Pharmacokinetics of methotrexate and 7-hydroxy-methotrexate in plasma and bone marrow of children receiving low-dose oral methotrexate

The importance of inhibition of a catabolic pathway of methotrexate metabolism in its efficacy for rheumatoid arthritis

Methotrexate (MTX), an antifolate, is the anchor drug for the treatment of rheumatoid arthritis (RA). It is inexpensive, effective, and generally safe. When clinical response is inadequate, biological therapies are commonly used in combination with MTX. However, biological agents have safety concerns (i.e. infections, malignancy) and the addition of a biologic agent is expensive, making strategies to improve MTX efficacy important. Inhibition of pathways of folate metabolism involving purine metabolism by MTX, have been traditionally emphasized as important in MTX efficacy. However, inhibition MTX catabolism may also be important. MTX is irreversibly hydroxylated to form 7-hydroxy methotrexate (7-OH-MTX) by aldehyde oxidase (EC 1.2.3.1) (AOX). Catabolism of MTX to 7-OH-MTX is the first metabolic process imposed on an oral dose of MTX and will alter subsequent interactions of MTX with other enzymes. 7-OH-MTX is less potent than MTX in the treatment of rat adjuvant arthritis. RA patients with a low capacity to catabolize MTX to 7-OH-MTX do better clinically than individuals who are rapid formers of 7-OH-MTX. Therefore, altering the catabolism of MTX may be an innovative way to improve MTX efficacy. Raloxifene is a FDA-approved therapy for postmenopausal osteoporosis and for the reduction of invasive breast cancers but has no known activity in RA. Raloxifene is a potent inhibitor of human liver AOX. Postmenopausal women with RA frequently have low bone mineral density and would be candidates for raloxifene and MTX combination therapy. The effect of raloxifene on MTX metabolism has never been studied. Our hypothesis is that in postmenopausal women with RA and osteoporosis treated with MTX and raloxifene, the inhibition of AOX with resultant decreased formation of 7-OH MTX; will increase MTX levels and improve MTX efficacy. This hypothesis could be studied in an open-label, proof of concept clinical study in individuals before and after the addition of raloxifene. Red blood cell MTX and 7-OH-MTX levels and RA disease activity (DAS28) would be measured. In possible future studies, there are dietary substances, as supplements, (e.g. epigallocatechin gallate in green tea and resveratrol) which inhibit human liver AOX which could be evaluated.

Inventory of oral anticancer agents: Pharmaceutical formulation aspects with focus on the solid dispersion technique

Dissolution from the pharmaceutical formulation is a prerequisite for complete and consistent absorption of any orally administered drug, including anticancer agents (oncolytics). Poor dissolution of an oncolytic can result in low oral bioavailability, high variability in blood concentrations and with that suboptimal or even failing therapy. This review discusses pharmaceutical formulation aspects and absorption pharmacokinetics of currently licensed orally administered oncolytics. In nearly half of orally dosed oncolytics poor dissolution is likely to play a major role in low and unpredictable absorption. Dissolution-limited drug absorption can be improved with a solid dispersion which is a formulation method that induces super-saturated drug dissolution and with that it enhances in vivo absorption. This review discusses formulation principles with focus on the solid dispersion technology and how it works to enhance drug absorption. There are currently three licensed orally dosed oncolytics formulated as a solid dispersion (everolimus, vemurafenib and regorafenib) and these formulations result in remarkably improved dissolution and absorption compared to what can be achieved with conventional formulations of the respective oncolytics. Because of the successful implementation of these three solid dispersion formulations, we encourage the application of this formulation method for poorly soluble oral oncolytics.

