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PubMedDate not supplied

Treatment of ectopic pregnancy by systemic methotrexate, transvaginal methotrexate, and operative laparoscopy.

OBJECTIVE: To evaluate the efficacy of treatment of ectopic pregnancy by local administration of methotrexate, systemic methotrexate, and laparoscopy. METHODS: This study was a retrospective analysis from the department of Obstetrics and Gynecology of two university-affiliated hospitals. Medical records of 40 patients who were treated by methotrexate from January 1991 to October 1994 and 66 patients who were treated surgically by laparoscopy from April 1986 to June 1994 were reviewed. Among the methotrexate group, 19 patients were treated by ultrasound-guided injection and 31 others were treated by intramuscular administration. Success rate of the primary treatment and the duration of hospitalization were examined for each group. The cases of methotrexate failure were characterized and compared with the primary laparoscopic group. RESULTS: The success rate was similar between the local (79.8%) and the systemic (66.7%) methotrexate groups. The primary laparoscopy group had a significantly higher success rate (95.5%) than the methotrexate group (72.5%); P < .01. When patients who had laparoscopy as their primary treatment (n = 66) were compared with those who underwent surgery after failed methotrexate treatment (n = 11), the primary laparoscopic group were seen to have shorter hospitalization time, smaller tubal diameter at surgery, and higher pre-operative hemoglobin level (P < .05). More patients in the methotrexate failure group (45.5%) had hemoperitoneum of > 500 mL than those in the primary laparoscopy group (1.5%; P < .001). CONCLUSIONS: There is no difference in efficacy between local and systemic methotrexate administration. Laparoscopic treatment of ectopic pregnancy is associated with a higher success rate than methotrexate treatment. Patients treated by laparoscopy after methotrexate failure were sicker than those who were treated by laparoscopy as their primary treatment.

Adult↗

PubMed1982

Identification and quantitation of methotrexate and methotrexate metabolites in clinical high-dose therapy by high pressure liquid chromatography and field desorption mass spectrometry.

High-pressure liquid chromatography in combination with field desorption mass spectrometry as techniques of high specificity and sensitivity have been applied to the identification and quantitation of the anticancer drug methotrexate and its metabolites which occur in clinical high-dose therapy. Field desorption mass spectra of methotrexate and several methotrexate and folic acid derivatives, when investigated as free acids or ammonium salts, yield abundant protonated molecular ions and a consistent pattern of structurally significant fragments. High-pressure liquid chromatographic separation of methotrexate metabolites was performed on reverse-phase, C-18 columns using a volatile, ammonium bicarbonate/acetate containing mobile phase that was especially suited for the field desorption mass spectral analysis of isolated metabolites, and provided the definite identification of 7-hydroxymethotrexate and 4-[[2,4-diamino-6-pteridinyl]methyl]methylamino]-benzoic acid in serum and urine of patients treated with high-dose methotrexate. The high intensity and stability of the [MH]+ ions was found suitable for the quantitation of methotrexate and related folate analogues by field desorption mass spectrometry. A synthetic methotrexate derivative, methotrexate-gamma-(2-hydroxy)ethyl-amide was used as internal standard for the quantitative determination of methotrexate in serum and urine. In a study to comparatively assess the potential of specific quantitation methods, serum and urine levels of methotrexate and its major metabolite, 7-hydroxymethotrexate were determined by (i) an enzyme immunoassay, (ii) reverse phase high-pressure liquid chromatography and (iii) field desorption mass spectrometry. Results obtained from four patients with osteogenic sarcoma receiving high-dose methotrexate/leucovorin rescue therapy consistently show the sustained elimination of 7-hydroxymethotrexate over several days, thus indicating the utility of specifically monitoring this nephrotoxic metabolite, at massive methotrexate doses.

Adult↗

PubMed1982

Treatment of nonmetastatic gestational trophoblastic disease: results of methotrexate alone versus methotrexate--folinic acid.

