Formation of methotrexate polyglutamates in purified myeloid precursor cells from normal human bone marrow

Methotrexate accumulation in target intestinal mucosa and white blood cells differs from non-target red blood cells of patients with Crohn's disease

BACKGROUND

Intracellular methotrexate polyglutamates (MTX-PGs) concentrations are measurable in red blood cells (RBCs) during MTX treatment. MTX-PG3 concentrations correlate with efficacy in patients with Crohn's disease (CD). Since RBCs are not involved in pathogenesis of CD and lack extended MTX metabolism, we determined MTX-PGs accumulation in peripheral blood mononuclear cells (PBMCs: effector cells) and intestinal mucosa (target cells) and compared those with RBCs as a potential more precise biomarker.

METHODS

In a multicentre prospective cohort study, blood samples of patients with CD were collected during the first year of MTX therapy. Mucosal biopsies were obtained from non-inflamed rectum and/or inflamed intestine. MTX-PGs concentrations in mucosa, PBMCs and RBCs were measured by liquid chromatography-tandem mass spectrometry.

RESULTS

From 80 patients with CD, a total of 27 mucosal biopsies, 9 PBMC and 212 RBC samples were collected. From 12 weeks of MTX therapy onwards, MTX-PG3 was the most predominant species (33%) in RBCs. In PBMCs, the distribution was skewed towards MTX-PG1 (48%), which accounted for an 18 times higher concentration than in RBCs. Long-chain MTX-PGs were highly present in mucosa: 21% of MTX-PGtotal was MTX-PG5. MTX-PG6 was measurable in all biopsies.

CONCLUSIONS

MTX-PG patterns differ between mucosa, PBMCs and RBCs of patients with CD.

The effects of drug transporters on the efficacy of methotrexate in the treatment of rheumatoid arthritis

The ATP-binding cassette (ABC) and solute carrier (SLC) transporter families consist of common drug transporters that mediate the efflux and uptake of drugs, respectively, and play an important role in the absorption, distribution, metabolism and excretion of drugs in vivo. Rheumatoid arthritis (RA) is an autoimmune disease characterized by erosive arthritis, and there are many RA patients worldwide. Methotrexate (MTX), the first-choice treatment for RA, can reduce the level of inflammation, prevent joint erosion and functional damage, and greatly reduce pain in RA patients. However, many patients show resistance to MTX, greatly affecting the efficacy of MTX. Many factors, such as irrational drug use and heredity, are associated with drug resistance. Considering the effect of drug transporters on drugs, many studies have compared the expression of drug transporters in drug-resistant and drug-sensitive patients, and abnormal transporter expression and transport activity have been found in patients with MTX resistance. Thus, drug transporters are involved in drug resistance. This article reviews the effects of transporters on the efficacy of MTX in the treatment of RA.

The evaluation of red blood cell folate and methotrexate levels during protocol M in childhood acute lymphoblastic leukemia

BACKGROUND

After High-Dose Methotrexate (HD-MTX), folinic acid rescue therapy (Leucovorin) is administered to reduce side effects in pediatric acute lymphoblastic leukemia (ALL) patients. Leucovorin and MTX are structural analogues, possibly competing for cellular transport and intracellular metabolism. We hypothesize that Leucovorin accumulates during consecutive courses, which might result in a lower MTX uptake.

METHODS

We prospectively measured red blood cell (RBC) folate and MTX levels during four HD-MTX and Leucovorin courses in 43 patients treated according the DCOG ALL-11 protocol with 2-weekly HD-MTX (5 g/m²/dose) and Leucovorin (15 mg/m²/dose) using LC-MS/MS. We estimated a linear mixed model to assess the relationship between these variables over time.

RESULTS

Both RBC MTX-PG and folate levels increased significantly during protocol M. MTX-PG_2-5 levels increased most substantially after the first two HD-MTX courses (until median 113.0 nmol/L, IQR 76.8-165.2) after which levels plateaued during the 3^d and 4th course (until median 141.3 nmol/L, IQR 100.2-190.2). In parallel, folate levels increased most substantially after the first two HD-MTX courses (until median 401.6 nmol/L, IQR 163.3-594.2) after which levels plateaued during the 3^d and 4th course (until median 411.5 nmol/L, IQR 240.3-665.6). The ratio folate/MTX-PG decreased significantly over time, which was mostly due to the relatively higher increase (delta) of MTX-PG.

CONCLUSION

These results suggest that the increase in RBC folate levels does not seem to have a large effect on RBC MTX levels. Future studies, assessing competition of Leucovorin and MTX on other cellular mechanisms which might negatively affect treatment efficacy, are necessary.

Patient-derived oral mucosa organoids as an in vitro model for methotrexate induced toxicity in pediatric acute lymphoblastic leukemia

We have recently established a protocol to grow wildtype human oral mucosa organoids. These three-dimensional structures can be maintained in culture long-term, do not require immortalization, and recapitulate the multilayered composition of the epithelial lining of the oral mucosa. Here, we validate the use of this model to study the effect of Leucovorin (LV) on Methotrexate (MTX)-induced toxicity. MTX is a chemotherapeutic agent used in the treatment of pediatric acute lymphoblastic leukemia. Although effective, the use of MTX often results in severe side-effects, including oral mucositis, which is characterized by epithelial cell death. Here, we show that organoids are sensitive to MTX, and that the addition of LV reduces MTX toxicity, in both a concentration- and timing-dependent manner. Additionally, we show that a 24 hour ‘pretreatment’ with LV reduces MTX-induced cell death, suggesting that such a pretreatment could decrease mucositis in patients. Taken together, we provide the first in vitro model to study the effect of MTX on wildtype oral mucosa cells. Our findings underscore the relevance of the clinically applied LV regimen and highlight the potential of this model to further optimize modifications in dosing and timing of Leucovorin on oral mucosa cells.

Glutamic Acid Increased Methotrexate Polyglutamation and Cytotoxicity in a CCRF-SB Acute Lymphoblastic Leukemia Cell Line

Background and Objectives: Acute lymphoblastic leukemia (ALL) is the most common type of cancer in childhood. The majority of patients respond to treatment, but those with resistant phenotypes suffer relapse or death. The antifolate methotrexate (MTX) is the most commonly used drug against ALL due to its efficacy. Once inside leukemic cells, MTX is metabolized into methotrexate polyglutamates (MTX-PG) by action of the enzyme folylpolyglutamate synthetase (FPGS), leading to a longer action compared to that of MTX alone. Materials and Methods: In this work, we demonstrated that the combination treatment of methotrexate and 5 and 10 mM glutamic acid could enhance methotrexate cytotoxicity in CCRF-SB (B-ALL) cells. In addition, MTX plus 20 mM glutamic acid was able to improve the synthesis of MTX-PG₅. Results: All treatments induced an increase in FPGS expression compared to that of the control group. Furthermore, we detected different cellular expression patterns of FPGS in the different treatments. Conclusion: Based on these findings, we demonstrated that levels of methotrexate polyglutamates (MTX-PGs) could be a key determinant of methotrexate-induced cytotoxicity in CCRF-SB acute lymphoblastic leukemia cells.

Aldehyde oxidase and its role as a drug metabolizing enzyme

Aldehyde oxidase (AO) is a cytosolic enzyme that belongs to the family of structurally related molybdoflavoproteins like xanthine oxidase (XO). The enzyme is characterized by broad substrate specificity and marked species differences. It catalyzes the oxidation of aromatic and aliphatic aldehydes and various heteroaromatic rings as well as reduction of several functional groups. The references to AO and its role in metabolism date back to the 1950s, but the importance of this enzyme in the metabolism of drugs has emerged in the past fifteen years. Several reviews on the role of AO in drug metabolism have been published in the past decade indicative of the growing interest in the enzyme and its influence in drug metabolism. Here, we present a comprehensive monograph of AO as a drug metabolizing enzyme with emphasis on marketed drugs as well as other xenobiotics, as substrates and inhibitors. Although the number of drugs that are primarily metabolized by AO are few, the impact of AO on drug development has been extensive. We also discuss the effect of AO on the systemic exposure and clearance these clinical candidates. The review provides a comprehensive analysis of drug discovery compounds involving AO with the focus on developmental candidates that were reported in the past five years with regards to pharmacokinetics and toxicity. While there is only one known report of AO-mediated clinically relevant drug-drug interaction (DDI), a detailed description of inhibitors and inducers of AO known to date has been presented here and the potential risks associated with DDI. The increasing recognition of the importance of AO has led to significant progress in predicting the site of AO-mediated metabolism using computational methods. Additionally, marked species difference in expression of AO makes it is difficult to predict human clearance with high confidence. The progress made towards developing in vivo, in vitro and in silico approaches for predicting AO metabolism and estimating human clearance of compounds that are metabolized by AO have also been discussed.

