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PubMed2000

Lymphomas in patients with connective tissue disease. Comparison of p53 protein expression and latent EBV infection in patients immunosuppressed and not immunosuppressed with methotrexate.

Cell cycle dysregulation as measured by p53 protein expression and latent Epstein-Barr (EBV) infection are important in the pathogenesis of lymphoma, particularly in immunosuppressed patients. Although latent EBV commonly is detected in lymphomas arising in patients with connective tissue disease who are immunosuppressed with methotrexate, p53 protein expression has not been reported. We compared the immunohistologic expression of p53 protein and the incidence of latent EBV infection in lymphomas arising in patients with connective tissue disease treated and not treated with methotrexate. Increased p53 staining was detected in 10 of 11 lymphomas arising in patients after methotrexate therapy vs 5 of 11 in patients not treated with methotrexate. Latent EBV was detected in 7 of 13 lymphomas arising in patients after methotrexate therapy vs 2 of 11 in patients not treated with methotrexate. Concordant p53 expression and latent EBV were detected in 5 of 7 lymphomas arising after treatment with methotrexate, including 1 that regressed after methotrexate therapy was withdrawn. These findings suggest that cell cycle dysregulation and EBV-related transformation are important in the pathogenesis of lymphomas arising in patients with connective tissue disease who are immunosuppressed with methotrexate.

Adolescent↗

PubMed2006

Population pharmacokinetics of high-dose methotrexate in children with acute lymphoblastic leukaemia.

OBJECTIVE: To develop and a priori validate a methotrexate population pharmacokinetic model in children with acute lymphoblastic leukaemia (ALL), receiving high-dose methotrexate followed by folinic acid rescue, identifying the covariates that could explain part of the pharmacokinetic variability of methotrexate. METHODS: The study was carried out in 49 children (aged 6 months to 17 years) who received high-dose methotrexate (3 g/m(2) per course) in long-term treatment. In an index group (37 individuals; 1236 methotrexate plasma concentrations), a population pharmacokinetic model was developed using a nonlinear mixed-effects model. The remaining patients' data (12 individuals; 278 methotrexate plasma concentrations) were used for model validation. Age, sex, total bodyweight (TBW), height, body surface area, lowest urine pH during infusion, serum creatinine, ALT, AST, folinic acid dose and length of rescue were analysed as possible covariates. The final predictive performance of the pharmacokinetic model was tested using standardised mean prediction errors. RESULTS: The final population pharmacokinetic model (two-compartmental) included only age and total bodyweight as influencing clearance (CL) and volume of distribution of central compartment (V(1)). For children aged < or =10 years: CL (L/h) = 0.287 . TBW(0.876); V(1) (L) = 0.465 . TBW, and for children aged >10 years: CL (L/h) = 0.149 . TBW; V(1) (L) = 0.437 . TBW. From the base to the final model, the inter-individual variabilities for CL and V(1) were significantly reduced in both age groups (30-50%). The coefficients of variation of the pharmacokinetic parameters were <30%, while residual and inter-occasional coefficients maintained values close to 40%. Validation of the proposed model revealed the suitability of the model. CONCLUSION: A methotrexate population pharmacokinetic model has been developed for ALL children. The proposed model could be used in Bayesian algorithms with a limited sampling strategy to estimate the systemic exposure of individual patients to methotrexate and adapt both folinic acid rescue and methotrexate dosing accordingly.

Adolescent↗

PubMed2002

Economic comparison of leflunomide and methotrexate in patients with rheumatoid arthritis: an evaluation based on a 1-year randomised controlled trial.

