Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Factors that reduce the intracellular concentration of triphosphorylated cytarabine (ara-CTP), the active form of cytarabine (ara-C), may induce chemoresistance in acute myeloid leukaemia (AML) patients. These factors include reduced influx of ara-C by the hENT1 transporter, reduced phosphorylation by deoxycytidine kinase (dCK), and increased degradation by high Km cytoplasmic 5'-nucleotidase (5NT) and/or cytidine deaminase (CDD). Increased levels of DNA polymerase alpha (DNA POL) and reduced levels of topoisomerase I (TOPO I) and topoisomerase II (TOPO II) have also been detected in ara-C-resistant cell lines. To determine whether these factors are implicated in clinical ara-C resistance, we analysed the expression of these parameters at diagnosis, using reverse transcription polymerase chain reaction, in the blast cells of 123 AML patients treated with ara-C. At diagnosis, hENT1, dCK, CDD, 5NT, TOPO I, TOPO II, DNA POL and MDR1 were expressed in 83%, 22%, 7%, 37%, 59%, 37%, 39% and 16% of patients respectively. In univariate analysis, patients with expression of 5NT or DNA POL at diagnosis had significantly shorter disease-free survival (DFS). In multivariate analysis, DNA POL positivity and hENT1 deficiency were related to a shorter DFS. In univariate analysis, patients with 5NT-positive blasts had significantly shorter overall survival (OS). In multivariate analysis, shorter OS was related to DNA POL positivity. These results suggest that expression of DNA POL, 5NT and hENT1 at diagnosis may be resistance mechanisms to ara-C in AML patients.
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PMID:In vivo mechanisms of resistance to cytarabine in acute myeloid leukaemia. 1206 Jan 21

Equilibrative nucleoside transporter 1 (ENT1) is a major regulator for the uptake of [(18)F]fluorothymidine ([(18)F]FLT), a promising positron emission tomography tracer for treatment monitoring. Various antimetabolites such as 5-fluorouracil often increase ENT1 activity and [(18)F]FLT uptake (flare) in spite of cell death. However, it has not yet been defined which agents induce [(18)F]FLT flare and what is the role of [(18)F]FLT flare in cell viability. Sixty cytotoxic agents from the LOPAC1280 library were screened for ENT1 activity in HeLa cells which predominantly express ENT1, and topoisomerase inhibitors (i.e., aurintricarboxylic acid, idarubicin, camptothecin and etoposide) were identified as potent inducers of ENT1 activity. The changes in ENT1 activity were closely correlated with [(3)H]FLT uptake (Spearman's correlation coefficient, r=0.66; P<0.01). Etoposide significantly increased ENT1 activity and [(3)H]FLT uptake accompanying cell cycle arrest at S/G2/M phase and the increase in TK1 expression and activity in both ENT1-low expressing HT29 and ENT1-high expressing MDA-MB-231 cells. The inhibition of ENT1 activity by dipyridamol or S-(p-nitrobenzyl)-6-thioinosine repressed the etoposide-induced cell death in HeLa cells, whereas it induced no changes in the other cell lines. In conclusion, etoposide is identified as a potent inducer for ENT1 activity and [(3)H]FLT uptake. The role of ENT1 activity by etoposide was cell-type dependent, which requests caution for the application of ENT1-mediated [(18)F]FLT flare for treatment monitoring.
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PMID:Etoposide increases equilibrative nucleoside transporter 1 activity and fluorothymidine uptake: screening of 60 cytotoxic agents. 2323 55