Facile Electrochemical Determination of Methotrexate (MTX) Using Glassy Carbon Electrode-Modified with Electronically Disordered NiO Nanostructures

Recently, the oxidative behavior of methotrexate (MTX) anticancer drug is highly demanded, due to its side effects on healthy cells, despite being a very challenging task. In this study, we have prepared porous NiO material using sodium sulfate as an electronic disorder reagent by hydrothermal method and found it highly sensitive and selective for the oxidation of MTX. The synthesized NiO nanostructures were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. These physical characterizations delineated the porous morphology and cubic crystalline phase of NiO. Different electrochemical approaches have been utilized to determine the MTX concentrations in 0.04 M Britton-Robinson buffer (BRB) at pH 2 using glassy carbon electrode (GCE)-modified with electronically disordered NiO nanostructures. The linear range for MTX using cyclic voltammetry (CV) was found to be from 5 to 30 nM, and the limit of detection (LOD) and limit of quantification (LOQ) were 1.46 nM and 4.86 nM, respectively, whereas the linear range obtained via linear sweep voltammetry (LSV) was estimated as 15-90 nM with LOD and LOQ of 0.819 nM and 2.713 nM, respectively. Additionally, amperometric studies revealed a linear range from 10 to70 nM with LOD and LOQ of 0.1 nM and 1.3 nM, respectively. Importantly, MTX was successfully monitored in pharmaceutical products using the standard recovery method. Thus, the proposed approach for the synthesis of active metal oxide materials could be sued for the determination of other anticancer drugs in real samples and other biomedical applications.

Pros and cons of the tuberculosis drugome approach--an empirical analysis

Drug-resistant Mycobacterium tuberculosis (MTB), the causative pathogen of tuberculosis (TB), has become a serious threat to global public health. Yet the development of novel drugs against MTB has been lagging. One potentially powerful approach to drug development is computation-aided repositioning of current drugs. However, the effectiveness of this approach has rarely been examined. Here we select the "TB drugome" approach--a protein structure-based method for drug repositioning for tuberculosis treatment--to (1) experimentally validate the efficacy of the identified drug candidates for inhibiting MTB growth, and (2) computationally examine how consistently drug candidates are prioritized, considering changes in input data. Twenty three drugs in the TB drugome were tested. Of them, only two drugs (tamoxifen and 4-hydroxytamoxifen) effectively suppressed MTB growth at relatively high concentrations. Both drugs significantly enhanced the inhibitory effects of three first-line anti-TB drugs (rifampin, isoniazid, and ethambutol). However, tamoxifen is not a top-listed drug in the TB drugome, and 4-hydroxytamoxifen is not approved for use in humans. Computational re-examination of the TB drugome indicated that the rankings were subject to technical and data-related biases. Thus, although our results support the effectiveness of the TB drugome approach for identifying drugs that can potentially be repositioned for stand-alone applications or for combination treatments for TB, the approach requires further refinements via incorporation of additional biological information. Our findings can also be extended to other structure-based drug repositioning methods.

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.

Dihydrofolate Reductase Enzyme Inhibition Assay for Plasma Methotrexate Determination Using a 96-Well Microplate Reader

Microplate reader assays offer several advantages over conventional spectrophotometric assays. We adapted the dihydrofolate reductase (DHFR) enzyme inhibition assay for use in a 96-well microplate reader to measure plasma methotrexate (MTX) concentrations. The assay is linear from 0.01 to 0.1 μmol/L. The within-run CVs at 0.03 μmol/L and 0.08 μmol/L MTX were 4.0% and 2.7%, respectively, and the interday (total) CVs were 7.6% and 1.8%. Cross-reactivity with the inactive MTX metabolite 2,4-diamino-N10-methylpteroic acid (DAMPA) was 3.9%, significantly less than that described with commercial immunoassays; with 7-hydroxymethotrexate cross-reactivity was 1.7%. In addition to sensitivity and specificity, the advantages of this assay are small sample volumes, simultaneous analysis of multiple samples, and rapid turnaround. Because of its greater specificity, the DHFR enzyme inhibition assay may be useful when DAMPA is present in plasma samples and HPLC is not available.

