Shi Degang, Shi Genming, Huang Gang, Zhang Jiren, Lartigau Eric
Cancer Center, Zhujiang Hospital, Southern Medical University, Guangzhou 510282, PR China.
J Exp Clin Cancer Res. 2009 Jun 2;28(1):72. doi: 10.1186/1756-9966-28-72.
The relapse of cancer after radiotherapy is a clinical knotty problem. Previous studies have demonstrated that the elevation of several factors is likely in some way to lead to the development of treatment tolerance, so it is necessary to further explore the problem of re-proliferated radioresistant cells to chemotherapeutic agents. In the present study, we aimed to investigate the chemosensitivity of radioresistant cells originated from the multicellular spheroids of A549 lung adenocarcinoma.
After irradiated with 25 Gy of 6 MV X-ray to A549 multicellular spheroids, whose 10th re-proliferated generations were employed as radioresistant cells, and the control groups were A549 parental cells and MCF7/VCR resistant cells. The chemo-sensitivity test was made by six kinds of chemotherapeutic drugs which were DDP, VDS, 5-Fu, HCP, MMC and ADM respectively, while verapamil (VPL) was used as the reversal agent. Then the treatment effect was evaluated by MTT assay, and the multidrug resistant gene expressions of mdr1 and MRP were measured by RT-PCR.
Both A549 parental cells and A549 derived radioresistant cells were resistant to DDP, but sensitive to VDS, 5-Fu, HCP, MMC and ADM. The inhibitory rates of VPL to these two types of cell were 98% and 25% respectively (P < 0.001). In addition, without drugs added, the absorbance value (A value) of A549 parental cells was 2-folds higher than that of their radioresistant cells (P < 0.001). As to the MCF7/VCR cells, they were resistant to DDP and VDS, but slight sensitive to MMC, ADM, 5-Fu, and HCP with 80% of inhibitory rate to VPL. The subsequent RT-PCR demonstrated that the Mdr1/beta2-MG and MRP/beta2-MG of all A549 cells were about 0 and 0.7 respectively, and those of MCF7/VCR cells were 35 and 4.36.
The chemosensitivity of A549 radioresistant cells had not changed markedly, and the decreased sensitivity to VPL could not be explained by the gene expression of mdr1 and MRP. It is possible that the changes in the cell membrane and decreased proliferate ability might be attributed to the resistance. Unlike multidrug resistance induced by chemotherapy, VPL may be not an ideal reverser to radioresistant cells. Therefore, the new biological strategy needs to be developed to treat recurring radioresistant tumor in combination with chemotherapy.
放射治疗后癌症复发是一个临床难题。以往研究表明，多种因素的升高可能在某种程度上导致治疗耐受性的产生，因此有必要进一步探讨再增殖的放射抗性细胞对化疗药物的问题。在本研究中，我们旨在研究源自A549肺腺癌多细胞球体的放射抗性细胞的化疗敏感性。
用25 Gy的6 MV X射线照射A549多细胞球体，将其第10代再增殖细胞用作放射抗性细胞，对照组为A549亲本细胞和MCF7/VCR抗性细胞。分别用顺铂（DDP）、长春地辛（VDS）、5-氟尿嘧啶（5-Fu）、羟基喜树碱（HCP）、丝裂霉素（MMC）和阿霉素（ADM）六种化疗药物进行化疗敏感性试验，同时用维拉帕米（VPL）作为逆转剂。然后通过MTT法评估治疗效果，并用RT-PCR检测多药耐药基因mdr1和MRP的表达。
A549亲本细胞和A549衍生的放射抗性细胞对DDP均耐药，但对VDS、5-Fu、HCP、MMC和ADM敏感。VPL对这两种细胞的抑制率分别为98%和25%（P<0.001）。此外，在不添加药物的情况下，A549亲本细胞的吸光度值（A值）比其放射抗性细胞高2倍（P<0.001）。对于MCF7/VCR细胞，它们对DDP和VDS耐药，但对MMC、ADM、5-Fu和HCP轻微敏感，对VPL的抑制率为80%。随后的RT-PCR表明，所有A549细胞的Mdr1/beta2-MG和MRP/beta2-MG分别约为0和0.7，而MCF7/VCR细胞的分别为35和4.36。
A549放射抗性细胞的化疗敏感性没有明显变化，对VPL敏感性降低不能用mdr1和MRP的基因表达来解释。细胞膜的变化和增殖能力的降低可能是导致抗性的原因。与化疗诱导的多药耐药不同，VPL可能不是放射抗性细胞的理想逆转剂。因此，需要开发新的生物学策略来联合化疗治疗复发性放射抗性肿瘤。
