Background & objective: No report was found on research of circadian rhythms of nasopharyngeal carcinoma(NPC). This study was designed to investigate the circadian rhythms of DNA synthesis and apoptosis correlated gene expression in bone marrow cells of nude mice bearing NPC and to collect necessary data for making clinical chronochemotherapy schedule of NPC.
Methods: Sixty-nine BALB/C nude mice were synchronized with an alternative lighting regimen with 12 hours in light and 12 hours in dark (LD 12:12) for at least 3 weeks. Human nasopharyngeal poorly differentiated squamous cell carcinoma (CNE-2) cells were implanted into each mouse. Ten days after transplantation, the mice were sacrificed, bone marrow cells were collected in the 3, 7, 11, 15, 19, and 23 hours after light onset (HALO). Single cell suspension was obtained and stained with propidium iodide. The cellular DNA content was measured by flow cytometry. Data were analyzed with analysis of variance(ANOVA) and Cosinor analysis. Proteins were extracted from bone marrow cells and determined; Bcl-2, p53, and p21 expression were tested using Western blot analysis.
Results: The proportion of bone marrow cells in phase G1, S, and G2/M varied according to circadian sampling time with statistical significance (ANOVA). Moreover, such variation in G1 and G2/M was statistically valid by Cosinor analysis with an acrophase located at 10.8 HALO and 1.8 HALO, respectively. The distribution curves of phase G1 and G2/M fit to Cosinor changes but not for S phase cells. The expression of p53 and Bcl-2 protein level in bone marrow cells varied in 24 h time scale. No p21 protein expression was found in this experiment.
Conclusion: DNA synthesis of bone marrow cells in nude mice bearing human nasopharyngeal poorly differentiated squamous cell carcinoma (CNE-2) cells varies according to circadian rhythm. The expression of p53 and Bcl-2 protein level in bone marrow cells varies in 24 h time scale.