Improved high-performance liquid chromatography determination of methotrexate and its major metabolite in plasma using a poly(styrene-divinylbenzene) column

A sensitive high-performance liquid chromatographic assay has been developed for measuring plasma concentrations of methotrexate and its major metabolite, 7-hydroxymethotrexate. Methotrexate and metabolite were extracted from plasma using solid-phase extraction. An internal standard, aminopterin was used. Chromatographic separation was achieved using a 15-cm poly(styrene-divinylbenzene) (PRP-1) column. This column is more robust than a silica-based stationary phase. Post column, the eluent was irradiated with UV light, producing fluorescent photolytic degradation products of methotrexate and the metabolite. The excitation and emission wavelengths of fluorescence detection were at 350 and 435 nm, respectively. The mobile phase consisted of 0.1 M phosphate buffer (pH 6.5), with 6% N,N-dimethylformamide and 0.2% of 30% hydrogen peroxide. The absolute recoveries for methotrexate and 7-hydroxymethotrexate were greater than 86%. Precision, expressed as a coefficient of variation (n=6), was <10% at each of five methotrexate concentrations in the range 2.5-50 ng/ml. The limits of quantitation of methotrexate were 1 and 2.5 ng/ml for methotrexate and 7-hydroxymethotrexate, respectively (using 1 ml plasma). A robust HPLC method has been developed for the reproducible quantitation of methotrexate in plasma of patients taking a weekly dose of methotrexate for rheumatoid arthritis.

Capillary electrophoretic drug monitoring of methotrexate and leucovorin and their metabolites

High-dose methotrexate is an important element of treatment protocols in childhood acute lymphocytic leukemia or osteosarcoma. A capillary electrophoretic method has been developed to measure peak levels and the metabolite pattern in patients with delayed methotrexate elimination. It serves to determine plasma levels of methotrexate, leucovorin and their metabolites, 7-hydroxymethotrexate, 2,4-diamino-N10 -methylpteroic acid and 5-methyltetrahydrofolic acid. For the determination of high concentrations (>10 microM) protein precipitation by acetonitrile will suffice for sample preparation. All other samples undergo solid-phase extraction and upgrading on C18 columns. Aminopterin, a therapeutic antecedent of methotrexate, serves as internal standard. Detection is done on a UV detector with a 300 nm filter. Five hundred microl of serum are needed to determine 0.2 microM of a specified substance (0.5 microM 5-methylterahydrofolic acid) with good precision and accuracy. For peak levels, 20 microl of capillary serum are sufficient.

Methotrexate plasma pharmacokinetics: importance of assay method

Intravenous methotrexate (MTX) therapy is widely used for treatment of various neoplastic diseases in children. The optimization of the MTX dose and/or the subsequent leucovorin rescue is based on pharmacokinetic data calculated from plasma concentrations collected after cessation of the MTX administration. The influence of the MTX assay method on the subsequent pharmacokinetic evaluation was studied in 13 children with acute lymphoblastic leukemia. Plasma samples were collected after administration of MTX (5-8 g/m2) as 24 h infusions. All samples were analyzed by five different analytical procedures, viz. liquid chromatography (LC), enzyme inhibition assay (EIA), two fluorescence polarization immunoassays (FPIA1 and FPIA2) and enzyme multiplied immunoassay (EMIT). Using measurements from the four non-chromatographic procedures, only about 50% of determined pharmacokinetic parameters (area under the plasma concentration time curve, calculated by the trapezoidal rule and from pharmacokinetic modelling, and the terminal half life time) were within the range 75-125% of the values obtained from LC data. We conclude that the clinical outcome of MTX therapy using estimated MTX pharmacokinetics as guidelines for proper dosing of MTX and/or leucovorin rescue might be affected by the lack of accuracy of non-chromatographic procedures for MTX analysis. There is still a need for improving the accuracy of the procedures aimed at therapeutic drug monitoring of MTX.

