Related Experiment Videos
O6-methylguanine-DNA methyltransferase activity in breast and brain tumors
I Preuss1, I Eberhagen, S Haas
1Nuclear Research Center Karlsruhe, Institute of Genetics, Germany.
Abstract:
The DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) is a main determinant of resistance of tumor cells to the cytostatic activity of chemotherapeutic alkylating agents (methylating and chloroethylating nitrosoureas) and is effective in protecting normal cells against genotoxic and carcinogenic effects resulting from DNA alkylation. Therefore, the level of expression of MGMT is significance for the response of both the tumor and the non-target tissue following application of nitrosoureas in tumor therapy. To determine the expression of MGMT in tumor tissue, we have assayed MGMT activity in 68 breast carcinomas and 38 brain tumors. There was a wide variation of MGMT expression in breast carcinomas ranging from below the level of detection up to 863 fmol/mg protein. About 4% of breast tumors did not display detectable MGMT, 15% had activity lower than 100 fmol/mg protein, and 26% expressed more than 500 fmol/mg. The mean level of expression was 321 fmol/mg. In brain tumors (astrocytoma WHO grade I, II, and III, and glioblastoma WHO grade IV) the MGMT activity was generally lower than in breast tumors, ranging from below the level of detection up to 238 fmol/mg. The mean level of expression was 55 fmol/mg. Five percent of the brain tumors had no detectable MGMT activity. The MGMT repair activity correlated well with the amount of MGMT protein present in tumor samples, as shown by Western-blot analysis, indicating that loss of MGMT repair activity is due to inability of these tumor cells to synthesize the protein.
Insights
The DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) influences chemotherapy response. MGMT expression varied widely in breast and brain tumors, impacting treatment effectiveness.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- O6-methylguanine-DNA methyltransferase (MGMT) is crucial for DNA repair, protecting against alkylating agent-induced damage.
- MGMT expression levels significantly impact tumor cell resistance and normal tissue response to chemotherapy.
- Understanding MGMT expression is vital for optimizing nitrosourea-based cancer therapies.
Purpose of the Study:
- To quantify MGMT expression levels in human breast and brain tumors.
- To correlate MGMT activity with protein levels and assess its role in treatment resistance.
Main Methods:
- Assayed MGMT activity in 68 breast carcinomas and 38 brain tumors.
- Utilized Western-blot analysis to determine MGMT protein levels.
- Analyzed MGMT expression variability across different tumor types and grades.
Main Results:
- Breast tumors showed wide MGMT expression (mean 321 fmol/mg), with some lacking detectable levels.
- Brain tumors exhibited generally lower MGMT activity (mean 55 fmol/mg), with 5% showing no detectable levels.
- MGMT activity strongly correlated with MGMT protein levels, indicating synthesis deficiency in low-activity tumors.
Conclusions:
- MGMT expression varies significantly in breast and brain tumors.
- Loss of MGMT activity in tumors is primarily due to a lack of protein synthesis.
- MGMT levels are a critical factor in predicting patient response to alkylating chemotherapy.