Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:Q06643 (non-Hodgkin's lymphoma)
 11,307 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Methotrexate (MTX) is a clinically important antifolate that has been used in combination with other chemotherapeutic agents in the treatment of malignancies including acute lymphocytic leukemia, osteosarcoma, carcinomas of the breast, head and neck, choriocarcinoma and non-Hodgkin's lymphoma. The primary target of MTX is the enzyme dihydrofolate reductase (DHFR) which catalyzes the reduction of folate and 7,8-dihydrofolate to 5,6,7,8-tetrahydrofolate. Understanding of MTX action has revealed how cells acquire resistance to this drug. The four known mechanisms of MTX resistance are a decrease in the uptake of the drug, a decrease in the retention of the drug due to defective polyglutamylation or an increase in polyglutamate breakdown, an increase in the enzyme activity and a decrease in the binding of MTX to DHFR. The molecular basis for some of these mechanisms has been elucidated in MTX resistant cell lines; in particular the occurrence of gene amplification resulting in increased DHFR and point mutations resulting in altered DHFR with reduced affinity for MTX. Cloning of the human folylpolyglutamate synthase gene and the reduced folate transport gene have been reported recently and should facilitate the identification of the molecular basis of these resistant phenotypes. DHFR protein has been shown to regulate its synthesis by exerting an inhibitory influence on its own translation. Addition of MTX relieves this inhibition thus providing a possible molecular explanation for the rapid rise in DHFR activity noted in some cells after MTX administration. Alterations in genes involved in regulating the cell cycle such as cyclin D1 and the retinoblastoma (Rb) gene have also been shown to influence cellular response to MTX. Overexpression of cyclin D1 in HT1080, a human fibrosarcoma cell line, results in decreased MTX sensitivity. The molecular basis of this observation is under investigation. Abnormalities in the Rb gene may also have profound effects on MTX sensitivity. Rb interacts with the family of transcription factors called E2F reducing transcription of genes that contain E2F binding sites in the promoter regions e.g. DHFR. When Rb is deleted or rendered nonfunctional levels of "free" or unbound E2F are high resulting in enhanced transcription of genes such as DHFR. This results in increased DHFR protein and may lead to MTX resistance. As the knowledge regarding mechanisms of resistance increases newer approaches to circumvent such resistance or to target resistant cells can be undertaken.
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PMID:Molecular mechanisms of resistance to antifolates, a review. 885 36

PDX (10-propargyl-10-deazaaminopterin) is a novel anti-folate with improved membrane transport and polyglutamylation in tumor cells. In prior studies, PDX exhibited enhanced efficacy over methotrexate (MTX) in lung and breast carcinoma xenografts. Because MTX is active in the treatment of aggressive non-Hodgkin's lymphoma (NHL), we compared the efficacy of PDX and MTX against five lymphoma cell lines: RL (transformed follicular lymphoma), HT, SKI-DLBCL-1 (diffuse large B cell), Raji (Burkitt's), and Hs445 (Hodgkin's disease). After 5-day continuous in vitro exposure, PDX demonstrated > 10-fold greater cytotoxicity than MTX in all cell lines (IC50PDX = 3-5 nM, IC50MTX = 30-50 nM). We then compared the in vivo effects of anti-folates against three established human NHL xenografts in NOD/SCID mice. Tumor bearing animals were treated with saline (control) or the maximum tolerated doses of MTX (40 mg/kg) or PDX (60 mg/kg) via an intraperitoneal route twice weekly for 2 weeks. Almost 90% of HT lymphomas treated with PDX completely regressed, whereas, those treated with MTX treatment had only modest growth delays. In two other xenografts, tumor bearing mice had complete regression rates of 56% (RL) and 30% (SKI-DLBCL-1) after PDX therapy. No regressions and only minor growth inhibition was noted after MTX therapy. RT-PCR analysis for the expression of genes involved in folate metabolism demonstrated that increased sensitivity to PDX correlated with higher RFC-1 gene expression with no difference in FPGS or FPGH levels, suggesting that measurement of tumor RFC-1 gene expression level may be a predictor of response to PDX. These results demonstrate that the PDX has markedly greater potential activity against human NHL than MTX and warrants further preclinical and clinical evaluation.
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PMID:Activity of a novel anti-folate (PDX, 10-propargyl 10-deazaaminopterin) against human lymphoma is superior to methotrexate and correlates with tumor RFC-1 gene expression. 1285 5