MTX, Methotrexate

Methotrexate (MTX, chemical structure shown in Fig. 1.) competitively inhibits the dehyrofolate reductase, an enzyme that plays an essential role in purine synthesis. The dehydrofolate reductase regenerates reduced folates when thymidine monophosphate is formed from deoxyuridine monophosphate. Without reduced folates cells are unable to synthesize thymine. Administration of N-5 tetrahydrofolate or N-5 formyl-tetrahydrofolate (folinic acid) can bypass this block and rescue cells from methotrexate activity by serving as antidote. 

The miscellaneous drugp are used to treat a variety of musculoskeletal disorders. Ffenicillamine, methotrexate (MTX), and hydroxychloroquine are used to treat rheumatoid arthritis in patients who have had an insufficient therapeutic response to or are intolerant of other antirheumatic drugp such as the sailcylates and NSAIDs. The Summary Drug Table Drug s Used to Tream Musculoskeletal Disorders provides additional information about these and other drug s. One compound, hylan G-F 20, listed in the Summary Drug Table is not used for rheumatoid arthritis, but rather, for osteoarthritis knee pain. It is a viscous, elastic... 

Among its inhibitors are methotrexate (MTX), trimethoprim, and other derivatives of pyrimidines, triazines, pteridines, and related heterocyclic compounds. Some of these inhibitors, such as MTX, bind more tightly to Escherichia coli enzyme than does the substrate dihydrofolate. This fact has been attributed to ion-pair formation between protonated MTX and a negative carboxyl, presumably Asp-27, as well as to hydrophobic interactions.33... 

The anticancer agent Methotrexate (MTX) was conjugated with LDH by a coprecipitation method. To synthesize the MTX-LDH conjugate, powdered MTX was dissolved in decarbonated water, and titrated with NaOH (0.5 M) solution to give a 0.043 M solution of MTX at pH 7. The mixed metal solution of Mg(N03)2-6H20 and A1 (N03)3-9H20 with molar ratio Mg/Al = 2/1 was added to the MTX solution and the solution was titrated with NaOH solution until pH 9.5 to produce yellowish precipitates [7,26]. 

Recently, Choy et al. also reported that LDHs are an efficient drug reservoir for folate derivatives [187]. Folic acid derivatives, folinic acid and methotrexate (MTX), have been successfully hybridized with Mg/Al LDHs by ion-exchange reactions. Cellular uptake tests with the MTX-LDH hybrids were carried out in the fibroblast (human tendon) and osteosarcoma (SaOS-2) cell lines by in vitro assay. They found that the LDH not only plays a role as a biocompatible delivery matrix for drugs but also facilitates a significant increase in the delivery efficiency. 

This chapter highlights some of the recent major pubhcations in the field of pharmacogenomics in RA and describes the implications of this field for future research and cUnical care. The pharmacogenetics of three major DMARDs (methotrexate [MTX], azathioprine [AZA], and sulfasalazine [SSZ]) and one class of biologic DMARDs, the tumor necrosis factor (TNF) antagonists, in RA, are reviewed. 

Let s start with three examples of antitumor drugs that work by the inhibition of DNA synthesis methotrexate (MTX, Methopterin), 5-fluorouracil (Fluril), and 6-mercaptopurine (Purinethol). These are all old cancer drags, marketed under numerous trade names, including those indicated above. Although the mechanism of action of each one is different, at the end of the day they all inhibit DNA synthesis. 

A randomized phase II trial comparing weekly methotrexate (MTX, 40-60 mg/m2) vs triweekly paclitaxel (175-225 mg/m2 by 3-h or 24-h infusion) in the recurrent or metastatic setting was prematurely closed as a result of toxicity and minimal response (76). 

Vermorken J, Catimel G, Mulder PD, et al. Randomized phase II trial of weekly methotrexate (MTX) versus two schedules of triweekly paclitaxel (taxol) in patients with metastatic or recurrent squamous cell carcinoma of the head and neck (SCCHN). ProcAnnu Meet Am Soc Clin Oncol 1999 18 A 1527. 

With the advent of biological-DMARD combinations with Methotrexate (MTX) a new era of therapy in autoimmune disease is introduced. DMARD-refractory autoimmune diseases are treated with combinations of a biological with MTX with achievement of improvements of ACR 20 and ASAS 20 in the majority of patients. A small minority of around 20% obtains improvements of ACR 70 and ASAS 70. ACR responses are American College of Rheumatology response criteria and ASAS stands for Assessment in Ankylosing Spondylitis. ACR and ASAS 20, 50 or 70 scores are exactly defined improvements of respectively 20%, 50% or 70%. 

Fig. 7. Synthesis of selectively protected methotrexate (MTX) derivative. The synthesis of ten-butyl ester of the ot-carboxyl group of the glutamic acid moiety in MTX from APA (4-amino-4-deoxy-N10-methylpteroic acid), an MTX precursor (according to [148])...

The safety and efficacy of Remicade when given in conjunction with methotrexate (MTX) were assessed in a multicenter, randomized, double-blind, placebo-controlled study of 428 patients with active rheumatoid arthritis despite treatment with MTX. All patients were to have received MTX for >6 months and be on a stable dose >12.5mg/week for 4 weeks prior to study. All Remicade and placebo groups continued their stable dose of MTX and folic acid. In addition to MTX, patients received placebo or Remicade by intravenous infusion at weeks 0, 2, and 6 followed by additional infusions every 4 or 8 weeks thereafter. The primary end point was the proportion of patients at week 30 who attained an improvement in signs and symptoms as measured by the American College of Rheumatology criteria (ACR 20). An ACR 20 response is defined as at least a 20% improvement in both tender and swollen joint counts and in 3 of 5 clinical criteria. At week 30, 43/86 (50%) of patients treated every 8 weeks with 3 mg/kg of Remicade plus MTX attained an ACR 20 compared with 18/88 (20%) of patients treated with placebo plus MTX ip < 0.001). 

This chapter focuses on genetic polymorphisms found in somatic DNA, particularly in the enzymes of the folate pathway, which is primarily targeted by methotrexate (MTX). Pediatric ALL treatment is comprised of multiple chemotherapy agents given in varied combinations over a several year time course. 

Three EPMEs based on macrocyclic glycopeptide antibiotics— vancomycin and teicoplanin (modified or not with acetonitrile)—were proposed for the determination of l- and D-enantiomers of methotrexate (Mtx) [48]. The linear concentration ranges for the proposed enantioselective membrane electrodes were between 10 6 and 10-3 mol/L for l- and D-Mtx. The slopes of the electrodes were 58.00 mV/pL-Mtx for vancomycin-based electrode, 57.60 mV/pD-Mtx for teicoplanin-based electrode and 55.40 mV/pD-Mtx for teicoplanin modified with acetonitrile-based electrode. The detection limits of the proposed electrodes were of 10 8 mol/L magnitude order. All proposed electrodes proved to be successful for the determination of the enantiopurity of Mtx as raw material and of its pharmaceutical formulations (tablets and injections). 

Zeng H, Chen ZS, Belinsky MG, et al. Transport of methotrexate (MTX) and folates by multidrug resistance protein (MRP) 3 and MRP1 effect of polyglutamylation on MTX transport. Cancer Res 2001 61 7225-7232. 

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