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PubMed1979

Vincristine-methotrexate combination chemotherapy and the influence of weight loss on experimental tumour growth.

According to pharmacokinetic reports, vincristine administration should precede methotrexate therapy. Our sequential treatment of L1210 leukaemic mice, in which vincristine was administered before methotrexate therapy, was as effective as treatment with the two drugs given simultaneously. In solid tumour experiments we were unable to show any increase in the antitumour effect of methotrexate when vincristine was injected before methotrexate administration. Consequently, we advocate the re-evaluation of the practice of vincristine leads to methotrexate therapy as used in many clinical protocols for the treatment of patients with osteosarcoma. Pretreatment with vincristine resulted in methotrexate-induced weight loss and sometimes in toxic death of the mice. Since the growth of tumours can be modified by regulation of the caloric intake of the host, this aspect was investigated in more detail. The effect of starvation, which was comparable to the effect of drug-induced weight loss, had a retarding effect on tumour growth. The growth rates of smaller tumour volumes were less severely affected than were those of large tumour masses.

Animals↗

PubMed1979

Effect of liposome-entrapped methotrexate on Ehrlich ascites tumor cells and uptake in primary liver cell tumor.

A therapeutically useful concentration (0,5 mg/ml) of Methotrexate was prepared in negatively charged artificial liposomes (lecithine: cholesterol: dicetylphosphate=5:5:1 molar ratios). Entrapment yield after separation on Sepharose 6B is nearly 100%. In contrast to free Methotrexate the liposome entrapped folic acid antagonist is eliminated only slowly by the kidneys and after intravenous application it is unevenly distributed in the body of mice, the highest concentrations being found in liver and spleen. Daily injections (7.5 mg/kg/day) of entrapped Methotrexate for 5 days into the tail vein of Ehrlich ascites tumor bearing mice reduced both tumor cell count and the production of ascites fluid about fourfold as compared to mice receiving the same dose of Methotrexate in the free form. Six hours after intravenous application of liposome entrapped Methotrexate the tissue concentration in normal liver is ca. 20-fold higher than when the same amount is applied in the free state. On the other hand, only a little uptake of liposome entrapped Methotrexate was detected in the tissue of nitrosamine-induced primary liver tumor when compared to normal liver tissue of rats.

Animals↗

PubMed1984

Nonlinear renal elimination kinetics of methotrexate due to saturation of renal tubular reabsorption.

The plasma concentration and urinary excretion of methotrexate were followed in twelve psoriatic patients after intravenous and oral doses of methotrexate ranging from 7.5 to 30 mg. In six of the patients, a nonlinear relation was found between the fractional amount of methotrexate excreted in the urine and the corresponding area under the plasma concentration-time curve. The methotrexate clearance was found to be increased during the initial high plasma concentration, probably due to saturation of the tubular reabsorption of methotrexate. Considerable interindividual variation was found in the apparent saturation point of the active reabsorption, but up to 500-800 ng/ml first order kinetics still applied. At plasma concentrations below saturation, the renal clearance of methotrexate ranged from 52-102 ml/min (mean +/- SD, 83 +/- 19.4 ml/min).

Absorption↗

PubMed1978

Pharmacokinetics of high-dose methotrexate treatment in children.

The pharmacokinetics of intravenous high-dose methotrexate were studied in two groups of children being treated for malignant diseases, mostly acute lymphatic leukemia. The peak serum level of methotrexate of 2.32--10(-5) mol/1 was found in children given 500 mg methotrexate/m2 by a 24 h infusion, and another group given 2790 mg/m2 during a 6 h infusion had serum levels as high as 2.16--10(-4) mol/1. The decay of serum concentration of methotrexate after completion of the infusion followed a diphasic curve, with an initial serum half-life of 4.8 h, followed by a second half-life of 34.4 h at distribution equilibrium. The apparent volume of distribution was 56.8 litres/m2. Significant levels of methotrexate were found in cerebrospinal fluid, but penetration into cerebrospinal fluid was slow. Urinary excretion of methotrexate was considerable. Four to five days after commencement of the infusion, urinary concentrations of methotrexate still exceeded the serum levels.

Child↗

PubMed1994

An extended-release formulation of methotrexate for subcutaneous administration.