OBJECTIVE: To compare disease-related medical care and productivity costs, and utilities, in 482 patients with rheumatoid arthritis randomised to receive leflunomide, methotrexate or placebo during a 12-month period. DESIGN AND SETTING: Prospective pharmacoeconomic analysis of a 1-year randomised double-blind trial set in North America. PERSPECTIVE: Societal and the Ontario Ministry of Health. METHODS: Information on healthcare resources, out-of-pocket expenses, loss of working time and time spent on chores, related to the disease or the medication, were collected at 4-week intervals and at study discontinuation. Rating scale and standard gamble (SG) utilities (0 = worse; 100 = best) were collected at baseline and at 6 and 12 months or study exit. Medical care costs in Canadian dollars (Can dollars) were calculated using Ontario reimbursement schedules. US patients' expenses were converted to Can dollars using 1995 purchasing power parity. Lost wages were calculated by age and gender according to 1995 Canadian wage data. All costs were adjusted to 1999 Can dollars and arithmetic mean costs were compared using the nonparametric bootstrap. Analysis of covariance was performed to compare utilities between groups. RESULTS: Mean (standard deviation) rating scale values and SG utilities, respectively, for leflunomide, methotrexate and placebo were 67.7 (18.0), 64.8 (18.1) and 57.5 (9.2), and 80.2 (22.1), 83.2 (18.0) and 77.0 (20.5). Both leflunomide and methotrexate had higher rating scale values (p < 0.05) compared with placebo; SG utilities were significantly different between methotrexate and placebo (p < 0.05). Annualised total rheumatoid arthritisb- or drug-related costs for leflunomide, methotrexate and placebo, respectively, were Can dollars 1761, Can dollars 1280 and Can dollars 1324, and medical care costs were Can dollars 753, Can dollars 620 and Can dollars 167 (all costs exclude drug acquisition and monitoring costs). Annual drug acquisition/ routine monitoring costs were estimated, respectively, at Can dollars 3853/Can dollars 483 for leflunomide and Can dollars 258/Can dollars 599 for methotrexate. Differences between overall costs (excluding drug acquisition and monitoring costs) and medical care costs were not statistically significant. The costs of treating patients with leflunomide were significantly higher than for methotrexate when drug acquisition and monitoring costs were included (p < 0.0001). CONCLUSIONS: No statistically significant differences in utilities could be found between leflunomide or methotrexate. When drug monitoring and acquisition costs are excluded, leflunomide has an otherwise similar economic profile compared with methotrexate, the current gold standard. The acquisition cost of leflunomide is a driving factor in increasing the costs of therapy. These higher costs need to be assessed relative to the therapeutic value of leflunomide.

Adolescent↗

PubMed1990

Rescue after intermediate and high-dose methotrexate: background, rationale, and current practice.

Pharmacologic rescue methods used in combination with intermediate and high-dose methotrexate therapy are reviewed, with special emphasis on rescue with nucleosides and folinic acid. The mechanism of action, pharmacokinetics, and clinical applications of the rescue agents are described in detail in view of the literature and also of the own findings of the authors. In spite of the promising results of the in vitro studies and in vivo experiments in animal models, the clinical value of thymidine as a rescue agent remains to be determined. Currently, the only indication to use thymidine instead of folinic acid following high-dose methotrexate is to prevent toxicity related to extremely high methotrexate levels in patients with delayed elimination of methotrexate. In spite of the widespread application of folinic acid rescue, the exact mechanism of its action is not fully understood. The rescue dose and schedule in the majority of clinical protocols is empirical, and the start of the rescue administration is too early, allowing less than 36 to 42 hours of exposure to methotrexate. Clinical and laboratory findings indicate that while the early start of FA administration is unnecessary for protecting normal cells, it is potentially dangerous in terms of reduction of the antitumor effect of methotrexate. Our findings suggest that less than the most widely used 12-15 mg/m2 per dose rescue may be sufficient in preventing methotrexate related toxicity in patients with normal elimination of the drug. In addition, reducing the dose of the rescue may be beneficial to achieve better therapeutic results with high-dose methotrexate. Due to methodological problems, the pharmacokinetics of folinic acid rescue has not been excessively studied in humans. Recent data indicate that the pharmacokinetics of folinic acid in children is characterized by great intra- and interpatient variability. The effect of food on the bioavailability of folinic acid has not yet been studied, though it is most frequently administered orally. The introduction of the pure l-stereoisomer of the rescue agent in the clinical practice may eliminate potential interactions with the d-isomer, and may also simplify the introduction of therapeutic drug monitoring for folinic acid as well. This could lead to more rational clinical use of folinic acid as a rescue agent following intermediate and high-dose methotrexate therapy.

Cell Survival↗

PubMed1998

Insulin-like growth factor-I (IGF-I) stimulates regrowth of the damaged intestine in rats, when administered following, but not concurrent with, methotrexate.