Two treatment regimens for nonmetastatic gestational trophoblastic disease are compared in this retrospective study. The course of 39 patients with nonmetastatic gestational trophoblastic disease treated with methotrexate alone is contrasted to that of 29 patients with nonmetastatic gestational trophoblastic disease who were treated with methotrexate alternated with folinic acid. Of those patients initially treated with methotrexate alone, 7.7% developed methotrexate-resistant disease and required a change in chemotherapy for induction of remission. In contrast, 27.5% of patients initially treated with methotrexate and folinic acid developed methotrexate-resistant disease and required a change in chemotherapy to achieve remission. Ultimately, remission was achieved in all patients. Methotrexate as single-agent chemotherapy was found to be consistently more toxic than methotrexate alternated with folinic acid. It is concluded that methotrexate with folinic acid at the dosage used in this study, while less toxic than methotrexate alone, is less effective than methotrexate alone in the induction of remission of nonmetastatic gestational trophoblastic disease.

Choriocarcinoma↗

PubMed1981

Methotrexate in the plasma and cerebrospinal fluid of children treated with intermediate dose methotrexate.

Serious complications can follow treatment with intermediate dose methotrexate of acute lymphoblastic leukemia in childhood. Toxicity has been shown to be correlated to plasma methotrexate concentrations. During intravenous infusions of methotrexate (500 mg/m2) the mean concentrations achieved 1 to 41/2 hours after the start of infusion were 1.3 X 10(-7) mol/l in cerebrospinal fluid and 1.7 X 10(-5) mol/l in plasma. At 72 hours after start of methotrexate infusion, plasma methotrexate concentrations were significantly higher in cases with symptoms of toxicity. In all the children who developed toxic symptoms 72-hour plasma methotrexate concentration was above 1 X 10(-7) mol/l. Assuming that leucovorin is given 48 hours after the start of methotrexate infusion, 72-hour plasma methotrexate is suitable for detection of patients at risk for toxicity. In children treated with intermediate dose methotrexate we therefore recommend estimating plasma methotrexate concentration 72 hours after the start of infusion, and instituting supplementary leucovorin when plasma methotrexate concentration exceeds 1 X 10(-7) mol/l.

Brain Neoplasms↗

PubMed1988

Methotrexate concentration levels in the cerebrospinal fluid during high-dose methotrexate infusions: an unreliable prediction.

In 25 children with lymphoid malignancies, 96 high-dose methotrexate infusions (3 g/m2) with a duration of 24 h have been administered as a part of the treatment schedule. A lumbar puncture was performed to apply methotrexate intrathecally. The moment of lumbar puncture during the infusion was chosen at different times. In 76 of the infusions the concentration of methotrexate in the cerebrospinal fluid and in plasma were determined just prior to the intrathecal administration. From the second to the eighth hour after the initiation of the infusion the concentration of methotrexate in the cerebrospinal fluid and in plasma were determined just prior to the intrathecal administration. From the second to the eighth hour after the initiation of the infusion the concentration of methotrexate in the cerebrospinal fluid appeared to be significantly lower than 16 or 24 h after the initiation of the infusion. Of all samples during the infusions, the plasma concentration varied a tenfold (2-20 X 10(-5) mol/L), but the cerebrospinal fluid concentration of methotrexate varied about a 300-fold (3.5-900 x 10(-8) mol/L). No correlation could be found between the plasma concentration of methotrexate and the cerebrospinal fluid concentration. It is concluded that the methotrexate concentration in the cerebrospinal fluid cannot be predicted by determining the plasma concentration. It takes at least 8 h of infusion before a steady-state concentration of methotrexate is reached in the cerebrospinal fluid. In high-dose methotrexate infusions without intrathecal therapy, the dose of 3 g/m2 is the minimum amount of methotrexate to reach the minimum therapeutic concentration 5 x 10(-7) mol/L) in the cerebrospinal fluid for the treatment of subclinical central nervous system invasion of malignant lymphoid cells. To maintain the minimum therapeutic concentration according to the CxT principle the duration of the infusion should be preferably longer than 24 h.

Adolescent↗

PubMed1984

Occurrence and significance of D-methotrexate as a contaminant of commercial methotrexate.