Do SNPs in folate pharmacokinetic pathway alter levels of intracellular methotrexate polyglutamates and affect response? A prospective study in Indian patients

This study investigated the impact of seven polymorphisms in genes of folate transport and (de)glutamation pathway on methotrexate polyglutamate levels and response in patients with rheumatoid arthritis. This prospective study included patients with rheumatoid arthritis. They were treated with methotrexate (up to 25 mg per week) for 24 weeks and categorized by EULAR response criteria into responders (good and moderate) and non-responders. Using real-time Taqman discrimination assay, SNPs were genotyped-rs1045642 (ABCB1 3435C>T), rs1128503 (ABCB1 1236C>T), rs10106 (FPGS 1994A>G), rs1544105 (FPGS G>A), rs11545078 (GGH 452C>T), rs3758149 (GGH -401C>T), and rs1051266 (RFC1 80G>A). RBC methotrexate polyglutamate_1-5(MTX-glu_1-5) levels were determined at 4, 8, 16, and 24 weeks using by reverse phase HPLC using C-18 column followed by post column photo-oxidation. This study included 117 patients with rheumatoid arthritis (M:F = 14:103). The mean dose of methotrexate at 24 weeks was 22.0 ± 4.0 mg, with data on DAS28(3) at 24 weeks available in 96 patients-61 responders and 35 non-responders. Minor allele of GGH 452C>T had an association with non-response (odds ratio 2.9, 95% CI 1.4-5.6) and assuming the dominance of C, the recessive genetic model found GGH 452C>T CC genotype (odds ratio 9.5, 95% CI 1.2 to 76.0) was significantly associated with response. However, there was no difference in MTX-glu_1-5 levels among the various genotypes of this SNP (p = 0.9). Other SNPs were neither associated with response nor with alteration in methotrexate polyglutamate levels. On logistic regression, GGH 452C>T CC genotype and DAS28(3) at baseline were independent predictors of response. GGH 452C>T CC genotype was associated with response to methotrexate. None of the SNPs affected MTX-glu_1-5levels.

Methotrexate limits inflammation through an A20-dependent cross-tolerance mechanism

Objectives

Methotrexate (MTX) is the anchor drug for treatment of rheumatoid arthritis (RA), but the mechanism of its anti-inflammatory action is not fully understood. In RA, macrophages display a proinflammatory polarisation profile that resembles granulocyte-macrophage colony-stimulating factor (GM-CSF)-differentiated macrophages and the response to MTX is only observed in thymidylate synthase⁺ GM-CSF-dependent macrophages. To determine the molecular basis for the MTX anti-inflammatory action, we explored toll-like receptor (TLR), RA synovial fluid (RASF) and tumour necrosis factor receptor (TNFR)-initiated signalling in MTX-exposed GM-CSF-primed macrophages.

Methods

Intracellular responses to TLR ligands, TNFα or RASF stimulation in long-term low-dose MTX-exposed human macrophages were determined through quantitative real-time PCR, western blot, ELISA and siRNA-mediated knockdown approaches. The role of MTX in vivo was assessed in patients with arthritis under MTX monotherapy and in a murine sepsis model.

Results

MTX conditioned macrophages towards a tolerant state, diminishing interleukin (IL)-6 and IL-1β production in LPS, LTA, TNFα or RASF-challenged macrophages. MTX attenuated LPS-induced MAPK and NF-κB activation, and toll/IL-1R domain-containing adaptor inducing IFN-beta (TRIF1)-dependent signalling. Conversely, MTX increased the expression of the NF-κB suppressor A20 (TNFAIP3), itself a RA-susceptibility gene. Mechanistically, MTX-induced macrophage tolerance was dependent on A20, as siRNA-mediated knockdown of A20 reversed the MTX-induced reduction of IL-6 expression. In vivo, TNFAIP3 expression was significantly higher in peripheral blood cells of MTX-responsive individuals from a cohort of patients with arthritis under MTX monotherapy, whereas MTX-treated mice exhibited reduced inflammatory responses to LPS.

Conclusions

MTX impairs macrophage proinflammatory responses through upregulation of A20 expression. The A20-mediated MTX-induced innate tolerance might limit inflammation in the RA synovial context, and positions A20 as a potential MTX-response biomarker.

Treatment efficacy and methotrexate-related toxicity in patients with rheumatoid arthritis receiving methotrexate in combination with adalimumab

Background

Treatment of rheumatoid arthritis (RA) with a combination of methotrexate (MTX)+adalimumab (ADA) is more effective than ADA monotherapy. We assessed the toxicity of different doses of MTX and treatment efficacy of ADA+MTX in two trials.

Methods

Data originated from CONCERTO, in patients with early RA initiating ADA+ 2.5, 5, 10 or 20 mg/week MTX for 26 weeks; and MUSICA, in patients with an inadequate response to MTX initiating ADA+ 7.5 or 20 mg/week MTX for 24 weeks. Efficacy was assessed by the American College of Rheumatology 50 (ACR50). Patient-reported MTX-related toxicity information was collected at each visit on 18 prespecified MTX-related adverse events (AE) in the MTX label.

Results

In CONCERTO, ACR50 rates increased over time, ranging from 54% to 68% at week 26, while AE rates remained steady, ranging from 2.4% to 17.8% at week 26. Of 395 patients, 113 (28.6%) reported 345 MTX-related AEs, including one serious AE (SAE, excessive fatigue and/or malaise); 10 AEs (in two patients) led to study discontinuation. In MUSICA, ACR50 rates increased over time, and were 32.3% and 37.5% at week 24, while MTX-related AE rates remained steady and were 6.5% at week 24. Of 309 patients, 71 (23%) reported 185 MTX-related AEs, including 5 SAEs (four infections and one fever/chills); six AEs (in four patients) led to study discontinuation.

Conclusion

In patients with RA initiating ADA+MTX combination, treatment efficacy was achieved and increased throughout both trials, while rates of MTX-related AEs remained steady. MTX-related AEs were observed in up to 30% of patients and most were mild. MTX was discontinued by 0.5%–1.3% of patients.

Trial registration number

MUSICA (NCT01185288), CONCERTO (NCT01185301), Post results.

Aplastic anemia in a lung adenocarcinoma patient receiving pemetrexed

Pemetrexed (PEM) is an antimetabolite drug that interferes with enzymes involved in DNA synthesis and also the folate-dependent metabolic processes necessary for DNA replication and homocysteine homeostasis. Continuation maintenance with PEM after induction therapy with PEM plus cisplatin has been the standard form of first-line chemotherapy for advanced non-squamous non-small cell lung cancer. The regimen has a low incidence of bone marrow suppression, and the incidences of anemia, leukopenia, neutropenia and thrombocytopenia exceeding grade 3 are less than 5%. Here we report a 68-year-old Japanese man with stage IIIB (cT4N3M0) lung adenocarcinoma who received 4 cycles of chemotherapy with PEM 500 mg/m² and cisplatin 75 mg/m² every three weeks, which resulted in a partial response, and then continued to receive maintenance PEM monotherapy. After 11 cycles of PEM maintenance therapy, the patient's platelet count decreased, and progressed to pancytopenia within two months. A bone marrow puncture revealed replacement with fatty marrow. As other diseases possibly responsible for pancytopenia were ruled out, we diagnosed the patient as having aplastic anemia. This is the first reported case of aplastic anemia to have occurred during PEM therapy. Clinicians should bear in mind that PEM can potentially trigger severe pancytopenia, including aplastic anemia.

Mechanism of action of methotrexate in rheumatoid arthritis, and the search for biomarkers

The treatment and outcomes of patients with rheumatoid arthritis (RA) have been transformed over the past two decades. Low disease activity and remission are now frequently achieved, and this success is largely the result of the evolution of treatment paradigms and the introduction of new therapeutic agents. Despite the rapid pace of change, the most commonly used drug in RA remains methotrexate, which is considered the anchor drug for this condition. In this Review, we describe the known pharmacokinetic properties and putative mechanisms of action of methotrexate. Consideration of the pharmacodynamic perspective could inform the development of biomarkers of responsiveness to methotrexate, enabling therapy to be targeted to specific groups of patients. Such biomarkers could revolutionize the management of RA.

The impact of 5-formyltetrahydrofolate on the anti-tumor activity of pralatrexate, as compared to methotrexate, in HeLa cells in vitro

PURPOSE

To investigate the impact of 5-formyltetrahydrofolate on the activities of pralatrexate, as compared to methotrexate (MTX), in vitro.