The effect of food on the absorption of methotrexate sodium tablets in healthy volunteers

OBJECTIVE

To examine the effect of food on the absorption and bioavailability of low-dose orally administered methotrexate sodium tablets.

METHODS

In this randomized, 2-way crossover study, a 7.5-mg dose of methotrexate (three 2.5-mg tablets) was administered to 12 healthy male volunteers after an overnight fast or within 10 minutes of consuming a high fat-content breakfast. Serum methotrexate concentrations over the next 24 hours were used to determine the area under the concentration-time curve (AUC), the maximum concentration, the time to maximum concentration (tmax), and the serum half-life for each phase.

RESULTS

Food delayed the tmax by approximately 30 minutes, but the extent of absorption, as measured by the AUC, for both phases was similar.

CONCLUSION

These results demonstrate that the bioavailability of low-dose orally administered methotrexate sodium tablets is not influenced by food.

Antineoplastic agents inhibit the growth of Streptococcus mutans and Streptococcus sanguis in vitro

The effect of methotrexate (MTX) and doxorubicin on the growth, metabolism and ultrastructure of Streptococcus mutans and Streptococcus sanguis was studied in vitro. Both anticancer drugs exerted an inhibitory effect on the oral streptococci. MTX was more inhibitory than doxorubicin. The minimum inhibitory concentrations (MICs) of MTX to S. mutans were 0.25-2.5 micrograms/ml and that of doxorubicin 0.2 mg/ml. The MICs of MTX and doxorubicin to S. sanguis were 0.025 micrograms/ml and 2.0-0.02 mg/ml, respectively. When saliva samples of patients with malignant tumors receiving various doses of MTX were analyzed, MTX was found to be secreted into the oral cavity at concentrations ranging from 0.014 to 4.486 micrograms/ml. The saliva of these patients was also found to inhibit the growth of S. mutans, and the inhibition zones were in accordance with the MIC values observed. The results suggest that anticancer therapy must be taken into account when the salivary microbiological findings of cancer patients are interpreted.

Pharmacokinetic study of methotrexate, folinic acid and their serum metabolites in children treated with high-dose methotrexate and leucovorin rescue

The pharmacokinetics of methotrexate (MTX), 7-hydroxymethotrexate (7-OHMTX), 2,4-diaminomethylpteroic acid (APA), folinic acid, and 5-methyltetrahydrofolate (5-MTHF) have been studied during 21 high-dose MTX (HDMTX) infusions (5 g.m-2 in 24 h) with leucovorin (LCV) rescue, a component of the therapy of 5 children with acute lymphoblastic leukemia (ALL). The median steady-state concentration of MTX was 66 mumol.l-1. Three elimination half-lifes were determined for MTX: 1.8 h, 6.4 h and a terminal 15 h. The median systemic MTX clearance was 110 mg.m-2.min-1. The 7-OHMTX level increased during each infusion and a Cmax of 19 mumol.l-1 was achieved at the end. Its initial half-life was 5 h and the terminal half-life was 12 h. Thus, the peak serum concentration ratio of 7-OHMTX to MTX was reached 24 h after the end of the infusion at a median ratio of 8. The MTX metabolite APA was detected in concentrations less than 0.06 mumol.l-1. The median folinic acid level during rescue, 48 h after starting the infusion, was 7.0 mumol.l-1 and 18 h following the last dose of LCV it was 0.44 mumol.l-1, leading to ratios of folinic acid to MTX of 31 and 6, respectively. The median 5-MTHF level during rescue was 0.44 mumol.l-1 with a median ratio of 5-MTHF to MTX of 2. Twenty infusions with 48 h MTX levels of less than 0.5 mumol.l-1 were without marked toxicity. Only one patient with a 48 h MTX concentration of 5.5 mumol.l-1 and a ratio of 5-MTHF to MTX of 0.08 suffered from ulcerating mucositis and septicaemia despite increased and prolonged LCV rescue.