BACKGROUND: We tested the ability of insulin-like growth factor-I (IGF-I) to reduce damage to the intestinal mucosa (mucositis) in rats injected with methotrexate. IGF-I was infused concurrent with methotrexate administration and compared to IGF-I administered following the withdrawal of methotrexate. METHODS: Rats were injected with methotrexate at the start of days 1, 2 and 3. IGF-I was infused for 5 days, commencing at the start of day 1 [concurrent administration] or at the start of day 4 [post-methotrexate administration]. RESULTS: IGF-I administered coincident with methotrexate failed to restore mucosal integrity to the damaged small intestine. IGF-I administered post methotrexate stimulated regrowth of the damaged intestine, particularly the ileum, with 22%, 32% and 29% increases in small intestinal weight, ileal villus height and ileal crypt depth respectively. CONCLUSIONS: Following intestinal damage of methotrexate, IGF-I primarily induced growth of the distal small intestine. The ineffectiveness of concurrently administered IGF-I may have represented an IGF-I induced recruitment of proliferating epithelial cells to the anti-proliferative effects of methotrexate.

Animals↗

PubMed2000

Trans-stimulation effects of folic acid derivatives on methotrexate transport by rat renal organic anion transporter, OAT-K1.

We examined the pharmacological role of the renal organic anion transporter OAT-K1, which localizes predominantly in the brush-border membranes of proximal straight tubules, in the urinary excretion of methotrexate and the possibility of its contribution to "folinic acid rescue." With Madin-Darby canine kidney (MDCK) cells stably transfected with OAT-K1 cDNA, OAT-K1-mediated methotrexate accumulation was inhibited in the presence of various folic acid derivatives. These derivatives included aminopterin, 5-methyltetrahydrofolic acid, unlabeled methotrexate, folinic acid (citrovorum factor, leucovorin), and folic acid with apparent inhibition constant values of 0.5, 1.2, 1.8, 8.2, and 14.1 microM, respectively. In contrast, 10 microM taurocholic acid and sulfobromophthalein did not inhibit OAT-K1-mediated methotrexate accumulation. In addition, methotrexate efflux was stimulated in the presence of inwardly directed gradients of aminopterin, 5-methyltetrahydrofolic acid, unlabeled methotrexate, folinic acid, and folic acid, but not of uric acid, taurocholic acid, and glutathione, indicating that OAT-K1-mediated methotrexate efflux is stimulated by a folic acid derivatives exchange. In conclusion, OAT-K1 was suggested to enhance the apical efflux of highly accumulated methotrexate in tubular epithelial cells and contribute at least in part to folinic acid rescue by exchanging intracellular methotrexate for extracellular folinic acid.

Aminopterin↗

PubMedDate not supplied

Effect of a synthetic analog of prostaglandin E1 on the intestinal mucosa of methotrexate-treated rats.

Administration of methotrexate to rats sometimes induces small intestinal damage. A synthetic analog of prostaglandin E1, OP-1206 [17S,20-dimethyl-trans-delta2-prostaglandin E1] may possibly provide therapeutic benefits to help recovery from such small intestinal damage. The purpose of this study was to evaluate the effect of OP-1206 on methotrexate-induced small intestinal damage in rats. Methotrexate (15 mg/kg body weight) was orally administered to rats once daily for 5 days. OP-1206 (0.5 microg/kg body weight) was orally administered to rats twice a day for 5 days and on the 6th day the small intestine of the rats were examined histologically and biochemically. The methotrexate treatment of rats caused a severe histological change in the small intestinal mucosa, whereas the treatment combined of OP-1206 with methotrexate showed similar histological features of the small intestinal mucosa as that of the control rats. On the other hand, an acute intestinal inflammation was evaluated by determining myeloperoxidase activity. The myeloperoxidase activity in the small intestinal mucosa of the methotrexate-treated rats increased remarkably, whereas that of the methotrexate and OP-1206-treated rats was significantly lower than that of the methotrexate-treated rats. Thus, it was shown histologically and biochemically that OP-1206 was effective in protecting the small intestine from methotrexate-induced damage.

Alprostadil↗

PubMedDate not supplied

A prospective, double-blind, randomized, placebo controlled trial of methotrexate in the treatment of giant cell arteritis (GCA).