METHODS

Cells were exposed to (6S)5-formyltetrahydrofolate (5-formylTHF) for 24 h, before or after a 6-h exposure to antifolates following which the cellular accumulation and activities of the drugs were evaluated in HeLa cells.

RESULTS

A 24-h delay between a 6-h exposure to antifolates and a subsequent 24-h exposure to 4 μM 5-formylTHF sustained the full activities of both antifolates. A 72-h interval was required between a single exposure of up to 4 μM 5-formylTHF and subsequent exposure to drugs to sustain activities of the antifolates. When cells were incubated with 4 μM 5-formylTHF for 24 h weekly, for 4 weeks, there was no significant increase in the IC50 for pralatrexate, but the MTX IC50 increased 2.5-fold as compared to cells growing continuously in 25 nM 5-formylTHF. This cyclical exposure to 5-formylTHF increased the cell folate pool by 16 %, had no significant effect on the intracellular pralatrexate level, but decreased intracellular MTX by 15 %. An extracellular concentration of MTX 50-fold higher than that of pralatrexate was required to achieve an intracellular level, and growth inhibition, comparable to that of pralatrexate.

CONCLUSIONS

Cyclical exposures to 5-formylTHF at levels in excess of what is achieved in most clinical "rescue" regimens do not affect pralatrexate accumulation nor antitumor activity in HeLa cells, in contrast to MTX. An important element in preserving pralatrexate activity is achieving a sufficient interval between exposure to 5-formylTHF and the next dose of antifolate.

Methotrexate polyglutamates in erythrocytes are associated with lower disease activity in juvenile idiopathic arthritis patients

OBJECTIVE

To determine association of erythrocyte methotrexate polyglutamates (MTX-PG) with disease activity and adverse effects in a prospective juvenile idiopathic arthritis (JIA) cohort.

METHODS

One hundred and thirteen JIA patients were followed from MTX start until 12 months. Erythrocyte MTX-PGs with 1-5 glutamate residues were measured at 3 months with tandem mass spectrometry. The outcomes were Juvenile Arthritis Disease Activity Score (JADAS)-27 and adverse effects. To determine associations of MTX-PGs with JADAS-27 at 3 months and during 1 year of MTX treatment, linear regression and linear mixed-model analyses were used. To determine associations of MTX-PGs with adverse effects during 1 year of MTX treatment, logistic regression was used. Analyses were corrected for JADAS-27 at baseline and co-medication.

RESULTS

Median JADAS-27 decreased from 12.7 (IQR: 7.8-18.2) at baseline to 2.9 (IQR: 0.1-6.5) at 12 months. Higher concentrations of MTX-PG3 (β: -0.006, p=0.005), MTX-PG4 (β: -0.015, p=0.004), MTX-PG5 (β: -0.051, p=0.011) and MTX-PG3-5 (β: -0.004, p=0.003) were associated with lower disease activity at 3 months. Higher concentrations of MTX-PG3 (β: -0.005, p=0.028), MTX-PG4 (β: -0.014, p=0.014), MTX-PG5 (β: -0.049, p=0.023) and MTX-PG3-5 (β: -0.004, p=0.018) were associated with lower disease activity over 1 year. None of the MTX-PGs was associated with adverse effects.

CONCLUSIONS

In the first prospective study in JIA, long-chain MTX-PGs were associated with lower JADAS-27 at 3 months and during 1 year of MTX treatment. Erythrocyte MTX-PG could be a plausible candidate for therapeutic drug monitoring of MTX in JIA.

The membrane transport and polyglutamation of pralatrexate: a new-generation dihydrofolate reductase inhibitor

PURPOSE

To characterize, directly and for the first time, the membrane transport and metabolism of pralatrexate, a new-generation dihydrofolate reductase inhibitor approved for the treatment for peripheral T-cell lymphoma.

EXPERIMENTAL DESIGN

[(3)H]pralatrexate transport was studied in unique HeLa cell lines that express either the reduced folate carrier (RFC) or the proton-coupled folate transporter (PCFT). Metabolism to active polyglutamate derivatives was assessed by liquid chromatography. These properties were compared to those of methotrexate (MTX).

RESULTS

The pralatrexate influx K t, mediated by RFC, the major route of folate/antifolate transport at systemic pH, was 0.52 μΜ, 1/10th the MTX influx K i. The electrochemical potential of pralatrexate within HeLa cells far exceeded the extracellular level and was greater than for MTX. In contrast, MTX transport mediated by PCFT, the mechanism of folate/antifolate absorption in the small intestine, exceeded that for pralatrexate. After a 6 h exposure of HeLa cells to 0.5 μM pralatrexate, 80 % of intracellular drug was its active polyglutamate forms, predominantly the tetraglutamate, and was suppressed when cells were loaded with natural folates. There was negligible formation of MTX polyglutamates. The difference in pralatrexate and MTX growth inhibition was far greater after transient exposures (375-fold) than continuous exposure (25-fold) to the drugs.

CONCLUSIONS

Pralatrexate's enhanced activity relative to MTX is due to its much more rapid rate of transport and polyglutamation, the former less important when the carrier is saturated. The low affinity of pralatrexate for PCFT predicts a lower level of enterohepatic circulation and increased fecal excretion of the drug relative to MTX.

Involvement of Multiple Transporters-mediated Transports in Mizoribine and Methotrexate Pharmacokinetics

Mizoribine is administered orally and excreted into urine without being metabolized. Many research groups have reported a linear relationship between the dose and peak serum concentration, between the dose and AUC, and between AUC and cumulative urinary excretion of mizoribine. In contrast, a significant interindividual variability, with a small intraindividual variability, in oral bioavailability of mizoribine is also reported. The interindividual variability is mostly considered to be due to the polymophisms of transporter genes. Methotrexate (MTX) is administered orally and/or by parenteral routes, depending on the dose. Metabolic enzymes and multiple transporters are involved in the pharmacokinetics of MTX. The oral bioavailability of MTX exhibits a marked interindividual variability and saturation with increase in the dose of MTX, with a small intraindividual variability, where the contribution of gene polymophisms of transporters and enzymes is suggested. Therapeutic drug monitoring of both mizoribine and MTX is expected to improve their clinical efficacy in the treatment of rheumatoid arthritis.

Genetic polymorphism of γ-glutamyl hydrolase in Chinese acute leukemia children and identification of a novel double nonsynonymous mutation

γ-Glutamyl hydrolase (GGH) plays a central role in folate metabolism and antifolate action. Polymorphism in the human GGH gene (GGH) was associated with efficacy and side effects of methotrexate for treatment of acute lymphoblastic leukemia (ALL). This study aimed to identify polymorphisms of GGH in Chinese. Seventy-one children with ALL, 25 children with acute myeloid leukemia (AML), and 132 children with nonmalignancy as control were included. Human GGH cDNAs were prepared and analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR)-denaturing gradient gel electrophoresis. The detected variants were further confirmed by DNA sequencing. Novel variant GGH cDNA was cloned, expressed, and characterized. Allelic frequency of GGH 452C→T polymorphism was determined as 9.2% (CT, 11/71; TT, 1/71) in the ALL group, 8.0% (CT, 4/25; TT, 0/25) in the AML group, and 9.1% (TT, 4/132; T/C, 16/132) in the controls, respectively. The total allelic frequency in the Chinese population (9.0%) was higher than those reported in Japanese (5.6%) and African Americans (4.4%), and was similar to Caucasians (10.0%). Association of 452TT+TC with increased rate of hepatotoxicity and mucositis was observed in the ALL patients. Two novel mutations were determined in the coding region of GGH in 2 boys with ALL: one of the mutations was a double nonsynonymous heterozygote (841AG+845AG, K257E/N258S), the other was a nonsynonymous heterozygote (797AG, K242R). The corresponding double-mutant protein showed unchanged enzymatic activity by functional analysis. Allele frequency of GGH C452T polymorphism is determined for the first time among Chinese. A novel double nonsynonymous mutation of GGH was identified in a boy with ALL.

Tumor necrosis factor-alpha promotes survival in methotrexate-exposed macrophages by an NF-kappaB-dependent pathway

Introduction

Methotrexate (MTX) induces macrophage apoptosis in vitro, but there is not much evidence for increased synovial macrophage apoptosis in MTX-treated patients. Macrophage apoptosis is reported, however, during clinical response to anti-tumor necrosis factor-alpha (TNF-α) treatments. This implies that TNF-α promotes macrophage survival and suggests that TNF-α may protect against MTX-induced apoptosis. We, therefore, investigated this proposal and the macrophage signaling pathways underlying it.

