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Ablation of O6-methylguanine-DNA methyltransferase
with O6-benzylguanine reduces the resistance of pediatric primary
brain tumor cell lines to temozolomide and BCNU
Michael S. Bobola, Richard Ellenbogen, Ryan Goff, John Silber
Children's Hospital and Regional Medical Center, Seattle, WA and University of
Washington, Seattle, WA.
E-mail: michael.bobola@seattlechildrens.org
The DNA methylating agent temozolomide (TMZ) and the chloroethylating agent BCNU
are important components in the adjuvant chemotherapy of pediatric primary brain
tumors.
We have examined the contribution of the DNA repair protein O6-methylguanine-DNA
methyltransferase (MGMT) to alkylator resistance in n pediatric glioma and n
medulloblastoma cell lines.
All lines display MGMT activity, ranging from 30 to
184 fmol/106 cells; activity is comparable in glioma (67 ± 32
fmol/106 cells) and medulloblastoma lines (98 ± 50 fmol/106
cells).
The dose required to reduce survival to 10% (LD10) for TMZ,
determined by clonogenic survival assay, varied 3-fold (334 µM to 915 µM)
among the lines.
Ablation of MGMT by O6-benzylguanine (O6-BG)
reduced LD10 for TMZ an average of 30 ± 16-fold, ranging from 15- to
71-fold, revealing that the contribution of MGMT to resistance is highly
variable.
Variability in resistance, manifested as a 6-fold range in LD10
persists after measurable MGMT is eliminated.
The lines display a 2-fold
difference in LD10 for BCNU (60 µM to 128 µM) and less dependence
on MGMT for BCNU resistance as evidenced by 2.8 ± 0.5-fold average reduction of
LD10 (range 2.0- to 4.2-fold) produced by O6-BG.
In
addition, variability in resistance persists after ablation of MGMT (19 µM to
51 µM).
Our findings document the contribution of MGMT to resistance to
clinical alkylators in pediatric gliomas and medulloblastomas, and support the
clinical use of O6-BG to suppress resistance to alkylators in
pediatric brain tumors in vivo.
Importantly, the variability in LD10
for both TMZ and BCNU that persists after ablation of MGMT indicates a
differential contribution of other resistance mechanisms to resistance.
Copyright © 2004 American Association for Cancer Research. All rights
reserved.
Source: http://aacr04.agora.com/planner/displayabstract.asp?presentationid=5652
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