OBJECTIVE: To determine if methotrexate has disease-controlling and corticosteroid (cs)-sparing effects in the treatment of giant cell arteritis (GCA). METHODS: This was a randomized, controlled, double-blind trial comparing methotrexate versus placebo in addition to corticosteroid therapy in patients with newly diagnosed giant cell arteritis. Patients with giant cell arteritis were enrolled and treated with high dose corticosteroids as well as methotrexate starting at 7.5 mg/week or placebo. Corticosteroids were tapered by the treating physician as guided by the clinical picture, with methotrexate or placebo dose increased by 2.5 mg/week for disease flare with a maximum allowable dose of 20 mg/week. After a clinically-defined remission and steroid discontinuation, methotrexate or placebo was tapered monthly to zero by 2.5 mg/week. RESULTS: Twenty-one patients were enrolled, 12 randomized to methotrexate, 9 to placebo. Baseline characteristics (age, height, weight, sedimentation rate, bone mineral density, total corticosteroid dose prior to randomization, and quality of life as measured by SF-36 and function as measured by AIMS) were comparable between groups. At completion, there was no significant difference between methotrexate- and placebo-treated patients with regard to the cumulative corticosteroid dose (6469 mg and 5908 mg respectively, p = 0.6), number of weeks to completion of steroids (68 and 60 respectively, p = 0.5), time (weeks) to taper prednisone to less than 10 mg prednisone/day (23 and 25 respectively, p = 0.5), bone mineral density in lumbar spine (p = 0.2) or hip (p = 0.4) at one year, or functional status as measured by AIMS and quality of life as measured by SF36. There was no late vision loss in either group, and only one major treatment-responsive relapse in a methotrexate-treated patient. There were few major corticosteroid-related side effects and these did not significantly differ between groups. CONCLUSION: With this study design, no corticosteroid-sparing benefit could be attributed to the combination of methotrexate with corticosteroid therapy for the treatment of patients with giant cell arteritis. Both groups did well, with few major corticosteroid-related side effects, and most patients were safely tapered off corticosteroids sooner than reported in many series. The shorter overall duration of steroid treatment in this study probably contributed to the remarkably low frequency of side effects, without increased ischemic risk for the patient.

Aged↗

PubMedDate not supplied

Methotrexate as the "anchor drug" for the treatment of early rheumatoid arthritis.

The two major advances over the 1990s in the treatment of rheumatoid arthritis (RA) were a shift in strategy from a "pyramid", in which disease modifying anti-rheumatic drugs (DMARDs) were deferred for several years, to the early aggressive use of DMARDs and widespread acceptance of methotrexate as the DMARD with the most long-term effectiveness and safety. Methotrexate courses are continued far longer than those of any other DMARD, an excellent indicator of greater effectiveness and safety. In one recent series, methotrexate was the first DMARD used in more than 80% of patients with RA. Studies which document the superiority of combinations of methotrexate with biological agents to methotrexate monotherapy select for only a minority of contemporary patients with RA who have severe disease activity and incomplete responses to methotrexate. In one locale, only 5% of patients met criteria for the Anti-Tumor Necrosis Factor Trial in RA with Concomitant Therapy (ATTRACT) trial and only 30% met the criteria for the Early Rheumatoid Arthritis (ERA) trial. In studies comparing methotrexate directly with biological agents, the biological agents have greater efficacy in patients with very severe disease, but the best results are seen in patients who take a combination of methotrexate and biologic agents. These data establish that methotrexate is the anchor drug and probably should be the first DMARD used in the majority of patients with RA at this time.

Antirheumatic Agents↗

PubMed2003

Mortality in rheumatoid arthritis patients treated with or without methotrexate.

BACKGROUND: Rheumatoid arthritis (RA) is a chronic disease associated with excess mortality. In 1974 a registry of RA patients was established at the Wichita Arthritis Center. It has been directed by its founder, Dr. Frederick Wolfe, ever since. The database for RA patients provided results for the present study and 1 of the 4 series reported previously. RESULTS: These are based on a consecutive series (after specific exclusions) of RA patients, 18 years of age and older, treated at the Wichita Arthritis Center, 1981 through 1999. During this period, 588 of the total 1240 RA patients were treated with methotrexate, and 652 patients did not receive any methotrexate. Total exposure amounted to 7584 patient-years, and total deaths numbered 191. An elaborate statistical method was developed by Wolfe and a team of Harvard epidemiologists to adjust for prognostic risk factors, which were higher in the methotrexate than in the non-methotrexate group. Detailed descriptive data were included in the database. Overall excess mortality in comparison with population rates was higher in the methotrexate than in the non-methotrexate group, but the unadjusted difference was not significant. Results for the 1981-1999 total Wichita cohort were compared with those of the 1974-1990 cohort and the 1983 Impairment Study (both before and after adjustment to the older age distribution of the Wichita patients). CONCLUSION: Mortality improved somewhat in the RA patients at the Wichita Center from 1974-1990 to 1980-1999. In the later period, mortality was lower in patients treated with methotrexate than in those not so treated. After the authors of the source article made adjustments for the increased RA severity in the patients treated with methotrexate, mortality was significantly lower in the methotrexate-treated group, with a mortality hazard ratio of 0.4 (95% confidence interval 0.2-0.8).