Methods

Caspase-3 activity, annexin-V binding/7-aminoactinomycin D (7-AAD) exclusion and cell-cycle analysis were used to measure steps in apoptosis of primary murine macrophages and cells of the RAW_264.7 macrophage cell line that had been exposed to clinically-relevant concentrations of MTX and TNF-α.

Results

MTX induces apoptosis in primary murine macrophages at concentrations as low as 100 nM in vitro. TNF-α, which has a context-dependent ability to increase or to suppress apoptosis, efficiently suppresses MTX-induced macrophage apoptosis. This depends on NF-κB signaling, initiated through TNF Receptor Type 1 ligation. Macrophage colony stimulating factor, the primary macrophage survival and differentiation factor, does not activate NF-κB or protect macrophages from MTX-induced apoptosis. A weak NF-κB activator, Receptor Activator of NF-κB Ligand (RANKL) is likewise ineffective. Blocking NF-κB in TNF-α-exposed macrophages allowed pro-apoptotic actions of TNF-α to dominate, even in the absence of MTX. MTX itself does not promote apoptosis through interference with NF-κB signaling.

Conclusions

These findings provide another mechanism by which TNF-α sustains macrophage numbers in inflamed tissue and identify a further point of clinical complementarity between MTX and anti-TNF-α treatments for rheumatoid arthritis.

Red blood cell methotrexate polyglutamates emerge as a function of dosage intensity and route of administration during pulse methotrexate therapy in rheumatoid arthritis

OBJECTIVE

MTX is a prodrug producing anti-arthritic effects through a folylpolyglutamate synthase-mediated activation to MTX polyglutamates (MTXPGs). Our objective was to characterize the pharmacokinetics of intracellular MTXPGs and the factors associated with their accumulation in adult RA patients treated with MTX weekly.

METHODS

MTX pharmacokinetics were evaluated in 47 MTX-naïve patients enrolled in an MTX dose-escalation study for an average of 20 weeks and 223 patients enrolled in a cross-sectional study under long-term MTX therapy. Short-chain (MTXPG1-2), long-chain (MTXPG3) and very long-chain (MTXPG4-5) concentrations were measured in circulating red blood cells using liquid chromatography. Statistical analyses consisted of non-linear mixed models, multivariate regression analyses and Wilcoxon signed-rank test.

RESULTS

The accumulation of MTXPG1-5 was sigmoidal and steady-state concentrations were achieved after 7 weeks of therapy. However, additional exposure and MTX dosage escalation produced a selective redistribution towards longer chain MTXPGs at the expense of shorter chain MTXPGs. Age, glomerular filtration rate and route of MTX administration were the most important predictors of MTXPG accumulation. In 10 patients, a switch from oral to parenteral MTX was associated with a 37% increase in long-chain MTXPGs, a 132% increase in very long-chain MTXPGs and a concomitant 31% reduction in disease activity (P<0.02).

CONCLUSION

The selective emergence of long-chain MTXPGs is function of dose, time of exposure and hence dosage intensity. Switching from oral to parenteral MTX produces a selective accumulation of longer chain MTXPGs that are known to be more potent inhibitors of de novo purine biosynthesis than shorter chain MTXPGs.

Pemetrexed: biochemical and cellular pharmacology, mechanisms, and clinical applications

Pemetrexed is a new-generation antifolate, approved for the treatment of mesothelioma and non-small cell lung cancer, currently being evaluated for the treatment of a variety of other solid tumors. This review traces the history of antifolates that led to the development of pemetrexed and describes the unique properties of this agent that distinguish it from other antifolates. These include (a) its very rapid conversion to active polyglutamate derivatives in cells that build to high levels and are retained for long intervals to achieve prolonged and potent inhibition of its major target enzyme thymidylate synthase, (b) its high affinity for three folate transporters, and (c) its marked sensitivity to the level of physiologic folates in cells. The latter results in the unique and paradoxical finding that when transport mediated by the major folate transporter (the reduced folate carrier) is impaired, pemetrexed activity is preserved. This is due to concurrent contraction of competing cellular physiologic folates and utilization of a novel second transport carrier for which pemetrexed has high affinity, recently identified as the proton-coupled folate transporter (PCFT). Laboratory studies are reviewed that raise the possibility of new approaches to the use of folic acid supplementation in clinical regimens with pemetrexed.

Identification of single nucleotide polymorphisms in the human gamma-glutamyl hydrolase gene and characterization of promoter polymorphisms

gamma-Glutamyl hydrolase (GGH) plays a central role in folate metabolism and antifolate action. Increased GGH activity has been found in rat hepatoma cells resistant to the cancer drug methotrexate (MTX). The aim of this study was to identify polymorphisms in the GGH gene that modulate GGH activity and that may affect methotrexate resistance. Exons of the human gamma-glutamyl hydrolase (hGGH) gene were amplified by polymerase chain reaction (PCR) from breast cancer tissue and leukemia cell lines. Single-stranded conformational polymorphism (SSCP) analysis was performed, and PCR products containing different patterns were cloned and sequenced. Six single nucleotide polymorphisms (SNPs) were identified, at bases -401C>T, -354G>T, -124T>G, +16T>C, +452C>T, and +1102A>G, relative to the A of the translation start codon being considered as +1. The SNP at +16, which changes codon -19 (relative to the start of the mature hGGH protein) in the endoplasmic reticulum targeting sequence of hGGH protein from cysteine to arginine, has previously been identified in this laboratory. The SNP at +452 changes the conserved hGGH protein codon 127 from threonine to isoleucine. The functions of SNPs in the promoter of the hGGH gene were studied by site-directed mutagenesis of a 516-bp region of the hGGH gene promoter in a luciferase reporter vector and transfection into HepG2 and MCF-7 cells. All of the promoter polymorphisms enhanced the production of luciferase compared to the wild-type hGGH gene promoter in HepG2 cells, and -401C>T and -124T>G enhanced luciferase expression in MCF-7 cells, suggesting that polymorphisms in the hGGH gene promoter may increase expression of hGGH protein.

Resistance to antifolates

The antifolates were the first class of antimetabolites to enter the clinics more than 50 years ago. Over the following decades, a full understanding of their mechanisms of action and chemotherapeutic potential evolved along with the mechanisms by which cells develop resistance to these drugs. These principals served as a basis for the subsequent exploration and understanding of the mechanisms of resistance to a variety of diverse antineoplastics with different cellular targets. This section describes the bases for intrinsic and acquired antifolate resistance within the context of the current understanding of the mechanisms of actions and cytotoxic determinants of these agents. This encompasses impaired drug transport into cells, augmented drug export, impaired activation of antifolates through polyglutamylation, augmented hydrolysis of antifolate polyglutamates, increased expression and mutation of target enzymes, and the augmentation of cellular tetrahydrofolate-cofactor pools in cells. This chapter also describes how these insights are being utilized to develop gene therapy approaches to protect normal bone marrow progenitor cells as a strategy to improve the efficacy of bone marrow transplantation. Finally, clinical studies are reviewed that correlate the cellular pharmacology of methotrexate with the clinical outcome in children with neoplastic diseases treated with this antifolate.

Efficient utilization of the reduced folate carrier in CCRF-CEM human leukemic lymphoblasts by the potent antifolate N(alpha)-(4-amino-4-deoxypteroyl)-N(delta)-hemiphthaloyl-L- ornithine (PT523) and its B-ring analogues

The potent nonpolyglutamatable dihydrofolate reductase inhibitor N(alpha)-(4-amino-4-deoxypteroyl)-N(delta)-hemiphthaloyl-L-o rnithine (PT523) and six of its B-ring (5-deaza, 8-deaza, and 5,8-dideaza) analogues were compared in terms of their ability to: (a) inhibit the growth of CCRF-CEM human leukemic lymphoblasts, and (b) utilize the reduced folate carrier (RFC) in these cells as measured in a competition assay of [(3)H]methotrexate ([(3)H]MTX) influx. The IC(50) values of the hemiphthaloylornithine derivatives against CCRF-CEM cells after 72 hr of drug exposure varied from 0.64 to 1.3 nM as compared with 14 nM for MTX and 4.4 nM for aminopterin (AMT). The K(i) values of these compounds in the [(3)H]MTX influx assay were in the 0.3 to 0.7 microM range as compared with a K(i) of 5.4 microM for AMT and a K(t) of 7.1 microM for MTX. As a group, the affinities of these compounds for the RFC were approximately 10-fold greater than those of their respective glutamate analogues. These results indicate that, in addition to their previously reported tight binding to dihydrofolate reductase, a property contributing to the high potency of PT523 and its B-ring analogs as inhibitors of tumor cell growth is their strong affinity for the RFC.

