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Imbalance of deoxyribonucleoside triphosphates, DNA double-strand breaks, and cell death caused by
Y Hirota1, A Yoshioka, S Tanaka
1Faculty of Pharmaceutical Sciences, Okayama University, Japan.
Abstract:
The mechanism of the cytotoxic action of 2-chlorodeoxyadenosine in mouse FM3A cells was investigated. Imbalance of the dNTP pools occurred within 3 h of treatment with 20 microM 2-chlorodeoxyadenosine; the dATP and dGTP pools were depleted and the dTTP pool increased. 2-Chlorodeoxyadenosine added to the culture medium broke mature DNA strands, giving fragments of 100-200 kilobase pairs as found by orthogonal-field-alternation gel electrophoresis. DNA strand breaks, measured by this technique, were observed in the treated cells about 12 h after the addition. The cells also lost viability at about 12 h. Breaks in the single and double strands of DNA, as measured by alkaline and neutral filter elution, became evident 18 h after treatment with 20 microM 2-chlorodeoxyadenosine; there were as many single-strand breaks as would be caused by 130 rads of gamma-ray irradiation. Double-strand breaks were equivalent to those caused by 2180 rads of gamma-ray irradiation. Comparison of the ratio of single- and double-strand breaks caused by 2-chlorodeoxyadenosine to that following radiation suggested that 2-chlorodeoxyadenosine broke only double strands. Cycloheximide inhibited the breakage of DNA double strands and the cell death caused by this compound. Flow cytometric studies of cytostasis brought about by 2-chlorodeoxyadenosine in FM3A cells showed that cells accumulated in the earlier part of the S phase. 2-Chlorodeoxyadenosine decreased DNA synthesis more than RNA or protein synthesis. The breaks in double strands of DNA were probably important in the cell death caused by 2-chlorodeoxyadenosine. The intracellular dNTP imbalance may trigger these events.
Insights
2-chlorodeoxyadenosine causes DNA double-strand breaks and cell death in mouse FM3A cells by disrupting nucleotide pools. Cycloheximide inhibits these cytotoxic effects, suggesting a protein synthesis-dependent mechanism.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- 2-chlorodeoxyadenosine (CdA) is a chemotherapeutic agent.
- Understanding its cytotoxic mechanism is crucial for optimizing cancer therapy.
- Previous studies suggest CdA interferes with DNA synthesis.
Purpose of the Study:
- To investigate the mechanism of cytotoxic action of 2-chlorodeoxyadenosine in mouse FM3A cells.
- To elucidate the role of DNA damage and nucleotide pool imbalance in CdA-induced cell death.
Main Methods:
- Treatment of FM3A cells with 20 microM 2-chlorodeoxyadenosine.
- Analysis of deoxynucleotide triphosphate (dNTP) pools.
- Orthogonal-field-alternation gel electrophoresis (PULSE-FIELD GEL ELECTROPHORESIS) for DNA strand breaks.
- Alkaline and neutral filter elution assays.
- Flow cytometry for cell cycle analysis.
- Inhibition studies with cycloheximide.
Main Results:
- CdA induced dNTP pool imbalance, depleting dATP and dGTP while increasing dTTP.
- DNA double-strand breaks were observed 12 hours post-treatment, preceding cell death.
- CdA-induced double-strand breaks were equivalent to 2180 rads of gamma irradiation.
- Cycloheximide inhibited DNA double-strand breaks and cell death.
- Cells accumulated in early S phase, with DNA synthesis being most affected.
Conclusions:
- 2-chlorodeoxyadenosine induces cell death primarily through DNA double-strand breaks.
- Intracellular dNTP imbalance is a likely trigger for these events.
- The cytotoxic mechanism of CdA involves protein synthesis, as indicated by cycloheximide's inhibitory effect.