Actuarial Analysis↗

PubMed1990

Pharmacokinetics of continuous infusion of methotrexate and teniposide in pediatric cancer patients.

Laboratory studies have demonstrated the ability of teniposide to markedly enhance the intracellular accumulation of methotrexate suggesting that combination therapy with these agents may produce clinical benefit. Studies of methotrexate and teniposide were conducted in 19 children with relapsed acute lymphocytic leukemia to evaluate the pharmacokinetics of this previously untested combination of agents given alone or in combination and to demonstrate the feasibility of a Bayesian dose optimization strategy. Patients were randomly assigned to receive intermediate dose methotrexate as a 24-h continuous infusion, administered either simultaneously with continuous infusion teniposide or sequentially with the teniposide infusion beginning 12 h after the end of the methotrexate infusion. Plasma samples were obtained during and after infusions at appropriate times for a comprehensive pharmacokinetic study of each drug. Two measured drug concentrations obtained during the infusion were used to adjust each patient's dose rate to achieve target values of 10 microM for methotrexate and 15 microM for teniposide. Pharmacokinetic parameters for teniposide were not different for patients given simultaneous methotrexate from parameters estimated for patients receiving teniposide 12 h after the end of the methotrexate infusion. Despite similar end of infusion methotrexate concentrations, 24-h postinfusion methotrexate concentrations were lower (0.137 versus 0.235 microM; P less than 0.05) in the patients receiving simultaneous infusions. The patient specific dose regimens yielded acceptably precise, minimally biased steady state drug concentrations. These pharmacokinetic results provide the basis for further clinical studies with this combination of antileukemic agents.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed1986

Hepatic parenchymal cell glutamylation of methotrexate studied in monolayer culture.

A detailed analysis of the gamma-glutamylation of methotrexate has been conducted in primary cultures of rat hepatic parenchymal cells in monolayer culture. The rates of glutamylation are concentration dependent and saturable when measured over a 6-h period at concentrations between 2 and 50 microM. The removal of folate and inclusion of insulin, dexamethasone, and tocopherol enhance glutamylation. Omission of methionine from the medium increases glutamylation, whereas the 6-h period of syntheses, methotrexate the reaction. During the 6-h period of syntheses, methotrexate diglutamate is the primary product, whereas the di- and triglutamates are the major cellular species when the incubation is extended to 24 h. Lower extracellular methotrexate concentrations result in the formation of relatively greater amounts of longer chain length derivatives. The accumulation of methotrexate polyglutamates at steady state is saturable and occurs by 24 h. The predominant species contain two to four glutamate residues, and the distribution depends upon the culture conditions and the extracellular methotrexate concentration. The turnover of cellular polyglutamates at saturation occurs at 30 to 40% of the total cell pool over a 6-h period. Placement of hepatocytes with saturating levels of methotrexate polyglutamates in medium lacking methotrexate results in the slow loss of all derivatives, and the rate of loss is inversely related to polyglutamate chain length. Following a pulse dose of methotrexate, hepatocytes continue to increase the chain length of the cellular pool of polyglutamates, and this process is impaired by addition of folinic acid to the medium. In the pulse experiments as in the longer term incubations, the primary species are the di- and triglutamates. The results demonstrate limited capacity of the hepatocytes to glutamylate longer chain length polyglutamate derivatives.

Animals↗

PubMed1989

Inherent resistance of human squamous carcinoma cell lines to methotrexate as a result of decreased polyglutamylation of this drug.