Inhibition of neutrophil migration soon after initiation of treatment with leflunomide or methotrexate in patients with rheumatoid arthritis: findings in a prospective, randomized, double-blind clinical trial in fifteen patients

OBJECTIVE

Leflunomide is a novel immunomodulating drug that has recently been approved as a disease-modifying antirheumatic drug for the treatment of rheumatoid arthritis (RA). The aim of this study was to determine the relationship between the clinical effects of leflunomide and neutrophil migration.

METHODS

The effects of leflunomide and methotrexate on neutrophil chemotaxis were studied in 15 RA patients who participated in a prospective, randomized, double-blind clinical trial. When possible, neutrophil numbers were counted in synovial fluid (SF) samples at baseline and after 14 days, 4 months, and 1 year of treatment. The chemotactic properties of peripheral blood neutrophils from RA patients treated with either leflunomide or methotrexate were studied by the Boyden chamber technique, using the activators formyl-methionyl-leucyl-phenylalanine (fMLP) and interleukin-8 (IL-8). The in vitro effects of A77 1726, the active metabolite of leflunomide, and methotrexate on peripheral blood neutrophils from 7 healthy control subjects were also investigated.

RESULTS

Both therapy groups exhibited clinical improvement, including rapid reductions in SF neutrophil counts and reduced joint swelling and tenderness. On day 14, 3 of 7 patients who received leflunomide showed no detectable effusions. There was a significant effect on neutrophil chemotaxis (P < 0.001), which was similar for leflunomide and methotrexate. The direct effects on the neutrophils diminished over time. Incubation of peripheral blood neutrophils from healthy controls with A77 1726 confirmed the inhibitory effect on chemotaxis.

CONCLUSION

Leflunomide treatment is beneficial in RA patients. Different mechanisms are operative in various phases of treatment, leading to decreased recruitment of inflammatory cells in the joints.

Accumulation of methotrexate polyglutamates, ploidy and trisomies of both chromosomes 4 and 10 in lymphoblasts from children with B-progenitor cell acute lymphoblastic leukemia: a Pediatric Oncology Group Study

Levels of accumulation of methotrexate polyglutamates were measured in vitro in lymphoblasts obtained at diagnosis from children with B-progenitor cell acute lymphoblastic leukemia (pro-B ALL). They were compared to numerical and structural chromosomal abnormalities present in these leukemic cells. In a series of 95 patients, the percent with high lymphoblast methotrexate polyglutamate levels increased with the increase in modal number of total chromosomes (p<0.001). Thus, lymphoblast methotrexate polyglutamate accumulation appeared to be closely linked to the extent of hyperdiploidy in childhood pro-B ALL. Lymphoblasts from 35 (88%) of the 40 children with hyperdiploid (>50 chromosomes) and 23 (88%) of 26 with hyperdiploid (DNA Index >1.16) pro-B ALL accumulated high levels of methotrexate polyglutamate, suggesting that they were more sensitive to methotrexate cytotoxicity. While children with hyperdiploid (DNA Index >1.16) pro-B ALL have a good prognosis, those with trisomies of both chromosomes 4 and 10, almost all of whom are hyperdiploid, have an even better outcome. There was no significant difference in methotrexate polyglutamate levels in lymphoblasts from 19 children with and 21 without trisomies of both chromosomes 4 and 10 (p = 0.25). The improved response to multi-agent chemotherapy conferred by the presence of trisomies of both chromosomes 4 and 10 in such patients may be due to increased sensitivity of their lymphoblasts to one or more anti-leukemic agents in addition to methotrexate.

Methotrexate in rheumatoid arthritis: an update with focus on mechanisms involved in toxicity

OBJECTIVES

To provide an update of the current knowledge of the mechanism of action of low-dose methotrexate (MTX) in the treatment of patients with rheumatoid arthritis (RA), with an emphasis on the mechanisms involved in toxicity. We also considered strategies currently used to prevent or decrease toxicity of MTX.

METHODS

We reviewed the literature dealing with the subjects of MTX treatment of RA, the mechanisms of action of low-dose MTX regarding efficacy and toxicity, and strategies used to prevent or decrease MTX toxicity.

RESULTS

MTX is a fast working and effective second-line antirheumatic agent (SLA). Its use is limited mainly because of side effects. The mechanisms of action regarding efficacy and toxicity are probably determined by different metabolic pathways. Recent data indicate that the antiinflammatory effect of MTX is mediated by adenosine. However, MTX side effects can only partly be explained by folate antagonism and may also depend on its action on other related metabolic pathways. The latter include the homocysteine-methionine-polyamine pathway and purine metabolism. Variants in these metabolic routes (ie, the C677T mutation in the methylene-tetrahydrofolate reductase [MTHFR] gene), may predispose to the development of side effects. Currently the most promising strategy to decrease or prevent toxicity of MTX is concomitant prescription of folic acid or folinic acid. Other strategies are currently under investigation.

CONCLUSIONS

MTX benefits a majority of RA patients. Approximately 30% of patients, however, abandon treatment because of drug-related side effects. Folic acid or folinic acid likely reduces MTX toxicity. More data, however, are needed to evaluate a potential detrimental effect on the antirheumatic efficacy of MTX.

Leucovorin and folic acid regimens for selective expansion of murine 5,10-methylenetetrahydrofolate pools

Mice bearing subcutaneously implanted EMT6 mammary adenocarcinoma were treated with leucovorin or folic acid by continuous subcutaneous infusion or bolus intraperitoneal injection. (6R)-5,10-Methylenetetrahydrofolate pools in cytosolic extracts of the tumor, marrow, and gut were measured by analysis of the ternary complex with thymidylate synthase (5,10-methylenetetrahydrofolate: dUMP C-methyltransferase, EC 2.1.1.45) and 5-fluoro-2'-deoxyuridylate, and the polyglutamate distribution in the (6R)-5,10-methylenetetrahydrofolate pool was analyzed by native gel electrophoresis. Bolus intraperitoneal administration of either leucovorin or folic acid caused dose-dependent expansion of the (6R)-5,10-methylenetetrahydrofolate pool in the tumor, but not in the marrow or gut. For example, the AUC (0-5 hr) in the tumor increased from a baseline value of 8.2 to 20 nmol/mg protein.hr after a bolus dose of 1.5 mmol/kg of leucovorin or folic acid, whereas the increase in marrow and gut was 2- to 4-fold lower. Continuous subcutaneous infusion at the same total dosage over 3 days gave AUC (0-96 hr) values of 134 nmol/mg protein.hr for controls as compared with 347 nmol/mg protein.hr for the leucovorin group and 254 nmol/mg protein.hr for the folic acid group. In contrast to bolus treatment, the increase in (6R)-5,10-methylenetetrahydrofolate in the marrow and small intestine with both leucovorin and folic acid infusion was similar to the increase in the tumor. Thus, intraperitoneal bolus injection was tumor selective, but subcutaneous continuous infusion was not. Longer-chain polyglutamates of (6R)-5,10-methylenetetrahydrofolate in the tumor after bolus treatment with 0.375 and 0.75 mmol/kg of leucovorin or folic acid increased relative to controls. At higher doses of 1.5 and 2.25 mmol/kg, an increase was observed only in the mono/diglutamate fraction. In marrow, on the other hand, the mono/diglutamate fraction, but not the longer-chain polyglutamates, increased at all doses. In the constant infusion regimen, longer-chain polyglutamates increased in all three tissues, though in gut and marrow the mono/diglutamate fraction increased more than in tumor. Leucovorin and folic acid were converted to (6R)-5,10-methylenetetrahydrofolate more efficiently but less selectively during a 3-day subcutaneous infusion than after an intraperitoneal bolus. Longer-chain polyglutamates were selectively increased in tumor by both regimens of leucovorin administration.

Prostaglandin and tumor necrosis factor secretion by peritoneal macrophages isolated from normal and arthritic rats treated with liposomal methotrexate

The effect of a novel liposomal preparation containing a phospholipid conjugate of methotrexate (MTX-LIPO) upon macrophage mediator release was investigated in normal and arthritic rats ex vivo. Peritoneal macrophages isolated from MTX-LIPO-treated arthritic rats and stimulated with lipopolysaccharide produced significantly less tumor necrosis factor (TNF) and prostaglandin (PGE2) than did macrophages isolated from saline-treated controls. In the same experimental system, free methotrexate only inhibited prostaglandin release, but it was more potent than MTX-LIPO in this respect. Additional studies are presently underway to investigate the effect of MTX-LIPO and MTX treatment upon the lipopolysaccharide-induced rise in plasma levels of various proinflammatory mediators in vivo. Haematopoietic toxicity was demonstrated in blood isolated from rats treated with free MTX, and this was as characterized by a significant reduction in reticulocyte count compared with MTX-LIPO and saline-treated rats.

