Treatments based on the phytochemical curcumin have much potential for use in cancer treatments because of their effects on a wide variety of biological pathways, including those regulating the cell division cycle and circadian clocks. Cancer incidence and progression are influenced by circadian clock cells in multiple organs and tissue types. According to chronotherapeutic studies aimed at optimizing cancer treatments based on the circadian cycle it is known that circadian clocks modify the effectiveness of cancer treatments. Thus, it is important to determine whether curcumin and similar chemotherapeutic treatments being tested against cancer in clinical trials are influenced by the circadian clock. Similarly, it is important to determine whether curcumin alters the timing activity of circadian clock cells. To understand how curcumin treatments and combinatorial therapies using curcumin with standard therapies can be made more effective, we characterized the impact of the circadian clock on the timing of cell death and cell division in curcumin-treated C6 glioma cells. A low-dose of curcumin was administered to cause a slow cell death rate while allowing enough remaining cells so that circadian rhythms of cell division and cell death could be monitored. Cell division and cell death at different phases of the clock were quantified using continuous time-lapse digital video microscopy in a cell incubator. Live cells were imaged during 4 day-sessions at 5-minute intervals. Both the cell division and apoptotic events were verified visually and quantified at each interval. The average cell death rate for 6 cultures had a period of 23.27 hours and the average period of the mitotic oscillations was 15.05 hours, outside the circadian range. The rate of apoptosis increased and the mitotic rate decreased as curcumin dosage was increased between 0 and 14 μM. Circadian rhythms in C6 cells were also examined by monitoring expression of the mPer2 gene, a core component of the circadian timing mechanism, through bioluminescence from a reporter gene producing a fusion protein of mPER2 and firefly luciferase. Circadian rhythms in cell death reached a peak 6-8 hours earlier than the known peak of the mPER2 rhythm in C6 cells, indicating the phase of the circadian cycle during which curcumin is most effective. Immunofluorescence imaging of activated apoptotic marker caspase-3 was performed at specific circadian phases to further quantify cell deaths events. These results indicate, for the first time, that efficacy of curcumin is under circadian control and that the rhythm is lost at higher curcumin concentrations. Furthermore, at 5 and 10 μM curcumin the circadian oscillator is uncoupled from mitotic oscillations that persist with an ultradian period expected for published C6 cell doubling times. This study could help in identifying the most effective times of day when curcumin and curcumin derivatives should be administered to cancer patients according to their circadian cycles.

Citation Format: Ashapurna Sarma, Michael Eric Geusz, Karunakar Samuel. Circadian control of cell death in glioma cells treated with curcumin. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1772. doi:10.1158/1538-7445.AM2015-1772

©2015 American Association for Cancer Research.
2015