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Mechanism by which caffeine potentiates lethality of nitrogen mustard
Abstract:
Caffeine is synergistic with many DNA-damaging agents in increasing lethality to mammalian cells. The mechanism is not well understood. Our results show that caffeine potentiates the lethality of the nitrogen mustard 2-chloro-N-(2-chloroethyl)-N-methylethanamine (HN2) by inducing damaged cells to undergo mitosis before properly repairing lesions in their DNA. Treatment with low doses of HN2 (0.5 microM for 1 hr) caused little lethality in baby hamster kidney cells (90% survival). These cells were arrested in G2 shortly after treatment with HN2 as shown by flow microfluorimetry and autoradiography. After an arrest of 6 hr, HN2-treated cells began to move into mitosis and from then on behaved like normal cells. Repair synthesis was shown to continue during the G2 arrest by using synchronized cells pulse labeled with [3H]thymidine after HN2 treatment and autoradiography. Caffeine (2mM) increased the lethality of HN2 by 5- to 10-fold. It prevented the G2 arrest. Caffeine did not prevent these HN2-treated cells from entering or completing S phase but rather allowed them to divide without finishing the repair processes and as a consequence caused nuclear fragmentation after mitosis. Caffeine-induced nuclear fragmentation and enhanced lethality were proportional, as shown with dose--response curves and time dependence. In addition, both lethality and nuclear fragmentation were abolished by low doses of cycloheximide, an inhibitor of protein synthesis.
Insights
Caffeine enhances the lethality of DNA-damaging agents like nitrogen mustard (HN2) by preventing cells from repairing DNA damage before mitosis. This leads to cell death and nuclear fragmentation, highlighting caffeine
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- Caffeine is known to synergize with DNA-damaging agents, increasing mammalian cell lethality.
- The precise molecular mechanisms underlying this synergistic effect remain largely unelucidated.
- Understanding these mechanisms is crucial for developing targeted cancer therapies and mitigating genotoxic stress.
Purpose of the Study:
- To investigate the mechanism by which caffeine potentiates the lethality of the nitrogen mustard HN2 in mammalian cells.
- To determine the role of cell cycle regulation and DNA repair in caffeine-induced sensitization to HN2.
- To elucidate the downstream effects of caffeine on HN2-treated cells, including nuclear integrity and cell division.
Main Methods:
- Treatment of baby hamster kidney cells with low doses of nitrogen mustard (HN2) and varying concentrations of caffeine.
- Cell cycle analysis using flow microfluorimetry and autoradiography to assess G2 arrest and progression into mitosis.
- Measurement of DNA repair synthesis via [3H]thymidine incorporation and autoradiography in synchronized cells.
- Evaluation of cell lethality, nuclear fragmentation, and protein synthesis inhibition using cycloheximide.
Main Results:
- HN2 treatment induced a G2 cell cycle arrest, allowing time for DNA repair synthesis.
- Caffeine (2mM) abrogated the HN2-induced G2 arrest, causing cells to enter mitosis with unrepaired DNA lesions.
- Caffeine significantly increased HN2-induced cell lethality (5- to 10-fold) and caused dose- and time-dependent nuclear fragmentation.
- Cycloheximide abolished both caffeine-enhanced lethality and nuclear fragmentation, suggesting a role for protein synthesis.
Conclusions:
- Caffeine potentiates HN2 lethality by disrupting the G2 checkpoint, forcing cells with DNA damage into mitosis.
- This premature cell division leads to unrepaired DNA lesions, resulting in nuclear fragmentation and cell death.
- The findings highlight caffeine's role as a radiosensitizer and suggest therapeutic strategies targeting cell cycle checkpoints.