Methotrexate is a cell-cycle phase-specific antimetabolite that requires prolonged exposure for optimal efficacy. However, the in vivo half-life is short, and repeated administrations are required for optimal efficacy. Methotrexate was encapsulated into a lipid-based drug-delivery system to create an extended-release formulation (Depo/methotrexate) for subcutaneous administration. Pharmacokinetics and efficacy studies were done in BDF1 mice. Depo/methotrexate increased the methotrexate plasma half-life by a factor of 190, from 0.53 to 100 h. Plasma peak levels of the encapsulated drug were 120-fold lower than those of unencapsulated methotrexate, whereas the AUCs (areas under the concentration-time curve) were similar. As a consequence of the extended drug release, the single-dose potency of methotrexate against the L1210 leukemia model was increased by a factor of about 130 without producing significant changes in the therapeutic index. In conclusion, Depo/methotrexate appears to have potential usefulness as an extended-release formulation of methotrexate.

Animals↗

PubMed1985

Low incidence of hepatotoxicity associated with long-term, low-dose oral methotrexate in treatment of refractory psoriasis, psoriatic arthritis, and rheumatoid arthritis. An acceptable risk/benefit ratio.

Thirty patients with psoriasis or other nonmalignant diseases had liver biopsies done before treatment with low-dose methotrexate, 15 mg/week, and then at one- to two-year intervals as long as they continued the methotrexate. All patients were symptomatically improved on this regimen. The 15 patients who had normal liver biopsies at the start of the study had normal biopsies after methotrexate. Fifteen others had minor hepatic histologic abnormalities before treatment. Eleven patients had fatty infiltration. Ten showed no significant change after treatment while one had increased fat and portal fibrosis on a fourth liver biopsy done seven years after MTX was begun. This last patient, a former alcohol abuser, continued methotrexate and showed no further worsening at 8 years. The remaining four had portal fibrosis before treatment. One patient had less fibrosis after methotrexate, two patients slightly more fibrosis, and one a marked increase in portal fibrosis. No patient developed cirrhosis or clinical liver disease. Our results suggest that in the absence of alcohol consumption, low-dose weekly methotrexate treatment rarely causes clinically significant liver damage.

Adult↗

PubMed1979

[High-dose methotrexate therapy in osteogenic sarcoma: plasma pharmakokinetics to predict toxicity (author's transl)].

In 22 patients with osteogenic sarcoma, treated with 103 high-dose methotrexate infusions (6-8.5 g/m2 in 4-6 h) plasma methotrexate levels were measured with a specific and rapid radioimmunoassay. Nontoxic infusions were associated with methotrexate concentrations below 8.0 X 10(-6) mol/l at 24 h, 8.0 X 10(-7) mol/l at 48 h and 4.25 X 10(-7)/mol/1 at 72 h. All patients with 48 h methotrexate levels above 1 X 10-6 mol/l manifested severe toxicity with myelosuppression and stomatitis due to delayed methotrexate excretion. Rise of serum creatinine was not reliable to predict oxicity. Determination of 48- and 72-h methotrexate concentrations proved to be a valuable method for identifying patients at high risk for toxic side effects. Additional citrovorum factor may thus be given in time.

Adolescent↗

PubMed1998

Methotrexate induces apoptotic cell death in human keratinocytes.

The mechanism by which low doses of methotrexate act in psoriasis to restore a clinically normal skin is poorly understood. Apoptosis is a programmed cell death activated when cell removal is needed. The purpose of the present work was to examine using an organotypical model of keratinocyte culture, the possibility that low doses of methotrexate can induce apoptosis of keratinocytes. Epidermal explants were cultivated on dead deepidermized dermis under air-exposed conditions. After 10 days, methotrexate (10(-7) M) was added. After a further 5 days, one part of each culture was fixed and submitted to routine histology, DNA nick end labelling (TUNEL) to detect DNA fragmentation (a molecular marker of apoptotic cell death) and immunohistochemical detection of p53 (a protein involved in apoptosis induced by DNA-damaging agents). The other part of each culture was processed for electron microscopy. A significant proportion of keratinocytes (1%) were damaged and exhibited the morphological features of apoptotic cell death. Immunohistochemical overexpression of p53 was detected in the basal layer of the cultures treated with methotrexate. Low doses of methotrexate induce apoptosis. This mode of action could explain the reduction in epidermal hyperplasia during treatment of psoriasis with methotrexate.

Apoptosis↗

PubMed1985

Low-dose methotrexate treatment of rheumatoid arthritis. Long-term observations.

