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Modulation of nitrosourea resistance in human colon cancer by O6-methylguanine
S L Gerson1, N A Berger, C Arce
1Department of Medicine, Ireland Cancer Center, Case Western Reserve, University School of Medicine, Cleveland, OH.
Abstract:
Human colon cancer is resistant to a variety of alkylating agents including the nitrosoureas. To specifically evaluate nitrosourea resistance, we studied the role of O6-alkylguanine-DNA alkyltransferase (alkyltransferase) which is known to repair nitrosourea-induced cytotoxic DNA damage. Alkyltransferase activity varied over a similar wide range in 25 colon cancer biopsies and 14 colon cancer cell lines but the activity was not correlated with differentiation status, Dukes' classification or in vitro growth characteristics. 1,3-Bis-(2-chloroethyl)-1-nitrosourea (BCNU) resistance and alkyltransferase activity were highly correlated (R2 = 0.929, P less than 0.001) in 7 different colon cancer cell lines, suggesting that the alkyltransferase is an important component of nitrosourea resistance in colon cancer cells. In the BCNU-resistant, high alkyltransferase VACO 6 cell line, inactivation of the alkyltransferase by O6-methylguanine caused a proportional decrease in the BCNU IC50, consistent with that predicted by the regression line. Enzyme inactivation was also associated with a marked increase in DNA cross-link formation. Because alkyltransferase correlates with BCNU resistance in colon cancer, and resistance can be reversed by inactivating the protein, the alkyltransferase may have an important role in nitrosourea resistance in human colon cancer cells. These data provide the rationale for clinical trials in colon cancer with biochemical modulators of the alkyltransferase to increase the therapeutic response to nitrosoureas.
Insights
O6-alkylguanine-DNA alkyltransferase (alkyltransferase) repairs DNA damage from nitrosoureas. High alkyltransferase activity strongly correlates with BCNU resistance in colon cancer, suggesting it
Area of Science:
- Oncology
- Molecular Biology
- Cancer Research
Background:
- Human colon cancer exhibits resistance to alkylating agents like nitrosoureas.
- O6-alkylguanine-DNA alkyltransferase (alkyltransferase) is a key enzyme in repairing DNA damage induced by nitrosoureas.
Purpose of the Study:
- To investigate the role of alkyltransferase in nitrosourea resistance in human colon cancer.
- To determine the correlation between alkyltransferase activity and resistance to 1,3-Bis-(2-chloroethyl)-1-nitrosourea (BCNU).
Main Methods:
- Assessed alkyltransferase activity in colon cancer biopsies and cell lines.
- Correlated BCNU resistance with alkyltransferase activity in colon cancer cell lines.
- Inactivated alkyltransferase in a resistant cell line to observe effects on BCNU sensitivity and DNA cross-linking.
Main Results:
- Alkyltransferase activity varied widely but did not correlate with differentiation or clinical stage.
- A strong positive correlation (R2 = 0.929) was found between BCNU resistance and alkyltransferase activity in colon cancer cell lines.
- Inactivation of alkyltransferase in a resistant cell line reduced BCNU IC50 and increased DNA cross-linking.
Conclusions:
- Alkyltransferase plays a significant role in mediating nitrosourea resistance in human colon cancer.
- The strong correlation suggests alkyltransferase is a critical factor in BCNU resistance.
- Targeting alkyltransferase activity could enhance nitrosourea efficacy in colon cancer treatment.