Methotrexate from various commercial sources has been found to contain 0.5 to 48% (w/w) of the enantiomer D-methotrexate. The two methotrexate enantiomers were separated by using chiral high-performance liquid chromatography with an octadecyl silica column and a mobile phase containing L-proline and cupric nitrate. For the assay of D-methotrexate impurity in commercial methotrexate, L-methotrexate was hydrolyzed with carboxypeptidase G1, and the remaining D-methotrexate was quantitated by high-performance liquid chromatography. The biological effects of D-methotrexate were investigated and compared to that of L-methotrexate. D-Methotrexate was found to be a good inhibitor of dihydrofolate reductase from both murine and human tumor cells, but was a poor inhibitor of L1210 and CCRF-CEM cell growth. In animal experiments with dogs and mice, D-methotrexate was rapidly absorbed from the intestine and excreted by the kidneys.

Animals↗

PubMed1987

Identification of methotrexate transport deficiency in mammalian cells using fluoresceinated methotrexate and flow cytometry.

We have studied the frequency of transport mutations in methotrexate-resistant Chinese hamster ovary cells using a rapid-flow cytometric technique. After saturating cells with fluoresceinated methotrexate, we examined the ability of hydrophilic and lipophilic antifolates to displace fluoresceinated methotrexate binding to dihydrofolate reductase. Cells with methotrexate transport deficiency are unable to take up methotrexate and thus retain the fluorescence, whereas the lipophilic antifolates displace fluoresceinated methotrexate equally well in sensitive and resistant cell lines. These resistant clones fail to take up methotrexate and occur with high frequencies upon single-step selections at methotrexate concentrations approximately equal to 7-fold the 50% killing concentration. The majority of such first-step resistant clones appear to derive their resistance solely from transport deficiency; they exhibit no overproduction of dihydrofolate reductase and no increase in either steady-state mRNA levels or gene copy number. Possible applications of the use of fluoresceinated methotrexate to the characterization of various mechanisms of methotrexate resistance in mixed cell populations are discussed.

Animals↗

PubMed1986

The influence of extracellular folate concentration on methotrexate uptake by human KB cells. Partial characterization of a membrane-associated methotrexate binding protein.

Methotrexate accumulation, subcellular distribution, metabolism, and cytotoxicity were studied in human epidermoid carcinoma (KB) cells that were exposed to a low extracellular concentration of methotrexate (25 nM) following culture in widely differing concentrations of folic acid. KB cells cultured in standard medium with a high folic acid concentration (2.3 microM) had high levels of cellular folate (21.4 pmol/10(6) cells). Five passages through low folate (2.7 nM) medium reduced the level of cellular folate to near physiologic levels (0.4-1.0 pmol/10(6) cells). In contrast to KB cells cultured in standard medium, in KB cells cultured in low folate medium, 1) methotrexate inhibited growth; 2) methotrexate uptake was markedly increased; 3) methotrexate polyglutamation was almost complete; 4) methotrexate binding to dihydrofolate reductase was markedly enhanced; and 5) significant methotrexate binding to a previously undescribed membrane-associated protein occurred. The amount of methotrexate bound to the membrane-associated protein from KB cells cultured in low folate medium equaled the quantities bound by dihydrofolate reductase. Further characterization of this membrane-associated protein indicated that it was soluble in solutions containing Triton X-100, was capable of binding folic acid as well as methotrexate, had an apparent Mr of 160,000 by gel filtration in the presence of Triton X-100, and was precipitated by antiserum to human placental folate receptor. This membrane-associated protein may play an important role in the uptake and metabolism of methotrexate under physiologic conditions.

Animals↗

PubMed1989

A fluorescein-methotrexate-based flow cytometric bioassay for measurement of plasma methotrexate and trimetrexate levels.