Three human squamous carcinoma cell lines (FaDu, A253, and SQCC/Y1) were tested for sensitivity to methotrexate (MTX) and trimetrexate, a second generation folate antagonist in clinical trials. Two of the three cell lines (A253 and SQCC/Y1) showed inherent resistance to methotrexate, when cytotoxicity was evaluated after short term exposure (4 and 24 h). In contrast, all three cell lines were markedly sensitive to trimetrexate, an antifolate which is taken up by cells by a different transport system than is methotrexate and which is not polyglutamylated. The basis for the natural resistance to methotrexate shown by two of the three cell lines was examined. Levels of dihydrofolate reductase activity, inhibition of this enzyme by methotrexate, and influx of MTX did not differ significantly between the three cell lines; however, resistance was correlated to the amounts of polyglutamates of methotrexate synthesized by the three cell lines. After a 24-h incubation with 10 microM MTX, the A253 cell line was able to form only 35.0 pmol/10(7) cells of polyglutamates, compared to 250 pmol/10(7) cells synthesized by the FaDu cell line, while the SQCC/Y1 cell line, intermediate in sensitivity to methotrexate, was able to form 145 pmol/10(7) cells of MTX polyglutamates. The A253 cell line contained less folylpolyglutamate synthetase activity compared to the FaDu and SQCC/Y1 cell lines. However, it is not clear if this difference is sufficient to explain the marked differences in polyglutamates of methotrexate found between the cell lines. We conclude that decreased polyglutamylation of methotrexate in some human squamous cell carcinomas may be the major contributing factor in inherent resistance to high dose pulse administration of this drug.

Antineoplastic Agents↗

PubMed1989

The role of liver biopsies in psoriatic patients receiving long-term methotrexate treatment. Improvement in liver abnormalities after cessation of treatment.

Liver biopsy specimens from 168 patients who underwent a total of 364 biopsies were examined. Of 83 patients receiving biopsies before methotrexate treatment, 14 had one or more risk factors predictive of liver abnormality but they had normal pretreatment biopsy specimens. Among 17 patients with abnormal biopsy specimens before methotrexate treatment, only 1 had an identifiable risk factor and 5 had abnormal results of liver function tests. The probability of a normal biopsy specimen after methotrexate treatment dropped below 50% at a cumulative methotrexate dose of 3115 mg for the 31 patients with biopsy specimens from before and after methotrexate treatment and 5776 mg for those who had biopsies only after methotrexate treatment; this difference was statistically significant and is thought to be related to the fact that the patients who had biopsies before and after methotrexate treatment had received most of their medication by the parenteral rather than the oral route. A significant association existed between biopsy grade after methotrexate treatment and obesity. Other risk factors were not correlated with biopsy grade. Blood chemistry tests were not predictive of histopathologic findings. Eight of 11 patients with fibrosis or cirrhosis showed meaningful improvement in liver histologic findings after methotrexate treatment had been withdrawn for 6 months or more; none had progression of abnormalities.

Adolescent↗

PubMed1986

Development of an assay system for the detection and classification of methotrexate resistance in fresh human leukemic cells.

An assay system was developed for the detection and classification of methotrexate resistance in fresh human leukemic cells. Mechanisms of resistance to be identified were: overexpression of dihydrofolate reductase, decreased cellular uptake of methotrexate, decreased affinity of dihydrofolate reductase for methotrexate, decreased polyglutamylation of methotrexate, and low thymidylate synthase activity. The initial screening procedure utilizes 3H release after addition of [5-3H]-2'-deoxyuridine as a measure of intracellular activity of thymidylate synthase and of DNA synthesis; 3H release is assayed after 3-h incubations with methotrexate, trimetrexate, or gamma-fluoromethotrexate and after 4-h incubations with these agents followed by a 6-h incubation in drug free medium. The pattern of DNA synthesis inhibition and recovery under these two sets of conditions establishes the presence or absence of methotrexate resistance and allows a tentative classification of the resistance mechanism involved. In combination with determinations of dihydrofolate reductase activity, methotrexate titration studies, and the determination of intracellular drug accumulations in vitro, the system is readily able to classify CCRF-CEM human leukemia cell lines possessing well defined mechanisms of resistance. The findings in seven leukemia patients are also reported. Applying tentative reference values, four patients showed biochemical evidence of methotrexate resistance: two patients had only a transport defect, one patient had evidence of both a transport defect and low thymidylate synthase activity, and one patient appeared to have decreased methotrexate polyglutamylation. Application of the assay system in larger numbers of patients is feasible and is required to establish adequate reference values for the evaluation of biochemical-clinical correlates.

Adolescent↗

PubMed1982

Biochemical correlates of responsiveness and collateral sensitivity of some methotrexate-resistant murine tumors to the lipophilic antifolate, metoprine.

