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Reductive alkylation of DNA by mitomycin A, a mitomycin with high redox potential
B F McGuinness1, R Lipman, J Goldstein
1Department of Chemistry, Columbia University, New York, New York 10027.
Abstract:
The mitomycins are a group of antitumor antibiotics that covalently bind to DNA upon reductive activation. Mitomycin A (1b; MA) is more toxic than its clinically useful mitomycin C (1a; MC). The greater toxicity of mitomycin A has been previously attributed to its higher reduction potential. In this report, the DNA alkylation products of reductively activated MA were isolated and characterized by conversion to the known 7-amino mitosene-deoxyguanosine adducts. The three major adducts formed were identified as a monoadduct, N2-(2"beta-amino-7"-methoxymitosen-1"alpha-yl)- 2'-deoxyguanosine (5), a decarbamoyl monoadduct, N2-(2"beta-amino-10"-decarbamoyl-7"-methoxymitosen-1"alpha-y l)-2'- deoxyguanosine (6), and a bisadduct, N2-(2"beta-amino-10"-deoxyguanosin-N2-yl-7-methoxymitosen-1" alpha- yl)-2'-deoxyguanosine (7). Under all reductive activation conditions employed, MA selectively alkylated the 2-amino group of guanine in DNA, like MC. In addition, both MA and MC alkylated DNA and cross-linked oligonucleotides to a similar extent. However, variations in the reductive activation conditions (H2/PtO2, Na2S2O4, or enzymatic) affected the distribution of the three major MA adducts in a different manner than the distribution of MC adducts was affected. A mechanism is proposed wherein the 7-methoxy substituent of MA allows initial indiscriminate activation of either of the drugs' two electrophilic sites. While oxygen inhibited cross-linking by MC, similar aerobic conditions exhibited little influence on the cross-linking ability of MA. Hence, the greater toxicity of MA may be influenced by increased and nonselective activation and cross-link formation in both aerobic and anaerobic cells. This effect is a direct consequence of the higher redox potential of MA as compared to MC.
Insights
Mitomycin A (MA) exhibits greater antitumor toxicity than Mitomycin C (MC) due to its higher redox potential, leading to increased and nonselective DNA alkylation and cross-linking under both aerobic and anaerobic conditions.
Area of Science:
- Biochemistry
- Molecular Biology
- Medicinal Chemistry
Background:
- Mitomycins are antitumor antibiotics that function via DNA covalent binding after reductive activation.
- Mitomycin A (MA) is more toxic than the clinically used Mitomycin C (MC), a difference previously linked to MA's higher reduction potential.
Purpose of the Study:
- To elucidate the DNA alkylation products of reductively activated Mitomycin A (MA).
- To compare the DNA alkylation and cross-linking capabilities of MA and Mitomycin C (MC) under various reductive activation conditions.
- To propose a mechanism explaining the differential toxicity and activation of MA and MC.
Main Methods:
- Isolation and characterization of DNA alkylation products from reductively activated MA.
- Conversion of adducts to known 7-amino mitosene-deoxyguanosine derivatives for identification.
- Comparison of DNA alkylation and oligonucleotide cross-linking extent between MA and MC under different reductive conditions (e.g., H2/PtO2, Na2S2O4, enzymatic, aerobic, anaerobic).
Main Results:
- Three major MA adducts were identified: a monoadduct, a decarbamoyl monoadduct, and a bisadduct, all involving alkylation at the 2-amino group of guanine.
- Both MA and MC demonstrated similar DNA alkylation and oligonucleotide cross-linking extents.
- Reductive activation conditions differentially affected the distribution of MA adducts compared to MC adducts.
- MA's cross-linking ability was minimally influenced by aerobic conditions, unlike MC, which was inhibited by oxygen.
Conclusions:
- The 7-methoxy substituent in MA facilitates indiscriminate activation of its electrophilic sites.
- MA's greater toxicity is likely due to increased and nonselective DNA activation and cross-link formation in both aerobic and anaerobic cells, stemming from its higher redox potential.
- MA represents a potent antitumor agent whose activity is modulated by its redox properties and activation pathways.