Flow cytometric analysis of marrow cell kinetics in children treated with high-dose MTX and CF rescue

Normal marrow cell kinetics were studied by flow cytometry with computer analysis in 11 children with malignancies who received high-dose MTX followed by CF rescue. Nine children with hematological tumors in remission each received an infusion of MTX over 24 h, followed by delayed CF rescue. In 8 of the 9, an accumulation of cells in early to mid-S phase and a decrease of cells in G2/M phase were observed at 24-48 h after the beginning of the MTX infusion. At 144 h after MTX infusion this kinetic perturbation disappeared and the DNA histogram returned to the same state as before therapy. Two children who had malignant bone tumors without marrow infiltration each received an infusion of MTX over 6 h with early CF rescue following an initial IV injection of vincristine. They did not have any prominent perturbation of marrow cell kinetics after MTX exposure, except for a transient increase of cells in G2/M phase. These results confirm that with the high-dose MTX therapy described above for hematological malignancies the impairment of marrow cell kinetics was much more severe and was soon followed by complete recovery, whereas with the therapy for solid tumors the impairment was much slighter.

Renal excretion and pharmacokinetics of methotrexate and 7-hydroxy-methotrexate following a 24-h high dose infusion of methotrexate in children

In children with lymphoid malignancies 18 courses of methotrexate (18-200 mg/kg) administered as a 24-h infusion were monitored. Plasma concentrations and renal excretion rates of methotrexate (MTX) and 7-hydroxymethotrexate (7-OHMTX) were determined. A low correlation was found between the administered dose of MTX and the body exposure to MTX or 7-OHMTX. Although 84% of the MTX eventually recovered from the urine was excreted during the 24 h of the infusion, the renal clearance of MTX was markedly lower during the time of the infusion than after it. There were courses with a low and others with a high renal clearance of MTX during the infusion, despite the same urine flow. A low MTX renal clearance was correlated with a high body exposure to MTX. As the same variations were also seen in the same patient during successive courses, pharmacokinetical characterization of patients appears questionable. The renal clearance of 7-OHMTX was significantly lower than the renal clearance of MTX, and the body exposure to 7-OHMTX ranged from 2-40% of the MTX body exposure. Treatment courses with a low or a high body exposure to 7-OHMTX were not associated with different urinary recoveries of the metabolite. Differences in MTX hydroxylation could not be substantiated. Because the concentration of 7-OHMTX is high soon after the end of an infusion, a specific method of MTX determination should be chosen for controlling treatment.

Drug level monitoring: cytostatics

The present review on the quantification of cytostatic drugs has mainly been focussed on chromatographic techniques. Special attention has been paid to the precautions that have to be taken into account to ensure the selectivity and accuracy of the various methods. The various cytostatics that have been dealt with are: alkylating agents, antimetabolites, vinca alkaloids, antibiotics, cis-diamminedichloroplatinum, podophyllotoxine derivatives, and nitrosoureas.

Systemic thermochemotherapy: toxicity and plasma pharmacokinetics of methotrexate and doxorubicin

Chemotherapy administered during systemic hyperthermia is more tumoricidal than either modality used alone. The purpose of this study was to evaluate plasma drug pharmacokinetics and host toxicity when methotrexate (MTX) or doxorubicin (adriamycin--ADR) was given at 37 or 43 degrees C. Eight dogs were heated to 43 degrees C for 1 hr without chemotherapy; eight dogs received MTX (5 mg/kg) and four dogs received ADR (2 mg/kg) intravenously as a constant infusion at 43 or 37 degrees C. Blood samples were obtained at 0, 1, 2, 24, and 48 hr. Mean plasma MTX levels were not significantly different at 1, 2, and 6 hours in 43 and 37 degrees C dogs, but at 24 and 48 hr mean plasma MTX levels were significantly elevated in heated (43 degrees C) dogs compared with sham-heated (37 degrees C) dogs. Plasma MTX concentration multiplied by time (area under curve) was 131 g . hr/liter in 43 degrees C dogs compared with 73 g . hr/liter in 37 degrees C dogs (P less than 0.001). Vomiting and bloody diarrhea lasted an average of 4 days in heated control dogs (no drugs) 4 days in 37 degrees C dogs, and 5 to 7 days in 43 degrees C MTX dogs. Mean plasma ADR levels were similar in 37 and 43 degrees C dogs at all time intervals. Vomiting and bloody diarrhea lasted at least 7 days in 43 degrees C dogs compared with only 1 day in 37 degrees C dogs treated with ADR.(ABSTRACT TRUNCATED AT 250 WORDS)