Uncertainty and variability in human exposure limits - a chemical-specific approach for ciprofloxacin and methotrexate

Human exposure limits (HELs) for chemicals with a toxicological threshold are traditionally derived using default assessment factors that account for variations in exposure duration, species sensitivity and individual sensitivity. The present paper elaborates a probabilistic approach for human hazard characterization and the derivation of HELs. It extends the framework for evaluating and expressing uncertainty in hazard characterization recently proposed by WHO-IPCS, i.e. by the incorporation of chemical-specific data on human variability in toxicokinetics. The incorporation of human variability in toxicodynamics was based on the variation between adverse outcome pathways (AOPs). Furthermore, sources of interindividual variability and uncertainty are propagated separately throughout the derivation process. The outcome is a two-dimensional human dose distribution that quantifies the population fraction exceeding a pre-selected critical effect level with an estimate of the associated uncertainty. This enables policy makers to set separate standards for the fraction of the population to be protected and the confidence level of the assessment. The main sources of uncertainty in the human dose distribution can be identified in order to plan new research for reducing uncertainty. Additionally, the approach enables quantification of the relative risk for specific subpopulations. The approach is demonstrated for two pharmaceuticals, i.e. the antibiotic ciprofloxacin and the antineoplastic methotrexate. For both substances, the probabilistic HEL is mainly influenced by uncertainty originating from: (1) the point of departure (PoD), (2) extrapolation from sub-acute to chronic toxicity and (3) interspecies extrapolation. However, when assessing the tails of the two-dimensional human dose distributions, i.e. the section relevant for the derivation of human exposure limits, interindividual variability in toxicodynamics also becomes important.

Methotrexate catabolism to 7-hydroxymethotrexate in rheumatoid arthritis alters drug efficacy and retention and is reduced by folic acid supplementation

OBJECTIVE

To assess the catabolism of methotrexate (MTX) to 7-hydroxy-MTX (7-OH-MTX) in patients with rheumatoid arthritis as well as the effect of folic acid and folinic acid on this catabolism.

METHODS

Urinary excretion of MTX and its catabolite, 7-OH-MTX, was measured in 2 24-hour urine specimens collected after MTX therapy. Urine samples were collected from patients after the sixth and seventh weekly doses of MTX. MTX and 7-OH-MTX concentrations were determined by high-performance liquid chromatography mass spectrometry. Swelling and pain/tenderness indices were used to measure symptoms before and at 6 and 7 weeks of therapy. Patients received either folic acid or folinic acid supplements (1 mg/day) from week 6 to week 7.

RESULTS

Folic acid inhibited aldehyde oxidase (AO), the enzyme that produces 7-OH-MTX, but folinic acid did not. Excretion of 7-OH-MTX (determined as a percentage of the dose of MTX or as mg 7-OH-MTX/gm creatinine) was not normally distributed (n=39). Patients with marked improvement in swelling and pain/tenderness indices had a lower mean 7-OH-MTX excretion level (P<0.05). Patients who received folic acid supplements had decreased 7-OH-MTX excretion (P=0.03). Relatively high 7-OH-MTX excretion was correlated with relatively high MTX excretion and with relatively low MTX retention in vivo (P<0.05) (n=35).

CONCLUSION

Our findings of a non-normal distribution of 7-OH-MTX excretion suggest that there are at least 2 phenotypes for this catabolism. Decreased 7-OH-MTX formation suggests folic acid inhibition of AO and a better clinical response, while increased 7-OH-MTX formation may interfere with MTX polyglutamylation and binding to enzymes and, therefore, may increase MTX excretion and decrease MTX retention and efficacy in vivo.

Mechanisms of antifolate resistance and methotrexate efficacy in leukemia cells

Antifolates are the first class of antimetabolites introduced to clinic about 6 decades ago. Now, after several years of administration of antifolates against malignancies and particularly leukemia, we are still trying to achieve a full understanding of the mechanisms of action and resistance to these agents. The present article covers different factors able to influence efficacy of antifolates on leukemic cells, the known mechanisms of resistance to methotrexate (MTX) and strategies to overcome these mechanisms. The dominant factors that are contributed to tolerance to cytocidal effects of MTX including pharmacokinetic factors, impaired transmembrane uptake as the most frequent rote of provoking resistance to MTX, augmented drug efflux, impaired intracellular polyglutamation as a determining process of drug efficacy, alterations in expression or activity of target enzymes and increased intracellular folate pools; and finally role of 7-hydroxymethotrexate on response or resistance to MTX will be discussed in more detail. Finally, strategies to overcome resistance to antifolates are discussed.

