[Circadian rhythms of DNA synthesis and telomerase expression in hepatic cancer transplanted in nude mice].

OBJECTIVE

To study the circadian rhythms of DNA synthesis and telomerase expression in hepatic cancer transplanted in nude mice.

METHOD

Sixteen BALB/C mice were synchronized with an alternative lighting regimen with 12 h for light and 12 h for darkness (12:12 LD) for 4 weeks. Hepatic cancer cells (SMMC-7721) were implanted into both flanks of each mouse. One week after transplantation, sampling from the tumor was conducted at 3, 9, 15 and 21 h after light onset (HALO). Single cell suspension was obtained and stained with propidium iodide. The cellular DNA content was measured by flow cytometry. Telomerase activity was measured by PCR-ELISA assay. Data were documented by ANOVA and Cosinor analysis.

RESULT

The proportion of tumor cells in phase G1, S, G2/M and telomerase activity varied according to circadian time with statistical significance, and the telomerase activity showed a synchronized variation. The distribution curves of both phase S and the expression level of telomerase were fit for Cosinor changes.

CONCLUSION

DNA synthesis and telomerase expression of SMMC-7721 cells transplanted into the nude mice varies according to the circadian rhythm. The results provide a guidance for laying down the chemotherapy protocol for human tumors, especially when the telomerase inhibitor was used as the anti-cancer agent.