Influence Of Circadian Genes HPer1 And HPer2 On Radiosensitivity Of Esophageal Cancer Cells

Objectives:Esophageal cancer is one of the most common malignant tumors in our country. Its mortality ranks the forth among all the cancers and it is a big threat to human health. Three major therapies for esophageal cancer available on nowadays include surgical resection, radiotherapy and chemotherapy. Surgical resection is the choice of treatment for those resectable tumors. Radiotherapy is also effective for the unresectable tumors. Radiotherapy may cause some side effects, such as esophageal and tracheal mucositis. Those side effects limit the target dose of radiation. So it's of great value to find a new way to maximize the treating effects for tumor tissues and minimize the side effects for normal tissues. According to the findings of chronobiology, the biologic rhythm of tumor cells is different from that of normal cells. This provides the theoretic base for treatment on different time points. The present study was designed to investigate the phase fluctuation of the circadian genes period1 and period2 expression levels, and then find out the difference of sensitivity of esophageal cancer cell lines to radiation when applied at different time points, hoping to provide some theoretical evidence for clinic radiochronotherapy.Methods:(1) The esophageal cancer cell lines Eca-109 were cultured in vitro. (2) The expression of hPer1 was induced by dark, and the expression of hPer2 by phorbol 12-myristate 13-acetate (PMA) treatment. (3) The expression of hPer1 and hPer2 was assayed by RT-PCR at different time points. (4) X-ray with 6MV energy was applied at the peak and valley expression time point of hPer1 and hPer2, respectively. The apoptosis rate of cell lines was detected by TUNEL assay and flow cytometry.Results:(1) The expression of clock genes hPer1 and hPer2 showed phase fluctuation as assayed by reverse transcription PCR. The peak expression of hPer1 was at 2AM, and the valley at 8AM. The peak expression of hPer2 was at 24 hours after the PMA treatment, and the valley at 12hours after treatment. (2) The apoptosis rate was higher when the cell lines were treated with 6MV X-ray at the valley expression of either hPer1 or hPer2 compared with that at the peak expression of each gene.Conlusions:The apoptosis rate of esophageal cancer cell lines was higher when they were treated with 6MV X-ray at the valley expression of of either hPer1 or hPer2 compared with that at the peak expression of each gene. The cell lines showed more sensitive to radiation at the valley expression of either gene. It suggested that radiochronotherapy for esophageal cancer might be superior to conventional radiotherapy.