Pharmacokinetic studies in children with cancer

We reviewed the current status of our knowledge of pharmacokinetics and pharmacodynamics of some anti-neoplastic drugs, used in the treatment of childhood cancer. Extrapolation of data from pharmacokinetic studies in adults to the paediatric population is often not feasible. Specific studies in children are needed. Of all reviewed anti-neoplastic drugs methotrexate appears to be most extensively studied. Methotrexate pharmacokinetics is correlated with toxicity and response to therapy, and it has been shown that individualized adaptive dosing of methotrexate is correlated with a better response to therapy without increasing toxicity in children with ALL and osteosarcoma. Of most of the other reviewed anti-neoplastic drugs it is demonstrated that pharmacokinetics is correlated with toxicity, and of some drugs a relationship of pharmacokinetics with response to therapy is demonstrated as well. In case of cytarabine, etoposide, and teniposide, individualized dosing also appears to be feasible. However, there is no evidence that this strategy improves response to therapy. Specifically data on pharmacokinetic and pharmacodynamic correlations and effect of pharmacokinetically guided, individualized dosing are important for the design of optimal cancer chemotherapy for individual patients. Unfortunately for a considerable number of anti-neoplastic drugs these specific data are lacking in children and future research is needed.

Use of methotrexate in juvenile idiopathic arthritis

Methotrexate (MTX) has transformed the outlook for children with juvenile idiopathic arthritis (JIA). Most of the evidence from uncontrolled clinical trials suggests that MTX is an effective agent for treating active JIA. Data from controlled clinical trials suggests that MTX has statistically significant effects on patient centred disability measures in JIA patients with active arthritis. Although we would like a much larger study directed evidence base for our use of the drug, the studies that have been done are sound and have been followed by a change in clinical expectations and advice that speak of qualitative evidence from clinical practice, confirming the scientifically acquired data. Randomised controlled multicentre trials using sufficient numbers of patients, including functional assessment and quality of life measures, are needed to confirm the long term efficacy and safety of MTX in JIA.

Separation methods for methotrexate, its structural analogues and metabolites

Methotrexate (MTX) is the prototype folate antagonist cytotoxic drug, employed in the therapy of solid tumors and leukaemias, and recently also as an immunosuppressive agent in organ transplantation, in the treatment of some autoimmune diseases and in the therapy of severe asthma. MTX is one of the very few antineoplastic drugs the therapeutic concentration monitoring of which is currently employed in clinical practice and can be routinely measured in biological samples by a number of different analytical techniques, among which are immunoenzymatic and chromatographic methods. Each technique has of course its own advantages in terms of sensitivity, specificity, speed, cost and level of expertise required. Along with therapeutic drug concentration monitoring and clinical pharmacology, fundamental research into the mechanism of action of antifolate drugs is still a field which requires the measurement of MTX, of its new analogues and of their metabolites in biological samples. This review summarizes the instrumental conditions and the performance of several published chromatographic methods employed to measure MTX, its metabolites and some analogues in clinical and biological research. More than 70 papers describing chromatographic assays for MTX and its metabolites have been published in the literature between 1975 and 2000. A wide array of experimental conditions for sample preparation, analyte separation and detection have been employed. According to their chemical properties, MTX, its metabolites and analogue drugs present in several biological samples (plasma, serum, saliva, urine, cerebrospinal fluid, tissue specimens) can be extracted, separated and detected under a variety of chromatographic conditions, i.e. on different stationary phases, under a wide choice of mobile phase conditions (acidic or neutral, employing ion-pair or micellar chromatography), followed by several detection techniques (UV-Vis spectrophotometry, pre- or post-column oxidation and fluorimetry, electrochemistry, mass spectrometry). Optimized methods allow simultaneous measurement within a few minutes of the plasma levels of MTX and its main metabolites at concentrations in the low-nM range. One special field which needs sensitive, fast and inexpensive methods for the detection and measurement of MTX is the monitoring of contamination in workplace environments, such as pharmaceutical industries and oncological hospital pharmacies, and in sewage waters. The measurement of the intracellular gamma-oligo-glutamate metabolites of biological folates, of MTX and of some analogue drugs is of great importance in basic pharmacological research. The existence of empirical quantitative relationships between the retention of individual oligomers under different chromatographic conditions and the number of added glutamic acid units allows identification of the metabolites even when authentic standards are not available.

