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Temozolomide Resistance in Glioblastoma Cell Lines: Implication of MGMT, MMR, P-Glycoprotein and CD133 Expression
Gloria Perazzoli1, Jose Prados2, Raul Ortiz3
1Institute of Biopathology and Regenerative Medicine (IBIMER), Granada, Spain.
Background:
The 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.
Methods:
Four 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.
Results:
Our 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.
Conclusions:
These 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.
Insights
Temozolomide (TMZ) resistance in glioblastoma is complex. The mismatch repair (MMR) complex, not just O6-methylguanine-DNA methyltransferase (MGMT), influences TMZ efficacy, especially in MGMT-deficient tumors.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Research
Background:
- Temozolomide (TMZ) is a key treatment for glioblastoma multiforme (GBM).
- TMZ resistance is a major cause of treatment failure in GBM patients.
- O6-methylguanine-DNA methyltransferase (MGMT) expression is linked to TMZ resistance, but other factors like the mismatch repair (MMR) complex, P-glycoprotein, and cancer stem cells may also play a role.
Purpose of the Study:
- To investigate the role of MGMT expression and methylation in TMZ resistance.
- To analyze the involvement of the MMR complex and P-glycoprotein in TMZ resistance.
- To explore the impact of TMZ treatment on CD133 expression in nervous system tumor cell lines.
Main Methods:
- Analysis of MGMT expression and promoter methylation in four nervous system tumor cell lines after TMZ treatment.
- Use of 5-aza-2'-deoxycytidine to demethylate the MGMT promoter and O(6)-benzylguanine to inhibit MGMT activity.
- Assessment of MMR complex and P-glycoprotein expression pre- and post-TMZ exposure, correlated with MGMT levels.
- Evaluation of CD133 expression following TMZ exposure.
Main Results:
- Two distinct groups of tumor cells were identified based on MGMT expression levels (low vs. high).
- Cell lines with low MGMT expression and low TMZ IC50 exhibited high MMR complex expression, while those with high MGMT and high TMZ IC50 lacked MMR complex expression.
- Modulation of MGMT expression in certain cell lines altered TMZ IC50, but P-glycoprotein and CD133 expression did not correlate with TMZ resistance.
Conclusions:
- The MMR complex is implicated in TMZ resistance, particularly in MGMT-deficient glioblastoma multiforme.
- These findings contribute to understanding TMZ resistance mechanisms.
- The results may inform the development of novel therapeutic strategies to enhance TMZ efficacy in glioblastoma patients.