Leucovorin rescue of human cancer and bone marrow cells following edatrexate or methotrexate

We have examined the cytotoxic activities of edatrexate (EDX) and methotrexate (MTX) and their reversal by leucovorin in nine human cancer cell lines and in human bone marrow CFU-GM cells. EDX was 3.7- to 123-fold more toxic than MTX against the cancer cell lines and 25-fold against the bone marrow cells. Lower EDX concentrates generally were needed to inhibit cancer cell growth relative to bone marrow cells, however, whereas bone marrow and cancer cell growth were more often susceptible to the same MTX concentrations. The new antifolate was metabolized to long-chain polyglutamates to a greater extent than MTX in seven cell lines. Leucovorin at 0.2 microM rescued two breast cancer and two non-small cell lung cancer cell lines to a lesser extent following EDX than MTX, but significant rescue was observed in two head and neck cancer cell lines that formed large amounts of polyglutamates. These cell lines also accumulated reduced folates to a greater extent than the other cell lines following leucovorin exposure. Leucovorin rescued bone marrow cells following MTX but only partially following the highest EDX concentrations. EDX may enjoy a better therapeutic index than MTX against some cancer cell lines relative to bone marrow precursor cells, especially after leucovorin rescue.

Acute and chronic suppression of leukotriene B4 synthesis ex vivo in neutrophils from patients with rheumatoid arthritis beginning treatment with methotrexate

OBJECTIVE

To compare the cumulative effects of oral methotrexate (MTX) therapy (after 6-8 weeks) with the acute effects (24 hours after a dose) on arachidonic acid metabolism by the 5-lipoxygenase (5-LO) pathway in neutrophils from patients with active rheumatoid arthritis (RA) who were beginning therapy with MTX.

METHODS

Neutrophils and monocytes were isolated from whole blood from 7 patients with RA, immediately before and 24 hours after their first weekly dose of 7.5 mg of MTX, and again after their dose at 6-8 weeks.

RESULTS

Total immunoreactive leukotriene B4 (LTB4) formation in neutrophils activated ex vivo with calcium ionophore A23187 was significantly suppressed (by 33%) before the 6-8-week dose, compared with the level before the first dose (mean +/- SEM 8.29 +/- 1.24 ng/10(6) cells at predose 6-8 weeks versus 12.29 +/- 2.13 ng/10(6) cells at predose 1; P = 0.03). Reductions were also observed after the first dose (27%; P = 0.07) and after the 6-8-week dose (43%; P = 0.05) compared with the respective predose levels. MTX treatment produced significant reductions in the total generation of 5-LO pathway products (5-hydroxyeicosatetraenoic acid + 6-trans-LTB4 + LTB4 + omega-oxidation products of LTB4) by calcium ionophore-activated neutrophils, as quantitated by integrated optical density after resolution on reverse-phase high-performance liquid chromatography. Decreases were observed after the first dose (26%; P = 0.025), immediately before the 6-8-week dose (23%; P = 0.05), and after the 6-8-week dose (47%; P = 0.0033) compared with levels before the first dose, and after the 6-8-week dose compared with the level before it (32%; P = 0.04). The generation of LTB4 by calcium ionophore-activated monocytes was not significantly affected by MTX therapy.

CONCLUSION

The significant decreases in the formation of omega-oxidation products of LTB4 and in the total generation of neutrophil 5-LO pathway products in the absence of a significant change in the release of 3H-arachidonic acid or the generation of platelet-activating factor suggest that the activity of the 5-LO enzyme in neutrophils is inhibited. We conclude that weekly oral MTX therapy in patients with active RA inhibits neutrophil 5-LO pathway product generation in a pattern consistent with inhibition of the activity of the 5-LO enzyme; an effect is observed after the first dose. The inhibition of 5-LO is cell-selective and cumulative, with a superimposed incremental inhibition observed after the weekly MTX dose.

Mechanism of leucovorin reversal of methotrexate cytotoxicity in human MCF-7 breast cancer cells

Previous studies have suggested that metabolic inhibition by methotrexate (MTX) is multifactorial and that cytotoxicity can be reversed by the reduced folate leucovorin. In this report we investigated the mechanism of leucovorin rescue in the MCF-7 human breast cancer cell line. Cells were exposed to various concentrations of MTX (0.5, 1.0, 3.0, and 10.0 microM) for 24 hr followed by rescue with labelled leucovorin (0.5 to 50 microM). The changes in the intracellular folate pools 24 hr following the addition of leucovorin were quantitated by high-pressure liquid chromatographic methods. The changes in the folate pools during rescue were compared with the ability of various concentrations of leucovorin to affect cellular rescue from MTX using a cloning assay. Our studies show that the total labelled intracellular folate pools increased in a log-linear fashion with respect to leucovorin exposure concentrations up to 100 microM. The degree of accumulation at a given leucovorin concentration was not significantly different in the absence or presence of MTX over the concentration range of 0.5 to 10 microM. Individual folate pool levels (tetrahydrofolate, 10-formyl tetrahydrofolate, 5-formyl tetrahydrofolate, 5-methyl tetrahydrofolate, and 5,10-methylene tetrahydrofolate) reached those present in cells not exposed to MTX at concentrations of leucovorin that were not adequate to rescue the MTX-treated cells. With exposure to concentrations of leucovorin capable of rescue, the individual folate pool levels were up to twelve times greater than those found in untreated cells, consistent with competition for catalytic activity at folate-dependent enzymes in addition to dihydrofolate reductase. The dihydrofolate pool also increased with increasing leucovorin concentration: but, unlike the reduced folates, this oxidized folate reached a maximal level that was dependent on the MTX concentration to which the cells had been exposed. This suggests that competition between MTX and leucovorin occurs at the level of dihydrofolate reductase via a competitive interaction with dihydrofolate in this intact cell system. The ability of leucovorin and its metabolites to compete with direct inhibitors of dihydrofolate reductase and other metabolically important folate-dependent enzymes appears to be associated with leucovorin rescue.

Methotrexate: mechanism of action in rheumatoid arthritis

Most studies of immune function in rheumatoid arthritis (RA) patients treated with methotrexate (MTX) show only marginal effects on humoral or cellular immune responses. These include measurements of lymphocyte subsets, proliferative responses to mitogens, immunoglobulin production, rheumatoid factor and immune complexes. The mechanism of action of MTX in RA might be more antiinflammatory than immunosuppressive. This is supported by the rapid clinical response to drug treatment and by data from in vitro and animal studies. The inhibition of interleukin-1 (IL-1) activity or other inflammatory cytokines by MTX may play an important role in the antiinflammatory effect of MTX. MTX effects in RA are not fully understood and further studies are needed to clarify its mechanism of action. MTX has crucial effects on the cascade of events initiated by some cytokines (IL-1, IL-6, tumor necrosis factor), which plays a major role in RA and other inflammatory diseases.

Reversal of methotrexate cytotoxicity to human bone marrow cells and leukemic K562 cells by leucovorin: methotrexate polyglutamates formation as a possible important factor

Methotrexate (MTX) is metabolized intracellularly to MTX-polyglutamates (MTX-PGs), which markedly inhibit several folate-dependent enzymes. Polyglutamation defect, therefore, is one of the important factors in drug resistance. In this study, reversal of MTX cytotoxicity by l-leucovorin (l-LV) was investigated using normal human bone marrow granulocyte progenitor cells (G-CFCs), and MTX-sensitive and -resistant leukemic K562 cell lines; the latter showed diminished polyglutamation. Cytotoxicity of 10(-7)M MTX to G-CFCs was completely reversed by an equimolar concentration of l-LV, but with higher MTX concentrations, relatively more l-LV was required. The reversal of MTX cytotoxicity by l-LV was more effective against bone marrow cells than MTX-sensitive K562 cells; this reversal seemed to be correlated to the total intracellular MTX levels as well as MTX-PG formation (low in bone marrow cells and high in K562 cells). When MTX-sensitive and -resistant K562 cells were incubated with MTX under conditions in which the total intracellular MTX levels of both cells were similar, successful reversal of MTX toxicity by l-LV was demonstrated in MTX-resistant cells, but not in MTX-sensitive cells, suggesting that an increase of MTX-PG formation in MTX-sensitive cells may explain the failure of l-LV to overcome MTX cytotoxicity. In addition to competitive reversal of MTX cytotoxicity by LV, noncompetitive reversal relating to variable formation of MTX-PGs is suggested to be another important factor in the mechanism of the reversal of MTX cytotoxicity by LV.