Immunosuppressive properties of methotrexate: apoptosis and clonal deletion of activated peripheral T cells

The folate antagonist methotrexate (MTX) is extensively used in graft-versus-host disease, rheumatoid arthritis, and other chronic inflammatory disorders. In addition to its antiinflammatory activity associated with increased release of adenosine, MTX exerts antiproliferative properties by inhibition of dihydrofolate reductase and other folate-dependent enzymes. However, the mechanisms of immunosuppressive properties associated with low-dose MTX treatments are still elusive. We report here that MTX (0.1-10 microM) induces apoptosis of in vitro activated T cells from human peripheral blood. PBL exposed to MTX for 8 h, then activated in drug-free medium, underwent apoptosis, which was completely abrogated by addition of folinic acid or thymidine. Apoptosis of activated T cells did not require interaction between CD95 (Fas, APO-1) and its ligand, and adenosine release accounted for only a small part of this MTX activity. Apoptosis required progression of activated T cells to the S phase of the cell cycle, as it was prevented by drugs or antibodies that interfere with IL-2 synthesis or signaling pathways. MTX achieved clonal deletion of activated T cells in mixed lymphocyte reactions. Finally, in vitro activation of PBL taken from rheumatoid arthritis patients after MTX injection resulted in apoptosis. Altogether, the data demonstrate that MTX can selectively delete activated peripheral blood T cells by a CD95-independent pathway. This property could be used as a new pharmacological end point to optimize dosage and timing of MTX administration. It may account for the immunosuppressive effects of low-dose MTX treatments.

Pharmacology and pharmacokinetics of methotrexate in rheumatic disease. Practical issues in treatment and design

Methotrexate (MTX) is among the most effective drugs for treatment of rheumatoid arthritis and has been proven valuable in the treatment of multiple other disorders of immune regulation. MTX has been administered at a wide range of doses and dose intervals, in conjunction with multiple other drugs, and in patients with a broad range of concomitant disorders. To design a safe and effective MTX treatment plan for an individual patient, the provider must have knowledge of the pharmacology and drug interactions of this effective but potentially dangerous medication. The first section of the article reviews MTX structure, pharmacology pharmacokinetics, and mechanisms of action in rheumatic disease. The second section examines factors that can be used to increase MTX efficacy and decrease toxicity.

Differences in methotrexate and 7-hydroxymethotrexate inhibition of folate-dependent enzymes of purine nucleotide biosynthesis

7-Hydroxymethotrexate (7-OH-MTX) is the major and, frequently the only, pteridine metabolite found in bone-marrow aspirates of patients chronically treated with low-dose oral methotrexate (MTX) [Sonneveld, Schultz, Nooter and Hahlen (1986) Cancer Chemother. Pharmacol. 18, 111-116]. The Ki values for MTX and 7-OH-MTX for avian liver 5-amino-imidazole-4-carboxamide ribonucleotide transformylase differ by 4.5-fold in favour of 7-OH-MTX as the better inhibitor, while Ki values for avian liver glycinamide ribonucleotide transformylase differ by 1.9-fold favouring MTX as the better inhibitor. Thus 7-OH-MTX possesses a different enzyme-inhibiting repertoire from its parent drug and this information may be useful in explaining the mechanism of action of low-dose MTX therapies used to treat autoimmune disease.

Plasma and urine levels of methotrexate and 7-hydroxymethotrexate in children with ALL during maintenance therapy with weekly oral methotrexate