Of 21 patients with rheumatoid arthritis who began to receive low-dose weekly methotrexate up to five years ago, 15 (71 percent) have continued to take this drug for a mean of 42 months and have received a mean total dose of 2,021 mg (range: 915 to 3,075). The clinical improvement noted at the first follow-up (11 months) was sustained throughout this follow-up period (42 months). Three patients (14 percent) have had complete clinical remission and nine others (43 percent) have had an excellent response. Methotrexate was discontinued in four patients between the first and second follow-up because of planned pregnancy (one), gastrointestinal toxicity (two), and fear of toxicity (one). Liver toxicity assessed in these 21 patients and four others receiving long-term methotrexate therapy revealed acute hepatitis in one and elevated transaminase levels in 12 (48 percent). Liver biopsy specimens in 17 patients after a mean of 1,950 mg of methotrexate (range: 915 to 3,125) revealed mild fibrosis in six and no cirrhosis. Methotrexate can continue to suppress rheumatoid synovitis over a prolonged period of time with minimal toxicity in most patients. Hepatic fibrosis and cirrhosis due to methotrexate may be less common in rheumatoid arthritis than has been reported in psoriasis.

Arthritis, Rheumatoid↗

PubMed1983

Structural requirements for anion substrates of the methotrexate transport system in L1210 cells.

A broad spectrum of structurally diverse anions reversibly inhibits the influx of methotrexate in L1210 cells. Several of the more effective anions and their respective inhibition constants (Ki values) were: 5-methyltetrahydrofolate (0.3 microM), bromosulfophthalein (2 microM), thiamine pyrophosphate (3 microM), 8-anilino-1-naphthalene sulfonate (7 microM), phthalate (20 microM), and AMP (50 microM). Moderate inhibition was observed with Pi (Ki = 400 microM) and other divalent inorganic anions, while small monovalent anions such as Cl- (Ki = 30 mM) were the least effective. When these same anions were tested for an effect on methotrexate efflux, stimulation was observed with some anions, while others had no effect. Enhancement was produced by folate compounds and p-amino-benzoylglutamate, small monovalent (e.g., Cl-, acetate, and lactate) and divalent (e.g., phosphate and succinate) anions, a few nucleotides (e.g., AMP), and thiamine pyrophosphate, while little or no effect was associated with trivalent anions (e.g., citrate), most nucleotides, and large organic anions (e.g., bromosulfophthalein, NAD, and NADP). Anions with the ability to promote methotrexate efflux in control cells lost this capacity upon exposure of the cells to an irreversible inhibitor of methotrexate influx. These results support the hypothesis that methotrexate transport proceeds via an anion-exchange mechanism and moreover provide evidence that anion substrates for this system can be identified by their ability to promote methotrexate efflux. Anions which appear most likely to participate in this exchange cycle in vivo are Pi and AMP.

Animals↗

PubMed1981

Transport of methotrexate in L1210 cells. Mechanism for inhibition by p-chloromercuriphenylsulfonate and N-ethylmaleimide.

Methotrexate transport in L1210 cells is highly sensitive to inhibition by p-chloromercuriphenylsulfonate (CMPS) and, to a lesser extent, by N-ethylmaleimide. A 50% reduction in the methotrexate influx rate occurred upon exposure of cells to 3 microM CMPS or 175 microM N-ethylmaleimide, while complete inhibition was achieved at higher levels of these agents. Dithiothreitol reversed the inhibition by CMPS, suggesting that a sulfhydryl residue is involved. This residue is apparently not located at the substrate binding site of the transport protein, since methotrexate failed to protect the system from inactivation by either CMPS or N-ethylmaleimide, and the transport protein retained the ability to bind substrate (at 4 degrees C) after exposure to these inhibitors (at 37 degrees C). Methotrexate efflux was also inhibition by CMPS (50% at 4 microM), indicating that both the uptake and efflux of methotrexate in L1210 cells occur via the same transport system. High concentrations of CMPS (greater than 20 microM) increased the efflux rate, apparently by damaging the cell membrane and allowing the passive diffusion of methotrexate out of the cell.

4-Chloromercuribenzenesulfonate↗

PubMed1985

Transport of folates at maternal and fetal sides of the placenta: lack of inhibition by methotrexate.

Folate (pteroylglutamate) and methotrexate rapid (seconds) uptake by the trophoblast was investigated from either the maternal or fetal circulations of the isolated dually-perfused guinea-pig placenta. Tissue uptake was measured by using a single-circulation paired-tracer (3H-test and 14C-extracellular marker) technique. [3H]Folate uptakes were 80 and 52% (mean) in perfusates without unlabelled folate, on maternal and fetal sides, respectively. There was negligible 3H-tracer backflux into the circulation up to 6 min probably due to metabolic sequestration. [3H]Methotrexate uptakes were about 85 and 22% on maternal and fetal sides, respectively; however these uptakes were followed by rapid and complete backflux of the label. Specific transplacental transfer of [3H]folate or [3H]methotrexate in either direction was not detectable within 5-6 min. At the brush-border side (maternal) uptake of [3H]folate was highly inhibited by 100 nM unlabelled folate or its reduced form, methyltetrahydrofolate (the main form in plasma); however, equimolar methotrexate (an antifolate chemotherapeutic agent) failed to produce any inhibition of folate uptake. Our findings demonstrate that on both sides of the placenta a high-affinity transport system exists for trophoblast uptake of folate compounds. For methotrexate, either a separate transport system may exist or methotrexate may have a very low affinity for the folate system. These results are distinct from the findings reported in mouse L1210 leukemia cells.