Theoretically required urinary flow during high-dose methotrexate infusion

The renal excretion of methotrexate (MTX) and its major metabolite 7-hydroxymethotrexate (7-OH-MTX) was analysed in 12 children with malignancies during 52 courses of high-dose methotrexate (H-D-MTX) infusion at dosages ranging from 0.7 to 8.4 g/m2. The peak concentrations of both MTX and 7-OH-MTX exceeded the aqueous solubilities of these compounds at low pH (less than or equal to 6.0). The cumulative MTX excretion in urine was 75%-98% of the administered amount of MTX, and the cumulative 7-OH-MTX excretion in the urine was 3%-15%. The theoretically required urinary flow (TRUF) was estimated as the minimum urine volume needed for complete resolution of MTX and its metabolites in urine. TRUF during MTX infusion from 0 to 6 h and from 6 to 12 h was correlated with the dosage of MTX, and these values were 0.1-1.8 ml/min/m2 at pH 7.0, 0.5-11.1 ml/min/m2 at pH 6.0, and 1.9-42.2 ml/min/m2 at pH 5.0 with dosages of 0.7 to 8.4 g/m2. The value of the theoretically required urinary flow is important to ensure adequate hydration and the optimum alkalinization schedule for massive MTX infusion.

Enzymatic synthesis of polyglutamate derivatives of 7-hydroxymethotrexate

7-Hydroxymethotrexate, an important metabolite of methotrexate, is a substrate for folylpolyglutamate synthetase (FPGS) isolated from rat liver and several human leukemia cell lines. The substrate activity it displays over a wide range of concentrations (0-200 microM) is nearly equivalent to that of methotrexate. The 7-hydroxy derivative of dichloromethotrexate is also a substrate for FPGS. The pattern of polyglutamate products synthesized by rat liver FPGS was nearly identical with both 7-hydroxymethotrexate and methotrexate. In addition, conversion of MTX polyglutamates to the corresponding 7-hydroxy compounds was demonstrated using partially purified rabbit liver aldehyde oxidase. The rate of conversion was concentration dependent, and the relative rate decreased as the MTX polyglutamate chain length increased. We propose that 7-hydroxymethotrexate polyglutamates may be formed by initial hydroxylation of methotrexate and subsequent polyglutamate formation or by direct hydroxylation of methotrexate polyglutamates. It was further shown that the relative substrate activity of folate analogs for folylpolyglutamate synthetase is dependent on the source of the enzyme.

Pharmacokinetics of methotrexate and 7-hydroxy-methotrexate in rabbits after intravenous administration

