Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.5.1.3 (dihydrofolate reductase)
 5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Considerable progress recently has been made in the systemic chemotherapy of disseminated skin neoplasms. Several agents are particularly useful in this regard: the nitrosoureas, methotrexate, actinomycin D, and dacarbazine. This paper reviews their pharmacologic disposition in man. The nitrosoureas have short plasma half-lives; however, they are extensively degraded to metabolites that persist in the body, and are only slowly excreted. Highly soluble in lipids, the nitrosoureas penetrate significantly into the central nervous system. Actinomycin D is only minimally metabolized in vivo; its elimination from the plasma shows a prolonged slow phase with a half-life of 36 hours; but its excretion is even slower than expected about 30% in a week. A potent inhibitor of dihydrofolate reductase, methotrexate exhibits a multiphasic plasma disappearance, and accumulates in tissues with high dihydrofolate reductase activities. At the normal therapeutic dosages, methotrexate is eliminated by the kidneys as the unchanged drug; appropriate dosage modifications are mandatory if renal function is compromised. Dacarbazine has a relatively short plasma half-life, and is rapidly excreted partly as the unchanged drug; it undergoes extensive biotransformation in the body. Like other antitumor agents, these drugs may cause gastrointestinal toxicities and myelosuppression; in addition each drug can have its own individual organ toxicity.
Int J Dermatol 1978 Oct
PMID:Clinical pharmacology of systemic chemotherapeutic agents in skin neoplasms. 73 Apr 48

The pharmacologic responses of normal and malignant epidermal cells to chemotherapeutic agents were examined in a system which consists of a serum-free "defined" medium. The effects of methotrexate (MTX), fluorodeoxyuridine (FUDR), and hydroxyurea upon cell growth, DNA synthesis, thymidylate synthase activity, and dihydrofolate reductase (DHFR) activity were compared in normal human epidermal keratinocytes (NHEK), newborn epidermal cells (NEC), human squamous cell carcinoma (SCC-25), and a methotrexate-resistant human squamous cell carcinoma (SCC-15R). Normal keratinocytes were found to be 10(3) to 10(4) times less sensitive to the effects of MTX and FUDR than the malignant cells with respect to growth and DNA synthesis. The differential sensitivity to MTX and FUDR was not due to differences in growth media, increased target enzyme activity, e.g., DHFR and thymidylate synthase, or impaired transport of these drugs. The results indicate that the mechanism for the increased sensitivity of the squamous cell carcinoma to MTX and FUDR must involve a process which is distal to the de novo synthesis of dTMP.
J Invest Dermatol 1990 May
PMID:A comparison of the effects of antitumor agents upon normal human epidermal keratinocytes and human squamous cell carcinoma. 213 84

Studies of the time course of methotrexate-derived antifolate activity (methotrexate activity) in plasma and skin of rats have been carried out to evaluate the hypothesis that the formation of therapeutically active poly-gamma-glutamyl conjugates of methotrexate in skin after systemic administration of the drug will result in the prolongation of methotrexate effects in skin. Such a finding may eventually bear on the use of the drug in the treatment of psoriasis. Three groups of 4 rats received a single i.v. dose of methotrexate, 5, 20, or 40 mg/kg, respectively. Serial skin and plasma samples were obtained over 48 h from each rat and analyzed for methotrexate activity by a dihydrofolate reductase enzyme inhibition assay. The values of pharmacokinetic parameters describing the disposition of the drug were calculated from plasma data using standard methods. Skin to plasma ratio of methotrexate activity was also calculated each time a skin sample was obtained. Pharmacokinetic parameter values and skin to plasma ratios were not significantly different between doses. Methotrexate activity declined biexponentially in plasma and skin. The terminal half-life in plasma (mean +/- SD) was 20.3 +/- 9.2 h. At early times, methotrexate activity in skin was less than plasma, but at later times activity in skin was an order of magnitude greater than that in plasma. In a preliminary study to determine whether the persistent activity in skin is associated with the presence of poly-gamma-glutamyl conjugates of methotrexate, a rat was dosed with tritiated methotrexate, 0.18 mg/kg, i.v., and skin was obtained 24 h later. Skin homogenate was treated with papain and applied to an anion-exchange column for cleanup prior to injection on a reversed-phase high-pressure liquid chromatography system. Methotrexate poly-gamma-glutamates were identified by elution with authentic standards and specific hydrolysis with carboxypeptidase G1.
J Invest Dermatol 1984 Jan
PMID:Persistence of antifolate activity in skin of rats following systemic administration of methotrexate. 669 Jun 31

