6 research outputs found
Effect of polymorphisms in folate-related genes on in vitro methotrexate sensitivity in pediatric acute lymphoblastic leukemia
We studied whether common polymorphisms in genes involved in folate
metabolism affect methotrexate (MTX) sensitivity. Ex vivo MTX sensitivity
of lymphoblasts obtained from pediatric patients with acute lymphoblastic
leukemia (ALL; n = 157) was determined by the in situ thymidylate synthase
inhibition assay after either continuous (21 hours; TSI(50, cont)) or
short-term (3 hours; TSI(50, short)) MTX exposure. DNA was isolated from
lymphoblasts obtained from cytospin slides. Polymorphisms in
methylenetetrahydrofolate reductase (MTHFR 677C>T, MTHFR 1298A>C),
methionine synthase (MTR 2756A>G), methionine synthase reductase (MTRR
66A>G), methylenetetrahydrofolate dehydrogenase (MTHFD1 1958G>A), serine
hydroxymethyl transferase (SHMT1 1420C>T), thymidylate synthase (TS 2R3R),
and the reduced folate carrier (RFC 80G>A) were detected by polymerase
chain reaction-restriction fragment length polymorphism (PCR-RFLP) or
real-time PCR. Patients with the MTHFR 1298AC variant or the MTRR 66
G-allele showed decreased in vitro MTX sensitivity measured under both
test conditions. SHMT1 1420TT homozygotes only showed decreased MTX
sensitivity in the TSI(50, cont). In conclusion, polymorphisms in the
folate-related genes MTHFR, MTRR, and SHMT1 are related to MTX resistance
in pediatric patients with ALL
Folates provoke cellular efflux and drug resistance of substrates of the multidrug resistance protein 1 (MRP1)
Cellular folate concentration was earlier reported to be a critical factor in the activity and expression of the multidrug resistance protein MRP1 (ABCC1). Since MRP1 mediates resistance to a variety of therapeutic drugs, we investigated whether the cellular folate concentration inf
Role of genomic factors beyond thymidylate synthase in the prediction of response to 5-fluorouracil
Differential mRNA expression of Ara-C-metabolizing enzymes explains Ara-C sensitivity in MLL gene-rearranged infant acute lymphoblastic leukemia
Infant acute lymphoblastic leukemia (ALL) is characterized by a high
incidence of mixed lineage leukemia (MLL) gene rearrangements, a poor
outcome, and resistance to chemotherapeutic drugs. One exception is
cytosine arabinoside (Ara-C), to which infant ALL cells are highly
sensitive. To investigate the mechanism underlying Ara-C sensitivity in
infants with ALL, mRNA levels of Ara-C-metabolizing enzymes were measured
in infants (n = 18) and older children (noninfants) with ALL (n = 24). In
the present study, infant ALL cells were 3.3-fold more sensitive to Ara-C
(P =.007) and accumulated 2.3-fold more Ara-CTP (P =.011) upon exposure to
Ara-C, compared with older children with ALL. Real-time quantitative
reverse trancriptase-polymerase chain reaction (RT-PCR) (TaqMan) revealed
that infants express 2-fold less of the Ara-C phosphorylating enzyme
deoxycytidine kinase (dCK) mRNA (P =.026) but 2.5-fold more mRNA of the
equilibrative nucleoside transporter 1 (hENT1), responsible for Ara-C
membrane transport (P =.001). The mRNA expression of pyrimidine
nucleotidase I (PN-I), cytidine deaminase (CDA), and deoxycytidylate
deaminase (dCMPD) did not differ significantly between both groups. hENT1
mRNA expression inversely correlated with in vitro resistance to Ara-C
(r(s) = -0.58, P =.006). The same differences concerning dCK and hENT1
mRNA expression were observe