MGMT (O6-Methylguanine-DNA Methyltransferase)
What it is
- A DNA repair enzyme that removes alkyl groups from the O6 position of guanine.
- Protects cells from the cytotoxic effects of alkylating agents (e.g., temozolomide, carmustine, lomustine).
Clinical Relevance in Oncology
- Glioblastoma multiforme (GBM):
- Temozolomide efficacy is strongly influenced by MGMT promoter methylation status.
- Methylated MGMT promoter → silences MGMT expression → less DNA repair → tumor cells more sensitive to temozolomide.
- Unmethylated MGMT promoter → active MGMT repairs DNA damage → resistance to temozolomide.
- Other tumors:
- Studied in colorectal, lung, and other solid tumors, but most clinically relevant in neuro-oncology.
Testing
- MGMT promoter methylation testing is standard in glioblastoma:
- Helps guide prognosis and treatment decisions (especially in elderly or frail patients).
- Patients with unmethylated MGMT may not benefit significantly from temozolomide, so radiotherapy alone may be considered.
Pharmacist Pearls
- Temozolomide + RT remains standard for GBM, but knowing MGMT status helps personalize therapy.
- Be aware of temozolomide resistance in MGMT-unmethylated tumors.
- Supportive care is critical with temozolomide (antiemetics, PJP prophylaxis in prolonged use, blood count monitoring).
In short, MGMT is a DNA repair enzyme. Its promoter methylation silences it, making glioblastomas more responsive to temozolomide.