Temozolomide Resistance in Glioblastoma Cell Lines: Implication of MGMT, MMR, P-Glycoprotein and CD133 Expression

Abstract

BackgroundThe use of temozolomide (TMZ) has improved the prognosis for glioblastoma multiforme patients. However, TMZ resistance may be one of the main reasons why treatment fails. Although this resistance has frequently been linked to the expression of O6-methylguanine-DNA methyltransferase (MGMT) it seems that this enzyme is not the only molecular mechanism that may account for the appearance of drug resistance in glioblastoma multiforme patients as the mismatch repair (MMR) complex, P-glycoprotein, and/or the presence of cancer stem cells may also be implicated.MethodsFour nervous system tumor cell lines were used to analyze the modulation of MGMT expression and MGMT promoter methylation by TMZ treatment. Furthermore, 5-aza-2’-deoxycytidine was used to demethylate the MGMT promoter and O(6)-benzylguanine to block GMT activity. In addition, MMR complex and P-glycoprotein expression were studied before and after TMZ exposure and correlated with MGMT expression. Finally, the effect of TMZ exposure on CD133 expression was analyzed.ResultsOur results showed two clearly differentiated groups of tumor cells characterized by low (A172 and LN229) and high (SF268 and SK-N-SH) basal MGMT expression. Interestingly, cell lines with no MGMT expression and low TMZ IC50 showed a high MMR complex expression, whereas cell lines with high MGMT expression and high TMZ IC50 did not express the MMR complex. In addition, modulation of MGMT expression in A172 and LN229 cell lines was accompanied by a significant increase in the TMZ IC50, whereas no differences were observed in SF268 and SK-N-SH cell lines. In contrast, P-glycoprotein and CD133 was found to be unrelated to TMZ resistance in these cell lines.ConclusionsThese results may be relevant in understanding the phenomenon of TMZ resistance, especially in glioblastoma multiforme patients laking MGMT expression, and may also aid in the design of new therapeutic strategies to improve the efficacy of TMZ in glioblastoma multiforme patients.

The effect of APOBEC3B deaminase on double-stranded DNA

“…5a) as well as other adducts 50 , leading to futile cycles of MMR and eventually DSBs. As expected, high levels of MGMT have been correlated with poor outcomes for such alkylating agent chemotherapy by repairing these genotoxic lesions [51][52][53][54] . As explained in the Results, we would expect that A3 deaminases could enhance the damage induced by MNNG, especially in the MGMT-deficient Hs578T cell line as the putative O 6 meG/C A3B substrate would not be directly repaired.…”

Juglone induces apoptosis of tumor stem-like cells through ROS-p38 pathway in glioblastoma

“…The number of animals in each group was 8. Juglone or TMZ was dissolved in DMSO and diluted in PBS; the final concentration of DMSO was 20 mg/ml [19]. PBS containing the same concentration of DMSO was used as vehicle control.…”

TMZ regulates GBM stemness via MMP14‐DLL4‐Notch3 pathway

“…For example, studies by Happold et al . and Perazzoli et al . demonstrate the mismatch repair complex consisting of MSH2, MSH3, MSH6 and PMS2 proteins and/or activity of ABC transporters in glioma cells may also regulate susceptibility to TMZ.…”

“…6 Although some studies demonstrated increased efficacy of TMZ treatment in cells with methylated O 6 -methylguanin-DNA methyltransferase promoter, 7,8 others showed no benefits, suggesting other machinery may be involved in GBM resistance to alkylating agents. For example, studies by Happold et al 9 and Perazzoli et al 10 demonstrate the mismatch repair complex consisting of MSH2, MSH3, MSH6 and PMS2 proteins and/or activity of ABC transporters in glioma cells may also regulate susceptibility to TMZ.…”