We describe a bioassay for the quantitation of plasma methotrexate and trimetrexate levels employing intact cells. This assay is based on the intracellular saturation of dihydrofolate reductase with fluorescein-methotrexate (F-MTX) and its dose-dependent displacement by methotrexate or trimetrexate as monitored by flow cytometry. Serially diluted methotrexate-containing plasma, representing a wide chemotherapeutic range, produces F-MTX displacement curves similar to those of standard methotrexate solutions. There is no interference by normal plasma components such as folate and its reduced forms. Plasma methotrexate or trimetrexate concentration is the product of the 50% displacing concentration of standard antifolate (IC50) and the reciprocal of the plasma dilution which yields the same displacement. F-MTX competition with standard methotrexate displayed linear displacement from 18.0 +/- 3.1 to 33.7 +/- 1.5 nM (n = 10). The standard trimetrexate calibration curve was linear from 0.28 +/- 0.03 to 1.5 +/- 0.33 nM (n = 8). Thus, the bioassay sensitivities for methotrexate and trimetrexate are at least 18 and 0.3 nM, respectively. Comparison of methotrexate levels in 10 plasma specimens from cancer patients determined by the clinical enzyme inhibition assay and by our bioassay showed a high degree of correlation (r = 0.987).

Flow Cytometry↗

PubMed1998

Systemic methotrexate therapy versus laparoscopic salpingostomy in tubal pregnancy. Part II. Patient preferences for systemic methotrexate.

OBJECTIVE: To investigate patient preferences for systemic methotrexate therapy relative to laparoscopic salpingostomy in the treatment of tubal pregnancy. DESIGN: Preference assessment in controlled clinical study. SETTING: Four hospitals and one infertility clinic. PATIENT(S): Forty patients who had been treated for tubal pregnancy and 40 nonpregnant controls. INTERVENTION(S): Preference for methotrexate therapy relative to salpingostomy was established during an interview. Two scenarios were offered for methotrexate therapy: one with and one without preceding diagnostic laparoscopy. Hypothetical tubal patency rates after methotrexate therapy were varied in both scenarios until patients switched in their initial preference. MAIN OUTCOME MEASURE(S): Preference for systemic methotrexate therapy. RESULT(S): Only a few patients switched in their initial preference when the tubal patency rate after systemic methotrexate therapy was varied. Most preferred methotrexate therapy without an increase in the tubal patency rate in a scenario without preceding diagnostic laparoscopy. A small group never opted for methotrexate therapy even when it would guarantee a 100% tubal patency rate. CONCLUSION(S): Systemic methotrexate therapy would be preferred by most patients as part of a completely nonsurgical management strategy. Tubal patency was a decisive factor for treatment preference in a minority of patients only.

Adult↗

PubMed2006

The effect of low pH on breast cancer resistance protein (ABCG2)-mediated transport of methotrexate, 7-hydroxymethotrexate, methotrexate diglutamate, folic acid, mitoxantrone, topotecan, and resveratrol in in vitro drug transport models.

Some cellular uptake systems for (anti)folates function optimally at acidic pH. We have tested whether this also applies to efflux from cells by breast cancer resistance protein (BCRP; ABCG2), which has been reported to transport folic acid, methotrexate, and methotrexate di- and triglutamate at physiological pH. Using Spodoptera frugiperda-BCRP membrane vesicles, we showed that the ATP-dependent vesicular transport of 1 muM methotrexate by BCRP is 5-fold higher at pH 5.5 than at physiological pH. The transport of methotrexate was saturable at pH 5.5, with apparent Km and Vmax values of 1.3 +/- 0.2 mM and 44 +/- 2.5 nmol/mg of protein/min, respectively, but was linear with drug concentration at pH 7.3 up to 6 mM methotrexate. In contrast to recent reports, we did not detect transport of methotrexate diglutamate at physiological pH, but we did find transport at pH 5.5. We also found that 7-hydroxy-methotrexate, the major metabolite of methotrexate, is transported by BCRP both at physiological pH and (more efficiently) at low pH. The pH effect was also observed in intact BCRP-overexpressing cells: we found a 3-fold higher level of resistance to both methotrexate and the prototypical BCRP substrate mitoxantrone at pH 6.5 as at physiological pH. Furthermore, with MDCKII-BCRP monolayers, we found that resveratrol, which is a neutral compound at pH < or = 7.4, is efficiently transported by BCRP at pH 6.0, whereas we did not detect active transport at pH 7.4. We conclude that BCRP transports substrate drugs more efficiently at low pH, independent of the dissociation status of the substrate.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed1993

Mechanism of action of methotrexate: experimental evidence that methotrexate blocks the binding of interleukin 1 beta to the interleukin 1 receptor on target cells.

