ABSTRACT
The most effective chemotherapeutic for glioblastoma (GBM) is the DNA alkylating agent temozolomide (TMZ). In a recent study by Hegi et al. benefit from TMZ was significantly associated with methylation of the promoter of the O6-methylguanine-DNA methyltransferase (MGMT) gene; however, the correlation was imperfect. Some patients with methylated tumors were short survivors and others with unmethylated tumors were long survivors. These exceptions have raised the possibility that TMZ response might be influenced by non-MGMT mechanisms. The effect of p53 status on response to TMZ was explored in traditional glioma cell lines (U87MG, U251MG, U343MG, U373MG, SF767, LN443 and LNZ308) and brain tumor initiating cells (BTICs--BT012, BT025, BT042, BT048, BT060 and BT069) in two ways: (1) inhibition of p53 by RNAi and (2) sensitivity in relation to intrinsic p53 status, either wild-type or mutant. Traditional glioma cell lines that did not express a functional p53 were significantly more sensitive to TMZ than cell lines with functionally intact wild-type p53 expression. Altered p53 expression or function had only minor effects on TMZ sensitivity in BTICs and tended to decrease sensitivity to TMZ. RNAi specific for p53 had little effect on sensitivity in p53 null glioma cells. Absence of a functional p53 increases TMZ sensitivity in traditional glioma cell lines, an effect that is independent of MGMT status, and not seen in BTICs. P53 status may influence response to TMZ in differentiated cells in a GBM with a negligible affect on its initiating cells.
Subject(s)
Antineoplastic Agents, Alkylating/pharmacology , Brain Neoplasms/drug therapy , Dacarbazine/analogs & derivatives , Drug Resistance, Neoplasm/genetics , Glioma/drug therapy , Neoplastic Stem Cells/drug effects , Tumor Suppressor Protein p53/metabolism , Blotting, Western , Brain Neoplasms/metabolism , DNA Methylation , Dacarbazine/pharmacology , Glioma/metabolism , Humans , Mutation/genetics , Neoplastic Stem Cells/metabolism , O(6)-Methylguanine-DNA Methyltransferase/metabolism , Promoter Regions, Genetic/genetics , RNA, Messenger/genetics , RNA, Small Interfering/genetics , Reverse Transcriptase Polymerase Chain Reaction , Temozolomide , Tumor Cells, Cultured , Tumor Suppressor Protein p53/antagonists & inhibitors , Tumor Suppressor Protein p53/geneticsABSTRACT
Investigating the biology of oligodendroglioma and its characteristic combined deletion of chromosomal arms 1p and 19q, mediated by an unbalanced translocation, t(1;19)(q10;p10), has been hampered by the lack of cell lines that harbor these traits. We grew cells from 2 anaplastic oligodendrogliomas in serum-free conditions. Serial propagation and expansion led to the establishment of permanent cell lines that maintained the genetic signature of the parent oligodendrogliomas and displayed features of brain tumor stem cells in vitro. One line was established from a treatment-naïve tumor and the other from a temozolomide resistant recurrent tumor. These lines may be important tools for understanding the biology of oligodendrogliomas and the function of their defining genetic traits.
Subject(s)
Brain Neoplasms/genetics , Chromosomes, Human, Pair 19/genetics , Chromosomes, Human, Pair 1/genetics , Oligodendroglioma/genetics , Brain Neoplasms/pathology , Cell Line, Tumor , Humans , Oligodendroglioma/pathology , Translocation, Genetic/geneticsABSTRACT
Molecular alterations in glioblastoma have the potential to guide treatment. Here, we explore the relationship between temozolomide (TMZ) response and O(6)-methylguanine DNA methyltransferase (MGMT) status in brain tumor initiating cells (BTICs). Methylation, expression, and sensitivity were assessed in 20 lines; associations were evaluated by Fisher's exact test. Some BTICs were sensitive. Sensitivity to TMZ was only associated with protein expression (P = .001). There were atypical BTICs including TMZ-resistant lines in which the methylation-specific PCR reaction revealed both methylated and unmethylated bands. BTICs are not uniformly resistant to TMZ; some are sensitive. MGMT status does not predict TMZ response with high precision.
