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Radiosensitization of human tumor cells by alpha-difluoromethylornithine
Abstract:
The effect of polyamine depletion on the radiosensitivity of a human tumor cell line was investigated. CAL 18 A cells, derived from a breast carcinoma, were incubated with alpha-difluoromethylornithine (DFMO)--a specific and irreversible inhibitor of ornithine decarboxylase (ODC)--at a 1 mM or 10-mM concentration for either 1 hr or 24 hr and irradiated thereafter. Survival curves of exponentially growing cells revealed a moderate but significant enhancement of radiosensitivity as compared to untreated irradiated cells. Maximum radiosensitization was observed at a concentration of 10 mM after 1 hr incubation. Plateau-phase cells were used to study the effect of polyamine inhibition on repair of radiation-induced potentially lethal damage (PLD). DFMO enhanced the radiation response and significantly inhibited PLD repair in these cells. Measurement of ODC indicated that this enzyme was markedly inactivated upon brief incubation of CAL 18 A cells with DFMO, reflecting a depletion of polyamine synthesis. These results extend findings that have demonstrated enhancement of drug-induced cytotoxicity, and raise the possibility of clinical use of this substance for potentiation of radiation response.
Insights
Polyamines depletion using alpha-difluoromethylornithine (DFMO) moderately enhanced breast cancer cell radiosensitivity. DFMO also inhibited potentially lethal damage repair, suggesting clinical potential for radiation therapy potentiation.
Area of Science:
- Oncology
- Molecular Biology
- Radiotherapy Research
Background:
- Polyamines are crucial for cell growth and proliferation.
- Inhibiting polyamine synthesis may sensitize tumor cells to radiation.
- Understanding polyamine's role in DNA repair is essential for optimizing cancer treatment.
Purpose of the Study:
- To investigate the impact of polyamine depletion on the radiosensitivity of human breast carcinoma cells (CAL 18 A).
- To assess the effect of alpha-difluoromethylornithine (DFMO) on the repair of radiation-induced potentially lethal damage (PLD).
Main Methods:
- CAL 18 A cells were treated with varying concentrations (1 mM, 10 mM) and durations (1 hr, 24 hr) of DFMO, an ornithine decarboxylase (ODC) inhibitor.
- Cells were subsequently irradiated, and survival curves were generated for exponentially growing cells.
- Plateau-phase cells were used to evaluate DFMO's effect on PLD repair.
- ODC activity was measured to confirm polyamine synthesis inhibition.
Main Results:
- DFMO treatment significantly enhanced the radiosensitivity of CAL 18 A cells compared to untreated controls.
- Maximum radiosensitization was observed with 10 mM DFMO after 1-hour incubation.
- DFMO significantly inhibited the repair of radiation-induced PLD in plateau-phase cells.
- DFMO effectively inactivated ODC, confirming polyamine depletion.
Conclusions:
- Polyamines depletion via DFMO enhances tumor cell radiosensitivity.
- DFMO inhibits the repair of potentially lethal radiation damage.
- These findings support the potential clinical application of DFMO to potentiate radiation therapy response in cancer patients.