Human melanomas are naturally resistant to methotrexate (MTX). The mechanism of intrinsic drug resistance has been explored in 3 melanoma cell lines not previously exposed to this agent. All 3 lines exhibited relative MTX resistance with ID50 values of greater than 1 microM. Drug uptake studies were performed over an extracellular concentration range of 0.1 to 10 microM MTX. The uptake was linear over the initial 10 min at all concentrations and subsequently reached plateau levels only at the 10 microM concentration. Lineweaver-Burke transformations yielded apparent Km (uptake) values of 1.4 to 5 microM, similar to data obtained from other human cell lines. The level of dihydrofolate reductase (DHFR) in the human melanoma cells ranged between 8.42 to 11.98 pmoles/mg protein. The melanoma DHFR levels are several fold higher than in MTX-sensitive human tumor lines and up to a hundred-fold higher than that measured in human brain tumor cells by our assay. The intrinsic resistance of these melanoma lines has therefore been attributed to elevated intracellular levels of DHFR.
J Invest Dermatol 1980 Oct
PMID:Natural resistance to methotrexate in human melanomas. 743 Jul

An open, 12-week, multicentre study was conducted to assess the efficacy of piritrexim isethionate in the treatment of severe psoriasis. Piritrexim isethionate is a lipid-soluble dihydrofolate reductase inhibitor which cannot form polyglutamates, and may be as effective as methotrexate in the treatment of psoriasis. If, as is suspected, but as yet unproven, methotrexate polyglutamates are responsible for the hepatotoxicity of methotrexate, piritrexim should be less hepatotoxic, and may offer an alternative to methotrexate therapy. Fifty-five patients were enrolled, of whom 41 completed the study. Patients were allocated to receive either 150, 225, 300, or 450 mg of piritrexim weekly, in divided doses over 72 h (low-dose groups, 150 and 225 mg), or over 36 h (300 and 450 mg groups). Twenty-four of the 41 patients who completed the study had a greater than 50% improvement in the severity of their psoriasis, as demonstrated by a reduction in the Psoriasis Severity Score, a measure analogous to the PASI scoring system. Adverse events were common, but mild, and were controlled by dose reduction. Piritrexim appears to be an effective therapy for severe psoriasis at doses of 300 and 450 mg weekly, in three divided doses over 36 h.
Br J Dermatol 1993 Nov
PMID:A multicentre 12-week open study of a lipid-soluble folate antagonist, piritrexim in severe psoriasis. 825 56

Methotrexate (MTX) inhibits DNA synthesis by competition with dihydrofolate reductase. Adverse cutaneous reactions to MTX are usually dose-related and have been mainly reported in patients receiving extremely large doses of chemotherapy. Painful erosion of psoriatic plaques has been often reported as an early sign of MTX toxicity, but cutaneous ulceration as a sign of MTX toxicity in patients without psoriasis has only been described in one case. We report a patient with rheumatoid arthritis and without psoriasis who developed cutaneous ulceration on the knuckles as a sign of MTX toxicity. Cutaneous ulceration by MTX toxicity is an exclusion diagnosis and its pathogenic mechanism may be multifactorial, including direct toxicity of the drug in addition to local factors.
Eur J Dermatol
PMID:Cutaneous ulceration as a sign of methotrexate toxicity. 1152 55

Methotrexate (MTX) is an antimetabolite and antifolate drug used in the treatment of cancer and autoimmune diseases. MTX inhibits DNA synthesis by competitive inhibition of dihydrofolate reductase in immunologically active cells. It also decreases inflammation by other mechanisms. Cutaneous toxicity is usually dose-related and generally occurs when recommended guidelines are ignored or there is a decrease in renal excretion. Self-medication is a problem with unknown prevalence. Signs of MTX toxicity include bone marrow suppression, hepatotoxicity, and mucocutaneous toxicity. Painful erosions of psoriatic plaques and, less commonly, erosions in patients without psoriasis have been reported as an early sign of MTX toxicity. To our knowledge, this is the first case of skin toxicity related to MTX that affected the normal skin and spared the psoriatic plaques.
Dermatol Online J 2010 Jun 15
PMID:Focal skin toxicity related to methotrexate sparing psoriatic plaques. 2057 71