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- Fotoohi, A K, et al.
(författare)
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Molecular mechanisms underlying the enhanced sensitivity of thiopurine-resistant T-lymphoblastic cell lines to methyl mercaptopurineriboside
- 2006
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Ingår i: Biochemical Pharmacology. - : Elsevier BV. - 0006-2952 .- 1356-1839. ; 72:7, s. 816-823
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Tidskriftsartikel (refereegranskat)abstract
- Methylmercaptopurine riboside (meMPR), a cellular metabolite of 6-mercaptopurine (6-MP), is a potent inhibitor of de novo purine synthesis (DNPS). Human MOLT4 T-lymphoblastic leukaemia cells that have acquired resistance to 6-MP or 6-thioguanine (6-TG) as a consequence of defective transport exhibit enhanced sensitivity to meMPR. HPLC-based analysis of the transport of meMPR revealed normal uptake of this compound by our thiopurine-resistant cell sublines, suggesting a route of transport distinct from that for 6-MP and 6-TG. Studies on the wild-type parental leukemic cells showed that adenosine, dipyridamole and nitrobenzylthioinosine inhibit uptake of meMPR to a significant extent, whereas Na+ ions have no influence on this process. Transfection of these leukemic cells with small interference RNA molecules targeting the gene encoding the first member of the family of equiliberative nucleoside transporters (ENT1) strongly reduced the initial rate of meMPR transport. Our resistant cell lines exhibited 30-52% reductions (p < 0.005) in their levels of mRNA encoding several proteins involved in de novo purine synthesis, i.e., aminoimidazole carboxamide ribonucleotide formyltransferase, glycinamide ribonucleotide transformylase and guanine monophosphate synthetase. Consequently, the rate of de novo purine synthesis in these resistant sublines was decreased by 50%. Furthermore, the levels of ribonucleoside triphosphates in these cells were significantly lower than in the non-resistant parental cells. In combination, a reduced rate of de novo purine synthesis together with low levels of ribonucleoside triphosphates can explain the enhanced sensitivity of our thiopurine-resistant cell lines to meMPR. In this manner, meMPR bypasses the mechanisms of resistance to thiopurines and is even more cytotoxic towards resistant than towards wild-type cells. © 2006.
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- Fotoohi, K, et al.
(författare)
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Interference of 7-hydroxymethotrexate with the determination of methotrexate in plasma samples from children with acute lymphoblastic leukemia employing routine clinical assays
- 2005
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Ingår i: Journal of Chromatography. B. - : Elsevier BV. - 1873-376X .- 1570-0232. ; 817:2, s. 139-144
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Tidskriftsartikel (refereegranskat)abstract
- The accuracy of two clinical assays, the enzyme-multiplied immunoassay (EMIT) and fluorescence polarization immunoassay (FPIA2), universally employed for measurement of plasma levels of methotrexate (MTX) in children administered a high dose of this drug for treatment of acute lymphoblastic leukemia was evaluated here. Because of its superior specificity, sensitivity, and precision, high performance liquid chromatography (HPLC) was selected as the reference method with which the other two procedures were compared using approximately 420 different plasma samples for method comparison. 7-Hydroxymethotrexate (7-OHMTX), the major plasma metabolite of MTX, that can be detected in plasma at relatively high concentrations for long periods following infusion of a high dose of MTX, was also quantitated by HPLC. Forty-two and 66 h after infusion, the plasma level of MTX was overestimated in 2% and 3% of the samples by the FPIA2 procedure in 5% and 31% by the EMIT assay. The overall correlation coefficients (r(2)) for the values obtained by FPIA2 or EMIT versus those based on HPLC were 0.989 and 0.663, respectively. The presence of 7-OHMTX exerted a highly significant influence (p = 0.0007 as determined by the unpaired t-test) on MTX measurement by the EMIT assay. We conclude that the rapid automated procedures routinely used at present and in particular EMIT, suffer from cross-reactivity with metabolites of MTX. Thus, the relatively high percentage of samples in which the level of MTX is overestimated at check-points by EMIT may result in longer periods of hospitalization, higher costs and prolonged administration of elevated doses of "rescue" leucovorin with an increased risk for relapse.
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