Animals↗

PubMed1988

Effect of methotrexate on long-chain fatty acid metabolism in liver of rats fed a standard or a defined, choline-deficient diet.

The effect of methotrexate on lipids in serum and liver and key enzymes involved in esterification and oxidation of long-chain fatty acids were investigated in rats fed a standard diet and a defined choline-deficient diet. Hepatic metabolism of long-chain fatty acids were also studied in rats fed the defined diet with or without choline. When methotrexate was administered to the rats fed the standard diet there was a slight increase in hepatic lipids and a moderate reduction in the serum level. The palmitoyl-CoA synthetase activity and the microsomal glycerophosphate acyltransferase activity in the liver of rats were increased by methotrexate. The data are consistent with those where the liver may fail to transfer the newly formed triacylglycerols into the plasma with a resultant increase in liver triacylglycerol content and a decrease in serum lipid levels. Fatty liver of methotrexate-exposed rats can not be attributed simply to a reduction of fatty acid oxidation as the carnitine palmitoyltransferase activity was increased. The methotrexate response in the rats fed the defined choline-deficient diet was different. There was a reduction in both serum and hepatic triacylglycerol and the glycerophosphate acyltransferase and palmitoyl-CoA synthetase activities. The carnitine palmitoyltransferase activity was unchanged. Hepatomegaly and increased hepatic fat content, but decreased serum triacylglycerol, total cholesterol and HDL cholesterol were found to be related to the development of choline deficiency as the pleiotropic responses were almost fully prevented by addition of choline to the choline-deficient diet. Addition of choline to the choline-deficient diet normalized the total palmitoyl-CoA synthetase and carnitine palmitoyltransferase activities. In contrast to methotrexate exposure, choline deficiency increased the mitochondrial glycerophosphate acyltransferase activity. The data are consistent with those of where fatty liver induction of choline deficiency may be related to an enhanced esterification of long-chain fatty acids concomitant with a reduction of their oxidation.

Animals↗

PubMed1984

Synthesis and evaluation of 2,4-diaminoquinazoline antifolates with activity against methotrexate-resistant human tumor cells.

In an attempt to find potent antifolates with selectivity against tumor cells with intrinsic or acquired resistance to methotrexate, eleven nonclassical 2,4-diaminoquinazoline antifolates were synthesized and tested as inhibitors of dihydrofolate reductase from L5178Y cells. Several compounds appeared to be good enzyme inhibitors, with I50 values around 1 nM. Two of the compounds were also good inhibitors of cell growth in vitro. One of these (PKC-32, 9-(2,4-diamino-5-methylquinazoline-6-methylene)aminophenanthren e) appeared to be 100-fold more potent than methotrexate as an inhibitor of growth of a methotrexate-resistant cell line with impaired transport for methotrexate. PKC-32 and PKC-155 were also tested against mouse tumors in vivo. PKC-32 was modestly active in vivo as compared with methotrexate. This drug may be a useful agent in the treatment of methotrexate-resistant tumors.

Animals↗

PubMed1988

Thermodynamic characterization of the interactions of methotrexate with dihydrofolate reductase by quantitative affinity chromatography.

Affinity chromatography on methotrexate-Sepharose has been used to evaluate dissociation constants for interactions of methotrexate with dihydrofolate reductase from Lactobacillus casei. Equilibrium constants of 0.25 microM and 0.6 nM were obtained for dissociation of the inhibitor from the enzyme-methotrexate and enzyme-NADPH-methotrexate complexes, respectively, these estimates being in good agreement with the corresponding published values for dihydrofolate reductase from Streptococcus faecium. By employing a different method for evaluating the thermodynamic dissociation constant for the enzyme-NADPH-methotrexate interaction, this investigation provides independent support for the inference drawn from published fluorescence quenching studies that the interaction of methotrexate with dihydrofolate reductase-NADPH complex is governed by a dissociation constant in the vicinity of 600 pM, a value slightly higher than, but approaching, the inhibition constant of 50-60 pM obtained by enzyme kinetic techniques.