Interleukin 1, a multifunctional cytokine, plays a central role in inflammatory processes and induction of the immune response. Target cells possess 200-5000 (or more) interleukin 1 receptors per cell, but they exhibit a full biological response when only 1-2% of these receptors are occupied by interleukin 1 alpha or 1 beta. Methotrexate has been reported to be beneficial in several inflammatory and autoimmune diseases. On the other hand, many of these diseases are known to share an overproduction of interleukin 1. It has been demonstrated that methotrexate has no influence on the interleukin 1 synthesis, so we focused our attention on the ability of methotrexate to interfere with the binding of interleukin 1 beta to the interleukin 1 receptor. The experiments were performed on monocytes, lymphocytes and granulocytes using a recombinant human cytokine probe. Methotrexate led to an astonishing decrease in the binding of interleukin 1 beta to the interleukin 1 receptor of peripheral blood cells, whereas methylprednisolone and indomethacin were not inhibitory. The inhibitory effect of methotrexate was dose dependent. An excess of interleukin 1 beta abolished the inhibition of cytokine binding by methotrexate. We also demonstrated that methotrexate does not affect the integrity of the interleukin 1 receptor or of the target cells. Our results demonstrate that methotrexate blocks the interleukin 1 beta-interleukin 1 receptor pathway. Methotrexate is therefore another interleukin 1 inhibitor and a clinically efficient anticytokine.

Flow Cytometry↗

PubMed1991

Identification of a highly glycosylated methotrexate membrane carrier in K562 human erythroleukemia cells up-regulated for tetrahydrofolate cofactor and methotrexate transport.

A K562 human erythroleukemia line (designated K562.4CF) was selected for increased tetrahydrofolate cofactor transport in a growth-limiting concentration (0.4 nM) of (6R,S)-5-formyltetrahydrofolate. K562.4CF cells exhibited elevated methotrexate uptake relative to parental cells, attributable to a 10-fold increased influx Vmax. The rate of methotrexate efflux in K562.4CF cells was somewhat increased (55%) as well. The transport system in K562.4CF cells had similar and high apparent binding affinities for methotrexate and 5-formyltetrahydrofolate and a markedly reduced affinity for folic acid, properties typically associated with the "classical" methotrexate/tetrahydrofolate cofactor transporter in tumor cells. Methotrexate uptake in K562.4CF cells decreased substantially under nonselective conditions; high levels of transport were restored in 0.4 nM 5-formyltetrahydrofolate. Treatment of parental and K562.4CF cells with N-hydroxysuccinimide methotrexate inhibited methotrexate influx. N-Hydroxysuccinimide-[3H]methotrexate (700 nM) radiolabeled a broadly migrating band at Mr 76,000-85,000. Incorporation from N-hydroxysuccinimide-[3H]methotrexate into this band was increased 7-fold in K562.4CF over parental cells and was blocked by unlabeled methotrexate, (6S)-5-formyltetrahydrofolate, or, to a lesser extent, folic acid. Whereas incubation with endoglycosidase F had no effect on the electrophoretic migration of the labeled protein, treatment with endoglycosidase F and glycopeptidase F, or endo-beta-galactosidase, reduced the apparent molecular weight to Mr approximately 52,000 or approximately 58,000, respectively. These results suggest that the high-affinity transporter in K562.4CF cells is an N-linked glycoprotein containing internal beta-galactosidic linkages in, or immediately after, unbranched poly-N-acetyllactosamine sequences. Differences in the level of glycosylation may, in part, account for the disparity in the apparent sizes of the homologous folate transport proteins from human and murine cells.