The pharmacokinetics of methotrexate (MTX) and 7-hydroxy-methotrexate (7-OH-MTX), a major metabolite, were investigated in rabbits after intravenous bolus injection and infusion using a specific HPLC assay. The arterial sampling (from the carotid artery) was used in all the studies since peculiar and significant arterial-venous differences in the plasma concentration of MTX and 7-OH-MTX were found following bolus administration of the drug. The disposition kinetics of MTX appeared polyexponential with a small terminal phase having a half-life of 10.2-27.5 hr. Extensive formation of 7-OH-MTX occurred at the two dose levels (15 and 50 mg/kg). Nonlinear disposition of MTX was reflected in several aspects of data analysis. A disproportionate increase in the AUC with dose was observed. An increase in dose not only reduced the mean total body clearance (7.49 vs. 4.26 ml/min/kg) and renal clearance (4.89 vs. 2.76 ml/min/kg), but also prolonged the mean residence time (26.2 vs. 43.3 min). The steady-state volume of distribution (Vss) of MTX was estimated to range from 0.16 to 0.25 L/kg. More than 90% of the dose was excreted as MTX and 7-OH-MTX within 8 hr after dosing. Renal clearances decreased with the increasing plasma levels, suggesting active tubular secretion as one of the excretion mechanisms. A similar pattern for renal clearance of 7-OH-MTX was obtained. Infusion studies of 7-OH-MTX revealed that this metabolite had a longer residence time and a larger Vss as compared with MTX, which were in accordance with its physicochemical properties. Essentially complete doses of 7-OH-MTX could be recovered in the rabbit urine.

Clearance studies of methotrexate and 7-hydroxy-methotrexate in rabbits after multiple-dose infusion

The concentration-dependent clearance of methotrexate (MTX) and its metabolite, 7-hydroxy-methotrexate (7-OH-MTX), was demonstrated in 5 rabbits using 7 infusion rates (10.5-323 mg/hr). Mean total body clearance (from 34.3 to 13.1 ml/min) and mean renal clearance (from 25.6 to 7.6 ml/min) of MTX were found to decrease with increasing steady-state plasma concentrations (from 5.1 to 412 micrograms/ml), whereas nonrenal clearances remained relatively constant. An essentially steady-state plasma level of 7-OH-MTX was achieved during each MTX infusion, and its renal clearance also decreased (from 37.3 to 6.5 ml/min) with increasing metabolite levels (from 1.8 to 293 micrograms/ml). Saturable renal tubular secretion appeared operative for both drug and metabolite since their renal clearance (based on the free drug) to inulin clearance ratios were much greater than unity and the ratios were markedly reduced in 2 rabbits after probenecid treatment. Plasma protein binding of MTX (56%) and 7-OH-MTX (49%) were independent of concentrations between 0.1 and 300 micrograms/ml. Negligible MTX metabolism was found in rabbit kidney homogenates, thus validating renal clearance measurement in the present study.

High-performance liquid chromatographic analysis of MTX, 7-OH-MTX and MTX derivatives: application to intracellular metabolism in tumor cells (HT 29)

In order to study the intracellular metabolism of Methotrexate (MTX) and the cytotoxicity of the antifolates, a specific paired-ion HPLC method has been developed which permits the simultaneous determination of DAMPA, MTX, 7-OH-MTX, MTX-G1, MTX-G2 and MTX-G3. Cells were incubated with 3H-MTX. The MTX metabolites were extracted, purified on SEP-PAK cartridges and further analysed by high-performance liquid chromatography (HPLC). The stationary phase was constituted by a C18 muBondapak and the mobile phase by 5 mM phosphate buffer (pH 7.4) containing 2.5 mM tetrabutylammonium nitrate. The elution was performed with a linear methanol gradient (20--30%). HPLC fractions were collected and radioactivity evaluated by beta counting (retention times: DAMPA = 12.93 min; MTX = 18.29 min; 7-OH-MTX = 21.13 min; MTX-G1 = 22.69 min; MTX-G2 = 26.81 min; MTX-G3 = 30.61 min). This analytical procedure was applied to separate and characterize multiple forms of MTX polyglutamate derivatives in HT 29, a human adenocarcinoma cell line varying the incubation time (4--18 h) and MTX concentration (0.6--10.6 micrometer). The incorporation process seems to be characteristic of a cell line resistant to MTX. The incorporation were very low and after a 4-h exposure time only 5% of the MTX was converted to polyglutamates. Between 1.6 and 10.6 microM MTX, no difference was observed in the polyglutamization. The defect in the incorporation of the drug and in the metabolization process in vitro could partially explain the failure of the MTX treatment in colorectal cancer.