Chromatography, Affinity↗

PubMed1994

Analysis of free fatty acid effect on methotrexate binding to albumin.

The binding of methotrexate to human serum albumin and the inhibitory effect of serum free fatty acids (FFA) have been studied by equilibrium dialysis with radiolabeled methotrexate. Methotrexate was bound to albumin via a single site (1.03 +/- 0.02) with a low affinity (1350 +/- 60 M-1). The effect of FFA on binding by albumin of methotrexate was analysed according to the classical inhibition models with computation of the free inhibitor concentration and was ascribed to an uncompetitive type of inhibition. These results were in agreement with the observed serum binding of methotrexate (45-50%) and allowed the simulation of the effect of various concentrations of FFA on methotrexate albumin binding in human serum.

Binding, Competitive↗

PubMed1994

Role of N-glycosylation in the structure and function of the methotrexate membrane transporter from CCRF-CEM human lymphoblastic leukemia cells.

The carrier protein for methotrexate and tetrahydrofolate cofactors (GP-MTX) in CCRF-CEM human lymphoblastic leukemia cells in a 117 kDa glycoprotein containing both N- and O-linked oligosaccharides (Matherly et al., J Biol Chem 267: 23253-23260, 1992). Tunicamycin, an inhibitor of N-glycosylation, was used to investigate the roles of asparagine-linked oligosaccharides in the structure, intracellular routing, and transport function of GP-MTX. Tunicamycin was growth inhibitory toward CCRF-CEM cells (IC50-0.80 micrograms/mL) and caused a potent suppression of [3H]mannose incorporation into nascent glycoproteins. From 1-3 micrograms/mL, inhibition of [3H]mannose incorporation was 66-87%, exceeding that for [35S]methionine incorporation by 2 to 4-fold. Tunicamycin (1 and 2 micrograms/mL) exposures decreased the median molecular masses of GP-MTX on immunoblots (to 82 and 67 kDa, respectively) and were accompanied by reduced maximal rates of methotrexate uptake (31 and 37%, respectively, of control levels). Conversely, the Ki values for methotrexate binding to the transporter were unaffected by tunicamycin treatments. The effects of tunicamycin on methotrexate influx closely correlated with lower levels of immunoreactive GP-MTX in plasma membranes and specific [3H]methotrexate binding to intact cells, suggesting that the transport effect was due to decreased numbers of carrier proteins at the membrane surface. The reduced molecular mass values for GP-MTX, which accompanied tunicamycin exposures, were further decreased (to 55 and 50 kDa at 1 and 2 micrograms/mL, respectively) by digestions with N-glycanase. Hence, despite the large loss of N-glycan from GP-MTX in tunicamycin-treated cells, residual core oligosaccharides remained. The sizes of hypoglycosylated GP-MTX following both treatments were similar to that of the functionally homologous methotrexate membrane carrier previously identified in L1210 murine leukemia cells.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed1996

Identification of efflux systems for large anions and anionic conjugates as the mediators of methotrexate efflux in L1210 Cells.

Two ATP-dependent efflux systems for methotrexate have been identified in inside-out vesicles from an L1210 mouse cell variant with a defective influx carrier for methotrexate. Transport at 40 muM [3H]methotrexate was separated by inhibitors into two components comprising 62 and 38% of total transport activity. The predominant route was inhibited by low concentrations of indoprofen (Ki=2.5 muM, 4-biphenylacetic acid (Ki=5.3 muM), and flurbiprofen (Ki=5.2 muM, whereas the second component showed a high sensitivity to the glutathione conjugates of bromosulfophthalein (Ki=0.08 muM), ethacrynic acid (Ki=0.52 muM, and 1-chloro-2,4-dinitrobenzene (Ki=0.77 muM). Bilirubin ditaurate was a potent inhibitor of both transport components (Ki=1.5 and 0.17 muM, respectively). Separation of transport activities without interference from the other route was achieved by adding an excess (100 muM) of either the glutathione conjugate of ethacrynic acid or biphenylacetic acid. Double-reciprocal plots of transport at various substrate concentrations gave Km values of 170 and 250 muM for methotrexate transport via the anion-sensitive and conjugate-sensitive routes, respectively. A comparison of inhibitor specificities indicated that the anion-sensitive transport activity in vesicles represents efflux system II for methotrexate in intact cells and is the same system identified previously in vesicles as an anion/anion conjugate pump. The conjugate-sensitive activity corresponds to efflux system I for methotrexate in intact cells and is the same system identified in vesicles as the high-affinity glutathione conjugate pump.

Adenosine Triphosphate↗