Affinity Labels↗

PubMed1988

Identification of the bromosulfophthalein-sensitive efflux route for methotrexate as the site of action of vincristine in the vincristine-dependent enhancement of methotrexate uptake in L1210 cells.

The mechanism by which vincristine enhances the uptake of methotrexate in leukemic L1210 mouse cells has been investigated. Methotrexate uptake after 30 min at 37 degrees C increased 44% relative to untreated controls in cells suspended in a 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid/bicarbonate-buffered saline medium containing 20 microM vincristine. This stimulation was half-maximal at a vincristine concentration of 4 microM. An enhancement of methotrexate uptake by vincristine was also observed in the presence of glucose but a reversal could be achieved by prior treatment of the cells with taxol, a drug which prevents microtubule disassembly by vincristine. When the effect of vincristine was determined on the individual influx and efflux components for methotrexate, the increased uptake of methotrexate correlated with the inhibition of the unidirectional efflux route for methotrexate that is sensitive to bromosulfophthalein. Inhibition of this route was half-maximal at 3 microM vincristine and it exceeded 90% at high concentrations of the inhibitor. Transport via the bidirectional exchange carrier for methotrexate was not affected by vincristine, while the unidirectional efflux route sensitive to probenecid was inhibited by vincristine but only at concentrations 10-fold higher than required to inhibit the bromosulfophthalein-sensitive route. Vincristine did not increase methotrexate uptake in CCRF-CEM lymphoblasts, a human cell line which contains much lower levels of bromosulfophthalein-sensitive efflux route for methotrexate. Concentrations of vincristine which inhibited the bromosulfophthalein-sensitive efflux route of L1210 cells by 80-90% had little or no effect on the intracellular pH or on intracellular levels of ATP, GTP, cyclic AMP, K+, or oxidized glutathione. A significant increase was observed in the cellular uptake of tetraphenylphosphonium ions, suggesting that vincristine causes a hyperpolarization of the plasma membrane.

Adenosine Triphosphate↗

PubMed1997

Methotrexate pharmacokinetics and effects in women receiving methotrexate 50 mg and 60 mg per square meter for early abortion.

OBJECTIVE: Our goal was to evaluate the pharmacokinetics and safety of methotrexate in doses of 50 mg/m2 and 60 mg/m2 in regimens for early abortion. STUDY DESIGN: A randomized controlled trial was performed in women requesting an abortion at < or = 49 days' gestation. Twenty women were treated with intramuscular methotrexate 50 mg/m2 (group 1) or 60 mg/m2 (group 2). Methotrexate levels were determined serially for the first 24 hours, then every 24 hours for 7 days. On the seventh day misoprostol 800 microg was administered vaginally. The misoprostol dose was repeated 24 hours later if abortion did not occur. RESULTS: Complete abortion occurred in 9 of 10 (90%, 95% confidence interval 56% to 100%) patients in group 1 and all 10 (100%, 95% confidence interval 69% to 100%; p = 0.99) in group 2. Methotrexate levels peaked within 1 to 2 hours and were nondetectable within 48 hours in all patients in group 1 and 72 hours in group 2. Both the maximum concentration of methotrexate and the area under the curve were significantly greater for group 2. Methotrexate clearance rates were 7.89 +/- 1.98 L/hr and 5.55 +/- 0.83 L/hr (p = 0.003), respectively. CONCLUSIONS: The serum levels of intramuscular methotrexate with 50 mg/m2 and 60 mg/m2 regimens indicate that these are safe treatment doses. Methotrexate 50 mg/m2 intramuscularly has the same clearance rates when administered during pregnancy as in a nonpregnant state, and maximum concentrations do not reach sustained toxic levels.

Abortifacient Agents, Nonsteroidal↗

PubMed1986

Pharmacokinetics of methotrexate and 7-hydroxy-methotrexate after high-dose (33.6 g/m2) methotrexate therapy.