A new high-performance liquid chromatographic assay was used to determine methotrexate (MTX) and its main metabolite, 7-hydroxymethotrexate (7-OH-MTX), in the plasma (n = 17) and urine (n = 14) of children (age 3-12 years) on maintenance therapy for acute lymphocytic leukemia (n = 14) or non-Hodgkin's lymphoma (n = 3). Each child received oral doses of weekly MTX (4.0-29 mg/m2) and daily 6-mercaptopurine (40-111 mg/m2). Plasma samples were collected daily from two children during the 1-week dose interval. A limited sampling strategy was designed, whereby 2 days of blood sampling were used in the other 15 patients. Morning urine samples were collected daily for 1 week following MTX intake from 14 of the children. MTX was detectable in all plasma and urine samples for the entire dose interval. The main metabolite, 7-OH-MTX, could be detected in plasma and urine from all patients on the first day after dose intake but only in a few patients during the whole dose interval. Interpatient variability of MTX and 7-OH-MTX levels was high at all points during the week. Significant correlation were found between the urinary MTX levels on days 2 and 7 and plasma MTX levels on day 2 after intake. No significant correlation was found between drug levels in plasma or urine and liver function tests in the children showing signs of mild liver injury. This assay provides a tool for further studies on the role of pharmacokinetics for the clinical effects of weekly oral low-dose MTX given alone or in combination with 6-mercaptopurine.

Effect of aspirin and sulindac on methotrexate clearance

The pharmacokinetics of low dose methotrexate (MTX) were evaluated in 12 rheumatoid arthritis patients in the presence and absence of steady-state levels of salicylic acid (ASA) and sulindac (SU). Using a Latin square design, patients were given MTX plus ASA (mean 3.4 g/day), MTX plus SU (mean 400 mg/day), or MTX alone. On a background of at least one year of regular MTX therapy, patients received 10 mg/m2 MTX iv (mean 17.8 mg) given after at least 2 weeks of treatment with each of the above regimens. Plasma concentrations of MTX and 7-hydroxymethotrexate (7-OH-MTX) were measured using HPLC. No differences in MTX clearance (Cl) were found comparing MTX alone, MTX + ASA, and MTX + SU. However, if one particular subject that had a very low clearance when receiving MTX alone was excluded, there was a statistically significant decrease in MTX clearance when either ASA or SUL were present. It is also noteworthy that ASA significantly increased the exposure of the subject to 7-OH-MTX and, to a lesser extent, so did sulindac. Since 7-OH-MTX has been shown to be an active metabolite when given for cytotoxic effects at higher doses and because it has been show to be nephrotoxic at doses a thousand-fold greater than used in rheumatoid arthritis, nonsteroidal anti-inflammatory drugs should be used cautiously with MTX until further large scale safety studies are conducted. The data indicate that if a clinically significant interaction were to occur, ASA is more likely than SU to interact with MTX.

6-Thioguanine nucleotide accumulation in red blood cells during maintenance chemotherapy for childhood acute lymphoblastic leukemia, and its relation to leukopenia

In the present study of 12 boys and 19 girls 2-16 years of age (median, 7 years) on oral 6-mercaptopurine (6MP) and methotrexate (MTX) maintenance therapy (MT) for non-B-cell acute lymphoblastic leukemia (ALL), we found that (a) during MT, 6-thioguanine nucleotides (6TGN) (the major cytotoxic metabolite of 6MP) accumulate in the erythrocytes (E-6TGN); (b) for patients receiving an unchanged dose of 6MP, no significant correlation could be demonstrated between the mean E-6TGN (mE-6TGN) and the dose of 6MP (r = -0.11, P = 0.28) (31 patients); (c) among 21 patients receiving 50-75 mg/m2 6MP, a variation of up to 3 orders of magnitude in mE-6TGN could be demonstrated, with the interindividual coefficient of variation (CV) in mE-6TGN for these patients being 0.31; (d) the median intraindividual CV in E-6TGN at an unchanged dose of 6MP was 0.11 (range, 0.04-0.18); and (e) the degree of myelodepression as measured by the mean white cell count was related to mE-6TGN (r = -0.55, P = 0.0006). These results indicate that E-6TGN could be a useful parameter for monitoring 6MP maintenance chemotherapy, although this needs to be explored in prospective studies.

Actions of medroxyprogesterone acetate on the efficacy of cytotoxic drugs: studies with human breast cancer cells in culture

Human breast cancer cells (MCF-7) showed increased responses to methotrexate and vincristine after a 48-hr pre-treatment with medroxyprogesterone acetate. The effect of the hormone, which was detectable at concentrations of between 10 and 100 nM, was independent of its growth-inhibitory action. These findings confirm a previous clinical study and have important implications with regard to the management of advanced breast cancer.