Cheng Jin-Jian, Hu Zhen, Xia Yun-Fei, Chen Zhong-Ping
State Key Laboratory of Oncology in Southern China, Guangzhou, Guangdong 510060, P. R. China.
Ai Zheng. 2006 Jan;25(1):45-50.
BACKGROUND & OBJECTIVE: Radiotherapy is one of the most important adjuvant treatments for patients with malignant glioma, but radiosensitivities of gliomas are widely various. This study was to induce human glioma cell line MGR2 to become a stable radioresistant cell subline, and investigate the mechanisms of radioresistance.
Human glioma cell line MGR2, with survival fraction of 2 Gy (SF(2)) of 0.18+/-0.05, was irradiated by intermittent high dose X-ray (2 Gy for 3 times, 5 Gy for 2 times). After each irradiation, the cells were cultured for 5 to 8 weeks and received irradiation again. The whole process of irradiation and culture lasted for 11 months. The cells derived from MGR2 were obtained and named MGR2R (MGR2 radiation induction). Double times of MGR2 and MGR2R cells were determined by MTT assay. Dose-survival curves, radiobiological parameters and SF2 were determined by colony-forming assay and line-quadratic model. The variation of their cell cycles was investigated by flow cytometry and cell cycle synchronization of serum-starvation.
The double time of MGR2 cells was 3.6 days, while that of MGR2R cells was 4.0 days. The growth rate of MGR2R cells was slower than that of MGR2 cells. Using colony-forming assay and line-quadratic model, the parameters of MGR2 and MGR2R were obtained. The alpha values of MGR2 and MGR2R were 0.447 and 0.089 (t=4.524, P=0.011), the beta values were 0.177 and 0.141 (t=1.562, P=0.193), and the SF(2) were 0.208 and 0.478 (t=-6.062, P=0.040), respectively. The radioresistance of MGR2R cells was stronger than that of MGR2 cells. The distribution of cell cycle in MGR2 cells after synchronization were 54.8% in G(1) phase, 30.9% in S phase, and 14.3% in G(2) phase; 24 h after loss of synchronization, the distribution of cell cycle were 35.9% in G(1) phase, 51.2% in S phase, and 12.8% in G(2) phase. The distribution of cell cycle in MGR2R cells after synchronization were 55.7% in G(1) phase, 27.8% in S phase, and 16.6% in G(2) phase; 24 h after loss of synchronization, the distribution of cell cycle were 56.4% in G1 phase, 26.7% in S phase, and 16.9% in G(2) phase. MGR2R cells appeared G(2) phase arrest before synchronization, and G1 phase arrest after loss of synchronization.
After intermittent high dose X-ray irradiation, radiosensitive cell line MGR2 has been induced to be relatively radioresistant (MGR2R). MGR2R cells grow slower and have G(1) phase and G(2) phase arrest which might relate to its radioresistance.
放射治疗是恶性胶质瘤患者最重要的辅助治疗手段之一，但胶质瘤的放射敏感性差异很大。本研究旨在诱导人胶质瘤细胞系MGR2成为稳定的放射抗性细胞亚系，并探讨其放射抗性机制。
人胶质瘤细胞系MGR2，2 Gy照射的存活分数（SF(2)）为0.18±0.05，采用间歇性高剂量X射线照射（2 Gy照射3次，5 Gy照射2次）。每次照射后，细胞培养5至8周后再次接受照射。照射和培养全过程持续11个月。获取来源于MGR2的细胞并命名为MGR2R（MGR2辐射诱导）。采用MTT法测定MGR2和MGR2R细胞的倍增时间。采用克隆形成试验和线性二次模型测定剂量存活曲线、放射生物学参数和SF2。通过流式细胞术和血清饥饿细胞周期同步化研究其细胞周期变化。
MGR2细胞的倍增时间为3.6天，而MGR2R细胞为4.0天。MGR2R细胞的生长速度比MGR2细胞慢。采用克隆形成试验和线性二次模型，获得MGR2和MGR2R的参数。MGR2和MGR2R的α值分别为0.447和0.089（t = 4.524，P = 0.011），β值分别为0.177和0.141（t = 1.562，P = 0.193），SF(2)分别为0.208和0.478（t = -6.062，P = 0.040）。MGR2R细胞的放射抗性强于MGR2细胞。同步化后MGR2细胞的细胞周期分布为G(1)期54.8%，S期30.9%，G(2)期14.3%；同步化解除24小时后，细胞周期分布为G(1)期35.9%，S期51.2%，G(2)期12.8%。同步化后MGR2R细胞的细胞周期分布为G(1)期55.7%，S期27.8%，G(2)期16.6%；同步化解除24小时后，细胞周期分布为G1期56.4%，S期26.7%，G(2)期16.9%。MGR2R细胞同步化前出现G(2)期阻滞，同步化解除后出现G1期阻滞。
经间歇性高剂量X射线照射后，放射敏感细胞系MGR2被诱导成为相对放射抗性的细胞系（MGR2R）。MGR2R细胞生长较慢，出现G(1)期和G(2)期阻滞，这可能与其放射抗性有关。
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