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O6-Alkylguanine-DNA alkyltransferase in normal colon tissue and colon cancer
Abstract:
O6-Alkylguanine-DNA alkyltransferase (AGT) is a DNA repair protein that reverses alkylation damage produced by chloroethylnitrosoureas and is a major determinant of cellular resistance to adjuvant chemotherapy with these drugs. AGT activity was measured in 119 samples from 69 patients, including normal, tumor, and diseased tissue, and 42 patients in which both normal and tumor tissue were assayed. The activity varied among individuals, but there was no statistically significant difference in average AGT activity among tumor, normal, and diseased tissue, or between men and women, or between young and old patients (< 70 or > 70 years). Few (3/49) tumor samples showed an absence of AGT activity (Mer- phenotype). The results indicate that nearly all colon cancers have significant AGT activity, and adjuvant chloroethylnitrosoureas chemotherapy must be modified, perhaps by the use of AGT biochemical modulators, to overcome this natural drug resistance.
Insights
O6-Alkylguanine-DNA alkyltransferase (AGT) is a DNA repair protein. Most colon cancers exhibit significant AGT activity, suggesting chemotherapy resistance, necessitating modified treatment strategies.
Area of Science:
- Biochemistry
- Molecular Biology
- Oncology
Background:
- O6-Alkylguanine-DNA alkyltransferase (AGT) is a critical DNA repair protein.
- AGT activity influences cellular resistance to chloroethylnitrosourea chemotherapy drugs.
- Understanding AGT levels is vital for optimizing cancer treatment strategies.
Purpose of the Study:
- To measure and analyze O6-Alkylguanine-DNA alkyltransferase (AGT) activity in various human tissues.
- To investigate the correlation between AGT activity and patient demographics (age, sex) and tissue type (normal, tumor, diseased).
- To assess the prevalence of AGT deficiency (Mer- phenotype) in colon cancer samples.
Main Methods:
- Enzyme activity assays were performed on 119 tissue samples from 69 patients.
- Samples included normal, tumor, and diseased tissues.
- Statistical analysis was used to compare AGT activity across different groups.
Main Results:
- AGT activity showed significant inter-individual variation but no significant differences between tumor, normal, or diseased tissues.
- No significant differences in AGT activity were observed based on sex or age (<70 vs. >70 years).
- Only a small fraction (3/49) of tumor samples exhibited a deficiency in AGT activity (Mer- phenotype).
Conclusions:
- The study concludes that nearly all colon cancers possess substantial AGT activity.
- This inherent AGT activity confers natural resistance to adjuvant chloroethylnitrosourea chemotherapy.
- Treatment strategies may require modification, potentially incorporating AGT biochemical modulators, to enhance efficacy.