The M5076 murine "ovarian" tumor which is naturally refractive to methotrexate was found to be highly responsive to the lipophilic antifolate, metoprine. M5076 cells were markedly deficient in mediated entry of methotrexate. This was in contrast to the L1210 leukemia, a tumor highly responsive to methotrexate but poorly responsive to metoprine. Two L1210 leukemia sublines, with acquired resistance to methotrexate by virtue of a deficiency in mediated entry of drug similar to that seen for M5076 cells, were found to be collaterally sensitive to metoprine. The insensitivity to methotrexate of the M5076 tumor and the two L1210 sublines is associated with low saturability (high Km) and reduced capacity (low Vmax) for mediated influx of drug. 5-Methyltetrahydrofolate, the major circulating folate in blood but not metoprine, shares this mediated route for entry. Therefore, a relatively low level of accumulation of this natural folate in these methotrexate-resistant tumors, in the face of a metoprine-induced blockade at the level of dihydrofolate reductase, probably accounts for the high sensitivity of these tumors to this lipophilic agent. Evidence for this notion was derived during transport and growth experiments in vitro using 5-formyltetrahydrofolate as a model folate coenzyme. The value for influx Vmax of this folate compound in a transport-deficient methotrexate-resistant subline compared to the parental L1210 was reduced to the same extent as that shown for methotrexate. Growth of this resistant L1210 subline showed a greater requirement for this model compound than did the parental line. Also, the concentration necessary for 50% inhibition by metoprine in the presence of this reduced folate was lower in the resistant subline. Inhibition of each cell line by metoprine, on the other hand, was the same when folic acid was used as the folate source. The implications of these findings for the use of lipophilic antifolates as alternative therapy for some methotrexate-resistant tumors are discussed.

Animals↗

PubMed1982

Enterohepatic circulation of methotrexate in rats in vivo.

The pharmacokinetics of the methotrexate enterohepatic cycle were studied in rats in vivo. For plasma levels of methotrexate between 10(-5) and 10(-8) M, biliary levels were directly proportional and concentrated 27-fold. When labeled methotrexate was administered in doses sufficient to achieve plasma levels of 10(-6) M, approximately 50% of methotrexate appeared in the bile in normal animals and up to 80% appeared in anephric animals. In spite of the high percentage of administered methotrexate which appeared in the bile, complete interruption of the enterohepatic cycle in otherwise normal animals did not affect the plasma decay curve of a bolus of methotrexate. The increased biliary excretion which occurred in animals with renal impairment was utilized with possible therapeutic implications. Bile drainage in these animals rapidly decreased plasma methotrexate levels compared to nondrained controls. This suggests that interruption of the methotrexate enterohepatic cycle may provide an alternative for the management of methotrexate toxicity associated with renal insufficiency.

Animals↗

PubMed1981

Relative frequency and kinetic properties of transport-defective phenotypes among methotrexate-resistant L1210 clonal cell lines derived in vivo.

Information was sought on the relative extent to which transport-defective, methotrexate-resistant phenotypes emerge among the total subpopulation of resistant phenotypes during therapeutic challenge of leukemic cells in vivo. A number of monoclonal methotrexate-resistant sublines of the L1210 leukemia were derived during methotrexate therapy of leukemic mice and biochemically characterized. Of the total number of 14 sublines derived, five exhibited altered [3H]methotrexate transport alone, five exhibited increased dihydrofolate reductase content alone (2- to 18-fold), and four showed alterations in both of these properties. Methotrexate binding and substrate turnover rate for dihydrofolate reductase appeared to be unchanged in any of the resistant sublines. The relative resistance of each subline was accounted for by the biochemical alterations observed. Among the transport-defective sublines, one subcategory showed a 3- to 4-fold reduction in apparent influx Vmax for [3H]methotrexate, a second category showed both a 5-fold reduction in influx Vmax and a 3-fold increase in the apparent influx Km, and one subline showed only a 2-fold increase in Km. Otherwise, Michaelis-Menten saturation kinetics for influx was observed in each case and in the case of the parental line and the other resistant sublines. None of the resistant sublines exhibited altered efflux of [3H]methotrexate. Steady-state levels measured for intracellular exchangeable (osmotically active) fractions of drug accurately reflected the values for specific kinetic parameters determined for each sensitive and resistant cell line. These studies show that transport-defective phenotypes represent a major category of methotrexate-resistant cell types which emerge initially from leukemic cell populations under therapy in mice. Based on considerations discussed here, it is reasonable to assume that a similar relative occurrence of this phenotype would result during methotrexate therapy of leukemia patients.

Animals↗