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Antagonistic interplay between antimitotic and G1-S arresting agents observed in experimental combination therapy
K R Johnson1, K K Young, W Fan
1Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston 29425, USA.
Abstract:
Paclitaxel is a naturally occurring antimitotic agent that has been shown to stabilize microtubules, induce mitotic arrest, and ultimately induce apoptotic cell death. The favorable clinical activity of paclitaxel has prompted considerable interest in combining paclitaxel with numerous other antineoplastic agents. Our previous studies have suggested 5-fluorouracil (5-FU), an antineoplastic agent that usually arrests tumor cells at the G1-S phase of the cell cycle, in combination with paclitaxel significantly represses paclitaxel-induced mitotic arrest and apoptosis. In the present study, we have extended this investigation to include several other antimitotic agents (vinblastine, colchicine, and nocodazole) in various combination schedules with the G1-S arresting agents 5-FU and hydroxyurea (HU). We found 5-FU, as well as HU, could significantly interfere with the overall cytotoxicity as compared with treatment with antimitotic agents alone. It appeared that 5-FU or HU severely limited the antimitotic agents' cytotoxic effects on both mitotic arrest and apoptosis. No combination of a G1-S arresting agent with an antimitotic agent in any schedule produced an antitumor effect greater than that of the antimitotic agent alone. In addition, biochemical examination revealed that 5-FU and HU blocked the antimitotic agent-induced increase of p21WAF1/CIP1 protein levels, as well as prevented the hyperphosphorylation of the bcl-2 and c-raf-1 proteins. These findings suggest that careful considerations may be necessary when combining antineoplastic agents that exert their cytotoxic action at different phases of the cell cycle.
Insights
Combining cell cycle arresting agents like 5-fluorouracil (5-FU) with antimitotic drugs such as paclitaxel can reduce chemotherapy effectiveness. These combinations may interfere with mitotic arrest and apoptosis, limiting overall cytotoxicity.
Area of Science:
- Oncology
- Cancer Cell Biology
- Pharmacology
Background:
- Paclitaxel is an antimitotic chemotherapy agent that induces cell death by stabilizing microtubules.
- Combining paclitaxel with other antineoplastic agents is of clinical interest.
- Previous studies indicated 5-fluorouracil (5-FU) can repress paclitaxel-induced effects.
Purpose of the Study:
- To investigate the effects of combining G1-S phase arresting agents (5-FU, hydroxyurea) with other antimitotic agents.
- To evaluate the impact of these combinations on cytotoxicity, mitotic arrest, and apoptosis.
- To examine the biochemical mechanisms underlying the observed effects.
Main Methods:
- Combination chemotherapy studies using various schedules.
- Assessment of cytotoxicity, mitotic arrest, and apoptosis.
- Biochemical analysis of protein level changes (p21WAF1/CIP1, bcl-2, c-raf-1).
Main Results:
- 5-FU and hydroxyurea (HU) significantly interfered with the cytotoxicity of antimitotic agents.
- Combinations of G1-S arresting agents with antimitotic agents did not enhance antitumor effects.
- 5-FU and HU blocked antimitotic agent-induced increases in p21WAF1/CIP1 and prevented hyperphosphorylation of bcl-2 and c-raf-1.
Conclusions:
- Combining antineoplastic agents with different cell cycle targets may reduce therapeutic efficacy.
- Careful consideration of drug combinations is necessary to avoid antagonistic effects.
- Findings highlight the importance of understanding cell cycle phase-specific drug actions in combination chemotherapy.