, studies analyzing this issue have struggled to obtain consistent, replicable results and no factor has yet been recognized to individually distinguish responders from nonresponders at treatment start. Variables possibly influencing drug effectiveness may be disease-, patient- or treatment-related, clinical or biological (genetic and nongenetic). In this review we summarize current evidence on predictors of response to MTX and other synthetic DMARDs, discuss possible causes for the heterogeneity observed and address its translation into daily clinical practice.

Para-aminosalicylic acid acts as an alternative substrate of folate metabolism in Mycobacterium tuberculosis

Folate biosynthesis is an established anti-infective target, and the antifolate para-aminosalicylic acid (PAS) was one of the first anti-infectives introduced into clinical practice on the basis of target-based drug discovery. Fifty years later, PAS continues to be used to treat tuberculosis. PAS is assumed to inhibit dihydropteroate synthase (DHPS) in Mycobacterium tuberculosis by mimicking the substrate p-aminobenzoate (PABA). However, we found that sulfonamide inhibitors of DHPS inhibited growth of M. tuberculosis only weakly because of their intracellular metabolism. In contrast, PAS served as a replacement substrate for DHPS. Products of PAS metabolism at this and subsequent steps in folate metabolism inhibited those enzymes, competing with their substrates. PAS is thus a prodrug that blocks growth of M. tuberculosis when its active forms are generated by enzymes in the pathway they poison.

The antifolates

This article focuses on the cellular, biochemical, and molecular pharmacology of antifolates and how a basic understanding of the mechanism of action of methotrexate, its cytotoxic determinants, mechanisms of resistance, and transport into and out of cells has led to the development of a new generation of antifolates, a process that continues in the laboratory and in the clinics. New approaches to folate-based cancer chemotherapy are described based on the targeted delivery of drugs to malignant cells.