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Senescence Is the Main Trait Induced by Temozolomide in Glioblastoma Cells
Lea Beltzig1, Christian Schwarzenbach1, Petra Leukel2
1Institute of Toxicology, University Medical Center, 55131 Mainz, Germany.
Abstract:
First-line drug in the treatment of glioblastoma, the most severe brain cancer, is temozolomide (TMZ), a DNA-methylating agent that induces the critical damage O6-methylguanine (O6MeG). This lesion is cytotoxic through the generation of mismatch repair-mediated DNA double-strand breaks (DSBs), which trigger apoptotic pathways. Previously, we showed that O6MeG also induces cellular senescence (CSEN). Here, we show that TMZ-induced CSEN is a late response which has similar kinetics to apoptosis, but at a fourfold higher level. CSEN cells show a high amount of DSBs, which are located outside of telomeres, a high level of ROS and oxidized DNA damage (8-oxo-guanine), and sustained activation of the DNA damage response and histone methylation. Despite the presence of DSBs, CSEN cells are capable of repairing radiation-induced DSBs. Glioblastoma cells that acquired resistance to TMZ became simultaneously resistant to TMZ-induced CSEN. Using a Tet-On glioblastoma cell system, we show that upregulation of MGMT immediately after TMZ completely abrogated apoptosis and CSEN, while induction of MGMT long-term (>72 h) after TMZ did not reduce apoptosis and CSEN. Furthermore, upregulation of MGMT in the senescent cell population had no impact on the survival of senescent cells, indicating that O6MeG is required for induction, but not for maintenance of the senescent state. We further show that, in recurrent GBM specimens, a significantly higher level of DSBs and CSEN-associated histone H3K27me3 was observed than in the corresponding primary tumors. Overall, the data indicate that CSEN is a key node induced in GBM following chemotherapy.
Insights
Temozolomide (TMZ) induces cellular senescence (CSEN) in glioblastoma, a late-stage response that is more prevalent than apoptosis. This senescence is linked to DNA damage and resistance, highlighting CSEN as a key chemotherapy-induced event in brain cancer.
Area of Science:
- Oncology
- Molecular Biology
- Cellular Biology
Background:
- Temozolomide (TMZ) is a first-line treatment for glioblastoma (GBM), inducing DNA damage via O6-methylguanine (O6MeG).
- O6MeG lesions trigger apoptosis through DNA double-strand breaks (DSBs) and mismatch repair.
- Previous research indicated O6MeG also induces cellular senescence (CSEN).
Purpose of the Study:
- To investigate the role and kinetics of TMZ-induced CSEN in glioblastoma.
- To explore the relationship between TMZ resistance, CSEN, and DNA repair mechanisms.
- To analyze the expression of CSEN markers in primary and recurrent GBM tumors.
Main Methods:
- Utilized a Tet-On glioblastoma cell system to control MGMT expression post-TMZ treatment.
- Quantified apoptosis and CSEN levels in response to varying MGMT induction timelines.
- Assessed DNA DSBs, reactive oxygen species (ROS), and histone methylation in CSEN cells.
- Examined radiation-induced DSB repair capacity in senescent cells.
- Analyzed GBM specimens for DSBs and H3K27me3 levels.
Main Results:
- TMZ-induced CSEN is a late response, occurring at a fourfold higher level than apoptosis.
- CSEN cells exhibit significant DSBs (extratelomeric), high ROS, oxidized DNA damage, and sustained DNA damage response activation.
- TMZ-resistant glioblastoma cells were also resistant to TMZ-induced CSEN.
- Immediate MGMT upregulation post-TMZ abrogated both apoptosis and CSEN; long-term MGMT induction did not affect these outcomes.
- MGMT upregulation in senescent cells did not impact their survival, indicating O6MeG is crucial for CSEN induction but not maintenance.
- Recurrent GBM specimens showed higher DSBs and CSEN-associated H3K27me3 compared to primary tumors.
Conclusions:
- Cellular senescence is a significant, late-stage response to TMZ chemotherapy in glioblastoma.
- TMZ resistance is associated with resistance to TMZ-induced CSEN.
- MGMT plays a critical role in the early response to TMZ, affecting both apoptosis and CSEN induction.
- CSEN is a key molecular event in glioblastoma following chemotherapy, with potential implications for treatment resistance and disease recurrence.
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