TY - JOUR
T1 - Differential methotrexate resistance in childhood T- versus common/preB- acute lymphoblastic leukemia can be measured by an in situ thymidylate synthase inhibition assay, but not by the MTT assay
AU - Rots, Marianne G.
AU - Pieters, Rob
AU - Kaspers, Gert Jan L.
AU - Van Zantwijk, Christina H.
AU - Noordhuis, Paul
AU - Mauritz, Rob
AU - Veerman, Anjo J.P.
AU - Jansen, Gerrit
AU - Peters, Godefridus J.
PY - 1999/2/1
Y1 - 1999/2/1
N2 - Methotrexate (MTX) is not cytotoxic to patient-derived acute lymphoblastic leukemia (ALL) cells in total-cell-kill assays, such as the 3- (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, putatively due to the rescue effects of hypoxanthine and thymidine released from dying cells. This was mimicked by a diminished methotrexate (MTX) cytotoxicity for the cell lines HL60 and U937 in the presence of hypoxanthine, thymidine, or lysed ALL cells. However, enzymatic depletion or inhibition of nucleoside membrane transport did not result in MTX dose- dependent cytotoxicity in patient samples. Alternatively, a thymidylate synthase inhibition assay (TSIA), based on inhibition of the TS-catalyzed conversion of 3H-dUMP to dTMP and 3H2O, correlated with the MTT assay for antifolate sensitivity in four human leukemia cell lines with different modes of MTX resistance. For 86 ALL patient samples, TSI50 values after 21 hours exposure to MTX were not different between T- and c/preB-ALL (P = .46). After 3 hours incubation with MTX followed by an 18-hour drug-free period, T-ALL samples were 3.4-fold more resistant to MTX compared with c/preB-ALL samples (P = .001) reflecting the clinical differences in MTX sensitivity. TSI50 values correlated with MTX accumulation (r = -.58, P < .001). In conclusion, the TSIA, but not the MTT assay, can measure dose-response curves for MTX in patient-derived ALL cells and showed relative MTX resistance in T-ALL compared with C/preB-ALL.
AB - Methotrexate (MTX) is not cytotoxic to patient-derived acute lymphoblastic leukemia (ALL) cells in total-cell-kill assays, such as the 3- (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, putatively due to the rescue effects of hypoxanthine and thymidine released from dying cells. This was mimicked by a diminished methotrexate (MTX) cytotoxicity for the cell lines HL60 and U937 in the presence of hypoxanthine, thymidine, or lysed ALL cells. However, enzymatic depletion or inhibition of nucleoside membrane transport did not result in MTX dose- dependent cytotoxicity in patient samples. Alternatively, a thymidylate synthase inhibition assay (TSIA), based on inhibition of the TS-catalyzed conversion of 3H-dUMP to dTMP and 3H2O, correlated with the MTT assay for antifolate sensitivity in four human leukemia cell lines with different modes of MTX resistance. For 86 ALL patient samples, TSI50 values after 21 hours exposure to MTX were not different between T- and c/preB-ALL (P = .46). After 3 hours incubation with MTX followed by an 18-hour drug-free period, T-ALL samples were 3.4-fold more resistant to MTX compared with c/preB-ALL samples (P = .001) reflecting the clinical differences in MTX sensitivity. TSI50 values correlated with MTX accumulation (r = -.58, P < .001). In conclusion, the TSIA, but not the MTT assay, can measure dose-response curves for MTX in patient-derived ALL cells and showed relative MTX resistance in T-ALL compared with C/preB-ALL.
UR - http://www.scopus.com/inward/record.url?scp=0032902787&partnerID=8YFLogxK
U2 - 10.1182/blood.v93.3.1067.403k01_1067_1074
DO - 10.1182/blood.v93.3.1067.403k01_1067_1074
M3 - Article
C2 - 9920857
AN - SCOPUS:0032902787
SN - 0006-4971
VL - 93
SP - 1067
EP - 1074
JO - Blood
JF - Blood
IS - 3
ER -