A Study About The Effects Of Low-dose Continuous Cisplatin Chemotherapy To The Cell Kinetics And Radiosensitivity Of Nasopharyngeal Carcinoma Cell Line CNE-1 In Vitro

Objective: Using cell culture method to study the cytotoxicity of low-dose continuous cisplatin chemotherapy which simulated metronomic chemotherapy and the effects on the cell cycle and radiosensitization combined with radiation in well-differentiated nasopharyngeal squamous cell carcinoma cell line CNE-1, and providing a high efficiency and low toxicity of new treatment modalities to nasopharyngeal concomitant chemoradiotherapy in clinic.Methods: MTT assay was used to evaluate the half inhibitory concentration (IC50) of cisplatin in nasopharyngeal carcinoma cell line CNE-1. The reference dose of low-dose chemotherapy was 1/5IC50, and IC70 was MTD reference dose. Observinging the effects of the treatment schedule of cisplatin on the cell kinetics in CNE-1. Cells of nasopharyngeal carcinoma were treated with cisplatin and radiation using four treatment protocols: 96-h exposure to the dose of cisplatin 1/5IC50 followed by irradiation(protocol A); 3-h exposure to the dose of IC70 immediately followed by irradiation(protocol B); 3-h exposure to IC70 followed by irradiation after a 93-h interval(protocol C) ; Cells which were not exposure to cisplatin cultured under the same conditions for 96-h followed by irradiation(protocol D). The survival fraction were determined by the cell clonogenic survival assays, and survival curve were drawn by the single-hit multitarget model to compare the radiosensitivity of these treatment protocols.Results: The IC50 of 72-h exposure to cisplatin in nasopharyngeal carcinoma cell line CNE-1 was 0.26μg/ml , and the dose of 1/5IC50 and IC70 was 0.05μg/ml and 0.72μg/ml, respectively. It had no significant toxicity when the dose of cisplatin is 0.05μg/ml, however the cell cycle study found that cell cycle accumulation at G2/M phase after 96-h exposure to this dose compared with the negative control group(P<0.05). 3-h exposure to the dose of cisplatin 0.72μg/ml with a 24-h interval and 93-h interval could induce significant G2/M phase arrest ,too(P<0.05), whereas no cell cycle shift immediately after 3-h exposure to the dose of cisplatin 0.72μg/ml compared with the negative control group(P>0.05). The values of SF2 in protocols A, B, C and D calculated by the single-hit multitarget model was 0.414±0.008, 0.502±0.010, 0.411±0.014 and 0.603±0.100, respectively, and the SER in protocols A, B and C was 1.429±0.110, 1.012±0.129 and 1.400±0.169, respectively.Conclusion: The protocol of low-dose continuous cisplatin chemotherapy cause G2/M phase arrest in nasopharyngeal carcinoma cell line CNE-1 in vitro, and when combined with radiotherapy could increase radiation sensitivity of CNE-1.