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Mutagenic damage to mammalian cells by therapeutic alkylating agents
1School of Medicine, Flinders University of South Australia, Adelaide, Australia. barbara.sanderson@flinders.edu.au
Abstract:
Cytotoxic alkylating agents used as therapeutics include nitrogen mustards, ethyleneimines, alkyl sulfonates, nitrosoureas and triazenes. Their reactivity with DNA, RNA and proteins can cause cell death. Side-effects of treatment include tissue toxicity and secondary malignancies, likely due to the genetic damage induced. The full mutagenic potential of alkylating agents may only be realised after they undergo metabolic activation, principally by cytochromes P450. Mutagenicity is related to the ability of alkylating agents to form crosslinks and/or transfer an alkyl group to form monoadducts in DNA. The most frequent location of adducts in the DNA is at guanines. Expressed mutations involve different base substitutions, including all types of transitions and transversions. The mutational spectra of alkylating agents on mammalian cells is distinct from that induced in bacterial cells, reflecting the different codon usage by bacteria and differences in DNA repair and replication enzymes. Mutations are induced by busulfan, chlorambucil (CAB), cyclophosphamide (CP, or its metabolite), dacarbazine, mechlorethamine, melphalan, mitomycin-C (MMC), nitrosoureas and thiotepa. Although dose-dependent, the relationship is not always linear. The molarities at which alkylating agents induce cell killing and mutations vary over three orders of magnitude. The mutagenic efficiency, of alkylating agents also varies, with some agents inducing three times more mutations for equivalent cell killing. The induction of micronuclei, sister chromatid exchanges, or chromosome aberrations is variable, but has been observed for CP, CAB, MMC, melphalan and triethylenemelamine. There is insufficient information to determine whether any synergistic effects of alkylating agents used in combination will influence the cytotoxic and mutagenic damage equally. Understanding the potential synergy of alkylating agents at the cellular and molecular level should allow improvement of the therapeutic efficacy of alkylating agents without increasing the unwanted mutation induction.
Insights
Alkylating agents, used in cancer therapy, can cause cell death and mutations by damaging DNA. Their mutagenic potential varies, and understanding this can improve cancer treatment efficacy while minimizing genetic damage.
Area of Science:
- Pharmacology
- Genetics
- Toxicology
Background:
- Cytotoxic alkylating agents are therapeutics including nitrogen mustards, ethyleneimines, alkyl sulfonates, nitrosoureas, and triazenes.
- These agents induce cell death through reactivity with DNA, RNA, and proteins, but can cause tissue toxicity and secondary malignancies due to genetic damage.
- Metabolic activation, primarily by cytochromes P450, is crucial for realizing the full mutagenic potential of these agents.
Purpose of the Study:
- To explore the mutagenic mechanisms and spectra of cytotoxic alkylating agents.
- To compare the mutagenic effects in mammalian versus bacterial cells.
- To understand the dose-response relationship and mutagenic efficiency of these agents.
Main Methods:
- Review of existing literature on alkylating agents, their DNA adduct formation, and induced mutations.
- Analysis of mutations induced by specific agents like busulfan, chlorambucil (CAB), cyclophosphamide (CP), dacarbazine, mechlorethamine, melphalan, mitomycin-C (MMC), nitrosoureas, and thiotepa.
- Examination of cytogenetic damage markers such as micronuclei, sister chromatid exchanges, and chromosome aberrations.
Main Results:
- Alkylating agents form DNA adducts, primarily at guanines, leading to base substitutions (transitions and transversions).
- Mutational spectra differ between mammalian and bacterial cells due to variations in codon usage and DNA repair/replication enzymes.
- The relationship between dose and mutation induction is not always linear, with significant variation in molarities for cell killing and mutation induction, and varying mutagenic efficiency.
Conclusions:
- Understanding the molecular mechanisms of alkylating agent-induced DNA damage and mutations is key to improving therapeutic efficacy.
- Further research is needed to determine synergistic effects of combined alkylating agent therapy on cytotoxic and mutagenic damage.
- Optimizing therapeutic strategies requires balancing cell killing with minimizing unwanted mutation induction.