Formation and disposition of 7-hydroxymethotrexate in rabbits

The metabolism of methotrexate in rabbits was investigated following 6 hr of infusion with [3',5',7-(3)H]methotrexate (50 mg/kg). Methotrexate and its metabolites were analyzed by an enzyme kinetic method, reverse phase high-performance liquid chromatography, and scintillation counting of radioactivity. 7-Hydroxymethotrexate was found to be a major metabolite in plasma, urine, bile and various tissues of rabbits. Cumulative production of 7-hydroxymethotrexate during the first 6 hr was 31.8% of the total dose. The peak 7-hydroxymethotrexate concentration in plasma was reached at the end of the infusion, and this concentration was higher than the methotrexate concentration. The plasma clearance of 7-hydroxymethotrexate was biphasic in nature and slower than that of methotrexate. The highest methotrexate concentration was found in kidney after 6 hr. This concentration was found to be 7.2 times greater than that in plasma. A higher ratio of 7-hydroxymethotrexate/methotrexate was found in liver, small intestine, kidney and testis when compared to plasma. Lung and kidney showed significant conversion of methotrexate to 7-hydroxymethotrexate in vitro, as did the liver.

An assay for methotrexate and its metabolites in serum and urine by ion-pair high-performance liquid chromatography

A high-performance liquid chromatographic assay for methotrexate and its metabolites, 7-hydroxy-methotrexate, 4-amino-4-deoxy-N10-methyl-pteroic acid and 7-hydroxy-4-amino-4-deoxy-N10-methyl-pteroic acid in the range 10 microg/l to 50 mg/l (2.2 x 10(-8) to 1.1. x 10(-4)M) has been developed using L-tryptophyl-L-glutamic acid as internal standard. Extraction was performed using an anion exchange resin (Dowex 1-X2) with subsequent ion-pair chromatography of the appropriate eluent fraction. The method has been found to be sensitive and precise for the analysis of both serum and urine, and may also be used for the quantitation of polyglutamyl metabolites.

Reversed-phase high-pressure liquid chromatographic determination of serum methotrexate and 7-hydroxymethotrexate

A reversed-phase high-pressure liquid chromatographic method for determining methotrexate and 7-hydroxymethotrexate in human serum is presented. A mobile phase of acetate buffer (0.2 M, pH 5.5 with 0.03 M ethylenediaminetetraacetate), methanol, and acetonitrile (85.3:8.4:6.3), passed through a mu Bondapak C18 column at 1.5 ml/min produced excellent resolution of sharp, symmetrical bands. An improved extraction process, using a sample preparation cartridge, resulted in analytical recoveries in excess of 90% for methotrexate and 70% for 7-hydroxymethotrexate, permitting the determination of serum concentrations of 2.20 and 2.13 x 10(-7) M, respectively, using only 200 microliter of serum. UV detection at 313 nm provided adequate sensitivity for each component. While the reproducibility for 7-hydroxymethotrexate was approximately equal to previous methods, that for methotrexate was greatly improved. Serum methotrexate data at selected time points following high dose methotrexate therapy are presented.

Sensitive and rapid high-performance liquid chromatographic method for the simultaneous determination of methotrexate and its metabolites in plasma, saliva and urine

A simple and sensitive high-performance liquid chromatographic assay of methotrexate (MTX) and its two active metabolites, 7-hydroxymethotrexate (7-OH-MTX) and and 2,4-diamino-N10-methylpteroic acid (APA) in plasma, saliva and urine was developed. The method involved deproteinization with acetonitrile followed by addition of isoamyl alcohol and ethyl acetate. After extraction the sample was chromatographed on a cation-exchange column and monitored at 313 nm. The retention times were 5, 7 and 9 min and detection limits 20, 10 and 5 ng/ml for 7-OH-MTX, MTX and APA, respectively. For concentrations greater than 100 ng/ml one-step deproteinization of 0.1 ml sample with 0.25 ml acetonitrile was satisfactory for sample preparations. The method has been evaluated in samples from patients and rabbits receiving MTX.