We have measured MTX and 7-OH-MTX in plasma and urine samples from a 9-year-old boy treated with six consecutive 24-h IV high-dose MTX courses (33.6 g/m2) after a relapse of ALL. The between-course pharmacokinetics of MTX and 7-OH-MTX were found to be highly reproducible. Both MTX and 7-OH-MTX elimination followed a biphasic curve, initial half-lives (t1/2(alpha] being 2.86 +/- 0.44 h and 5.14 +/- 0.46 h (mean +/- SD) and second-phase biological half-lives (t1/2(beta] being approximately 18 and 16 h, respectively. The apparent volume of distribution for MTX was 0.8 L/kg, whereas the corresponding value for 7-OH-MTX was threefold less. Since clearance of MTX was within the range reported for lower doses, the data suggest that MTX pharmacokinetics are not dose-dependent up to 33.6 g/m2.

Child↗

PubMed1983

Predictions of a network thermodynamics computer model relating to the mechanism of methotrexate rescue by 5-formyltetrahydrofolate and to the importance of inhibition of thymidylate synthase by methotrexate-polyglutamates.

Computer modeling has been a valuable tool for clarifying the mechanism of action of antifolates. Some consequences of folyl and antifolyl polyglutamate synthesis can be addressed by adaptation of a network thermodynamic computer model of methotrexate action. Reversal or prevention of methotrexate cytotoxicity by 5-formyltetrahydrofolate has widely been assumed to occur through the delivery of reduced folate in substrate amounts for thymidylate synthesis, by-passing the effects of methotrexate at dihydrofolate reductase. This mechanism is inconsistent with experimental data which shows that "rescue" is a competitive phenomenon and that the transport process is incapable of delivering reduced folate at an adequate rate. Computer modeling studies are presented which predict that expansion of the total folate pool as folylpolyglutamates with "rescue" would reduce the inhibitory effect of MTX on thymidylate synthesis. Dihydrofolate polyglutamates could then accumulate to the high level needed to displace methotrexate from the small fraction of sites on dihydrofolate reductase that are sufficient to sustain tetrahydrofolate synthesis. Experimental studies with Ehrlich ascites tumor cells support this prediction. It is likely that a critical step in the protection of normal host tissues in high dose-rescue treatment regimens is the conversion of exogenously supplied 5-formyltetrahydrofolate to polyglutamyl derivatives and accumulation of total intracellular folate to higher than normal levels. Other computer simulations are presented which examine the potential significance of direct inhibition of thymidylate synthase by polyglutamyl forms of methotrexate. The model predicts that in cells with biochemical properties similar to methotrexate sensitive L1210 cells, inhibition of dihydrofolate reductase would still be the predominant site of action unless the thymidylate synthase Ki for a methotrexate polyglutamate is below about 0.1 microM. However, in methotrexate-resistant cells with elevated dihydrofolate reductase but normal membrane transport and polyglutamylation, thymidylate synthase may be the more important target enzyme.

Computers↗

PubMed1984

Plasma methotrexate levels in patients with gestational trophoblastic neoplasia treated by two methotrexate regimens.

Plasma methotrexate levels were measured in six patients with nonmetastatic and three patients with "low-risk" metastatic gestational trophoblastic neoplasia who were treated by two different methotrexate regimens. Five patients were treated with 16 cycles consisting of methotrexate, 1 mg/kg (days 1, 3, 5, and 7) followed in 24 hours by citrovorum factor, 0.1 mg/kg (days 2, 4, 6, and 8). Cycles alternated between intravenous and intramuscular administration. Statistical differences in plasma levels were found at 1 and 48 hours between the two routes of administration but probably were not of clinical importance. The plasma levels at the time of citrovorum factor administration were below that necessitating citrovorum factor rescue. Four patients were treated with alternating cycles of intravenous or intramuscular methotrexate, 0.5 mg/kg for 5 consecutive days without citrovorum factor. A total of 15 cycles demonstrated no difference in plasma levels at 1, 12, and 24 hours between intravenous and intramuscular administration. Statistical differences in plasma methotrexate levels were noted between the two methotrexate regimens only with intramuscular administration but were not of clinical importance. The reduced toxicity of the methotrexate-citrovorum factor may be due to the scheduling of the methotrexate and not to the citrovorum factor.

Antineoplastic Combined Chemotherapy Protocols↗