Further studies on the pharmacologic effects of the 7-hydroxy catabolite of methotrexate in the L1210 murine leukemia cell

This paper describes studies that further explore the pharmacologic activity of the 7-hydroxy catabolite of methotrexate (7-OH-MTX). A 3-hr exposure of L1210 leukemia cells to 100 microM 7-OH-MTX produced negligible suppression of cell growth despite the build-up of intracellular polyglutamyl congeners to levels 2.7 times greater than the dihydrofolate reductase (DHFR) binding capacity. There was no evidence for direct inhibition of DHFR under these conditions based upon measurements of cellular tetrahydrofolate cofactor and dihydrofolate levels, nor was there suppression of [3H]deoxyuridine incorporation into DNA or [14C]formate incorporation into purines. When the interval of exposure to 100 microM 7-OH-MTX was increased to 6 hr, cell growth was inhibited by 60% and there was mild (approximately 50%) inhibition of purine and thymidylate biosynthesis associated with a small increase in cellular dihydrofolate and a small decline in cellular tetrahydrofolates. Consistent with weak inhibition of DHFR was the absence of significant binding of 7-OH-MTX polyglutamates to DHFR as assessed by gel filtration of cell extracts. Mild direct inhibition of purine biosynthetics by 7-OH-MTX- or MTX-polyglutamyl congeners was demonstrated based upon inhibition of [14C]formate incorporation into purines in cells pretreated with fluorodeoxyuridine so as to prevent tetrahydrofolate cofactor depletion or dihydrofolate polyglutamate build-up. Effects of a 6-hr exposure of cells to 100 microM 7-OH MTX on cell growth were reversed completely by 10 microM leucovorin; effects on cells containing comparable levels of MTX polyglutamyl congeners were unaffected by leucovorin. These studies demonstrate very weak inhibition of L1210 leukemia cell growth and purine, pyrimidine and tetrahydrofolate synthesis by the polyglutamyl congeners of 7-OH-MTX. The data suggest that effects of 7-OH-MTX polyglutamates on folate-requiring enzymes are not likely to play an important role in moderate-dose MTX regimens. However, pharmacologic activity may be expressed in high-dose MTX protocols when high blood levels of 7-OH-MTX are sustained over long intervals to the extent to which polyglutamate congeners accumulate in tumor cells and add to the much more potent inhibitory effects of MTX polyglutamates already present. Pharmacologic activity, however, would be diminished, if not completely reversed, by the concurrent administration of leucovorin.

Formation and retention and biological activity of N10-propargyl-5,8-dideazafolic acid (CB3717) polyglutamates in L1210 cells in vitro

The formation, retention and biological activity of the polyglutamate metabolites of the thymidylate synthase (TS) inhibitor N10-propargyl-5,8-dideazafolic acid (CB3717) has been investigated in L1210 murine leukaemia cells grown in vitro. CB3717 polyglutamates were measured by HPLC using high specific activity 3H-CB3717. Following the exposure of cells to 50 microM CB3717 for 6, 12 and 24 hr total cellular radioactivity corresponded to 4.5 +/- 1.5, 6.8 +/- 3.6 and 5.9 +/- 3.4 microM drug derived material, respectively. Of this material, greater than 70%, 57 +/- 3% and 51 +/- 5% was in the form of unchanged CB3717 at 6, 12 and 24 hr respectively. The remaining radioactivity was associated with polyglutamate metabolites of CB3717, predominantly the tetra and pentaglutamate forms. Following the removal of extracellular drug after incubation for 24 hr and resuspension in drug free medium, unchanged CB3717 was lost rapidly from the cells such that after 6 hr it accounted for only 5% of total cellular radioactivity. In contrast, levels of CB3717 tetra and pentaglutamates declined solely due to dilution during cell division. Measurement of the whole cell TS activity by 3H-deoxyuridine incorporation into DNA indicated that, despite the loss of unchanged CB3717 from the cell, enzyme activity remained suppressed (less than 10% of control) for at least 24 hr after resuspension in drug free medium. The TS inhibitory activity of the polyglutamated metabolites of CB3717 was investigated using enzyme purified from L1210 cells. As inhibitors, the metabolites were 26-, 87-, 119- and 114-fold more potent than CB3717 as the di-, tri-, tetra- and pentaglutamate forms, respectively. However, as inhibitors of dihydrofolate reductase prepared from rat liver, CB3717 polyglutamates were no more than 5-fold More potent than the parent compound. This study has shown that CB3717 can undergo polyglutamation in tumour cells and that the metabolites are preferentially retained giving rise to prolonged TS inhibition. By virtue of their potent TS inhibitory activity these metabolites are, therefore, most probably the intracellular effectors of CB3717 cytotoxicity.

Impairment of methotrexate (MTX)-polyglutamate formation of MTX-resistant K562 cell lines

We examined the mechanism of methotrexate (MTX) resistance in five K562 cell subclones resistant to MTX. Based on a clonogenic assay, the IC50S of these MTX-resistant clones were 10 to 40 microM MTX, indicating 2,000 to 5,000-fold resistance as compared to that of the parent cell line. The doubling times of these MTX-resistant K562 cell lines are longer (27-60 hr) than that of the parent K562 cell line (24 hr). One-hour MTX accumulation in the resistant cells cells was 70-80% of that in parent cells. To investigate the formation of MTX-polyglutamates (MTX-PGs), resistant cells were incubated with 3H-MTX (1 or 10 microM) for 24 hr in the presence of thymidine and deoxyinosine to prevent cytotoxicity. MTX (-Glu1) and the polyglutamate metabolites (MTX-Glu2, -Glu3, -Glu4 and -Glu5) were analyzed by a high-pressure liquid chromatography (HPLC) technique. After a 24-hr incubation with 10 microM MTX, the total concentration of intracellular MTX reached 39 to 89 nmol/g protein, only 20 to 40% of the MTX level of the parent K562 cells. The HPLC analysis revealed that less than 2% of intracellular MTX was in the form of high-molecular MTX-PGs (MTX-Glu3, -Glu4 and -Glu5) in the five MTX-resistant K562 cell lines, while in the parent cells MTX-Glu3-5 comprised 46% of the total intracellular MTX. These data indicate the possibility that impairment of MTX-PG formation, with transport alteration, may be a special mechanism for the high level of resistance to this agent in human leukemic cells.

In vivo decline of methotrexate and methotrexate polyglutamates in age-fractionated erythrocytes

Methotrexate (MTX) accumulates in erythrocytes (ery) during weekly MTX administration, and the ery-MTX concentration reaches a steady state after 4-6 weeks. In order to study MTX accumulation and metabolism to polyglutamate derivatives in different age populations of red blood cells, we took erythrocytes from 12 children with ALL who were receiving maintenance treatment with MTX and 6-MP and separated them according to age on a discontinuous Percoll gradient. When the erythrocytes of these children were separated according to specific gravity a normal distribution was obtained. Age fractionation was confirmed by the exponential decline of the erythrocyte aspartate aminotransferase (ery-ASAT) and by the reticulocyte counts. The ery-MTX declined with increasing red blood cell age in an exponential manner no different from the decline of the ery-ASAT. The youngest population of red blood cells contained 2.3-5.9 (mean 3.8) times more MTX than the oldest population. By linear regression analysis the t1/2 of the ery-MTX was 19-79 days (mean 37 days). The ery-MTX t1/2 seemed to be directly related to the amount of MTX which had been metabolized to MTX-glu3-5. The decline of the ery-MTX was predominantly due to selective disappearance of MTX-glu1+2, whereas MTX-glu3-5 changed to a much lesser extent with advancing red blood cell age. The present investigation showed that steady-state ery-MTX concentration was determined by (1) the amount of MTX added to the circulation by the reticulocytes, (2) the in vivo loss predominantly of MTX with low numbers of glutamyl derivatives from erythrocytes, and (3) the loss of MTX from destroyed red blood cells. The observed in vivo disappearance of MTX from erythrocytes offers a possible explanation of the observation that the ery-MTX steady state was reached after 4-6 weeks of unaltered weekly MTX treatment.

