5 research outputs found
Resistance to different classes of drugs is associated with impaired apoptosis in childhood acute lymphoblastic leukemia
Resistance of leukemic cells to chemotherapeutic agents is associated with
an unfavorable outcome in pediatric acute lymphoblastic leukemia (ALL). To
investigate the underlying mechanisms of cellular drug resistance, the
activation of various apoptotic parameters in leukemic cells from 50
children with ALL was studied after in vitro exposure with 4 important
drugs in ALL therapy (prednisolone, vincristine, l-asparaginase, and
daunorubicin). Exposure to each drug resulted in early induction of
phosphatidylserine (PS) externalization and mitochondrial transmembrane
(Deltapsim) depolarization followed by caspase-3 activation and
poly(ADP-ribose) polymerase (PARP) inactivation in the majority of
patients. For all 4 drugs, a significant inverse correlation was found
between cellular drug resistance and (1) the percentage of cells with PS
externalization (<.001 < P <.008) and (2) the percentage of cells with
Deltapsim depolarization (.002 < P <.02). However, the percentage of cells
with caspase-3 activation and the percentage of cells with PARP
inactivation showed a significant inverse correlation with cellular
resistance for prednisolone (P =.001; P =.001) and l-asparaginase (P =.01;
P =.001) only. This suggests that caspase-3 activation and PARP
inactivation are not essential for vincristine- and daunorubicin-induced
apoptosis. In conclusion, resistance to 4 unrelated drugs is associated
with defect(s) upstream or at the level of PS externalization and
Deltapsim depolarization. This leads to decreased activation of apoptotic
parameters in resistant cases of pediatric AL
Decreased PARP and procaspase-2 protein levels are associated with cellular drug resistance in childhood acute lymphoblastic leukemia
Drug resistance in childhood acute lymphoblastic leukemia (ALL) and acute
myeloid leukemia (AML) is associated with impaired ability to induce
apoptosis. To elucidate causes of apoptotic defects, we studied the
protein expression of Apaf-1, procaspases-2, -3, -6, -7, -8, -10, and
poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) in cells from
children with acute lymphoblastic leukemia (ALL; n = 43) and acute myeloid
leukemia (AML; n = 10). PARP expression was present in all B-lineage
samples, but absent in 4 of 15 T-lineage ALL samples and 3 of 10 AML
cases, which was not caused by genomic deletions. PARP expression was a
median 7-fold lower in T-lineage ALL (P < .001) and 10-fold lower in AML
(P < .001) compared with B-lineage ALL. PARP expression was 4-fold lower
in prednisolone, vincristine and L-asparaginase (PVA)-resistant compared
with PVA-sensitive ALL patients (P < .001). Procaspase-2 expression was
3-fold lower in T-lineage ALL (P = .022) and AML (P = .014) compared with
B-lineage ALL. In addition, procaspase-2 expression was 2-fold lower in
PVA-resistant compared to PVA-sensitive ALL patients (P = .042). No
relation between apoptotic protease-activating factor 1 (Apaf-1),
procaspases-3, -6, -7, -8, -10, and drug resistance was found. In
conclusion, low baseline expression of PARP and procaspase-2 is related to
cellular drug resistance in childhood acute lymphoblastic leukemia
Asparagine synthetase expression is linked with L-asparaginase resistance in TEL-AML1-negative but not TEL-AML1-positive pediatric acute lymphoblastic leukemia
Resistance to L-asparaginase in leukemic cells may be caused by an
elevated cellular expression of asparagine synthetase (AS). Previously, we
reported that high AS expression did not correlate to L-asparaginase
resistance in TEL-AML1-positive B-lineage acute lymphoblastic leukemia
(ALL). In the present study we confirmed this finding in TEL-AML1-positive
patients (n = 28) using microarrays. In contrast, 35
L-asparaginase-resistant TEL-AML1-negative B-lineage ALL patients had a
significant 3.5-fold higher AS expression than 43 sensitive patients (P <
.001). Using real-time quantitative polymerase chain reaction (RTQ-PCR),
this finding was confirmed in an independent group of 39 TEL-AML1-negative
B-lineage ALL patients (P = .03). High expression of AS was associated
with poor prognosis (4-year probability of disease-free survival [pDFS]
58% +/- 11%) compared with low expression (4-year pDFS 83% +/- 7%; P =
.009). We conclude that resistance to l-asparaginase and relapse risk are
associated with high expression of AS in TEL-AML1-negative but not
TEL-AML1-positive B-lineage ALL
Sensitivity to L-asparaginase is not associated with expression levels of asparagine synthetase in t(12;21)+ pediatric ALL
The (12;21) translocation resulting in TEL/AML1 gene fusion is present in
about 25% of childhood precursor B-lineage acute lymphoblastic leukemia
(ALL) and is associated with a good prognosis and a high cellular
sensitivity to L-asparaginase (L-Asp). ALL cells are thought to be
sensitive to L-Asp due to lower asparagine synthetase (AS) levels.
Resistance to L-Asp may be caused by an elevated cellular level of AS or
by the ability of resistant cells to rapidly induce the expression of the
AS gene on L-Asp exposure. AS may be a target regulated by t(12;21). We
studied the relationship between t(12;21) and the mRNA level of AS to
investigate a possible mechanism underlying L-Asp sensitivity. Real-time
quantitative reverse transcription-polymerase chain reaction (RT-PCR)
analysis surprisingly revealed that 30 patients positive for t(12;21)
expressed 5-fold more AS mRNA compared with 17 patients negative for
t(12;21) (P =.008) and 11 samples from healthy controls (P =.016). The
mRNA levels of AS between t(12;21)(-) ALL and healthy controls did not
differ. No difference was found between ALL patients positive or negative
for t(12;21) in the capacity to up-regulate AS after in vitro L-Asp
exposure, excluding a defective capacity for t(12;21) cells in
up-regulating AS on L-Asp exposure. Moreover, no correlation was observed
between AS mRNA expression and sensitivity to L-Asp. We conclude that the
sensitivity of t(12;21)(+) childhood ALL to L-Asp is not associated with
the expression level of the AS gene. Furthermore, we contradict the
general thought that leukemic cells specifically lack AS compared with
normal bone marrow and blood cells
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