Methotrexate and its polyglutamate derivatives in erythrocytes during and after weekly low-dose oral methotrexate therapy of children with acute lymphoblastic leukemia

Methotrexate and methotrexate polyglutamates were quantitatively determined in red blood cells from 12 children with acute lymphoblastic leukemia who were treated with MTX (15-20 mg/m2 per week) and daily 6-mercaptopurine orally during the steady-state period of erythrocyte MTX concentration (ery-MTX). The terminal decline of the ery-MTX and its polyglutamate metabolites were determined for up to 15 weeks after cessation of MTX treatment. Methotrexate polyglutamates with 2-4 extra glutamyl derivatives (MTX-glu2-5) constituted 75% of the MTX in the entire red blood cell population. MTX-glu3 was the principal metabolite; no MTX-glu6-7 was identified. After discontinuation of MTX therapy, the ery-MTX declined in a non-linear manner because of different half-lives for the individual polyglutamates. From about 5 weeks until 13-15 weeks after the last MTX dose, the erythrocyte MTX elimination curve was linear. The approximate half-life of MTX-glu1 was 2-3 days; for MTX-glu2 it was 4-15 days. The concentration of MTX-glu3-5 remained constant in the erythrocyte throughout its life span and declined only with age-dependent destruction of the red blood cell. It was calculated that 80%-90% of MTX in newly formed reticulocytes was MTX-glu1+2, the remainder being MTX-glu3-5. Mature red blood cells did not form methotrexate polyglutamates to any significant degree. There was a significant correlation between the amount of MTX-glu3-5 and the steady -state ery-MTX, which to some extent explained the interindividual variation of the ery-MTX in children with ALL in maintenance therapy.

Inhibition of neutrophil chemotaxis in methotrexate-treated rheumatoid arthritis patients

Polymorphonuclear cell (PMN) chemotaxis was assessed using the in vitro under agarose assay in ten rheumatoid arthritis patients prior to and following a single 10-mg dose of methotrexate (MTX). PMNs obtained from patients after MTX showed a decreased chemotactic migration response to both zymosan activated serum (P less than 0.005) and N-formyl-L-methionyl-L-phenylalanine (P less than 0.01). In similar conditions, no significant difference in chemotactic migration could be detected in six rheumatoid arthritis patients not on MTX. In contrast to the in vivo effects of MTX, there was no inhibition of normal PMN chemotactic migration following a 30-min in vitro incubation of the cells with MTX (P less than 0.99).

Methotrexate metabolism in mutant Chinese hamster ovary cells lacking dihydrofolate reductase

To study the influence of the level of dihydrofolate reductase (DHFR) on methotrexate (MTX) metabolism, the formation of methotrexate polyglutamates (MTXPGs) and the retention of the drug were examined in Chinese hamster ovary cells (DUKXB11) lacking DHFR and in control cells (CHO-UTC). Both cells accumulated MTXPGs poorly. After a 24-hr incubation with 1.0 microM [3H]MTX, the level of total MTX in DUKXB11 cells was 40% of that in CHO-UTC cells, reflecting the lack of DHFR-bound MTX and MTXPGs in the mutant cells. MTXPGs accounted for a higher proportion of the intracellular MTX in DUKXB11 than in CHO-UTC cells (25 vs 18%). Following exposure to 3.0 microM MTX for 24 hr, total drug levels were similar in both cell lines, and MTXPGs constituted even more of the intracellular drug in DUKXB11 cells compared to CHO-UTC cells (34 vs 23%). DUKXB11 cells accumulated longer MTXPGs (MTXG1u3,4) compared to CHO-UTC cells (MTXG1u2,3), following exposure to both 1.0 and 3.0 microM MTX. The longer MTXPGs in the mutant cells may have resulted from the lack of DHFR in them. Binding of MTXPGs to DHFR in CHO-UTC may interfere with their further polyglutamylation. When cells were resuspended in drug-free buffer for 1 hr following a 24-hr incubation with MTX, the retention of drug was less in DUKXB11 cells (46%) than in CHO-UTC cells (78%), due mainly to a greater loss of unmetabolized MTX in the mutant cells (89%) than in control cells (26%). Nevertheless, the amount of non-exchangeable unmetabolized MTX retained in DUKXB11 cells following exposure to 3.0 microM MTX exceeded the MTX-binding capacity. These studies demonstrate that DHFR-deficient cells accumulated more and longer MTXPGs than control cells. In addition, they suggest that some unmetabolized MTX was retained in cells not bound to DHFR.

Effect of methotrexate on intracellular folate pools in purified myeloid precursor cells from normal human bone marrow

We investigated the effects of the antifolate methotrexate on intracellular folate pools of human myeloid precursor cells (MPCs). Immature MPCs, representing 3.2% of the original marrow population, were selected from normal human bone marrow by immune rosetting. The intracellular folate pools were labeled by incubation with 5 X 10(-8) M [3H]5-formyl-FH4 and were quantitated by high performance liquid chromatography. The predominant folates were 5-methyl-tetrahydrofolate (5-methyl-FH4) (36%), 10-formyl-FH4 (41.4%), 5-formyl-FH4 (12.3%), and FH4 (10.3%). A 12-h exposure to 1 microM methotrexate (MTX) resulted in a 34% reduction in the intracellular concentration of 10-formyl-FH4, a 61% decrease in 5-formyl-FH4, and a 62% decrease in 5-methyl-FH4, as well as the appearance and progressive expansion of the FH2 and 10-formyl-FH2 pools. These changes were maximal after 4 h of incubation with MTX. Paralleling the changes in folates, particularly the increase in FH2, were a 64% reduction in myeloid colony formation and a 77% depression of de novo purine synthesis after 4 h of MTX. We conclude that MTX does not produce quantitative depletion of 10-formyl-FH4 and that its antipurine effect may be mediated by direct inhibition of de novo purine synthesis by FH2 and, at later time points, by MTX polyglutamates.

Methotrexate kinetics in myeloid bone marrow cells and peripheral neutrophils

The pharmacokinetics of methotrexate (MTX) in the proliferating and the maturing myeloid compartments of the bone marrow and in the neutrophils of the peripheral blood was investigated in four patients with malignant non-Hodgkin's lymphoma after treatment with 24-h MTX infusions (500-790 mg/m2) followed by leukovorin rescue. The myeloid bone marrow cells were separated into two fractions, using a two-step discontinuous Percoll gradient with densities of 1.076 and 1.095 g/ml. The upper fraction consisted predominantly of immature bone marrow cells plus lymphocytes, and the lower fraction contained the mature myeloid bone marrow cells. Cells in the proliferating (immature) myeloid compartment took up and retained MTX to a much greater extent than the mature myeloid cells and the neutrophils. Two days after the MTX infusion no MTX was detected in the neutrophils in spite of a general rise in the total neutrophil count. MTX reappeared in the neutrophils on day 8 in concentrations not related to the concentrations in the proliferating myeloid cells during the MTX infusion. The time of reappearance of MTX in the neutrophils was in accordance with the time it takes for cells in the proliferating pool of the bone marrow to mature and be released into the circulation. No neutropenia was seen after the MTX infusions.

Methotrexate analogues-27. Dual inhibition of dihydrofolate reductase and folylpolyglutamate synthetase by methotrexate and aminopterin analogues with a gamma-phosphonate group in the side chain

gamma-Phosphonate analogues of methotrexate (MTX) and aminopterin (AMT) were synthesized from 4-amino-4-deoxy-N10-methylpteroic acid and 4-amino-4-deoxy-N10-formylpteroic acid, respectively, by reaction with methyl D,L-2-amino-4-phosphonobutyrate followed by gentle alkaline hydrolysis. The products were compared with the corresponding D,L-homocysteic acid derivatives as inhibitors of dihydrofolate reductase and folylpolyglutamate synthetase, and as inhibitors of cell growth in culture. The gamma-phosphonates were somewhat less active than either the gamma-sulfonates or the parent drugs as inhibitors of murine dihydrofolate reductase. The MTX gamma-sulfonate and gamma-phosphonate analogues were equally inhibitory toward mouse liver folylpolyglutamate synthetase (Ki = 190 microM), but in the AMT series the gamma-phosphonate (Ki = 8.4 microM) was more potent than the gamma-sulfonate (Ki = 45 microM). The AMT analogues were consistently more inhibitory than the MTX analogues against cultured L1210 murine leukemia cells, but neither the gamma-phosphonates nor the gamma-sulfonates were as potent as their respective parent drugs. The gamma-phosphonate analogue of MTX was three times more potent than MTX against the MTX-resistant mutant line L1210/R81, but the AMT gamma-phosphonate was less potent than AMT; however, these differences were small in comparison with the level of resistance to all these compounds in the L1210/R81 line. The results suggest that N10-methyl and N10-unsubstituted compounds altered at the gamma-position do not necessarily follow identical structure-activity patterns in every test system.